JPH04162480A - Laser diode drive circuit - Google Patents

Abstract

PURPOSE:To easily vary an optical output by controlling a bias current or a pulse current to be applied to a laser diode so that an output of a mark rate detecting circuit becomes equal to an output of an average value detecting circuit and an extinction ratio becomes constant in the case of externally varying a gain of the mark detecting circuit. CONSTITUTION:A pulse current control circuit 8 controls, from a high level value detected by a peak detection circuit 6 and a low level value detected by a bottom detecting circuit 7, a current source 16 which supplies a pulse current to a laser diode 1 so that an extinction ratio becomes a constant. A bias current control circuit 9 controls a current source 15 which supplies a bias current to the laser diode 1 so that an output of a average value detecting circuit 5 becomes equal to an output of a mark rate detecting circuit 10. When a signal for changing a gain of the mark rate detecting circuit 10 is inputted from an optical output varying terminal (e), the pulse current control circuit 8 and bias current control circuit 9 operate so that an output of the mark rate detecting circuit 10 becomes equal to an output of the average value detecting circuit 5 and an extinction ratio becomes constant. Thereby, a bias current and a pulse current to be applied to the laser diode 1 can be controlled automatically.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a laser diode drive circuit that can vary optical output.

[Conventional technology]

FIG. 2 is a circuit diagram showing a conventional laser diode drive circuit.

In the figure, ■ is a laser diode drive circuit section, and variable resistor 107. Resistor 108. )Ran resistor 10
9, 110 and a current source 106. Current source 1
06 serves to supply a bias current to the laser diode 101. ■ is the laser diode control section,
A photodiode 102 for detecting the optical output of the laser diode 101, a preamplifier 103 for amplifying the output of the photodiode 102. It includes a mark wheel detection circuit 105 and a bias current control circuit 104 that detect the mark rate of the data signal input to the laser diode drive circuit. The bias current control circuit 104 is connected to the preamplifier 103
The bias current to the laser diode 101 is controlled so that the output of the mark rate detection circuit 105 becomes equal to the output of the mark rate detection circuit 105. In the figure, a predetermined voltage is applied to the v and W terminals, data signals with different polarities are input to the X and y terminals, and a control signal for controlling the output of the mark rate detection circuit 105 is input to the two terminals. is input.

In the laser diode drive circuit configured in this way, when varying the optical output, the mark rate detection circuit 10
At this time, the variable resistor 107 is adjusted so that the optical output waveform and extinction ratio of the laser diode 101 are not deteriorated.

[Problem to be solved by the invention]

However, with such conventional laser diode drive circuits, adjustment to vary the optical output is complicated;
There was a problem in that the optical output could not be easily varied.

[Means to solve the problem]

The present invention was proposed to solve these problems, and includes a peak detection circuit that detects the high level value of the optical output of a laser diode, and a bottom detection circuit that detects the low level value of the optical output of the laser diode. , an average value detection circuit that detects the average value of the optical output of the laser diode, a mark rate detection circuit that detects the mark rate of the manually input data signal and outputs it with an externally variable gain added, and a peak detection circuit. A pulse current control circuit that controls the pulse current flowing through the laser diode so that the extinction ratio becomes a constant value based on the high level value detected by the bottom detection circuit and the low level value detected by the bottom detection circuit, and the output of the average value detection circuit. The laser diode includes a bias current control circuit that controls the bias current flowing through the laser diode so that the output of the mark rate detection circuit becomes equal to the output of the mark rate detection circuit.

[Effect]

Therefore, according to this invention, when the gain of the mark rate detection circuit is varied externally, the output of the mark rate detection circuit changes, and the output of the mark rate detection circuit is made equal to the output of the average value detection circuit, and the extinction ratio is kept constant. The bias current and pulse current flowing through the laser diode are controlled so that.

〔Example〕

Hereinafter, a laser diode drive circuit according to the present invention will be explained in detail.

FIG. 1 is a circuit diagram showing an embodiment of this laser diode drive circuit.

In the figure, I' is a laser diode drive circuit section, and resistor 20. It comprises a transistor 21.22 and a current source 15.16. A current source 15 serves to supply a bias current to the laser diode 1. The transistors 21, 22 and the current source 16 serve to superimpose a high frequency pulse current on the bias current to the laser diode l. ■” is the laser diode control section,
a photodiode 2 for detecting the optical output of the laser diode 1; 6. A peak detection circuit that detects the high level value of optical output from the output of the photodiode 2. Bottom detection circuit 7 that detects the low level value of optical output from the output of photodiode 2
．． Average value detection circuit for detecting the average value of optical output from the output of photodiode 2 5. The mark rate detection circuit 10 detects the mark rate of the data signal input to the laser diode drive circuit, adds an externally variable gain, and outputs the signal.The mark rate detection circuit 10 includes a pulse current control circuit 8 and a bias current control circuit 9. The pulse current control circuit 8 includes a peak detection circuit 6
From the high level value detected by the bottom detection circuit 7 and the low level value detected by the bottom detection circuit 7, the extinction ratio is set to a constant value.
A current source 16 that supplies pulsed current to the laser diode 1
It plays the role of controlling. The bias current control circuit 9 is
It serves to control the current source 15 that supplies bias current to the laser diode 1 so that the output of the average value detection circuit 5 and the output of the mark rate detection circuit 10 become equal. In the figure, a predetermined voltage is applied to terminals a and b, and data signals with different polarities are input to terminals c and d. Further, the e terminal is a variable optical output terminal, and a signal for controlling the gain of the mark rate detection circuit 10 is input thereto.

Next, a method of varying the optical output in the laser diode drive circuit configured as described above will be explained.

In FIG. 1, when a signal that changes the gain of the mark rate detection circuit 10 is inputted from the optical output variable terminal e, the output of the mark rate detection circuit 10 changes, and the output of the mark rate detection circuit 10 changes and the output of the average value detection circuit 5 becomes equal. The pulse current control circuit 8 and the bias current control circuit 9 operate so that the extinction ratio becomes constant and the bias current and pulse current flowing through the laser diode 1 are automatically controlled.

〔Effect of the invention〕

As is clear from the above explanation, according to the laser diode drive circuit of the present invention, when the gain in the mark rate detection circuit is varied externally, the output of the mark rate detection circuit changes, and the output of the mark rate detection circuit and the output of the average value detection circuit change. The bias current and pulse current flowing through the laser diode are controlled so that the extinction ratio is constant and the extinction ratio is constant, and the optical output can be easily varied without deteriorating the extinction ratio. It becomes like this.

[Brief explanation of drawings]

FIG. 1 is a circuit diagram showing an embodiment of a laser diode drive circuit according to the present invention, and FIG. 2 is a circuit diagram showing a conventional laser diode drive circuit. ■...Laser diode, 2...Photodiode,
5... Average value detection circuit, 6... Peak detection circuit, 7
... Bottom detection circuit, 8... Pulse current control circuit,
9... Bias current control circuit, 10... Mark rate detection circuit, 15.16... Current source, 21.22... Transistor, e... Optical output variable terminal.

Claims (1)

[Scope of Claims] A peak detection circuit that detects a high level value of the optical output of a laser diode, a bottom detection circuit that detects a low level value of the optical output of the laser diode, and an average value of the optical output of the laser diode. a mark rate detection circuit that detects the mark rate of the input data signal and outputs the mark rate with an externally variable gain added thereto; a high level value detected by the peak detection circuit and the bottom a pulse current control circuit that controls the pulse current flowing through the laser diode so that the extinction ratio becomes a constant value based on the low level value detected by the detection circuit; and a bias current control circuit that controls a bias current flowing through the laser diode so that the output is equal to that of the laser diode.