JPH02296381A - Detection circuit for deterioration in semiconductor laser - Google Patents

Abstract

PURPOSE:To prevent the LD deterioration signal from falsely transmitted due to any input signal disconnection by a method wherein a mark rate detection circuit is made to detect the mark rate of input signals. CONSTITUTION:A current voltage converter 51 converts the output photoelectric current of a photodetector element 22 detecting the output from a semiconductor laser (LD) 21 into voltage signals. A mark rate detector 52 detects the mark rate of input signals. An amplifier 53 amplifies the output signals from the current voltage converter 51 and the output signals from the mark rate detector 52. A bias current controller 54 controls the bias current from a semiconductor laser 21. A comparator 55 compares the output from the amplifier 53 with set up value to detect any deterioration in the semiconductor laser 21. Through these procedures, only the deterioration in the LD module can be accurately detected.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a semiconductor laser deterioration detection circuit used in optical transmitters of digital optical communications.

BACKGROUND ART 2 FIG. 2 shows the configuration of a conventional semiconductor laser deterioration detection circuit. In FIG. 2, a semiconductor laser (Laser
The diode (hereinafter referred to as LD) 1 is supplied with a bias current In by a transistor 2 and a pulse current Ip by a pulse drive current source 3, so that it emits light with an optical output Po as shown in FIG. It has become.

At this time, a light receiving element (Ph
(hereinafter referred to as PD) 4, an amplifier 6 including a resistor 5, and a transistor 2.
c Power Control 1 circuit (hereinafter referred to as APC circuit) is configured, and the optical output of the LDI is an average value P a
When the above LDI deteriorates for some reason and the threshold current value increases, the bias current In increases by the APC circuit, and the optical output of the LDI is maintained at the average value Pav. However, when the upper limit value I Bmax of the driving ability of transistor 2 is exceeded, it is no longer possible to increase the bias current In, and therefore, the light output P of the LDI decreases, and the base potential of transistor 20 decreases. It rises further.

Here, when the potential set by the resistor 7.8 (for example, the optical output P corresponds to half the initial optical output level Po) is exceeded, the comparator 11 including the resistor 9.1.0 is activated, and the LD
Lo from alarm (ALM) 12 as an abnormality in the optical output of I.
Outputs a w-level LD deterioration signal. 13 is a resistor connected to the emitter of transistor 2.

In this way, when LDl deteriorates, the conventional LD deterioration detection circuit described above can detect this and output an LD deterioration signal.

Problems to be Solved by the Invention However, in the conventional semiconductor laser deterioration detection circuit described above, when the input signal is lost or when the LD is forced from the outside,
When the output of I is stopped, the LD module (LD
There was a problem in that the LD deteriorated signal was output and switched even though there was no abnormality in the device (in which the I, PD4, coupling to the optical fiber, etc. were integrated) itself.

The present invention is intended to solve these conventional problems.
It is an object of the present invention to provide an excellent LD deterioration detection circuit that can accurately detect only the deterioration of an LD module.

Means for Solving the Problems In order to achieve the above objects, the present invention provides current-voltage conversion means for converting the output photocurrent of a light receiving element that detects the output of a semiconductor laser into a voltage signal, and detects the mark rate of the input signal. mark ratio detection means for amplifying the output signal of the current-voltage conversion means and the output signal of the mark ratio detection means; and bias current control for controlling the bias current of the semiconductor laser based on the output of the amplification means. and comparing means for comparing and determining the output of the amplifying means with a set value to detect deterioration of the semiconductor laser.

Effects The present invention has the following effects due to the above structure. In other words, if the input signal disappears, the mark rate detection circuit detects this, and as soon as the optical output decreases,
As a PC circuit, the bias current to 5-7 is output so as to cancel out the amount that works to increase the current, so the bias point of the LD is kept constant, and it is possible to prevent false alarms of LD deterioration signals due to input signal disconnection. .

Embodiment FIG. 1 shows an embodiment of the present invention, and 21 is L.
D, 22 is a PD that receives the light from LD 21 as monitor light;
23 is a pulse drive current source into which the input signal Data is input;
24 is a resistor connecting the non-inverting input terminal and output terminal of the amplifier 25; 26 is a resistor connecting the output terminal of the amplifier 25 and the summing amplifier 2;
A resistor 27 connects between the inverting input terminal of the summing amplifier 29 and the output terminal of the amplifier 38. A resistor 28 connects the inverting terminal and the output terminal of the summing amplifier 29. 30 3 is a resistor connected between the output terminal of the summing amplifier 29 and the inverting input terminal of the amplifier 32; 31 is a resistor connected between the inverting input terminal and the output terminal of the amplifier 32;
3 is a transistor whose collector is connected to LD2] and whose base is connected to the output terminal of the amplifier 32, 34 is a resistor connected to the emitter of the transistor 33, and 35 is an input signal Dat.
36 is a resistor that connects the non-inverting input terminal of the amplifier 25 and the non-inverting input terminal of the amplifier 38; 37 is an amplifier; A second reference voltage V r e f is applied to the inverting input terminal of No. 38.
, 39 is a resistor connected between the inverting input terminal and output terminal of the amplifier 380, 40.41 is a voltage dividing resistor that divides the first reference voltage Vref1, 42 is a voltage dividing resistor 40
．． 41 is a resistor connected between the connection point P and the non-inverting input terminal of the amplifier 43, 44 is a resistor connecting between the non-inverting input terminal and the output terminal of the amplifier 43, and 45 is an alarm connected to the output terminal of the amplifier 43 ( ALM).

Note that the first reference voltage Vrefx is supplied to the non-inverting input terminals of the amplifiers 25, 29, and 32, respectively, and the output terminal of the amplifier 32 and the inverting input terminal of the amplifier 43 are still connected directly. It is connected.

The resistor 24 and the amplifier 25 constitute a current-voltage conversion means 5 which converts the output photocurrent of the PD 22 into a voltage signal,
The resistors 36 and 39 and the amplifier 38 constitute a mark rate detection means 52 for detecting the mark rate of the input signal Data', and the resistor 28 and the summing amplifier 29 constitute the output signal and the mark rate of the current-voltage converting means 51. The resistor 3J and the amplifier 32 constitute an amplifying means 53 that adds and amplifies the output current of the detecting means 52.
The resistor 44 and the amplifier 4-3 constitute a bias current control means 54 that controls the bias current IB of the amplifier 5.
3 and a set value to detect deterioration of the LD2].

Next, the operation of the above embodiment will be explained. Assuming that the mark rate of the input signal Data is 1/2, the input Data' of the mark rate detection means 52 is the reference voltage Vref3.
, and the output of the amplifier 38 is equal to the first reference voltage Vr
ef1 and does not contribute to the input of the summing amplifier 29. Still, since amplifiers 29 and 32 are each inverting amplifiers, the polarity of the output of amplifier 25 remains unchanged and drives the base of transistor 33.

Therefore, LD21, PD22, amplifiers 25.29.
The APC circuit composed of transistors 32 and 33 operates in the same manner as the conventional example described in FIG.

Here, considering the case where the input signal Data is disconnected, the optical output of the LD 21 decreases, the output potential of the amplifier 25 increases, the output potential of the amplifier 29 decreases, and the amplifier becomes the base potential of the transistor 330. 32 is going to rise, and the bias current IB of LD2] is going to be increased.

However, at this time, the input signal D a ta' of the mark rate detection means 52 decreases, so the output potential of the amplifier 38 decreases, and as a result, the bias point of the LD 21 falls below the original frequency at the threshold value in FIG. will be biased towards the point.

In this way, according to the above embodiment, the mark rate detection means 5
2, regardless of the mark rate of the input signal Data, L
Since the bias point of D21 is biased to the threshold of LD21, even if the input signal is cut off, the optical output will exceed the upper limit value Inmax of the driving ability of the transistor 33 without falsely reporting an LD deterioration signal. It has the advantage that it is possible to issue an output for determining LD deterioration only when it decreases.

Effects of the Invention As is clear from the above embodiments, the present invention detects the mark rate of the input signal and thereby maintains the bias point of the LD constant regardless of the mark rate 9.\-7. Moreover, even if the input signal is cut off, the LD deterioration signal is not erroneously reported, and the deterioration of the LD module can be correctly determined.

[Brief explanation of drawings]

FIG. 1 is a circuit diagram of a semiconductor laser deterioration detection circuit according to an embodiment of the present invention, FIG. 2 is a circuit diagram of a conventional semiconductor laser deterioration detection circuit, and FIG. 3 is a current-optical output characteristic diagram of a semiconductor laser. . 21-Semiconductor laser (LD), 22-Photodetector (PD)
), 51... Current-voltage conversion means, 52 Mark rate detection means, 53... Amplification means, 54 Bias current control means, 55 Comparison means.

Claims (1)

[Claims] A semiconductor laser as a light source, a light receiving element for detecting the output of the semiconductor laser, a current-voltage conversion means for converting the output photocurrent of the light receiving element into a voltage signal, and a mark rate detection means for detecting the mark rate of the input signal. an amplification means for amplifying the output signal of the current-voltage conversion means and an output signal of the mark rate detection means; bias current control means for controlling the bias current of the semiconductor laser by the output of the amplification means; and an output of the amplification means. A semiconductor laser deterioration detection circuit, comprising: comparison means for comparing and determining the deterioration of the semiconductor laser with a set value.