JPS58171138A - Optical transmission and reception system - Google Patents

Abstract

PURPOSE:To reduce the near-end crosstalk, by adjusting the polarity and the phase of a part of the electric signal, which drives an optical element of the transmission side to cancel the transmission signal which comes around to a reception signal through an optical branching equipment. CONSTITUTION:A transmission digital signal 101 is converted to a transmission optical signal 103 through a driving circuit 11 and a light emitting element 12 and is transmitted to an optical fiber 22 through an optical coupling branching equipment 21. The transmission digital signal 101 is applied to an adding circuit 33 through a polarity inverting circuit 23, a phase adjusting circuit 24, and an amplitude adjusting circuit 25. A reception optical signal 301 from the fiber 22 is applied to a photodetector 31 after leak components of the transmission optical signal 103 are superposed to this signal 301 through the optical coupling branching equipment 21, and this signal 301 is converted to an electric signal and is impressed to the adding circuit 33 through an amplifying circuit 32. The adding circuit 33 outputs the reception signal, where crosstalk components of the transmission optical signal 103 are eliminated, to a reception equalizing circuit 34. An equalized signal 304 is converted to a required reception digital signal 305 by a discriminating circuit 35.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to optical transmission/reception (Ft method) in a system that performs bidirectional digital optical transmission using a single optical fiber.

In optical bidirectional transmission, near-end crosstalk, in which the transmitted optical output leaks into the received optical input at the near end, often poses a problem. especially,
When the loss of the transmission path is large, the received light level is low, so the ratio of the main signal level to the crosstalk signal level becomes relatively small. Conventionally, optical bidirectional transmission has been carried out using wavelength multiplexed bidirectional transmission as shown in FIG. 1 or bidirectional transmission of the same wavelength as shown in FIG. 2. In these figures, 1 is a transmitting circuit, 2 is a receiving circuit, 3 is an optical fiber, 4 is a wavelength multiplexing filter, and 5 is a directional coupler. Although wavelength division multiplexing transmission can keep near-end crosstalk relatively small, it is relatively expensive because it requires a wavelength filter that separates each wavelength and a light emitting source with different wavelengths. On the other hand, bidirectional transmission with the same wavelength can be configured using a light source with the same wavelength as the directional coupler, so it may be relatively inexpensive, but what about the crosstalk inside the directional coupler? The drawback is that the transmission distance cannot be extended due to the influence of reflection at the fiber connection point.

An object of the present invention is to provide a simple optical transmission and reception system that can reduce the effects of near-end crosstalk in optical bidirectional transmission.

To this end, the present invention utilizes a system that performs bidirectional digital optical transmission using a single fiber, branches the electrical pulse signal that drives the optical element on the transmitting side, and manually adjusts the polarity, phase, and amplitude. This signal is added to the pulse waveform signal from the far end that has been photoelectrically converted by the receiving circuit at the near end, and the resulting signal is waveform-equalized and identified to obtain a received digital signal. This is what I did.

The present invention will be described below with reference to the drawings.

FIG. 3 and FIG. 4 are diagrams showing an embodiment of an optical transmitting/receiving circuit and waveforms of each part thereof when implementing the present invention. The transmission digital signal 101 is sent to the drive II by the drive circuit 11.
The signal is converted into a JJtIL flow signal 102, drives the light emitting element 12, and becomes a transmission optical signal 103.

This signal passes through a coupler/brancher (wavelength multiplexing filter or directional coupler) 21 and is sent to the far end via an optical fiber 22. The transmitted digital signal 101 is further branched,
Polarity inversion circuit 23, phase adjustment circuit 24, amplitude adjustment circuit 2
5 and becomes the crosstalk cancellation signal 201. On the other hand, a received optical signal 301 sent from the far end is supplied to the light receiving element 31 through the coupler/brancher 21 . It is assumed that a part of the transmitted optical signal 103 is further superimposed on this signal due to near-end crosstalk. The signal converted into photocurrent by the light receiving element 31 is
Amplified by the amplifier circuit 32, the received electrical waveform signal 302
becomes. The adder circuit 33 adds the above-mentioned crosstalk cancellation signal 201 to this signal, and the obtained addition output signal 303 is band-limited in the reception equalization circuit 34 to become an equalized waveform signal 3θ4, which is identified by the identification circuit 35. This results in the required received digital signal 305. The amplitude and phase of the crosstalk cancellation signal 20i can be adjusted manually using the amplitude adjustment circuit 25 and the phase adjustment circuit 24, and are adjusted so that the crosstalk component of the addition output signal 303 is minimized when setting the vJ period. Just leave it there.

As described above, according to the present invention, distance limitations due to crosstalk in optical fiber bidirectional transmission can be eliminated. The influence of the phase setting error of the crosstalk cancellation signal 201 becomes smaller as the speed of the digital signal becomes slower.

The same is true even if the crosstalk signal is due to reflections at several points at the near end. Therefore, the present invention is useful when applied to the case where relatively low-speed digital signals are transmitted bidirectionally.

[Brief explanation of the drawing]

Figure 1 is a diagram of a conventional optical transmitter/receiver circuit using a wavelength multiplexing bidirectional transmission system, Figure 2 is a diagram of a conventional optical transmitter/receiver circuit using a wavelength multiplexing bidirectional transmission system, and Figure 3 is a diagram of a conventional optical transmitter/receiver circuit using a wavelength multiplexing bidirectional transmission system. A diagram showing an example of a transmitting/receiving circuit! FIG. J4 is a diagram showing waveforms of various parts of the optical transmitter/receiver circuit of FIG. 3. 11... Drive circuit, 12... Light emitting element, 21...
Coupling/branching device, 22... Optical fiber, 23... Polarity inversion circuit, 24... Phase adjustment circuit, 25... Amplitude adjustment circuit, 31... Light receiving element, 32... Amplifying circuit, 33
-...Addition circuit, 34...Reception equalization circuit, 35-...
identification circuit. Agent Patent Attorney Toshiyoshi Somekawa Figure 1 Figure 3 Figure 4 Crosstalk cancellation signal 201 207--

Claims (1)

[Claims] In an optical transmission/reception system that performs bidirectional digital optical transmission using a single optical fiber, an electric pulse signal that drives an optical element on the transmitting side is split and polarized. A signal whose phase and amplitude are manually adjusted is generated, and this signal is added to a pulse waveform signal from the far end that has been photoelectrically converted by a receiving circuit at the near end, and the resulting signal is waveform-equalized for identification. An optical transmission/reception method characterized by obtaining a received digital signal.