JPS6010794A - Semiconductor laser drive circuit - Google Patents

Abstract

PURPOSE:To avoid effects caused by oscillatory noises in a circuit and surges, and to compensate the reduction of luminosity caused by a use for a prolonged term automatically by constituting the circuit while a semiconductor laser and a photodiode as one of the elements in a phase-locked loop. CONSTITUTION:When a laser 19 emits light by fixed power, input voltage to a VCO1 14 drops and output frequency reduces when a rheostat 13 is varied and output voltage gradually drops. Output voltage from a phase comparator 15 receiving signals from the VCO1 14 and a low-pass filter 16 drops because the phase of the VCO1 14 is made later than that of a VCO2 22 at that time. Output currents from a constant current circuit constituted by two P-N-P type transistors 17, 18 increase, and voltage generated from a load resistor 20 increases, and output voltage from an inverting type amplifier 21, on the other hand, drops. Since the output voltage drops input voltage to the VCO2 22, the output frequency of the VCO2 22 reduces, and coincides with the output frequency of the VCO1 14 in phase, and the whole circuit is stabilized when luminosity from the laser 19 increases.

Description

[Detailed description of the invention] Technical fields> The present invention relates to a semiconductor laser drive circuit.

<Prior Art> In recent years, semiconductor laser drive circuits have been equipped with a semiconductor laser 1 and a semiconductor laser 1 in the same package 3, as shown in FIG. Many structures are used that incorporate a photodiode 2 or the like that receives a portion of the light emitted power and outputs a current corresponding to the light emitted power to the outside. However, this semiconductor laser 1 has the property of being destroyed if the maximum rating is exceeded even momentarily due to the effects of amplitude noise, surges, etc. in the circuit when operated near the maximum emission power rating. are doing. Another disadvantage is that it gradually deteriorates when used for a long time, and the light emitting power decreases even when driven at a constant current.

<Object of the Invention> The present invention has been made in view of the above-mentioned drawbacks, and is capable of avoiding the effects of amplitude noise and surges in the circuit, and
It is an object of the present invention to provide a semiconductor laser drive circuit that can automatically correct a decrease in light emission power due to long-term use.

<Structure of the invention>.

The unique feature of the Kyohatsu is that the semiconductor laser and photodiode are configured as one element in a phase-locked loop (hereinafter referred to as PI, 'L').

The present invention provides a phase comparator that compares a reference frequency signal of a variable frequency oscillator and a frequency signal of a voltage controlled oscillator, a constant current circuit that supplies current according to the output of the phase comparator,
A semiconductor laser driven by the output current of this constant current circuit, and a photoelectric conversion element that is incorporated in the same package as this semiconductor laser and detects the emission power of the semiconductor laser. A voltage controlled oscillator that outputs a predetermined frequency signal in response to the voltage controlled oscillator is provided, and the output frequency signal of the voltage controlled oscillator is introduced into the phase comparator.

<Example> Hereinafter, the present invention will be explained in detail based on the drawings.

FIG. 2 is a block diagram showing a semiconductor laser drive circuit of the present invention.

The output frequency from the variable frequency oscillator 4 and the output frequency from the voltage controlled oscillator (hereinafter referred to as VCO) 6 are input to the phase comparator 5, and the output frequency is proportional to the phase difference due to the frequency from both the oscillators 4 and 6. A voltage is applied to an amplifier 7 and the amplified output is passed through a low pass filter 8. The output of this low-pass filter 8 is input to a constant current circuit 9,
The constant current circuit 9 outputs a current proportional to the output of the phase comparator 5, and the semiconductor laser 10 receives the current from the constant current circuit 9 and emits light.

A photoelectric conversion element 11, for example a photodiode, incorporated in the same package as the semiconductor laser 10 receives a part of the light emitted from the semiconductor laser 10, converts a current proportional to the light emission power into a voltage, and outputs the is input to an amplifier 12 which amplifies it to a predetermined level. The output of this amplifier 12 is input to the VCO 6 to become an output frequency signal, which is fed back to the phase comparator 5. First, the operation will be explained.

When the phase of the input variable frequency oscillator 4 advances, in other words, when the phase of the VCO (i) lags, the output voltage fluctuates in the direction of increasing, and the phase comparator 5 becomes inverted. , when the phase is delayed, that is, when the phase of the VCO 6 is advanced, the output voltage fluctuates in the direction of decreasing.Now, the variable frequency oscillator 4 oscillates at a predetermined frequency, and as shown in Fig. 2 □ When the semiconductor laser drive circuit mainly consisting of the phase comparator 5 and VCO 6 shown in FIG. A voltage is generated. Since this constant voltage is supplied to the semiconductor laser 10 via the constant current circuit 9, the semiconductor laser 10 can maintain a constant emission power.

Next, in this state, if the output frequency of the variable frequency oscillator 4 is increased, the phase of the output frequency from the VCO 6 is delayed, and the output voltage of the phase comparator 5 increases. Therefore, the current supplied from the constant current circuit 9 to the semiconductor laser 10 increases, and the light emission power increases. A photoelectric conversion element 11 receives part of the emission power of the semiconductor laser 10.
The output current of amplifier 7 increases, and the output voltage of amplifier 7 also increases,
The input voltage to VCO6 increases.

By the way, since the VCO 6 changes the output frequency in proportion to the input voltage, as the input voltage increases, the output frequency also inevitably increases, and eventually the variable frequency oscillator 4
The output frequency signal will match in phase.

That is, this effect is such that when the frequency of the variable frequency oscillator 4 is increased, the emission power of the semiconductor laser 10 is increased, and conversely, when the frequency of the variable frequency oscillator 40 is decreased, the emission power of the semiconductor laser 1G is decreased. It shows. Therefore, it can be seen that the emission power of the semiconductor laser 10 can be controlled by increasing or decreasing the frequency of the variable frequency oscillator 4.

The case where the frequency of the variable frequency oscillator 40 is changed has been described above.Next, the oscillation frequency of the variable frequency oscillator 4 is set to a predetermined value, and the button is pressed so that the emission power of the semiconductor laser 10 becomes a constant value. Shows the case of continuous operation. In this state, unless the frequency of the variable frequency oscillator 4 is changed, the output of the phase comparator 5 is constant, and the input voltage to the constant current circuit 9 is also constant, so the current supplied to the semiconductor laser 10 is also constant. is maintained. Therefore,
The emission power from the semiconductor laser 10 is controlled to a constant value.

By the way, even though the current supplied to the semiconductor laser 10 is kept constant, if the semiconductor laser 10 itself deteriorates and its emission power decreases, the output of the photoelectric conversion element 11 receiving this emission power will be: Since it decreases in proportion to the deterioration, the input voltage to VCO6 also inevitably decreases, and this V
The output phase from the COB is delayed. That is, vco
6's output frequency will decrease. When the phase of this VCO (3) lags, the output of the phase comparator 5 increases inversely, and as a result, the current supplied to the semiconductor laser 10 increases. Therefore, the emission power from the semiconductor laser 10 increases. Then, the button control is performed so that the initial setting value, that is, the value before the semiconductor laser 10 deteriorates.From the above-mentioned effects, even if the semiconductor laser 10 deteriorates and the emission power decreases, the semiconductor laser 10 It can be seen that the supplied current increases and the emission power is maintained at the same value as before deterioration.

Next, a specific example of the semiconductor laser drive circuit according to the present invention will be shown.

In FIG. 3, a variable resistor 13 is a resistor that sets the input voltage to the VCO 8i4, and the output of the VCO 114 is input to a phase comparator 15 and a low-pass filter 16. A constant current circuit is constituted by PNP type transistors 17 and 18. The laser 19 has a structure in which a semiconductor laser 1 and a photodiode 2, that is, a photoelectric conversion element, are incorporated in a package 3 shown in FIG. As shown in FIG. 3, a load resistor 20 is connected to the photodiode 2 for converting the output current into voltage. The output voltage of this load resistor 20 is amplified by an inverting amplifier 21. The configuration is such that vC0222 operates in response to the output voltage of the inverting amplifier 21. 1 The operation will be explained below.

Now, depending on the value set with the variable resistor 13, the laser 1
9 is emitting light with a constant power, when the variable resistor 13 is varied to lower the output voltage, vco, 14
As the input voltage decreases, the output frequency decreases. At this time, the phase of the VCO 14 lags behind the phase of the VCO 222, so the output voltages of the phase comparator 15 and low-pass filter 16 that receive this signal decrease. Then, the output current of the constant current circuit composed of the two PNP transistors 17 and 18 increases, the voltage generated from the load resistor 20 increases, and the output voltage of the inverting amplifier 21 decreases. . And this output voltage is VCO222
Since the input voltage to VCO 114 is lowered, the output frequency of VCO 114 will necessarily decrease
The entire circuit becomes stable when the emission power of the laser 19 increases so that the output frequency and phase match. Similarly, when the output voltage is increased by varying the variable resistor 13, the entire circuit becomes stable when the emission power of the laser 19 decreases.

Note that this embodiment uses a PNP type toe in the constant current circuit.
- Since transistors 17, 18 are used, the operation is reversed to that described in the block diagram shown in FIG. That is, in the circuit shown in FIG. 2, when the output frequency of the variable frequency oscillator 4 is increased, the emission power of the semiconductor laser 10 is increased, but in the circuit shown in FIG.
The configuration is such that the emission power of the laser 19 decreases when the frequency of the laser 19 is increased. However, the operating principle is the same, so similar effects occur, and the control characteristics of the entire circuit do not change at all.

<Effects of the Invention> As explained above, according to the present invention, amplitude impulse-like noise generated in the drive circuit of the semiconductor laser is input to the semiconductor laser, thereby avoiding destruction of the semiconductor laser. . Further, when the semiconductor laser is used near the maximum rated output, it is particularly effective against the destruction of one semiconductor laser. Furthermore, even if the semiconductor laser deteriorates due to long-term use and the emission power decreases, it is easily corrected, so that stable emission power can be obtained, which is a great advantage.

[Brief explanation of the drawing]

FIG. 1 is a circuit diagram showing a configuration in which a semiconductor laser and a photodiode are incorporated in the same package, FIG. 2 is a block diagram of a semiconductor laser drive circuit showing an embodiment of the present invention, and FIG. 3 is a block diagram of a semiconductor laser drive circuit showing an embodiment of the present invention. FIG. 3 is a circuit diagram showing a specific example. 4. Variable frequency oscillator, 5. Phase comparator, 6. Voltage controlled oscillator, 7. Amplifier, 8. Low pass filter, 12. Amplifier, 9. Constant current circuit, 10. Semiconductor. Laser, 11... Photoelectric conversion element. Patent applicant Sharp Co., Ltd. Agent Patent Attorney Nishi 1) New-11-

Claims (1)

[Claims] A phase comparator that compares the reference frequency signal of the variable frequency oscillator and the frequency signal of the voltage controlled oscillator, and a constant current circuit that supplies current according to the output of this phase comparator, and is driven by the output current of this constant current circuit. 1. A semiconductor laser that is assembled into the same package as the semiconductor laser; −
It is equipped with a photoelectric conversion element that detects the emission power of the generated conductor laser, and a voltage controlled oscillator that outputs a predetermined frequency signal according to the detection output of this photoelectric conversion element, and the output frequency signal of this voltage controlled oscillator is A semiconductor laser drive circuit characterized by being incorporated into a phase comparator.