JPH067608B2 - Semiconductor laser light output adjustment device - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to an apparatus for adjusting the optical output of a semiconductor laser element in a drive circuit for driving the semiconductor laser element.

(Prior Art) Conventionally, for example, a circuit for driving a semiconductor laser element used in a video disk, a laser printer, etc. is generally disclosed in Japanese Patent Laid-Open No. 57-92884. In this drive circuit, the laser light from the laser diode is given to the photodiode, and the output of the photodiode is given to the inverting input of the operational amplifier via the resistor. The operational amplifier has a reference voltage set by adjusting a variable resistance on the non-inverting input side connected to the non-inverting input terminal via a resistor and a reference voltage connected to the inverting input terminal via the resistor. The output voltage of the photodiode, which is set by adjusting the variable resistance on the inverting input side, is compared and amplified.

By the way, the variable resistor on the inverting input side adjusts the output voltage from the photodiode applied to the inverting input terminal of the operational amplifier. That is, the laser diode has a different optical output depending on the operating characteristics, which changes the current flowing through the photodiode and changes the voltage applied to the inverting input terminal of the operational amplifier. Therefore, the voltage applied to the inverting input terminal of the operational amplifier is adjusted to a predetermined level by the variable resistor on the inverting input side, and the amplification degree of the operational amplifier is determined by the variable resistor on the non-inverting input side. The reference voltage is adjusted, and the output of the operational amplifier determines the optical output of the laser diode.

As described above, in the conventional circuit, two circuits are provided for one operational amplifier.
The optical output of the laser diode is adjusted by the individual variable resistors. Therefore, when there are variations in the characteristics of the laser diode, the variable resistance on the inverting input side is adjusted, and the operating characteristics of the operational amplifier are changed accordingly, so that the variable resistance on the non-inverting input side must also be adjusted. I have a problem. Further, since one operational amplifier is used for comparison and amplification, if the amplification factor is increased, abnormal oscillation operation of the circuit or the like occurs, so that the adjustment range of the output voltage by the variable resistor is narrowed and the optical output adjustment is performed. There was a problem that the work was difficult.

(Object of the Invention) The present invention has been made in view of the above-mentioned conventional problems, and a semiconductor laser capable of easily adjusting the optical output of the semiconductor laser element even if the operating characteristics of the semiconductor laser element vary. An object is to provide a light output adjusting device.

(Structure of the Invention) The present invention compares and amplifies a first output voltage corresponding to the magnitude of a current flowing through a light receiving element that receives laser light from a semiconductor laser element and a predetermined first reference voltage, A first amplifier circuit for deriving an output voltage, and a first variable resistor for varying the amplification factor of the first amplifier circuit to adjust a change in the second output voltage caused by variations in the characteristics of the semiconductor laser device to a predetermined level. A second amplifier circuit for comparing and amplifying the second output voltage and a predetermined second reference voltage to derive a laser light output voltage for determining the light output from the semiconductor laser device; It has a second variable resistor for varying the amplification degree and adjusting the optical output of the semiconductor laser device.

With this configuration, the fluctuation of the optical output due to the variation in the characteristics of the semiconductor laser device can be adjusted by the first variable resistor, and the optical output of the semiconductor laser device can be adjusted by the second variable resistor.

(Embodiment) FIG. 1 is a block diagram showing the overall configuration of a semiconductor laser light output adjusting apparatus according to an embodiment of the present invention. In FIG. 1, a laser diode LD which is a semiconductor laser device
Responds to the modulation signal from the modulation circuit A in the active state of the transistor TR, and supplies the laser light to the photodiode PD which is a light receiving element. The amplifier circuit B performs an amplifying operation as described later to amplify the voltage across the resistor R1 to a predetermined level. The sample hold circuit C samples and holds the output from the amplifier circuit B in response to the sampling signal from the sampling signal generating circuit F. The comparison amplifier D compares the level of a predetermined reference voltage with the output from the sample hold circuit C and amplifies the level. The operational amplifier G amplifies the output from the comparison amplifier D, activates the transistor TR, and drives the laser diode LD.

2 is an amplifier circuit B shown in FIG. 1 which is a feature of the present invention.
It is an electric circuit diagram of.

In FIG. 2, the laser diode LD outputs laser light by the operation as described above. The photodiode PD receives the laser light from the laser diode LD and causes the monitor current I1 to flow through the resistor R1. Therefore, a first output voltage V1 determined by the resistance value of the resistor R1 and the monitor current I1 is generated at the connection point between the anode of the photodiode PD and the resistor R1, and the first output voltage V1 is generated.
Is applied to the non-inverting input terminal of the first operational amplifier 1 which is the first amplifier circuit. The inverting input terminal of the first operational amplifier 1 is supplied with the first reference voltage E1 set by the first variable resistor VR1 and the resistor R2. First variable resistor VR
1 is the variation of the operating characteristics of the laser diode LD,
This is for adjusting the first reference voltage E1 so that the second output voltage V2, which is the output of the first operational amplifier 1, becomes a predetermined level even if the monitor current I1 changes. Therefore, the first operational amplifier 1 compares the level of the first reference voltage E1 set by adjusting the first variable resistor VR1 with the first output voltage V1 applied to the non-inverting input terminal, amplifies the level, and outputs the second output. The voltage V2 is derived.

The second operational amplifier 2, which is the second amplifier circuit, has a second output voltage V2 applied to its non-inverting input terminal and a second reference voltage E2 set by a second variable resistor VR2 and a resistor R3.
Are compared in level and amplified to derive a laser light output voltage V3 in response to the laser light from the laser diode LD. The second variable resistor VR2 connected to the output terminal of the second operational amplifier 2 and its inverting input terminal adjusts the level of the second reference voltage E2 applied to its inverting input terminal, thereby providing the second operational amplifier. The level of the laser light output voltage V3 derived from the output terminal is adjusted by changing the amplification degree of No.2.

Here, the amplification operation of the amplification circuit B will be described using a relational expression.

In the first operational amplifier 1, the voltage applied to its non-inverting input terminal is V1, and the voltage applied to its output terminal is V1.
2. If the resistance value of the resistor R2 is r2 and the resistance value of the first variable resistor VR1 is Vr1, then V1 = r2 / (r2 + Vr1) .V2 ... (1)

In the second operational amplifier 2, the voltage applied to its non-inverting input terminal is V2, and the voltage derived at its output terminal is V2.
3, the resistance value of the resistor R3 is r3, and the resistance value of the second variable resistor VR2 is Vr2, V2 = r3 / (r3 + Vr2) · V3 ... (2)

Further, the voltage V1 of the first expression is obtained by the following third expression.

V1 = r1 · I1 (3) where r1 is the resistance value of the resistor R1 and I1 is the resistance R
It is a current flowing through 1.

If the optical output of a certain laser diode LD is P0 and the monitor current flowing through the photodiode PD and the resistor R1 at that time is I0, P0 = αI0 (4) where α is a proportional constant determined by the operating characteristics of the laser diode LD. is there.

Therefore, the optical output of any laser diode LD is
From the first to fourth equations, P = αI1 = P0 / I0.V1 / r1 = P0 / I0.V3 / r1.r2 / (r2 + Vr1) .r3 / (r3 + Vr2) (5). In this fifth formula, P0 / I0 · V3 / r1
R2 / (r2 + Vr1) is a value that the monitor current I0 due to the variation in the operating characteristics of the laser diode LD is adjusted by the first variable resistor VR1, and r3 / (r3 + Vr2)
Is the optical output of the laser diode LD to the second variable resistor VR.
It is adjusted by 2.

Next, a specific light output adjusting operation of the laser diode LD will be described.

For example, the maximum light output of the laser diode LD is 5 mW
And the resistance values of the resistors R1, R2 and R3 are 1 KΩ and the resistance values of the first variable resistors VR1 and VR2 are 30 KΩ. Further, the output voltage V3 of the second operational amplifier 2 is set to 3V so as to be substantially equal to the reference voltage applied to the comparison amplifier D shown in FIG. Further, the optical output of a certain laser diode LD, that is, P0 shown in the fourth equation is set to 3 mW.

Therefore, the optical output in the drive state of an arbitrary laser diode LD is P = 3 / I0 · 3/1 · 1 / (1 + Vr1) · 1 / (1 + Vr2) (6) Use maximum output 4m
When set to W, the values of the first term to the third term on the right side of the sixth expression may be the numerical value 4. That is, 9 / I0 (1 + Vr1) = 4 (7) Due to the relationship of the seventh equation, the laser diode L
Even if the monitor current I0 changes due to variations in the operating characteristics of D, the maximum output of the laser diode LD can be kept constant by adjusting the resistance value Vr1 of the first variable resistor VR1. For example, the first variable resistor VR1 may be adjusted so that Vr1 = 21.5, 6.5, 1.25 when I0 = 0.1, 0.3, 1.0. When the first variable resistor VR1 is adjusted in this way, the optical output of the laser diode LD is, for example, 4 m at the second variable resistor VR2.
It can be adjusted from W to 0.13 mW.

As described above, the variation of the optical output of the laser diode LD due to the variation of the operating characteristics of the laser diode LD can be adjusted by the first variable resistor VR1, and the optical output of the laser diode LD is adjusted by the second variable resistor VR2. can do.

The resistor R2, the first variable resistor VR1 and the resistor R2 necessary for the operation of the first operational amplifier 1 and the second operational amplifier 2
3. The connection of the second variable resistor VR2 is not limited to the configuration of the above-described embodiment, and various connection configurations performing similar operations can be applied.

(Effect of the Invention) As described above, according to the present invention, the first output voltage corresponding to the magnitude of the current flowing in the light receiving element that receives the laser beam from the semiconductor laser element and the predetermined first reference voltage are set. The first variable resistor for varying the amplification degree of the first amplifier circuit that performs comparative amplification to derive the second output voltage can adjust the change in the second output voltage caused by the variation in the characteristics of the semiconductor laser device to a predetermined level. A second laser light output voltage that determines the light output from the semiconductor laser device by comparing and amplifying the second output voltage and a predetermined second reference voltage.
The optical output of the semiconductor laser device can be adjusted by the second variable resistor that changes the amplification degree of the amplifier circuit.

Therefore, the adjustment of the variation in the characteristics of the semiconductor laser device and the adjustment of the optical output of the semiconductor laser device can be shared, and the adjustment work at the time of use or manufacturing can be simplified. Further, not only the semiconductor laser element of the same usage standard, but also the semiconductor laser element of other usage standards can be used similarly if the adjustment as described above is performed, so that the usage range of the semiconductor laser element is Get wider

Further, the optical output of the semiconductor laser device is amplified in two stages of the first amplifier circuit and the second amplifier circuit, and the amplification degree is adjusted by the first variable resistor and the second variable resistor, respectively. The second amplification circuit can be operated in a range in which each amplification degree is low, an abnormal oscillation is less likely to occur, and the circuit operation is stable.

[Brief description of drawings]

FIG. 1 is a block diagram showing an overall configuration of a semiconductor laser light output adjusting device according to an embodiment of the present invention, and FIG. 2 is an electric circuit diagram of an amplifier circuit B shown in FIG. 1 ... 1st operational amplifier, 2 ... 2nd operational amplifier, LD ... Laser diode, PD ... Photodiode, VR1 ... 1st
Variable resistance, VR2 ... Second variable resistance.

Claims (1)

[Claims] 1. A second output voltage is obtained by comparing and amplifying a first output voltage corresponding to the magnitude of a current flowing through a light receiving element for receiving a laser beam from a semiconductor laser element and a predetermined first reference voltage. A first amplifier circuit to be derived, a first variable resistor for varying the amplification factor of the first amplifier circuit, and adjusting a change in the second output voltage caused by variations in the characteristics of the semiconductor laser device to a predetermined level; 2 output voltage and predetermined second
Of the semiconductor laser device by varying the amplification degree of the second amplifier circuit for comparing and amplifying the laser light output voltage for determining the light output from the semiconductor laser device, A semiconductor laser light output adjusting device comprising: a second variable resistor for adjusting a light output.