JPH04356741A - Laser drive circuit - Google Patents

Abstract

PURPOSE:To offer a laser driving device which can correct the decrease of light output due to thermal equilibrium so that the light output after being decreased because of the thermal equilibrium becomes a prescribed value for recording, and can execute the optimum recording in the case that a semiconductor laser is driven at an open loop by a constant current. CONSTITUTION:The semiconductor laser 1 is made to emit the light output for the recording by driving it by the constant current, and difference between the light output for the recording at the beginning of drive by the constant current and the light output after the lapse of prescribed time is detected by a light output difference detecting means 20. A driving current or control voltage corresponding to the difference of the light output is calculated by a computing element 26. At the time of the recording, the driving current IAD calculated by the computing element 26 and corresponding to the difference of the light output is added to the constant current IL. Thus, in the case that the semiconductor laser 1 is driven at the open loop by the constant current, the decrease of the light output due to the thermal equilibrium is corrected so that the light output after the decrease due to the thermal equilibrium becomes the prescribed value for the recording, and the optimum recording can be executed.

Description

[Detailed description of the invention]

0001

[Industrial Application Field] The present invention uses a focused light spot of a semiconductor laser beam to record a signal on an optical disk, or to erase, reproduce, or erase a recorded signal on an optical disk.
Among optical disk devices that perform overwriting, the present invention particularly relates to a semiconductor laser drive circuit that controls the optical output of a semiconductor laser.

0002

[Background Art] In recent years, in optical disk devices, one control method for semiconductor laser drive circuits is to perform closed-loop control at the start of recording in order to control optical output with high precision and high speed. A hold method is used in which the control voltage is held when a predetermined recording light output is reached and control is performed in an open loop.

A semiconductor laser drive circuit using a conventional hold method will be explained. FIG. 7 shows the configuration of a semiconductor laser drive circuit using this conventional hold method. Figure 7
, 1 is a semiconductor laser, 2 is a photodetector that generates a monitor current IM according to the optical output of the semiconductor laser 1, and 3 is a current-voltage converter that converts the monitor current IM into a monitor voltage VM using a resistor RI. A differential amplifier 4 compares the monitor voltage VM with a reference voltage VR for setting the optical output, and generates a control voltage VS. There are two reference voltages VR, a reference voltage VP for reproduction (No. 5) and a reference voltage VW for recording (No. 6), one of which is selected by the analog switch SW1 and the analog switch SW2. The selection is controlled by the recording gate WG indicating the recording section and the output of the inverter 7. Analog switch SW3 is controlled by hold gate HLD and provides control voltage VS to buffer amplifier 9. Analog switch SW3, capacitor 8,
Buffer amplifier 9 constitutes a sample hold circuit. Control voltage VS when analog switch SW3 is on
is sampled, and the control voltage VS is held when the analog switch SW3 is off. The control voltage VSH, which is the output of the buffer amplifier 9, is connected to a transistor 10 that constitutes a constant current source with a resistor RL of 11, and is connected to a transistor 10 that constitutes a constant current source.
A drive current IL is applied to. The drive current IL is modulated by two transistors 12 and 13 that perform switching. Switching is controlled by the recording signal WDT and the inverter 14.

The operation of the conventional semiconductor laser drive circuit configured as described above will be described below with reference to FIG.

[0005] In the following explanation, it is assumed that all operations of the analog switch are turned on when the signal at the control terminal is "high" and turned off when the signal is "low".

The signals in FIG. 8 are shown from the top, (a) is the recording gate WG indicating the recording section, (b) is the hold gate HLD indicating the hold section, (c) is the recording signal WDT recorded on the optical disk, (d) ) is the reference voltage VR that sets the optical output.
, (e) is the control voltage VSH of the buffer amplifier 9 that controls the drive current IL, and (f) is the optical output of the semiconductor laser 1. The optical output is relatively the same as the monitor voltage VM of the current-voltage converter 3.

[0007] The period up to time t1 indicates a reproduction section. record game
The output WG is "low", and the analog switch SW1 is on and the analog switch SW2 is off. At this time, the reference voltage VP for reproduction of the analog switch SW1 is connected to the reference voltage VR for setting the optical output. Hold gate H
LD is "high", analog switch SW3 is turned on, and control voltage VSH for buffer amplifier 9 is sampled as control voltage VSP for reproduction. The recording signal WDT is "high", and all of the drive current IL of the constant current source flows to the semiconductor laser 1. From this, the closed-loop servo operates so that the optical output of the semiconductor laser 1 becomes the reproduction optical output set by the reference voltage VP.

At time t1, the recording gate WG becomes "high" and the setting of the optical output for recording begins. The recording gate WG is "high", the analog switch SW1 is off, and the analog switch SW2 is on. At this time, the recording reference voltage VW of the analog switch SW2 is connected to the reference voltage VR for setting the optical output. hold gate HL
D remains "high", the analog switch SW3 is turned on, and the recording control voltage VSW is sampled as the control voltage VSH of the buffer amplifier 9. The recording signal WDT is "high", and all of the drive current IL of the constant current source flows to the semiconductor laser 1. From this, a closed-loop servo operates so that the optical output of the semiconductor laser 1 becomes the recording optical output set by the reference voltage VW.

At time t2, hold gate HLD
becomes “low”. The analog switch SW3 is turned off, and the control voltage VSH of the buffer amplifier 9 is held at the recording control voltage VSW. The recording signal WDT becomes a modulated signal to be recorded on the optical disc, and the drive current IL is modulated. Thereby, the optical output of the semiconductor laser 1 is set to the recording optical output in an open loop by the control voltage VSW held by the buffer amplifier 9, and is modulated by the recording signal WDT.

At time t3, the recording gate WG becomes "low" and the recording returns to the reproduction. Recording Gate WG”
When the analog switch SW1 is "low", the analog switch SW1 is on and the analog switch SW2 is off.The reference voltage VP for regeneration of the analog switch SW1 is connected to the reference voltage VR.The hold gate HLD becomes "high" and the analog switch SW3 is turned off. is on, the control voltage VSH of the buffer amplifier 9 is sampled from the control voltage VSP for reproduction.The recording signal W
DT is "high" and all of the drive current IL of the constant current source flows to the semiconductor laser 1. From this, a closed loop servo operates so that the optical output of the semiconductor laser 1 becomes the reproduction optical output set by the reference voltage VP.

[0011]

However, in the conventional configuration described above, the optical output is controlled in an open loop with a constant current generated by the held control voltage VSW during recording modulation. Therefore, if the thermal balance of the semiconductor laser 1 is not sufficient, constant current driving has a problem in that the optical output fluctuates due to temperature changes in the semiconductor laser 1 during recording. When a semiconductor laser is driven with a constant current, fluctuations in optical output due to thermal equilibrium are generally called droop, and this droop will be explained using FIG. 9.

In FIG. 9, from the top, the optical output, control voltage VSH, and drive current IL are shown. The period up to time t4 indicates a reproduction section. The control voltage VSH is such that the reproduction control voltage VSP is sampled, the drive current IL of the constant current source 10 is set so that the reproduction drive current IP flows, and the optical output becomes the reproduction optical output.
Closed loop servo works.

At time t4, setting of optical output for recording begins. The recording control voltage VSW is sampled as the control voltage VSH. The driving current IL of the constant current source 10 is such that the recording driving current IW flows and the optical output is set to a predetermined recording setting value PS.
A closed-loop servo works to ensure that.

At time t5, the control voltage VSH is held at the recording control voltage VSW. Semiconductor laser 1
is driven with a constant current IW by the control voltage VSW held by the buffer amplifier 9. The optical output of the semiconductor laser 1 is set to a predetermined recording setting value PS in an open loop, and is modulated by the recording signal WDT.

When the semiconductor laser 1 has not reached thermal equilibrium, the optical output when driven with a constant current changes due to thermal changes. As shown in FIG. 9, the predetermined setting value PS set at time t5 is set at time t6 after a certain period of time.
In this case, it decreases to PD. Thermal equilibrium is reached at time t6, and thereafter the change in optical output decreases.

As described above, when the semiconductor laser 1 is driven with a constant current, there is a problem when the optical output decreases from a predetermined set value due to thermal equilibrium. Generally, in an optical disc device, the optical output changes in a direction in which the optical output decreases. If the laser drive circuit has the above-mentioned droop problem, the fluctuation of the optical output will further decrease, and recording will not be performed optimally.

The present invention solves the above-mentioned conventional problems, and provides a semiconductor laser drive circuit that can correct the decrease in optical output due to droop when a semiconductor laser is driven with a constant current in an open loop, and can perform optimal recording. The purpose is to provide.

[0018]

[Means for Solving the Problems] In order to achieve this object, the semiconductor laser drive circuit of the present invention includes a hold means for holding a control voltage, and a constant current source that flows a drive current corresponding to the control voltage to the semiconductor laser. , an optical output difference detection means for detecting the difference between the optical output of recording at the beginning of driving with a constant current and the optical output of recording after a predetermined period of time, using a monitor signal; an arithmetic means for converting and outputting a driving current or a control voltage for the semiconductor laser corresponding to the difference; and a constant current source for flowing a constant current corresponding to the optical output of recording by means of a control voltage held by a holding means during recording; and addition means for adding a drive current or control voltage corresponding to the difference in optical output calculated by the calculation means.

[0019]

[Operation] According to the above-described structure, the semiconductor laser is driven with a constant current to emit a recording optical output before recording. The optical output of recording at the beginning of driving with a constant current,
After a predetermined period of time has elapsed and the semiconductor laser reaches thermal equilibrium, the difference between the recording optical output and the optical output is detected. This difference in optical output becomes the optical output difference due to droop. The driving current of the semiconductor laser that generates this optical output difference is calculated. When the original recording on the optical disk starts, a drive current corresponding to the optical output difference due to droop is added to a constant current driven by the control voltage held by the hold means. In this way, when the semiconductor laser is driven with a constant current, the decrease in optical output due to droop is corrected by adding the drive current calculated in advance. As a result, when driving with a constant current using a held control voltage, the optical output for recording does not fall below a predetermined set value over time, making it possible to perform optimal recording.

[0020]

DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings.

FIG. 1 shows the configuration of a semiconductor laser drive circuit in a first embodiment of the present invention. The parts added to FIG. 7, which is the configuration of the conventional example described above, will be explained. In FIG. 1, 20 surrounded by a broken line is a light output difference detection means;
21 is a peak detection circuit that detects the peak value VMP of the monitor voltage VM, and 22 is an AD converter that converts the analog voltage of the peak value VMP into digital data. The AD converter 22 has two internal circuits, each of which outputs digital data D1 and D2. AD converter 22 is controlled by chip select signal CS. 23 and 24 are memory M1 and memory M2, respectively. The outputs of the memories 23 and 24 are subtracted by a subtracter 25, resulting in optical output difference data D3. 26 is an arithmetic unit, which calculates D1 from the optical output difference data D3.
A control voltage VA that causes a drive current to flow according to the optical output difference between and D2
Calculate D. The control voltage VAD is the analog switch S
It is connected via W4 to the base of a transistor 27 that constitutes a constant current source. A constant current source made up of the added resistor 28 and transistor 27 causes a drive current IAD to flow in accordance with the control voltage VAD. The semiconductor laser 1 has a driving current I
L and drive current IAD are added, and drive current ILD flows. 28 is a resistor RL, and 29 is a base resistor RB of the transistor 27. The analog switch SW4 is controlled by an addition signal ADD obtained by ANDing the signal passed through the inverter 30 of the hold gate HLD and the test signal TEST by an AND circuit 31.

The operation of the semiconductor laser drive circuit of this embodiment configured as described above will be explained below with reference to FIG. The operation can be roughly divided into two types: one is to detect the optical output difference without actually recording on the optical disc, and the other is to actually record on the optical disc using the detected optical output difference.

First, the operation when detecting the optical output difference will be explained using FIG. 2. The signals in FIG. 2 are from top to bottom: (a) is the monitor voltage VM indicating the optical output, (b) is the peak value VMP obtained by detecting the peak of the monitor voltage VM, and (c) is the AD converter 2.
2 chip select signal CS, (d) is the AD converter 22
, (e) is another output data D2 of the AD converter 22, (f) is the optical output difference data D3 of the subtracter 25, and (g) is the control voltage that is the output of the arithmetic unit 26. VAD, (h) is the hold gate HLD, (i)
is the test signal TEST, (j) is the addition signal ADD, (k
) is the drive current IL corresponding to the recording optical output, (l) is the drive current IAD corresponding to the optical output difference, and (m) is the drive current IL
The drive current ILD that actually flows through the semiconductor laser 1 is the sum of the drive current IAD and the drive current IAD.

At time t7, setting of optical output for recording begins. Since the test signal TEST shown in (i) is always "low", the addition signal ADD shown in (j) is also always "low". Therefore, the analog switch SW4 is off, and the drive current I shown in (l) is generated by the constant current source of the transistor 27.
AD is zero. Therefore, the drive current IL shown in (m)
D is always equal to the drive current IL shown in (k).

Between time t7 and time t8, the drive current IL shown in (k) is controlled in a closed loop from the reproduction drive current IP to the recording drive current IW, and is adjusted to a predetermined recording setting value P.
S is set.

At time t8, the hold gate HLD shown in (h) becomes "low", the control voltage is held, and the semiconductor laser 1 is driven by the constant current IW by the held control voltage.

On the other hand, at time t8, the chip select signal CS shown in (c) becomes "high" and the peak value VMP
is subjected to AD conversion, and output data D1 shown in (d) is output. At this time, since the semiconductor laser 1 has just entered open-loop control, the influence of droop due to thermal equilibrium is the smallest, and the optical output is equal to the predetermined set value PS. Therefore, the output data D1 AD-converted at time t8 represents the peak of optical output for recording when driven with a constant current IW.

While being driven with a constant current IW, the optical output of the semiconductor laser 1 decreases from a predetermined set value PS due to droop due to thermal equilibrium.

At time t9, thermal equilibrium is established and the optical output stabilizes at PD, which is lower than the predetermined set value PS. At this time, the chip select signal CS shown in (c) is "high"
, and the optical output PD, which is the peak value VMP at this time, is A
D conversion is performed, and output data D2 shown in (e) is output.

Output data D1 and D2 are subtracted by a subtracter 25, and the difference between the peak optical output and the optical output after a predetermined time when driven with a constant current IW is optical output difference data D3.
is output as Here, the difference between optical output PS and PD is d
If PD, dPD is represented by optical output difference data D3.

Using the optical output difference data D3, the arithmetic unit 26
is the drive voltage V of the semiconductor laser 1 according to the optical output difference dPD
Calculate AD and output.

Next, the relationship between the optical output difference dPD calculated by the calculator 26 and the control voltage VAD will be explained using FIGS. 3 and 4.

FIG. 3 shows the drive current I in the configuration of FIG.
A constant current source composed of a transistor 27 and a resistor RL, which conducts AD, is extracted. For simplicity, the modulation stages of transistors 12 and 13 are omitted. In Figure 3,
VCC is the power supply voltage, VAD is the control voltage of the arithmetic unit 26, I
AD is a drive current flowing through the semiconductor laser 1.

Here, assuming that the base-emitter voltage of the transistor 27 is VBE, the relationship between the control voltage VAD and the drive current IAD is as shown in the following equation (1) (Equation 1).

[0035]

[Equation 1] IAD=(VCC-VBE-VAD)/RL
(1) Next, the relationship between the drive current and optical output of the semiconductor laser 1 will be explained using FIG. 4. In FIG. 4, the horizontal axis represents the drive current,
The light output is plotted on the vertical axis. When the drive current starts flowing from zero and exceeds the threshold current ITH, the optical output rises. Above the threshold current ITH, the optical output rises linearly with respect to the drive current. The slope of optical output with respect to this drive current is called slope efficiency. Slope efficiency S
L can be calculated from the optical outputs P1 and P2 for the drive currents I1 and I2 at two points, as shown in FIG. Drive current I2
If the difference between the drive current I1 and the drive current I1 is dI, and the difference between the optical output P2 and the optical output P1 is dP, calculation can be performed as shown in the following equation (2) (Equation 2).

[0036]

[Math. 2] SL=(P2-P1)/(I2-I1)
=dP/dI

(2) Next, the optical output difference dPD due to droop
The relationship between the drive current IAD that corrects the slope efficiency S
Using L, it can be calculated as shown in the following equation (3) (Math. 3).

[0037]

[Formula 3] IAD=dPD/SL

(3) Equations (1), (3) (Math. 1) and (Math. 3)
), the relationship between the optical output difference dPD due to droop and the control voltage VAD can be expressed as shown in the following equation (4).

[0038]

[Formula 4] VAD=VCC-VBE-RL・IAD
=VCC-VBE-RL・(dPD/SL)
(4) From this, if we measure the optical output difference dPD due to droop, the optical output difference d
It is possible to calculate the control voltage VAD that causes the drive current IAD corresponding to the PD to flow.

Next, with reference to FIG. 5, a case will be described in which, after detecting the optical output difference dPD and calculating the control voltage VAD, actual recording is performed on the optical disc.

The signals in FIG. 5 are shown from the top, (a) is the monitor voltage VM indicating the optical output, (b) is the recording gate WG indicating the recording section, and (c) is the recording signal WDT recorded on the optical disk.
, (d) is a hold gate HLD indicating a hold section,
(e) is a test signal TEST that indicates whether the recording is original recording on the optical disc or recording that detects the optical output difference, and (f) is the addition that controls the analog switch SW4 that adds the drive current IAD to correct the optical output difference. Signal ADD, (g) is the drive current IL from the constant current source of the transistor 10, (h) is the drive current IAD according to the optical output difference dPD due to the constant current source of the transistor 27, (i) is the drive current actually applied to the semiconductor laser 1. Drive current IL and drive current IAD with flowing drive current ILD
is added.

At time t11, the recording gate W shown in (a)
G becomes "high" and the recording optical output setting begins. At the same time, the test signal TEST shown in (e) becomes "high", indicating that the original recording on the optical disc is to begin. The addition signal ADD shown in (f) is "low", and the drive current IAD shown in (h) is zero. The drive current ILD of the constant current source shown in (i) is equal to the drive current IL shown in (g), a recording drive current IW flows, and closed-loop control is applied so that the optical output becomes a predetermined set value PS.

At time t12, the hold gate HLD shown in (d) becomes "low" and the control voltage is held.
The drive current IL shown in (g) caused by the constant current source of the transistor 10 causes a constant current IW to flow. The addition signal ADD shown in (e) becomes "high" and the analog switch SW4 is turned on. The control voltage VAD is applied to the transistor 27 through the analog switch SW4, and the transistor 27
A drive current IAD flows in accordance with the optical output difference dPD. From this, the semiconductor laser 1 has a drive current I of (i)
As shown in LD, IW+IAD, which is the sum of constant current IW and drive current IAD, flows.

As shown in the optical output in (a), at time t12
The optical output starts from a point dPD higher than the predetermined recording setting value PS by the amount of the drive current IAD added. IW+IA, which is the sum of constant current IW and drive current IAD
While being driven at D, the optical output of the semiconductor laser 1 decreases from the initial set value PS+dPD due to thermal equilibrium. At time t13, thermal equilibrium is established, and the optical output drops from the initial setting value PS+dPD by dPD, that is, settles at the predetermined recording setting value PS. Later,
Until time t14 when recording ends, the semiconductor laser 1 is in thermal equilibrium, and the optical output is stably controlled at a predetermined recording setting value PS.

As described above, according to this embodiment, there is a holding means for holding the control voltage, a constant current source for flowing a driving current corresponding to the control voltage to the semiconductor laser, and a recording light source driven with a constant current. an optical output difference detection means for detecting the difference between the output and the recording optical output after a predetermined period of time using the monitor signal; and a semiconductor laser drive current corresponding to the difference in the optical output detected by the optical output difference detection means. A calculation means for calculating a control voltage, and a constant current source that flows a constant current corresponding to the optical output of recording by the control voltage held by the hold means during recording, and driving corresponding to the difference in the optical output calculated by the calculation means. By providing an addition means for adding current or control voltage, when a semiconductor laser is driven with a constant current in an open loop, the optical output due to thermal equilibrium can be adjusted so that the optical output after decreasing due to thermal equilibrium becomes a predetermined value for recording. It is possible to correct the decrease and perform optimal recording.

Next, a second embodiment of the present invention will be described. In the second embodiment, the optical disc is driven with a constant current when the optical disc is not loaded, and the optical output difference detection means detects the difference between the optical output of recording at the beginning and the optical output of recording after a predetermined period of time. It is something to do.

[0046] If no optical disc is loaded, the optical disc device is in a non-operating state even if the power is on. If this state is utilized to detect the optical output difference, no time loss will occur. If the detected optical output difference is held, there is no need to measure the optical output difference before recording, and the recording operation can be started immediately. As described above, according to this embodiment, by detecting the optical output difference after the power is turned on and with no optical disc loaded, the time when the optical disc device is not operating can be used effectively, and the optical output difference can be detected. The time required for detection can be effectively eliminated.

Next, a third embodiment of the present invention will be described. In the third embodiment, the recording signal WDT is fixed at "high" as during reproduction and no modulation is performed, and the optical output of the initial recording and the recording after a predetermined time are determined by driving with a constant current. The optical output difference detection means detects the difference in optical output between the two.

Since the recording optical output is not modulated,
The light output is direct current, and the peak detection circuit 21 required in the first embodiment is no longer required. Furthermore, since the optical output is a direct current, the time required to reach thermal equilibrium can be reduced compared to modulated optical output. As a result, the optical output difference can be detected easily and at high speed.

As described above, according to this embodiment, the peak detection circuit 21 is not required by fixing the recording signal WDT in the same manner as during reproduction and detecting the optical output difference in recording without modulation. The optical output difference can be detected at high speed.

Next, a fourth embodiment of the present invention will be described. In the fourth embodiment, after the power is turned on, the semiconductor laser 1 is caused to emit light for a predetermined period of time at the optical output during reproduction, and then driven with a constant current to obtain the optical output for initial recording and for the recording after a predetermined period of time. A light output difference detection means for detecting a difference in light output is activated.

After the power is turned on, the semiconductor laser 1 is not emitting light, so the temperature is low. In this state, if the optical output for recording is immediately emitted and the difference in optical output due to thermal equilibrium is detected, the semiconductor laser 1 will not reach thermal equilibrium sufficiently and a detection error will occur. In order to prevent this, after turning on the power, the semiconductor laser 1 is made to emit light at the reproduction optical output for a predetermined period of time.
Increase the temperature of the semiconductor laser 1. After that, when the semiconductor laser 1 is driven with a constant current to emit recording optical output,
It is possible to accurately detect the difference in optical output of records that have reached thermal equilibrium.

As described above, according to this embodiment, after the power is turned on, the semiconductor laser 1 is made to emit light for a predetermined period of time at the optical output during reproduction, and then the difference in optical output during recording is detected. By bringing the two into a sufficient thermal equilibrium state, it is possible to accurately detect the difference in optical output.

In the fourth embodiment of the present invention, after the power is turned on, the semiconductor laser 1 is made to emit light at the optical output for reproduction, but this is between the optical output for recording and the optical output for reproduction. , it doesn't matter what.

Next, a fifth embodiment of the present invention will be described. The fifth embodiment detects the optical output when the semiconductor laser 1 is caused to emit light with two or more different driving currents, calculates the slope efficiency which is the ratio of the difference in optical output to the difference in driving current,
The difference in optical output detected by the optical output difference detection means is converted into a corresponding drive current or control voltage using the calculated slope efficiency.

The slope efficiency SL of the semiconductor laser 1 tends to vary depending on the temperature. This will be explained using FIG. 6. In FIG. 6, the horizontal axis represents the drive current of the semiconductor laser 1, and the vertical axis represents the optical output. Two lines indicate the relationship between drive current and optical output when the semiconductor laser 1 is at room temperature and high temperature.

First, at room temperature, the optical outputs for drive currents I1 and I2 are P1 and P2. At this time, the slope efficiency S
L1 is expressed as the following equation (5) (Math. 5).

SL=(P2-P1)(I2-I1)
(
5) Next, when the temperature rises, the slope efficiency slopes, and the drive current increases to I1' and I2' to output the same optical outputs P1 and P2. The slope efficiency SL2 at this time is expressed by the following formula (6)
It is expressed as (Equation 6).

SL2=(P2-P1)/(I2'-I1')
(6) As the slope efficiency SL changes depending on the temperature,
When calculating a corresponding drive current from the same optical output difference, if a fixed value slope efficiency SL is used, the error in the drive current becomes large. In the worst case, an excessive drive current is added to the recording drive current, and the optical output of the semiconductor laser 1 greatly exceeds the set value of the recording optical output, resulting in destruction.

Therefore, as shown in FIG. 6, the slope efficiency SL is calculated by causing the semiconductor laser to emit light at two or more different points, and the drive current or control voltage corresponding to the optical output difference is determined by the calculated slope efficiency SL. can be calculated accurately.

As described above, according to this embodiment, by causing the semiconductor laser to emit light at two or more different points, calculating the slope efficiency, and using the calculated slope efficiency, the drive current or Control voltage can be calculated accurately regardless of temperature. Note that in the fifth embodiment, the slope efficiency was calculated using two drive currents, but any number of points may be used as long as it is two or more points.

Furthermore, in the first embodiment, the optical output after a predetermined period of time was detected once to determine the optical output difference;
This may be detected more than once.

[0062]

As described above, according to this embodiment, when a semiconductor laser is driven with a constant current in an open loop, the optical output is adjusted by thermal equilibrium so that the optical output after decreasing due to thermal equilibrium becomes a predetermined value for recording. It is possible to correct the decrease in data and perform optimal recording.

[Brief explanation of drawings]

FIG. 1 is a circuit diagram showing the configuration of a semiconductor laser drive circuit in a first embodiment of the present invention.

FIG. 2 is an operational waveform diagram for explaining the optical output difference detection operation of the semiconductor laser drive circuit in the first embodiment.

[Fig. 3] A circuit diagram showing the configuration of a constant current source in the first embodiment.

[Figure 4] Characteristic diagram showing the relationship between the drive current and optical output of the semiconductor laser in Example 1

FIG. 5 is an operation waveform diagram for explaining the recording operation of the semiconductor laser drive circuit in the first embodiment.

FIG. 6 is a characteristic diagram for explaining the temperature characteristics of the slope efficiency of a semiconductor laser in another embodiment of the present invention.

[Figure 7] Circuit diagram showing the configuration of a conventional semiconductor laser drive circuit

[Fig. 8] Operation waveform diagram for explaining the operation of a conventional semiconductor laser drive circuit

[Figure 9] Operation waveform diagram for explaining the decrease in optical output due to thermal equilibrium of a conventional semiconductor laser

[Explanation of symbols]

1 Semiconductor laser 2 Photodetector 3 Current voltage converter 4 Differential amplifier 5 Reference voltage for playback 6.Reference voltage for recording 9 Buffer amplifier 10 Transistor 20 Optical output difference detection means 21 Peak detection circuit 22 AD converter 25 Subtractor

Claims (6)

[Claims] Claim 1: A semiconductor laser that generates a light beam;
a photodetector that generates a monitor signal corresponding to the optical output of the semiconductor laser; a reference voltage generating means that generates a reference voltage corresponding to the optical output to be set; a differential amplifier that generates a control voltage that controls the optical output of the semiconductor laser to a predetermined optical output; and a hold means that holds the control voltage of the differential amplifier;
a constant current source that flows a drive current in accordance with the control voltage to the semiconductor laser; a modulation means that modulates the drive current according to a recording signal; and a light output for recording at the beginning of driving with a constant current and after a predetermined period of time has elapsed. an optical output difference detection means for detecting a difference in optical output between recordings using the monitor signal; and an operation for calculating a drive current or control voltage of the semiconductor laser corresponding to the difference in optical output detected by the optical output difference detection means. means, and a drive current or a control current corresponding to the difference in the optical output calculated by the calculation means, to the constant current source that flows a constant current corresponding to the optical output of recording by the control voltage held by the holding means during recording. A laser drive circuit comprising: addition means for adding voltage; 2. The optical output difference detection means detects the difference between the optical output of recording at the beginning of driving with a constant current and the optical output of recording after a predetermined period of time when the optical disc is not loaded. The laser drive circuit according to item 1. 3. In a state where the recording signal is fixed and the drive current is not modulated, the optical output difference detection means detects the optical output of recording at the beginning of driving with a constant current and the optical output of recording after a predetermined period of time. 2. The laser drive circuit according to claim 1, wherein the laser drive circuit detects a difference between the two. 4. After turning on the power, the semiconductor laser is caused to emit light for a predetermined period of time at the optical output during reproduction, and then the optical output difference detection means is driven with a constant current and detects the optical output when the recording starts and a predetermined period of time has elapsed. 2. A laser drive circuit according to claim 1, which detects a difference in optical output in subsequent recording. 5. After turning on the power and causing the semiconductor laser to emit light at a predetermined optical output for a predetermined time, the optical output difference detection means:
2. The laser driving circuit according to claim 1, wherein the laser driving circuit detects the difference between the optical output of recording at the beginning of driving with a constant current and the optical output of recording after a predetermined period of time. 6. The calculation means calculates the ratio of the difference in light output to the difference in drive current (slope efficiency) from each light output when light is emitted with two or more drive currents, and detects the difference in light output. The laser drive circuit according to claim 1, wherein the drive current or control voltage corresponding to the difference in optical output detected by the means is calculated using slope efficiency.