JPS6340378B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to optical communication systems, and particularly to optical multiplex transmission systems.

In recent years, optical communication systems have made remarkable progress, and their applications are expanding to a variety of fields.One of their advanced uses is the simultaneous transmission of multiple optical signals in one or both directions through a single optical transmission path. Optical multiplexing transmission systems that do this are being considered.

Conventionally, this type of optical multiplexing transmission system consists of a wavelength division multiplexing transmission system that performs unidirectional or bidirectional multiplex transmission by combining light sources with different emission wavelengths and optical demultiplexers, and a wavelength division multiplexing system that performs unidirectional or bidirectional multiplex transmission by wavelength division. A bidirectional multiplex transmission system is being considered that uses an optical directional coupler and utilizes the directionality of the optical directional coupler to separate transmitted signals based only on differences in transmission direction.

The former wavelength division multiplexing transmission method allows long-distance transmission, but has the disadvantage of requiring the preparation of multiple types of light sources with different emission wavelengths.

On the other hand, in the latter direction, although it is simple, the transmitted optical signal is not received by the local station due to backscattering in the optical transmission line, reflection at the end face of the optical connector, or imperfect directionality of the optical directional coupler. It has the disadvantage that it can only be used for very short distance transmission because it interferes with the device and degrades the optical reception sensitivity, and it also has the disadvantage that it cannot be applied to unidirectional multiplex transmission.

SUMMARY OF THE INVENTION Therefore, an object of the present invention is to eliminate such drawbacks and provide a simple optical multiplex transmission system that is capable of bidirectional, relatively long-distance multiplex transmission even when light sources having substantially the same emission wavelength range are used. It's about doing.

According to the present invention, a first optical transmitter and a first optical receiver are optically connected via a first optical demultiplexer at one end of a single optical fiber transmission line, and a first optical receiver is optically connected at one end of a single optical fiber transmission line via a first optical demultiplexer. a second optically connected via a second optical demultiplexer;
In an optical transmission system that includes an optical transmitter and a second optical receiver, and performs bidirectional optical communication via the optical fiber, the first and second optical transmitters emit substantially the same light. The light source includes a light source that emits light in a wavelength band, and the light in the first wavelength band is selected by the first optical demultiplexer among the light generated by the light source of the first optical transmitter, and the light is transmitted through the optical fiber. Among the light generated by the light source of the second optical transmitter, the light in a second wavelength band different from the first wavelength band is received by the second optical receiver through the second optical receiver. There is obtained an optical transmission system characterized in that the optical signal is selected by a demultiplexer and is received by the first optical receiver via the optical fiber.

In this optical multiplex transmission system, although the light sources of the plurality of optical transmitters have substantially the same emission wavelength range, what is coupled to the optical transmission line via the optical demultiplexer are some mutually different wavelength components. In addition, it is selectively demultiplexed to a specific optical receiver with low loss depending on the optical demultiplexer on the other side, so it is effectively the same principle as the wavelength division multiplexing transmission system, making it possible to perform two-way comparisons. A simple optical multiplex transmission system that can perform long-distance multiplex transmission using light sources of the same wavelength can be obtained.

Next, the present invention will be explained in detail with reference to the drawings.

FIG. 1 is a block diagram showing the configuration of a first embodiment of the present invention, which relates to an optical multiplex transmission system that performs bidirectional multiplex transmission on a single optical transmission path.

In FIG. 1, the light sources of the optical transmitters 11 and 12 are light emitting diodes having approximately the same emission wavelength range, while the optical demultiplexer 31 uses a light emitting diode whose cutoff wavelength is approximately equal to the emission center wavelength of the light sources. A short wavelength transmission filter is used that transmits short wavelength light and reflects long wavelength light, and the optical demultiplexer 32 has a cutoff wavelength that is approximately equal to the emission center wavelength of the light source and transmits long wavelength light. , a long-wavelength transmission filter is used that reflects short-wavelength light.

Therefore, when the optical signal sent from the optical transmitter 11 passes through the optical demultiplexer 31, the long wavelength components are blocked, and almost only the short wavelength components enter the optical transmission line 41. After this optical signal propagates through the optical transmission line 41,
The optical signal is incident on the optical demultiplexer 32, but since most of this optical signal has short wavelength components, it is almost totally reflected.
The signal is input to the optical receiver 22, where it is converted into an electrical signal and then regenerated into the original signal.

On the other hand, in the optical transmission line 41, the reflected light that is backscattered or reflected at the end face returns to the optical demultiplexer 31 of the own station, but since most of the short wavelength components are short wavelength components, the majority of the reflected light is sent to the optical demultiplexer 31. It is transmitted, and only a small portion is reflected and goes around to the optical receiver 21.

Furthermore, in the case of an optical signal sent out from the optical transmitter 12, the long wavelength component is sent out to the optical transmission path 41 through the optical demultiplexer 32, and transmitted to the optical receiver 21 in the same manner as described above. Similarly, only a small portion of the reflected light from the transmission path 41 goes around to the optical receiver 22.

Therefore, compared to the conventional system that simply uses an optical directional coupler instead of the optical demultiplexers 31 and 32, the rate at which the optical transmission signal goes around to the optical receiver of the local station can be significantly reduced, and the Since the permissible loss of the transmission line can be increased, relatively long-distance bidirectional multiplex transmission is possible.

In each of the above embodiments, a short wavelength transmission filter or a long wavelength transmission filter is used for the optical demultiplexers 31 to 32, but a band transmission filter is used to set one cutoff wavelength to the emission center wavelength of the light source. Similar performance can be obtained by combining them. Further, in the first embodiment, the optical transmitter is connected to the transmission side of the optical demultiplexer, but the same characteristics can be obtained even if the optical transmitter is connected to the reflection side.

Note that the cutoff wavelength of the optical demultiplexer does not need to exactly match the emission center wavelength of the light source; it is sufficient that it roughly matches, and the emission wavelength range of the two light sources also needs to roughly match. If the wavelength ranges are slightly different, you can obtain better characteristics than in the case of the same wavelength range by allocating the locations where the light source is used to reduce loss in relation to the transmission wavelength range of the optical demultiplexer. I can do things.

Note that an interference filter using a dielectric multilayer film can be used as the above-mentioned filter, and any other filter can be used as long as it reflects light outside the transmission range.

It is also possible to use an optical demultiplexer using a prism, a diffraction grating, or the like.

Furthermore, although the above embodiments involved bidirectional multiplex transmission of two waves, it is also possible to use a prism, a diffraction grating, etc. as the optical demultiplexer, or a combination of multiple filters with different cutoff wavelengths. Multiplex transmission can also be performed.

As described in detail above, according to the present invention, a simple optical multiplex transmission system capable of bidirectional multiplex transmission can be obtained even if light sources having the same emission wavelength range are used.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing an embodiment of the present invention. In the figure, 11 to 12... optical transmitter, 2
1-22... Optical receiver, 31-32... Optical demultiplexer, 41... Optical transmission line.

Claims (1)

[Claims] 1 A first optical transmitter and a first optical receiver optically connected via a first optical demultiplexer at one end of a single optical fiber transmission line, and a second optical demultiplexer at the other end. The optical transmission system includes a second optical transmitter and a second optical receiver that are optically connected to each other via a fiber, and performs bidirectional optical communication via the optical fiber. The second optical transmitter is comprised of a light source that emits light in substantially the same emission wavelength band, and the second optical transmitter is comprised of a light source that emits light in substantially the same emission wavelength band, and
Light in a wavelength band of Light in a second wavelength band different from the first wavelength band is selected by the second optical demultiplexer and received by the first optical receiver via the optical fiber. Features of optical transmission system.