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| United States Patent |
6,456,381
|
|
Nakamura
, et al.
|
September 24, 2002
|
Apparatus for and method of using optical interference of light propagating
through an optical fiber loop
Abstract
A signal/vibration detecting technique employs a simple structure to
identify a target optical fiber among many and carry out a bidirectional
conversation through the target optical fiber. First ends of optical
fibers (202A, 202B), one of which is a target optical fiber, are connected
to an optical transceiver (201). Second ends of the optical fibers are
connected to each other to form a loop. A local unit (203) is installed at
the loop. The local unit vibrates the loop, and the optical transceiver
emits lights so that the lights are oppositely propagated through the
loop. The propagated lights are coupled together so that they interfere
with each other. In the intensity of the interfering lights, a change
corresponding to the vibration is detected to identify the target optical
fiber. Once the target optical fiber is identified, it is used to carry
out a conversation between the optical transceiver and the local unit.
| Inventors:
|
Nakamura; Yasushi (Tokyo, JP);
Unami; Yoshiharu (Tokyo, JP);
Niimi; Shinichi (Tokyo, JP)
|
| Assignee:
|
Fujikura Ltd. (Tokyo, JP)
|
| Appl. No.:
|
299580 |
| Filed:
|
April 27, 1999 |
Foreign Application Priority Data
| Apr 28, 1998[JP] | 10-119565 |
| May 13, 1998[JP] | 10-130846 |
| May 28, 1998[JP] | 10-147635 |
| Current U.S. Class: |
356/483; 385/12 |
| Intern'l Class: |
G01B 009/02 |
| Field of Search: |
356/483
385/12,24
359/577,578
|
References Cited [Referenced By]
U.S. Patent Documents
| 4375680 | Mar., 1983 | Cahill et al. | 367/149.
|
| 4536861 | Aug., 1985 | Graindorge et al.
| |
| 5355208 | Oct., 1994 | Crawford et al.
| |
| 5379357 | Jan., 1995 | Sentsui et al. | 385/11.
|
| Foreign Patent Documents |
| 3039235 | May., 1982 | DE.
| |
| 5-346598 | Dec., 1993 | JP.
| |
Primary Examiner: Font; Frank G.
Assistant Examiner: Natividad; Phil
Attorney, Agent or Firm: Sughrue Mion, PLLC
Claims
What is claimed is:
1. A method of identifying a target optical fiber cable among many,
comprising the steps of:
connecting each end of a plurality of optical fibers to each other to form
a loop having two open ends;
connecting an optical transceiver to the open ends of the loop;
emitting a light from a light source of the optical transceiver;
splitting the light by a splitter-coupler of the optical transceiver;
making the split lights incident to the open ends of the loop,
respectively, so that the split lights are oppositely propagated through
the loop;
coupling the oppositely propagated lights so that they interfere with each
other;
converting the interfering lights by a photo-detector of the optical
transceiver into an electric signal that indicates the intensity of the
interfering lights and is responsive to a change in the phase difference
between the lights; and
detecting in the electric signal a physical change applied to the target
optical fiber cable that contains at least a part of the loop, to identify
the target optical fiber cable.
2. A method of identifying a target optical fiber cable among many
according to claim 1, vibration is applied to the target optical cable as
the physical change.
3. A method of identifying a target optical fiber cable among many
according to claims, an optical delay unit is inserted to a portion of the
loop.
4. A method of identifying a target optical fiber among many, comprising
the steps of:
connecting each end of a plurality of optical fibers including the target
optical fiber to each other to form a loop having two open ends;
connecting an optical transceiver to the open ends of the loop;
emitting a light from a light source of the optical transceiver;
splitting the light by a splitter-coupler of the optical transceiver;
making the split lights incident to the open ends of the loop,
respectively, so that the split lights are oppositely propagated through
the loop;
coupling the oppositely propagated lights so that they interfere with each
other;
converting the interfering lights by a photo-detector of the optical
transceiver into an electric signal that indicates the intensity of the
interfering lights and is responsive to a change in the phase difference
between the lights; and
detecting in the electric signal a physical change applied to the loop to
identify the target optical fiber.
5. A method of identifying a target optical fiber among many according to
claim 4, vibration is applied to the loop as the physical change.
6. A method of identifying a target optical fiber among many according to
claim 4, an optical delay unit is inserted to a portion of the loop.
Description
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a signal/vibration detecting technique
employing optical interference. The technique emits lights into open ends
of a loop made of a plurality of optical fibers so that the lights are
propagated clockwise and counterclockwise, respectively, through the loop,
couples the propagated lights together so that they interfere with each
other, and detects a physical change such as vibration applied to the loop
by observing a change in the intensity of the interfering lights.
The present invention also relates to a technique of applying the
signal/vibration detecting technique to identify a target optical fiber
cable among many during, for example, cable changing and removing work.
The present invention also relates to a technique of applying the
signal/vibration detecting technique to identify a target optical fiber
among optical fibers contained in a cable and use the identified target
optical fiber to carry out a conversation without cutting the optical
fiber.
2. Description of the Prior Art
Various sensors and detectors that use optical interference caused on
optical fibers and lasers have been proposed. For example, a Mach-Zhehnder
interferometer emits a laser light from a light source, splits the laser
light into two so that the two split lights pass through two optical
paths, couples the lights so that they interfere with each other, and
detects a phase shift between the lights according to a change in
interference fringes.
This technique is applicable to provide a simple structure consisting of a
laser and a loop made of a plurality of optical fibers to detect a
physical change such as vibration applied to the loop.
The technique is also applicable to identify a target optical fiber cable
among many, or identify a target optical fiber among optical fibers
contained in a cable and carry out a conversation through the target
optical fiber.
This technique is applicable to changing and removing work of optical fiber
cables in a telephone tunnel or a manhole. During such work, the technique
is used to identify a target optical fiber cable among many cables so that
erroneous cables may not be cut. When changing an optical fiber to another
in a given cable, the technique is used to identify the target optical
fiber among many optical fibers contained in the cable.
To identify a target optical fiber cable, a prior art emits a light into an
end of the cable, applies ultrasonic waves to the cable, monitors
polarization of the light propagated through the cable influenced by the
ultrasonic waves, and identifies the cable.
Another prior art emits a light from a light source and splits it into two
by an optical coupler. The split lights are made incident to two different
optical fibers contained in a target optical fiber cable. The split lights
are propagated through the optical fibers, are coupled together by an
optical coupler at the other end of the cable, and are received by a
photo-detector. Vibration is applied to the cable. The vibration causes
stress on the cable to change the lengths of optical paths through which
the split lights are propagated. This changes a phase difference and
polarization plane between the propagated lights, thereby changing the
intensity of interference of the coupled lights at the end of the cable.
According to this change, the cable is identified even if it is laid among
many cables.
These prior arts are applicable to identify a target optical fiber among
optical fibers contained in a cable.
The prior arts mentioned above must change polarization planes to identify
a target optical fiber cable or a target optical fiber. If there is an
outside factor to change polarization planes, the prior arts are unable to
correctly identify the target cable or fiber. As a result, the prior arts
achieve only a poor probability of 70% in identifying a target cable or
fiber. This probability will further deteriorates depending on the
material of a target cable or fiber. In addition, the prior arts require
expensive devices.
The prior arts malfunction when the difference between the lengths of two
optical fibers for propagating lights exceeds a coherent length. The prior
arts need an additional optical coupler be installed at the receiver side
of a cable, and if lights propagated through two optical fibers in the
cable are polarized orthogonally, do not work because no interference
occurs between the propagated lights.
On the other hand, the signal/vibration detecting technique of the present
invention employs a simple, low-cost structure to surely identify a target
optical fiber cable or a target optical fiber.
A target optical fiber identified according to any one of the techniques
mentioned above can be used without being cut to carry out a conversation
between distant work sites during cable/fiber changing and removing work.
To achieve such conversation, a prior art bends the target optical fiber to
cause a loss, changes the radius of the bend, and uses brightness
modulation due to the radius change. Another prior art distorts the
optical fiber and uses a change in polarization of the optical fiber due
to the distortion.
The prior art using brightness modulation applies vibration with, for
example, a speaker to the optical fiber to change the radius of the bend
formed on the optical fiber. The change in the radius changes a loss to
change brightness, thereby modulating a light passed through the optical
fiber. This technique is employed by an optical conversation method
disclosed in Japanese Unexamined Patent Publication No. 4-368629 and by an
optical fiber bend setting method for an optical fiber conversation
apparatus disclosed in Japanese Unexamined Patent Publication No.
5-264909.
Japanese Unexamined Patent Publication No. 7-38502 discloses an optical
fiber conversation apparatus that makes lights enter into and exit from
the side of an optical fiber. A transmitter emits a light from a light
source, modulates the brightness of the light, and makes the light
incident to a bend of the optical fiber. A receiver converts leakage
lights from a bend of the optical fiber into an electric signal.
The technique of the Japanese Unexamined Patent Publication No. 4-368029
vibrates a bend of an optical fiber to change the brightness of a light,
thereby modulating the light. The degree of modulation of this technique
is 9%, which is very low, and therefore, must be compensated. In addition,
vibrating an optical fiber needs a complicated mechanism to increase the
size and cost of the technique.
The technique of the Japanese Unexamined Patent Publication No. 7-38502
makes a light enter into and exit from the side of an optical fiber, to
cause large optical coupling losses. As a result, this technique is unable
to realize a large dynamic range and clear conversation.
The technique of changing polarization planes by ultrasonic waves is unable
to secure a conversation if external factors make the polarization planes
orthogonal to each other.
On the other hand, the signal/vibration detecting technique of the present
invention employs a simple, inexpensive structure to improve the degree of
modulation and reduce mechanical load on an optical fiber that is used for
conversation.
SUMMARY OF THE INVENTION
An object of the present invention is to provide a signal/vibration
detecting technique employing optical interference and a simple structure
made of a laser and a loop of a plurality of optical fibers.
Another object of the present invention is to provide a technique of
identifying a target optical fiber cable among many with the use of the
signal/vibration detecting technique employing optical interference and a
simple, inexpensive apparatus.
Still another object of the present invention is to provide a technique of
identifying a target optical fiber among many and using the identified
optical fiber to carry out a conversation at an improved degree of
modulation and reduced load on the optical fiber, with the use of the
signal/vibration detecting technique.
In order to accomplish the objects, a first aspect of the present invention
provides an apparatus for detecting a signal based on optical
interference, having a light source, a photo-detector, a loop made of a
plurality of optical fibers and having open ends, and a splitter-coupler
connected to the open ends of the loop. The light source emits a light,
which is split by the splitter-coupler. The split lights are made incident
to the open ends of the loop, respectively, so that the split lights are
oppositely propagated through the loop. The oppositely propagated lights
are coupled by the splitter-coupler so that they interfere with each
other. The interfering lights are converted by the photo-detector into a
signal that indicates the intensity of the interfering lights and is
responsive to a change in the phase difference between the lights.
According to the signal from the photo-detector, the first aspect detects a
physical change applied to the loop and changed the phase difference
between the oppositely propagated lights.
A second aspect of the present invention provides a method of detecting a
signal based on optical interference, including the steps of emitting a
light from a light source, splitting the light by a splitter-coupler,
making the split lights incident to open ends of a loop made of a
plurality of optical fibers so that the split lights are oppositely
propagated through the loop, coupling the propagated lights by the
splitter-coupler so that they interfere with each other, converting the
interfering lights by a photo-detector into a signal that indicates the
intensity of the interfering lights and is responsive to a change in the
phase difference between the lights, and detecting, according to the
signal from the photo-detector, a physical change applied to the loop and
changed the phase difference between the lights.
A third aspect of the present invention adds, to the method of the second
aspect, the step of inserting a delay unit in the loop or between the loop
and the splitter-coupler, to delay the lights propagated through the loop.
Even if being applied to the midpoint of the loop, the physical change
surely causes, due to the delay unit, a phase difference between the
lights oppositely propagated through the loop, and therefore, is surely
detectable according to the signal provided by the photo-detector.
A fourth aspect of the present invention provides an apparatus for
detecting vibration based on optical interference, having a light source,
a photo-detector, a loop made of a plurality of optical fibers and having
open ends, and a splitter-coupler connected to the open ends of the loop.
The light source emits a light, which is split by the splitter-coupler.
The split lights are made incident to the open ends of the loop,
respectively, so that the split lights are oppositely propagated through
the loop. The oppositely propagated lights are coupled by the
splitter-coupler so that they interfere with each other. The interfering
lights are converted by the photo-detector into a signal that indicates
the intensity of the interfering lights and is responsive to a change in
the phase difference between the lights caused by vibration applied to the
loop.
According to the signal from the photo-detector, the fourth aspect detects
a physical change, i.e., vibration applied to the loop and changed the
phase difference between the oppositely propagated lights.
A fifth aspect of the present invention provides a method of detecting
vibration based on optical interference, including the steps of emitting a
light from a light source, splitting the light by a splitter-coupler,
making the split lights incident to open ends of a loop made of a
plurality of optical fibers so that the split lights are oppositely
propagated through the loop, coupling the oppositely propagated lights by
the splitter-coupler so that they interfere with each other, converting
the interfering lights by a photo-detector into a signal that indicates
the intensity of the interfering lights and is responsive to a change in
the phase difference between the lights, and detecting, according to the
signal from the photo-detector, vibration applied to the loop and changed
the phase difference between the lights.
A sixth aspect of the present invention adds, to the method of the fifth
aspect, the step of inserting a delay unit in the loop or between the loop
and the splitter-coupler, to delay the lights oppositely propagated
through the loop.
Even if being applied to the midpoint of the loop, the vibration surely
causes, due to the delay unit, a phase difference between the lights
oppositely propagated through the loop, and therefore, is surely
detectable according to the signal from the photo-detector.
A seventh aspect of the present invention provides an apparatus for
identifying a target optical fiber cable among many, having a light
source, a photo-detector, a loop made of a plurality of optical fibers and
having open ends, and a splitter-coupler. The splitter-coupler is
connected to the light source, the photo-detector, and the open ends of
the loop. The light source emits a light. The splitter-coupler receives
the light, splits the light, makes the split lights incident to the open
ends of the loop, respectively, so that the split lights are oppositely
propagated through the loop, receives the oppositely propagated lights,
couples the received lights so that they interfere with each other, and
supplies the interfering lights to the photo-detector. The photo-detector
converts the interfering lights into an electric signal that indicates the
intensity of the interfering lights and is responsive to a change in the
phase difference between the lights. According to the electric signal, the
seventh aspect detects a physical change applied to the target optical
fiber cable that contains at least a part of the loop.
An eighth aspect of the present invention provides an apparatus for
identifying a target optical fiber cable among many, having a light
source, a photo-detector, a loop made of a plurality of optical fibers and
having open ends, and a splitter-coupler. The splitter-coupler is
connected to the light source, the photo-detector, and the open ends of
the loop. The light source emits a light, which is received by the
splitter-coupler. The splitter-coupler splits the light, makes the split
lights incident to the open ends of the loop, respectively, so that the
split lights are oppositely propagated through the loop, receives the
oppositely propagated lights, couples the received lights so that they
interfere with each other, and supplies the interfering lights to the
photo-detector. The photo-detector converts the interfering lights into an
electric signal that indicates the intensity of the interfering lights and
is responsive to a change in the phase difference between the lights.
According to the electric signal, the eighth aspect detects vibration
applied to the target optical fiber cable that contains at least a part of
the loop.
A ninth aspect of the present invention provides an apparatus for
identifying a target optical fiber cable among many, having an optical
transceiver connected to open ends of a loop made of a plurality of
optical fibers and a local unit for applying vibration to loop. The
optical transceiver has a light source for emitting a light, a
splitter-coupler for splitting the light, making the split lights incident
to the open ends of the loop, respectively, so that the lights are
oppositely propagated through the loop, receiving the oppositely
propagated lights, and coupling the received lights so that they interfere
with each other, and a photo-detector for converting the interfering
lights into an electric signal. This electric signal indicates the
intensity of the interfering lights, is responsive to a change in the
phase difference between the lights caused by the vibration applied to the
loop, and is used to identify the target optical fiber cable that contains
at least a part of the loop.
Any one of the seventh to ninth aspects of the present invention picks up a
plurality of optical fibers in a target optical fiber cable, or at least
one of them in a target optical fiber cable and others in another optical
fiber cable. Each end of the picked-up optical fibers is connected to each
other into a loop having two open ends.
The light source emits a light. The splitter-coupler splits the light and
makes the split lights incident to the open ends of the loop,
respectively, so that the lights are oppositely propagated through the
loop. The oppositely propagated lights are received and coupled by the
splitter-coupler to that they interfere with each other. The interfering
lights are supplied to the photo-detector.
Under this state, the local unit applies a physical change, which may be
pressure, bend, tension, or vibration, to optical fiber cables including
the target cable one after another.
The photo-detector converts the interfering lights from the
splitter-coupler into an electric signal that indicates the intensity of
the interfering lights and is responsive to a change in the phase
difference between the lights. When the local unit applies the physical
change to the target optical fiber cable that contains at least a part of
the loop, the signal from the photo-detector shows a change corresponding
to the physical change. As a result, one can identify the target optical
fiber cable among many cables.
A tenth aspect of the present invention provides a method of identifying a
target optical fiber cable among many, including the steps of connecting
each end of a plurality of optical fibers to each other to form a loop
having two open ends, connecting an optical transceiver to the open ends
of the loop, emitting a light from a light source of the optical
transceiver, splitting the light by a splitter-coupler of the optical
transceiver, making the split lights incident to the open ends of the
loop, respectively, so that the split lights are oppositely propagated
through the loop, coupling the oppositely propagated lights so that they
interfere with each other, converting the interfering lights by a
photo-detector of the optical transceiver into an electric signal that
indicates the intensity of the interfering lights and is responsive to a
change in the phase difference between the lights, and detecting in the
electric signal a physical change applied to the target-optical fiber
cable that contains at least a part of the loop.
An eleventh aspect of the present invention provides a method of
identifying a target optical fiber cable among many, including the steps
of connecting each end of a plurality of optical fibers to each other to
form a loop having two open ends, connecting an optical transceiver to the
open ends of the loop, emitting a light from a light source of the optical
transceiver, splitting the light by a splitter-coupler of the optical
transceiver, making the split lights incident to the open ends of the
loop, respectively, so that the split lights are oppositely propagated
through the loop, coupling the oppositely propagated lights so that they
interfere with each other, converting the interfering lights by a
photo-detector of the optical transceiver into an electric signal that
indicates the intensity of the interfering lights and is responsive to a
change in the phase difference between the lights, and detecting, in the
electric signal, vibration applied to the target optical fiber cable that
contains at least a part of the loop.
A twelfth aspect of the present invention adds, to any one of the tenth and
eleventh aspects, the step of inserting a delay unit in the loop or
between the loop and the optical transceiver, to delay the lights
oppositely propagated through the loop.
Even if being applied to the midpoint of the loop, the physical change or
vibration surely causes a phase difference between the lights oppositely
propagated through the loop, and therefore, is surely detectable according
to the signal from the photo-detector.
A thirteenth aspect of the present invention provides an apparatus for
identifying a target optical fiber among many, having a light source, a
photo-detector, a loop made of a plurality of optical fibers and having
open ends, and a splitter-coupler. The splitter-coupler is connected to
the light source, the photo-detector, and the open ends of the loop made
of the a plurality of optical fibers including the target optical fiber.
The light source emits a light. The splitter-coupler splits the light,
makes the split lights incident to the open ends of the loop,
respectively, so that the split lights are oppositely propagated through
the loop, receives the oppositely propagated lights, couples the received
lights so that they interfere with each other, and supplies the
interfering lights to the photo-detector. The photo-detector converts the
interfering lights into an electric signal that indicates the intensity of
the interfering lights and is responsive to a change in the phase
difference between the lights. According to the electric signal, the
thirteenth aspect detects a physical change applied to loop.
A fourteenth aspect of the present invention provides an apparatus for
identifying a target optical fiber among many, having a light source, a
photo-detector, a loop made of a plurality of optical fibers and having
open ends, and a splitter-coupler. The splitter-coupler is connected to
the light source, the photo-detector, and the open ends of the loop made
of the a plurality of optical fibers including the target optical fiber.
The light source emits a light. The splitter-coupler splits the light,
makes the split lights incident to the open ends of the loop,
respectively, so that the split lights are oppositely propagated through
the loop, receives the oppositely propagated lights, couples the received
lights so that they interfere with each other, and supplies the
interfering lights to the photo-detector. The photo-detector converts the
interfering lights into an electric signal that indicates the intensity of
the interfering lights and is responsive to a change in the phase
difference between the lights. According to the electric signal, the
fourteenth aspect detects vibration applied to the loop.
A fifteenth aspect of the present invention provides an apparatus for
identifying a target optical fiber among many, having an optical
transceiver and a local unit. The optical transceiver is connected to open
ends of a loop made of a plurality of optical fibers including the target
optical fiber. The local unit applies vibration to the loop. The optical
transceiver has a light source for emitting a light, a splitter-coupler
for splitting the light, making the split lights incident to the open ends
of the loop, respectively, so that the lights are oppositely propagated
through the loop, receiving the oppositely propagated lights, and coupling
the received lights so that they interfere with each other, and a
photo-detector for converting the interfering lights into an electric
signal. The electric signal indicates the intensity of the interfering
lights, is responsive to a change in the phase difference between the
lights caused by the vibration applied to the loop, and is used to
identify the target optical fiber.
Any one of the thirteenth to fifteenth aspects of the present invention
picks up a target optical fiber and another optical fiber in a given
cable, connects one ends of the picked-up optical fibers to each other
through an optical connector to form a loop having two open ends. The
light source emits a light. The splitter-coupler splits the light and
makes the split lights incident to the open ends of the loop,
respectively, so that the split lights are oppositely propagated through
the loop. The oppositely propagated lights are received and coupled by the
splitter-coupler so that they interfere with each other. The interfering
lights are supplied to the photo-detector.
Under this state, the local unit applies a physical change, which may be
pressure, bend, tension, or vibration, to optical fibers in the cable one
after another.
The photo-detector converts the interfering lights into an electric signal
that indicates the intensity of the interfering lights. When the local
unit applies the physical change to the target optical fiber, the signal
from the photo-detector shows a change corresponding to the physical
change. As a result, one can identify the target optical fiber.
A sixteenth aspect of the present invention provides a method of
identifying a target optical fiber among many, including the steps of
connecting each end of a plurality of optical fibers including the target
optical fiber to each other to form a loop having two open ends,
connecting an optical transceiver to the open ends of the loop, emitting a
light from a light source of the optical transceiver, splitting the light
by a splitter-coupler of the optical transceiver, making the split lights
incident to the open ends of the loop, respectively, so that the split
lights are oppositely propagated through the loop, coupling the oppositely
propagated lights so that they interfere with each other, converting the
interfering lights by a photo-detector of the optical transceiver into an
electric signal that indicates the intensity of the interfering lights and
is responsive to a change in the phase difference between the lights, and
detecting in the electric signal a physical change applied to the loop.
A seventeenth aspect of the present invention provides a method of
identifying a target optical fiber among many, including the steps of
connecting each end of a plurality of optical fibers including the target
optical fiber to each other to form a loop having two open ends,
connecting an optical transceiver to the open ends of the loop, emitting a
light from a light source of the optical transceiver, splitting the light
by a splitter-coupler of the optical transceiver, making the split lights
incident to the open ends of the loop, respectively, so that the split
lights are oppositely propagated through the loop, coupling the oppositely
propagated lights so that they interfere with each other, converting the
interfering lights by a photo-detector of the optical transceiver into an
electric signal that indicates the intensity of the interfering lights and
is responsive to a change in the phase difference between the lights, and
detecting, in the electric signal, vibration applied to the loop.
An eighteenth aspect of the present invention adds, to any one of the
sixteenth and seventeenth aspects, the step of inserting a delay unit in
the loop or between the loop and the optical transceiver, to delay the
lights propagated through the loop.
Even if being applied to the midpoint of the loop, the physical change or
vibration surely causes a phase difference between the lights oppositely
propagated through the loop, and therefore, is surely detectable according
to the signal from the photo-detector.
A nineteenth aspect of the present invention provides an optical fiber
communication apparatus having an optical transceiver connected to open
ends of a loop made of a plurality of optical fibers including a target
optical fiber, and a local unit attached to the loop. The optical
transceiver has a light source for emitting a light, a first microphone
for converting a voice into an electric signal, a driver for modulating
the light from the light source according to the electric signal from the
first microphone, a splitter-coupler for splitting the light from the
light source, making the split lights incident to the open ends of the
loop, respectively, so that the lights are oppositely propagated through
the loop, receiving the oppositely propagated lights, and coupling the
received lights so that they interfere with each other, a first
photo-detector for converting the interfering lights into an electric
signal, and a first voice unit for demodulating the electric signal from
the first photo-detector into a voice signal. The local unit has a bender
for bending the loop, a second photo-detector for receiving leakage lights
from the bend of the loop and converting them into an electric signal, a
second voice unit for demodulating the electric signal from the second
photo-detector into a voice signal, a second microphone for converting a
voice into an electric signal, and a vibrator for applying vibration to
the loop according to the electric signal from the second microphone.
At a first work point at the open ends of the loop, the first microphone
converts a voice into an electric signal, and the driver modulates a light
from the light source according to the electric signal. The
splitter-coupler splits the light from the light source and makes the
split lights incident to the open ends of the loop. At a second work point
where the local unit is installed, the bender bends the loop, the second
photo-detector receives leakage lights from the bend and converts them
into an electric signal, and the second voice unit demodulates the
electric signal into a voice signal.
At the second work point, the second microphone converts a voice into an
electric signal, and the vibrator vibrates the loop according to the
electric signal. At this time at the first work point, the
splitter-coupler couples the lights oppositely propagated through the loop
to make the lights interfere with each other. The first photo-detector
converts the interfering lights into an electric signal that indicates the
intensity of the interfering lights and is responsive to a change in the
phase difference between the lights. The first voice unit demodulates the
electric signal into a voice signal, which is used to reproduce the voice
entered by the local unit.
The nineteenth aspect enables the first and second work points to carry out
a conversation between them through the loop once the target optical fiber
that forms a part of the loop is identified.
A twentieth aspect of the present invention structures the apparatus of the
nineteenth aspect such that the driver of the optical transceiver
FM-modulates a light from the i light source, the first voice unit of the
optical transceiver AM-demodulates a signal from the first photo-detector
into a voice signal, and the second voice unit of the local unit
FM-demodulates a signal from the second photo-detector into a voice
signal.
The twentieth aspect differently modulates and demodulates a signal from
the optical transceiver to the local unit and a signal from the local unit
to the optical transceiver so that each of the optical transceiver and
local unit can clearly reproduce a voice signal sent from the opposite
party without crosstalk.
A twenty-first aspect of the present invention provides an optical fiber
communication method including the steps of connecting each end of a
plurality of optical fibers to each other through an optical connector to
form a loop having two open ends, connecting an optical transceiver to the
open ends of the loop, attaching a local unit to the loop between the
optical transceiver and the optical connector, and carrying out
optical-transceiver steps and local-unit steps. The optical-transceiver
steps include emitting a light from a light source, converting a voice
into an electric signal by a first microphone, modulating the light from
the light source by a driver according to the electric signal from the
first microphone, splitting the light from the light source by a
splitter-coupler, making the split lights incident to the open ends of the
loop, respectively, so that the split lights are oppositely propagated
through the loop, coupling the oppositely propagated lights by the
splitter-coupler so that they interfere with each other, converting the
interfering lights into an electric signal by a first photo-detector, and
demodulating the electric signal into a voice signal by a first voice
unit. The local-unit steps include bending the loop, receiving leakage
lights from the bend by a second photo-detector, converting the leakage
lights by the second photo-detector into an electric signal, demodulating
the electric signal into a voice signal by a second voice unit, converting
a voice into an electric signal by a second microphone, and vibrating the
loop by a vibrator according to the electric signal from the second
microphone, thereby carrying out a conversation between the optical
transceiver and the local unit.
A twenty-second aspect of the present invention adds, to the twenty-first
aspect, the step of inserting a delay unit in the loop or between the loop
and the optical transceiver, to delay the lights propagated through the
loop.
Even if the second work point is at the midpoint of the optical-fiber loop,
the twenty-second aspect surely causes a phase difference between the
lights oppositely propagated through the loop and surely detects a signal
applied to the loop by the local unit, according to the signal from the
first photo-detector.
A twenty-third aspect of the present invention adds, to any one of the
twenty-first and twenty-second aspects, the steps of FM-modulating a light
from the light source by the driver of the optical transceiver,
AM-demodulating a signal from the first photo-detector into a voice signal
by the first voice unit of the optical transceiver, and FM-demodulating a
signal from the second photo-detector into a voice signal by the second
voice unit of the local unit.
This aspect employs different modulation techniques for a signal from the
optical transceiver to the local unit and for a signal from the local unit
to the optical transceiver, so that each of the optical transceiver and
local unit may clearly reproduce voice from a signal sent from the
opposite party without crosstalk.
Other and further objects and features of the present invention will become
obvious upon an understanding of the illustrative embodiments about to be
described in connection with the accompanying drawings or will be
indicated in the appended claims, and various advantages not referred to
herein will occur to one skilled in the art upon employing of the
invention in practice.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a block diagram showing an apparatus for detecting a
signal/vibration based on optical interference according to an embodiment
of the present invention;
FIGS. 2A to 2D are waveform diagrams showing various signals in the
apparatus of FIG. 1;
FIG. 3 is a block diagram showing a use of the apparatus of FIG. 1;
FIGS. 4A and 4B are waveform diagrams showing a vibration signal and phase
shifts caused in propagated lights by the vibration signal according to
the embodiment of FIG. 1
FIGS. 5A to 5C are waveform diagrams showing output signals of a
photo-detector of the apparatus of FIG. 1 that change in response to
applied vibration;
FIG. 6 is a block diagram showing an apparatus for detecting a
signal/vibration based on optical interference according to another
embodiment of the present invention;
FIG. 7 is a block diagram showing an apparatus for detecting a
signal/vibration based on optical interference according to still another
embodiment of the present invention;
FIG. 8 is a block diagram showing a test model of an apparatus for
detecting a signal/vibration based on optical interference according to
the present invention;
FIG. 9 is a block diagram showing another test model of an apparatus for
detecting a signal/vibration based on optical interference according to
the present invention;
FIG. 10 is a block diagram showing an apparatus for identifying a target
optical fiber cable according to still another embodiment of the present
invention;
FIG. 11 is a block diagram showing an optical transceiver applicable to the
apparatus of FIG. 10;
FIG. 12 is a block diagram showing an apparatus for identifying a target
optical fiber cable according to still another embodiment of the present
invention;
FIG. 13 is a block diagram showing an optical transceiver applicable to the
apparatuses of FIGS. 10 and 12;
FIG. 14 is a block diagram showing an apparatus for identifying a target
optical fiber according to still another embodiment of the present
invention;
FIG. 15 is a block diagram showing an apparatus for identifying a target
optical fiber according to still another embodiment of the present
invention;
FIG. 16 is a block diagram showing an optical transceiver applicable to the
apparatuses of FIGS. 14 and 15;
FIG. 17 is a block diagram showing an optical transceiver having a
communication function applicable to the apparatuses of FIGS. 14 and 15;
FIG. 18 is a block diagram showing a local unit having a communication
function applicable to the apparatuses of FIGS. 14 and 15;
FIG. 19 is a block diagram showing a local unit having a communication
function applicable to the apparatuses of FIGS. 14 and 15;
FIG. 20 is a block diagram showing an optical transceiver having a
communication function applicable to the apparatuses of FIGS. 14 and 15;
and
FIG. 21 is a block diagram showing a local unit having a communication
function applicable to the apparatuses of FIGS. 14 and 15.
DETAILED DESCRIPTION OF THE EMBODIMENTS
Various embodiments of the present invention will be described with
reference to the accompanying drawings. It is to be noted that the same or
similar reference numerals are applied to the same or similar parts and
elements throughout the drawings, and the description of the same or
similar parts and elements will be omitted or simplified. For the sake of
simplicity, each light source is DC-modulated if not specifically
mentioned, and each splitter-coupler has equal splitting and coupling
efficiencies.
FIG. 1 shows an apparatus for detecting a signal/vibration based on optical
interference according to an embodiment of the present invention. A light
source 1 is a laser diode which is excited by a driver 10 and emits a
laser light. The light is split by a splitter-coupler 2, and the split
lights are made incident to open ends of a loop 3 made of the plurality of
optical fibers so that the split lights are oppositely propagated through
the loop in the clockwise direction A and counterclockwise direction B.
Hereinafter, the light propagated in the clockwise direction A is referred
to as the light A or wave A, and the light propagated in the
counterclockwise direction as the light B or wave B. After propagation
through the loop, the lights A and B are coupled together so that they
interfere with each other. The interfering lights are detected by a
photo-detector (photo-detector) 5 made of a photodiode. The photo-detector
5 converts the interfering lights into an electric signal that indicates
the intensity of the interfering lights. The electric signal is amplified
by an amplifier 11, and the amplified signal is provided outside.
FIGS. 2A to 2D show phases of the lights A and B oppositely propagated
through the loop 3. FIG. 2A shows the lights A and B just split by the
splitter-coupler 2 with the splitter-coupler 2 being an optical fiber
coupler. Since a cross port of the optical fiber coupler causes a phase
shift of .pi./2 to the light passing there, there is a shift of .pi./2
between the phases of the lights A and B. FIG. 2B shows waveforms of the
lights A and B oppositely propagated through the loop 3 and reached the
splitter-coupler 2. Although the lights A and B are oppositely propagated,
the lights pass through the same optical path, i.e., the loop 3 and
therefore, they receive the same loss and phase change due to the
reversibility of light. Accordingly, the lights A and B have substantially
equal amplitudes and phases except the phase difference of FIG. 2A. After
the opposite propagation, the lights A and B are coupled together by the
splitter-coupler 2 so that they interfere with each other as shown in FIG.
2C. When the light B passes through the cross port of the splitter-coupler
2, its phase is again shifted by .pi./2, and therefore, the phases of the
lights A and B are shifted by .pi. in total with respect to each other.
If the wavelength of the light emitted by the light source 1 is 1.3 .mu.m,
a period thereof is 4.times.10.sup.-15 sec because the velocity of light
in vacuum is about 300,000 km/sec. Accordingly, the abscissa of each of
FIGS. 2A to 2C represents a time span of about 10.sup.-15 sec.
Generally, photo-detectors (photo-detectors) convert only the intensity of
a light into an electric signal and do not convert the phase thereof. As a
result, the photo-detectors provide a constant DC signal corresponding to
a DC signal of a light source. When the splitter-coupler 2 is an optical
fiber coupler, the lights A and B involve a phase difference of n after
they are oppositely propagated through the loop 3. Therefore, under nearly
ideal conditions, the output of the splitter-coupler 2 is as shown in FIG.
2D.
FIG. 3 is a block diagram showing the apparatus of FIG. 1 with vibration
being applied to a part of the loop 3. The light source 1 is excited by
the driver 10 and emits a light, which is split by the splitter-coupler 2
into lights A and B. The lights A and B are propagated clockwise and
counterclockwise, respectively, through the loop 3 and are subjected to
vibration at a vibration point P. The oppositely propagated lights A and B
are coupled by the splitter-coupler 2 so that they interfere with each
other. The interfering lights are converted by the photo-detector 5 into
an electric signal that indicates the intensity of the interfering lights.
The electric signal is amplified by the amplifier 11 and is provided
outside.
Changes on the lights A and B due to the vibration will be explained with
reference to FIGS. 4A and 4B. FIG. 4A shows a waveform V of the vibration
applied to the vibration point P of the loop 3. Due to the vibration, the
loop 3 locally contracts and expands to change the length thereof, i.e.,
the length of the optical path of the lights A and B. As a result, the
phases of the lights A and B are changed at the vibration point P
depending on the amplitude of the vibration signal V as shown in FIG. 4B.
Since the lights A and B are oppositely propagated through the loop 3 they
oppositely receive an equal phase shift due to the change in the length of
the optical. path. Thereafter, the lights are coupled by the
splitter-coupler 2 into interfering lights, which are converted by the
photo-detector 5 into an electric signal that indicates the intensity of
the interfering lights. The electric signal is amplified by the amplifier
11 and is provided outside.
FIGS. 5A to 5C show the phases of the lights A and B oppositely propagated
through the loop 3. The phases of the lights A and B arriving at the
splitter-coupler 2 are shifted from each other as shown in FIG. 5A. The
phase shift corresponds to a delay time t1 that corresponds to the
difference between the distances for which the lights A and B travel from
the vibration point P to the splitter-coupler 2. The splitter-coupler 2
couples the received lights A and B into interference waves whose envelope
E changes according to the amplitude of the applied vibration, as shown in
FIG. 5B. Light is a wave having a period of about 10.sup.-15 sec, and
therefore, a change in the intensity of light is expressed with an
amplitude envelope E in a time span of about 10.sup.-4 sec. The
photo-detector 5 provides an electric signal F whose waveform is
substantially equal to the vibration waveform applied to the loop 3 as
shown in FIG. 5C. If there is no vibration, the photo-detector 5 provides
an electric signal of nearly zero as shown in FIG. 2D.
If the difference between the distances for which the lights A and B must
travel from the vibration point P to the splitter-coupler 2 is zero, i.e.,
if the vibration point P is at the midpoint of the loop 3 the lights A and
B are vibrated at the same time and simultaneously arrive at the
splitter-coupler 2. In this case, the phases of the lights A and B are
equally influenced by the vibration, and the phase difference between them
(FIG. 5A) becomes nearly zero. Then, no phase shift is observed in the
interfering lights made of the lights A and B, and therefore, it is
impossible to detect the vibration.
If the vibration signal is of 1 kHz to 1 MHz, a signal period thereof is
10.sup.-3 to 10.sup.-6 sec, and therefore, the abscissa of any one of
FIGS. 5A to 5C represents a time span of about 10.sup.-3 to 10.sup.-6 sec.
If the difference between the distances the lights A and B must travel
from the vibration point P to the splitter-coupler 2 is 1 km, the delay
time t1 is about 10.sup.-6 sec because a group velocity in the optical
fiber is about 200,000 km/sec.
The apparatus for detecting a signal/vibration based on optical
interference of the present invention will be explained with mathematical
expressions. For the sake of simplicity of explanation, it is assumed that
the light source 1 is a laser diode that emits a DC-modulated light and
the splitter-coupler 2 is a 3-dB optical coupler whose splitting and
coupling efficiencies are equal to each other. light from the light source
1 is split by the splitter-coupler 2 into lights A and B of substantially
the same power. The lights A and B are oppositely propagated through the
loop 3 and are coupled together by the splitter-coupler 2 into interfering
lights. The interfering lights are detected by the photo-detector 5, which
is a photodiode and provides an electric signal representing the intensity
of the interfering lights.
Since the lights A and B are generated at the same time by the same light
source 1 and are oppositely propagated through the same loop 3 they
simultaneously arrive at the splitter-coupler 2 and are coupled together
thereby. If no phase shift is applied to the lights A and B, the lights
interfere with each other at the same phase in the splitter-coupler 2.
When a vibrator 6 applies vibration to the vibration point P of the loop 3
the loop 3 locally expands and contracts, to change the phases of the
lights A and B at the same period as that of the vibration.
In FIG. 4B, .phi.(t) is a phase shift applied by the vibrator 6 at the
vibration point P to the electric field of a light propagated through the
loop 3. The light A is emitted by the light source 1 at a certain time
point and is propagated through the loop 3. The phase of an electric field
of the light A is shifted by the vibrator 6 at the vibration point P at
time ta. The light B is emitted by the light source 1 simultaneously with
the light A and is oppositely propagated through the loop 3. The length of
an optical path to the vibration point P for the light B is longer than
that for the light A, and therefore, the light B arrives the vibration
point P temporally behind the light A and the phase of the electric field
of the light B is shifted by the vibrator 6 at time tb. As a result, a
phase shift .phi.(ta) in the electric field of the light A differs from a
phase shift .phi.(tb) in the electric field of the light B due to the
difference between ta and tb. The difference between ta and tb is
dependent on the position of the vibration point P in the loop 3 and
corresponds to the difference between the phase shifts .phi.(ta) and
.phi.(tb).
The phases of the electric fields of the lights A and B are shifted at the
vibration point P, and the lights A and B are coupled together by the
splitter-coupler 2. FIG. 5A shows the waveforms of the phases of the
electric fields of the lights A and B arrived at the photo-detector 5.
At the vibration point P, the light A receives the phase shift .phi.(ta)
and the light B the phase shift .phi.(tb). An angular frequency of light
is no, and the amplitudes of the electric fields of the lights A and B
entering the loop 3 from the splitter-coupler 2 are A and B, respectively.
The lengths of clockwise and counterclockwise optical paths of the lights
A and B along the loop 3 are equal to each other. The influence of
polarization is ignored for the sake of simplicity of calculations.
The electric field of the light A phase-shifted by the vibrator 6 and
arrived at a receiving face of the photo-detector 5 is expressed as
follows:
Ea(t)A cos (.chi..sub.0 t+.phi.(t.sub.a)) (1)
In the splitter-coupler 2, the phases of coupled lights at a cross port are
.pi./2 behind those of emitted lights at a through port. Since the light B
is passed through the cross port of the splitter-coupler 2 twice, the
electric field of the light B is expressed as follows:
Eb(t)=B Cos (.chi..sub.0 t+.phi.(t.sub.b)-.pi.) (2)
The photo-detector 5 receives the overlapping of the electric fields of the
expressions (1) and (2), and an optical current of the received lights is
proportional to the power of the lights. Therefore, an output current I of
the photo-detector 5 is expressed as follows:
##EQU1##
This expression is developed and rearranged, and a term related to an
optical angular velocity that the photo-detector 5 is unable to detect is
ignored. Then, the output current I is expressed as follows:
##EQU2##
This expression shows that a signal reproduced from the optical current
involves a change of .vertline..phi.(ta)-.phi.(tb)+.pi..vertline. that
corresponds to a phase shift .phi.(t) at the vibration point P, i.e., a
change in the amplitude of the vibration at the vibration point P.
If the vibration point P is at the midpoint of the loop 3,
.phi.(ta)=.phi.(tb) to make the difference zero. In this case, the
expression (4) provides a constant to cause no change in the output of the
photo-detector 5. If the level of the signal reproduced from
.vertline..phi.(ta)-.phi.(tb)+.pi..vertline. is smaller than a noise
level, it is impossible to detect the signal. To secure the level of the
reproduced signal so that the signal is detectable,
.vertline..phi.(ta)-.phi.(tb)+.pi..vertline. must sufficiently be large.
For this purpose, an optical delay unit 7 is installed at the midpoint of
the loop 3 as shown in FIG. 6. The delay unit 7 is made of a drum of an
optical fiber whose length is dependent on the properties of the
apparatus. The delay unit 7 secures a sufficient time difference of
"ta-tb" so that the reproduced signal based on the output of the
photo-detector 5 is surely detectable.
In the embodiments mentioned above, the light source 1 emits a light to the
splitter-coupler 2, and the photo-detector 5 converts the output of the
splitter-coupler 2 into an electric signal, which is used to detect a
physical change or vibration applied to the loop 3. The light source 1,
driver 10, photo-detector 5, amplifier 11, etc., may be arranged in a
signal processing unit. In this case, the apparatus of the present
invention is provided with an optical input terminal 8 for supplying an
optical signal to the splitter-coupler 2 and an optical output terminal 9
for receiving an optical signal from the splitter-coupler 2, as shown in
FIG. 7. The input and output terminals 8 and 9 are connected to the signal
processing unit that contains the light source, driver, photo-detector,
amplifier, etc.
A concrete example of the apparatus for detecting a signal/vibration based
on optical interference according to the present invention will be
explained. A single-mode optical fiber (SMF) of 10 km in length and 1.3
.mu.m in wavelength is looped, and ends of the loop are connected to an
optical coupler. The optical coupler is connected to a 1.3-.mu.m
semiconductor laser and a PID photo-detector, thereby forming the
apparatus for detecting a signal/vibration based on optical interference.
The semiconductor laser is connected to a continuous-wave oscillator to
continuously oscillate the laser in response to a DC signal. The PID
photo-detector is connected to an amplifier whose output is observed with
an oscilloscope.
A 10-kHz vibrator is connected to a small speaker, which is connected to a
part of the loop. When the vibrator generates a 10-kHz vibration signal,
one can observe a corresponding 10-kHz signal on the output of the
amplifier without distortion.
To determine an optimum structure for the apparatus for detecting a
signal/vibration based on optical interference, many tests were carried
out. Results of the tests will be explained.
Test 1
FIG. 8 shows a basic test system. Two optical fibers 21 and 22 are each 20
km long. Ends of the optical fibers 21 and 22 are connected to a master
unit 23 through optical connectors 24. The other ends of the optical
fibers 21 and 22 are connected to supplemental optical fibers 25 and 26
each of 2 m long. A part of the optical fiber 26 is formed a bend 27, and
a local unit 28 is attached thereto. The other ends of the optical fibers
25 and 26 are connected to an optical delay unit 29 of 2 km long.
The optical fibers are each a single mode fiber (SMF), and the optical
connectors are each an FC connector.
The master unit 23 incorporates a DFB (distributed feedback) laser diode of
1.55 .mu.m in wavelength serving as the light source 1 of FIGS. 3 and 6, a
pulse unit (serving as the driver 10) for carrying out a 20-kHz pulse
modulation, a photodiode serving as the photo-detector 5, a
splitter/coupler (2), and an amplifier (11) for amplifying an electric
signal provided by the photo-detector 5. The master unit 23 also has a
microphone terminal 30 for superposing, on a light emitted from the light
source 1, a voice signal provided by a microphone, and an earphone
terminal 31 for an earphone for converting a signal from the amplifier 11
into a voice signal.
The local unit 28 has a photo-detector (not shown) for receiving leakage
lights from the bend 27, an earphone terminal 32 for an earphone for
converting an electric signal from the photo-detector into a voice signal,
and a microphone terminal 33 for applying vibration to the bend 27
according to a voice signal provided by a microphone.
To carry out a test with the arrangement of FIG. 8, a signal is applied to
the microphone terminal 33 of the local unit 28, and the output of the
earphone terminal 31 of the master unit 23 is measured by a spectrum
analyzer. The input signal applied to the local unit 28 is a sine wave of
1 kHz and 40 mV RMS.
A comparison test is made with a 1.55-.mu.m DFB laser diode serving as the
light source 1 and a continuous-wave oscillator serving as the driver 10
to make the laser diode continuously emit a light. Other conditions are
the same as those of the main test.
Test results show that the main test with the laser source 1 emitting a
20-kHz pulse light is superior, in S/N ratio by about 30 dB, to the
comparison test with the laser source 1 emitting a continuous light.
Test 2
The test 1 shows that the 20-kHz pulse light is effective as a source
light. Accordingly, test 2 employs the 20-kHz pulse light and changes the
type of the source light and measures the spectrum waveform of a
reproduced signal. The other arrangements of the test 2 are the same as
those of the test 1. The input signal to the local unit 28 is a 1-kHz,
40-mV RMS sine wave.
The 1.55-.mu.m DFB laser diode found to be effective in the test 1, a
1.55-.mu.m Fabry-Perot laser diode, a 1.55-.mu.m SLD, and a 1.55-.mu.m
band ASE (a broad optical output from an optical amplifier) are used one
after another as the light source 1.
Results of the tests show that the DFB laser diode of high coherency is
optimum. The test results also show that the other light sources are
applicable depending on using conditions.
Test 3
This test examines a proper length for the optical delay unit 29 of FIG. 8.
The light source 1 is a DFB laser diode that provides a 20-kHz pulse
light. The length of the delay unit 29 is changed among 1, 2, 3, and 4 km.
The input signal to the local unit 28 is a 1-kHz, 40-mV RMS sine wave.
Test results show that 2 km and uppers are effective for the delay unit 29.
According to the tests 1 to 3, an optimum system for making the master unit
23 correctly reproduce a voice signal applied by the local unit 28 to the
optical-fiber loop may employ:
a DFB laser diode as a light source;
a pulse light emitted from the DFB laser diode; and
an optical delay unit of about 2 km long.
Test 4
FIG. 9 shows a test system employing no optical delay unit 29. The
difference between optical paths in directions A and B from a local unit
28 to a master unit 23 in an optical-fiber loop 35 is changed between 20
km and 40 km to examine a change in the characteristics of the master unit
23 of reproducing a voice signal applied by the local unit 28. In FIG. 9,
the same parts as those of FIG. 8 are represented with the same reference
marks.
A result of the test shows that the longer the optical path difference, the
larger the amplitude of a reproduced signal. It is preferable, therefore,
that the local unit 28 must be positioned so as to maximize the optical
path difference.
Each apparatus of the present invention mentioned above is capable of
faithfully reproducing vibration applied to an optical-fiber loop.
Therefore, the apparatus is applicable to carry out a conversation between
the optical transceiver (master unit) 23 and the local unit 28 by
converting a voice signal into an electric signal at the local unit,
vibrating the loop according to the electric signal, and reproducing the
voice signal from the vibration at the master unit and by converting a
voice signal into an electric signal at the master unit, modulating an
optical signal according to the electric signal at the master unit, and
reproducing the voice signal from the modulated optical signal at the
local unit.
The splitter-coupler of any one of the embodiments of the present invention
may be made of an optical fiber coupler, an optical wave guide coupler, a
half-mirror system, etc. The optical-fiber loop of any one of the
embodiments may be made of single-mode optical fibers or multi-mode
optical fibers. If the latter are employed, each optical fiber must be
short and vibration applied thereto must be of low frequency. The light
source of any one of the embodiments may be a laser or any other such as
an LED. If the LED is employed, each optical fiber must be short and
vibration applied thereto must be of low frequency. Instead of vibration,
any other physical change such as a shock may be applied to the
optical-fiber loop so that the apparatus of the present invention may
detect the physical change according to a corresponding phase shift in
propagated lights. The optical-fiber loop as a whole may serve as a part
for sensing a physical quantity. To improve sensitivity, optical fibers
may be arranged in multiple loops. The loop or loops may have a converting
element such as an electro-optic sensor for sensing an electric field and
a magnetic field and a physical-optic sensor for sensing pressure, to
efficiently convert a physical quantity into a phase shift of propagated
lights.
An apparatus for identifying a target optical fiber cable among many
according to the present invention will be explained. This apparatus
utilizes the principle of the technique for detecting signal/vibration
based on the optical interference of the light propagating through the
optical fiber loop set forth above. At a work site in, for example, a
manhole, one must identify a target optical fiber cable among many cables
laid at the site. The target cable may be a cable to be replaced or
removed. At the start of the work, the target cable to be removed or
replaced is disconnected from light transmitting and receiving devices
equipped in a telephone station or relay station, and the work is
successively carried out from a site to another. Accordingly, both ends of
the target cable are known. However, at each intermediate site, it is
difficult to identify the target cable because many cables are laid at
each site. To easily identify the target cable, the present invention
provides an apparatus of FIG. 10.
The apparatus of FIG. 10 employs an optical transceiver 101 installed at an
end of a target optical fiber cable 103. The optical transceiver 101 is
connected to arbitrary two optical fibers 105 and 106 contained in the
target cable 103. At a work site, a vibrator 102 successively vibrates
cables laid at the site one after another. At the other end 104 of the
target cable 103, the optical fibers 105 and 106 are connected to each
other through an optical connector 107 to form a loop.
The optical transceiver 101 makes lights incident to the optical fibers 105
and 106 so that the lights are oppositely propagated through the loop of
the optical fibers 105 and 106, receives the propagated lights, detects a
vibration signal in the received lights, and determines whether or not the
cable vibrated by the vibrator 102 is the target cable 103. The optical
transceiver 101 mainly consists of a light source 111 for emitting a laser
light, a splitter-coupler 112, and a photo-detector (photo-detector) 113.
To identify the target cable 103, the optical transceiver 101 is connected
to one ends of the optical fibers 105 and 106 contained in the target
cable 103. The other ends of the optical fibers 105 and 106 are connected
to each other through the connector 107 to form a loop. At a work site,
the vibrator 102 vibrates cables laid at the site one after another. If
the cable being vibrated is the target cable 103, the optical transceiver
101 detects it. This will be explained in more detail.
The light source 111 emits lights A and B into the optical fibers 105 and
106 so that the lights A and B are oppositely propagated through the loop
of the optical fibers 105 and 106.
The propagated lights A and B interfere with each other at the
splitter-coupler 112, the interference being constant as long as no
vibration is applied by the vibrator 102 to the loop. If the vibrator 102
vibrates the loop, a change occurs in the interference. The change is
detectable by observing a signal from the photo-detector 113. The
photo-detector 113 receives the interfering lights and converts them into
an electric signal. The waveform of the electric signal can be observed on
an oscilloscope. The electric signal can lightplified and converted into
sound, which can be heard on a speaker. Also, the electric signal can be
analyzed by a spectrum analyzer.
The vibrator 102 vibrates cables one after another, and the optical
transceiver 101 recognizes when the target cable 103 is vibrated according
to a change in the interfering lights.
FIG. 11 shows the details of the optical transceiver 101. Optical
connectors 115A and 115B are connected to two optical fibers contained in
a target cable. An isolator 116 is a directional optical coupler. The
light source 111 is a light emitting diode or a laser diode. The isolator
116 transfers a light from the light source 111 to the splitter-coupler
112 and blocks any light from the splitter-coupler 112 to the light source
111. A power stabilizer 117 makes the light source 111 emit a pulse light
and stabilizes the power of the pulse light. A modulator 119 FM-modulates
the pulse light according to an oscillation frequency of an oscillator
118. If required, the light source 111 may be DC-oscillated. In this case,
the modulator 119 is omitted.
The splitter-coupler 112 receives a light from the isolator 116, splits the
light, and transfers the split lights to the optical connectors 115A and
115B. Also, the splitter-coupler 112 receives lights from the optical
connectors 115A and 115B, couples the lights so that they interfere with
each other, and transfers the interfering lights to the photo-detector
113. The photo-detector 113 converts the interfering lights into an
electric signal, which is amplified by an amplifier 119.
The output of the amplifier 119 is converted into a voice signal by a
speaker 120 and an earphone 121 so that one may hear sound. The output of
the amplifier 119 is also supplied to an output terminal 122, which is
connected to an oscilloscope 123. The oscilloscope 123 displays an
waveform of the output of the output terminal 122.
If the vibrator 102 (FIG. 10) is close to the midpoint of the loop of the
optical fibers 105 and 106, optical paths for lights oppositely travelling
from the vibration point toward the optical transceiver 101 will be equal
to each other. This minimizes a change in the interference between the
lights A and B.
To solve this problem, an arrangement of FIG. 12 of the present invention
inserts an optical delay unit 108 in place of the optical connector 107
(FIG. 10) between the optical fibers 105 and 106, to produce a large
difference between the optical paths for lights oppositely travelling from
the vibration point toward the optical transceiver 101. This improves the
correctness of the optical transceiver 101 in identifying a target cable.
FIG. 13 shows a simple optical transceiver 101 applicable to the
apparatuses of FIGS. 10 and 12. The optical transceiver 101 has a
splitter-coupler 112 that operates like that of FIG. 11, optical
connectors 115A and 115B connected to ends of optical fibers, an optical
input terminal 141, and an optical output terminal 142.
To identify a target cable, the input terminal 141 is connected to an
external light source 144. The light source 144 may be a laser diode or an
LED, which is driven by an oscillator 143. The light source 144 emits a
light into the input terminal 141.
The output terminal 142 is connected to an optical oscilloscope 145 to
directly display a waveform of interfering lights. The output terminal 142
may be connected to an O/E converter 146 for converting an optical signal
from the output terminal 142 into an electric signal whose waveform is
displayed on an oscilloscope 147.
The optical transceiver 101 is capable of identifying a target cable like
those of FIGS. 10 to 12.
In any one of the above embodiments, arbitrary two optical fibers to form a
loop may be both in a target cable, or one in the target cable and the
other in another cable in the same route, or one in the target cable and
the other in another cable in a different route.
FIG. 14 shows an apparatus for identifying a target optical fiber according
to still another embodiment of the present invention. This apparatus also
utilizes the principle of the technique for detecting signal/vibration
based on the optical interference of the light propagating through the
optical fiber loop.
The apparatus identifies a target optical fiber among optical fibers
contained in a given cable. If required, the identified optical fiber is
used to carry out a conversation.
The apparatus consists of an optical transceiver 201, which has a light
source 211 for emitting a laser light, a splitter-coupler 212, and a
photo-detector (photo-detector) 213.
If it is required only to identify a target optical fiber, a local unit 203
may be the vibrator 102 of FIG. 10.
The optical transceiver 201 is connected to ends of optical fibers 202A and
202B contained in an optical fiber cable 202. One of the optical fibers
202A and 202B is a target optical fiber. The other ends of the optical
fibers 202A and 202B are connected to each other through an optical
connector 204 to form a loop.
Lights A and B are oppositely propagated through the loop. If the local
unit 203 applies no vibration to the loop, the lights A and B cause a
constant interference. If the local unit 203 applies vibration to the
loop, a change is caused in the interference between the lights A and B,
and the change appears in a signal provided by the optical transceiver
201.
The local unit 203 is operated at a work site to vibrate optical fibers
contained in the cable 202 one after another. At a site where the optical
transceiver 201 is installed, a signal from a speaker attached to the
optical transceiver 201 or a waveform on an oscilloscope connected to the
optical transceiver 201 is observed to identify the target optical fiber.
If the local unit 203 is at the midpoint of the loop, i.e., if optical
paths for lights oppositely travelling from the local unit 203 toward the
optical transceiver 201 are equal to each other, the difference between
the optical paths is nearly zero to cause no phase difference between the
lights even if vibration is applied to the loop by the local unit 203. In
this case, no phase change is observed in the interference of the
propagated lights, and therefore, it is impossible to detect the
vibration. To solve this problem, the present invention provides an
arrangement of FIG. 15. This embodiment employs an optical delay unit 205
in place of the optical connector 204 (FIG. 14) between the optical fibers
202A and 202B. The delay unit 205 is made of an optical fiber coil of, for
example, 2 km long that is dependent on requirements.
FIG. 16 shows a simple optical transceiver 201 applicable to the
apparatuses of FIGS. 14 and 15. Optical connectors 215A and 215B are
connected to optical fibers one of which is a target optical fiber. An
optical input terminal 216 is connected to a light source 221 such as a
laser diode. An oscillator 220 modulates a light emitted by the light
source 221, and the modulated light is transferred to the input terminal
216. A splitter-coupler 212 provides interfering lights to an optical
output terminal 217.
The splitter-coupler 212 splits a light from the input terminal 216 and
supplies the split lights to the optical connectors 215A and 215B,
respectively. The splitter-coupler 212 couples lights from the optical
connectors 215A and 215B so that they interfere with each other and
supplies the interfering lights to the output terminal 217. The optical
connectors 215A and 215B, input terminal 216, output terminal 217, and
splitter-coupler 212 are formed in one body.
The output terminal 217 is connected to an optical oscilloscope 222 that
directly displays the waveform of interfering lights provided by the
output terminal 217. The output terminal 217 may be connected to an O/E
converter 223 that converts the interfering lights from the output
terminal 217 into an electric signal whose waveform is displayed on an
oscilloscope 224.
Combinations of the apparatus for identifying a target optical fiber and an
optical fiber communication apparatus according to the present invention
will be explained. Each combination is based on one of the embodiments of
FIGS. 14 and 15. This apparatus also utilizes the principle of the
technique for detecting signal/vibration based on the optical interference
of the light propagating through the optical fiber loop.
FIG. 17 shows an optical transceiver 201 and FIG. 18 shows a local unit
203, for identifying a target optical fiber and carrying out a
conversation through the target optical fiber. The local unit 203 forms a
bend 300 at a part of an arbitrary optical fiber among many contained in a
cable 202. The local unit 203 has a photo-detector 301 for receiving
leakage lights from the bend 300, and a vibrator 302 for vibrating the
optical fiber.
The details of the optical transceiver 201 will be explained. Optical
connectors 215A and 215B are connected to two optical fibers 202A and 202B
one of which is a target optical fiber. The other ends of the optical
fibers 202A and 202B are connected to each other to form a loop. An
isolator 216 transfers a light from a light source 211 to a
splitter-coupler 212 and blocks any light from the splitter-coupler 212 to
the light source 211. The light source 211 is a laser diode and is driven
by a power stabilizer 217, to emit a pulse light of constant power at
predetermined intervals. The power stabilizer 217 may be a pulse FM
circuit of simple structure.
A modulator 219 FM-modulates a pulse signal provided by the power
stabilizer 217 according to a voice signal that is provided through a
microphone 220 and an amplifier 221.
A photo-detector (photo-detector) 213 is a photodiode. The splitter-coupler
212 couples lights oppositely propagated through the optical-fiber loop so
that the lights interfere with each other. The photo-detector 213 converts
the interfering lights into an electric signal. An amplifier 222 amplifies
the electric signal. A demodulator 223 AM-demodulates the amplified signal
and provides a voice-band signal, which is processed by an earphone 224
into a voice. Instead of the earphone 224, a speaker 225 may reproduce the
voice.
FIG. 19 shows a concrete example of the local unit 203 of FIG. 18. On the
receiver side of the local unit 203, a bender 303 forms a bend 300 on the
optical fiber 202A. A photo-detector (photo-detector) 301 receives leakage
lights from the bend 300 and converts them into an electric signal. An
amplifier 304 amplifies the electric signal. A demodulator 305 is an FM
demodulator which FM-demodulates the electric signal into a voice signal
originated by the optical transceiver 201. The voice signal is amplified
by an amplifier 306. The amplified signal is converted into voice by an
earphone 307 or a speaker 308.
The local unit 203 has a vibrator 302, which may be an audio speaker.
Vibration on a cone sheet of the speaker directly vibrates the optical
fiber 202A. Accordingly, the transmitter side of the local unit 203 only
includes a microphone 311 and a driver 312.
A method of identifying a target optical fiber will be explained.
To identify a target optical fiber, any one of the arrangements of FIGS. 14
and 15 is employed. Ends of the optical fibers 202A and 202B, one of which
is the target optical fiber, are connected to each other through the
optical connector 204 or the optical delay unit 205, to form a loop. The
local unit 203 is installed at a work site, and the vibrator 302 is
attached to one of the optical fibers contained in the cable 202. The
bender 303 forms a bend 300 on the optical fiber.
The optical connectors 215A and 215B of the optical transceiver 201 are
connected to the optical fibers 202A and 202B.
In the optical transceiver 201, the power stabilizer 217 drives the light
source 211 to emit a pulse laser light of constant power. The
splitter-coupler 212 splits the light and makes the split lights incident
to the optical fibers 202A and 202B, respectively, so that the split
lights are propagated clockwise and counterclockwise, respectively,
through the loop of the optical fibers 202A and 202B. At this time, the
microphone 311 of the local unit 203 provides a sound signal, e.g., a
1-kHz sine wave. According to the sound signal, the vibrator 302 vibrates
the optical fibers contained in the cable 202 one after another.
In the optical transceiver 201, the splitter-coupler 212 couples the
oppositely propagated lights so that they interfere with each other. The
photo-detector 213 converts the interfering lights into an electric
signal, and the amplifier 222 amplifies the electric signal. The amplified
signal is transferred to the demodulator 223.
The 1-kHz vibration signal applied by the vibrator 302 to the optical-fiber
loop is audible. Therefore, if the electric signal provided by the
photo-detector 213 includes the vibration signal, the demodulator 223
reproduces the audible vibration signal so that one can hear the sound
through the earphone 224 or speaker 225 and determine whether or not the
optical fiber now being vibrated by the vibrator 302 of the local unit 203
is the target optical fiber.
It is effective to carry out the works of identifying the target optical
fiber on the conditions of the test 3 set forth above.
Once the target optical fiber, i.e., one of the optical fibers 202A and
202B is identified, the optical-fiber loop that contains the target
optical fiber is used to carry out a conversation between the optical
transceiver 201 and the local unit 203. This will be explained.
The optical transceiver 201 and local unit 203 employ the microphones 220
and 311 for sending voice and the earphones 224 and 307 or the speakers
225 and 308 for reproducing the voice.
<Voice Transmission from Optical Transceiver 201 to Local Unit 203>
One at the optical transceiver 201 produces a voice to the microphone 220.
The microphone 220 provides a corresponding voice signal and the amplifier
221 amplifies the voice signal. According to the amplified voice signal,
the modulator 219 FM-modulates a pulse drive signal of the power
stabilizer 217. According to the FM-modulated drive signal, the light
source 211 emits a pulse light, which is split by the splitter-coupler
212. The split lights are made incident to the optical fibers 202A and
202B that form a loop. Although the FM-modulated optical pulse signal
returns to the optical transceiver 201 through the loop, the voice entered
to the microphone 220 is never reproduced by the optical transceiver 201
because the optical transceiver 201 incorporates no demodulator for
FM-modulated signals.
The local unit 203 receives the split lights that are based on the
FM-modulated optical pulse signal. The lights leak from the bend 300 and
are received by the photo-detector 301, which converts them into an
electric signal. The electric signal is amplified by the amplifier 304 and
is supplied to the demodulator 305.
The electric signal provided by the photo-detector 301 is based on the
FM-modulated optical pulse signal originated by the optical transceiver
201. Accordingly, the demodulator 305 FM-demodulates the electric signal
to reproduce the original voice signal. The voice signal is amplified by
the amplifier 306 and drives the earphone 307 or the speaker 308 that
emits the original voice sent from the optical transceiver 201.
<Voice Transmission from Local Unit 203 to Optical Transceiver 201>
The optical transceiver 201 always emits usual optical pulse signals that
are not FM-modulated to the optical fibers 202A and 202B. Under this
state, one at the local unit 203 produces voice to the microphone 311.
The voice is converted by the microphone 311 into an electric signal, which
is supplied to the driver 312. According to the electric signal, the
driver 312 drives the vibrator 302. Namely, vibration corresponding to the
voice is applied to the optical fiber 202A.
The vibration changes a phase difference between the lights oppositely
propagated through the optical-fiber loop. The propagated lights are
coupled together by the splitter-coupler 212 of the optical transceiver
201, to make the lights interfere with each other. The interfering lights
are converted by the photo-detector 213 into an electric signal. This
electric signal shows a change corresponding to the vibration applied by
the local unit 203.
The electric signal from the photo-detector 213 is amplified by the
amplifier 222, is AM-demodulated by the demodulator 223, and is played by
the earphone 224 or the speaker 225 as the voice entered by the local unit
203.
In this way, each apparatus for identifying a target optical fiber of the
present invention is capable of providing a communication function without
cutting the optical fibers.
Instead of the optical delay unit 205 (FIG. 15), an optical delay unit 230
may be arranged in an optical path between the splitter-coupler 212 and
the optical connector 215A, as indicated with a dotted line in FIG. 17.
FIG. 20 is a block diagram showing an optical transceiver having a
communication function applicable to the apparatuses of FIGS. 14 and 15,
and FIG. 21 is a block diagram showing a local unit having a communication
function applicable to the same apparatuses. In addition to the LI
embodiments of FIGS. 17 and 19, the embodiments of FIGS. 20 and 21 have a
call function.
In FIG. 20, the optical transceiver 201 additionally has a call signal
generator 231 and a call switch (SW) 232 on the transmission side thereof.
The output of the call signal generator 231 is supplied to an amplifier
221. The reception side of the optical transceiver 201 additionally has a
call signal detector 233 and a buzzer 234. The call signal detector 233
receives the output of a demodulator 223 and drives the buzzer 234. The
output of the call signal detector 233 may be supplied to a speaker 225.
The transmission side also has a signal generator 241 for generating a
signal used to identify a target optical fiber, and a switch (SW) 242. The
output of the signal generator 241 is supplied to a power stabilizer 217
that drives a light source 211. The other parts of the optical transceiver
201 are the same as those of the optical a transceiver 201 of FIG. 17.
In FIG. 21, the reception side of the local unit 203 additionally has a
call signal detector 321 and a buzzer 322. The call signal detector 321
receives the output of an amplifier 306 and drives the buzzer 322. The
transmission side of the local unit 203 additionally has a call signal
generator 323 and a call switch (SW) 324. The output of the call signal
generator 323 is supplied to a driver 312 that provides a vibration signal
to drive a vibrator 302. The reception side of the local unit 203 also has
a detector 325 for detecting the signal used to identify a target optical
fiber. The detector 325 receives the output of an amplifier 304 and drives
the buzzer 322. The other parts of the local unit 203 are the same as
those of the local unit 203 of FIG. 19.
The apparatus employing the optical transceiver 201 of FIG. 20 and the
local unit 203 of FIG. 21 first identifies a target optical fiber to be
used to carry out a conversation. More precisely, the switch 242 of the
optical transceiver 201 is manipulated to make the signal generator 241
generate a modulation signal (a rectangular wave of 270 Hz) to AM modulate
a pulse drive signal provided by the power stabilizer 217. The
AM-modulated drive signal drives the light source 211 to emit a pulse
light. The light is split by a splitter-coupler 212, and the split lights
are supplied to optical fibers 202A and 202B.
In the local unit 203, leakage lights from a bend 300 of the optical fiber
202A are received by a photo-detector 301, which converts them into an
electric signal. The electric signal is amplified by the amplifier 304.
The output of the amplifier 304 is supplied to a demodulator 305 and the
detector 325. Since the demodulator 305 demodulates only FM signals, it
never responds to the AM signal for identifying the target optical fiber.
On the other hand, the detector 325 detects the amplified AM signal of 270
Hz and demodulates the same to drive the buzzer 322. Hearing the sound
from the buzzer 322, one at the local unit 203 recognizes that the optical
fiber 202A is the target optical fiber.
Once the local unit 203 identifies the target optical fiber, a conversation
is achievable between the optical transceiver 201 and the local unit 203
without cutting the optical fiber. To start a conversation from the local
unit 203, the call switch 324 is manipulated. Then, the call signal
generator 323 generates a call signal of predetermined frequency,
according to which the vibrator 302 vibrates the optical fiber 202A, to
change a phase difference between the lights oppositely propagated through
the loop of the optical fibers 202A and 202B.
The propagated lights are received by the optical transceiver 201. A
photo-detector 213 converts the lights into an electric signal, and a
demodulator 223 AM-demodulates the electric signal. The call signal
detector 233 detects the call signal in the demodulated signal and drives
the buzzer 234 or speaker 225 so that one at the optical transceiver 201
may recognize the call from the local unit 203.
Thereafter, a conversation is carried out between the optical transceiver
201 and the local unit 203 through the optical-fiber loop without cutting
the loop as explained with reference to FIGS. 17 and 19.
A call from the optical transceiver 201 to the local unit 203 will be
explained. The call switch 232 is manipulated to make the call signal
generator 231 generate a call signal of predetermined frequency. The call
signal is amplified by an amplifier 221. According to the amplified call
signal, a modulator 219 FM-modulates a pulse drive signal provided by the
power stabilizer 217. According to the modulated signal, the light source
211 emits an optical pulse light. The light is split by the
splitter-coupler 212, and the split lights are transferred to the local
unit 203 through the optical fibers 202A and 202B.
In the local unit 203, leakage lights from the bend 300 of the optical
fiber 202A are received by the photo-detector 301, which converts them
into an electric signal. The electric signal is amplified by the amplifier
304. The output of the amplifier 304 is supplied to the demodulator 305
and detector 325. Since the signal originated by the optical transceiver
201 this time is FM-modulated, the signal detector 325 never responds to
it, and the demodulator 305 demodulates it into the call signal. The call
signal is amplified by the amplifier 306. The call signal detector 321
detects the call signal and drives the buzzer 322. Hearing the sound from
the buzzer 322, one at the local unit 203 recognizes the call from the
optical transceiver 201.
Thereafter, a conversation is carried out between the optical transceiver
201 and the local unit 203 through the optical-fiber loop without cutting
the loop as explained with reference to FIGS. 17 and 19.
The local unit 203 may have an optical power meter so that the local unit
203 can provide all functions needed for optical work, such as carrying
out a conversation, identifying a target optical fiber, and measuring
optical power. This is convenient because equipment to be carried among
work sites is only the local unit.
Although the embodiments install the local unit on one of the two optical
fibers that form a loop, the local unit may be installed on both the two
optical fibers. The latter installation is effective when two optical
fibers are taped up and are unable to separate from each other so that
they must simultaneously be vibrated and bent.
Two optical fibers that form a loop according to the present invention are
each preferably a single mode fiber (SMF). Multimode optical fibers are
employable if they are short or if detectors of good S/N ratio are
employed. A light source for the present invention is preferably a laser
diode. If multimode optical fibers are employed, the light source may be
an LED. A DFB laser of high interference is preferred as a light source
for the present invention when long optical fibers are employed or when
detectors of poor S/N ratio are employed.
Two optical fibers to form a loop may be contained in the same cable, or in
different cables, or in cables laid in different routes.
Instead of using the connector 107 to connect ends of two optical fibers to
each other, the ends may be fused together or may be connected to each
other by V-groove connection. Instead of using a vibrator to vibrate a
part of a loop of optical fibers, one may apply a physical change such as
a shock to the loop by hitting a part of the loop or a part of a cable
that contains a part of the loop. This may cause a phase shift between
lights oppositely propagated through the loop so that one at the optical
transceiver may hear the hitting sound from a speaker or observe a
corresponding waveform on an oscilloscope, to identify a target optical
fiber cable or a target optical fiber.
* * * * *
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