JP3109467B2 - Optical transmitter - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to an optical transmitter using a laser diode applied to an optical communication system.

[0002]

2. Description of the Related Art A conventional optical transmitter is disclosed in Japanese Unexamined Patent Publication No. 4-291.
As disclosed in Japanese Patent No. 977, a reference voltage is generated based on an average value extracted from the data signal so that the optical output waveform of the semiconductor laser can be kept within a certain range regardless of the fluctuation of the data signal. In this case, a circuit provided with a reference voltage generating circuit was used.

As a prior art disclosed in Japanese Patent Application Laid-Open No. 4-162480, a laser diode driving circuit includes a peak detection circuit, a bottom detection circuit, an average value detection circuit, and the like. Some include a mark ratio detection circuit, a pulse current control circuit, and a bias current control circuit.

Further, as a prior art disclosed in Japanese Patent Laid-Open No. 5-63273, in order to provide a laser diode driving circuit which operates at a low power supply voltage and is suitable for integration into an integrated circuit,
An amplifier circuit compares the voltages generated from the current mirror circuit and the reference voltage circuit inside the laser diode drive circuit, amplifies the difference voltage, and outputs the amplified voltage. There has been provided a bias supply circuit for supplying the bias.

In a conventional semiconductor laser driving circuit of an optical transmitter, a pulse current 11 is generated from a data signal by a semiconductor laser driving circuit 1 including a current mirror circuit 5 as shown in FIG. It was configured to be driven.

[0006]

However, according to the above-described method, when the power supply voltage applied to the entire circuit of the optical transmitter changes, the voltage applied to the current mirror circuit 5 also changes. There was a problem that it fluctuated.

For example, when the power supply voltage decreases, the voltage applied to the current mirror circuit 5 also decreases.
The amplitude value of 1 decreases accordingly. When the amplitude value of the pulse current 11 decreases, the automatic output control circuit (APC circuit) 4 works to keep the optical output power constant, and the bias current 12 is controlled to increase. This means that although the bias current 12 is set to the optimum bias current [Ith] in the normal state, there is a disadvantage that the bias current 12 deviates from the optimum value due to the fluctuation of the power supply voltage. I do.

The present invention has been made under such a background, and it is possible to prevent the fluctuation of the bias current even when the power supply voltage fluctuates, and to improve the characteristics and performance of the optical transmitter. It is intended to provide a transmitter.

[0009]

According to the present invention, a semiconductor laser for converting a data signal into an optical signal is provided.
A semiconductor laser driving circuit based on a current mirror circuit operated by the data signal, a mark ratio detection circuit for detecting a mark ratio of the data signal and generating a mark ratio detection voltage, and a photodiode for emitting back surface light emitted from the semiconductor laser. And a current which outputs an optical output level detection voltage proportional to the optical output level of the semiconductor laser
A voltage conversion circuit, the mark ratio detection voltage and the light output level;
An automatic output control circuit that controls the optical output level to be constant by changing a bias current as a control signal with a bell detection voltage ;
An optical transmitter is provided, wherein a current flowing through the current mirror circuit is controlled to a predetermined value.

According to a second aspect of the present invention, the predetermined value is controlled so that a current flowing through the current mirror circuit becomes a constant value by adding a constant current control circuit to the current mirror circuit. 2. The optical transmitter according to claim 1, wherein the amplitude value of the pulse current flowing through the semiconductor laser is prevented from changing.

[0011]

DESCRIPTION OF THE PREFERRED EMBODIMENTS One embodiment of the present invention will be described below with reference to the drawings. FIG. 1 is a block diagram showing a configuration of an optical transmitter according to one embodiment of the present invention.
In this figure, an optical transmitter includes a semiconductor laser 7 for converting a data signal into an optical signal, a semiconductor laser drive circuit 1 for driving the semiconductor laser 7, a mark detection voltage 10 for detecting a mark rate of the data signal. And a current / current for transmitting a light output level detection voltage 9 proportional to the light output level by the photodiode 6 receiving light emitted from the back of the semiconductor laser 7 by the photodiode 6.
It comprises a voltage conversion circuit 3 and an automatic output control circuit (hereinafter abbreviated as an APC circuit) 4 for controlling the optical output level to be constant by inputting the optical output level detection voltage 9 and changing the bias current 12. .

Further, inside the semiconductor laser drive circuit 1, there is provided a constant current control circuit 8 for controlling the current flowing through the current mirror circuit 5 to a constant value even when the power supply voltage fluctuates.

Next, the operation of the embodiment of FIG. 1 will be described with reference to FIG.
This will be described with reference to FIG. In FIG. 2, in a steady state, the bias current 12 is set to be the optimum bias current [Ith]. At this time, since the APC circuit 4 controls the bias current 12 to be an optimum value in order to keep the light output level constant, the deterioration of the light output waveform and the extinction ratio in the steady state occurs. Absent.

In this state, if the power supply voltage applied to the entire optical transmitter circuit fluctuates, the voltage applied to the current mirror circuit 5 also fluctuates, but the constant current control circuit 8 keeps the current flowing through the current mirror circuit 5 constant. As a result, the amplitude value of the pulse current 11 does not change, and as a result, the fluctuation of the bias current 12 can be prevented.

As described above, the current mirror circuit 5 and the constant current control circuit 8 are provided inside the semiconductor laser driving circuit 1, and the current mirror circuit 5 always supplies a constant current even when the power supply voltage fluctuates. to continue. Therefore, even when the power supply voltage fluctuates, the amplitude value of the pulse current does not change, so that the fluctuation of the bias current can be prevented, and the characteristics of the optical output waveform and the extinction ratio can be improved.

The operation of one embodiment of the present invention has been described above in detail with reference to the drawings. However, the present invention is not limited to this embodiment, and a design change or the like may be made without departing from the gist of the present invention. The present invention is also included in the present invention.

[0017]

As described above, according to the present invention, by adding a constant current control circuit to the current mirror circuit inside the semiconductor laser drive circuit, the bias current can be changed even when the power supply voltage changes. Can be prevented, whereby the effect of improving the characteristics of the optical output waveform and the extinction ratio can be obtained.

[Brief description of the drawings]

FIG. 1 is a block diagram showing a configuration of an optical transmitter according to an embodiment of the present invention.

FIG. 2 is a characteristic diagram showing an operation of the optical transmitter in FIG. 11;

FIG. 3 is a block diagram showing a configuration of an optical transmitter according to a conventional technique.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Semiconductor laser drive circuit 2 Mark rate detection circuit 3 Current / voltage conversion circuit 4 Automatic output control circuit (APC circuit) 5 Current mirror circuit 6 Photodiode 7 Semiconductor laser 8 Constant current control circuit 9 Light output level detection voltage 10 Mark rate detection Voltage 11 Pulse current 12 Bias current

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI H04B 10/28 (56) References JP-A-9-232635 (JP, A) JP-A-4-291977 (JP, A) JP-A-4-162480 (JP, A) JP-A-5-63273 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) H04B 10/00 H01S 3/136

Claims (2)

(57) [Claims] 1. A semiconductor laser for converting a data signal into an optical signal, a semiconductor laser driving circuit including a current mirror circuit operated by the data signal, and a mark ratio of the data signal is detected to generate a mark ratio detection voltage. a mark rate detecting circuit, and a current / voltage conversion circuit for the rear surface emission light is received by the photodiode and outputs an optical output level detected voltage proportional to the light output level of the semiconductor laser from the semiconductor laser, the mark ratio detection Voltage and the light output level detection voltage
An optical output control circuit configured to control the optical output level to be constant by changing a bias current as a control signal , wherein the current flowing through the current mirror circuit is controlled to a predetermined value. Optical transmitter characterized by the above-mentioned. 2. The predetermined value is controlled such that a current flowing through the current mirror circuit becomes a constant value by adding a constant current control circuit to the current mirror circuit.
2. The optical transmitter according to claim 1, wherein a fluctuation of an amplitude value of a pulse current flowing through the semiconductor laser is prevented.