JP2684697B2 - Semiconductor laser drive circuit - Google Patents

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a semiconductor laser drive circuit, and more particularly to a GH
The present invention relates to a circuit for driving a semiconductor laser, which uses a field-effect transistor used in a transmitting section of high-speed digital optical communication exceeding z.

(Prior Art) FIG. 2 shows an example of a conventional semiconductor laser drive circuit.

In the conventional driving circuit of this type of semiconductor laser, the capacitor 3 is connected between the source electrode S of the field effect transistor 1 and the reference potential 9, and the resistor 2 is connected between the source electrode S and the power source V. Between the drain electrode D and the reference potential, a resistor 4 and a semiconductor laser 5 are connected in series, a resistor 8 is connected in parallel with a capacitor 8, and a direct current bias supply circuit 6 is connected to the cathode of the semiconductor laser 5. I'm running.

(Problems to be Solved by the Invention) This conventional semiconductor laser drive circuit is provided with a semiconductor laser 5
A speed-up capacitor 8 is connected in parallel with the resistor 4 in order to compensate for the pattern effect due to the oscillation delay, etc. However, as the frequency becomes higher, the influence of mounting and the variation of the semiconductor laser become larger. It is necessary to change the value of the condenser 8 to obtain the best optical waveform. However, since the conventional circuit has the configuration as shown in FIG. 2, it is necessary to replace the capacitor 8 to compensate for the pattern effect of the optical waveform, and there is a drawback that the compensation capacitance cannot be continuously varied. .

An object of the present invention is to solve the above drawbacks and to provide a semiconductor laser drive circuit capable of continuously changing the capacitance between the resistance terminals between the drain of the field effect transistor and the laser diode.

(Means for Solving the Problem) In order to achieve the eye movement, the semiconductor laser drive circuit according to the present invention connects a first capacitor between a source electrode of a field effect transistor and a reference potential, and connects the source electrode to the source electrode. A first resistor is connected to a power source, a series circuit of a second resistor and a laser diode is connected between the drain electrode of the field effect transistor and a reference potential, and the second resistor and the laser diode are connected. A laser diode by connecting a DC bias supply circuit to a common connection point of the field effect transistor and a second capacitor connected in parallel with the second resistor, and supplying a pulse current to the gate of the field effect transistor. In a semiconductor laser drive circuit for oscillating a laser, a second field effect transistor is connected in parallel to the second resistor instead of the second capacitor. However, by controlling the gate voltage of the second field effect transistor, the capacitance applied between the terminals of the second resistor is continuously changed.

Hereinafter, the present invention will be described in more detail with reference to the drawings.

FIG. 1 is a circuit diagram showing an embodiment of a semiconductor laser drive circuit according to the present invention.

In the figure, 1 and 7 are field effect transistors (hereinafter referred to as FET
Is abbreviated. ), 2 and 4 are resistors, 3 is a capacitor, 5 is a semiconductor laser diode, and 6 is a DC bias supply circuit.

When a pulse signal is input to the gate electrode G of FET1, a drive pulse current corresponding to the input pulse signal is obtained. When the drive pulse current is injected into the semiconductor laser diode 5, the semiconductor laser diode 5 oscillates. However, the semiconductor laser diode 5 causes an oscillation delay with respect to the pulse of the first bit and delays the light emission, so that the pattern effect occurs and the optical waveform deteriorates.

The present invention connects a second FET 7 in parallel with the resistor 4 to compensate for this. As a result, the drain-source capacitance of the FET 7, the gate-source capacitance, the gate-drain capacitance, and the resistance 4 increase the speed of the drive pulse current waveform, and the first bit pulse has an overshoot.

In general, in the high frequency region, the amount of deterioration of the optical waveform due to the pattern effect is not uniform because the mounting effect and the variation of the semiconductor laser diode 5 are large.

Therefore, it becomes necessary to change the capacity to be compensated, and the higher the frequency is, the smaller the capacity value becomes, which makes it difficult to realize the normal discrete component.

In the present invention, this capacitance for optical waveform compensation is realized by the drain-source capacitance, the gate-source capacitance, and the gate-drain capacitance of the second FET 7. These capacitances are a function of current, and can be changed continuously by controlling the gate voltage of FET7.

(Effects of the Invention) As described above, the present invention is the second embodiment instead of the speed-up capacitor connected in parallel to the resistor between the drain electrode of the field effect transistor and the laser diode.
Of the second field effect transistor is connected, and the capacitance can be continuously changed by controlling the drain-source capacitance, the gate-source capacitance, and the gate-drain capacitance of the second field-effect transistor by the gate voltage. This is possible, and there is an effect that the optical waveform can be easily compensated and optimized simply by changing the voltage.

[Brief description of the drawings]

FIG. 1 is a circuit diagram showing an embodiment of a semiconductor laser drive circuit according to the present invention, and FIG. 2 is a diagram showing an example of a conventional semiconductor laser drive circuit. 1,7 ...... Field effect transistor 2,4 ...... Resistance, 3,8 ...... Capacitor 5 ...... Semiconductor laser diode 6 ...... DC bias supply circuit

Claims (1)

(57) [Claims] 1. A first electrode is connected between a source electrode of a field effect transistor and a reference potential, a first resistor is connected between the source electrode and a power source, and a drain electrode of the field effect transistor. A second resistor and a laser diode in series circuit between the second resistor and the reference potential.
A DC bias supply circuit is connected to a common connection point of the resistor and the laser diode, and a second bias is connected in parallel with the second resistor.
In a semiconductor laser drive circuit that oscillates the laser diode by supplying a pulse current to the gate of the field-effect transistor in parallel with the second resistor instead of the second capacitor. A second field-effect transistor is connected to and the gate voltage of the second field-effect transistor is controlled to continuously change the capacitance applied between the terminals of the second resistor. Semiconductor laser drive circuit.