JPH0590673A - Optical transmitter - Google Patents

Abstract

PURPOSE:To obtain an optical transmitter outputting stable optical output power, in which there is no pulse-width distortion, by constantly controlling the peak value of optical output power and controlling an optical output wave form so as to eliminate the distortion of the optical output waveform by the peak value and mean value of optical output power. CONSTITUTION:A laser diode 4 is driven by using a driver circuit 3 by input data. The back light of the laser diode 4 driven is monitored by a photodiode 5, monitored currents are converted into voltage by a current-voltage conversion circuit 10, and a peak value is monitored by a peak value detector 6 and a mean value by a first mean value detector 7. The driver circuit 3 is supplied with voltage detected by the peak value detector 6, and the driving currents of the laser diode 14 are controlled. Voltage detected by the first mean value detector 7 and voltage detected by a second mean value detector 8 are compared and amplified by an amplifier 9, output voltage is fed as the control voltage of a bias circuit 2, and the pulse width of an optical output waveform is controlled.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a laser diode driving technique used for optical communication.

[0002]

2. Description of the Related Art FIG. 2 is a block diagram showing a conventional optical transmitter. In the figure, 1 is a data input terminal, 3 is a drive circuit, 4 is a laser diode, and 5 is a back light of a laser diode. The photodiode 10 is a current / voltage converter that converts the current flowing in the photodiode into a voltage, and 6 is a peak value detector that detects the peak value of the output voltage of the current / voltage converter.

Next, the operation will be described. Input terminal 1
The data input to is supplied to the drive circuit 3 that drives the laser diode. The drive circuit 3 controls the laser diode 4 with a drive current according to the output of the peak value detector 6. The driven laser diode 4 emits light with optical output power according to the drive current. The back light of the light emitted from the laser diode 4 is monitored by the photodiode 5. The photodiode 5 causes a monitor current to flow according to the power of the back light, and the current / voltage conversion circuit 10 converts the monitor current into a voltage. The converted voltage is detected by the peak value detector 6, and the detected voltage is supplied to the drive circuit 3. The drive circuit 3 is
A constant optical output power can be obtained by controlling the current so that the output of the peak value detector 6 is constant.

[0004]

Since the conventional optical transmitter is constructed as described above, the peak value of the optical output power can be controlled to be constant, but when the bias current of the laser diode is not appropriate or the temperature is low. There was a problem that the optical output waveform was distorted due to the fluctuation.

The present invention has been made to solve the above problems, and an object thereof is to make the peak value of optical output power constant without causing distortion in the optical output waveform.

[0006]

An optical transmitter according to the present invention detects a peak value of optical output power, and further detects an average value of optical output power and an average value of binary input signals to obtain a laser diode. The modulation current and the DC bias current flowing in the control circuit are controlled.

[0007]

In the optical transmitter according to the present invention, the peak value of the optical output power is controlled to be constant by the drive current of the laser diode, and the ratio between the average value of the optical output power and the peak value of the optical output power is fixed. Thus, by controlling the input signal of the DC bias circuit, the pulse width distortion of the optical output waveform is eliminated.

[0008]

EXAMPLES Example 1. An embodiment of the present invention will be described below with reference to the drawings. In FIG. 1, 1 is a data input terminal, 2 is a bias circuit for applying a laser diode DC bias, 3 is a drive circuit for driving a laser diode, 4
Is a laser diode, 5 is a photodiode that monitors the back light of the laser diode, 6 is a peak value detector that detects the peak value of the output voltage of the current / voltage converter, and 7 is the average output voltage of the current / voltage converter. A first average value detector for detecting a value, 8 is a second average value detector for detecting and amplifying an average value of binary values, and 9 is an output voltage of the first average value detector and a second average value detector. An amplifier 10 for comparing and amplifying the output voltage of the average value detector is a current / voltage converter for converting the current flowing through the photodiode into a voltage.

In the optical transmitter configured as described above, binary transmission data is supplied to the data input terminal 1 and input to the drive circuit 3. The drive circuit 3 controls the optical output power of the laser diode 4 with a drive current according to the output voltage of the peak value detector 6. Driven laser diode 4
Emits light with an optical output power according to the drive current, and of the light emitted by the laser diode 4, the back light is monitored by the photodiode 5. The photodiode 5 causes a monitor current to flow according to the power of the back light, and the current / voltage conversion circuit 10 converts the monitor current into a voltage. The converted voltage is detected by the peak value detector 6, and the detected voltage is supplied to the drive circuit 3. The drive circuit 3 can obtain a constant optical output power by controlling the current so that the output of the peak value detector is constant.

The average value of the voltage converted by the current / voltage conversion circuit 10 is detected by the first average value detector 7. Here, the binary transmission data supplied to the data input terminal 1 detects the average value by the second average value detector 8 and is amplified by a certain factor. The voltage amplified by the second average value detector 8 by a certain factor and the voltage whose average value is detected by the first average value detector 7 are comparatively amplified by the amplifier 9 so as to be constant.

Further, the amplifier 9 supplies the DC voltage as a control voltage for the bias circuit 2 so as to give a direct current bias so that the optical output waveform of the laser diode 4 is not distorted. Can be supplied.

[0012]

As described above, according to the present invention, the peak value of the optical output power of the laser diode is controlled to be constant,
Since the pulse width is controlled by the average value and peak value of the optical output power to eliminate the distortion of the optical waveform, there is no bias current in the laser diode, and the threshold current value of the laser diode fluctuates due to temperature fluctuations. Even with this, there is no distortion of the optical waveform, and stable optical output power can be obtained.

[Brief description of drawings]

FIG. 1 is a block diagram showing a first embodiment of the present invention.

FIG. 2 is a block diagram showing a configuration of a conventional optical transmitter.

[Explanation of symbols]

 1 Input Terminal 2 Bias Circuit 3 Drive Circuit 4 Laser Diode 5 Photodiode 6 Peak Value Detector 7 First Average Value Detector 8 Second Average Value Detector 9 Amplifier 10 Current / Voltage Converter Circuit

Claims (1)

[Claims] 1. A laser diode, a bias circuit for applying a DC bias to the laser diode, a drive circuit for driving the laser diode, a photodiode for monitoring the back light of the laser diode, and a current flowing through the photodiode converted into a voltage. A current / voltage converter, a peak value detector that detects a peak value of the output voltage of the current / voltage converter, and a first average value detector that detects an average value of the output voltage of the current / voltage converter. A second average value detector for detecting an average value of binary values and multiplying it by a fixed amount; and an amplifier for comparing and amplifying output voltages of the first average value detector and the second average value detector. An optical transmitter characterized in that.