JP2004022704A - Control circuit for semiconductor laser light output - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an APC circuit by which a pull-in time is reduced and an influence from the disturbance of an APC loop is reduced. <P>SOLUTION: In the APC circuit, a comparing and amplifying means for comparing a set output by an optical output setting means with a detected output of an optical output of a semiconductor laser by an optical output detection means to output the compared result comprises two systems of comparing and amplifying means which differentiate the loop band of a circuit. The band is set wide in a pull-in operation in a semiconductor laser light output control circuit, and the band is set narrow in the other operation. <P>COPYRIGHT: (C)2004,JPO

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a semiconductor laser light output control circuit.
[0002]
[Prior art]
Semiconductor lasers are extremely small and respond quickly, and are therefore widely used as light sources for optical disk devices, optical communication devices, and laser printers.
[0003]
Among rewritable optical disks used in the above optical disk apparatuses, phase-change optical disks and magneto-optical disks are widely known as rewritable optical disks. These optical disks have different laser beam outputs when recording, reproducing and erasing. I have.
[0004]
For example, a phase-change optical disc records data by changing the crystal structure using laser light, and utilizes "0" and "0" based on the fact that the reflectivity differs depending on the change in crystal structure (crystal or amorphous). 1 "is recorded.
[0005]
During recording, the output of the laser beam is increased (for example, 30 mW or more) in order to form recording marks called pits on the optical disk, and during reproduction, information is read out without destroying the pits. A laser beam having a low output (for example, about 3 mW) is applied to the optical disc.
[0006]
Regarding recording, mark edge recording for recording changes at both ends of a recording mark and mark position recording for placing information at the center position of the recording mark are known. Research on rewritable phase-change optical disks using edge recording is in progress.
[0007]
A write strategy is known as a modulation technique for suppressing a data error due to a shape distortion of a mark in the mark edge recording. This technology divides a recording waveform by a laser beam into a plurality of short pulses and irradiates the laser beam with the laser beam. It suppresses heat accumulation at the rear end of the recording mark and causes a tear-drop phenomenon of the recording mark (the rear portion of the recording mark is (Which is wider than the front) and distortion of the recording mark is eliminated.
[0008]
FIG. 8 shows an example of the write strategy. Note that T in the drawing indicates a bit period of one bit of the recording data.
[0009]
The laser drive waveform is a modulation waveform that combines pulse width modulation and intensity modulation.It uses multiple laser pulses with three types of power levels, changes the number of pulses according to the recording mark length to be created, and changes the pulse width and level. By setting the width optimally, an optimum recording mark can be formed.
[0010]
If the three types of power levels are a peak level, an erase level, and a cool level in descending order, irradiating the disk with the laser light of the peak level melts the recording film of the disk, and then quenches (cool level), and An amorphous (non-crystalline) state having a low reflectance is obtained. This is used as a recording mark.
[0011]
When the disk is irradiated with the erase level laser light, the recording film becomes crystalline. That is, the portion that was in an amorphous state before the irradiation with the laser beam becomes a crystalline state, and the portion that was originally in the crystalline state remains in the crystalline state, so that the recording mark can be erased and overwriting (overwriting) Rewriting).
[0012]
On the other hand, in order to obtain an error rate at which recording and reproduction can be performed on a recent high-density, high-transfer-rate optical disk, it is necessary to sufficiently control the laser beam intensity in each of the modes (reproduction, recording, and erasure). . However, since a semiconductor laser has a remarkable change in temperature characteristics of drive current versus optical output characteristics, an APC (Auto Power Control) circuit, a so-called semiconductor laser optical output control circuit, is required to set the optical output to a desired intensity. Become.
[0013]
This APC circuit is roughly classified into the following two types.
[0014]
1) Sample hold method
This is because the light output of the semiconductor laser is monitored by a photodiode during a power setting period called an ALPC section to be described later, and the light receiving current (proportional to the light output of the semiconductor laser) generated in this photodiode is equal to the light emission command signal. Thus, an optical / electrical negative feedback loop for controlling the drive current of the semiconductor laser is formed, and the control value of the drive current is held even in the ALPC section other than the ALPC section. And modulates it.
[0015]
2) Real-time method
This is because the light output of the semiconductor laser is monitored by a photodiode, and the drive of the semiconductor laser is constantly performed so that the light receiving current (proportional to the light output of the semiconductor laser) generated in the photodiode is equal to the light emission command signal. This constitutes an optical / electrical negative feedback loop for controlling current.
[0016]
FIG. 10 shows the sample hold APC circuit.
[0017]
In the figure, LD1 is a semiconductor laser that outputs a laser beam for irradiating the optical disk, PD2 is a photodiode that monitors the optical output of the semiconductor laser LD1, and 3 is a monitor that converts a monitor current IPD output from the photodiode PD2 into a voltage. Current-voltage conversion circuit, 4 is an error amplifier, 5 is an optical power setting voltage switch circuit, 6 ₁ , 6 ₂ ... 6 _n Is the optical power setting voltage, 7 ₁ , 7 ₂ ... 7 _n Is a sample hold circuit, 8 ₁ , 8 ₂ ... 8 _n Is the sample hold circuit 7 ₁ , 7 ₂ ... 7 _n Hold circuit control terminals respectively provided in ₁ , 9 ₂ ... 9 _n Is a voltage-current conversion circuit, 10 is a switch circuit, and 11 is a driver including a current amplifier.
[0018]
The error amplifier 4 includes an output voltage of the current-voltage conversion circuit 3 and an optical power setting voltage 6. ₁ , 6 ₂ ... 6 _n Is detected and output as an error voltage. The optical power setting voltage switch circuit 5 has an optical power setting voltage 6. ₁ , 6 ₂ ... 6 _n Is selected and output, and the same optical power setting voltage 6 ₁ , 6 ₂ ... 6 _n Is a set voltage for setting the laser power.
[0019]
Sample hold circuit 7 ₁ , 7 ₂ ... 7 _n Is a circuit for holding the error voltage output from the error amplifier 4. The sample-and-hold circuit 7 ₁ , 7 ₂ ... 7 _n The sample gate signal for controlling the hold operation of the hold circuit control terminal 8 ₁ , 8 ₂ ... 8 _n Is input to
[0020]
Voltage-current conversion circuit 9 ₁ , 9 ₂ ... 9 _n Is the sample hold circuit 7 ₁ , 7 ₂ ... 7 _n Is converted into a current signal, and the switch circuit 10 is connected to the voltage / current conversion circuit 9 ₁ , 9 ₂ ... 9 _n The output is switched.
[0021]
The driver 11 is a voltage-current conversion circuit 9 switched by the switch circuit 10. ₁ , 9 ₂ ... 9 _n Amplifies the current signal output from the semiconductor laser LD1 to drive the semiconductor laser LD1. Further, the switch circuit 10 is provided with a control terminal (not shown) to which a switching timing signal for controlling the switching operation of the switch circuit 10 is input.
[0022]
Next, the operation of the sample-and-hold APC circuit will be described. For example, in the magneto-optical disk format, as shown in FIG. 9A, an address section and a power section are arranged before the data section (recording area) of each sector. The ALPC (Auto Laser Power Control) section, which is a set period, is provided.
[0023]
Address information of the sector is recorded in the address section. The address information is read in the reproduction mode, and in the section of the ALPC section, power levels for reproduction, erasure, and recording are set. In other sections, the sample and hold circuit 7 selected by the switch circuit 10 ₁ , 7 ₂ ... 7 _n Voltage-current conversion circuit 9 based on the control value held by ₁ , 9 ₂ ... 9 _n Causes the semiconductor laser LD1 to emit light in accordance with the current value output by.
[0024]
According to this method, the set value is determined by causing the semiconductor laser to emit DC light in the ALPC section. FIGS. 9B to 9E show power setting selection signals in the ALPC section, and FIG. 9F shows optical output waveforms set in the ALPC section.
[0025]
In the sample-and-hold method described above, the monitor current IPD, which is the light-receiving current of the photodiode PD2 that has received the optical output, is converted into a voltage by the current-voltage conversion circuit 3, and the voltage and the voltage are selected by the optical power setting voltage switch circuit 5. The optical power setting voltage 6 ₁ Are input to the error amplifier 4. At this time, the sample and hold circuit 7 ₁ Is the hold circuit control terminal 8 ₁ As a result, the sampling state is selected and the negative feedback loop is closed. As a result, negative feedback is applied so that the + and-input voltages of the error amplifier 4 are balanced, and the output voltage of the error amplifier 4 is determined.
[0026]
The control voltage output from the error amplifier 4 is converted to a voltage / current conversion circuit 9 ₁ , And is amplified by the driver 11 to drive the semiconductor laser LD1.
[0027]
That is, the hold circuit control terminal 8 ₁ The sample gate signal input to the input terminal is set to the high level, and the output voltage of the current-voltage conversion circuit 3 and the optical power setting voltage 6 ₁ The semiconductor laser LD1 is driven based on the control voltage output from the error amplifier 4 to set the laser power.
[0028]
Then, by setting the band of the negative feedback loop to a wide band of about several MHz, the setting of the laser power is sufficiently performed in 1 μs. The control voltage of the laser power is applied to the hold circuit control terminal 8. ₁ The sample and hold circuit 7 is set by setting the sample gate signal applied to the ₁ Is held. In the same manner, setting of other optical powers is performed in the same manner. Thereafter, in the data section (recording area) of the sector, the voltage-current conversion circuit 9 generated by the held control voltages is used. ₁ , 9 ₂ ... 9 _n Is switched by the switch circuit 10, the semiconductor laser LD1 can be controlled.
[0029]
However, in the above-described APC circuit of the sample-and-hold method, although the loop bandwidth is set to a wide band of about several MHz, the setting for the laser power is sufficiently performed in 1 μs. Since several μs is considerably longer than the generation period of the laser pulse at the time of recording, it affects the life of the semiconductor laser LD1. Further, since the data section in the magneto-optical disk format is in the hold state, the temperature droop characteristic and the relaxation oscillation of the semiconductor laser LD1 cannot be corrected, and the light emission power at DC set by the ALPC section and the data section cannot be corrected. However, there is a problem that a difference occurs in the light emission power in the recording pulse.
[0030]
Therefore, a real-time APC circuit that can always control the driving current of the semiconductor laser has been attracting attention.
[0031]
FIG. 11 shows a real-time APC circuit. In FIG. 11, the same or corresponding components as those in FIG. 10 are denoted by the same reference numerals and description thereof will be omitted.
[0032]
In the figure, 11 ₁ Is a voltage V obtained by converting the monitor current IPD output from the photodiode PD2 to a current-voltage value. _S , A peak value detection circuit, ₂ Is similarly the voltage V _S , A bottom value detection circuit to which _n Is similarly the voltage V _S Is an average value detection circuit to which is input, and corresponds to the three types of power levels (peak power, erase power, and cool power) described above.
[0033]
4 ₁ , 4 ₂ , 4 _n Is the error amplifier, 6 ₁ , 6 ₂ , 6 _n Is an optical power setting voltage, and the error amplifier 4 ₁ Is the peak value detection circuit 11 ₁ Output and optical power setting voltage 6 ₁ And the error amplifier 4 ₂ Is the bottom value detection circuit 11 ₂ Output and optical power setting voltage 6 ₂ And the error amplifier 4 _n Is the average value detection circuit 11 _n Output and optical power setting voltage 6 _n Is to be compared with
[0034]
This APC circuit is different from the sample-and-hold type APC circuit shown in FIG. _S To the peak value detection circuit 11 according to the optical power to be set. ₁ , Bottom value detection circuit 11 ₂ , Average value detection circuit 11 _n And outputs the detected power and the optical power setting voltage 6 ₁ , 6 ₂ , 6 _n To each error amplifier 4 ₁ , 4 ₂ , 4 _n To generate a control voltage for each set power.
[0035]
That is, the monitor current IPD of the photodiode PD2 that has received the light output is converted into the voltage V by the current-voltage conversion circuit 3. _S And performs peak value detection, bottom value detection, and average value detection. Each output of peak value detection, bottom value detection, and average value detection, and the optical power setting voltage 6 ₁ , 6 ₂ , 6 _n The respective error voltages of ₁ , 4 ₂ , 4 _n And as a result, the error amplifier 4 ₁ , 4 ₂ , 4 _n Negative feedback is applied so that the + and-input voltages of the error amplifier 4 are balanced, and the output voltage of the error amplifier 4 is determined.
[0036]
The output voltage is converted to a voltage / current conversion circuit 9 ₁ , 9 ₂ ... 9 _n Then, the semiconductor laser LD1 is converted into a current, the semiconductor laser LD1 is generated by the switch circuit 10 and amplified by the driver 11 to drive the semiconductor laser LD1.
[0037]
In the real-time APC circuit, in the case of binary control, the peak value detection circuit 11 is used. ₁ , Bottom value detection circuit 11 ₂ Only, and no sample gate signal input is required. In the case of control with three or more values, it is necessary to gate each detection section.
[0038]
[Problems to be solved by the invention]
However, the above-described real-time APC circuit, that is, the semiconductor laser light output control circuit still has the following problems.
[0039]
That is, unlike the sample-and-hold method, the real-time APC circuit does not need to set the power in chronological order, so that a sufficient area of the ALPC section can be obtained, and the pulse is always controlled. The light output can be controlled stably with respect to the temperature droop characteristic of the LD 1.
[0040]
However, this real-time method has a problem that it responds to disturbances in the loop band.
[0041]
For example, as shown in FIG. 12, for the write CLK shown in FIG. 12A and the recorded data of the 5T mark and 5T space shown in FIG. 12B, only the final cool (PostCool) shown in FIG. When the laser driving is performed, if the frequency band is limited by the driving circuit, the semiconductor laser LD1, and other parasitic capacitances and parasitic inductances, as shown in the laser driving waveform (1) shown in FIG. Due to the narrow width, it does not fall and the cool level becomes uneven.
[0042]
Bottom value detection circuit 11 ₂ Performs a sampling / holding operation in accordance with the gate pulse signal shown in (e) to detect only the cool level, but when the bottom level of the laser drive waveform (1) is detected, the bottom hold shown in (f) Like a waveform, it fluctuates in a cycle of 1/10 of the Write CLK (a).
[0043]
Assuming that the frequency of the write CLK (a) is 50 MHz, the bottom hold fluctuates in a cycle of 5 MHz. If the APC loop band is a wide band of several MHz, it responds to this fluctuation (g). As shown in the waveform (2) of the laser drive waveform shown in FIG.
[0044]
From the above, it is necessary to reduce the loop bandwidth as much as possible to reduce the disturbance, but if the bandwidth is narrowed, the pull-in time for setting the laser power in the APC circuit becomes longer and the ALPC section also becomes longer. . On the other hand, in order to improve the recording density of the optical disk in the future, it is necessary to reduce the number of ALPC sections as much as possible to increase the data area, which is a recording area, and there is a problem that this conflicts.
[0045]
An object of the present invention is to provide a semiconductor laser light output control circuit that can solve the above-mentioned problems.
[0046]
Means for Solving the Invention
In order to solve the above problem, according to the present invention, the current supply means for driving the semiconductor laser, the light output detection means for detecting the light output of the semiconductor laser, and the light output detection means detect the light output. Light output detection means for detecting light output, light output setting means for providing a set value of light output in the recording mode of the semiconductor laser, setting output by the light output setting means and detection output by the light output detection means, A comparison amplifier for comparing the data and outputting a comparison result; and a comparison result supply unit for supplying the comparison result to the current supply unit. In a semiconductor laser light output control circuit for controlling an output to a desired intensity, the comparison and amplification means is constituted by two systems of comparison and amplification means for making the loop band of the circuit different. Both provided system switching means for switching a comparison and amplification means of the same two systems.
[0047]
According to the second aspect of the present invention, the switching of the two systems of comparison and amplification means is performed by switching from the wide band to the narrow band after a predetermined time has elapsed from the transition from the reproduction mode to the recording mode.
[0048]
BEST MODE FOR CARRYING OUT THE INVENTION
The present invention provides a current supply unit for driving a semiconductor laser, an optical output detection unit for detecting an optical output of the semiconductor laser, an optical output detection unit for detecting an optical output detected by the optical output detection unit, Light output setting means for giving a set value of light output in the recording mode of the laser, and a comparison and amplification means for comparing a setting output by the light output setting means with a detection output by the light output detection means and outputting a comparison result; And a comparison result supply means for supplying the comparison result to the current supply means, and a semiconductor laser light output for controlling the light output of the semiconductor laser for recording, reproducing, and erasing data on the optical disk to a desired intensity. In the control circuit, the comparison / amplification means is constituted by two systems of comparison / amplification means for changing the loop band of the circuit, and the two systems of comparison / amplification means are switched. It is provided with a unified switching means.
[0049]
That is, in a semiconductor laser light output control circuit (APC circuit), which is roughly classified into a sample hold method and a real-time method, the problem that the real-time APC circuit is susceptible to disturbances in the circuit has been solved. With the above-described configuration, the APC circuit widens the loop band during the pull-in of the ALPC section, and narrows the loop band in the data section, thereby reducing the pull-in time and reducing the influence of the APC loop disturbance. As small as possible, a stable APC operation is realized, and light output control can be performed efficiently and accurately.
[0050]
When controlling the optical output of a semiconductor laser for recording, reproducing, and erasing data on an optical disk to a desired intensity, in the recording mode, the setting of the optical output for recording is performed by a recording signal in a data portion (recording) of each sector. This is performed within a power setting period called an ALPC (Auto Laser Power Control) section set together with the address section before the (area).
[0051]
When setting the recording power level in the ALPC unit, if the bandwidth of the APC circuit is a wide band of several MHz, the signal pull-in to the circuit is completed in a short time of several μs to a desired level.
[0052]
Thereafter, in the recording area, the band of the APC circuit is reduced to a narrow band, and while the influence of disturbance in the APC circuit is eliminated as much as possible, the control of the recording pulse is always performed, so that the temperature droop of the semiconductor laser is reduced. The light output can be controlled stably with respect to the characteristics.
[0053]
For this purpose, the setting output of the light output setting means for giving the setting value of the light output in the recording mode of the semiconductor laser and the monitor signal from the light output detecting means for monitoring and detecting the light output of the semiconductor laser are detected by the light output detecting means. Then, two sets of comparing and amplifying means for comparing the detection output with the setting output and outputting a comparison result are provided so that the band of the APC circuit can be switched. The light output control and the light output control in another section are executed in a state where the band of the APC circuit is switched.
[0054]
In addition, it is desirable that the switching of the two systems of comparison amplification means be switched from a wide band to a narrow band after a lapse of a predetermined time from the transition from the reproduction mode to the recording mode.
[0055]
That is, in the reproduction mode, a constant weak light output is performed, so that the band may be kept wide. However, when the mode is shifted to the recording mode, the band is switched to the narrow band as described above. At this time, there is a margin for the time until the above-described pull-in time in the ALPC section ends, and the mode is switched from the wide band to the narrow band after a lapse of a predetermined time from the reproduction mode to the recording mode.
[0056]
Therefore, the optical output control at the time of power setting in the ALPC section in the optical disk format can be executed in a wide band in a short time, and in the recording mode, the optical output control is performed in real time while ensuring the narrow band and avoiding the influence of disturbance as much as possible. It becomes executable.
[0057]
In this way, it is possible to simultaneously shorten the pull-in time of the APC circuit in the ALPC section, stabilize the waveform in the recording area, and control the optical output of the semiconductor laser with high accuracy. It becomes.
[0058]
Hereinafter, embodiments of the present invention will be described more specifically with reference to the drawings.
[0059]
FIG. 1 shows an example of a semiconductor laser light output control circuit (hereinafter, referred to as an “APC circuit”) according to the present invention.
[0060]
As shown in FIG. 1, the APC circuit according to the present embodiment includes a driver 11 as a current supply unit for driving the semiconductor laser LD1, and a photodiode PD2 as an optical output detection unit for detecting the optical output of the semiconductor laser LD1. A current-voltage conversion circuit 3 for converting the monitor current IPD detected by the photodiode PD2 into a voltage; and a voltage V converted by the current-voltage conversion circuit 3 as the light output detection means. _S Value detection circuit 11 to which is input ₁ Similarly, the voltage V _S Value detection circuit 11 to which is input ₂ Similarly, the voltage V _S Average detection circuit 11 to which is input _n And an optical power setting voltage 6 as an optical output setting means for assigning an optical output setting value in the recording mode of the semiconductor laser LD1. ₁ , 6 ₂ ... 6 _n And each optical power setting voltage 6 ₁ , 6 ₂ ... 6 _n Output values and corresponding peak value detection circuits 11 corresponding thereto. ₁ , Bottom value detection circuit 11 ₂ , Average value detection circuit 11 _n A pair of error amplifiers 4 for comparing the detection output with ₁ , 4 ₂ , 4 _n And 20 ₁ , 20 ₂ , 20 _n And a pair of these error amplifiers 4 ₁ , 20 ₁ , 4 ₂ , 20 ₂ , 4 _n , 20 _n Switch 21 for switching between ₁ , 21 ₂ , 21 _n And the error amplifier 4 ₁ , 4 ₂ , 4 _n And 20 ₁ , 20 ₂ , 20 _n A voltage-current conversion circuit 9 for performing voltage-current conversion as comparison result supply means for supplying the comparison result output from any one of the above to the driver 11 ₁ , 9 ₂ ... 9 _n And the voltage-current conversion circuit 9 ₁ , 9 ₂ ... 9 _n And a changeover switch 15 for switching the output.
[0061]
The feature of the present invention is that, as described above, two types of error amplifiers 4 having different loop bands of the APC circuit are used as the comparison and amplification means. ₁ , 4 ₂ , 4 _n And error amplifier 20 ₁ , 20 ₂ , 20 _n And the configuration is such that the comparison amplification means is configured in two systems, and the selection switch 21 is used as a system switching means for switching the comparison amplification means of the two systems. ₁ , 21 ₂ , 21 _n Has been established.
[0062]
That is, the APC circuit according to the present embodiment is different from the real-time APC circuit (see FIG. 11) described in the related art in that a new error amplifier 20 is provided in correspondence with peak power, erase power, and cool power. ₁ , 20 ₂ , 20 _n And the selection switch 21 ₁ , 21 ₂ , 21 _n Is added.
[0063]
This APC circuit has a voltage V obtained by converting the monitor current IPD into a current-voltage, similarly to the conventional real-time APC circuit. _S Can always be pulse-controlled in accordance with the set optical powers of peak, erase, and cool, and by adding the above-mentioned new configuration, the light at the time of power setting in the ALPC section in the optical disc format can be set. The bandwidth of the APC circuit can be switched between a wide band and a narrow band by the output control and the optical output control in other sections.
[0064]
In the figure, S is a control signal generation circuit for switching the band of the APC circuit between a wide band and a narrow band. The circuit S will be described later.
[0065]
FIG. 2 shows an example of the open loop characteristics of the present APC circuit.
[0066]
That is, a frequency at an open loop gain of 0 dB is called a crossover frequency, and this is a loop band. In the present embodiment, in the primary system in which the loop band is determined only by the error amplifier, error amplifiers 4 having different crossover frequencies are used. ₁ , 4 ₂ , 4 _n And error amplifier 20 ₁ , 20 ₂ , 20 _n By switching these, the bandwidth of the APC circuit is switched. Here, the error amplifier 4 ₁ , 4 ₂ , 4 _n To the broadband, error amplifier 20 ₁ , 20 ₂ , 20 _n Is narrowed to 1/10 of the narrow band, and the band of the APC circuit is switched between a wide band and a narrow band.
[0067]
FIG. 3 shows the error amplifier 4 used in the present embodiment. ₁ , 4 ₂ , 4 _n , 20 ₁ , 20 ₂ , 20 _n FIG.
[0068]
The crossover frequency is
ω = gm / C.
[0069]
gm: voltage-current conversion gain
Gm_1 = 1 / (R1 + 2re)
gm_2 = 1 / (R2 + 2re)
By setting R1 and R2 arbitrarily, it is possible to produce error amplifiers having different crossover frequencies. The band can be switched by turning on / off the current source of the error amplifier by the predetermined control signal A.
[0070]
The error amplifier 4 ₁ , 4 ₂ , 4 _n , 20 ₁ , 20 ₂ , 20 _n FIG. 4 is a circuit diagram showing another example of the embodiment.
[0071]
The operation is the same as the circuit described in FIG.
The crossover frequency is
given by ω = gm / C,
Gm_1 = 1 / (R1 + 2re)
gm_2 = 1 / (R2 + 2re)
Is represented by The band can be switched by turning on / off the current source of the error amplifier by the predetermined control signal A. Note that this circuit has a wider operating point.
[0072]
An example of a method of generating a control signal A for switching a band will be described with reference to a control signal generation circuit S shown in FIG. Note that the method of generating the control signal is not limited to using the illustrated control signal generation circuit S.
[0073]
As shown in FIG. 5A, the charging current (Icharge) and the discharging current (Idischarge) are turned on / off in response to a reproduction / recording (Read / write) signal, and the capacitor C1 is discharged and charged.
[0074]
By reducing the current on the discharge side to slow down the speed at which the voltage Va drops and setting the threshold voltage V1 of the comparator arbitrarily, as shown in the timing chart of FIG. A signal Vb that falls with a delay of μs is generated. This time can be arbitrarily set according to the capacity of the capacitor C1, the threshold voltage V1, and the charge / discharge current.
[0075]
Using the signal Vb as a control signal, the error amplifier 4 described above is used. ₁ , 4 ₂ , 4 _n , 20 ₁ , 20 ₂ , 20 _n The band of the APC circuit can be switched several μs after the recording mode is set.
[0076]
In addition, the above-described error amplifier 4 ₁ , 4 ₂ , 4 _n , 20 ₁ , 20 ₂ , 20 _n The switching between the two systems of comparison amplification means is performed after switching from the reproduction mode to the recording mode and after a predetermined time has elapsed, switching from the wide band to the narrow band.
[0077]
That is, in the reproduction mode, a constant weak light output is performed, so that the band may be kept wide. However, in the present embodiment, when the mode shifts to the recording mode, the band is switched to the narrow band as described above. At this time, a margin is given to the time until the pull-in time in the ALPC section in the above-mentioned optical disc format is completed, and the mode is switched from the wideband mode to the narrowband mode after a lapse of a predetermined time after the transition from the reproduction mode to the recording mode. It is.
[0078]
FIG. 6 shows a laser drive current waveform when the band is switched in the APC circuit according to the present embodiment.
[0079]
As shown in the figure, the APC circuit for recording starts the recording operation by the recording signal of the reproduction / recording signal, and when the loop band is switched to a wide band of several MHz, it reaches a desired level in a short time of several μs. The pull-in operation is completed. The band is switched to the narrow band by the control signal Vb with a margin for the time when the pull-in operation is completed. At the time of this switching, the error amplifier 4 having the above-described configuration is used. ₁ , 4 ₂ , 4 _n , 20 ₁ , 20 ₂ , 20 _n Is used, it is possible to perform band switching without causing a level fluctuation that occurs when the error amplifier is switched in the laser drive current.
[0080]
As described above, according to the present embodiment, the power setting in the ALPC section in the optical disk format is completed within the time period of several μs until the drawing operation is completed and the drawing operation is completed, as described above, In the subsequent recording area, the optical output is controlled in real time in a narrow band with little influence of disturbance, so that the pull-in time can be shortened and the waveform in the recording area can be stabilized at the same time, and The optical output of the semiconductor laser can be controlled with high accuracy.
[0081]
FIG. 7 shows an APC circuit as another embodiment.
[0082]
This is because in the embodiment described above, a pair of error amplifiers 4 provided for each of the peak power, the erase power, and the cool power are provided. ₁ , 20 ₁ , 4 ₂ , 20 ₂ , 4 _n , 20 _n , The detected optical output of the semiconductor laser LD1 is converted to a peak value detection circuit 11 ₁ , Bottom value detection circuit 11 ₂ , Average value detection circuit 11 _n Input the detection output detected by the above, and also set the optical power setting voltage 6 provided for each of peak power, erase power, and cool power. ₁ , 6 ₂ , 6 _n In contrast, the APC circuit shown in FIG. 7 uses the peak value detection circuit 11 for detecting the detected optical output of the semiconductor laser LD1. ₁ , Bottom value detection circuit 11 ₂ , Average value detection circuit 11 _n And an optical power setting voltage 6 that is switched and output via the optical power setting voltage switch circuit 5. ₁ , 6 ₂ , 6 _n Peak value detection circuit 12 for detecting ₁ , Bottom value detection circuit 12 ₂ , Average value detection circuit 12 _n And a configuration including:
[0083]
In this embodiment as well, the switching of the band is possible, and the same effect as in the previous embodiment can be obtained.
[0084]
【The invention's effect】
The present invention is implemented in the form described above, and has the following effects.
[0085]
(1) According to the first aspect of the present invention, a current supply means for driving a semiconductor laser, an optical output detection means for detecting an optical output of the semiconductor laser, and an optical output detected by the optical output detection means. A light output detecting means for detecting, a light output setting means for providing a set value of the light output in the recording mode of the semiconductor laser, and a setting output by the light output setting means and a detected output by the light output detecting means. A comparison amplifying means for outputting a comparison result to the current supply means, and a comparison result supply means for supplying the comparison result to the current supply means. In the semiconductor laser light output control circuit for controlling the intensity of the laser beam, the comparison and amplification means is constituted by two systems of comparison amplification means for differentiating the loop band of the circuit. Provided line switching means for switching a comparison amplification means. Therefore, in the pull-in operation in the semiconductor laser light output control circuit, the band can be widened and the band can be narrowed in other cases. A stable APC operation is realized to enable efficient and accurate light output control.
[0086]
(2) According to the second aspect of the present invention, the two systems of comparison and amplifying means are switched from the wide band to the narrow band after a lapse of a predetermined time from the reproduction mode to the recording mode. The optical output control at the time of power setting in the ALPC section in the optical disk format can be executed in a wide band in a short time, and in the recording mode, the optical output control can be executed in real time while the influence of disturbance is minimized as much as possible. .
[Brief description of the drawings]
FIG. 1 is a circuit diagram showing a first embodiment of a semiconductor laser light output control circuit (APC circuit) according to the present invention.
FIG. 2 is a graph showing an example of an open loop characteristic of an APC circuit.
FIG. 3 is an explanatory diagram illustrating an example of a circuit of an error amplifier.
FIG. 4 is an explanatory diagram illustrating an example of a circuit of an error amplifier.
FIG. 5 is an explanatory diagram illustrating an example of a control signal generation method for switching a band.
FIG. 6 is an explanatory diagram showing a laser drive current waveform when a band is switched.
FIG. 7 is an APC circuit diagram according to another embodiment.
FIG. 8 is an explanatory diagram showing an example of a write strategy.
FIG. 9 is a waveform diagram including a magneto-optical disk format diagram and an optical output waveform set in the ALPC section.
FIG. 10 is a circuit diagram illustrating an example of a sample-and-hold APC circuit.
FIG. 11 is a circuit diagram showing an example of a real-time APC circuit.
FIG. 12 is an explanatory diagram showing an influence of disturbance in a loop band in the APC circuit.
[Explanation of symbols]
LD1 Semiconductor laser
PD2 photodiode (light detection means)
3 Current-voltage conversion circuit
4 ₁ , 4 ₂ , 4 _n Error amplifier (comparison amplification means)
6 ₁ , 6 ₂ , 6 _n Optical power setting voltage
9 ₁ , 9 ₂ , 9 _n Voltage-current conversion circuit (comparison result supply means)
10. Changeover switch (comparison result supply means)
11 Driver (current supply means)
11 ₁ Peak value detection circuit
11 ₂ Bottom value detection circuit
11 _n Average detection circuit
20 ₁ , 20 ₂ , 20 _n Error amplifier (comparison amplification means)
21 ₁ , 21 ₂ , 21 _n Selection switch

Claims (2)

Current supply means for driving a semiconductor laser,
Light output detection means for detecting the light output of the semiconductor laser,
Light output detection means for detecting the light output detected by the light output detection means,
Light output setting means for giving a set value of light output in the recording mode of the semiconductor laser,
Comparison amplification means for comparing the setting output by the light output setting means and the detection output by the light output detection means and outputting a comparison result,
A semiconductor laser light output control for controlling the light output of a semiconductor laser for recording, reproducing, and erasing data on an optical disk to a desired intensity, comprising a comparison result supply means for supplying the comparison result to the current supply means In the circuit,
A semiconductor laser light output control circuit, wherein the comparison and amplification means is constituted by two systems of comparison amplification means for differentiating the loop band of the circuit, and system switching means for switching the two systems of comparison amplification means is provided. . 2. The semiconductor laser light output control circuit according to claim 1, wherein the switching of the two systems of comparison amplification means switches from a wide band to a narrow band after a lapse of a predetermined time from a transition from a reproduction mode to a recording mode.

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