JPH01162391A - Semiconductor laser drive circuit - Google Patents

Abstract

PURPOSE:To restrain a resonant phenomenon independently of the change of a bias current by a method wherein the cutoff frequency of a semiconductor laser current is controlled to coincide with the resonant frequency of the semiconductor with reference to a detected bias current. CONSTITUTION:A bias current and a modulating current are made to flow through a semiconductor laser 12 by a bias power source and a modulation power source through the intermediary of a bias current detecting section 2. The bias current detected by the bias current detecting section 2 is amplified by a amplifier 6. The amplified voltage Vc is applied to a variable condenser of a current bias circuit. A cutoff frequency of the current of the semiconductor laser 1 is controlled to coincide with the resonant frequency of the semiconductor laser through the voltage of the condenser.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a driving circuit for a semiconductor laser used in optical communication, optical information processing, etc.

[Prior art]

For example, the June 1981 issue of the magazine Electronic Science, page 18 states that the modulation characteristics of the optical output of a semiconductor laser are highly dependent on the modulation frequency, and that there is a resonance phenomenon that responds resonantly around several G11z (gigahertz). It has been shown that when a semiconductor laser is rapidly modulated at a frequency of GHz or higher, distortion occurs in the optical output.

FIG. 8 is a graph showing the relationship between the optical output intensity of the semiconductor laser and the modulation frequency when such a resonance phenomenon occurs, with the vertical axis representing the optical intensity and the horizontal axis representing the modulation frequency.

As is clear from this figure, the optical output intensity is determined by the bias current I
When B is 12 (Hz < I+), the resonant frequency of the semiconductor laser is fr.

Then, it changes rapidly around the resonant frequency fr, and reaches a maximum at the resonant frequency fr+. Also, the bias current
8 is I, the resonant frequency of the semiconductor laser is f
r, becomes higher fr2, and the optical output is at the resonant frequency frz
Maximum at . Therefore, a method to solve this problem is to connect the semiconductor laser in parallel with a series resonant circuit consisting of a coil, a capacitor, and a resistor, and to adjust the resonant frequency of the semiconductor laser and the cutoff frequency of the current of the semiconductor laser by the resonant circuit. The resonant frequency component of the current injected into the semiconductor laser is attenuated to suppress the resonance phenomenon.

[Problem that the invention seeks to solve]

As mentioned above, in a semiconductor laser drive circuit that simply connects a semiconductor laser and a resonant circuit in parallel, the resonant frequency of the semiconductor laser changes depending on the bias current to the semiconductor laser, so if the bias current changes, resonance occurs. The problem is that the phenomenon cannot be completely suppressed.

SUMMARY OF THE INVENTION In view of these problems, it is an object of the present invention to provide a semiconductor laser drive circuit that can suppress the resonance phenomenon even when the bias current to the semiconductor laser changes.

[Means for solving problems]

A semiconductor laser drive circuit according to the present invention is a semiconductor laser drive circuit in which a current bypass circuit made of a resonant circuit is connected in parallel to a semiconductor laser, and includes a bias current detection section that detects a bias current of the semiconductor laser.
The present invention is characterized in that it is configured to control the cut-off frequency of the current of the semiconductor laser in relation to the detected bias current so as to keep it at the resonant frequency of the semiconductor laser.

[Effect]

The modulation characteristics of a semiconductor laser are as follows: If the resonant frequency is fr, the photon lifetime is τ2, the carrier lifetime is τ5, the threshold current is L, and the bias current is IB, then the resonant frequency r is, and the resonant frequency fr changes with the bias current IB. do.

Injection efficiency of modulation current into semiconductor laser by resonant circuit η
is attenuated as the modulation frequency becomes higher, as shown in FIG. The cutoff frequency fc of the current of the semiconductor laser is controlled in relation to the bias current detected by the bias current detection section. Therefore, the modulation characteristics of a semiconductor laser provided with a resonant circuit are as shown in FIG. 4, which is the sum of the modulation characteristics of the semiconductor laser itself multiplied by the injection efficiency η.

Therefore, when the cutoff frequency fc of the semiconductor laser current is controlled to match the resonant frequency fr of the semiconductor laser, the modulation characteristics of the semiconductor laser are as shown in Fig. 5, and the modulation characteristics are as shown in Fig. 5. Resonance phenomena can be suppressed regardless.

〔Example〕

The present invention will be described in detail below with reference to drawings showing embodiments thereof.

FIG. 1 is a block diagram of a semiconductor laser drive circuit according to the present invention. A bias power supply 3 is connected between the anode and cathode of the semiconductor laser 1 via a bias current detection section 2, and a modulation type ti, 4 is connected to the bias power supply 3 in parallel. Further, a current bypass circuit 5, which is a resonant circuit consisting of a resistor and a capacitor, is connected in parallel to the semiconductor laser 1. The output of the bias current detection section 2 is given to a current bypass circuit 5 via an amplifier 6.

FIG. 2 shows an actual circuit of the semiconductor laser drive circuit shown in FIG. A resistor R5 (1Ω) is connected in series to the semiconductor laser 1. The current bypass circuit 5 has a resistor R, (0,1Ω)
and capacitor cF' (0,1μF) and variable capacitor C
It consists of a series resonant circuit with 4.

The bias current detection section 2 consists of a parallel circuit of a resistor RE (1Ω) and a capacitor C3 (1 μF). In addition, a coil LT (1 ml) is connected in series to the bias power supply 3, and a capacitor CT (0.1μF) is connected to the modulation power supply 4.
) are connected in series. The cutoff frequency of the current of the semiconductor laser 1 is controlled by the voltage applied to the variable capacitor C2.

The bias current is detected by the difference voltage between the voltage drop of the resistor RII and the voltage drop of the capacitor C11, and the amplified voltage (2) of the difference voltage is applied to the variable capacitor C1 to adjust the cut-off frequency of the semiconductor laser 1. It is designed to match the resonant frequency.

Now, the semiconductor laser 1 has a bias power supply 3 and a modulation type A4.
Accordingly, a bias current and a modulation current flow through the bias current detection section 2. This modulates the optical output of the semiconductor laser. The bias current detected by the bias current detection section 2 is amplified by the amplifier 6, and the resulting voltage VC is applied to the variable capacitor CP of the current bypass circuit 5, and the voltage
. Accordingly, the cutoff frequency fc of the current of the semiconductor laser 1 is controlled to the resonance frequency fr of the semiconductor laser.

By the way, the injection efficiency η (semiconductor laser current/modulation current) of the modulation current into the semiconductor laser 1 is: (2) where Jω is the angular frequency. Since Rs>>Rp and C,'>>C, equation (2) becomes. As a result, the current cutoff frequency fc of the semiconductor laser
Hato becomes. To set fc=fr (resonant frequency), (
1).

From equation (4), iJ must be. Also, since the relationship between the variable capacitor CP and the applied voltage VC is (5), from equation +61, the relationship between the bias current and the voltage VC applied to the variable capacitor is (however, A
is the capacitance of the variable capacitor CP). The photon life τ2, carrier life τ8, threshold current 1fh, and capacitance A of the variable capacitor of the semiconductor laser used in this example are as follows: τS = I Xl0-9 seconds τP - I Xl0-"
seconds I th - 10 mA A = 2 x 10'', and by substituting this into equation (7), it can be seen that the relationship between the bias current (8) and the applied voltage (2) must be set as follows, for example.

Vc =50IB -1,9・(81 This relationship is shown in Fig. 3. In Fig. 3, the vertical axis is the applied voltage of the variable capacitor CP.), and the horizontal axis is the bias current IB of the semiconductor laser. The applied voltage vc is -1.5 V at a bias current of 10 mA, and changes linearly connecting the two points, which are 0.1 V at a bias current of about 38 mA.

In other words, by setting the magnification of amplifier 6 to 50 times and setting the offset voltage to -1.9■, formula (8) is satisfied, and f
It can be automatically adjusted so that c=fr.

6 and 7 show actual measurements of the modulation characteristics when the bias current of the semiconductor laser drive circuit of the present invention was 27 mA and 20 mA. As is clear from this figure, in the conventional drive circuit, the bias current is 27 m
In the case of A, when the modulation frequency is about 7 G1-1z, the optical output increases rapidly and a resonance phenomenon appears, but in the drive circuit of the present invention, the resonance phenomenon is suppressed although a slight increase is observed.

Further, when the bias current is 20 mA, a resonance phenomenon appears at about 5 Gllz in the conventional drive circuit, but it is suppressed in the same manner as described above in the drive circuit of the present invention. Therefore, it was confirmed that no resonance phenomenon occurs even if the bias current changes.

〔effect〕

As described in detail above, according to the present invention, the cutoff frequency of the semiconductor laser current is controlled in relation to the bias current flowing through the semiconductor laser so as to match the resonant frequency of the semiconductor laser, so that The resonance phenomenon of a semiconductor laser can be suppressed. Therefore, it is possible to provide a semiconductor laser drive circuit that does not cause distortion in the optical output of the semiconductor laser even when high-speed modulation is performed.

[Brief explanation of the drawing]

Figures 1 and 2 are block diagrams and actual circuit diagrams of the semiconductor laser drive circuit according to the present invention, Figure 3 is a graph showing the relationship between bias current and voltage applied to the variable capacitor, and Figure 4 is the modulation frequency. FIG. 5 is a graph showing the relationship between modulation frequency and optical output intensity.
6 and 7 are graphs showing actually measured relationships between modulation frequency and optical output, and FIG. 8 is a graph showing the relationship between modulation frequency and optical output intensity in a conventional semiconductor laser drive circuit. 1... Semiconductor laser 2... Bias current detection section 3
... Bias power supply 4 ... Modulation power supply 5 ... Current bypass circuit (resonant circuit) patent Applicant Sanyo Electric Co., Ltd. agent Patent attorney Noboru Kono 1-'1- Math 8 - Tada's thoughts Screaming - Jubiki 1 to 15 Niken 10R boat bag = 1-2 + 3 (

Claims (1)

[Claims] 1. In a semiconductor laser drive circuit comprising a semiconductor laser and a current bypass circuit made of a resonant circuit connected in parallel, a bias current detection section for detecting a bias current of the semiconductor laser is provided, and the detected bias 1. A driving circuit for a semiconductor laser, characterized in that the circuit is configured to control the cut-off frequency of the current of the semiconductor laser in relation to the current so as to make it equal to the resonant frequency of the semiconductor laser.