JPH06274919A - Semiconductor laser driving controller - Google Patents

Abstract

PURPOSE:To ensure the service life of a semiconductor laser (LD), and to stabilize a recording and reproduction signal by appropriately controlling the amplitude of high frequency superimposing currents according to the oscillation intensity of an LD at the time of superimposing high frequency currents, and driving the LD in order to remove a noise resulted from a return light or the like. CONSTITUTION:A laser control circuit 141 receives the output of a light receiving element PD which detects the output of an LD 9, and supplies a laser control signal (LS) to the base of a transistor(Tr) Q1. In the Tr Q1, laser driving currents (ia) according to the LS are allowed to run, an emitter potential V is turned to a value corresponding to the currents (ia), and the output of a high frequency oscillator as high frequency currents (ic) amplified by a Tr Q2 is superimposed on the currents (ia). At that time, when the LS is allowed to emit a light by a low or high power by the LS, the amplification factor of the Tr Q2 is increased or decreased by the Tr Q1 and Q3, and the amplitude of the currents (ic) is increased or decreased. Thus, the amplitude of the currents (ic) can be appropriately controlled according to the emission intensity of the LD 9, the service life of the LD can be ensured, and the recording and reproduction signal can be stabilized.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical information recording / reproducing device, and more particularly to improvement of a semiconductor laser drive control device thereof.

[0002]

As is well known, in an optical information recording / reproducing apparatus, a semiconductor laser (laser diode: hereinafter simply referred to as LD) is used for recording / reproducing information on / from an optical recording medium such as an optical disk. That is, LD
By irradiating the optical recording medium with the laser light from the optical system through the objective lens, recording and reproducing of predetermined information is performed.

In this case, the LD drive circuit drives the LD with a large pulse current corresponding to the information to be recorded at the time of recording information, and drives the LD with a required DC current at the time of reproducing information. . By the way, such a drive current of the LD has a great influence on the life of the LD. Therefore, the LD drive circuit is required to be capable of strictly controlling the drive current of the LD.

On the other hand, the reflected light component from the optical recording medium is LD
The so-called return light, which is injected into the laser, adversely affects the laser light emitting operation of the LD and is a major cause of generation of undesired noise in recording and reproducing information.

Therefore, a recent LD drive circuit superimposes a high frequency current of, for example, 1 GHz on the drive current of the LD so as to emit a laser beam, so that the noise due to the return light as described above is generated. I am trying to remove it.

[0006]

However, in the LD driving circuit based on such a high frequency superposition method, as shown in FIG. 4, the high frequency current C having a constant amplitude is always superposed regardless of the emission intensity of the LD. Therefore, as shown by C2 in FIG. 4, there is a drawback that the peak value remarkably rises to a large power level particularly at high power emission, and the life of the LD is significantly impaired so as to cause destruction of the LD.

Therefore, the present invention has been made in view of the above points, and when the LD is driven by superimposing a high frequency current in order to remove the noise caused by the returning light, L
A semiconductor laser drive control device improved so as to secure the life of the LD and contribute to stabilization of the recording / reproducing signal by controlling the high frequency superimposed current to have an appropriate amplitude according to the emission intensity of D. Is intended to provide.

[0008]

In order to solve the above-mentioned problems, according to the present invention, high-frequency means for outputting a predetermined high-frequency signal, a semiconductor laser for irradiating a predetermined object with laser light, and said semiconductor A laser control means for generating a laser current control signal corresponding to a laser beam from a laser, a laser current supplied to the semiconductor laser according to a laser current control signal from the laser control means, and a high frequency from the high frequency means. There is provided a semiconductor laser drive control device comprising: a laser drive unit that varies an output and superimposes it on the set laser current.

[0009]

According to the above-mentioned solution means, the amplitude of the high frequency output from the high frequency oscillator is changed in accordance with the laser current control signal corresponding to the laser current to be detected in order to cause the laser to emit the prescribed amount of light. That is, during low-power light emission, the amount of superposition of high-frequency current increases, the light emission operation of the semiconductor laser is stable, and noise generation can be suppressed. Further, during high-power light emission, the amount of superposition of high-frequency current is small, and the maximum output rating of the semiconductor laser is not exceeded, so that the life can be secured.

[0010]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings. FIG. 1 shows a case where it is applied to an optical information recording / reproducing apparatus as an example. In FIG. 1, grooves (tracks) are formed on the surface of an optical disk (optical recording medium) 1 in a spiral shape or a concentric shape. The optical disk 1 is rotated by a motor 2 at a constant speed, for example. The motor 2 is controlled by a motor control circuit 18. Recording and reproduction of information with respect to the optical disc 1 is performed by the optical head 3. The optical head 3 is fixed to a drive coil 13 that constitutes a movable part of a linear motor. The drive coil 13 is connected to the linear motor control circuit 17. This linear motor control circuit 17 includes a linear motor position detector 26
Are connected. This linear motor position detector 26
Detects the optical scale 25 provided on the optical head 3 and outputs a position signal.

A permanent magnet (not shown) is provided in the fixed portion of the linear motor, and the drive coil 13 is excited by the linear motor control circuit 17 so that the optical head 3 moves in the radial direction of the optical disk 1. It is supposed to be moved to. An objective lens 6 is held on the optical head 3 by a leaf spring (not shown).

The objective lens 6 is moved in the focusing direction (optical axis direction of the lens) by the drive coil 5, and is movable in the tracking direction (direction orthogonal to the optical axis of the lens) by the drive coil 4.

Laser light generated by a semiconductor laser (laser diode: LD) 9 as a light source driven by the laser control circuit 141 and the laser drive circuit 142 is collimator lens 11a and half prism 11.
b, the light is irradiated onto the optical disc 1 through the objective lens 6.

The reflected light from the optical disk 1 is guided to the half prism 11c via the objective lens 6 and the half prism 11b, and one light split by the half prism 11c is paired via the condenser lens 10. Is guided to the tracking position sensor 8. The other light split by the half prism 11c is guided to the pair of focus position sensors 7 via the condenser lens 11d and the knife edge 12. The output signal of the tracking position sensor 8 is supplied to the tracking control circuit 16 via the differential amplifier OP1.

The track difference signal (differential signal) output from the tracking control circuit 16 is supplied to the linear motor control circuit 17 and also to the drive coil 4 in the tracking direction via the amplifier 27. Further, the focus position sensor 7 outputs a signal regarding the focus point of the laser light. This signal is supplied to the focusing control circuit 15 via the differential amplifier OP2.

The output signal of the focusing control circuit 15 is supplied to the focusing drive coil 5 via the amplifier 28.
And is controlled so that the laser beam is always in perfect focus on the optical disc 1.

The sum signal of the outputs of the tracking position sensor 8 in the state where focusing and tracking are performed as described above is the pit (recording information) formed on the track.
The unevenness of is reflected. This signal is supplied to the data signal processing circuit 19, and the information is reproduced in this data signal processing circuit 19.

The laser control circuit 14, focusing control circuit 15, tracking control circuit 16, linear motor control circuit 17, motor control circuit 18, data signal processing circuit 19 and the like are controlled by the CPU 23 via the bus line 20. It has become so. The CPU 23 is adapted to perform a predetermined operation according to a program stored in the memory 24.

Numerals 21 and 22 are A / D converters and D / A converters used for exchanging information between the focusing control circuit 15, the tracking control circuit 16, the linear motor control circuit 17 and the CPU 23, respectively. It is a vessel.

Further, a light receiving element (laser monitor diode) PD as a detecting means for detecting the amount of light emitted from the semiconductor laser 9 is provided in the vicinity of the semiconductor laser 9, and the detection output by the light receiving element PD is as described above. It is adapted to be supplied to the laser drive circuit 142 via the laser control circuit 141. FIG. 2 shows the laser control circuit 141.
It shows the details of. The anode of the light receiving element PD is grounded, and the cathode is connected to the inverting input terminal of the operational amplifier IC ₁ . The non-inverting input terminal of the operational amplifier IC ₁ is grounded.

[0021] The output terminal IC ₁ 'to the operational amplifier via a variable resistor (first adjusting means) Rf for adjusting the photocurrent of the light receiving element PD, is connected to the inverting input of the operational amplifier IC ₁ In addition, it is connected to the fixed contact S ₂₁ of the switch circuit IC ₂ controlled by the CPU 23.

The fixed contact S ₂₂ constituting the switch circuit IC ₂ is grounded via the power source −ES ₁ , as shown in the figure, and the movable contact S ₂₃ is connected to the operational amplifier IC via the resistor R _1.
It is connected to the inverting input terminal ₃ and to the negative electrode of a resistor R ₂ and a power source -E _S2 (second adjusting means) capable of varying the voltage. The positive electrode is grounded to the power source -E _S2. This power -E _S2 is adjusted to the emission threshold of the semiconductor laser 9 is made.

The non-inverting input terminal of the operational amplifier IC ₃ is grounded, the output terminal thereof is connected to the inverting input terminal of the operational amplifier IC ₃ via a resistor R ₃ , and the recorded information from the CPU 23 is recorded. Is connected to a fixed contact S ₄₁ of a switch circuit IC ₄ used for on / off control of a laser beam emitted according to the recording signal corresponding to.

The fixed contact S ₄₂ which constitutes the switch circuit IC ₄ is grounded, and the movable contact S ₄₃ determines the feedback characteristic through the resistor R ₄ and the capacitor C to determine the non-operation of the operational amplifier IC ₅ . It is connected to the inverting input terminal.

The inverting input terminal of the operational amplifier IC ₅ is connected to the movable contact S ₄₃ of the switch circuit IC ₄ and also to the emitter of the transistor Q1 of the laser drive circuit 142 described later via the resistor R ₅ . The output terminal is connected to the cathode of the semiconductor laser 9 as a laser current control signal output terminal through the base collector of the transistor Q1 of the laser driving circuit 142. The anode of the semiconductor laser 9 is connected to the power supply V _CC .

On the other hand, the connection point a between the movable contact piece S ₂₃ of the switch circuit IC ₂ and the resistor R ₁ is connected to the inverting input terminals of the operational amplifier IC ₆ and the operational amplifier IC ₇ , respectively.

The non-inverting input terminal of the operational amplifier IC ₆ is
Of the resistors R ₆ , R ₇ , and R ₈ connected between the power source V _EE and the ground, they are connected to the connection point between the resistors R ₆ and R ₇ . The non-inverting input terminal of the operational amplifier IC ₇ is connected to the connection point between the resistors R ₇ and R ₈ .

A reference voltage is set for each of the operational amplifiers IC ₆ and IC ₇ by the resistors R _{6 to} R ₈ . That is, according to the set reference voltage and the voltage at the connection point a, the operational amplifier IC ₆
From the operational amplifier IC ₇ and a ready signal from the operational amplifier IC ₇ to the CPU 23.
In the above structure, normally, as shown in FIG. 2, the switch circuit IC ₂ controls the movable contact piece S by the control of the CPU 23.
₂₃ is connected to the fixed contact S ₂₁ . In addition, the switch circuit I
C ₄ is the control of the CPU 23, the movable contact piece S ₄₃ is the fixed contact S ₄₁ for example in response to a recording signal corresponding to recording information
Connected to. Therefore, the transistor Q1 of the laser drive circuit 142 is turned on via the operational amplifier IC ₅ , and the semiconductor laser 9 emits light with a predetermined output.

The laser light emitted by the semiconductor laser 9 is applied to the optical disc 1 to contribute to the recording or reproduction of the record information, and is detected by the light receiving element PD. That is, when the semiconductor laser 9 emits light, a photocurrent flows through the light receiving element PD according to the amount of emitted light. If this photocurrent is i _M , a voltage of −I _M Rf appears at the connection point a between the movable contact piece S ₂₃ of the switch circuit IC ₂ and the resistor R ₁ . Thus, the voltage at the connection point b between the output terminal and the switch circuit fixed contact S ₄₁ of IC ₄ of the operational amplifier IC ₃ is, I _M Rf - a _{- (E S2) = I M} Rf + E S2.

[0030] Thus, the semiconductor laser 9, via the laser drive circuit 142, the voltage I _M Rf + laser current i _L flows by laser current control signal corresponding to the E _S2, the semiconductor laser 9 by the laser current i _L is The emission is controlled. However, in practice, the laser drive circuit 14 described later
2, the high frequency current is superimposed on the laser current i _L. Here, when the light amount of the semiconductor laser 9 decreases, the photocurrent i _M flowing through the light receiving element PD decreases. Therefore, the voltage at the connection point _{a (I M Rf + E S2} )
Is lowered. In this case, the operational amplifier IC ₅ is an inverting amplifier. Therefore, the laser current control signal for the semiconductor laser 9 is directed to increase the laser current i _L in reverse, so that the emission intensity of the semiconductor laser 9 is increased.
When the emission intensity of the semiconductor laser 9 increases,
On the contrary, the photocurrent i _M of the light receiving element PD increases and the voltage (I _M Rf + E _S2 ) at the connection point a increases. Therefore, since the laser current control signal is directed to decrease the laser current i _L , the emission intensity of the semiconductor laser 9 is reduced.

As described above, in the laser control circuit 141,
By performing negative feedback control according to the output of the light receiving element PD, for example, when the light amount of the semiconductor laser 9 is decreased, the light amount is increased, and when the light amount of the semiconductor laser 9 is increased, The amount of light is reduced to output a laser current control signal that makes the amount of light emitted from the semiconductor laser 9 constant.

On the other hand, at the time of adjustment, in the switch circuit IC ₂ , the movable contact S ₂₃ of the switch circuit IC ₂ is controlled by the CPU _{23 and the} fixed contact S _22.
In the switch circuit IC ₄ , the movable contact piece S ₄₃ is connected to the fixed contact S _{41 under} the control of the CPU 23. In this state, the power source -E _S2 is adjusted so that the semiconductor laser 9 emits light with a specified light amount. Thereby, the emission threshold of the semiconductor laser 9 is adjusted.

Then, the variable resistor Rf is adjusted to adjust the output end of the operational amplifier IC ₁ and the fixed contact S of the switch circuit IC _2.
Voltage at the connection point c between ₂₁ to be the same as the voltage of the power source -E _S1 (pseudo monitor signal). Thereby, the photocurrent of the light receiving element PD is adjusted. Then, after the adjustment, switching to the fixed contact S ₂₁ side movable contact piece S ₂₃ of the switching circuit IC ₂ by the control of the CPU 23. Thus, the system is to be operating normally, the voltage of the connection point a relative specific light amount of the semiconductor laser 9 is set to -E _S1.

[0034] Thus, by adjusting the power -E _S2 and a variable resistor Rf individually, independently 3-5 fold variation in with the photocurrent of the light-emitting threshold and the light receiving element PD of the semiconductor laser 9 Can be corrected. As a result, the voltage at the connection point a can be accurately made to correspond to the light emission amount of the semiconductor laser 9. Therefore, the detected value of the ready signal can be increased to about 80% of the normal value, and the detected value of the alarm signal can be increased to about 150% of the normal value.

Therefore, various troubles caused by abnormal light emission of the semiconductor laser 9, for example, possibility of damaging a recording film (not shown) of the optical disk 1 due to excessive output light emission can be avoided with high accuracy. Become.

Further, by switching to the pseudo monitor signal (-E _S1 ), it is possible to easily adjust the variation of the light emission threshold of the semiconductor laser 9 and the photocurrent of the light emitting element PD, and thus the connection point a. The voltage of can be set accurately and quickly.

Therefore, for example, when the gain of the photocurrent of the light receiving element PD is increased, the output of the semiconductor laser 9 is decreased, and the light emission threshold of the semiconductor laser 9 and the light of the light receiving element PD which are not independent in one system. It is possible to solve various problems that occur when the electric current and the electric current are individually adjusted, and to make these adjustments easy. Next, the laser drive circuit 142 as an essential part of the present invention will be described with reference to FIG.

In FIG. 3, the laser drive circuit 142 for driving the semiconductor laser 9 by receiving the laser current control signal from the laser control circuit 141 as described above and superposing the high frequency current on the corresponding laser current i _L , The output terminal of the laser control circuit 141 includes a transistor Q1 whose base is connected.

The collector of the transistor Q1 is connected to the cathode of the semiconductor laser 9 and the capacitor C
It is connected via 11 to the collector of the transistor Q2. The emitter of the transistor Q1 is a resistor R11.
It is connected to the base of the transistor Q3 via a resistor R12 while being grounded via. The emitter of the transistor Q2 is grounded, and the collector thereof is connected to the power supply V _CC through the inductance L11. The transistor Q3 has its emitter grounded and its collector connected to the base of the transistor Q2.

The collector of the transistor Q3 is connected to the power supply V _CC via the resistor R13 and is also connected to the output terminal of the high frequency oscillator RF OSC via the capacitor C11.

When the laser current control signal is supplied to the base of the transistor Q1 in the above configuration, the laser drive current i _a (the laser current I described above) corresponding thereto is supplied.
₍ Corresponding to _L ) is determined, and the emitter potential V of the transistor Q1 becomes a value corresponding to the laser drive current i _a . The output of the high frequency oscillator RF OSC is superimposed on the laser drive current i _a as the high frequency current i _c amplified by the transistor Q2. Now, the laser current control signal from the laser control circuit 141 is transmitted to the semiconductor laser 9
Is at a level to emit light with low power.

At this time, since the emitter potential V of the transistor Q1 drops, the collector current of the transistor Q3 decreases and the base current of the transistor Q2 increases. That is, at this time, since the amplification factor of the transistor Q2 is increased, the amplitude of the high frequency current i _c is increased.

That is, at this time, in the laser characteristic diagram shown in FIG. 4, since the laser current is centered on a and the high frequency current C is superimposed on it, the laser emission intensity is centered on a'at a low power level. Is given by the amplitude C1. It should be noted that the generation of signal noise during recording and reproduction during light emission at a low power level is improved by superposition of high frequencies. Next, it is assumed that the laser current control signal from the laser control circuit 141 is at a level at which the semiconductor laser 9 emits light with high power.

At this time, since the emitter potential V of the transistor Q1 rises, the collector current of the transistor Q3 increases and the base current of the transistor Q2 decreases. That is, at this time, since the amplification factor of the transistor Q2 is lowered, the amplitude of the high frequency current i _c is reduced.

That is, at this time, in the laser characteristic diagram shown in FIG. 4, since the laser current is centered on b and the high frequency current d is superposed on it, the laser emission intensity is centered on b'at a low power level. Is given by the amplitude d1. It should be noted that the signal noise of recording and reproduction at the time of light emission of this high power level has a relatively small value as shown in FIG.

As described above, the laser drive circuit 1 of the present invention
Reference numeral 41 changes the amplitude of the high frequency output from the high frequency oscillator RF OSC according to the laser current control signal corresponding to the laser current to be detected in order to cause the laser to emit a prescribed amount of light. That is, at the time of low-power light emission, the amount of superposition of the high-frequency current i _c increases, the light emitting operation of the semiconductor laser 9 becomes stable, and noise generation can be suppressed.

Further, at the time of high power emission, the high frequency current i
_Since the amount of superposition of _c is reduced, the maximum output rating of the semiconductor laser is not exceeded, and the life can be secured. The present invention is not limited to the above-mentioned embodiments, and it goes without saying that various modifications can be made without departing from the spirit of the present invention.

[0048]

As described above, according to the present invention, when the LD is driven by superimposing a high frequency current in order to remove the noise caused by the returning light or the like, the emission intensity of the LD is reduced. Accordingly, by controlling the high-frequency superimposed current so as to have an appropriate amplitude, it is possible to provide a semiconductor laser drive control device improved so as to secure the life of the LD and contribute to the stabilization of the recording / reproducing signal. It will be possible.

[Brief description of drawings]

FIG. 1 is a configuration diagram showing an embodiment of the present invention.

FIG. 2 is a detailed view of a part of FIG.

FIG. 3 is a detailed view of a part of FIG.

FIG. 4 is a characteristic diagram showing an operation and an effect of the present invention in correspondence with a conventional one.

[Explanation of symbols]

1 ... Optical disc, 3 ... Optical head, 9 ... Semiconductor laser,
141 ... Laser control circuit, 142 ... Laser drive circuit, I
C ₁ , IC ₃ , IC ₅ , IC ₆ , IC ₇ ... Operational amplifier,
IC ₂ , IC ₄ ... switch circuit, PD ... light receiving element, Rf
... variable resistance, -E _S2 ... power, TR, Q1, Q2, Q3 ...
Transistor, RF OSC ... High frequency oscillator, R11,
R12, R13 ... resistors, C11, C12 ... capacitors,
L11 ... Inductance, _Vcc ... Power supply.

Claims (1)

[Claims] 1. A high-frequency means for outputting a predetermined high-frequency signal, a semiconductor laser for irradiating a predetermined object with laser light, and a laser control means for generating a laser current control signal corresponding to the laser light from the semiconductor laser. And a laser drive means for setting a laser current to be supplied to the semiconductor laser according to a laser current control signal from the laser control means and varying a high frequency output from the high frequency means to superimpose on the set laser current. A semiconductor laser drive control device comprising: