Optical: systems and elements – Optical amplifier – Optical fiber
Reexamination Certificate
1999-03-08
2001-10-30
Hellner, Mark (Department: 3662)
Optical: systems and elements
Optical amplifier
Optical fiber
C356S073100, C359S199200
Reexamination Certificate
active
06310718
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention is related to an optical amplifying apparatus including an optical amplifier capable of directly optically-amplifying an input signal light, and is related to a method for detecting break points within a light transmission line of the optical amplifying apparatus and an optical transmitting apparatus containing the above-described optical amplifying apparatus, and further related to a bidirectional wavelength division multiplexing optical transmitting apparatus with employment of this optical amplifying apparatus.
2. Description of the Related Art
In middle and long distance optical fiber communication systems, optical amplifiers are employed so as to amplify signal light attenuated in transmission fibers. As optical amplifiers, optical fiber amplifiers and semiconductor optical amplifiers are widely utilized. These optical amplifiers may directly amplify signal light by using rare-earth doped optical fibers as amplification media.
In any of these optical amplifiers, the light is propagated from the input side into which the signal light is inputted, to the output side from which the amplified signal light is outputted. When the light is propagated along the direction opposite to the above-described propagation direction, namely the light is entered from the output side of the optical amplifier to the input side thereof, this optical amplifier is operated under unstable conditions. In the worst case, the oscillation operation occurs, so that the optical amplifier is brought into a very unstable condition. This unstable operation may cause very serious problems in the optical transmission which should be originally carried out under stable condition by the optical amplifier. In general, such optical isolators are arranged on an input side of an optical amplifier and an output side thereof, and these optical isolators may pass the light along the above-described forward direction, but may interrupt the light propagated along the reverse direction.
To investigate a condition of an optical transmission line in an optical transmission apparatus, a loss and a break point are detected which occur in this transmission line. Normally, an optical time domain reflectometer is employed so as to test the loss and the break point of the optical transmission line. However, in an optical transmitting apparatus having plurality of optical repeaters containing optical amplifiers arranged at a half way point of the optical transmission line, the above-explained test is carried out only in such a limited optical transmission line defined from one optical repeater up to another optical repeater adjacent to the first-mentioned optical repeater in order that no optical amplifier is involved in a certain optical transmission line whose condition should be tested. Therefore, the condition test is merely and successively performed only between the adjoining optical repeaters. In other words, there is a problem that the condition test cannot be executed within a single test cycle with respect to the overall optical transmission line defined from one terminal station to the other terminal station.
When an optical amplifier is arranged in an optical transmission line, light cannot be propagated within this optical transmission line along the reverse direction. As a result, there is another problem that a bidirectional wavelength division multiplexing optical transmitting apparatus cannot be constituted in connection with the above-explained problem.
SUMMARY OF THE INVENTION
An object of the present invention is to provide an optical amplifying apparatus and also to provide a transmission-line break point detecting method of an optical transmitting apparatus containing this optical amplifying apparatus, by which even when the optical amplifier is contained in the transmission line, the optical time domain test can be carried out by entering test light from one terminal station.
Another object of the present invention is to provide a bidirectional wavelength division multiplexing optical transmitting apparatus with employment of the optical amplifier, by which even when the optical amplifier is arranged in the optical transmission line, two sets of light having different wavelengths can be transmitted via a single optical fiber in a bidirectional manner.
To solve the above-described problems, an optical amplifying apparatus of the present invention is provided with such a detour optical line for selectively entering the light having a first wavelength &lgr;1 into an optical amplifier, and for selectively not entering light having a second wavelength &lgr;2 into the optical amplifier, in addition to such an optical amplifier for amplifying the light having the first wavelength &lgr;1 which is inputted from an optical input unit, and for outputting the amplified light from an optical output unit.
In the conventional optical amplifying apparatus, when the light which is propagated along the reverse direction is entered into the optical amplifier, the operation of this conventional optical amplifying apparatus becomes very unstable. In the worst case, the oscillating operation will occur. To avoid this difficulty, optical isolators are arranged at front and rear ends of an amplifying optical fiber so as to prevent penetration of the return light. As a consequence, in the case that optical amplifier is arranged in the optical transmission line, the break point cannot be detected by using the optical time domain reflectometer.
To solve this problem, in the optical amplifying apparatus of the present invention, the light having the first wavelength of “&lgr;1” which constitutes the original signal light may be optically amplified by the light amplifier, and thereafter the amplified signal light is outputted to the rear-sided optical fiber. On the other hand, when the break point occurring in the optical transmission line is detected, while the light having the second wavelength of “&lgr;2” different from the above-described signal light is employed as the test light, this test light is entered from the input terminal of the optical transmission line provided of the front-sided fiber, so that this test light can be transmitted to the rear-sided fiber via the above-explained detour optical path without passing through the optical amplifier. The return light, which is required to detect the break point, supplied from the rear-sided optical fiber is not propagated to the optical amplifier, but is returned via the detour optical path to the input terminal. As a result, while this return light is not entered into the optical amplifier, the return light of the optical transmission path is returned to the input terminal. Then, the variation in the intensity of this return light with respect to the time lapse can be measured.
The above-described detour optical line of the optical amplifying apparatus according to the present invention is arranged by a first wavelength division multiplexer (referred to as “WDM”) arranged at a pre-stage of an optical input unit, and a second wavelength division multiplexer arranged at a post stage of an optical output unit, and a detour transmission line for detouring both the first and second wavelength division multiplexers to be connected thereto. The light having the first wavelength &lgr;1 which is entered from the first port of the first wavelength division multiplexer is outputted to the second port, and also the light having the second wavelength &lgr;2 which is inputted from the first port is outputted to the third port. The amplified light which is entered from the fifth port of the second wavelength division multiplexer is outputted to the fourth port, and also the light having the second wavelength &lgr;2 which is entered from the fourth port is outputted to the sixth port. The third port of the first wavelength division multiplexer is connected to the sixth port of the second wavelength division multiplexer by the detour transmission line.
The optical amplifying apparatus, according to the present inven
Hellner Mark
McGinn & Gibb PLLC
NEC Corporation
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