JP2707837B2 - Semiconductor laser drive circuit - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

TECHNICAL FIELD The present invention relates to a semiconductor laser drive circuit,
In particular, the present invention relates to a semiconductor laser drive circuit using a field-effect transistor used in a transmission section of high-speed digital optical communication.

[0002]

2. Description of the Related Art Conventionally, this type of semiconductor laser drive circuit has
As shown in FIG. 2, a bypass capacitor 3 and a Zener diode 4 are connected in parallel between a source electrode S of a field-effect transistor (hereinafter abbreviated as FET) 1 and a reference power supply -V. The resistor 2 was connected between the source electrode S and the power supply -V. Further, a semiconductor laser diode 5 is connected to a drain electrode D which is a drive output terminal of the FET 1.
And a DC bias supply circuit 8 for applying a pre-bias to the DC bias supply circuit 8.

In such a configuration, when a pulse signal is input to the gate electrode G of the FET 1, the source potential is made constant by the Zener diode 4 and the source resistor 2, and is determined by the drain-source voltage VDS. A drive current is obtained.

That is, the DC bias supply circuit 8
The laser diode 5 is excited to the vicinity of the light emission threshold, and in that state, the FET 1 is turned on / off in response to a pulse signal given to the FET 1, and the laser diode 5 emits light, so that a receiving side (not shown) is formed by optical communication. Information is transmitted to the device.

The input stage of the DC bias supply circuit 8 is provided with a choke coil (not shown) for separating the circuit from other parts in an AC manner.

However, in the above-described conventional semiconductor laser drive circuit, when optically modulating the semiconductor laser, it is difficult to compensate for the light emission delay and relaxation oscillation of the semiconductor laser, that is, the deterioration of the optical output waveform due to the so-called pattern effect. . That is, due to these phenomena, there is a drawback that the optical output waveform is blunted and jitter occurs at the rising portion.
There is also a drawback that it is necessary to provide a coil for separating the DC bias supply circuit in an AC manner.

[0007]

SUMMARY OF THE INVENTION It is an object of the present invention to provide a semiconductor laser drive circuit capable of effectively compensating for the deterioration of the optical output waveform.

Another object of the present invention is to provide a semiconductor laser drive circuit capable of reducing circuit components.

[0009]

A semiconductor laser drive circuit according to the present invention includes a switching transistor that is turned on and off by a predetermined pulse, a semiconductor laser diode that is driven by the transistor, one end connected to a drive output end of the transistor, and the other end. And a bias supply circuit for applying a pre-bias to the laser diode via the delay element, the delay element having a delay amount of 1/4 of the pulse period.

[0010]

Next, the present invention will be described with reference to the drawings.

FIG. 1 is a circuit diagram of an embodiment of a semiconductor laser drive circuit according to the present invention, and the same parts as those in FIG. 2 are denoted by the same reference numerals. In the figure, the circuit of this embodiment is F
ET 1, resistors 2, 6, 9, 10, bypass capacitor 3, zener diode 4, semiconductor laser diode 5, delay element 7, and DC bias current supply circuit 8.

In the semiconductor laser drive circuit of the present embodiment having such a configuration, when a pulse signal (RZ signal) is input to the gate electrode of the FET 1, the source potential of the FET 1 is fixed by the Zener diode 4 and the resistor 2. Therefore, a pulse current corresponding to the input pulse is obtained. When modulating the semiconductor laser diode 5 with this pulse current,
The light modulation waveform is greatly deteriorated by the pattern effect due to the light emission delay of the semiconductor laser diode or the relaxation oscillation. In particular, the phenomenon occurs as jitter at the rising edge of the optical modulation waveform.

In order to suppress the deterioration of the deteriorated optical modulation waveform, it is necessary to compensate the pulse current waveform. Therefore, in this embodiment, the drain terminal D of the above-described FET 1 is used.
In series with the semiconductor laser diode 5 connected to
The delay element 7 connected in series with the resistor is connected, and the DC bias supply circuit 8 is connected to the terminal of the delay element 7, thereby suppressing the deterioration of the optical modulation waveform. Further, since the output terminal of the delay element is terminated by the resistor 10, a mismatch occurs, and the degree of the mismatch from the terminal is opposite to that of the pulse input from the terminal and is shifted by the delay amount of the delay element. A corresponding pulse is superimposed on the main signal line. The terminal of the delay element 7 is grounded.

At this time, the amount of delay is set to λ
If it is set to / 4 (λ is the wavelength), a pulse waveform conversion as shown in FIG. 3 occurs. That is, referring to FIG. 3, at point A in the circuit of FIG. 1, a waveform corresponding to the pulse signal given to the FET 1 can be observed. 7
Are delayed by λ / 2 and superimposed in opposite phases. As a result, the overlapping portion exceeds 0 [V], and an overshoot effect is produced.

It should be noted that, in practice, the waveform does not become a rectangular wave as shown by a solid line, but becomes a waveform which becomes blunt as shown by a broken line. In order to correctly obtain the delay amount of λ / 2, a well-known variable delay line may be provided and finely adjusted.

As described above, since the semiconductor laser diode is modulated with the waveform converted by the delay element, it is possible to suppress the jitter at the rising portion of the optical modulation waveform. If the value of the terminating resistor 10 is optimized, the amount of the reflected wave can be adjusted, and the degree of jitter compensation can be varied. If the resistance value is zero, that is, if it is grounded, total reflection will occur.

Furthermore, since the delay element is generally configured to include a coil, there is an advantage that the use of the inductance component can reduce the influence of AC on the DC bias supply circuit. Note that the delay element 7 may be one that matches the characteristic impedance of the circuit pattern (microstrip line). For example, if the characteristic impedance of the circuit pattern is 50 [Ω], the delay element 7 having a characteristic impedance of 50 [Ω] may be used.

By utilizing the fact that the level of overshoot changes when the terminating resistance value is changed, another signal waveform can be superimposed on the reflected wave. For example, a variable resistor circuit may be provided in place of the terminating resistor 10 in FIG. 1, and a modulation signal may be applied to its control terminal. In this way, light intensity modulation can be realized.

[0019]

As described above, according to the present invention, a semiconductor laser diode connected to a drive output terminal of a switching transistor is connected to a delay element to which a terminating resistor is connected, so that a rising portion of an optical modulation waveform can be obtained. There is an effect that waveform deterioration such as jitter can be suppressed.

Further, by connecting a DC bias supply circuit for supplying a DC bias via the delay element,
Since no choke coil is required at the input stage of the circuit, the mounting area of components can be reduced and the cost can be reduced.

[Brief description of the drawings]

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

FIG. 2 is a circuit diagram of a conventional semiconductor laser diode drive circuit.

FIG. 3 is a waveform chart of each part in FIG. 1;

[Explanation of symbols]

 Reference Signs List 1 transistor 5 semiconductor laser diode 7 delay element

Claims (1)

(57) [Claims] 1. A switching transistor which is turned on / off by a predetermined pulse, a semiconductor laser diode driven by the transistor, one end is connected to a drive output end of the transistor, the other end is terminated, and the delay amount is set to A delay element that is 1/4 of the pulse period;
A bias supply circuit for applying a pre-bias to the laser diode via the delay element.