JPH01133385A - Optical output control circuit - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention This invention relates to a light output control circuit for keeping the output light intensity of a semiconductor laser constant.

2. Description of the Related Art A conventional optical output control circuit of this type is intended to maintain a constant intensity of light output from a semiconductor laser, as shown in FIG. In FIG. 3, 1 is a bias circuit for supplying a bias current to the semiconductor laser, 2 is a semiconductor laser drive circuit for supplying an electric signal to the semiconductor laser, 3 is a light receiving circuit, 4 is a semiconductor laser, and 5 is a semiconductor laser drive circuit for supplying an electric signal to the semiconductor laser. A smoothing circuit, 6 a comparator, 9 an optical fiber, and the optical output control circuit includes a bias circuit 1, a light receiving circuit 3, a smoothing circuit 6, and a comparator 6.

The operation will be explained below. The semiconductor laser 4 is biased by a direct current from the bias circuit 1 and emits light in response to a digital signal from the semiconductor laser drive circuit 2.

The light emitted from the front of the semiconductor laser 4 is transmitted through an optical fiber 9.
The light that propagates to and exits from the rear enters the light receiving circuit 3,
This light receiving circuit 3 detects the average value of the output light intensity of the semiconductor laser 4.

In addition, in order to make the output light intensity from the semiconductor laser 4 constant regardless of the mark rate of the output signal from the semiconductor laser drive circuit 2, the digital signal from the semiconductor laser drive circuit 2 is averaged by a smoothing circuit 6, and the light receiving circuit 3 A comparator 6 compares the output signal with the output signal from the bias circuit 1, and the output signal is fed back to the bias circuit 1.

For example, when the output light intensity of the semiconductor laser 4 increases due to a change in temperature, etc., the light receiving circuit 3 detects this, and the bias circuit 1 decreases the bias current to increase the output light intensity of the semiconductor laser 4.
Reduce the output light intensity.

As described above, the intensity of the output light from the semiconductor laser 4 is kept constant.

Problems to be Solved by the Invention In the conventional circuit described above, for example, when the mark rate of the output signal of the semiconductor laser drive circuit 2 is constant, the LD is Bias current is controlled. Therefore, external light other than the direct output light from the semiconductor laser 4, such as reflected light within the fiber,
When the light enters the light receiving circuit 3, the light receiving circuit 3 detects both the output light of the semiconductor laser 4 and the external light. The problem is that the current decreases and the output light intensity of the semiconductor laser decreases. That is, the intensity of light incident on the light receiving circuit 3 is kept constant.

In view of this point, the present invention aims to provide a light output control circuit that can keep the output light intensity of a semiconductor laser constant regardless of the intensity of external light.

Means for Solving the Problems In order to solve the above-mentioned problems, the present invention provides a method for detecting a digital signal having the same pattern as the digital signal supplied to the semiconductor laser by a light receiving circuit and passing the output signal from the semiconductor laser through the gate. It is used as a control signal, and furthermore, the average value of the output signal from the gate is compared with the average value of the digital signal which is the control signal, and the bias current of the semiconductor laser is determined from the output.

Function: With this configuration, even if external light enters the light receiving circuit when the semiconductor laser is not emitting light, the output light intensity of the semiconductor laser can be kept constant.

EXAMPLES Hereinafter, examples of the present invention will be described with reference to the drawings. FIG. 1 shows a 10-step diagram of an optical output control circuit in an embodiment of the present invention. In FIG. 1, the optical output control circuit includes bias circuit 1. Light receiving circuit 8. Gate 7, smoothing circuit 1
o and 11. It consists of a comparator 12. The operation will be explained below. The semiconductor laser 4 is biased by a direct current from the bias circuit 1 and emits light in response to a digital signal output from the semiconductor laser drive circuit 2. One of the output lights of the semiconductor laser 4 is made incident on the light receiving circuit 8, where it is converted into an electrical signal and is input into the gate 7.

Furthermore, a digital signal outputted from the semiconductor laser drive circuit 2 having the same pattern as the signal sent to the semiconductor laser 4 is used as a control signal for the gate 7, and its timing is set as a control signal for the semiconductor laser 4.
The signal sent from the semiconductor laser 4 passes through the light receiving circuit 8 and enters the gate 7 in synchronization with the timing. By doing so, only the signal component directly output from the semiconductor laser 4 among the signals from the light receiving circuit 8 passes through the gate 7. Next, in order to correct the mark ratio, the digital signal from the semiconductor laser drive circuit 2 and the output signal from the gate 7 are each averaged by smoothing circuits 10 and 11,
A comparator 12 compares the two signals, and the result is fed back to the bias circuit 1 to keep the optical output from the semiconductor laser 4 constant.

Next, the operation of this circuit will be briefly explained.

Now, the optical signal that enters the optical fiber 9 from the semiconductor laser 4 is reflected at a part such as an optical connector, and returns to the semiconductor laser 4.
Assume that the light returns to the point and enters the light receiving circuit 8. Assume that this returned light is incident on the semiconductor laser 4 when it is not emitting light. At this time, the output waveform from the light receiving circuit 8 becomes as shown in FIG. 2(a). When this signal is input to the gate 7, the direct output signal component from the semiconductor laser 4 passes through due to the gate control signal from the semiconductor laser drive circuit 2 as shown in FIG. The signal component due to the light is blocked because the gate control signal is off, and the signal component due to the returned light is excluded from the output waveform of the gate 7, as shown in FIG. 2C. Therefore, the signal component due to the returned light does not affect the bias circuit 1.

Effects of the Invention As described above, the present invention receives output light from a semiconductor laser, inputs the signal to a gate whose control signal is a digital signal from a semiconductor laser drive circuit, and transmits the result to a gate that uses a digital signal from a semiconductor laser drive circuit as a control signal. By feeding back to the bias circuit, even if external light enters the light receiving circuit when the semiconductor laser is not emitting light, the output light intensity of the semiconductor laser can be kept constant almost unaffected by the intensity of the external light. This realizes an excellent optical output control circuit that can perform

[Brief explanation of the drawing]

FIG. 1 is a block diagram of an optical output control circuit according to an embodiment of the present invention, FIG. 2 is an operational waveform diagram of the same output control circuit, and FIG.
The figure is a 10-part configuration diagram of a conventional optical output control circuit. 1...Bias circuit, 2...Semiconductor laser drive 9...Optical fiber, 10.11...
...Smoothing circuit, 12...Comparator. Figure 1 Figure 2 Figure G Imma t P1 victory Figure 3

Claims (1)

[Claims] A second digital signal having a pattern equal to the first digital signal supplied to the semiconductor laser is used as a control signal when the output signal from the semiconductor laser detected by the light receiving circuit is passed through the gate, and the output signal from the gate is An optical output control circuit characterized in that the optical output control circuit is configured to compare an average value of the second digital signal with an average value of the second digital signal, and feed the result back to the bias circuit of the semiconductor laser.