JPH08191269A - Optical communication system - Google Patents

Abstract

PURPOSE: To avoide the influence of level variation and offset variation in a received signal by executing Manchester encoding at a transmitting side and differentially detecting a change point in a received signal at a receiving side. CONSTITUTION: Manchester codes '10' and '01' corresponding to data '0' and '1' are normally used for fixing a mark rate. Manchester encoded data formed by exclusive OR between data (1) and a clock (2) through an exclusive OR circuit 11 are converted into an optical signal (3) by a light modulator 12 and the optical signal (3) is sent and transmitted up to an opposite photodetector through a prescribed optical transmission line. An optical signal (3) ' received by a photodetecting element 21 is converted into an electric signal, which is amplified by a linear amplifier 22. The amplified received signal is branched into two signals and one received signal (4) is inputted to the plus terminal of a differential amplifier 23. The other received signal is delayed to a 1/2 bit delay signal (5) through a 1/2 bit delay 24 and the signal (5) is inputted to the minus terminal of the amplifier 23. Data (8) are reproduced through a discriminator 25.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical communication system for transmitting an optical signal which causes high-speed level fluctuation and offset fluctuation.

[0002]

2. Description of the Related Art Conventional optical receivers deal with level fluctuations and offset fluctuations of optical signals by automatic gain control for making signal levels constant and automatic threshold value control for making thresholds follow signal levels. . For example, there is a configuration that configures a high-speed feedback system to change the threshold of the discriminator (Y.Ota, et al., "DC-1Gb / s Burst-Mode Compatible.
Receiver for Optical Bus Application ", J.of Lightw
ave Technol., Vol.10, No.2, Feb.). However, with this method, there is a trade-off relationship between the response speed of the feedback system and the allowable amount of level fluctuation, and it was not possible to bring both into the best state at the same time. That is, the automatic gain control and the automatic threshold control cannot cope with high-speed and large level fluctuations and offset fluctuations, and it is necessary to keep the mark ratio of the signal constant. For this reason, it cannot be applied to burst signals used in packet switching systems and the like.

[0003]

In the optical packet switching or the optical cross connect, the route is different for each optical packet signal, so that the level fluctuation and the offset fluctuation occur due to the difference in the number and characteristics of the optical components passing through. However, it is difficult to realize an automatic gain control circuit and an automatic threshold control circuit that follow the high-speed level fluctuation and offset fluctuation of the optical packet signal. Therefore, when using the conventional signal identification and reproduction method using a threshold value, it is necessary to reduce the allowable range of level fluctuation and offset fluctuation, which is a major obstacle in realizing optical packet switching or optical cross-connect. Was becoming.

An object of the present invention is to provide an optical communication system capable of identifying and reproducing an optical signal whose level and offset fluctuate at high speed.

[0005]

SUMMARY OF THE INVENTION An optical communication system of the present invention comprises an optical transmitter configured to Manchester code a digital data signal to be transmitted, convert it into an optical signal and transmit the optical signal, and a received optical signal. An optical receiver configured to reproduce a digital data signal by generating a difference signal having a difference from the signal power of 1/2 bit before, and discriminating the difference signal by a predetermined threshold value. 1).

The optical receiver receives a light signal and converts the light signal into an electric signal, a branching means for branching the output signal of the light receiving element into two, and an output signal of one of the branching means delayed by 1/2 bit. The delay unit, a differential amplifier that takes the difference between the other output signal of the branching unit and the output signal of the delay unit, and a discriminator that discriminates the differential signal output from the differential amplifier (claim 2). .

The optical receiver comprises an optical branching unit for branching a received optical signal into two, an optical delay unit for delaying one output optical signal of the optical branching unit by 1/2 bit, and an output light for the other output of the optical branching unit. The difference detection means for taking the difference between the signal and the optical signal delayed by 1/2 bit and converting it to an electric signal, and the discriminator for discriminating the difference signal output from the difference detection means (claim 3). .

[0008]

When the digital data signal is Manchester encoded, the data "0" becomes "10" and the data "1" becomes "01". In the optical receiver, the signal is (1 → →
0), that is, a negative potential for the data "0", and a positive potential for the signal (0 → 1), that is, a positive potential for the data "1". The original digital data signal can be reproduced by identifying the potential of the difference signal with the clock of the original data signal with the zero potential as the threshold value.

Since the polarity of the differential signal is not affected by the level fluctuation and the offset fluctuation of the received optical signal, the discrimination reproduction is possible even with the threshold of the discriminator fixed at zero potential.

[0010]

FIG. 1 shows the configuration of a first embodiment of an optical transmitter and an optical receiver used in an optical communication system of the present invention.
FIG. 2 is a timing chart for explaining the operations of the optical transmitter and the optical receiver in the first embodiment. Figure 1 (a)
Is a configuration of an optical transmitter for Manchester encoding a digital data signal. “1” for data “0”
The Manchester code that is “01” for 0 ”and data“ 1 ”is a code that is normally used to make the mark ratio constant, and the exclusive OR circuit 11 performs an exclusive OR of data and clock. It is generated by taking.
The Manchester-encoded data is the optical modulator 1
At 2, the light signal is converted into an optical signal and transmitted, and is transmitted to an opposing optical receiver via a predetermined optical transmission path.

FIG. 1 (b) shows the configuration of an optical receiver which reproduces original data from an Manchester-encoded optical signal. The optical signal 'received by the light receiving element 21 is converted into an electric signal and amplified by the linear amplifier 22. The amplified received signal is equally divided into two, one of the received signals is input to the + terminal of the differential amplifier 23, and the other received signal becomes a 1 / 2-bit delay signal via the 1 / 2-bit delay unit 24. , To the negative terminal of the differential amplifier 23. The differential signal output from the differential amplifier 23 is input to the discriminator 25, and data is reproduced by discriminating at the timing of the clock.

The difference signal, which is the difference between the received signal and the 1 / 2-bit delay signal, has a negative potential when the received signal changes (1 → 0), that is, when the data is “0”, and (0 → When it changes to 1), that is, when the data is “1”, the potential becomes positive. Therefore, the discriminator 2
Data can be reproduced by identifying the difference signal with the zero potential as a threshold value in 5. The clock is
As shown in FIG. 2, the discrimination timing in the discriminator 25 is given. In this way, even if level fluctuations, offset fluctuations, and noise are added to the received optical signal, it is possible to perform a discrimination operation that is not affected by those fluctuations. That is, it is not necessary to dynamically change the threshold of the discriminator 25.

FIG. 3 shows the configuration of a second embodiment of the optical receiver. The feature of this embodiment is that, as shown in FIG. 3A, the received optical signal 'is equally branched by the optical coupler 31, one of the optical signals is input to the + terminal of the balanced receiver 32, and the other is input. The optical signal is input to the negative terminal of the balanced receiver 32 via the 1 / 2-bit delay line 33. The signal obtained by amplifying the output signal of the balanced receiver 32 by the linear amplifier 22 becomes the same as the differential signal output from the differential amplifier 23 of the first embodiment. Other configurations and operations are similar to those of the optical receiver of the first embodiment.

Instead of the balanced receiver 32 and the linear amplifier 22, as shown in FIG. 3B, two light receiving elements 21-1 and 21-2 and a linear light receiving element for amplifying the output signal of each light receiving element are provided. The same applies to the configuration including the amplifiers 22-1 and 22-2 and the differential amplifier 23. FIG. 4 shows an experimental result using the configuration of the second embodiment.

In this experiment, a manner of reproducing a data by generating a 2.5 Gbit / s Manchester code, receiving an optical signal having a level difference of about 10 dB, will be shown. ′ Is the received optical signal, is the differential signal output from the balanced receiver 32, and is the reproduced data output from the discriminator 25. In addition, ', and correspond to FIG. The received optical signal 'has a level variation and an offset variation, but since the difference is taken by the balanced receiver 32, it can be correctly identified even if the threshold potential of the discriminator 25 is fixed to zero (near the center of the figure). Recognize.

[0016]

As described above, the optical communication system of the present invention has a configuration in which Manchester coding is performed on the transmission side and difference points of the received signal are detected on the receiving side, so that the level fluctuation and offset of the received signal are offset. The influence of fluctuation can be avoided. Therefore, even when the optical signal level and the offset fluctuate at high speed for each packet, the digital data signal can be transmitted without using a special control circuit.

[Brief description of drawings]

FIG. 1 is a block diagram showing the configuration of a first embodiment of an optical transmitter / optical receiver used in an optical communication system of the present invention.

FIG. 2 is a timing chart for explaining the operation of the optical transmitter / optical receiver in the first embodiment.

FIG. 3 is a block diagram showing the configuration of a second embodiment of the optical receiver.

FIG. 4 is a diagram showing an experimental result using the configuration of the second embodiment.

[Explanation of symbols]

 11 exclusive OR circuit 12 optical modulator 21 light receiving element 22 linear amplifier 23 differential amplifier 24 1/2 bit delay device 25 discriminator (D flip-flop) 31 optical coupler 32 balanced receiver 33 1/2 bit delay line

Claims (3)

[Claims] 1. An optical communication system for transmitting an optical signal between an optical transmitter and an optical receiver which face each other via an optical transmission line, wherein the optical transmitter performs Manchester encoding of a digital data signal to be transmitted, The optical receiver is configured to transmit the converted optical signal, and the optical receiver generates a difference signal that is the difference between the received optical signal and the signal power 1/2 bit before, and outputs the difference signal. The optical communication system is characterized in that the digital data signal is reproduced by discriminating the optical disc by a predetermined threshold value. 2. The optical communication system according to claim 1, wherein the optical receiver includes a light receiving element that receives an optical signal and converts the optical signal into an electric signal, and a branching unit that branches an output signal of the light receiving element into two. A delay unit that delays one output signal of the branching unit by 1/2 bit, a differential amplifier that takes a difference between the other output signal of the branching unit and the output signal of the delaying unit, and an output from the differential amplifier. And a discriminator for discriminating a differential signal according to the present invention. 3. The optical communication system according to claim 1, wherein the optical receiver delays a received optical signal into two, and an optical signal output from one of the optical branching means by 1/2 bit. Output from the difference detecting means, and an optical delay means for making the difference, a difference detecting means for taking a difference between the other output optical signal of the optical branching means and the optical signal delayed by the 1/2 bit, and converting it to an electric signal. An optical communication system comprising a discriminator for discriminating a differential signal.