JPH11298080A - Apparatus and method for driving semiconductor laser - Google Patents

Abstract

PROBLEM TO BE SOLVED: To allow the duty ratio of the light signal of a semiconductor laser to be automatically adjusted to a normal value by comprising a means for driving the semiconductor laser, based on the result of a comparison of a duty ratio detected by a detecting means with specified duty ratio. SOLUTION: A duty ratio comparator adjuster circuit 39 utilizes a signal of mean value as a control signal and adequately adjusts the duty ratio of an input data signal according to the delay of a laser diode 23 so as not to generate a specified value, thereby resolving the deviation of a voltage waveform converted by a circuit 32, wave forms inverted by a repetitive amplifier 33 become the same waveform, signal waveforms passed through the respective logic buffers 34, 35 becomes the same waveform, an exclusive-ORed signal waveform in an exclusive OR circuit 36 becomes flat without deviation, and this operation is repeated to allow the duty ratio of the light signal of the semiconductor laser to be automatically adjusted for a normal value.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a semiconductor laser driving apparatus and method for driving a semiconductor laser used in an optical transmitter or the like.

[0002]

2. Description of the Related Art FIG. 3 is a block diagram showing a conventional semiconductor laser driving device. The semiconductor laser drive device 10 includes a duty ratio adjustment circuit 11, a signal drive circuit 1,
2 and the semiconductor laser 13 are connected in this order.
4. Average value detection circuit 15 and DC bias control circuit 16
Are connected in this order, and the output terminal of the DC bias control circuit 16 is connected to the semiconductor laser 13.

The operation of such a configuration will be described. An input data signal is sent to a signal drive circuit 12 via a duty ratio adjustment circuit 11. Then, the semiconductor laser 13 is driven based on the data signal. The light pulse generated from the semiconductor laser 13 is
4, the pulse signal is sent to the average value detection circuit 15 and the average value is detected.

The average value is sent to the DC bias control circuit 16 to control the DC bias current of the semiconductor laser 13. The light emission delay generated by the semiconductor laser 13 is compensated by the duty ratio adjustment circuit 11 while observing the light pulse. Through the above operation, the optical output power is controlled so as to be constant with time or the like.

[0005]

However, according to the conventional semiconductor laser driving device 10, the delay amount of the duty ratio adjustment circuit 11 is fixed, but the required delay amount differs depending on the semiconductor laser. Each time 13 is replaced, the duty ratio adjustment circuit 11 also needs to be replaced or adjusted to one having an appropriate delay amount. In addition, since the delay amount of the semiconductor laser 13 also changes due to variations in electronic components such as LSIs and temperature fluctuations, it has been difficult to maintain an appropriate duty ratio of light pulses of the semiconductor laser 13.

SUMMARY OF THE INVENTION It is therefore an object of the present invention to provide a driving apparatus and a driving method for a semiconductor laser capable of automatically adjusting a duty ratio of an optical signal of the semiconductor laser to a normal value.

[0007]

According to the present invention, there is provided a semiconductor laser driving apparatus for driving a semiconductor laser to output an optical signal having a predetermined duty ratio. Detecting means for detecting a duty ratio of an optical signal, and driving means for comparing the duty ratio detected by the detecting means with the predetermined duty ratio and driving the semiconductor laser based on a result of the comparison. A semiconductor laser driving device is provided.

According to another aspect of the present invention, there is provided a semiconductor laser driving apparatus for driving a semiconductor laser to output an optical signal having a predetermined duty ratio by receiving an optical signal from the semiconductor laser. A photoelectric conversion unit that outputs a current signal, a current-voltage conversion circuit that converts the current signal from the photoelectric conversion unit into a voltage signal, and an inverted voltage signal that inverts the voltage signal from the current-voltage conversion circuit. A first logic circuit that compares the inverted voltage signal from the inverting circuit with a predetermined threshold value and outputs a first comparison signal; and the voltage from the current / voltage conversion circuit. The signal is compared to a predetermined threshold to
A second logic circuit that outputs a comparison signal of the first and second logic circuits; an exclusive OR circuit that takes an exclusive OR of the first and second comparison signals from the first and second logic circuits; An average value detection circuit that detects an average value of a signal from the sum circuit;
A duty ratio adjustment circuit for adjusting a duty ratio of an optical signal of the semiconductor laser to the predetermined duty ratio based on a signal from the average value detection circuit. I do.

According to another aspect of the present invention, there is provided a semiconductor laser driving method for driving a semiconductor laser to output an optical signal having a predetermined duty ratio by photoelectrically converting the optical signal from the semiconductor laser. Calculate the positive and negative signals of the photoelectrically converted signal, take the exclusive OR of the positive and negative signals, detect the average value of the signal obtained by taking the exclusive OR, and detect the average value A duty ratio of an optical signal of the semiconductor laser is adjusted to the predetermined duty ratio based on the following.

According to the above arrangement, the light output waveform of the semiconductor laser is monitored by the monitoring photoelectric conversion means, and the average value is detected by taking the exclusive OR of the positive and negative data of the output waveform. Thus, since the deviation of the duty ratio of the optical output waveform of the semiconductor laser is determined, when the duty ratio is deviated, the duty ratio can be automatically adjusted to a normal value.

[0011]

FIG. 1 is a block diagram showing an embodiment of a driving device for a semiconductor laser according to the present invention. The semiconductor laser driving device 20 includes an automatic output power control circuit (A
A PC 21, a laser driver circuit 22, and a laser diode (semiconductor laser) 23 are connected in this order, and a duty ratio adjustment unit 30 is connected to the laser driver circuit 22.

The duty ratio adjusting section 30 has an output terminal of a photodiode (photoelectric conversion means) 31 connected to an input terminal of a current / voltage conversion circuit 32.
Is connected to the input terminal of the inverting amplifier 33 and the logical buffer 35.
The output terminal of the inverting amplifier 33 is connected to the input terminal of the logical buffer 34, and the output terminal of each of the logical buffers 34 and 35 is connected to the input terminal of an exclusive OR circuit (exclusive logical circuit) 36. It is connected.

The output terminal of the exclusive OR circuit 36 is connected to the resistor 37 and the capacitor 38 (average value detection circuit), and further connected to the input terminal of the duty ratio adjustment circuit 39, and the output terminal of the duty ratio adjustment circuit 39 is connected. The configuration is connected to the input terminal of the laser driver circuit 22.

Here, the function of each unit will be described. The automatic output power control circuit 21 performs control to keep the optical output power of the laser diode 23 constant. Laser driver circuit 22
Drives the laser diode 23 based on a control signal from the automatic output power control circuit 21. The photodiode 31 receives an optical signal from the laser diode 23 and converts it into a current signal. The current / voltage conversion circuit 32 converts a current signal from the photodiode 31 into a voltage signal. The output amplitude of the electric signal is kept constant by the operation of the automatic output power control circuit 21.

The inverting amplifier 33 has a gain of 1 and inverts the voltage signal from the current / voltage conversion circuit 32. The logic buffer 34 has a threshold level set at the center of the amplitude of the input signal, and shapes the voltage signal from the inverting amplifier 33 with the threshold. The threshold level of the logic buffer 35 is also set at the center of the amplitude of the input signal.
The voltage signal from the current / voltage conversion circuit 32 is shaped by the threshold value. These thresholds can be easily set because the output amplitude of the electric signal of the current / voltage conversion circuit 32 is kept constant.

The exclusive OR circuit 36 performs an exclusive OR operation on the signals from the logical buffers 34 and 35.
The resistor 37 and the capacitor 38 detect an average value of a signal from the exclusive OR circuit 36. The duty ratio adjustment circuit 39 includes, for example, a delay circuit, and appropriately adjusts the duty ratio of the input data signal in accordance with the delay amount of the laser diode 23 based on the average value from the resistor 37 and the capacitor 38.

In such a configuration, the operation is shown in FIG.
This will be described with reference to FIG. FIG. 2 is a diagram showing signal waveforms at respective points a to e of the semiconductor laser driving device 20 of FIG. 1, and FIG. 2A shows a case where control by the duty ratio adjustment unit 30 is not performed. FIG. 7B shows a case where the control by the duty ratio adjustment unit 30 is performed.

First, when the control by the duty ratio adjusting unit 30 is not performed (FIG. 2A), the voltage waveform converted by the current / voltage conversion circuit 32 has a duty ratio (y / y / x) is shifted. Then, the voltage waveform inverted by the inverting amplifier 33 is shifted as shown by a '.

Therefore, the signal waveform passing through the logical buffer 34 and the signal waveform passing through the logical buffer 35 are b and c.
As shown in (d), the signal waveform exclusive-ORed by the exclusive OR circuit 36 has a difference as shown in (d). Therefore, the signal waveform of the average value detected by the resistor 37 and the capacitor 38 has a predetermined value as shown by e.

Next, when the control by the duty ratio adjustment unit 30 is performed (FIG. 2B), the duty ratio adjustment circuit 39 uses the signal of the above average value as a control signal, as shown in e. The duty ratio of the input data signal is set so that a predetermined value does not occur.
Adjust appropriately according to the delay amount. Thus, the voltage waveform converted by the current / voltage conversion circuit 32 has a duty ratio (y / x) of 1 as shown in a, and the deviation is eliminated.

The voltage waveform inverted by the inverting amplifier 33 has the same waveform as a as shown by a '. Therefore, the signal waveform that has passed through the logical buffer 34 and the signal waveform that has passed through the logical buffer 35 have the same waveform as indicated by b and c, and the signal waveform obtained by performing an exclusive OR operation in the exclusive OR circuit 36 is as follows: As shown in FIG. 4D, a flat waveform having no deviation is obtained.

By repeating the above operation, the optical output waveform of the laser diode 23 is constantly monitored and the duty ratio is constantly controlled so as to be optimal.
The duty ratio of the optical output waveform of the laser diode 23 can be kept constant regardless of the variation of the laser diode 23 and other components.

[0023]

As described above, according to the present invention, the duty ratio of the optical signal of the semiconductor laser can be automatically adjusted to a normal value, and a highly accurate optical transmitter can be provided. it can.

[Brief description of the drawings]

FIG. 1 is a block diagram showing an embodiment of a semiconductor laser driving device according to the present invention.

FIG. 2 is a diagram showing signal waveforms at points a to e of the semiconductor laser driving device of FIG.

FIG. 3 is a block diagram showing a conventional semiconductor laser driving device.

[Explanation of symbols]

 Reference Signs List 20 semiconductor laser drive device 21 automatic output power control circuit (APC) 22 laser driver circuit 23 laser diode (semiconductor laser) 30 duty ratio adjustment unit 31 photodiode (photoelectric conversion means) 32 current / voltage conversion circuit 33 inverting amplifier 34 logic Buffer 35 Logic Buffer 36 Exclusive OR Circuit (Exclusive Logic Circuit) 37 Resistor 38 Capacitor 39 Duty Ratio Adjustment Circuit

Claims (4)

[Claims] 1. A semiconductor laser driving device for driving a semiconductor laser to output an optical signal having a predetermined duty ratio, wherein: a detecting unit for detecting a duty ratio of an optical signal output from the semiconductor laser; And a driving unit for driving the semiconductor laser based on a result of the comparison between the detected duty ratio and the predetermined duty ratio. 2. A driving device for a semiconductor laser for driving a semiconductor laser to output an optical signal having a predetermined duty ratio, comprising: photoelectric conversion means for receiving an optical signal from the semiconductor laser and outputting a current signal; A current-voltage conversion circuit that converts the current signal from the photoelectric conversion unit into a voltage signal; an inversion circuit that inverts the voltage signal from the current-voltage conversion circuit to output an inversion voltage signal; A first logic circuit that compares the inverted voltage signal with a predetermined threshold value and outputs a first comparison signal; and compares the voltage signal from the current / voltage conversion circuit with a predetermined threshold value. A second logic circuit that outputs a second comparison signal; an exclusive OR circuit that takes an exclusive OR of the first and second comparison signals from the first and second logic circuits; Logical disjunction An average value detection circuit that detects an average value of a signal from the semiconductor device, and a duty ratio adjustment circuit that adjusts a duty ratio of an optical signal of the semiconductor laser to the predetermined duty ratio based on a signal from the average value detection circuit. A driving device for a semiconductor laser, comprising: 3. A method of driving a semiconductor laser to output an optical signal having a predetermined duty ratio by driving the semiconductor laser, wherein the optical signal from the semiconductor laser is photoelectrically converted, and the positive and negative polarities of the photoelectrically converted signal are provided. The signals of the positive and negative signals are exclusive-ORed, the average value of the exclusive-ORed signals is detected, and based on the detected average value, the optical signal of the semiconductor laser is calculated. A method for driving a semiconductor laser, comprising: adjusting a duty ratio to the predetermined duty ratio. 4. A method of driving a semiconductor laser to output an optical signal having a predetermined duty ratio by driving a semiconductor laser, wherein a duty ratio of an optical signal output from the semiconductor laser is detected, and the detected optical signal is detected. And driving the semiconductor laser based on a result of the comparison between the predetermined duty ratio and the predetermined duty ratio.