JPH0323729A - Bidirectional optical pcm transmitter - Google Patents

Abstract

PURPOSE:To prevent the waveform of a reception signal deteriorating by setting the duty factor of an optical transmission signal less than 50%, and setting the difference of the phase of the reception signal from an opposite station and that of a crosstalk signal from its own station at the 1/2 of the cycle period of the transmission signal. CONSTITUTION:Directional couplers 3 at both poles are connected with each other with one optical fiber transmission line 4, and a PCM signal whose duty factor is less than 50% is used in optical transmitters at both stations. The difference of the phase of the reception signal from the opposite station at the optical receiver 2 and that of the crosstalk signal from the optical transmitter 1 of its own station is adjusted so as to be set at the 1/2 of the cycle period of the transmission signal with a phase delay adjusting circuit 5. Such phase delay adjustment can be performed, for example, by adjusting the length of an optical fiber. In such a manner, no effect of the crosstalk signal 7 from the optical transmitter 1 is applied on the transmission signal 6 from the opposite station, which prevents the waveform deterioration.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention places directional couplers (optical directional couplers) connecting an optical transmitter and an optical receiver at both ends, and uses a single optical fiber transmission line. Day for both stations? Bidirectional optical PC related to bidirectional optical PCM transmission equipment connecting couplers, especially improving the effects of transmission line deterioration due to crosstalk of received signals
This relates to the M transmission device.

[Conventional technology]

Conventionally, two-way optical P using a directional coupler
When a CM transmission device fails, its own station's transmitted signal leaks into the receiving side, adversely affecting signals transmitted from other stations.

In other words, the influence of crosstalk causes waveform deterioration at the receiving point as intersymbol interference, and it is necessary to take into account the deterioration in the S/N design of the system as an optical reception power penalty.

FIG. 3 is a diagram showing a received waveform at an optical receiver in a conventional bidirectional optical PCM transmission device. In this figure 3,
T indicates the repetition period of the transmitted signal, and 8 indicates the waveform deterioration of the received signal due to the crosstalk signal from the local optical transmitter. In addition,
In this figure 3, P with a duty of 100% is used as a transmission signal.
A case using a GM signal is shown. TM indicates time.

[Problem to be solved by the invention]

In the conventional bidirectional optical PCM transmission device described above, transmission path degradation due to crosstalk from the local optical transmitter is subtracted as an optical reception power penalty from the attenuation amount allocated to transmission path loss. There is a problem in that the relay transmission distance that guarantees the error rate is short and limited.

The crosstalk signal here is generally generated by a directional coupler. The influence of crosstalk signals due to reflections at the enclosure and connection points is also considered, and here we will consider either of these dominant factors.

[Means to solve the problem]

The bidirectional optical PCM transmission device of the present invention is a bidirectional optical PCM transmission device in which a directional coupler connected to an optical transmitter and an optical receiver is placed at both ends, and the directional couplers at both stations are connected via a single optical fiber transmission line. In the device, the optical transmitters of both stations use PCM signals of DT-5096 or lower, and the phase of the transmitted signal from the opposing station that is present in one optical receiver and the optical transmitter of the same station as that optical receiver is determined. A circuit for adjusting the phase delay of the transmission signal from the optical transmitter is added to the optical transmitter so that the phase difference between the crosstalk signals becomes 1/2 of the transmission signal repetition period.

[For production]

In the present invention, the duty of the optical transmission signal is set to 50% or less, and the difference between the phase of the reception signal from the opposing team at the receiving point and the phase of the crosstalk signal from the optical transmitter of the own side is calculated as the repetition of the transmission signal. b Set to 1/2 of the return period.

〔Example〕

Hereinafter, embodiments of the present invention will be described in detail based on the drawings.

FIG. 1 is a block diagram showing an embodiment of a bidirectional optical PCM transmission device according to the present invention.

In the figure, 1 is an optical transmitter, 2 is an optical receiver, 3 is a directional coupler, and 4 is an optical fiber transmission line.

Then, the optical transmitters of both stations are PCs whose duty is below SOS.
M signal is used. 5 is the difference between the phase of the transmission signal from the opposing station that is applied to one optical receiver and the phase of the crosstalk signal from that optical receiver and the optical transmitter of the same station, which is 1/2 of the transmission signal repetition period. This phase delay adjustment circuit 5 is added to the optical transmitter 1, and is a phase delay adjustment circuit for adjusting the phase delay of a transmission signal from the optical transmitter. In the figure, arrows represent the flow of signals.

Next, the operation of the embodiment shown in FIG. 1 will be explained.

The phase difference between the phase of the received signal from the opposing station at the optical receiver 2 and the phase of the crosstalk signal from the local optical transmitter 1 is adjusted to 1/2 of the repetition period of the transmitted signal by the phase delay adjustment circuit 5. It will be adjusted so that This phase delay adjustment circuit 5 can be realized, for example, by adjusting the length of the optical fiber.

In addition, as another embodiment that achieves the same function as the phase delay adjustment circuit 5, a means for adjusting the phase of the clock signal that shapes the optical output waveform of the optical transmitter 1 can be considered.

FIG. 2 is a diagram showing the received waveform at the optical receiver a2 in the present invention. In FIG. 2, reference numeral 6 indicates a transmission signal from the game player, and reference numeral 7 indicates a crosstalk signal from the optical transmitter 1. Further, T indicates a transmission signal repetition period, and TM indicates time.

As shown in FIG. 2, according to the present invention, when the duty of the transmission signal is 50% or less, the crosstalk signal 7 from the optical transmitter 1 is transmitted to the phase adjustment circuit 5. 6 and does not cause waveform deterioration.

〔Effect of the invention〕

As explained above, in this proposal, the duty of the optical transmission signal is set to 50% or less, and the phase of the received signal from the opposing team at the receiving point and the phase of the crosstalk signal from the optical transmitter on the own side are Setting the difference to 1/2 of the repetition period b of the transmitted signal has the effect of making it possible to ignore the optical power penalty due to the waveform deterioration of the received signal due to the crosstalk signal.

[BRIEF DESCRIPTION OF THE DRAWINGS] FIG. 1 is a block diagram showing an embodiment of a bidirectional optical PCM transmission device according to the present invention, FIG. 2 is a diagram showing received waveforms in an optical receiver according to the present invention, and FIG. The figure shows a conventional bidirectional optical PCM
FIG. 3 is a diagram showing a received waveform at an optical receiver in a transmission device. 1・●●● Optical transmitter, 2・・●● Optical receiver, 3...●
Directional coupler 4●...Optical fiber transmission line, 5...Phase delay adjustment circuit. ! #Applicant NEC Corporation

Claims (1)

[Claims] In a bidirectional optical PCM transmission system, directional couplers connected to an optical transmitter and optical receiver are placed at both ends, and the directional couplers at both stations are connected via a single optical fiber transmission line. Using a PCM signal of 50% or less, the difference between the phase of the transmission signal from the opposing station at one optical receiver and the phase of the crosstalk signal from the optical transmitter of the same station is calculated as 1 of the transmission signal repetition period. 2. A bidirectional optical PCM transmission device, characterized in that a circuit for adjusting the phase delay of a transmission signal from the optical transmitter so that the phase delay becomes /2 is added to the optical transmitter.