JPH0453286A - Intermittent communication laser drive circuit - Google Patents

Abstract

PURPOSE:To enable laser rays to be controlled in output level at a higher speed by a method wherein an optical output is directly detected by a monitoring photodetective element, the detected output is directly compared with a transmission signal level, and the compared result is fed back to a laser device to control it is optical output. CONSTITUTION:The optical output 12 of a laser 1 oscillated by a laser drive circuit 11 is detected by a laser optical output monitoring photodetector 2. The output of the photodetector 2 is converted into voltage through an instantaneous output detector 9, whereby an output can be instantaneously detected. At this point, the detected laser ray output is inputted into an error detection amplifier 4 to constitute a negative feedback loop. The transmission signal of a transmission signal generating circuit 10 is inputted into the error detection amplifier 4 through the intermediary of an input signal rise-time varying device 13. A capacitive element 13a is connected to the input signal rise-time varying device 13 to enable it to control the inputted transmission signal in rise-time. As mentioned above, a negative feedback loop can be optimized through the adjustment of it in circuit response time outside, so that an excellent optical output rise characteristics can be obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a drive circuit for instantaneous control of laser light output.

[Prior art] Laser drive circuits used in conventional optical communications detect laser light output using an average value method using an integrator or a peak value detection method using a peak detector, and use the detected value as a set value. The optical output of the laser was controlled by comparing the values and feeding back a value corresponding to the difference. Additionally, a transmission bow was newly added to the laser to perform digital transmission. Hereinafter, the details of the circuit for this purpose will be explained with reference to the drawings. That is, in FIG. 3, a semiconductor laser 1 is emitted by a transmission signal generating circuit 6, and an optical output 12 from the semiconductor laser 1 is received by a light receiving element 2 for monitoring the optical output, and an optical signal is generated by a low-pass filter circuit. The average value is detected by the output detection section 3. The output signal of this optical output detection section 3 is input to an error detection amplifier 4, and a reference voltage generator 7
compared to a reference voltage from The optical output of the laser 1 is then controlled by comparing it with this reference voltage value and feeding back a value corresponding to the difference to the bias current supply circuit 5.

On the other hand, the optical output 12 from the J: sea urchin semiconductor laser 1 shown in FIG. 4 and is compared with the reference voltage from the reference voltage generator 7, and a value corresponding to the difference is sent to the bias current supply circuit 5.
The optical output of the laser is controlled by feedback to the laser.

[Problems to be Solved by the Invention] As described above, the laser drive circuit in the conventional communication system uses an integrator or a peak value detector in the laser light output detection section, so there is a delay in light output detection. As a result, the transient characteristics of the laser light output are shown in Figure 5 (a).
There was an overshoot at the rising edge as shown in . The overcurrent flowing through the laser due to this overshoot (a) accelerates the deterioration of the laser. In addition, in conventional communication systems (continuous laser light output),
Overshoot occurs only at system startup, so
This problem does not arise if the system is operated for a sufficient period of time without reducing this overshoot l-, but in an intermittent communication system, overshoot occurs every time a signal is transmitted, which affects laser deterioration and waveform distortion. This has the disadvantage of causing problems such as signal errors caused by the system, which deteriorates the reliability of the system.

This invention was made in response to this kind of situation.
Provided is a laser drive circuit for intermittent communication that eliminates the deficiencies of the prior art described above and can perform faster laser output control by increasing the speed of laser light output detection, and a laser drive circuit. The purpose of this study is to provide a method for optimizing the transient characteristics at the rise time of .

[Means and effects for solving the problem] This invention has the following features:
Detects the optical output directly from the monitor light receiving element,
The purpose of this method is to manually input the error detection amplifier and directly compare the result with the transmission signal level, and then feedback control the laser light output, thereby speeding up the control of the laser light output level.

In addition, this invention consists in adding a capacitive element to the input part of the transmission signal in order to eliminate overshoot at the rise of the laser light output in a laser drive circuit for intermittent communication, which results in negative feedback. This is to improve the transient characteristics when the laser light output rises and falls when the response speed of the part is increased.

[Example] Hereinafter, the present invention will be described in detail based on the drawings. 1st
The figure is a block diagram showing the configuration of a laser drive circuit for intermittent communication according to an embodiment. A laser 1 is oscillated by a laser drive circuit 11, and a laser beam 12 is received by a light receiving element 2 for monitoring optical output. This light reception signal is sent to the instantaneous output detector 9
Change the voltage as is. This is input to the error detection amplifier 4, and on the other hand, the signal from the transmission signal generation circuit 1O is input to the error detector 4, and this is compared with the voltage from the instantaneous output detector 9, and the difference output is calculated. The output of the error detection amplifier 4 is fed back to the laser driving section 11.

In this way, by eliminating the delay in the optical output detection time and directly comparing the level with the transmission signal, it is possible to achieve a high-speed and stable optical output without overshoot at the rise time, as shown in the optical output waveform diagram in Figure 6. can be controlled.

Next, another embodiment of the present invention will be described based on FIG. The light output 12 of the laser 1 oscillated by the laser drive circuit 11 is received by the light receiving element 2 for monitoring laser light output. This signal is sent to the light receiving element 2 by the instantaneous output detector 9.
Converts the output directly into voltage, making output detection instantaneous. The detected laser light output is transferred to the error detection amplifier 4.
input to form a negative feedback loop. A transmission signal from a transmission signal generation circuit 10 is input to the same error detection amplifier 4 via an input signal rise time variable device 13. A capacitive element 13a is connected to this input signal rise time variable device 13, so that the rise time of the input transmission signal can be adjusted.

By configuring the circuit so that the circuit response time can be adjusted outside the negative feedback loop, it is possible to optimize the negative feedback loop, so that good optical output characteristics can be obtained.

F. Effects of the invention As explained above, the intermittent communication laser drive circuit of the invention has the following remarkable effects.

■The set optical output can be stably obtained from the start of the laser output. Immediately, transmission without overshoot becomes possible.

■It is economical because the circuit configuration and number of elements can be reduced.

■ Fluctuations in laser light output due to temperature changes, etc. can be controlled at high speed.

■Since the laser light output can be controlled at high speed, overshoot does not appear in the light output, making it possible to extend the life of the laser, thereby improving reliability and economic efficiency.

(2) Since the output is not detected as an average value, signal transmission with a duplex ratio other than 50% is possible.

■The structure is simplified because the transmission signal can be used as is for level purposes.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing the configuration of a laser drive circuit for intermittent communication according to an embodiment of the present invention. FIG. 2 is a block diagram showing the configuration of a laser drive circuit for intermittent communication according to another embodiment of the invention. 3 and 4 are block diagrams showing the configuration of a conventional laser drive circuit, FIG. 5 is a waveform diagram when the conventional laser drive circuit is used for intermittent communication, and FIG. 6 is a block diagram showing the configuration of a conventional laser drive circuit. FIG. 6 is a waveform diagram when the laser drive circuit is used for intermittent communication. l... Laser 2... Light receiving element for optical output monitoring 3... Optical output detection section 4... Error detection amplifier 5
...Bias current supply circuit 6...Transmission signal generation circuit 7...Reference voltage generator 8.
・Peak value detector 9 ・Instantaneous output detector 10・
... Transmission signal generation circuit] 1 ... Laser drive circuit 13 ... Input signal rise time variable device Patent applicant Hitachi Cable, Ltd.

Claims (2)

[Claims] (1) In a laser drive circuit for intermittent communication, the output light from the laser is received by a monitoring light receiving element, this output is converted to voltage by an instantaneous output detector, inputted to an error detector, and then output from a transmission signal generation circuit. 1. A laser drive circuit for intermittent communication, characterized in that the difference signal is negatively fed back to the laser drive circuit to control laser light output. (2) controlling the time constant of the transmission signal input to the error detection amplifier to reduce the difference with the delay time of optical output detection;
A laser drive circuit for intermittent communication according to claim (1), characterized in that an input signal rise time variable device is inserted between the transmission signal generation circuit and the error detection amplifier so as to improve the transient characteristics at the rise of the optical output. .