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| United States Patent |
5,907,429
|
|
Sugata
|
May 25, 1999
|
Optical amplifier
Abstract
An optical amplifier is disclosed, which comprises an optical amplifying
unit for amplifying an optical signal, a light output monitoring unit for
monitoring the light output of the optical amplifying unit, a control unit
for controlling the optical amplifying unit by comparing the light output
of the optical amplifying unit monitored by the light output monitoring
unit with a specified reference value so as to cause the light output of
the optical amplifying unit to take a predetermined output value and an
input light level detecting unit for detecting the input light level of
the optical signal. The control unit controls the light output level of
the optical amplifying unit by changing the reference value used for
comparison according to the input light level detected by the input light
level detecting unit. By employing simple means for controlling the gain
of the optical amplifying unit according to the input light level of the
optical signal to be inputted, proper amplification control is performed
without making the optical amplifier complex even when a change occurs in
the number of input wavelengths.
| Inventors:
|
Sugata; Akihiko (Kawasaki, JP)
|
| Assignee:
|
Fujitsu Limited (Kawasaki, JP)
|
| Appl. No.:
|
982646 |
| Filed:
|
December 2, 1997 |
Foreign Application Priority Data
| Current U.S. Class: |
359/341.42; 359/337; 398/37; 398/38; 398/97 |
| Intern'l Class: |
H01S 003/131; H04B 010/00 |
| Field of Search: |
359/134,160,337,341
|
References Cited [Referenced By]
U.S. Patent Documents
| 5138621 | Aug., 1992 | Gato et al. | 372/28.
|
| 5463487 | Oct., 1995 | Epworth | 359/124.
|
| 5664131 | Sep., 1997 | Sugiya | 359/341.
|
| 5680247 | Oct., 1997 | Okuno | 359/141.
|
| 5764404 | Jun., 1998 | Yamane et al. | 359/341.
|
| Foreign Patent Documents |
| 5129701 | Feb., 1993 | JP.
| |
| 5-129701 | May., 1993 | JP.
| |
Other References
Lachel et al, Conf. Opt. Fifer Commun. vol. 6, pp. 84-85, Feb. 21, 1997;
Abst, only herewith.
|
Primary Examiner: Moskowitz; Nelson
Attorney, Agent or Firm: Staas & Halsey
Claims
What is claimed is:
1. An optical amplifier for amplifying a wavelength multiplexed signal
obtained by multiplexing an optical signal having a plurality of
wavelengths and controlling an amplification gain so as to cause an
amplified output to take a constant value, said optical amplifier
comprising:
an optical amplifying unit for amplifying an optical signal to be inputted;
a light output monitoring unit for monitoring a light output of said
optical amplifying unit;
a control unit for controlling said optical 15 amplifying unit by comparing
said light output of said optical amplifying unit monitored by said light
output monitoring unit with a specified reference value so as to cause
said light output of said optical amplifying unit to take a predetermined
output value; and
an input light level detecting unit for detecting an input light level of
said optical signal to be inputted,
wherein said control unit controls a light output level of said optical
amplifying unit by changing said reference value used for comparison
according to said input light level detected by said input light level
detecting unit.
2. An optical amplifier as claimed in claim 1, wherein said input light
level detecting unit includes a light receiving unit for receiving said
optical signal to be inputted and a reference value change information
supplying unit for supplying a reference value change information to said
control unit by comparing information regarding a received light detected
by said light receiving unit with a preset auxiliary reference value
according to a multiple signal number.
3. An optical amplifier as claimed in claim 1, wherein said input light
level detecting unit includes a light receiving unit for receiving said
optical signal to be inputted, a received light change information
arithmetic unit for calculating information regarding a change in received
light information detected by said light receiving unit between two points
of time and a reference value change information supplying unit for
supplying reference value change information to said control unit by
comparing said received light information detected by said light receiving
unit with a preset auxiliary reference value according to a multiple
signal number using said change information of said received light
information between said two points of time as a trigger signal.
4. An optical amplifier for amplifying a wavelength multiplexed signal
obtained by multiplexing an optical signal having a plurality of
wavelengths,
said optical amplifier being constructed in a manner that a light output
level of said optical amplifier is controlled to a specified level by
supplying a compensating optical signal to an input side of an optical
amplifying unit according to information regarding a multiple signal
number of an optical signal to be inputted.
5. An optical amplifier for amplifying a wavelength multiplexed number
obtained by multiplexing an optical signal having a plurality of
wavelengths, said optical amplifier comprising:
an optical amplifying unit for amplifying an optical signal to be inputted;
a light output monitoring unit for monitoring a light output of said
optical amplifying unit;
a control unit for controlling said optical amplifying unit by comparing
said light output of said optical amplifying unit monitored by said light
output monitoring unit with a specified reference value so as to cause
said light output of said optical amplifying unit to take a predetermined
output value;
a multiple signal number detecting unit for detecting information regarding
a multiple signal number of said optical signal to be inputted;
a compensating optical signal generation light source for supplying a
compensating signal to an input side of said optical amplifying unit; and
a light source control unit for controlling said compensating optical
signal generation light source according to said multiple signal number
information detected by said multiple signal number detecting unit so as
to cause said light source to output said compensating optical signal
which causes a light output level of said optical amplifying unit to take
a specified level.
6. An optical amplifier as claimed in claim 5, wherein said multiple signal
number detecting unit includes a light receiving unit for receiving said
optical signal to be inputted and a filter unit for detecting multiple
signal number information from information regarding a received light
detected by said light receiving unit.
7. An optical amplifier as claimed in claim 6, wherein said filter unit
includes a plurality of filters in order to deal with said plurality of
wavelengths.
8. An optical amplifier as claimed in claim 5, wherein said multiple signal
number detecting unit includes a wavelength variable filter for making a
filter wavelength variable in order to deal with said plurality of
wavelengths.
9. An optical amplifier as claimed in claim 5, wherein said multiple signal
number detecting unit includes a spectroscope unit for dividing said
optical signal to be inputted into portions by considering wavelengths and
a light receiving unit for individually receiving said portions of said
optical light obtained by said division performed by said spectroscope
unit.
10. An optical amplifier as claimed in claim 5, wherein said multiple
signal number detecting unit includes a light receiving unit for receiving
said optical signal to be inputted and a multiple signal number outputting
unit for outputting multiple signal number information from information
regarding a received light detected by said light receiving unit.
11. An optical amplifier as claimed in claim 5, wherein said compensating
optical signal generation light source includes a plurality of light
sources in order to deal with said plurality of wavelengths.
12. An optical amplifier as claimed in claim 5, wherein said compensating
optical signal generation light source includes a light source for making
a transmitted wavelength variable in order to deal with said plurality of
wavelengths.
13. An optical amplifier as claimed in claim 5, wherein said compensating
optical signal generation light source supplies a compensating optical
signal containing bits of control information superimposed on each other
to said input side of said optical amplifying unit.
14. An optical amplifier for amplifying a wavelength multiplexed signal
obtained by multiplexing an optical signal having a plurality of
wavelengths,
said optical amplifier being constructed in a manner that a compensating
optical signal is supplied to an input side of an optical amplifying unit
and a light output level of said optical amplifier is controlled according
to information regarding a multiple signal number of an optical signal to
be inputted.
15. An optical amplifier for amplifying a wavelength multiplexed signal
obtained by multiplexing an optical signal having a plurality of
wavelengths, said optical amplifier comprising:
an optical amplifying unit for amplifying an optical signal to be inputted;
a light output monitoring unit for monitoring a light output of said
optical amplifying unit;
a control unit for controlling said optical amplifying unit by comparing
said light output of said optical amplifying unit monitored by said light
output monitoring unit with a specified reference value so as to cause
said light output of said optical amplifying unit to take a predetermined
output value;
a multiple signal number detecting unit for detecting information regarding
a multiple signal number of said optical signal to be inputted;
a compensating optical signal generation light source for supplying a
compensating optical signal to an input side of said optical amplifying
unit; and
a light source control unit for controlling said compensating optical
signal generation light source according to said multiple signal number
information detected by said multiple signal number detecting unit so as
to cause said light source to output said compensating optical signal
which causes a light output level of said optical amplifying unit to take
a specified level,
wherein said control unit controls said light output level of said optical
amplifying unit by changing said reference value used for comparison
according to said multiple signal number information of said optical
signal to be inputted, which is detected by said multiple signal number
detecting unit.
16. An optical amplifier as claimed in claim 15, wherein said multiple
signal number detecting unit includes a reference value change information
supplying unit for supplying reference value change information to said
control unit according to said detected multiple signal number information
.
Description
BACKGROUND OF THE INVENTION
(1) Field of the Invention
The present invention relates to an optical amplifier which is suitably
used for a wavelength multiplexed optical transmission system.
(2) Description of the Related Art
In a trunk line optical communication system, with the attainment of a high
speed designed for lengthening a distance and increasing a capacity in
recent years, optical modulators and electronic circuits which can deal
with such a situation have been developed. However, it has been extremely
difficult to provide an electronic circuit to be used in a region of 10
Gb/s or higher. Accordingly, a study has also been made on a system which
can attain large capacitance for the transmission of an optical signal by
using a wavelength multiplexing technology.
Referring to FIG. 26, there is shown a typical wavelength multiplexed
optical transmission system. This wavelength multiplexed optical
transmission system denoted by a code 80 includes terminal stations 20A,
20B and 20c, a repeater station 20D and optical amplifiers 20a to 20f.
The terminal stations 20A, 20B and 20C are points in which transmitting and
receiving of information are performed through an optical fiber.
Each of the terminal stations has transmitting and receiving units. The
repeater station 20D performs a relaying operation according to
information regarding a terminal station to which information should be
transmitted from a certain terminal station. For example, the repeater
station 20D has a signal branching unit or a signal dividing unit, and
divides an optical signal having certain wavelength information from the
terminal station 20A into portions having wavelength information
appropriate for the terminal stations 20B and 20C.
The optical amplifiers 20a to 20f amplify optical signals among the
terminal stations 20A to 20C interconnected by the optical fiber. The
power of a light attenuated during transmission of an optical signal is
amplified. The repeater station 20D also has built-in optical amplifiers
similar to the optical amplifiers 20a to 20f.
With the wavelength multiplexed optical transmission system 80 shown in
FIG. 26, when a multiple optical signal having a plurality of wavelengths
is to be transmitted from the terminal station 20A to the terminal
stations 20B and 20C, an optical signal having wavelengths of, for
instance .lambda.1 to .lambda.4, from the terminal station 20A, is divided
into some portions by the repeater station 20D. Then, the portions of the
optical signal having wavelengths of, for instance .lambda.1 and
.lambda.3, are transmitted to the terminal station 20B, and the portions
of the optical signal having wavelengths of, for instance .lambda.2 and
.lambda.4, are transmitted to the terminal station 20C. During this
period, the portions of the optical signal are amplified by the optical
amplifiers 20a to 20f in order to prevent the portions of the signal to be
transmitted from being attenuated.
Referring to FIG. 27 which is a block diagram, there is shown an example of
a 4-wave multiplex transmitting unit in a typical optical transmission
system. This 4-wave multiplex transmitting unit includes light sources
81-1 to 81-4, modulators 82-1 to 82-4, driving circuits 831 to 83-4 and a
coupler 85.
The light sources 81-1 to 81-4 output optical signals having specified
wavelengths (.lambda.1 to .lambda.4). The modulators (MOD1 to MOD4) 82-1
to 82-4 modulate the optical signals outputted from the light sources 81-1
to 81-4 by signals from the later-described driving circuits 83-1 to 83-4.
The coupler 85 synthesizes outputs (multiplexes wavelengths) from the
modulators 82-1 to 82-4.
The driving circuits (DRIV1 to DRIV4) 83-1 to 83-4 drive the modulators
82-1 to 82-4 respectively based on main signals (data signals; DATA1 to
DATA4).
With the 4-wave multiplex transmitting unit, optical signals having various
wavelengths (.lambda.1 to .lambda.4) are modulated by the modulators 82-1
to 82-4.
These modulated optical signals are multiplexed by the coupler 85 and then
outputted to the optical amplifiers.
Referring now to FIG. 28 which is a block diagram, there is shown a
constitution of a typical optical amplifier. This optical amplifier
denoted by a code 90 includes an optical amplifying unit 91, a light
branching circuit 92, a light receiver 93, a comparator 94 and a pumping
light source control circuit 95. The optical amplifying unit 91 amplifies
an optical signal which has been inputted. The inputted optical signal was
multiplexed by the coupler 85 in the previous stage. For this optical
amplifying unit 91, for instance, a unit composed by combining an erbium
doped optical fiber (referred to as EDF, hereinafter) with a pumping light
source (referred to as LD; LASER DIODE, hereinafter) for supplying an
exciting light to this EDF is used. The light branching circuit 92
branches a portion of the optical signal amplified by the optical
amplifying unit 91. This circuit 92 includes, for instance an optical
coupler.
The light receiver 93 converts the optical signal branched by the light
branching circuit 92 into an electric signal by using a receiving element.
The comparator 94 compares an output from the light receiver 93 with a
specified reference value (REFERENCE). The pumping control circuit (PUMP
LD CONTROL CIRCUIT) 95 receives an output from the comparator 94, adjusts
an output from the pumping light source of the optical amplifying unit 91
and corrects its deviation from the reference value.
With the optical amplifier 90 constructed in the above-noted manner, after
a portion of an inputted optical signal is branched and compared with a
specified value, the gain of the optical amplifying unit 91 is controlled
based on the result of this comparison. Accordingly, an average value
among lights outputted from the optical amplifier 90 can be maintained
constant.
However, there is a problem inherent in the system, which employs optical
amplification relaying like that described above. More particularly, since
a stable transmission system is realized by always maintaining constant an
average value among lights outputted from the optical amplifier 90 and
regulating the fluctuation of light receiving power for the terminal
stations 20A to 20C, even in the case of N-wavelength multiplex
transmission in which a plurality (N) of wavelengths are multiplexed,
power for respective wavelengths based on average value control can be
maintained constant if the input levels of the wavelengths are the same.
However, for example, if a wavelength path is switched to another in the
middle way of a transmission line or if the number of wavelengths for an
input signal is reduced in the optical amplifier 90 because of a failure
or maintenance work, average value control like that described above only
results in the increase of output power for the respective wavelengths.
In other words, for N-wavelength multiplex transmission, if the average
output power of the optical amplifier 90 is Po, light power per wave for
the output of this optical amplifier 90 is PoN. In this condition, if no m
waves contained in N waves (m<N) are inputted any longer for one reason or
another, light power per wave for the output of the optical amplifier 90
becomes Po/(N-m) and thus power per wave is increased.
To further describe the foregoing problem by taking a 2-wave multiplexing
system as an example, assuming that power for each wavelength outputted
from the optical amplifier 90 is +6 dBm, when an optical signal inputted
to the optical amplifier 90 is reduced from two waves to one wave because
of a failure or the like, output power of one wave outputted from the
optical amplifier 90 is increased by 3 dB to be +9 dBm. If this power
exceeds a threshold value in which an optical fiber nonlinear effect (SBS;
stimulated Brillouin scattering, SPM; self phase modulating effect, or the
like) is produced, a light waveform is deteriorated and thus transmission
quality is also deteriorated.
Efforts have been made to develop a technology as means for solving the
above-discussed problem. For example, referring to JP-A-95097/1996, there
is disclosed a technology for always keeping a signal light output for
each wavelength at a proper level by controlling the light output level of
an optical amplifier so as to change the level according to the number of
multiple signals in a wavelength multiplexed light signal when the
wavelength multiplexed light signal produced by multiplexing an optical
signal having a plurality of different wavelengths is to be amplified.
However, with the technology disclosed in JP-A-95097/1996, since the number
of wavelength multiplexed light signals is directly detected and the light
output level of the optical amplifier is controlled according to this
detected number of wavelength multiplexed light signals, means for
detecting the number of wavelength multiplexed light signals inevitably
becomes complex. Consequently, the optical amplifier as a whole becomes
complex and costs are increased.
SUMMARY OF THE INVENTION
The present invention was made in order to solve the problems discussed
above. It is a first object of the present invention to provide an optical
amplifier, which is not made complex and can perform proper amplification
control even when a change occurs in the number of input wavelengths by
employing simple detecting means for controlling the gain of an optical
amplifying unit according to the input light level of an optical signal to
be inputted.
It is a second object of the present invention to provide an optical
amplifier, which can maintain stable transmission quality without
increasing output power even when a change occurs in the number of input
wavelengths by supplying a compensating optical signal to the input side
of an optical amplifying unit so as to control a light output level to a
specified level according to information regarding the number of multiple
signals for an optical signal to be inputted.
It is a third object of the present invention to provide an optical
amplifier, which can shorten a time until its operation is normally
started and adjust the shortage of a compensating optical signal based on
gain control by simultaneously performing supplying of a compensating
optical signal to the input side of an optical amplifying unit and
controlling of the gain of the optical amplifying unit according to the
input light level of an optical signal to be inputted.
In order to achieve the first object, according to an aspect of the present
invention, there is provided an optical amplifier for amplifying a
wavelength multiplexed signal produced by multiplexing an optical signal
having a plurality of wavelengths and controlling an amplification gain so
as to cause an amplified output to take a fixed value, which comprises an
optical amplifying unit for amplifying an optical signal to be inputted, a
light output monitoring unit for monitoring the light output of the
optical amplifying unit, a control unit for controlling the optical
amplifying unit by comparing the light output of the optical amplifying
unit monitored by the light output monitoring unit with a specified
reference value so as to cause the light output of the optical amplifying
unit to take a predetermined output value and an input light level
detecting unit for detecting the input light level of the optical signal
to be inputted. The control unit changes the reference value used for
comparison according to an input light level detected by the input light
level detecting unit and thereby controls the light output level of the
optical amplifying unit.
With the optical amplifier constructed in the above-noted manner, since
gain control can be performed for the optical amplifying unit according to
the input light level of the optical signal to be inputted, even when a
change occurs in the number of multiplexed wavelengths, the number of
multiplexed wavelengths can be easily detected without making a circuitry
complex unlike the optical amplifier for directly detecting the number of
wavelengths. Accordingly, the optical amplifier can be simplified and its
performance as a whole can be greatly improved.
In addition, since the optical amplifier enables sure detection of the
number of multiplexed wavelengths, output power for each wavelength can be
maintained constant and highly reliable transmission quality is assured
without any reduction in the quality of a light waveform.
In order to achieve the second object, according to another aspect of the
present invention, there is provided an optical amplifier for amplifying a
wavelength multiplexed signal produced by multiplexing an optical signal
having a plurality of wavelengths, which is constructed in such a manner
that the light output level of the optical amplifier is controlled to a
specified level by supplying a compensating optical signal to the input
side of an optical amplifying unit according to multiple signal number
information regarding an optical signal to be inputted.
This optical amplifier for amplifying a wavelength multiplexed signal
produced by multiplexing an optical signal having a plurality of
wavelengths comprises an optical amplifying unit for amplifying an optical
signal to be inputted, a light output monitoring unit for monitoring the
light output of the optical amplifying unit, a control unit for
controlling the optical amplifying unit by comparing the light output of
the optical amplifying unit monitored by the light output monitoring unit
with a specified reference value so as to cause the light output of the
optical amplifying unit to take a predetermined output value, a multiple
signal number detecting unit for detecting multiple signal number
information regarding the optical signal to be inputted, a compensating
optical signal generation light source for supplying a compensating
optical signal to the input side of the optical amplifying unit and a
light source control unit for controlling the compensating optical signal
generation light source according to the multiple signal number
information detected by the multiple signal number detecting unit so as to
cause the light source to output the compensating optical signal, which in
turn causes the light output level of the optical amplifying unit to take
a specified level.
With the optical amplifier constructed in the above-noted manner, since a
compensating optical signal is supplied to the input side of the optical
amplifying unit according to the multiple signal number of an optical
signal to be inputted, output power for each wavelength can be controlled
to a constant level without changing the circuitry of the feedback control
system of the existing optical amplifying unit.
In order to achieve the third object, according to yet another aspect of
the present invention, there is provided an optical amplifier for
amplifying a wavelength multiplexed signal produced by multiplexing an
optical signal having a plurality of wavelengths, which is constructed in
such a manner that a compensating optical signal is supplied to the input
side of an optical amplifying unit and the light output level of the
optical amplifier is controlled according to multiple signal number
information regarding an optical signal to be inputted.
This optical amplifier for amplifying a wavelength multiplexed signal
produced by multiplexing an optical signal having a plurality of
wavelengths comprises an optical amplifying unit for amplifying an optical
signal to be inputted, a light output level monitoring unit for monitoring
the light output of the optical amplifying unit, a control unit for
controlling the optical amplifying unit by comparing the light output of
the optical amplifying unit monitored by the light output monitoring unit
with a specified reference value so as to cause the light output of the
optical amplifying unit to take a predetermined value, a multiple signal
number detecting unit for detecting multiple signal number information
regarding the optical signal to be inputted, a compensating optical signal
generation light source for supplying a compensating optical signal to the
input side of the optical amplifying unit and a light source control unit
for controlling the compensating optical signal generation light source
according to the multiple signal number information detected by the
multiple signal number detecting unit so as to cause the light source to
output the compensating optical signal, which in turn causes the light
output level of the optical amplifying unit to take a specified level. The
control unit changes the reference value used for comparison according to
the multiple signal number information regarding the optical signal to be
inputted, which is detected by the multiple signal number information
detecting unit, and thereby controls the light output level of the optical
amplifying unit.
With the optical amplifier constructed in the above-noted manner, since
supplying of a compensating optical signal and the gain control of the
optical amplifying unit can be simultaneously performed based on multiple
signal number information, a time needed until the compensating optical
signal is normally started (transition state) can be shortened by
controlling performed by the feedback system having quicker responsiveness
and the number of wavelengths equivalent to the shortage of optical
signals can be adjusted by controlling performed by the feedback system
irrespective of the number of installed light sources (compensating
optical signal quantity). Accordingly, a circuitry can be reduced in size
and degree of flexibility can be increased when a system is constructed.
BRIEF DESCRIPTION OF THE DRAWINGS
These and other objects, features and advantages of the present invention
will become more apparent upon reading of the following detailed
description and drawings, in which:
FIG. 1 is a block diagram showing an aspect of the present invention;
FIG. 2 is a block diagram showing another aspect of the present invention;
FIG. 3 is a block diagram showing yet another aspect of the present
invention;
FIG. 4 is a block diagram showing a constitution of an optical amplifier of
a first embodiment of the present invention;
FIG. 5 is a view illustrating a detection level range for a 2-wave
multiplexed signal of the first embodiment of the present invention;
FIG. 6 is a block diagram showing a first modified example of the optical
amplifier of the first embodiment of the present invention;
FIG. 7 is a block diagram showing a constitution of a window comparator of
the first modified example of the first embodiment of the present
invention;
FIG. 8 is a view illustrating comparison performed in an input light level
detecting unit of the first modified example of the first embodiment of
the present invention;
FIG. 9 is a view illustrating another example of comparison performed in
the input light level detecting unit of the first modified example of the
first embodiment of the present invention;
FIG. 10 is a block diagram showing a constitution of an optical amplifier
of a second embodiment of the present invention;
FIG. 11 is a block diagram showing an internal constitution of a multiple
signal number detecting unit of the second embodiment of the present
invention;
FIG. 12 is a block diagram showing a constitution of a first modified
example of the multiple signal number detecting unit of the second
embodiment of the present invention;
FIG. 13 is a block diagram showing an internal configuration of a
wavelength detecting circuit of the multiple signal number detecting unit
shown in FIG. 12;
FIG. 14 is a block diagram showing an example of a filter sweep voltage of
a filter sweep circuit of the multiple signal number detecting unit shown
in FIG. 12;
FIGS. 15(a) to 15((c) are timing charts respectively illustrating the
operation of the wavelength detecting circuit of the multiple signal
number detecting unit shown in FIG. 12;
FIG. 16 is a block diagram showing a constitution of a second modified
example of the multiple signal number detecting unit of the second
embodiment of the present invention;
FIG. 17 is a block diagram showing a constitution of a third modified
example of the multiple signal number detecting unit of the second
embodiment of the present invention;
FIG. 18 is a block diagram showing a light source and its surrounding
portion of the second embodiment of the present invention;
FIG. 19 is a block diagram showing a light source and its surrounding
portion of the modified example of the second embodiment of the present
invention;
FIG. 20 is a block diagram showing a constitution of an optical amplifier
of a third embodiment of the present invention;
FIG. 21 a block diagram of an internal constitution of a multiple signal
number detecting unit of the third embodiment of the present invention;
FIG. 22 is a block diagram showing a constitution of a first modified
example of the multiple signal number detecting unit of the third
embodiment of the present invention;
FIG. 23 is a block diagram showing a constitution of a second modified
example of the multiple signal number detecting unit of the third
embodiment of the present invention;
FIG. 24 is a block diagram showing a constitution of a third modified
example of the multiple signal number detecting unit of the third
embodiment of the present invention;
FIG. 25 is a block diagram showing an example of a 4-wave multiplex
transmitting unit of a terminal station in an optical transmission system
of the second embodiment of the present invention;
FIG. 26 is a block diagram showing a typical optical transmission system;
FIG. 27 is a block diagram showing an example of a 4-wave multiplex
transmitting unit of a terminal station in the typical optical
transmission system; and
FIG. 28 is a block diagram showing a constitution of a typical optical
amplifier.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
(a) Aspects of the Invention
First, the aspects of the present invention will be described with
reference to the accompanying drawings.
Referring to FIG. 1 which is a block diagram showing an aspect of the
present invention, an optical amplifier 10 shown comprises an optical
amplifying unit 1, a light output monitoring unit 2, a control unit 3 and
an input light level detecting unit 4.
The optical amplifying unit 1 amplifies an optical signal which has been
inputted. The light output monitoring unit 2 monitors the light output of
the optical amplifying unit 1. The control unit 3 controls the optical
amplifying unit 1 by comparing the light output of the optical amplifying
unit 1 monitored by the light output monitoring unit 2 with a specified
reference value so as to cause the light output of the optical amplifying
unit 1 to take a predetermined output value. The input light level
detecting unit 4 detects the input light level of the optical signal which
has been inputted. In the control unit 3, the light output level of the
optical amplifying unit 1 is controlled by changing the reference value
used for comparison according to the input light level detected by the
input light level detecting unit 4.
In this case, the input light level detecting unit 4 may include a light
receiving unit for receiving an optical signal which has been inputted and
a reference value change information supplying unit for supplying
reference value change information to the control unit 3 by comparing
information regarding the received light detected by this light receiving
unit with a preset auxiliary reference value according to a multiple
signal number.
With the optical amplifier 10 of the present invention, since the gain of
the optical amplifying unit 1 can be controlled according to the input
light level of an optical signal which has been inputted, compared with
the optical amplifier for directly detecting the number of wavelengths,
the number of multiplexed wavelengths can be easily detected without
making a circuitry complex even when a change occurs in the number of
multiplexed wavelengths. Accordingly, the optical amplifier can be
simplified and its performance as a whole can be greatly improved.
Also, since the number of multiplexed wavelengths can be surely detected,
output power for each wavelength can be maintained constant and highly
reliable transmission quality is assured without any reduction in the
quality of a light waveform.
Furthermore, the input light level detecting unit 4 may include a light
receiving unit for receiving an optical signal which has been inputted, a
received light change information arithmetic unit for calculating
information regarding a change in received light information between two
points of time, which has been detected by this light receiving unit, and
a reference value change information supplying unit for supplying
reference value change information to the control unit 3 by comparing the
received light information detected by the light receiving unit with a
preset auxiliary reference value according to a multiple signal number by
using the change information about the received light information between
the two points of time obtained by this received light change information
arithmetic unit as a trigger signal.
With the optical amplifier 10 of the present invention, in addition to its
simplified constitution, since the gain of the optical amplifying unit is
controlled when a change occurs in received light information between the
two points of time, efficient comparison can be performed without being
influenced by a fluctuation in a received light quantity after the passage
of time. Accordingly, the performance of the optical amplifier can be
improved and power consumption can be reduced.
Referring now to FIG. 2 which is a block diagram showing another aspect of
the present invention, an optical amplifier 11 shown comprises an optical
amplifying unit 1, a light output monitoring unit 2, a control unit 3A, a
multiple signal number detecting unit 5, a light source control unit 6 and
a compensating optical signal generation light source 7. The codes similar
to those described above denote like elements or almost like elements and
thus, detailed description thereof will be omitted.
The control unit 3A controls the optical amplifying unit 1 by comparing the
light output of the optical amplifying unit 1 monitored by the light
output monitoring unit 2 with a specified reference value so as to cause
the light output of the optical amplifying unit 1 to take a predetermined
output value. The specified reference value is a fixed value.
The multiple signal number detecting unit 5 detects multiple signal number
information regarding an optical signal which has been inputted. The
compensating optical signal generation light source 7 supplies a
compensating optical signal to the input side of the optical amplifying
unit 1. The light source control unit 6 controls the compensating optical
signal generation light source 7 according to the multiple signal number
information detected by the multiple signal number detecting unit 5 so as
to cause the light source 7 to output a compensating optical signal, which
in turn causes the light output level of the optical amplifying unit 1 to
take a specified level.
In this case, the multiple signal number detecting unit 5 may include a
light receiving unit for receiving an optical signal which has been
inputted and a filter unit for detecting multiple signal number
information from received light information detected by this light
receiving unit. The filter unit may include a plurality of filters in
order to deal with a plurality of wavelengths.
With the optical amplifier 11 of the present invention thus constructed,
since a compensating optical signal is supplied to the input side of the
optical amplifying unit 1 according to a multiple signal number for an
optical signal which has been inputted, output power for each wavelength
can be controlled to a constant level without changing the circuitry of
the feedback control system of the existing optical amplifying unit.
In addition, in order to deal with a plurality of wavelengths, the multiple
signal number detecting unit 5 may include a wavelength variable filter
which can make a filter wavelength variable.
With the optical amplifier 11 of the present invention thus constructed,
since an omitted wavelength can be detected by using the wavelength
variable filter for making a filter wavelength variable, a circuitry can
be reduced in size. Accordingly, the optical amplifier can be greatly
reduced in weight.
The multiple signal number detecting unit 5 may also include a spectroscope
unit for dispersing a light for an optical signal which has been inputted
by considering wavelengths and a light receiving unit for individually
receiving the lights obtained by dispersing performed by this spectroscope
unit.
With the optical amplifier 11 of the present invention thus constructed,
since an optical signal which has been inputted can be independently
received, wavelength information can be surely detected. Accordingly,
degree of flexibility can be greatly increased when a system is
constituted for the optical amplifier.
The multiple signal number detecting unit 5 may further include a light
receiving unit for receiving an optical signal which has been inputted and
a multiple signal number output unit for outputting multiple signal number
information from information regarding the received light detected by this
light receiving unit.
With the optical amplifier 11 of the present invention thus constructed,
since a compensating optical signal can be controlled according to an
input light level, a circuitry can be simplified compared with the optical
amplifier for directly detecting the number of wavelengths. Accordingly,
the optical amplifier can be reduced in weight and costs can be reduced.
In order to deal with a plurality of wavelengths, the compensating optical
signal generation light source 7 may include a plurality of light sources
or a light source which can make a transmitted wavelength variable. This
compensating optical signal generation light source 7 can also supply a
compensating optical signal in which control information is superimposed
on another to the input side of the optical amplifying unit 1.
With the optical amplifier 11 of the present invention thus constructed,
since a compensating optical signal is supplied to the input side of the
optical amplifying unit 1 according to a multiple signal number for an
optical signal which has been inputted, output power for each wavelength
can be controlled to a constant level without changing the circuitry of
the feedback control system of the existing optical amplifying unit.
Furthermore, with the optical amplifier 11 of the present invention
constructed in the above-noted manner, since a reference value is obtained
according to detected wavelengths and the number of multiplexed
wavelengths by using the wavelength variable filter for making a filter
wavelength variable, a circuitry can be reduced in size. Accordingly, the
entire optical amplifier can be greatly reduced in size and weight.
Referring now to FIG. 3 which is block diagram showing yet another aspect
of the present invention, an optical amplifier 12 shown comprises, as in
the case of the optical amplifier 11 shown in FIG. 2, an optical
amplifying unit 1, a light output monitoring unit 2, a control unit 3B, a
multiple signal number detecting unit 5, a light source control unit 6 and
a compensating optical signal generation light source 7.
In this case, the optical amplifier 12 is constructed in such a manner that
according to multiple signal number information regarding an optical
signal which has been inputted, a compensating optical signal is supplied
to the input side of the optical amplifying unit 1 and the light output
level of the optical amplifier 12 is controlled. Specifically, the control
unit 3B controls the light output level of the optical amplifying unit 1
by changing a reference value used for comparison according to information
regarding the multiple signal number detected by the multiple signal
number detecting unit 5 for an optical signal which has been inputted. The
other codes similar to those described above denote like elements or
almost like elements and thus, description thereof will be omitted.
The multiple signal number detecting unit 5 may include a reference value
change information supplying unit for supplying reference value change
information to the control unit 3B according to the detected multiple
signal number information.
With the optical amplifier 12 of the present invention constructed in the
above-noted manner, since supplying of a compensating optical signal based
on the multiple signal number information and controlling of the gain of
the optical amplifier 12 can be simultaneously performed, a time needed
until the compensating optical signal is normally started (transition
state) can be shortened by controlling of a feedback system having quicker
responsiveness and the number of wavelengths equivalent to the shortage of
optical signals can be adjusted by controlling of the feedback system
irrespective of the number of installed light sources (quantity of
compensating optical signal). Accordingly, a circuitry can be reduced in
size and degree of flexibility can be increased when a system is
constituted.
Next, the preferred embodiments of the present invention will be described
with reference to the accompanying drawings.
(b) First Embodiment of the Invention
Referring to FIG. 4 which is a block diagram showing the optical amplifier
of the first embodiment of the present invention, an optical amplifier 13
shown comprises an optical amplifying unit 1, a light receiver (photo
detector) 2, a control unit 3, a level detecting unit 4 and first and
second light branching circuits 8 and 9.
The first light branching circuit 8 branches a portion of an optical signal
which has been inputted. This circuit 8 includes, for instance an optical
coupler. The optical amplifying unit 1 amplifies an optical signal which
has been inputted. For this unit 1, a unit composed by combining, for
instance an erbium doped optical fiber (EDF) with a pumping light source
(LD; LASER DIODE) for supplying an exciting light to this EDF is used. The
optical amplifying unit 1 is controlled by the later-described control
unit 3.
The second light branching circuit 9 branches a portion of the optical
signal from the optical amplifying unit 1. This circuit 9 also includes,
for instance an optical coupler. The light receiver (light output
monitoring unit) 2 monitors the light output of the optical amplifying
unit 1. Specifically, the light receiver 2 converts an optical signal into
an electric signal by using a receiving element.
The control unit 3 controls the optical amplifying unit 1 by comparing the
light output of the optical amplifying unit 1 monitored by the light
receiver 2 with a specified reference value so as to cause the light
output of the optical amplifying unit 1 to take a predetermined output
value. This control unit 3 includes a comparator 30 and a pumping light
source control circuit 31.
The comparator 30 compares an electric signal outputted from the light
receiver 2 with a specified reference value. Specifically, this comparator
3 uses an output from the later-described level detecting unit 4 as a
reference value.
The pumping light source control circuit (PUMP LD CONTROL CIRCUIT) 31
controls a pumping light source (PUMP LD, not shown) incorporated in the
optical amplifying unit 1 based on an output from the comparator 30. This
circuit 31 performs feedback control so as to cause a difference between
an output from the light receiver 2 and a specified reference value to be
0. In this way, output power for each wavelength can be maintained
constant.
The light receiver 2 and the control unit 3 configure an optical amplifier
control circuit and function to control the gain of the optical amplifying
unit 1. When light transmission is to be cut off, the control unit 3 can
temporarily stop controlling by detecting a signal to this effect.
The level detecting unit (input light level detecting unit) 4 detects the
input light level of an optical signal which has been inputted. This unit
4 includes a light receiver 40, a comparator 41 and a level converting
unit 42.
The light receiver (light receiving unit) 40 receives an optical signal
which has been inputted. Specifically, the light receiver 40 converts an
optical signal from the first light branching circuit 8 into an electric
signal (electric level) by using a receiving element.
The comparator 41 compares a signal detected by the light receiver 40 with
a preset auxiliary reference value according to a multiple signal number
(the number of input wavelengths). The comparator 41 includes comparator
circuits 41-1 to 41-n (n is a natural number) corresponding in number to
the number of input wavelengths. By comparing a signal which has been
inputted with a preset auxiliary reference value (REF-1 to REF-N; N is a
natural number), the comparator 41 can detect the existence of a reduction
in the number of wavelength multiplexed signals (the number of
wavelengths). In other words, the comparator 41 can output control signals
in stages according to the number of wavelengths.
The operation of the comparator 41 will be described below by taking the
use of a 4-wave multiple signal as an example. It is assumed that a value
is set for the auxiliary reference value (REF 1) of the comparator circuit
41-1 according to a signal indicating that the number of wavelengths is 1,
a value is set for the auxiliary reference value (REF 2) of the comparator
circuit 41-2 according to a signal indicating that the number of
wavelengths is 2, a value is set for the auxiliary reference value (REF 3)
of the comparator circuit 41-3 according to a signal indicating that the
number of wavelengths is 3 and further, a value is set for the auxiliary
reference value (REF 4) of the comparator circuit 41-4 according to a
signal indicating the number of all wavelengths.
In this condition, for example, when the optical signals of all the
wavelengths are inputted, "1" (H level) is outputted from the comparator
circuit 41-4 to the level converter 42 of the subsequent stage (i.e.,
"0","0", "0" and "1"). When the signal of the wavelength number 1 is
inputted, "1" is outputted from the comparator circuit 41-2 for the
wavelength number 2 and "0" is outputted from each of the other comparator
circuits 41-1, 41-3 and 41-4 (i.e., "0", "1", "0" and "0").
In other words, in this case, it can be understood that although the
optical signals of two wavelengths have been inputted, the optical signals
of three or four wavelengths have not been inputted.
The auxiliary reference value has a certain width (range) and an output
value is changed when a level after photoelectric conversion in the light
receiver 40 is within this certain range. For example, referring to FIG. 5
which illustrates a detecting level range for a 2-wave multiple signal, a
detecting level range can be set to a section A shown in the drawing when
a receiving level (registered value) is one wave (.lambda.1). Accordingly,
the number of wavelengths can be surely detected even when a fluctuation
occurs in an input light.
In other words, during a normal period, the average value level of input
signals (.lambda.1+.lambda.2) for the 2-wave multiple signal takes a range
denoted by a section B shown in FIG. 5. Two waves (.lambda.1+.lambda.2)
are detected when a received input signal is within the range denoted by
the section B. One wave (.lambda.1) is detected when a received input
signal is within the range denoted by the section A.
The level converting unit 42 converts information compared by the
comparator 41 into a reference value having a predetermined level. Its
output is supplied to the comparator 30. Specifically, this level
converting unit 42 includes an address converting unit 42A, a memory
control unit 42B, a memory 42C, an analog/digital converting circuit (A/D)
42D and a voltage generating unit 42E.
The address converting unit 42A converts signals from the comparator
circuits 41-1 to 41-n into addresses respectively. The memory 42C holds a
content (REF value) for each wavelength. The analog/digital converting
circuit 42D converts analog information from the memory 42C into digital
information.
The memory control unit 42B reads the REF value of an address from the
memory 42C based on information regarding the address from the address
converting unit 42A. The voltage generating unit 42E outputs a reference
voltage based on a digital signal obtained by conversion. The control unit
3 performs comparison for an input optical signal by using this reference
voltage (reference value). An output inputted from the voltage generating
unit 42E to the control unit 3 will be referred to as reference value
change information, hereinafter.
The comparator 41 and the level converting unit 42 constitute a reference
value change information supplying unit 43.
Circuit constants in the control unit 3 and the level detecting unit 4 are
set in such a manner that the output light level of the optical amplifying
unit 1 (optical amplifier 13) becomes constant at a predetermined value
(P) during a normal period (no reduction occurs in the number of
wavelengths) and the output light level of the optical amplifying unit 1
(optical amplifier 13) becomes P(N-M)/N (N; input wavelength number and M;
reduced wavelength number) during an abnormal period (a reduction occurs
in the number of wavelengths). Accordingly, even when a change occurs in
the number of multiplexed wavelengths for an optical signal which has been
inputted, a predetermined value can be outputted.
As described above, in the optical amplifier 13, the control unit 3 can
control the light output level of the optical amplifying unit 1 by
changing a reference value used for comparison according to the input
light level detected by the level detecting unit 4.
In other words, a large correlation exists between this input light level
(light quantity) and a multiple signal number and the reduced number of
wavelengths (multiple signal number) can be detected from the size of a
received light level. Accordingly, compared with the optical amplifier for
directly detecting the number of wavelengths, output power per wave can be
maintained constant during multiplexing without making a circuitry
complex.
In the optical amplifier 13 of the first embodiment constructed in the
above-noted manner, as shown in FIG. 4, after a wavelength multiplexed
signal (optical signal) is inputted, the optical signal is branched into
portions by the first light branching circuit 8. Then, the portion of the
optical signal branched to the optical amplifying unit 1 side is amplified
by the optical amplifying unit 1 and further branched by the second light
branching circuit 9. Then, the portion of the optical signal branched to
the light receiver 2 side by the second light branching circuit 9 is
converted into an electric signal by the light receiver 2 and compared
with a reference value change information by the comparator 30.
The reference value change information used for comparison is generated by
the level detecting unit 4 based on another portion of the optical signal
obtained by branching performed by the first light branching circuit 8.
Specifically, in the level detecting unit 4, after the portion of the
optical signal obtained by branching performed by the first light
branching circuit 8 is inputted, the level of this optical signal is
converted into an electric signal by the light receiver 40 and then
compared with an auxiliary reference value set beforehand in each of the
comparator circuits 41-1 to 41-n according to a multiple signal number.
The result of this comparison is converted into a reference value having a
predetermined level by the level converting unit 42 and then outputted.
The output from the level detecting unit 4, which has been obtained as a
result of the foregoing processing, is used as the above-noted reference
value change information.
The comparator 30 compares the output from the light receiver 2 with the
reference value having a predetermined level which is generated by the
level detecting unit 4. Then, the comparator 30 controls the pumping light
source of the optical amplifying unit 1 via the pumping light source
control circuit 31 based on the result of this comparison. Accordingly,
output power for the optical signal from the optical amplifier 13 is
maintained constant.
With the optical amplifier 13 thus constructed, since the gain of the
optical amplifying unit 1 can be controlled according to the input light
level of an optical signal which has been inputted, compared with the
amplifier for directly detecting the number of wavelengths, the number of
multiplexed wavelengths can be easily detected without making a circuitry
complex even when a change occurs in the number of multiplexed
wavelengths.
Therefore, the optical amplifier can be simplified and the performance of
the amplifier as a whole can be greatly improved. In addition, since the
number of multiplexed wavelengths can be surely detected, output power for
each wavelength can be maintained constant and highly reliable
transmission quality is assured without any reductions in the quality of a
light waveform.
According to the method for outputting the comparison result of the input
light level in the comparator 41, "1" is outputted only from the
comparator circuit (comparator circuit 41-2 corresponding to the
wavelength number 2 in the above-described example) corresponding to the
number of wavelengths (total number of wavelengths) which have been
inputted. However, for instance if the comparator circuits are for the
number of wavelengths which have been inputted, "1" may be outputted from
all the comparator circuits.
In other words, in the above-described example (the signal of a wavelength
number 2 has been inputted), "1" may be outputted from the comparator
circuit 41-1 corresponding to the wavelength number 1 and the comparator
circuit 41-2 corresponding to the wavelength number 2 and "0" may be
outputted from the comparator circuits 41-3 and 41-4 (i.e., "1", "1", "0",
and "0"). In this case, addresses in the address converting unit 42A of
the subsequent stage can be set so as to be respectively converted into
corresponding addresses as in the foregoing case.
(b1) Modified Example of the First Embodiment
Referring to FIG. 6 which is a block diagram showing the modified example
of the first embodiment of the present invention, an optical amplifier 14
shown comprises an optical amplifying unit 1, a light receiver 2, a
control unit 3, a level detecting unit 4A and first and second light
branching circuits 8 and 9. Codes similar to the foregoing codes denote
like elements or almost like elements and thus, detailed description
thereof will be omitted.
The level detecting unit (input light level detecting unit) 4A includes a
light receiver 40, an amplifier 44, an analog/digital converting circuit
45, a timer 46A, a sampling circuit 46B, a memory 46C, first and second
comparators 46D and 47 and a level converting unit 48. The light receiver
(light receiving unit) 40 is similar or almost similar to the light
receiver shown in FIG. 4 and thus, its detailed description will be
omitted.
The amplifier 44 amplifies an electric signal obtained by photoelectric
conversion performed by the light receiver 40. The analog/digital
converting circuit (A/D) 45 converts an output (analog signal) from the
amplifier 44 into a digital signal. The timer 46A outputs a specified
sampling timing signal to the later-described sampling circuit 46B.
The sampling circuit 46B samples digital data from the analog/digital
converting circuit 45 according to a predetermined sampling timing signal
(time interval) from the timer 46A and outputs the sampled data to the
later-described memory 46C and first and second comparators 46D and 47.
The memory 46C holds (stores) data from the sampling circuit 46B and is
constituted as, for instance a latch circuit.
The first comparator 46D compares current received light information from
the sampling circuit 46B with past received light information stored in
the memory 46C. If the result of comparison discovers that changes have
occurred in these bits of received light information between the two
points of time, in other words if a difference between the current and
past multiple signal numbers is discovered, the first comparator 46D
outputs a trigger signal to the second comparator 47. Thus, in the first
comparator 46D, the quantity of a received light can be detected according
to a timewise change.
The timer 46A, the sampling circuit 46B, the memory 46C and the first
comparator 46D constitute a received light change information arithmetic
unit 46. In this received light change information arithmetic unit 46,
information regarding a change in the received light information between
the two points of time as described above is calculated.
The second comparator 47 compares an output (received light information)
from the sampling circuit 46B with a preset auxiliary reference value
according to a multiple signal number. The second comparator 47 includes
comparator circuits 47-1 to 47-n (n is a natural number) corresponding in
number to the number of input wavelengths. Specifically, when a trigger
signal from the first comparator 46D is received, the second comparator 47
compares the input signal with a preset auxiliary reference value (REF-1
to REF-N).
The level converting unit 48 converts the information compared by the
second comparator 47 into a reference value having a predetermined level.
Specifically, the unit 48 functions in a manner similar to that for the
level converting unit 42 shown in FIG. 4. This output (reference value) is
supplied as reference value change information to be used by the control
unit 3. The second comparator 47 and the level converting unit 48
constitute a reference value change information supplying unit 43A.
Referring to FIG. 8 which illustrates comparison performed in the level
detecting unit 4A of the modified example, if a current time is .tau.-1 as
shown, a past level stored in the memory 46C (received light quantity at a
time .tau.-2) is compared with a current level from the sampling circuit
46B (received light quantity at a time of .tau.-1) in the first comparator
46D. In this case, since the received light levels are equal to each other
(.tau.n; initial level for both), no difference in comparing results is
determined. Accordingly, no trigger signals are outputted from the first
comparator 46D (second comparator 47 is OFF).
Thereafter, when a time becomes .tau.0, a past level stored in the memory
46C (.tau.n; received light quantity at a time of .tau.-1) is compared
with a current level from the sampling circuit 46B (.lambda.n-1; received
light quantity at a time of .tau.0) in the first comparator 46D. In this
case, since the received light levels are different from each other, a
difference in comparing results is determined. Accordingly, a trigger
signal is outputted from the first comparator 46D and then the second
comparator 47 is started (second comparator 47 is ON).
The comparator circuits 47-1 to 47-n of the second comparator 47 shown in
FIG. 6 are configured respectively as window comparators 47A-1 to 47A-n 20
like those shown in FIG. 7. In this case, two reference values (REF.sub.i
U and REF.sub.i D; i is a natural number) are set in each of the window
comparators 47A-1 to 47A-n. Accordingly, even when a fluctuation occurs in
input received light information, such a fluctuation can be flexibly dealt
with by preventing its influence on comparing and detecting operations.
In other words, in this case, for example as shown in FIG. 9, since the
level of an auxiliary reference value (reference level) in the second
comparator 47 has a sufficient range (REF-1; see the arrow A of FIG. 9), a
timewise change (see the arrow C of FIG. 9) caused by the deterioration of
a received light quantity (.lambda.n) after the lapse of time (see the
arrow B of FIG. 9) can be dealt with.
As described above, according to the modified example, information
regarding received lights between two point of time, present and past, is
sampled by the sampling circuit 46B for an optional period and when a
change occurs in the information regarding the received lights between
these two points of time, comparing with a specified auxiliary reference
value is performed. Accordingly, the existence of a reduction in the
number of wavelength multiplexed signals can be detected while considering
a timewise change in a received light quantity.
With the optical amplifier 14 of the modified example constructed in the
above-noted manner, as in the case of the optical amplifier 13 described
above with reference to FIG. 4, after a wavelength multiplexed signal
(optical signal) is inputted, a portion of the optical signal is branched
by the first light branching circuit 8. Then, a portion of the optical
signal branched to the optical amplifying unit 1 side is amplified by the
optical amplifying unit 1 and further branched by the second light
branching circuit 9. Thereafter, the portion of the optical signal
branched to the light receiver 2 side by the second light branching
circuit 9 is converted into an electric signal by the light receiver 2 and
compared with reference value change information by the comparator 30.
The reference value change information used for the above-described
processing is generated by the level detecting unit 4A based on another
portion of the optical signal obtained by branching performed by the first
light branching circuit 8 in a manner below. In the level detecting unit
4A, after a portion of an optical signal obtained by branching performed
by the first light branching circuit 8 is inputted, this portion is
converted into an electric signal by the light receiver 40, amplified by
the amplifier 44 and then converted into a digital signal by the
analog/digital converting circuit 45. Then, this digital signal is sampled
by the sampling circuit 46B based on a timing from the timer 46A and
outputted to the memory 46C and the first comparator 46D.
Thereafter, in the first comparator 46D, current received light information
from the sampling circuit 46B is compared with past received light
information stored in the memory 46C. If the result of this comparison
shows that a change has occurred in the received light information between
these two points of time, a trigger signal is outputted to the second
comparator 47. On the other hand, if the result of the comparison shows no
change between the current received light information and the past
received light information, no trigger signals are outputted.
Then, upon having received the trigger signal from the first comparator
46D, the second comparator 47 compares the received light information from
the sampling circuit 46B with an auxiliary reference value. The result of
this comparison is then converted into a reference value having a
predetermined level by the level converting unit 48 and outputted. The
output from the level detecting unit 4A which has been obtained through
the above-described processing is used as the reference value change
information.
Thereafter, in the comparator 30, the output from the light receiver 2 is
compared with the reference value change information generated by the
level detecting unit 4A. The pumping light source of the optical
amplifying unit 1 is then controlled by the pumping light source control
circuit 31 based on the result of this comparison. Accordingly, the level
of output power for the optical signal from the optical amplifier 14 is
maintained constant.
With the optical amplifier 14 of the modified example, since the
constitution of the amplifier is simplified as in the case of the first
embodiment and the gain of the optical amplifying unit 1 is controlled
when a change occurs in received light information between the two points
of time, efficient comparison can be performed without being affected by a
fluctuation in a received light quantity after the lapse of time.
Accordingly, the performance of the optical amplifier can be improved and
power consumption can be reduced.
(c) Second Embodiment of the Invention
Referring to FIG. 10 which is a block diagram showing the constitution of
the optical amplifier of the second embodiment of the present invention,
an optical amplifier 15 shown comprises an optical amplifying unit 1, a
light receiver 2, a control unit 3A, a wavelength monitoring circuit 5, a
light source control circuit 6, a light source 7, first and second light
branching circuits 8 and 9, a memory 50, an encoding circuit 51, an
oscillator 52, a driving circuit 53 and a coupler 70. Codes similar to the
codes described above denote like elements or almost like elements and
thus, detailed description thereof will be omitted.
The control unit 3A controls the optical amplifying unit 1 by comparing the
light output of the optical amplifying unit 1 monitored by the light
receiver 2 with a specified reference value so as to cause the light
output of the optical amplifying unit 1 to take a predetermined output
value. The control unit 3A includes a comparator 30A and a pumping light
source control circuit (PUMP LD CONTROL CIRCUIT) 31.
The comparator 30A compares an electric signal outputted from the light
receiver 2 with a specified reference value. Different from the first
embodiment, this specified value is used as a fixed value. For the pumping
light source control circuit 31, a circuit similar or almost similar to
that in the first embodiment is shown and thus, its detailed description
will be omitted. Also, as in the case of the first embodiment, during
cutting off of light transmission, this control unit 3A can detect a
signal to this effect and temporarily stop its control operation.
The wavelength monitoring circuit (multiple signal number detecting unit) 5
detects multiple signal number information for an optical signal which has
been inputted. As shown in FIG. 11, this monitoring circuit 5 includes a
light receiver 500, a filter unit 501, a comparator 502 and a logic
circuit 503.
The light receiver (light receiving unit) 500 receives an optical signal
which has been inputted. The filter unit 501 detects multiple signal
number information from information regarding a received light detected by
the light receiver 500. Specifically, the filter unit 501 includes a
plurality of band-pass filters 501-1 to 501-n (n is a natural number) for
a plurality of wavelengths. Superimposed signal components (e.g., f1 to f4
from oscillators 84-1 to 84-4 described later with reference to FIG. 25)
are selectively outputted.
In other words, when the filter unit 501 is installed in the optical
amplifier 13 as the receiving side of the optical transmission system, for
example as shown in FIG. 25, the oscillators 84-1 to 84-4 are installed in
the transmitting side of a corresponding terminal station. The optical
transmission system shown in FIG. 25 is for illustration of an example of
a 4-wave multiplex transmitting unit. Codes similar to the codes described
above denote like elements or almost like elements (see FIG. 27) and thus,
detailed description thereof will be omitted.
Specifically, the 4-wave multiplex transmitting unit shown in FIG. 25
superimposes frequencies (f1 to f4) on main signals (DATA 1 to DATA 4) by
the oscillators 84-1 to 84-4 for optical signals having wavelengths
(.lambda.1 to .lambda.4). These modulated optical signals are multiplexed
by a coupler 85 and then outputted to an optical amplifier.
The comparator 502 shown in FIG. 11 compares an output from the filter unit
501 with a specified referenced value. In order to deal with a plurality
of wavelengths, the comparator 502 includes a plurality of comparator
circuits 502-1 to 502-n (n is a natural number). In each of the comparator
circuits 502-1 to 502-n, a multiple signal which has been inputted is
compared with each reference value and the existence of the wavelength
component of the signal which has been inputted is detected. In other
words, an output (wavelength information) from the comparator 502
corresponds to the number of wavelengths which have reached the optical
amplifier 15.
Specifically, in the comparator 502, if the result of comparison shows no
difference between the multiple signal which has been inputted and each
reference value (no reduction has occurred in the number of wavelengths),
"0" (L level) is outputted. On the other hand, if the result of comparison
shows the existence of a difference (a reduction has occurred in the
number of wavelengths), "1" (H level) is outputted.
The operation of the comparator 502 will now be described by taking the use
of a 4-wave multiple signal as an example. It is assumed that a specified
reference value for the comparator circuit 502-1 is set to a value
according to the signal of a wavelength .lambda.1, a specified reference
value for the comparator circuit 502-2 is set to a value according to the
signal of a wavelength .lambda.2, a specified reference value for the
comparator circuit 502-3 is set to a value according to the signal of a
wavelength .lambda.3 and a specified reference value for the comparator
circuit 502-4 is set to a value according to the signal of a wavelength
.lambda.4.
In this condition, when the optical signals of all the wavelengths are
inputted, "0" is outputted from all of the comparator circuits 502-1 to
502-4. When the signals of the wavelengths .lambda.1 and .lambda.2 are
inputted, "1" is outputted from the comparator circuits 502-3 and 502-4
for the wavelengths .lambda.3 and .lambda.4 to which no inputs have been
made (i.e., "0", "0", "1" and "1").
The result of comparison performed by the comparator 502 is outputted as
wavelength information (.lambda. information) to the later-described
encoding circuit 51 and the light source control circuit 6. The result of
comparison is also outputted as information used for determining the
existence of wavelengths to the later-described logic circuit 503.
The logic circuit (OR) 503 performs an ORing operation for an output from
the comparator 502. Specifically, the logic circuit 503 includes an OR
circuit and outputs "1" (H level) when "1" is outputted from any one of
the comparator circuits 502-1 to 502-n. In other words, the logic circuit
503 can detect the existence of wavelengths which have not been inputted
(sometimes referred to as non-input wavelengths, hereinafter).
An output signal from the logic circuit 503 is used, as described later, to
control the actuation of each of the oscillator 52, the driving circuit 53
and the light source control circuit 6 (controlling of power ON/OFF).
The memory 50 stores information regarding all the wavelengths of a
multiple signal number having a plurality of wavelengths which have been
inputted and the identification number of a repeater (repeater ID) in
which the optical amplifier 15 is incorporated. The memory 50 outputs
information requested by the later-described encoding circuit 51.
The encoding circuit 51 encodes wavelength information outputted from the
wavelength monitoring circuit 5. The encoding circuit 51 optionally reads
the repeater ID of the optical amplifier 15 and wavelength information
(wavelength code) appropriate for a non-input wavelength from the memory
50. The encoding circuit 51 performs encoding based on a signal from the
later-described oscillator 52.
The oscillator 52 decides a transmission speed for encoding performed by
the encoding circuit 51. The oscillator 52 outputs a timing signal to the
encoding circuit 51 based on power ON information from the wavelength
monitoring circuit 5. The driving circuit (modulation circuit) 53
modulates the later-described light source 7. This driving circuit 53 is
also actuated based on power ON information from the wavelength monitoring
circuit 5.
The light source control circuit (light source control unit) 6 controls the
light source 7 (this light source 7 includes a plurality of light sources
as described later) according to multiple signal number information
detected by the wavelength monitoring circuit 5 so as to cause the light
source to output a compensating optical signal, which in turn causes the
light output level of the optical amplifying unit 1 to take a specified
level. The light source control circuit 6 selects and actuates a light
source appropriate for an optical signal having a wavelength which has not
been inputted.
This light source control circuit 6 is also actuated based on power ON
information from the wavelength monitoring circuit 5. In other words, the
oscillator 52, the driving circuit 53 and the light source control circuit
6 are actuated by receiving power ON information from the wavelength
monitoring circuit 5 only when wavelengths which have not been inputted
are detected.
After the light source 7 has been actuated, actuation and control by the
light source control circuit 6 are performed based on a temperature and a
current.
The light source (compensating optical signal generation light source) 7
supplies a compensating optical signal to the input side of the optical
amplifying unit 1. Specifically, as shown in FIG. 8, the light source 7
includes a plurality of light sources 7-1 to 7-n (n is a natural number)
for producing optical signals having wavelengths .lambda.1 to .lambda.n so
as to deal with a plurality of wavelengths (all the wavelengths .lambda.1
to .lambda.n used in the transmission system). When a reduction occurs in
a wavelength number for signals which have been inputted, the light source
7 supplies compensating optical signals from the light sources 7-1 to 7-n
for outputting optical signals having wavelengths equivalent in number to
the reduced wavelength number to the input side of the optical amplifying
unit 1.
In other words, the light sources 7-1 to 7-n output optical signals having
the same wavelengths as the wavelengths (non-input wavelengths) determined
to be unoperated by the wavelength monitoring circuit 5. In the
compensating optical signal, the bits of information (control information)
obtained by the wavelength monitoring circuit 5, the memory 50 and the
encoding circuit 51 are superimposed on one another.
A code 71 shown in FIG. 18 denotes an optical coupler. Optical signals from
the light sources 7-1 to 7-n are multiplexed by this optical coupler 71.
An output from the optical coupler 71 is supplied to the input side of the
optical amplifying unit 1 (to the coupler 70 provided in a stage before
the optical amplifying unit 1 in the case of FIG. 10).
The coupler 70 synthesizes a compensating optical signal from the light
source 7 with an input optical signal from the first light branching
circuit 8. Specifically, a portion of the input optical signal from the
first light branching circuit 8, whose wavelength number has been reduced,
is compensated for by a compensating optical signal from the light source
7.
Accordingly, since a constant light quantity is always outputted from the
coupler 70, the light output level of the optical amplifying unit 1 can be
maintained at a specified level. In FIG. 10, the optical signal from the
light source 7 is inputted to the coupler 70 located in the stage before
the optical amplifying unit 1. But any position of the input side of the
optical amplifying unit 1 can be selected for this purpose.
In the optical amplifier 15, since the multiple signal number of an optical
signal which has been inputted is monitored and a compensating optical
signal like that described above is outputted based on the information
regarding the multiple signal number, the condition (non-input wavelength
number) of the repeater station (repeater station 20D in the case of FIG.
26) can be understood from control information regarding the compensating
optical signal which has been outputted in each of the terminal stations
20A to 20C (see FIG. 26).
With the optical amplifier 15 of the second embodiment constructed in the
above-noted manner, as shown in FIG. 10, after a wavelength multiplexed
signal (optical signal) is inputted, a portion of this optical signal is
branched by the first light branching circuit 8. The portion of the
optical signal branched to the wavelength monitoring circuit 5 side is
converted into an electric signal by the light receiver 500 as in the case
of the first embodiment described above with reference to FIG. 11. Then,
signal components are selectively outputted by the filter unit 501 and
respectively compared with set reference values by the comparator 502.
Each of the result of this comparison is outputted as wavelength
information to the encoding circuit 51 and the light source control
circuit 6 and as information for determining the existence of wavelengths
to the logic circuit 503.
Now, the operations of the wavelength monitoring circuit 5 and its
surrounding units when a reduction occurs in the number of wavelengths
will be described. For example, if the optical signal of a wavelength
.lambda.2 is not inputted, in the wavelength monitoring circuit 5, "1" is
outputted from the comparator circuit 502-2 while "0" is outputted from
each of the other comparator circuits 502-1 and 502-3 to 502-n. These
outputs are then transmitted to the encoding circuit 51, the light source
control circuit 6 and the logic circuit 503 in the subsequent stages.
From the logic circuit 503, power ON information is outputted to the
oscillator 52, the driving circuit 53 and the light source control circuit
6 based on the output from the comparator 502-1. The encoding circuit 51
then reads the repeater ID of the optical amplifier 15 and wavelength
information (wavelength code) appropriate for the wavelength .lambda.2
from the memory 50 based on a timing signal from the oscillator 52 and
encodes the repeater ID and the wavelength information. The light source
control circuit 6 causes the light source 7-2 to output an optical signal
appropriate for the wavelength .lambda.2 based on a driving operation
performed by the driving circuit 53.
Thereafter, the compensating optical signal outputted from the light source
7-2 is synthesized with an input optical signal from the first light
branching circuit 8 by the coupler 70. In the optical amplifying unit 1,
this synthesized optical signal is subjected to gain control based on a
control signal processed by the light receiver 2 and the control unit 3
and then outputted as a specified optical signal.
With the optical amplifier 15 constructed in the above-noted manner, since
a compensating optical signal is supplied to the input side of the optical
amplifying unit 1 according to the multiple signal number of an optical
signal which has been inputted, output power for each wavelength can be
controlled to a constant level without changing the circuitry of the
feedback control system of the existing optical amplifying unit 1.
(c1) Modified Example of the Wavelength Monitoring Circuit 5 of the Second
Embodiment
In the optical amplifier 15 of the second embodiment, the wavelength
monitoring circuit 5 is used as means for detecting multiple signal number
information for an optical signal which has been inputted. However, as
means (mode) for detecting such multiple signal number information, for
instance the following three means ›modified examples (A) to (C)! can be
used instead.
(A) First Modified Example of the Wavelength Monitoring Circuit 5
In the detailed description of the second embodiment, reference was made to
the wavelength monitoring circuit 5 in which the filter unit 501 included
the plurality of filters so as to deal with the plurality of wavelengths.
However, for example, as shown in FIG. 12, a wavelength monitoring circuit
5A having a wavelength variable filter 504 for making a filter wavelength
variable can be used for the present invention. In this case, the
wavelength monitoring circuit 5A includes, in addition to the wavelength
variable filter 504, a filter sweep circuit 505, a light receiver 506 and
a wavelength detecting circuit 507.
The filter sweep circuit 505 sweeps the filter wavelength of the wavelength
variable filter 504 in a fixed cycle. Upon receiving a predetermined
signal (filter sweep voltage; Vsp) corresponding to the filter wavelength
of the wavelength variable filter 504, the filter sweep circuit 505
decides the filter wavelength of the wavelength variable filter 504.
Specifically, the filter sweep voltages and the filter wavelengths of the
wavelength variable filter 504 correspond to one another one for one as
shown in FIG. 14. For example, when a filter sweep voltage is 1V, a
wavelength is set so as to allow the signal of a wavelength .lambda.1 to
be passed. When a voltage is 2V, a wavelength is set so as to allow the
signal of a wavelength .lambda.2 to be passed.
The filter sweep circuit 505 may perform sweeping in a step form (e.g.,
when the wavelengths .lambda.1 to .lambda.4 are used, the filter for the
wavelength .lambda.5 or over is not selected) and alternatively in a
linear form (i.e., the circuit 505 sweeps all the wavelengths in sequence)
so as to select only the wavelengths to be actually used. Further, this
filter sweep circuit 505 outputs a timing for performing sweeping as a
timing signal (Timing CLK) to the later-described wavelength detecting
circuit 507 ›timing signal; see FIG. 15(a)!.
The light receiver 506 receives an optical signal which has been inputted
via the wavelength variable filter 504 and converts this optical signal
into an electric signal. The output (Vpd) of the light receiver 506 is
supplied to the later-described wavelength detecting circuit 507.
The wavelength detecting circuit 507 detects the wavelengths which have not
been inputted based on the timing signal from the filer sweep circuit 505
and the output from the light receiver 506. For example, as shown in FIG.
13, the wavelength detecting circuit 507 includes a waveform shaping
circuit 507A, an exclusive OR circuit 507B, a gate circuit (GATE) 507C, a
memory 507D, a memory reading circuit 507E, a counter 507F and a counter
reset circuit 507G.
The waveform shaping circuit 507A shapes the waveform of a signal which has
been inputted from the light receiver 506 to a rectangular wave ›voltage
Vpd-2; see FIG. 15(b)!. The waveform is shaped based on a specified
reference value (Ref 1). In other words, when the signal which has been
inputted exceeds this reference value, "1" (H level) is outputted. When
the signal does not exceed the reference value, "0" (L level) is
outputted. In FIG. 15, the total wavelength number of a multiple signal
which has been inputted is shown to be "4" (.lambda.1 to .lambda.4). In
this case, it can be understood that the signal of the wavelength
.lambda.3 has not been inputted.
The exclusive OR circuit (EXOR) 507B performs exclusive ORing for the
output from the comparator 502 and the timing signal from the filter sweep
circuit 505. A bit becomes a state of "1" (i.e., "1" is outputted) for the
wavelength which has not been inputted (omitted wavelength) ›voltage Vf;
see FIG. 15(c)!. Also, during this period, ON information is
simultaneously outputted to the oscillator 52, the driving circuit 53 and
the light source control circuit 6 in the subsequent stage.
The counter 507F outputs a count value based on the timing signal from the
filter sweep circuit 505. For example, when the total wavelength number of
a multiple signal which has been inputted is 4, count values of "1 to 4"
are outputted to the later-described gate circuit 507C and the counter
reset circuit 507G. In other words, "1" is outputted for the wavelength
.lambda.1 and "2" is outputted for the wavelength .lambda.2.
The counter reset circuit 507G outputs a reset signal ("0") when a count
number is satisfied. For example, when the total multiplex number of a
signal which has been inputted is "4", after counting is made up to "4",
the counter reset circuit 507G resets the counter 507F and the
later-described memory reading circuit 507E.
The gate circuit 507C outputs "1" (opens the gate) based on a count value
from the counter 507F when "1" is outputted from the exclusive OR circuit
507B. For example, when the signal of the wavelength .lambda.3 contained
in a 4-wave multiplexed signal is not inputted, with a count value from
the counter 507F set to "3", a signal ("1") based on the wavelength
.lambda.3 which has not been inputted is outputted to the memory 507D. ON
information outputted from the exclusive OR circuit 507B may be outputted
from this gate circuit 507C.
The memory 507D stores the signal outputted from the gate circuit 507C. The
memory reading circuit 507E reads information stored in the memory 507D by
using a reset signal from the counter reset circuit 507G as a trigger
signal. The information read by the memory reading circuit 507E is
outputted as .lambda. information to the encoding circuit 51 and the light
source control circuit 6.
Thus, in the wavelength monitoring circuit 5A shown in FIG. 12, after an
optical signal is inputted from the first light branching circuit 8, this
optical signal is passed through the wavelength variable filter 504 and
then subjected to photoelectric conversion by the light receiver 506 and
then, in the wavelength detecting circuit 507, detection of a wavelength
which has not been inputted like that described above with reference to
FIG. 13 is performed based on an electric signal from the light receiver
506 and a timing signal from the filter sweep circuit 505.
The specific process will be described below by taking as an example
non-inputting of the wavelength .lambda.3 contained in a multiple signal
having a total wavelength number of "4". Upon receiving an output (Vpd)
from the light receiver 506, the wavelength detecting circuit 507 first
shapes the output to a rectangular wave by the waveform shaping circuit
507A ›see FIG. 15(b)!. Then, the wavelength detecting circuit 507 performs
exclusive ORing for this rectangular wave and a timing clock outputted
from the filter sweep circuit 505 ›see FIG. 15(a)! by the exclusive OR
circuit 507B and thereby outputs a bit for the omitted wavelength ›Vf; see
FIG. 15(c)!.
On the other hand, counting is made by the counter 507F based on the timing
clock from the filter sweep circuit 505. In the gate circuit 507C, the
gate is opened according to this counting when an output (Vf) from the
exclusive OR circuit 507B is "1". A count value obtained at this time is
stored in the memory 507D. In this case, a count number 3 is recorded.
Then, the counter reset circuit 507G resets the counter 507F to "0" when a
count number from the counter 507F is 4 and sends a reset signal to the
memory reading circuit 507E. The memory reading circuit 507E then performs
reading from the memory by using this reset signal as a trigger signal.
This information is outputted as .lambda. information to the encoding
circuit 51 and the light source control circuit 6.
With the wavelength monitoring circuit 5A configured in the above-noted
manner, since an omitted wavelength can be detected by using the
wavelength variable filter 504 which can make a filter wavelength
variable, a circuitry can be reduced in size. Accordingly, the optical
amplifier can be greatly reduced in weight.
(B) Second Modified Example of the Wavelength Monitoring Circuit 5
In the second embodiment and the first modified example (A), the wavelength
monitoring circuit 5 and 5A having filters were described. However, for
example, as shown in FIG. 16, a wavelength monitoring circuit 5B having a
plurality of light receivers 509-1 to 509-n so as to deal with a plurality
of wavelengths can be used for the present invention. In this case, the
wavelength monitoring circuit 5B includes a spectroscope unit
(spectrometer) 508, a light receiver 509 and a logic circuit 510.
The spectroscope unit 508 divides an optical signal which has been inputted
into some lights by considering its wavelengths. The light receiver 509
individually receives the lights obtained by division performed by the
spectroscope unit 508. In each of the plurality of light receivers 509-1
to 509-n provided so as to deal with a plurality of wavelengths .lambda.1
to .lambda.n, the optical signal is converted into an electric signal by
using a light receiving element.
An output from each of the light receivers 509-1 to 509-n is outputted as
wavelength information (.lambda. information) to the encoding circuit 51
and the light source control circuit 6 as in the case shown in FIGS. 11
and 12. This output is also supplied to the later-described logic circuit
510 as information used for determining the existence of wavelengths.
The logic circuit 510 performs an ORing operation for the output from the
light receiver 509. As in the case of the logic circuit 503 (see FIG. 11),
this logic circuit 510 can detect the existence of wavelengths which have
not been inputted.
With the wavelength monitoring circuit 5B configured in the above-noted
manner, since optical signals which have been inputted can be individually
received, wavelength information can be surely detected. Accordingly,
degree of flexibility can be greatly increased when a system is
constituted for the optical amplifier.
(C) Third Modified Example of the Wavelength Monitoring Circuit 5
In the second embodiment, the wavelength monitoring circuit 5 (see FIG. 11)
for detecting multiple signal number information for an input optical
signal was described. However, for example, as shown in FIG. 17, a
wavelength monitoring circuit 5C for detecting an input light level can be
used for the present invention.
In this case, the wavelength monitoring circuit 5C includes a light
receiver 511, a comparator 512, a logic circuit 513 and a wavelength
information supplying unit 519. The light receiver 511 and the logic
circuit 513 function in manners similar to those for the light receiver
500 and the logic circuit 503 shown in FIG. 11 and thus, detailed
description thereof will be omitted.
The comparator 512 compares an output from the light receiver 511 with a
specified reference value. The comparator 512 includes a plurality of
comparator circuits 512-1 to 512-n so as to deal with a plurality of
wavelengths (all the wavelengths .lambda.1 to .lambda.n used in the
transmission system). In this comparator 512, each wavelength is detected
from the input level of an optical signal received by the light receiver
511.
The wavelength information supplying unit 519 outputs wavelength
information based on an input light level obtained by comparison performed
by the comparator 512. Specifically, the wavelength information supplying
unit 519 includes an address converting unit 519A, a memory control unit
519B and a memory 519C.
The address converting unit 519A converts a signal from each of the
comparator circuits 512-1 to 512-n into an address. The memory 519C stores
wavelength information for each wavelength. The memory control unit 519B
reads wavelength information from the memory 519C based on address
information from the address converting unit 519A, the address information
corresponding to the address in this case. The wavelength information from
the memory 519C is outputted to the encoding circuit 51 and the light
source control circuit 6.
The comparator 512, the logic circuit 513 and the wavelength information
supplying unit 519 shown in FIG. 15 constitute a multiple signal number
output unit. Multiple signal number information (wavelength information)
is outputted from information regarding a light received by the light
receiver 511 (received light level).
Therefore, with the wavelength monitoring circuit SC configured in the
above-noted manner, since an input light level can be detected, compared
with the optical amplifier for directly detecting a wavelength number, a
circuitry can be simplified. Accordingly, the optical amplifier can be
reduced in weight and costs.
(c2) Modified Example of the Light Source 7 in the Second Embodiment
Next, the modified example of the light source 7 in the second embodiment
will be described. In the second embodiment, as shown in FIG. 18, the
light source 7 having the plurality of light sources 7-1 to 7-n so as to
deal with a plurality of wavelengths was described in detail. However, for
example, as shown in FIG. 19, a light source 7A which can make a
transmitted wavelength variable so as to deal with a plurality of
wavelengths can be used for the present invention.
In this case, the light source 7A includes a plurality of wavelength
variable light sources 7A-1 to 7A-m (m<n; equivalent to "total wavelength
number-smallest operation wavelength number" during the operation of the
transmission system). In each of these wavelength variable light sources
7A-1 to 7A-m, an optical signal having a wavelength equivalent to a
wavelength which has not been inputted is outputted based on a control
signal from a light source control circuit 6A. The light source control
circuit 6A performs control based on a temperature or a current and
outputs a control signal according to wavelength information. A code 72
shown in FIG. 19 denotes an optical coupler. This optical coupler 72
multiplexes an optical signal outputted from each of the wavelength
variable light sources 7A-1 to 7A-m.
Thus, with the light source 7A shown in FIG. 19, since a transmitted
wavelength can be made variable, a circuitry can be reduced in size.
Accordingly, the entire optical amplifier can be reduced in size.
(c3) Others
The wavelength variable light sources 7A-1 to 7A-m provided in the light
source 7A may be contained in a normal light source 7 (see FIG. 18), in
which each of the light sources is fixed for each wavelength, as in the
case of the second embodiment. In this case, wavelength control is
performed by changing the temperature of each of these light sources (0.1
nm/.degree. C., generally). In other words, the optical signal of a
wavelength which has not been set can be dealt with by changing the
temperatures of the other set light sources.
Therefore, compared with the use of the normal light source 7 in which each
of the light sources is fixed for each wavelength like that shown in FIG.
18, the number of light sources to be installed can be reduced. Compared
with the use of the wavelength variable light sources 7A-1 to 7A-m like
that shown in FIG. 19, costs can be reduced. Accordingly, the optical
amplifier can be reduced in size and weight.
Furthermore, in the second embodiment, the light sources 7 and 7A
respectively include the pluralities of light sources 7-1 to 7-n and 7A-1
to 7A-m. However, each of these light sources 7 and 7A may include only
one such light source. In this case, for a wavelength which has not been
inputted (cut wavelength), input total power supplied to the optical
amplifying unit 1 can be coincided with that during a normal period by
increasing a current for this light source. Wavelength control is
performed based on a temperature also in this case.
Therefore, since a light source for one wavelength can be used also for the
other wavelengths, a circuitry can be greatly reduced in size.
(d) Third Embodiment of the Invention
Referring to FIG. 20 which is block diagram showing the constitution of the
optical amplifier of the third embodiment of the present invention, a an
optical amplifier 16 shown is obtained as a result of a gain control
improvement made for the optical amplifying unit 1 of the second
embodiment.
More particularly, in the second embodiment, the existing optical
amplifying unit 1 is used by compensating for the shortage of an input
optical signal by a compensating optical signal based on the multiplexed
wavelength number of the signal which have not been inputted. On the other
hand, in the third embodiment, the shortage of an input optical signal is
compensated for by a compensating optical signal and the gain of the
optical amplifying unit 1 is controlled based on the multiplexed
wavelength number of the input optical signal (input light level).
A control unit 3B shown in FIG. 20 controls the optical amplifying unit 1
so as to cause the light output of the optical amplifying unit 1 to take a
predetermined value. This control processing is performed by comparing the
light output of the optical amplifying unit 1 monitored by a light
receiver 2 with a specified reference value as in the cases of the control
units 3 and 3A described above respectively with reference to FIGS. 4 and
10. The control unit 3B includes a comparator 30B and a pumping light
source control circuit (PUMP LD CONTROL CIRCUIT) 31. Specifically, the
comparator 30B performs comparison for an output from the light receiver 2
by using an output from a later-described wavelength monitoring circuit 5D
as a reference value.
The wavelength monitoring circuit 5D detects information regarding the
multiple signal number of an optical signal which has been inputted. As
shown in FIG. 21, this wavelength monitoring circuit SD includes a light
receiver 500, a filter unit 501, a comparator 502, a logic circuit 503 and
a reference value change information supplying unit 514. In other words,
the wavelength monitoring circuit 5D shown in FIG. 21 is composed by
adding the reference value change information supplying unit 514 to the
wavelength monitoring circuit 5 shown in FIG. 11.
The reference value change information supplying unit 514 supplies
reference value change information to the control unit 3B according to
detected multiple signal number information. This unit 514 includes an
adder 514A and a level converting unit 514B. The adder 514A adds together
outputs from a plurality of comparator circuits 502-1 to 502-n.
The level converting unit 514B converts information obtained by addition
performed by the adder 514A into a reference value having a predetermined
level. Specifically, this level converting unit 514B functions in a manner
similar to that for the level converting unit 42 shown in FIG. 4. An
output (reference value change information) from the level converting unit
514B is supplied to the control unit 3B. In the control unit 3B, this
output is used as a reference value by the comparator 30B.
Thus, in the third embodiment, a compensating optical signal is supplied to
the input side of the optical amplifying unit 1 according to information
regarding the multiple signal number of an optical signal which has been
inputted, a light output level is controlled to a specified level and the
gain of the optical amplifying unit 1 is controlled according to the
multiple signal number information (input light level).
According to the technology disclosed in the third embodiment, by
simultaneously performing supplying of a compensating optical signal and
controlling of the gain of the optical amplifying unit 1, a time needed
until the compensating optical signal is normally started (transition
state) can be shortened by the control operation of a feedback system
which responds more quickly. In addition to the above-noted manner, the
optical amplifier 16 can function in a manner described below.
In the optical amplifier 16 shown in FIG. 20, if the light source 7 is
composed of one light source (only an optical signal for one wave is
outputted), when an input optical signal is reduced by two waves or more,
an optical signal of only one wave can be outputted from the light source
7. Accordingly, for two or more wavelengths, light amplification control
is performed in the control unit 3B by changing the reference value.
In other words, the wavelength shortage of the optical signal can be
sufficiently dealt with by performing the gain control (control processing
performed by the feedback system) of the optical amplifying unit 1 in the
control unit 3B even in the simply structured optical amplifier in which
the light source 7 includes only one light source. It can thus be
understood that light amplification control can be performed irrespective
of the number of light sources installed in the light source 7
(compensating optical signal quantity).
Therefore, with the optical amplifier 16 constructed in the above-noted
manner, since means for performing both supplying of a compensating
optical signal and controlling of the gain of the optical amplifying unit
1 based on multiple signal number information is provided, a time needed
until the compensating optical signal is normally started (transition
state) can be shortened by a control operation performed by the feedback
system which responds more quickly. Moreover, since the wavelength
shortage of an optical signal can be adjusted by a control operation
performed by the feedback system irrespective of the number of light
sources installed in the light source 7 (compensating optical signal
quantity), a circuitry can be reduced in size. Accordingly, degree of
flexibility can be increased when a system is constituted.
(d1) Modified Examples of the Wavelength Monitoring Circuit 5D in the Third
Embodiment
In the optical amplifier 16 of the third embodiment, the wavelength
monitoring circuit 5D is used as means for detecting the multiple signal
number information of an optical signal which has been inputted. In this
case, as means (modes) for detecting this multiple signal number
information, for example the following three means ›(A) to (C)! can also
be used.
(A) First Modified Example of the Wavelength Monitoring Circuit 5D
In the third embodiment, the wavelength monitoring circuit SD having the
plurality of filters in the filter unit 501 so as to deal with the
plurality of wavelengths was described in detail. However, a wavelength
monitoring circuit 5E having a wavelength variable filter 504 for making a
filter wavelength variable like that shown in FIG. 22 can be used for the
present invention. In this case, the wavelength monitoring circuit SE
includes, in addition to the wavelength variable filter 504, a filter
sweep circuit 505, a light receiver 515, a wavelength detecting circuit
507 and a smoothing circuit 516.
In other words, the wavelength monitoring circuit 5E is configured by
adding the smoothing circuit 516 to the wavelength monitoring circuit 5A
shown in FIG. 12.
The light receiver 515 receives an optical signal which has been inputted
via the wavelength variable filter 504 and converts this optical signal
into an electric signal. The electric signal is outputted to the
wavelength detecting circuit 507 and the later-described smoothing circuit
516.
Detection of the existence of all the input wavelengths by the wavelength
variable filter 504 needs a specified period (fixed cycle). However, in
the first modified example, as described above, wavelength detection
information having a time range from the wavelength variable filter 504 is
outputted as an electric signal from the light receiver 515 to the
wavelength detecting circuit 507 and the smoothing circuit 516.
The smoothing circuit 516 performs an averaging operation for the output
from the light receiver 515 (this output contains the wavelength detection
information having a time range from the wavelength variable filter 504).
An output from the smoothing circuit 516 is used as a reference value in
the control unit 3B according to the number of multiplexed wavelengths.
In other words, the simply configured smoothing circuit 516 can output a
reference value according to the number of multiplexed wavelengths without
using a memory such as a shift register.
With the wavelength monitoring circuit 5E configured in the above-noted
manner, since a reference value can be obtained by using the wavelength
variable filter 504 for making a filter wavelength variable according to
the result of wavelength detection and the number of multiplexed
wavelengths, a circuitry can be reduced in size. Accordingly, the entire
optical amplifier can be reduced in size and weight. Also, a reference
value can be outputted by a simple configuration according to the number
of multiplexed wavelengths even if a memory such as a shift register or
the like is not used.
(B) Second Modified Example of the Wavelength Monitoring Circuit 5D
In the third embodiment and the first modified example (A), the wavelength
monitoring circuit 5D having the plurality of filters 501-1 to 501-n and
the wavelength monitoring circuit 5E having the wavelength variable filter
504 were respectively described in detail. However, a wavelength
monitoring circuit 5F having a plurality of light receivers 509-1 to 509-n
so as to deal with a plurality of wavelengths like that shown in FIG. 23
can be used for the present invention. In this case, the wavelength
monitoring circuit 5F is configured by adding a reference value change
information supplying unit 517 to the wavelength monitoring circuit 5B
shown in FIG. 16.
The reference value change information supplying unit 517 supplies
reference value change information to the control unit 3B according to
detected multiple signal number information. This reference value change
information supplying unit 517 includes an adder 517A and a level
converting unit 517B. The adder 517A adds together outputs from the
plurality of light receivers 509-1 to 509-n. The level converting unit
517B converts information obtained by addition performed by the adder 517A
into a reference value having a predetermined level. Specifically, this
converting unit 517B functions in a manner similar to that for the level
converting unit 42 shown in FIG. 4. Its output (reference value change
information) is supplied to the control unit 3B. In the control unit 3B,
this information is used as a reference value by the comparator 30B.
With the wavelength monitoring circuit 5F configured in the above-noted
manner, since optical signals which have been inputted can be individually
received, wavelength information can be surely detected. Accordingly,
degree of flexibility can be greatly increased when a system is
constituted for the optical amplifier.
(C) Third Modified Example of the Wavelength Monitoring Circuit 5D
In the third embodiment, the wavelength monitoring circuit SD (see FIG. 21)
for detecting the multiple signal number information of an optical signal
which has been inputted was described in detail. However, a wavelength
monitoring circuit 5G for performing not only detecting of an input light
level but also changing of the reference value of the feedback system like
that shown in FIG. 24 can be used for the present invention.
The wavelength monitoring circuit 5G is configured by adding a level
converting unit 518 to the wavelength monitoring circuit 5C shown in FIG.
17. This level converting unit 518 functions in a manner similar to that
for the level converting unit 42 shown in FIG. 4 and thus, description
thereof will be omitted.
With the wavelength monitoring circuit 5G configured in the above-noted
manner, since an input light level can be detected, a circuitry can be
simplified compared with the optical amplifier for directly detecting the
number of wavelengths. Accordingly, the optical amplifier can be reduced
in weight and costs. Further, with this wavelength monitoring circuit 5G,
since the reference value of the feedback system can be changed, the
operational speed of the entire amplifier can be made faster.
(e) Others
The wavelength monitoring circuits 5 and 5A to 5G and the light sources 7
(7-1 to 7-n) and 7A (7A-1 to 7A-m) of the second and third embodiments are
not limited to the above-described combinations. These elements can be
freely combined together. Therefore, a necessary circuit can be configured
according to conditions to be used and degree of flexibility can be
greatly increased when a system is constituted for the optical amplifier.
* * * * *
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