JPS59215136A - Noise level supervising device of semiconductor laser - Google Patents

Abstract

PURPOSE:To detect the fluctuation in a transmission characteristic in the operation of a line by superimposing a pilot signal on an analog signal so as to apply light intensity modulation to a semiconductor laser, receiving a part of this output light, converting the light into an electric signal and extracting noise component by a BPF so as to supervise its level. CONSTITUTION:An output of a pilot signal source 2 is coupled to an output of an analog electric signal source 1 by a coupler 3 and its output is amplified by an amplifier 4. The intensity modulation is applied to the semiconductor laser 5 by an output signal of the amplifier 4 and an output is obtained from a light output terminal 11. Further, a part of an output of the laser 5 is intercepted by a photodetector 6 and an amplifier 7 amplifies a transmission signal including noise near the pilot signal P. The noise component near the frequency of the pilot signal P from the output of the amplifier 7 is extracted by the BPF8, its output is rectified by a rectifier circuit 9, a discriminating circuit 10 supervises the noise level during the operation of line to detect the fluctuation in the transmission characteristic.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention provides an optical communication system that modulates the light intensity of a semiconductor laser with an analog electrical signal (by monitoring the operating state of the semiconductor laser, especially the fluctuations in the noise level due to fluctuations in the oscillation spectrum). The present invention relates to a semiconductor laser noise level monitoring device.

Conventionally, in optical communication systems, the operating state of a semiconductor laser has been monitored, such as the optical output level and bias current of the semiconductor laser, and deterioration of the semiconductor laser has only been detected based on this.

In the case of a light intensity modulation method using an analog electrical signal, it is necessary not only that the optical output level of the semiconductor laser be a predetermined value, but also that the semiconductor laser have good noise characteristics. Semiconductor laser noise level fluctuations are caused by fluctuations in the semiconductor laser's oscillation spectrum due to deterioration of the semiconductor laser itself, an increase in the degree of modulation, temperature changes, or reflected return light from an external optical transmission path. Something,
Although fluctuations can be monitored to some extent by monitoring the bias current, it is insufficient. In optical intensity modulation methods using analog electrical signals, the transmission characteristics of the original fiber transmission line tend to change significantly due to fluctuations in the noise level in the semiconductor laser, so the noise level must be monitored on the transmitting side. In the past, even if it was necessary to monitor the line while it was in operation, it was possible to monitor it while the line was in operation.

SUMMARY OF THE INVENTION An object of the present invention is to solve the above-mentioned conventional drawbacks and to provide a device that can monitor the noise level of a semiconductor laser while the line is in operation.

Describing the structure of the present invention, the present invention employs an optical communication system that modulates the light intensity of a semiconductor laser with an analog electrical signal (2) an analog electrical signal source for modulating a semiconductor laser, and an analog electrical signal source for monitoring the noise level. A pilot signal source installed in a light receiving element that receives a part of the light and converts it into an electrical signal, a bandpass filter that extracts a noise component generated by the pilot signal from the output of the light receiving element, a rectifier circuit that rectifies the bandpass filter output, and a rectifier that rectifies the bandpass filter output. This is a semiconductor laser noise level monitoring device that includes a discrimination circuit that discriminates the magnitude of noise by discriminating the magnitude of circuit output.

The present invention will be explained below by way of examples with reference to the drawings.

FIG. 1 is a block diagram showing one embodiment of the present invention. In FIG. 1, the output of an analog electrical signal source 1 is combined with the output of a pilot electrical signal source 2 by a coupler 3;
The signal is amplified by an amplifier 4. The semiconductor laser 5 outputs an optical output whose intensity is modulated by the output signal of the amplifier 4,
It is sent out from the optical output terminal 11 to the transmission line. On the other hand, a part of the optical output of the semiconductor laser 5 is intercepted by the light receiving element 6 and amplified by the amplifier 7. The signal amplified at this time is
As shown in the figure, it consists of a transmission signal a, a noise signal α in the same band, a pilot signal p having a higher frequency than the transmission signal α, and a noise TLp generated in the vicinity of this signal p. The output of this amplifier 7 is passed through a bandpass filter 8.
The noise component of the pilot signal frequency (excluding the portions very close to the pilot signals p and c) is extracted by . The output of the bandpass filter 8 is rectified by a rectifier circuit 9,
A discrimination circuit 10 monitors whether the noise level changes.

In each of the circuits described above, the noise characteristics of the amplifiers 4 and 7 and the light receiving element 6 are sufficiently better than the noise characteristics of the semiconductor laser 5. The semiconductor laser 5 deteriorates over time, increases the degree of modulation,
Changes in the oscillation spectrum occur due to temperature changes or reflected return light from an external optical transmission path, resulting in low frequency noise rL with a peak in the DC region. The component ru also occurs, so
With the configuration of this example, the noise level generated by the semiconductor laser 5 is monitored.

As shown in Figure 2, the frequency range of noise near the pilot signal frequency changes depending on the noise level.
Depending on the magnitude of the output of the bandpass filter 8, the magnitude of the noise level generated in the semiconductor V-zer 5 can be detected.

With the above-described configuration, the noise level of the semiconductor laser 5 is detected on the transmitting side while the semiconductor laser 5 remains in the line Ji state, and the transmission characteristics after transmission to the optical fiber transmission line can be monitored to some extent. Moreover, since the noise component also changes depending on the magnitude of the modulation distortion component generated by the semiconductor laser 5, it becomes possible to monitor the modulation distortion to some extent.

As explained above, according to the present invention, a pilot signal is superimposed on an analog electrical signal to modulate the optical intensity of a semiconductor laser, and a part of the output light of the semiconductor laser is received and converted into an electrical signal. Since it is configured to extract the noise component using a bandpass filter and monitor the level, it is possible to detect fluctuations in the noise characteristics of the semiconductor V-za and fluctuations in the optical fiber transmission characteristics based on this even during recall operation. become.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a block circuit diagram of an embodiment of the present invention, and FIG. 2 is a diagram showing the frequency characteristics of the signal and noise input to the bandpass filter 8 of FIG. 1. ■...Analog electrical signal source, 2...Pilot signal source, 3...Coupler, 4, 7...
...Amplifier, 5...half, O-pay-the, 6...
・Light receiving element, 8...bandwidth), 9...
... Rectifier circuit, 10 ... Discrimination circuit, 11 ...
...Optical output terminal to the transmission line.

Claims (1)

[Claims] An optical communication system that modulates the optical intensity of a semiconductor laser with an analog electrical signal includes an analog electrical signal source for modulating, a pilot signal source installed to monitor the noise level, and both of the above. A coupler that combines an analog electrical signal from a signal source with a pilot signal, a semiconductor laser that is modulated by the output signal from this coupler, and a part of the emitted light output of this semiconductor laser that is received and converted into an electrical signal. A light receiving element, a bandpass filter that extracts a noise component generated by the pilot signal from the output of the light receiving element, a rectifier circuit that rectifies the output of the bandpass filter, and a rectifier circuit that determines the magnitude of the output of the rectifier circuit to determine the magnitude of the noise. 1. A noise level monitoring device for a semiconductor laser, comprising a discrimination circuit for identifying the noise level.