JPH02107030A - Optical communication equipment - Google Patents

Abstract

PURPOSE:To decrease an error rate and pulse width distortion by feeding back the optical level to the a light receiving side, and maintaining a light emitting level at which the light receiving level is optimized. CONSTITUTION:In optical communication equipment A, the optical signal on an optical fiber cable 3B is converted into an electric signal by a light receiving element 2A and a light receiving circuit 9A. Optical level information corresponding to the light receiving level of optical communication equipment B is made into a light emitting level control 6A signal to drive a light emitting element 1A by means of an optical level information detecting circuit 7A, and controls the light emitting level of the light emitting element 1A. In such a way, since the light receiving level is fed back, and the optimum light receiving level can be maintained by a light receiving edge, the error ratio is decreased the pulse width distortion is reduced, and the lives of the light emitting element and light receiving element can be extended.

Description

[Detailed Description of the Invention] [Object of the Invention] (Industrial Application Field) The present invention relates to an optical communication device that transmits signals using light as a medium.

(Prior Art) In recent years, the market for optical communications has continued to expand due to the realization of large-capacity communications by Rei Takakura and excellent resistance to electromagnetic interference. At the same time, various efforts have been made to improve pulse width distortion and error rate in response to optical level fluctuations caused by elongation of optical gaples, reduction in luminous efficiency of light emitting elements, changes in optical cable loss, increased loss in optical connectors, etc. Pulse width distortion in optical communications is caused by the fact that due to excessive optical input, the threshold level, which should be at 1/2 of the maximum level, becomes a relatively low level position, and the pulse width changes by the rise and fall time fluctuations, and due to excessive optical input. Due to the saturation of the amplifier, the rise and fall propagation time differences further widen, which directly affects the error rate, which is the accuracy of optical communication.

Even if the level of light received by the pond is insufficient, the error rate increases.

Therefore, maintaining a stable optical level greatly contributes to improving the performance of optical communication devices.

FIG. 3, FIG. 4, and FIG. 5 show examples of conventional configurations for stabilizing light level and reducing pulse width distortion.

FIG. 3 shows the basic configuration of an optical transmission device. Transmission signal 14
is input to the transmitting circuit 4 and drives the light emitting element 1. An optical signal output from the light emitting element 1 is transmitted to the light receiving element 2 through the optical fiber 3. In the light receiving circuit 9, the light receiving element 2C
The input optical signal is converted into an electrical signal and becomes a received signal 15 to realize optical communication. Here, the light emission level of the optical signal takes into account the coupling loss of the optical connector, the loss of the optical cable, etc., and is fixed at the time of initial adjustment to a level that sufficiently responds to the sensitivity of the light receiving element and minimizes pulse width distortion. However, there is a drawback that the light receiving level decreases and becomes insufficient due to increased loss of the optical cable 3, the light emitting element T, and the light receiving cable 2 due to aging, which increases the error rate.

FIG. 4 shows an optical receiver that changes the threshold level in order to improve pulse width distortion due to fluctuations in the received light level. The maximum value of the electrical signal corresponding to the received light level is the peak hold capacitor of the hold circuit 18 <CH)
The voltage is maintained at 1/2 of the maximum value by two voltage dividing resistors (R) connected to the output. This voltage is always 1.0% of the maximum input light level. /2 voltage, and by using it as a threshold voltage, pulse width distortion can be improved. However, in this method, since the holding capacitor (C11) has a specific time constant, if the input light level is maintained at 0, the threshold level decreases due to self-discharge and pulse width distortion occurs in the 1st-order data. The biggest drawback was that this occurred. Therefore, this method has been limited to 50% duty data transmission such as pi-phase.

FIG. 5 shows an optical receiver using the gain control method.

The received light level is converted into an electrical signal by the light receiving circuit 9 and input to the gain control amplifier circuit 16 . This gain control amplifier circuit 16 improves the saturation of the amplifier at the time of excessive input by feedback from the automatic gain control (^GC) circuit 17, and aims to reduce pulse width distortion and expand the dynamic range.

(Problem to be solved by the invention) As described above, it is possible to temporarily improve the error rate by semi-fixing the conventional received light level, or to change the threshold level after converting changes in the received light level into electrical signals. 1. The method of stabilizing the output level using an automatic gain@control circuit to avoid saturation of the amplifier circuit and improving pulse width distortion prevents the light level on the light emitting side from being too low or too high, or emitting light at a level higher than necessary. It had no suppressive effect and was not a fundamental measure to improve the error rate and pulse width distortion. Furthermore, it has not been possible to prevent a decrease in the luminous efficiency of the light emitting element and deterioration of the light receiving element due to excessive light level emission.

The present invention has been made in view of the above circumstances, and controls the light emission level by feeding back the light level amount of the light receiving section to the light emitting side, reduces pulse width distortion due to excessive light level, and improves the light emitting element and light receiving side. It is an object of the present invention to provide an optical communication device that can be protected from element deterioration.

[Structure of the Invention] (Means for Solving the Problem) In order to achieve the above object, the present invention converts an electrical signal into an optical signal in a light emitting element of an optical transmitter, and transmits the signal to an optical receiver via an optical fiber cable. In an optical communication device that converts an optical signal into an electrical signal corresponding to a light level using a light-receiving element, the optical communication device on the receiving side receives an optical signal output from the optical communication device on the transmitting side, and converts the unreceived optical signal into an electrical signal corresponding to the optical level. After smoothing, the signal is converted from analog to digital and digitally encoded, and then returned to the transmitting end to recognize the light level reaching the optical receiver at the receiving end as a digital code, and this digital code is used for transmission. The structure is such that the light emitting elements at the ends are controlled so that they emit light at an optimal level.

(Function) The optical communication devices on the transmitting side and the receiving side can mutually feed back the status of the received light level and maintain the optimum optical reception level, reducing the error rate due to insufficient received light level, excessive pulse generation, and optical Pulse width distortion caused by deterioration of fiber cables, light emitting elements, and light receiving elements can be reduced.

(Example) An embodiment of the present invention will be described with reference to FIG.

FIG. 1 shows an optical communication device A having two identical functions.

B is the optical transmitter 12A (12B) and the optical receiver 13B (73
^) are connected to each other by optical fiber cables 3A (3B). The operation of optical communication device A will be explained. The optical signal of the optical fiber cable 3B is transmitted to the light receiving element 2A.
, is converted into an electrical signal by the light receiving circuit 9A. This electrical signal level is proportional to the optical level.2 The normal transmission signal is amplified by an amplifier circuit 8^ and then used as a received signal 15^. On the other hand, the light level information corresponding to the light reception level of the optical communication device B becomes a signal for the light emission level control 6^ that drives the light emitting element 1^ by the light level information detection circuit 7A, and changes the light emission level of the light emitting element 1^. . The operation of feeding back the light receiving level as described above and maintaining the optimum light receiving level at the light receiving end will be explained.

When the optical communication device A starts up from the stopped state of the optical communication devices A and B, the optical transmitter 12A connects the light emitting element 1^ and the light receiving cable 2.
An optical signal with a maximum light emission level preset to an extent that does not affect the deterioration of the characteristics of B is outputted as optical level information for a certain period of time, and then stopped.

Next, when the optical communication device B starts up, it outputs light level information of the maximum light emission level, as in the case where the optical communication device B does not start up. This optical signal passes through the optical fiber cable 3B and reaches the light receiving element 2A for the optical communication device.

Figure 2 shows the difference between the maximum light emitting level "A" of the light emitting element 1B and the light receiving level "C" of the light receiving cable 2A which is attenuated by the optical transmission loss W which is a combination of the coupling loss of the optical connector, the loss of the optical fiber cable, etc. Indicates the person in charge. After converting the optical signal attenuated by the optical transmission loss W into an electrical signal in the light receiving circuit 9A''c, the DC component, which has been smoothed by the integration circuit R111^ and becomes proportional to the received light level, is received by the A/D converter 10A. It becomes a digital code corresponding to the level.This digital code drives the light emitting element 1A by the transmission switch 5A and is outputted to the optical fiber cable 3^ as an optical signal.Optical communication device B
Then, the digital code is received, electrically converted by the light receiving circuit 9B, and amplified by the amplifier circuit 8B.
Enter in 7B. Light level +L? The l output circuit 7B decodes the light level reaching the light receiving element 2^ when the optical transmitter 12B outputs light level information at the maximum light emission level from the digital code, and compares it with the output maximum light emission level. Optical transmission loss W can be detected. Now, the optical transmitter 12B is at a steady light emission level of 1 unit, which is the optimum light reception level of the light receiving element 2^ and the optical transmission loss W, and the light emitting element 1B
It is what drives the. After this operation is completed, the optical communication device A also performs the same operation, thereby enabling mutual optical transmission in the best condition. Therefore, it is possible to reduce the error rate, reduce pulse width distortion, and extend the life of the light emitting element and the light receiving element. Moreover, further effects can be obtained by performing this operation periodically after predicting the deterioration characteristics of the light emitting element and the light receiving element.

[Effects of the Invention] The present invention makes it possible to feed back the light level at the light receiving end to the light emitting side and maintain the light emitting level at which the light receiving level is optimal, thereby reducing the error rate, which was the biggest drawback in optical transmission. This has the effect of almost eliminating pulse width distortion.

[Brief explanation of the drawing]

FIG. 1 is a configuration diagram of an embodiment of an optical communication device according to the present invention;
FIG. 2 is a diagram showing the light level of the present invention, and FIG. 3 is a diagram showing the light level of the sub-#1.
FIG. 4 is a diagram showing another example of the conventional device, and FIG. 5 is a diagram showing still another example of the conventional device.

Claims (1)

[Claims] In an optical communication device, an electrical signal is converted into an optical signal by a light emitting cable of an optical transmitter, and then converted into an electrical signal corresponding to the light level by a light receiving element of an optical receiver via an optical fiber cable. An optical communication device on the receiving side receives an optical signal output from an optical communication device, smooths the received optical signal, converts it from analog to digital, and returns it to the transmitting end. An optical communication device characterized in that the level of light reaching an optical receiver is recognized by a digital code, and the digital code is used to control a light emitting element at a transmitting end so that it emits light at an optimum level.