JP2000315836A - Laser diode deterioration determining device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To determine deterioration of a laser diode and to correct decrease in light output due to deterioration. SOLUTION: This laser diode deterioration determining device is composed of a photodiode PD, which detects light output of a laser diode LD placed in series between a power supply and a ground, an operational amplifier 23 which calculates a difference between the output current of the photodiode PD and a first reference value and a transistor 25 whose base is connected to the output of the operational amplifier 23 and which is interposed between the laser diode and the ground for controlling the drive current of the laser diode.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an apparatus for determining deterioration of a laser diode used as a light source of an optical communication apparatus.

[0002]

2. Description of the Related Art The characteristics of the above-mentioned laser diode are deteriorated by operating time, temperature or environmental conditions, and as a result, it is inevitable that the luminous efficiency is reduced. Such a decrease in luminous efficiency causes a sudden failure of the optical network system. Therefore, various measures are required to prevent this from occurring.

FIG. 2 shows a conventional example of a laser diode deterioration alarm generation circuit. The photodiode PD and the laser diode LD are driven by a driving circuit (LDDRV) 9
It is connected to the. This drive current is detected by the current detector 7 as a voltage across the resistor R1 interposed in series between the laser diode LD and the ground. The temperature sensor 1 detects the temperature around the laser diode LD, and this temperature detection signal is digitized by the A / D converter 2 and stored in the memory 3 over the entire temperature range. The temperature data stored in the memory 3 is converted into an analog signal by a D / A converter 4 and further multiplied by a predetermined coefficient in a calculator 5. It is supplied as a voltage Vr. The comparator 6 compares the output Va of the current detector 7 with the reference voltage Vr, and generates an alarm if the output Va exceeds the reference voltage Vr.
The light output of the laser diode LD is kept constant by an automatic output control circuit (APC) 10. The photodiode PD detects the optical output of the laser diode LD fed back to the APC 10 and uses the detected optical output to output the laser diode L by the drive circuit 9.
The drive current of D is controlled.

[0004]

The above circuit has the following problems to be solved. 1. Regardless of the presence or absence of deterioration, all laser diode current values are detected and compared with a reference value, so it is difficult to accurately determine only deterioration. 2. The above circuit merely detects the deterioration of the laser diode and does not compensate for the decrease in the optical output corresponding to the degradation. To compensate for the optical output, an independent automatic output control circuit 1 is used.
0 is required. 3. Since it is necessary to adjust both the automatic output control circuit and the alarm generation circuit, the manufacturing process becomes complicated, which hinders automation of the process. Further, since an automatic output control circuit and an alarm generation circuit that consume power independently of each other are required, the power consumption of the entire photodetector increases.

SUMMARY OF THE INVENTION The present invention has been proposed in view of the above circumstances, and has as its object to easily compensate for deterioration of a laser diode with a simple circuit configuration and reduce power consumption.

[0006]

A laser diode deterioration judging device according to the present invention comprises: a light receiving means for detecting an optical output of a laser diode provided in series between a power supply and a ground point;
Calculating means for calculating the difference between the output current of the light receiving means and a first reference value; and a base connected to the output of the calculating means and driving the laser diode interposed between the laser diode and a ground point. And a transistor for controlling current. Further, in the deterioration judging device of the present invention, the laser diode is provided with temperature correction means for controlling a driving current of the laser diode in accordance with an ambient temperature in parallel with the transistor. Further, the deterioration judging device of the present invention is provided with a comparator for comparing the current of the transistor with a second reference value and outputting an alarm signal on condition that the current exceeds the second reference value. .

[0007]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a block diagram of the alarm device. In FIG. 1, the same components as those in FIG. 2 are denoted by the same reference numerals, and the description will be simplified. Reference numeral 11 denotes a temperature sensor, and the temperature sensor 11 detects an ambient temperature of the laser diode LD. The analog output of the temperature sensor 11 is digitized by an A / D converter 12, and the temperature data is stored in an address of a ROM 13 as storage means for storing a relationship between a temperature and a bias current value of an optimum laser diode at the temperature. Used as That is, the optimum bias current value stored in the ROM 13 corresponding to the temperature data is read out, and this current value is supplied to the LD drive control circuit 21 via the D / A converter 14. The LD drive control circuit 21 controls the laser diode LD to supply an optimal current according to the ambient temperature to the laser diode LD.
The other end of the laser diode LD whose one end is connected to the power supply Vcc is connected.

One end of a photodiode PD for detecting the optical output of the laser diode LD is connected to Vcc,
The other end is grounded via a resistor 22 to generate a current Ir corresponding to the light output of the laser diode LD.

The non-ground side of the resistor 22 is connected to the operational amplifier 2.
3 inverting input. The operational amplifier 23
Is grounded via a filter capacitor C. Further, a predetermined reference voltage Vr is supplied to a non-inverting input of the operational amplifier 23. R3 and R4 are
This is a voltage dividing resistor for setting the inverted input voltage of the operational amplifier 23 to a predetermined value.

The output of the operational amplifier 23 is supplied to the base of a transistor 25 via a filter circuit 24 which outputs a signal having a predetermined waveform according to the output. The transistor 25 has a collector connected to the laser diode L.
D is connected to the other end, and the emitter is grounded via a resistor 32. The laser diode drive current Id flowing through the resistor 32 is detected as the voltage of the non-ground terminal of the resistor 32, supplied to the comparator 31, and compared with the reference voltage Vref. Note that the entire portion surrounded by a broken line in FIG. 1 constitutes a laser diode output control circuit.

The operation of the laser driving circuit configured as described above will be described. When the temperature sensor 11 detects the ambient temperature of the laser diode, the laser diode LD is driven by a predetermined drive current corresponding to this temperature. The optical output of the laser diode is detected as a current Ir of the photodiode PD, and the current Ir is supplied to the operational amplifier 23 as a voltage of the detection resistor 22.

The operational amplifier 23 outputs the difference between the voltage value and the reference voltage Vr, and supplies the difference to the base of the transistor 25. Here, when the laser diode LD deteriorates and the light output obtained by the drive current corresponding to the ambient temperature decreases, the output current Ir of the photodiode PD decreases, and as a result, the output current Ir is detected by the operational amplifier 23 (reference). When the output corresponding to the difference (from the voltage Vr) increases, the base current of the transistor 25 increases, the drive current of the laser diode LD increases, and the optical output increases. By such a correction, a required light output can be ensured regardless of deterioration. The current I flowing through the transistor 25 is
When d increases and exceeds a predetermined reference voltage Vref, the comparator 31 outputs a warning indicating deterioration.

[0013]

As described above, according to the present invention,
The light output of the laser diode is detected by the photodiode, and the output of the difference between this output and the reference value is used to control the base current of the transistor interposed in the laser diode drive circuit. Can be reliably detected, and the drive current can be adjusted to keep the light output constant. Further, since this circuit is provided in parallel with the circuit for correcting the drive current of the laser diode for temperature, it is possible to reliably compensate for the decrease in optical output due to the deterioration of the laser diode regardless of the ambient temperature. . Further, by comparing the current flowing through the transistor with a reference, a deterioration alarm can be output without using a special circuit.

[Brief description of the drawings]

FIG. 1 is a circuit diagram of one embodiment of the present invention.

FIG. 2 is a circuit diagram of a conventional example.

[Explanation of symbols]

11 temperature sensor 21 LD drive control circuit 2
2 Detection resistor 23 Operational amplifier 25 Transistor 3
1 Comparator 32 Detection resistor LD Laser diode PD Photodiode

Claims (3)

[Claims] 1. A light receiving means for detecting an optical output of a laser diode provided between a power supply and a ground point, a calculating means for calculating a difference between an output current of the light receiving means and a first reference value,
A laser diode deterioration judging device, comprising: a base connected to the output of the calculating means; and a transistor interposed between the laser diode and a ground point for controlling a driving current of the laser diode. 2. A laser diode deterioration judging device according to claim 1, wherein said laser diode is provided with a temperature correcting means for controlling a drive current of said laser diode in accordance with an ambient temperature in parallel with said transistor. 3. A comparator for comparing the current of said transistor with a second reference value and outputting a warning signal on condition that said second reference value is exceeded. 3. The laser diode deterioration determination device according to 2.