JPH04276673A - Laser diode drive 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]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a laser diode drive circuit for controlling the magnitude of current applied to a laser diode.

Laser diodes are widely used as electrical/optical conversion devices in optical communications, which are rapidly developing in recent years.

0003

[Prior Art] In order to stabilize the light emission level of a laser diode at a predetermined constant level, an automatic light output control circuit (auto power control circuit) is used to control the sum of the bias current applied to the laser diode and the light emission current to be constant. Laser diode drive circuits with circuits) are widely used.

[0004] Here, the ratio between the bias current value and the light emitting current value is determined as a constant that takes into account the specified current value (threshold current) that changes due to forward power fluctuations due to temperature and differential efficiency fluctuations. .

[0005]

[Problems to be Solved by the Invention] The environmental conditions in which devices are used are becoming more severe year by year, and the development of optical components that can satisfy these conditions is progressing. However, the load on the optical system of the laser diode module is becoming increasingly severe, and the differential efficiency of the laser diode tends to deteriorate, especially at high temperatures.Depending on the constant, the extinction ratio at high temperatures may no longer be satisfied, resulting in line errors, etc. It may cause

Furthermore, it is desirable to set the bias current as close to the threshold current value as possible, which is advantageous in terms of characteristics.

SUMMARY OF THE INVENTION It is therefore an object of the present invention to provide a laser diode drive circuit that can set the bias current as high as possible and satisfy the extinction ratio in an operating environment with large temperature fluctuations.

[0008]

[Means for Solving the Problems] In order to achieve the above object, the laser diode drive circuit of the present invention has a bias voltage that applies a bias current to a laser diode 1, as shown in FIG. 1 for explaining an embodiment. a driving circuit 3 for driving the laser diode 1; A light output automatic control circuit 7 outputs a control signal to the drive circuit 4, detects the magnitude of the bias current, compares the detected value with a preset threshold value, and determines whether the detected value is the same as the one described above. When it is larger than the threshold, a control signal of a magnitude corresponding to the difference is added to the output signal from the automatic light output control circuit 7 and inputted to the light emission drive circuit 4;
The present invention is characterized in that it includes an extinction ratio correction circuit 10 that changes the ratio between the magnitude of the bias current and the magnitude of the light emission current.

Note that the threshold value is set to a value that satisfies the extinction ratio at high temperatures, and the light emission current given to the laser diode 1 by the light emission drive circuit 4 is a pulse current.

0010

[Function] When the bias current of the laser diode 1 increases due to temperature exceeding the set temperature or deterioration of the laser diode 1, and the current value exceeds the threshold value, a signal corresponding to the difference is sent from the optical output automatic control circuit 7. The signal is added to the output signal of and input to the light emission drive circuit 4.

Then, the laser diode 1
Since the light emitting current given to the bias current increases, the automatic light output control circuit 7 outputs a control signal to the bias drive circuit 3 to reduce the bias current.

0012

[Embodiment] An embodiment will be described with reference to the drawings.

In FIG. 1, 1 is a laser diode, 2 is a laser diode, and 2 is a laser diode.
receives the backward light output of laser diode 1,
This is a photodiode for optical output monitoring that outputs an electrical signal according to the intensity of the light.

Reference numeral 3 denotes a bias drive circuit that applies a bias current to the laser diode 1 at a level corresponding to an input control signal. Reference numeral 4 denotes a light emitting drive circuit that provides the laser diode 1 with a light emitting current of a level corresponding to an input control signal.

Reference numeral 5 denotes a flip-flop which inputs digital signal data and a clock pulse and outputs latched data to the light emission drive circuit 4 at the timing of the clock pulse. In the light emitting drive circuit 4, the signal pulse input from the flip-flop 5 is converted into a light emitting current, and the light emitting pulse current is applied to the laser diode 1.

A monitor detection circuit 6 detects an output signal from the monitor photodiode 2, and its detection output and an output signal from the flip-flop 5 are input to an automatic optical output control circuit 7.

The automatic optical output control circuit 7 determines the input level from the monitor detection circuit 6 at the timing of the input signal from the flip-flop 5, and the input level becomes a predetermined constant level. like,
A control signal is output to the bias drive circuit 3 and the light emission drive circuit 4.

At this time, the ratio of the bias current control signal output to the bias drive circuit 3 and the light emission current control signal output to the light emission drive circuit 4 is a preset constant, In this case, the ratio between the bias current value given to the laser diode 1 and the emission current value is maintained constant.

Reference numeral 11 denotes a comparator which inputs a signal corresponding to the bias current value from the bias drive circuit 3 and compares the magnitude with a preset high temperature threshold. The high temperature threshold is set to a bias current value that can satisfy the extinction ratio at high temperatures (for example, 60 degrees Celsius), and the bias current value input from the bias drive circuit 3 is set to the high temperature threshold. When the difference is greater than the value, the comparator 11 outputs a control signal having a magnitude corresponding to the difference.

The control signal output from the comparator 11 is a light emission current control signal for controlling the magnitude of the output of the light emission drive circuit 4, and is the light emission current control signal output from the light output automatic control circuit 7. are added in the adder 12 and input to the light emission drive circuit 4.

According to the embodiment device configured as described above, there is no output from the comparator 10 under the operating environment of the normal temperature range, and the bias current and the light emitting current are controlled by a predetermined value by the optical output automatic control circuit 7. It is controlled to take the ratio. Then, when the bias current becomes large due to the operating environment temperature being higher than that or in a deterioration mode, and exceeds the threshold value, a light emission current control signal corresponding to the difference between the bias current and the threshold value is added to the light emission drive circuit 4. The light emitting current increases as the light is input. Then, the automatic light output control circuit 7 reduces the bias current by the amount that the light emitting current has increased.

In this way, the bias current value is controlled so as not to exceed the threshold value even when the operating environment temperature is exceeded or when the device is deteriorated, thereby ensuring a proper extinction ratio.

[0023]

[Effects of the Invention] According to the laser diode drive circuit of the present invention, when the operating environment temperature deviates from normal temperature, the bias current exceeds the threshold value and the extinction ratio cannot be guaranteed with only control by the automatic optical output control circuit. When this occurs, the bias current is automatically suppressed below the threshold value by the extinction ratio correction circuit, which has the excellent effect of always guaranteeing a proper extinction ratio even if there are fluctuations in the environmental temperature.

[Brief explanation of the drawing]

FIG. 1 is a circuit block diagram of an embodiment.

[Explanation of symbols]

1 Laser diode 3 Bias drive circuit 4. Light emitting drive circuit 7. Optical output automatic control circuit 10 Extinction ratio correction circuit

Claims (3)

[Claims] 1. A bias drive circuit (3) for supplying a bias current to a laser diode (1), a light emission drive circuit (4) for supplying a light emission current to the laser diode (1), and a drive circuit (4) for supplying a light emission current to the laser diode (1); a light output automatic control circuit (7) that outputs a control signal to the bias drive circuit (3) and the light emission drive circuit (4) so as to control the sum of the current and the bias current to a constant level; detects the magnitude of the detected value and compares the detected value with a preset threshold, and when the detected value is larger than the threshold, the optical output automatic control circuit outputs a control signal of a magnitude corresponding to the difference. (
7) is added to the output signal from the light emitting drive circuit (4).
), and changes the ratio between the magnitude of the bias current and the magnitude of the light emission current (10).
A laser diode drive circuit comprising: 2. The laser diode drive circuit according to claim 1, wherein the threshold value is set to a value that satisfies an extinction ratio at high temperatures. 3. The laser diode drive circuit according to claim 1, wherein the light emission current given to the laser diode (1) by the light emission drive circuit (4) is a pulse current.