JPH0765403A - Laser diode drive - Google Patents

Abstract

(57) [Abstract] [Purpose] There is no possibility that a reverse voltage higher than the reverse rated voltage due to the supply of high frequency current for modulation is applied to the laser diode from the start of the operation of the APC loop. To do. The delay circuit 60 starts the supply of the modulation current signal IUHF from the oscillation circuit 32 to the laser diode LD at a timing after the operation of the optical output automatic control loop by the APC control circuit 31 is started.
ias is greater than or equal to a certain value, in other words, the optical output voltage signal f
It is at the time when apc exceeds the set experimental value.
In this way, there is no possibility that a reverse voltage higher than the reverse rated voltage due to the supply of the modulation current signal IUHF will be applied to the laser diode LD.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION The present invention relates to, for example, a magneto-optical (M
O) A laser diode drive device suitable for use in a disk drive.

[0002]

2. Description of the Related Art Conventionally, in an optical disk drive such as an MO disk drive, recording or reproducing processing is performed on an optical disk by using laser light output from a laser diode.

A large bias current is supplied to the laser diode during the recording process on the MO disk as compared with during the reproducing process, so that the laser light output becomes relatively large. Further, during reproduction processing on an MO disk, laser light is emitted by a combined current in which a relatively small bias current and a high-frequency current, which is a modulation current, are superimposed.

In order to perform stable recording / reproducing,
The emission output of the laser light is constantly controlled according to the recording or reproducing state. The technology to control the light output constantly is the light output automatic control technology, so-called APC (automatic power co
ntrol) technology. In the conventional APC technology, A is started from the time when the bias current is supplied to the laser diode.
The operation of the PC loop is started.

[0005]

By the way, in the case of superposing a high frequency current on a bias current at the time of reproduction processing, an AC coupling technique is adopted in order to simplify the circuit configuration. That is, for example, the high frequency signal output from the UHF band oscillator is supplied to the cathode side of the laser diode through the capacitor.

During the reproducing process, the UHF band oscillator is oscillated at the same time when the operation of the APC loop is started, and the high frequency current is supplied to the laser diode at the same time when the supply of the bias current is started.

However, in the conventional technique in which the high frequency current is supplied to the laser diode at the same time as the operation of the APC loop is started, a reverse voltage due to the supply of the high frequency current is applied to the laser diode immediately after the start. If the voltage applied in the reverse direction is equal to or higher than the reverse rated voltage of the laser diode, the laser diode may be damaged.

After a constant bias current is supplied, a high-frequency current is superimposed on the bias current to operate, so that there is no possibility that a reverse voltage is applied to the laser diode.

The present invention has been made in consideration of such a problem, and a reverse voltage higher than the reverse rated voltage due to the supply of the high frequency current as the modulation current from the start of the operation of the APC loop is generated. It is an object of the present invention to provide a laser diode driving device that has no possibility of being applied to a laser diode.

[0010]

According to the present invention, for example, as shown in FIG. 5, a laser diode LD and a light which detects a light emission L of the laser diode LD and outputs a current signal Sp according to a light emission output. Detecting means PD and current signal Sp
Current-voltage conversion means 51 for converting the voltage into a voltage signal fapc
And a first comparison means 54 for comparing the voltage signal fapc with the reference value Vref and outputting the error voltage signal Verror.
And an optical output automatic control loop means having a laser diode driving means 26 for converting the error voltage signal Verror into a current signal Ibias and supplying the current signal Ibias to the laser diode LD, and a modulation current IUHF of the laser diode LD is supplied to the laser diode LD. The light emitting output (fapc) is set after the operation of the light output automatic control loop means is started at the timing of starting the supply of the modulation current IUHF from the oscillation means 32 to the laser diode LD.
And a control means which is set after the value becomes equal to or more than the set value V ₁ .

Further, according to the present invention, as shown in FIG. 3, the control means is provided with a delay means 60 having a constant delay time td.
It is what

Further, according to the present invention, as shown in FIG.
The control means is the second comparing means 63 for comparing the light emission output (fapc) with the set value V ₁ .

Furthermore, in the present invention, as shown in FIG. 7, the control means is a third comparison means 63 for comparing the signal VLPC supplied to the laser diode drive means 26 with a set value V _2. is there.

[0014]

According to the present invention, the oscillation means 3 is controlled by the control means.
The timing of starting to supply the modulation current IUHF to the laser diode LD from 2 is set after the light emission output fapc exceeds the set value after the operation of the light output automatic control loop means is started. Therefore, there is no possibility that a reverse voltage higher than the reverse rated voltage due to the supply of the high frequency current, which is the modulation current IUHF, is applied to the laser diode LD from the start of the operation of the optical output automatic control loop. be able to.

As the control means, the delay means 60 and the second comparison means 6 for comparing the light emission output fapc with the set value V _1.
3 or the signal VLP supplied to the laser diode LD
Third comparing means 6 for comparing C with the set value V ₂
3 can be used.

[0016]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of a laser diode driving device of the present invention will be described below with reference to the drawings.

FIG. 1 shows a schematic structure of an optical disk drive to which an embodiment is applied. In FIG. 1, data or commands output from an external host computer 1 are SCSI interface 2 and controller 3.
Are stored in the buffer memory of the CPU 4 or are decoded by the CPU 4. The controller 3 interfaces the host computer 1 and the optical disk drive, and ECC (error correction code)
Encode and decode.

Reference numeral 10 is a magneto-optical (MO) disk, and the information signal recorded on the MO disk 10 is read by, for example, a 6-division photodiode constituting the optical pickup 11. The read information signal is passed through the current / voltage conversion circuit 12 to the amplification circuit 13, the amplification circuit 14, and the servo processing circuit 15 as a shaping pit signal RF, a magnetic field inversion signal MO, and a biaxial error signal FTerror which is a focus / tracking error signal. Supplied.

The servo processing circuit 15 performs focus / tracking servo of the optical pickup 11 through a biaxial device among actuators 16 having a biaxial device and a slide device based on the biaxial error signal FTerror, and at the same time, the CPU 4 or the controller 3 Based on a seek address from the encoder and a position signal from an encoder (not shown) that detects a position in the radial direction, a slide servo of the optical pickup 11 is performed through a slide device of the actuator 16.

On the other hand, the shaped pit signal RF amplified by the amplifier circuit 13 is converted into a binary signal by the pulse detection circuit 17, and P
Signal processing circuit 19 having LL and recording / reproducing processing circuit 2
Supplied to zero. As is well known, this binary signal has M
It includes a sector address, a track address, a PLL pattern, etc. of the O disk 10.

The signal processing circuit 19 creates a data read / write clock in cooperation with the voltage controlled oscillator circuit 21 based on the above-mentioned PLL pattern or the like. The data read / write clock output from the voltage controlled oscillator circuit 21 is supplied to the signal processing circuit 19 and the recording / reproducing processing circuit 20.

Then, the signal processing circuit 19 reads the address based on the data read / write clock and supplies it to the recording / reproducing processing circuit 20. The recording / reproducing processing circuit 20 determines the pulse detection circuit 1 based on this address.
The recorded data is reproduced and demodulated from the binary signal of the magnetic field inversion signal MO supplied from the circuit 8. In addition, the recording / reproducing processing circuit 20
In addition to demodulation of recording data, modulation of recording data, detection of sector mark, detection of data, ID (index)
And the data transfer with the controller 3. As described above, the reproduced and demodulated record data is temporarily stored in the buffer memory constituting the CPU 4 through the communication line 24, and then the error correction process (ECC process) is decoded by the controller 3, and then the SCSI interface is used. 2 to the host computer 1.

On the other hand, the recording data supplied from the host computer 1 and stored in the buffer memory of the CPU 4 is supplied to the recording / reproducing processing circuit 20 through the communication line 24. The recording data in the recording / reproducing processing circuit 20 is
The data is supplied to the LD driver 26 and the coil driver 27 after being subjected to predetermined modulation based on the data read / write clock. A laser diode ON signal LDON is also supplied from the recording / reproducing processing circuit 20 to the LD driver 26.

The laser diode ON signal LDON causes the laser diode constituting the optical pickup 11 to emit light, and the light output from the laser diode and the direction of the magnetic field generated by the magnetic field generating coil 29 driven by the coil driver 27 cause the MO disk 10 to emit light. Magnetically recorded. The magneto-optical recording method may be either an optical modulation method in which the MO disk 10 is magnetized in a fixed direction in advance or a magnetic field modulation method in which the magnetic field is modulated by the modulation coil 29.

For example, in the light modulation system, as is well known,
During recording, the recording film that has been magnetized in a certain direction in advance is irradiated with a laser beam, so that the recording film is heated to a temperature above the Curie point and the coercive force is lowered. When the recording film is cooled by shutting off the laser beam by controlling by the control by, the information is recorded while the direction of the applied magnetic field is stored, and the information can be recorded in the direction of the applied magnetic field. .

When reading information from the recorded MO disk 10, a modulation ON signal MODON which is a laser beam having an emission output smaller than that of the laser beam at the time of recording and which is output from the APC control circuit 31. High-frequency current signal (hereinafter, also referred to as modulation current signal) IUH which is a modulation current signal output from the oscillation circuit 32 by
A laser diode of the optical pickup 11 irradiates the MO disk 10 with a laser beam of a current superposed by F through the coupling capacitor 33, and the reflected light from the MO disk 10 is detected to determine the direction of magnetization. The recorded information is reproduced by detecting the direction of rotation of the plane of polarization.

The recorded information is reproduced by the magnetic field inversion signal MO as described above. The high frequency current signal IUHF is superimposed during the reproducing operation (reading) in order to reduce noise of the laser diode and prevent hopping of the frequency deviation of the laser diode. In this embodiment, the frequency of the high frequency current signal IUHF is selected to be about 300 MHz.

The amount of light emitted from the laser diode (emission output) is detected by, for example, a photodiode as a front monitor, which constitutes the optical pickup 11, and the optical output voltage signal fap is passed through the current-voltage conversion circuit 12.
It is supplied to the APC control circuit 31 as c. The APC control circuit 31 supplies the laser diode driver drive signal VLPC to the laser diode driver 26 based on the optical output voltage signal fapc and the like. The laser diode driver 26 uses this laser diode driver drive signal VL.
The bias current signal Ibias corresponding to the PC is supplied to the laser diode forming the optical pickup 11. The laser diode oscillates when the bias current signal Ibias exceeds a certain value, and emits laser light having an optical output according to the value of the bias current signal Ibias.

FIG. 2 shows a schematic structure of the optical pickup 11 in the optical block 9 of the optical disk drive of FIG. In FIG. 2, the laser diode LD includes
The bias current signal Ibias is supplied from the LD driver 26, and the high frequency current signal Ibias is supplied from the oscillation circuit 32.
UHF is supplied.

In this case, the bias current signal Ibias above the laser oscillation level is supplied, and the high frequency current signal IU is supplied.
When HF is supplied, the laser light L modulated by the high frequency is output from the laser diode LD. The laser light L output from the laser diode LD is collimated by the collimator lens 41. The laser light L emitted from the collimator lens 41 passes through the deflection beam splitter 42 and a part of the laser light L is converted into galvanometer mirrors 43 and 45.
The MO disk 10 is illuminated through the degree mirror 44 and the objective lens 45.

The laser light L reflected by the MO disk 10 passes through the objective lens 45, the 45-degree mirror 44, the galvanometer mirror 43, the deflecting beam splitter 42, the Wollaston prism 46, the doublet lens 47 and the multi-lens 48, and is divided into six parts. The light enters the photoelectric conversion surface of the diode 49. The laser light L incident on the photoelectric conversion surface of the six-division photodiode 49 is converted into a current signal, and then converted into a biaxial error signal FTerror through the current-voltage conversion circuit 12 (see FIG. 1) and supplied to the servo processing circuit 15. It The servo processing circuit 15 performs the above-mentioned servo processing.

On the other hand, a collimator lens 41 and a deflecting beam splitter 42 are outputted from the laser diode LD.
The remaining part of the laser light L emitted through is a photodetector and is incident on a photodiode PD as a front monitor. The photodiode PD is a laser L
Is detected and the optical output current signal Sp corresponding to the light emission output of the laser diode LD is output.

FIG. 3 shows the detailed structure of the first embodiment. Note that, in FIG. 3, components corresponding to those shown in FIGS. 1 and 2 are designated by the same reference numerals, and detailed description thereof will be omitted.

In FIG. 3, the cathode side of the photodiode PD is connected to a positive power source + V _CC , the anode side is grounded through a resistor 51, and is connected to the plus side input of a buffer 52 composed of an operational amplifier. ing. The output side of the buffer 52 is connected to the minus side input, and is also connected to the input side of the amplifier 53.

Therefore, the optical output current signal Sp corresponding to the emission output of the laser light L output from the laser diode LD.
Generates a voltage across the resistor 51, and the voltage is supplied to the input side of the amplifier 53 as the optical output voltage signal fapc through the buffer 52. In order to facilitate understanding of the embodiment, the amplification degree of the amplifier 53 is 1. When the amplification degree is 1, the amplifier 53 may be omitted.

Therefore, the optical output voltage signal fapc is
As it is, the differential amplifier is supplied to the minus side input terminal (comparison input terminal) of the comparison amplifier 54 having the amplification degree A as the first comparison means. This comparison amplifier 54
The reference value signal (reference signal) Vref is supplied from the reference value signal generating power supply 50 to the plus side input terminal (reference input terminal) of the amplifier through the amplifier 55 having an amplification factor of 1.

An error voltage signal Verror appears at the output side of the comparison amplifier 54. The error voltage signal Verror is expressed by the following equation 1.

[0038]

## EQU1 ## Error = A (Vref-fapc)

The error voltage signal Verror is supplied to the plus side input terminal of the differential amplifier 56. Differential amplifier 5
The attenuation signal Vt is supplied from the attenuation signal oscillator 57 to the negative input terminal of 6. Therefore, the differential amplifier 5
The laser diode driver drive signal VLPC shown in Expression 2 appears on the output side of 6. The attenuation signal Vt is the laser diode ON signal LD from the recording / reproducing processing circuit 20.
It is generated when ON is supplied to the control input terminal of the attenuation signal oscillator 57 through the terminal 58.

[0040]

## EQU00002 ## VLPC = Error-Vt

This laser diode driver drive signal V
The LPC is supplied to one input terminal of the laser diode driver 26. In this case, the laser diode ON signal LDON is supplied from the recording / reproducing processing circuit 20 to the other input terminal of the laser diode driver 26.

The laser diode driver 26 supplies the bias current signal Ibias corresponding to the laser diode driver drive signal VLPC to the laser diode LD after the arrival of the laser diode ON signal LDON.

In this case, since the modulation current signal IUHF is supplied from the oscillation circuit 32 to the cathode of the laser diode LD through the capacitor 33, the modulation current signal IUHF is superimposed on the bias current signal Ibias,
Laser light L generated by these combined currents is emitted from the laser diode LD.

The modulation current signal IUHF is the modulation enable signal MO supplied to the terminal 59 from a signal generation circuit (not shown) which constitutes the APC control circuit 31 (see FIG. 1).
Supply starts when the modulation ON signal MODON delayed by the delay circuit 60 having the delay time td is supplied to the control terminal of the oscillation circuit 32, and the capacitor 3
3 is supplied to the laser diode LD. As the delay circuit 60, a CR delay circuit including a capacitor and a resistor, a monostable multivibrator, or the like can be used. In this embodiment, the delay time t
d is about 300 ms.

Next, the operation of the example of FIG. 3 (embodiment 1) will be described with reference to the waveform chart shown in FIG.

When reading a recording signal from the MO disk 10 is started, as shown in FIG. 4A, first, as shown in FIG. 4A, a laser diode ON signal LDON which changes from a low level to a high level at time t ₁ (see the time axis of FIG. 4H). Is supplied from the recording / reproducing processing circuit 20 to the laser diode driver 26 and the attenuation signal oscillator 57. At the same time, at time t
The modulation enable signal MODEN (see FIG. 4B) that changes from low level to high level when 0 is supplied from the APC control circuit 31 to the input side of the delay circuit 60 through the terminal 59.
The laser diode ON signal LDON and the modulation enable signal MODEN are the same signal, and the recording / reproducing processing circuit 20
From the terminal 59 to the input side of the delay circuit 60.

A signal obtained by delaying the modulation enable signal MODEN by the delay time td in the delay circuit 60 is supplied to the control terminal of the oscillation circuit 32 as the modulation ON signal MODON (see FIG. 4G). The setting of the delay time td will be described later.

On the other hand, laser diode ON signal LDON
Is supplied to the control terminal of the decay signal oscillator 57 at time t ₁
Therefore, the attenuation signal oscillator 57 generates an attenuation signal Vt (see FIG. 4C) that monotonically decreases from a predetermined voltage level and supplies it to the negative input side of the differential amplifier 56.

From time t ₁ to time t ₂ , since the laser diode LD does not oscillate, the photodiode PD
The optical output current signal Sp detected by is approximately zero value. Therefore, from time t ₁ to time t _{2, the} optical output voltage signal f supplied to the negative input side of the comparison amplifier 54.
apc is also a zero value, and the error voltage signal Verror, which is the output signal of the comparison amplifier 54, is as shown in FIG. 4F.
It holds a constant voltage value (amplification A × reference value signal V _ref ). Therefore, during that period, a monotonically increasing signal, which is almost the inverted signal of the attenuation signal Vt, appears as the laser diode driver drive signal VLPC on the output side of the differential amplifier 56.

This laser diode driver drive signal V
Bias current signal Ibias obtained by voltage-current converting LPC
Are supplied to the laser diode LD.

Then, at time t ₂ , the laser diode LD enters the laser oscillation region and the optical output voltage signal fa
pc increases rapidly (see time point t _{2 and} after in FIG. 4E). Then, the error voltage signal Verror also sharply decreases,
The laser diode driver signal VLPC also increases sharply.

At time t ₃ when the laser diode LD is biased relatively deeply in the forward direction, the modulation ON signal MODON shifts from the low level to the high level, whereby the modulation current signal IUHF from the oscillation circuit 32 is transferred to the coupling capacitor 33. Is supplied so as to be superimposed on the bias current Ibias. After the time point t ₄ , the light emission output of the laser diode LD is held at a constant value corresponding to the reference value signal Vref. The laser diode L
At time t ₃ when D is biased relatively deeply, the modulation on signal is changed from low level (off state) to high level (on state).
The reason is that even if the laser diode LD is reverse biased on the high level side of the modulated current signal IUHF, the reverse rated voltage of the LD is not exceeded. The delay time td of the delay circuit 60 that determines the time point t ₃ can be experimentally determined by observing between both ends (cathode end and anode end) of the laser diode LD with an oscilloscope or the like.

As described above, according to the first embodiment,
The delay circuit 60 causes the modulated current signal I
After the operation of the optical output automatic control loop by the APC control circuit 31 is started (time point t ₁ ), the bias current signal I is supplied at the timing when UHF is supplied to the laser diode LD.
The time t ₃ is when the bias is a certain value or more, in other words, the optical output voltage signal fapc is a value that is the set experimental value or more. In this way, there is no possibility that a reverse voltage higher than the reverse rated voltage due to the supply of the modulation current signal IUHF will be applied to the laser diode LD.

FIG. 5 shows the configuration of the second embodiment. Figure
FIG. 6 is a waveform diagram provided for explaining the operation of the second embodiment. This
In the second embodiment, the delay circuit 60 of the first embodiment is replaced.
Then, the comparator 63 as the second comparison means and this comparison
Comparison result signal S which is an output binary signal of the device 63 ₂And terminal 5
With the modulation enable signal MODEN supplied from
An AND circuit 64 that takes a logical product is used. and
The output signal of the circuit 64 is generated as the modulation ON signal MODON.
It is supplied to the vibration circuit 32.

In the second embodiment, the comparator 63 compares the optical output voltage signal fapc with the set value signal V ₁ which is a DC voltage supplied from the set value signal generating power supply 65, and as shown in FIG. 6E. Then, when the voltage value of the optical output voltage signal fapc exceeds the set value signal V ₁ (time point t ₃ ), the comparison result signal S ₂ (see FIG. 6G) shifts from the low level to the high level. The comparison result signal S ₂ is supplied to the oscillation circuit 32 as the modulation ON signal MODON through the AND circuit 64, so that the modulation current signal IUHF is superimposed on the bias current signal Ibias.

According to the second embodiment, the optical output current signal fapc of the laser diode LD is directly compared with the set value signal V ₁ . Therefore, the modulation current signal IUH must be biased after the laser diode LD is biased relatively deeply.
Since F is supplied, in other words, the modulation current signal IUHF is supplied after the reverse bias voltage due to the modulation current signal IUHF becomes within the reverse rated voltage of the laser diode LD. Excellent as compared to Example 1. In the second embodiment, when the modulation enable signal MODEN is not used, the AND circuit 64 may be omitted and the output of the comparator 63 may be directly connected to the control input terminal of the oscillation circuit 32.

FIG. 7 shows the configuration of the third embodiment. FIG. 8 is a waveform diagram provided for explaining the operation of the third embodiment. In the third embodiment, the comparison input terminal of the comparator 63 of the second embodiment is connected to the output side of the differential amplifier 56, and the laser diode driver signal VLPC is used as the comparison signal. In response to this, the reference value input terminal of the comparator 63 as the third comparing means is supplied with the set value signal V ₂ which is a DC voltage from the set value signal generating power supply 65.

Also in this third embodiment, FIG. 8D and FIG.
As can be seen from G, the result is a laser diode LD
When the optical output voltage signal fapc of No. 2 becomes higher than a certain value, the comparison result signal S ₃ which is the output signal of the comparator 63 is inverted, and the modulation current signal IUHF is supplied from the oscillation circuit 32 to the laser diode. Become. In addition, this Example 3
Also in the above, if the modulation enable signal MODEN is not used, the AND circuit 64 may be omitted and the output of the comparator 63 may be directly connected to the control input terminal of the oscillation circuit 32.

As described above, according to the first to third embodiments,
There is no possibility that a reverse voltage higher than the reverse rated voltage due to the supply of the modulation current signal IUHF will be applied to the laser diode LD.

The present invention is not limited to the above-mentioned embodiment of the disk drive, and does not depart from the gist of the present invention.
Of course, various configurations such as application to an image recording / reproducing apparatus using a laser can be adopted.

[0061]

As described above, according to the present invention, the timing for starting the supply of the modulation current from the oscillation means to the laser diode by the control means is set after the operation of the optical output automatic control loop means is started. After the light output exceeds the set value. Therefore, there is no possibility that a reverse voltage higher than the reverse rated voltage will be applied to the laser diode due to the supply of the high frequency current that is the modulation current from the start of the operation of the optical output automatic control loop. The effect of being able to be achieved is achieved.

As the control means, the delay means, the second comparing means for comparing the light emission output with the set value, or the third comparing means for comparing the output signal of the first comparing means with the set value.
The comparison means may be used.

[Brief description of drawings]

FIG. 1 is a block diagram showing a schematic configuration of an example of an optical disk drive to which an embodiment of a laser diode driving device according to the present invention is applied.

FIG. 2 is a diagram showing a detailed configuration of the optical pickup in the example of FIG.

FIG. 3 is a circuit block diagram showing a basic configuration of a first embodiment of a laser diode driving device according to the present invention.

FIG. 4 is a waveform diagram provided for explaining the operation of the first embodiment.

FIG. 5 is a circuit block diagram showing the basic configuration of a second embodiment of the laser diode driving device according to the present invention.

FIG. 6 is a waveform diagram provided for explaining the operation of the second embodiment.

FIG. 7 is a circuit block diagram showing a basic configuration of a third embodiment of the laser diode driving device according to the present invention.

FIG. 8 is a waveform diagram provided for explaining the operation of the third embodiment.

[Explanation of symbols]

 11 Optical Pickoff 26 LD Driver 54 Comparison Amplifier 56 Differential Amplifier 57 Attenuation Signal Generator 60 Delay Circuit LD Laser Diode PD Photodiode fapc Optical Output Voltage Signal Ibias Bias Current Signal IUHF Modulation Current Signal LDON Laser Diode On Signal MODEN Modulation Enable Signal MODON Modulation ON signal Error Error voltage signal Vref Reference value signal

Claims (4)

[Claims] 1. A laser diode, photodetection means for detecting emitted light of the laser diode and outputting a current signal according to the light emission output, current-voltage conversion means for converting the current signal into a voltage signal, and the voltage. Automatic optical output control having first comparing means for comparing a signal and a reference value to output an error voltage signal, and laser diode driving means for converting the error voltage signal into a current signal and supplying the current signal to the laser diode. The loop means, the oscillating means for supplying the laser diode modulating current to the laser diode, and the timing for starting the supplying of the modulating current from the oscillating means to the laser diode are the operation of the optical output automatic control loop means. And a control means for controlling the emission output after the emission output becomes equal to or more than a set value. Drive. 2. The laser diode driving device according to claim 1, wherein the control means is a delay means having a constant delay time. 3. The laser diode drive apparatus according to claim 1, wherein said control means is second comparison means for comparing said light emission output with a set value. 4. The laser diode drive device according to claim 1, wherein said control means is third comparison means for comparing a signal supplied to said laser diode driver with a set value.