JPH0645672A - Light transmission circuit - Google Patents

Abstract

PURPOSE:To provide a light transmission circuit with a low power consumption which maintains the output average value and the degree of light modulation of light signal regardless of the temperature fluctuation of an LD diode. CONSTITUTION:A photo diode 2, an average value detection circuit 7, a voltage comparison circuit 6, and an LD bias current drive circuit 5 control the bias current of a laser diode (LD) 1, thus automatically controlling the output level of light signal. A memory 9 stores the input level data of analog signal to the LD 1 generating a light signal with the same degree of light modulation regardless of change in temperature near the LD 1. A temperature sensor 3 detects the temperature near the LD 1 and an A/D 10 generates a temperature close to the digital detection temperature. The memory 9 supplies an input level data corresponding to the detection nearby temperature to a D/A 8, the D/A 8 controls a variable gain amplification circuit 4 according to an analog input level data, and an analog signal at a level maintaining the degree of light modulation to be constant at any nearby temperature is set to the output of the amplification circuit 4.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical transmitter circuit, and more particularly to an optical transmitter circuit for an analog optical transmission system.

[0002]

2. Description of the Related Art An optical transmission circuit in a conventional optical transmission system for transmitting an optical signal whose analog amplitude is constant, such as frequency modulation and phase modulation, will be described with reference to the block diagram of FIG.

In this optical transmission circuit, the input analog electric signal amplified by the amplifier circuit 13 is a laser diode (LD).
When input to 11, the LD 11 emits an optical signal modulated with an analog electric signal. A part of the optical signal output from the LD 11 is converted into an electric signal by the photodiode (PD) 2. The average value detection circuit 7 detects the average value of the output of the PD 2, and the voltage comparison circuit 6 compares the output of the average value detection circuit 7 with the reference voltage given to the reference side. The output of the voltage comparison circuit 6 controls the LD bias current drive circuit 5. The LD bias current drive circuit 5 changes the bias current of the LD 11 by negative feedback control to make the average value of the optical output emitted from the LD 11 constant.

The LD 11 uses a thermostat element (Peltier element) to keep the temperature of the LD element constant, and the threshold value variation and the differential quantum efficiency (DEQ) of the LD element (LD11) due to temperature variation. It prevents fluctuations.

[0005]

In this conventional optical transmission circuit, the PD 2, the average value detection circuit 7, the voltage comparison circuit 6 and the L
The automatic light output control circuit composed of the D bias current drive circuit 5 keeps the average light output value constant even when the threshold value of the LD 11 fluctuates.
The degree of optical modulation cannot be made constant due to fluctuations in the differential quantum efficiency of 1.

Therefore, in the conventional optical transmission circuit, the temperature of the LD element is kept constant by using a constant temperature element (Peltier element), and the fluctuation of the threshold value and the differential quantum efficiency due to the temperature fluctuation are prevented. The degree of modulation was kept constant.
However, this method causes a new problem that the consumption current increases due to the driving of the Peltier device.

[0007]

The optical transmission circuit of the present invention comprises:
A laser diode responsive to an analog signal and a bias current that is modulated with an amplitude corresponding to the level of the analog signal and produces an optical signal at an output level corresponding to the bias current; and an electrical signal from a portion of the optical signal. In response to the output of the voltage comparator circuit, a mean value detection circuit that detects the mean value of the electric signal, a voltage comparison circuit that compares a predetermined reference voltage with the mean value of the electric signal. And an LD bias current drive circuit that controls the bias current so that the output level of the optical signal becomes a level corresponding to the reference voltage. In the optical transmission circuit, the optical transmission circuit further includes a vicinity of the laser diode. A temperature sensor for detecting a temperature, and an input of the analog signal to be supplied to the laser diode corresponding to a nearby temperature. A memory for storing a bell as input level data; a modulation level reading circuit for reading the corresponding input level data from the memory in response to a temperature in the vicinity of the laser diode detected by the temperature sensor; And an analog signal level setting circuit for setting an input level of an analog signal supplied to the laser diode in response to the input level data.

[0008]

The present invention will be described below with reference to the drawings. FIG. 1 is a block diagram showing the configuration of an embodiment of the present invention.

This optical transmission circuit, like the optical transmission circuit shown in FIG. 2, has a PD 2, an average value detection circuit 7, and a voltage comparison circuit 6.
And an LD bias current drive circuit 5 are provided. In addition, in this optical transmission circuit,
The laser diode (LD) 1 that transmits an optical signal is shown in FIG.
The constant temperature element is removed from the LD 11 shown in FIG.

In this optical transmission circuit, when the input analog signal is supplied, the variable gain amplifier circuit 4 amplifies the input analog signal and uses it as the modulation current of the LD 1. In addition, the automatic optical output control circuit outputs the optical signal output from LD1 to PD2.
Monitor and convert it into an electric signal, and the average value detection circuit 7 detects the average value of this electric signal. The voltage comparison circuit 6 compares the output of the average value detection circuit 7 with the reference voltage given to the reference side, and the output of the voltage comparison circuit 6 controls the LD bias current drive circuit 5. The LD bias current control circuit 5 controls the bias current of the LD1 so that the average output value of the optical signal from the LD1 is constant. The LD 1 weights the bias current with the analog-type modulation current from the variable gain amplifier circuit 4, and outputs an optical signal modulated with the analog signal.

Here, a temperature sensor 3 is installed near the LD1, and the temperature sensor 3 detects the temperature near the LD1. The memory 9 also stores, as input level data, the level of the modulation current (analog signal) that keeps the optical modulation degree of the LD 11 constant even if the neighborhood temperature changes.
The input level data consists of data such as DEQ corresponding to the temperature near the LD 11 detected by the temperature sensor 3.

The temperature sensor 3 is an analog-digital converter (A / D) 10 for converting the temperature near the LD 1 into analog data.
Convert to. The A / D 10 converts the near temperature into digital data and supplies it to the memory 9. When the memory 9 is supplied with the digital data, the memory 9 converts the input level data of the corresponding near temperature into a digital-analog converter (D / A).
A) Output to 8. The analog input level data from the D / A 8 controls the gain of the variable gain amplifying circuit 4, and the variable gain amplifying circuit 4 sets the analog signal of the level corresponding to this input level data in the LD 1. Therefore, the LD 1 keeps the output level of the optical signal constant by the automatic optical output control circuit and controls the automatic optical modulation degree including the variable gain amplification circuit 4, the temperature sensor 3, the A / D 10, the memory 9 and the D / A 8. The circuit outputs an optical signal whose optical modulation degree is kept constant.

[0013]

As described above, according to the present invention, in addition to making the average value of the optical signal output by the conventionally used automatic optical output control circuit constant, the level of the analog signal maintaining a constant optical modulation degree is set by the laser diode. Is stored in correspondence with the near temperature of the laser diode, the temperature near the laser diode is detected, and the level of the analog signal supplied to the laser diode is set to the stored analog signal level for each detected temperature. It has an effect that the modulation degree of the optical signal can be kept constant.

Further, there is an effect that the current consumption can be significantly reduced as compared with the conventional optical transmitter circuit having the laser diode with the constant temperature element.

[Brief description of drawings]

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

FIG. 2 is a block diagram of a conventional optical transmission circuit.

[Explanation of symbols]

 1, 11 Laser diode (LD) 2 Photo diode (PD) 3 Temperature sensor 4 Variable gain amplification circuit 5 LD bias current drive circuit 6 Voltage comparison circuit 7 Average value detection circuit 8 Digital-analog converter (D / A) 9 Memory 10 analog-digital converter (A / D) 13 amplifier

Claims (2)

[Claims] 1. A laser diode responsive to an analog signal and a bias current that is modulated with an amplitude corresponding to the level of the analog signal and produces an optical signal at an output level corresponding to the bias current; A photodiode that generates an electric signal from a part, an average value detection circuit that detects an average value of the electric signal, a voltage comparison circuit that compares a predetermined reference voltage with the average value of the electric signal, and the voltage comparison circuit. An optical transmission circuit comprising: an LD bias current drive circuit that controls the bias current so as to set an output level of the optical signal to a level corresponding to the reference voltage in response to a circuit output, wherein the optical transmission circuit further comprises: A temperature sensor for detecting the temperature near the laser diode, and the analog sensor to be supplied to the laser diode corresponding to the temperature near the temperature sensor. A memory for storing the input level of the input signal of the scanning signal as input level data; a modulation level reading circuit for reading the corresponding input level data from the memory in response to the temperature in the vicinity of the laser diode detected by the temperature sensor; And an analog signal level setting circuit for setting an input level of an analog signal supplied to the laser diode in response to the input level data from the level reading circuit. 2. A laser diode responsive to an analog signal and a bias current that is modulated with an amplitude corresponding to the level of the analog signal and produces an optical signal at an output level corresponding to the bias current; A photodiode that generates an electric signal from a part, an average value detection circuit that detects an average value of the electric signal, a voltage comparison circuit that compares a predetermined reference voltage with the average value of the electric signal, and the voltage comparison circuit. An optical transmission circuit comprising: an LD bias current drive circuit that controls all bias currents so that the output level of the optical signal becomes a level corresponding to the reference voltage in response to a circuit output. A temperature sensor for detecting a temperature near the laser diode, and the analog sensor to be supplied to the laser diode corresponding to the temperature near the temperature sensor. A memory for storing the input level of the signal as an input level data, A for converting the detected temperature near to a digital signal /
A D converter, a modulation level reading circuit for reading the input level data corresponding to the digital signal from the memory in response to the digital signal, and a D / C for converting the input level data into analog input level data.
An optical transmitter circuit comprising: an A converter; and a variable gain amplifier circuit that sets an input level of the analog signal to the laser diode in response to the analog input level data.