JPS59215133A - Circuit for detecting deterioration in semiconductor laser - 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 (a) Technical Field of the Invention The present invention has a semiconductor laser that outputs light, a transistor that supplies a pre-bias current to the semiconductor laser, and feeds back the optical output to the pre-biased laser. Related to an optical transmitter that controls a bias current and stabilizes the optical output,
In particular, the present invention relates to a semiconductor laser deterioration detection circuit capable of detecting deterioration in which the semiconductor laser becomes open.

(b) Prior Art and Problems FIG. 1 shows a block diagram of a semiconductor laser deterioration detection circuit of a conventional optical transmitter.

In the figure, 1 is a semiconductor laser, 2 is a photodetector, 3 is a differential amplifier, 4 and 5 are transistors, 6 is a voltage detector, 7 is a comparator, RI to R6 are resistors, C is a capacitor, -■ is a Negative DC voltage, vs is comparison voltage, and L indicates choke.

To explain the circuit shown in FIG. 1, a semiconductor laser 1 is connected to a haple bias supply transistor 4 and a pulse modulation transistor 5, each of which has a current Io.

Is flows and performs pulse modulation. The light receiving element 2 is a light-to-electrical conversion element that monitors the output light of the semiconductor laser 1, and a current flows therethrough in accordance with the light intensity.

Therefore, a voltage corresponding to the light intensity is generated across R4.

In the differential amplifier 3, this voltage and the resistors R2 and R.

The difference voltage is output by comparing the comparison voltage obtained by dividing the negative 'e pressure -■ with The pre-bias current Io is increased to increase the optical output.

In this way, feedback control is performed to keep the optical output constant. In order to detect the pre-bias current Io at this time, a voltage across the resistor Rs is detected by a voltage detector 6 and input to a comparator 7. When the semiconductor laser 1 deteriorates, the optical output decreases, so the pre-bias current Io increases and the output voltage of the voltage detector 6 also increases. The comparator 7 converts the output voltage of the voltage detector 6 into a predetermined comparison voltage v8.
When the comparison voltage Vs becomes larger than that, it is determined that the semiconductor laser 1 has deteriorated, and a deterioration detection signal is output. However, deterioration of the semiconductor laser 1 includes deterioration in which the semiconductor laser 1 becomes open, but the conventional circuit shown in FIG. 1 has the disadvantage that such deterioration cannot be detected.

(c) Object of the Invention In view of the above drawbacks, an object of the present invention is to provide a semiconductor laser deterioration detection circuit capable of detecting deterioration even in the case of open deterioration of a semiconductor laser.

(d) Structure of the Invention In order to achieve the above object, the present invention includes the following steps to increase the optical output when the semiconductor laser deteriorates and the optical output decreases.
Focusing on the fact that the prebias control voltage fed back to the prebias current supply transistor in the direction of increasing the prebias current increases regardless of the type of deterioration of the semiconductor laser, we added a transistor to monitor the prebias control voltage. , deterioration of the semiconductor laser is detected when this pre-bias control voltage becomes larger than a predetermined value.

(e) Examples of the invention An embodiment of the present invention will be described below with reference to the drawings.

FIG. 2 is a block diagram of a semiconductor laser deterioration detection circuit of an optical transmitter according to an embodiment of the present invention.

Components in the figure that have the same functions as those in FIG. 1 are indicated by the same symbols.

4' and 8 are transistors, 7' is a comparator, R[gamma] to R are resistors, VB2 is a comparison voltage, and L/ indicates a positive error.

The difference between FIG. 2 and FIG. 1 is that the pre-bias control voltage of comparator 3 is applied to the base of pre-bias supply transistor 4' and also to the base of transistor 8, and the resistor R0 of the collector circuit of transistor 8 is The voltage at both ends is applied to the comparator 7' and compared with the comparison voltage Va' to output a deterioration detection signal.

That is, the pre-bias control voltage increases as the semiconductor laser 1 deteriorates, regardless of the type of deterioration (including open state) of the semiconductor laser 1. Therefore, the voltage across the resistor R0 between the collector and ground of the transistor 8 also increases. When the voltage across this resistor Re becomes larger than a predetermined comparison voltage Vs', it is determined that the semiconductor laser 1 has deteriorated, and the comparator 7
' and outputs a deterioration detection signal. In this way, deterioration can be detected when the semiconductor laser 1 deteriorates and the pre-bias current increases beyond a certain value, or when the semiconductor laser 1 becomes open.

(f) Effects of the Invention As explained in detail above, according to the present invention, there is an effect that deterioration can be avoided regardless of the deterioration mode of the semiconductor laser.

[Brief explanation of drawings]

FIG. 1 is a block diagram of a semiconductor laser deterioration detection circuit of a conventional optical transmitter, and FIG. 2 is a block diagram of a semiconductor laser deterioration detection circuit of an optical transmitter according to an embodiment of the present invention. In the figure, 1 is a semiconductor laser, 2 is a photodetector, 3 is a differential amplifier, 4.4', 5.8 are transistors, 6 is a 1-voltage detector, 7.7' is a comparator, and R1-R9 are Resistor, C is a capacitor, L, L' are chokes, -■ is negative DC voltage,
Va and Vg' indicate comparison voltages.

Claims (1)

[Claims] It has a semiconductor laser that outputs light and a first transistor that supplies a pre-bias current to the semiconductor laser, and feeds back the optical output to control the pre-bias current and stabilize the optical output. In the optical transmitter, the second
The base of the transistor is connected to the base of the first transistor, and a load resistor is provided at the collector of the second transistor, and the voltage across the load resistor is monitored to detect any deterioration of the semiconductor laser. A semiconductor laser deterioration detection circuit characterized by: