Optics: measuring and testing – By light interference – Using fiber or waveguide interferometer
Reexamination Certificate
2002-07-25
2004-11-30
Turner, Samuel A. (Department: 2877)
Optics: measuring and testing
By light interference
Using fiber or waveguide interferometer
Reexamination Certificate
active
06825935
ABSTRACT:
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. 4-368029 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
Nakamura Yasushi
Niimi Shinichi
Unami Yoshiharu
Fujikura Ltd.
Lyons Michael A.
Turner Samuel A.
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