JPS62219988A - Optical output control circuit for laser diode module - Google Patents

Abstract

PURPOSE:To prevent the forward output light of a laser diode element from being changed even when the dark current of a photodetector is changed by detecting the AC component in the output current of the photodetector and controlling the optical output so that the magnitude of the AC component is constant. CONSTITUTION:A bias source and bias modulator 6 gives a photodetector 3 a prescribed DC bias voltage and modulated signals with an arbitrary frequency and a constant amplitude which are superposed on the bias voltage by the bias modulator. The AC component of monitor output current, applied to an AC component detecting circuit 7, is detected thereby. The AC component signals are applied to an automatic output power control (APC) driving circuit 4, compared with a reference value, a driving signal is produced in accordance with an error to operate a laser diode (LD) element 2 and a feedback control is conducted so that the magnitude of the AC component signals is constant. In this case, even though the dark current of the photodetector is changed, the AC component of the monitor output current is not changed and therefore the light output of the LD element 2 is not changed.

Description

[Detailed Description of the Invention] [Summary] A DC bias voltage and a C AC signal superimposed thereon are applied to a light receiving element that detects the rear output light of a laser diode element, and an AC component in the output current of the light receiving element is detected.・By performing pre-output control so that the magnitude of C1 remains constant, even if the dark current of the light receiving element changes,
To prevent fluctuations in the forward output light of a laser diode element.

[Industrial application field]

The present invention relates to an automatic output control (PC) IIIK operating device for a laser diode (LD) module, and in particular to an LD-e module that does not cause optical output fluctuations due to changes in the dark current of a light receiving element that detects the optical output of an LD element. This relates to an APC drive device.

LD module APCl! The dynamic device is used, for example, for continuous operation tests of LD modules. APC driving of the LD module is performed by a round of feedback control in which the optical output of the LD element is detected by the light receiving element and fed back to the APC drive circuit, and the LD element is operated by the drive current generated by the drive circuit. It is also desired that the light output does not change even when the dark current of the light-receiving element changes.

[Conventional technology]

In the conventional LD module APC drive device, the LD
APC control was performed by directly feeding back the output current of a light receiving element that converts the optical output of the element into an electrical signal.

FIG. 5 shows a conventional LD module APC driving device, in which 1 indicates an LD module, and LD element 2
, includes a monitoring light receiving element 5 consisting of an APD. Reference numeral 4 denotes a PC drive circuit that performs APC drive control using the output current of the light-receiving element 3 to generate a drive current, and 5 converts the output light of the LD element 2 from optical to electrical and generates a light output signal according to the optical output. This is a light receiving sensor.

In FIG. 5, the rear output light of the LD element 2 is transferred to the light receiving element 3.
The monitor current generated by conversion is supplied to the APC drive circuit 4, and the APC drive circuit 4 generates a drive current according to predetermined control characteristics. The LD element 2 generates output light in the forward and backward directions according to this drive current. In this way, the loop feedback control is performed, and the monitor current of the light receiving element 3 becomes constant (), and therefore the optical output of the LD element 1 represented by the monitor current also becomes constant. Light receiving sensor 5
converts the front output light of the LD element 1 into light/'&l and generates a light output signal indicating the light output.

In this way, the monitor current of the light receiving element in the LD module represents the optical output of the LD element, and this is used to perform APC control as described above, and also to determine the life of the LD element in the LD module continuous operation test. etc.

[Problem that the invention seeks to solve]

In the LD module APC driving device, an avalanche photodiode (APD) is used as a light receiving element that detects the optical output of the LD element. The output current of an APD element usually includes a dark current, the magnitude of which changes depending on temperature and aging. When the dark current of the light-receiving element increases and the monitor current becomes larger, the APC drive circuit performs the same control as when the optical output of the LD element is increased, and in order to decrease the driving current, the optical output of the LD element increases. decreases.

In this way, in conventional devices, due to a change in the dark current of the light receiving element, the driving current changes due to the same control as when the optical output of the LD element changes even though the optical output of the LD element does not change. Therefore, there is a problem that the optical output of the LD element changes.

[Means for solving problems]

FIG. 1 shows the basic structure of the present invention to solve the problem of the conventional technology.
02) and outputs the signal obtained by monitoring the signal to the drive circuit (1
03) and operates the laser diode element (101) by the output of the drive circuit (103), the light output control circuit includes the following means.

Reference numeral 104 denotes a bias means, which is a monitor light receiving element (1
02) is given a bias voltage modulated by an AC signal.

105 is a detection means, which includes a monitor light receiving element (102
) is detected.

By giving this detection signal to the drive circuit (103), the drive circuit (103)
By performing feedback control, the optical output of the laser diode element (101) is controlled to be constant.

[Effect]

FIG. 3 shows the relationship between the bias voltage and monitor output current in a light receiving element consisting of an APD. In FIG. 5, human shows the characteristics of the light receiving element under normal conditions, and B shows the characteristics when the dark current increases, which generally shows a tendency for the characteristics to shift in parallel as the dark current increases.

In Fig. 3, when the bias voltage at the light receiving element is modulated with an AC signal of an arbitrary frequency f, the magnitude E of the AC signal component in the monitor current generated from the light receiving element is B for the person in Fig. 3 as well. The same is true for .

Therefore, if the optical output is controlled by the detection signal consisting of the alternating current component of the monitor output current of the light receiving element, the optical output from the laser diode element will not change regardless of the change in the dark current.

〔Example〕

FIG. 2 shows one embodiment of the present invention.
The same parts as in the figure are indicated by the same numbers, 6 is a bias source and a bias modulation section, and 7 is an alternating current component detection circuit.

Further, FIG. 4 shows the relationship between the bias voltage and monitor output current when there is optical input.

In FIG. 2, the bias source and bias modulator 6 apply a constant DC bias voltage from the bias source to the light receiving element 3, and the bias modulator superimposes it on this bias voltage with a constant amplitude of an arbitrary frequency. gives a modulated signal. In FIG. 4, EA indicates this bias voltage, and by superimposing the modulation signal on it,
An alternating current e1 is generated in the monitor output current of the light receiving element.

The LD element 2 emits light by a drive current from the APC drive circuit 4, and the light from the back is input to the light receiving element 5. The light-receiving element 3 generates an output current corresponding to the input light level, and a bias voltage is added to the output current K to generate, for example, the bias voltage EB in FIG. 4. It has been shown that this produces an alternating current of the monitor output current, depending on the characteristics of the APD. The voltage b is generally greater than the voltage b depending on the characteristics of the light receiving element.

The monitor output current is applied to an alternating current component detection circuit 7, and an alternating current of the monitor output current is detected. The signal of this social gathering is applied to the human PC driving circuit 4, which compares the magnitude of the signal of this social gathering with a reference value, generates a driving signal according to the error, and drives the LD element 2. By operating it, feedback control is performed so that the magnitude of the signal from this social gathering is constant.

The alternating current of the monitor output current is determined by the optical output of the LD element 2 when the bias voltage applied from the bias source is constant, so by performing the control described above, the LD
APC driving is performed to keep the optical output of the element 2 constant.

In this case, even if the dark current of the light-receiving element changes, the characteristics of the light-receiving element only shift in parallel as explained in FIG.
The optical output of element 2 does not vary.

〔Effect of the invention〕

As explained above, according to the present invention, even if the dark current of the light receiving element in the laser diode module changes, the optical output of the laser diode module does not change. Therefore, according to the present invention, in a continuous operation test of a laser diode module, etc., it is possible to accurately evaluate fluctuations in the forward output light of the laser diode module without being affected by the dark current of the light receiving element.

[Brief explanation of drawings]

Fig. 1 is a diagram showing the basic configuration of the present invention, Fig. 2 is a diagram showing an embodiment of the invention, Fig. 3 is a diagram showing the monitor output current when the dark current changes, and Fig. 4 is a diagram showing the monitor output current when the dark current changes. FIG. 6 is a diagram showing monitor output current when there is optical input. Yes FiAIJ Nagisa Izumi LD Seven Ter-l ^P(at/
% 4rmz"), 1...Laser diode (L
D) Module 2...Laser diode (LD) element 3...Light receiving element 4 for monitoring -APC drive circuit 5...Light receiving sensor 6...Bias source and bias variable Ia section 7...AC component detection circuit

Claims (1)

[Scope of Claims] A signal obtained by monitoring the output light of the laser diode element (101) with a monitoring light receiving element (102) is fed back to the drive circuit (103), and the signal obtained by monitoring the output light of the laser diode element (101) is fed back to the drive circuit (103). A light output control circuit that operates a laser diode element (101) with a current includes bias means (104) for applying a bias voltage modulated with an AC signal to the monitor light-receiving element (102), and a monitor light-receiving element (102). detection means (105) for detecting the magnitude of the AC signal component in the monitor output signal of (102);
), wherein the detection signal is fed back to the drive circuit (103) to control a drive signal for the laser diode element (101).