JPH0369030A - Control system for laser diode - Google Patents

Abstract

PURPOSE:To attain stable laser control by controlling a laser diode while adopting both control to fix the quantity of monitor light and high frequency superimposing. CONSTITUTION:In an erase / write mode, a fundamental current source 300 makes a current flow required for a laser diode LD to emit 7mW light, for example. Then, a constant switch circuit 100 outputs a constant corresponding to the current to flow to a photodiode PD when the LD emits the 7mW light. In the erase / write mode, when erase / write data are '1', the current to be outputted from the current source 300 flows to the LD. When the LD emits the 7mW light, the output of a current subtraction part 200 is zero. A target value is 1mW, for example, an adjustment part 210 outputs a value showing the increase of the current. By the additional current of a variable current source 220, the LD emits 8mW light. In a read mode, a pulse-shaped current switch instruction signal is applied to a current switch circuit 310 and the circuit 100 outputs zero. Accordingly, the LD is operated so that the average of light emission amount goes to 1mW.

Description

[Detailed Description of the Invention] [Summary] Regarding the control of a laser diode in a rewritable optical disk device, the present invention aims to control the current of the laser diode by employing both APC and high frequency superposition. an LD, a photodiode PD that flows a current according to the amount of light emitted by the LD, and a basic current source that outputs a predetermined current value in read mode and another predetermined current value in erase/write mode; A current switch circuit that causes a current output from a basic current source to flow through the LD in response to a current switch switching instruction signal, a constant switch circuit that outputs a constant of a predetermined value or a constant of zero in response to a constant switch switching instruction signal, and a PD. a current subtraction section that outputs a value obtained by subtracting the constant output from the constant switch circuit from the current value flowing through the current subtraction section, an adjustment section that outputs a value according to the difference between the target value and the output of the current subtraction section, and an output of the adjustment section. The present invention includes a variable current source that outputs a current according to the current, and a high frequency superimposition circuit section that outputs a switching instruction signal to the current switch circuit and the constant switch circuit.

[Industrial application field]

The present invention relates to control of a laser diode in a rewritable optical disk device.

[Conventional technology]

Laser diode (
In the control of the LD (hereinafter abbreviated as LD), there is a read state with low output power and a write (erase) state with high power.When the output power is low, the LD enters the noise region and the S/N of the reproduced signal deteriorates. do.

As a countermeasure against this problem, a method has been adopted in which the power is set to a level higher than the low power (outside the LD noise region), high-speed switching is performed using this power, and the effective value power is lowered. This is called high frequency superposition.

On the other hand, the light emitting power of the LD changes according to the temperature change. Therefore, the light amount of the LD is monitored so that the light emitting power is constant, and the control (Aut) is used to keep the monitored light amount constant.
o Power Control) is performed.

[Problem to be solved by the invention]

However, conventionally, there has been no method for achieving both APC and high frequency superimposition.

The present invention was created in view of this point, and aims to control the current flowing through the laser diode in a rewritable optical disk device by employing both APC and high frequency superposition. .

[Means to solve the problem]

FIG. 1 is a diagram explaining the principle of the present invention. The laser of the present invention
The diode control system consists of a laser diode LD, a photodiode PD that flows a current according to the amount of light emitted by the laser diode LD, and a photodiode PD that outputs a predetermined current value in read mode and performs write mode.
Basic current source 3 that outputs a current of another predetermined value in mode
00, and the basic current source 300 according to the current switch switching instruction signal.
A current switch circuit 310 that flows the current output from the laser diode LD, a constant switch circuit 100 that outputs a constant of a predetermined value or a constant of zero according to a constant switch switching signal, and a current that flows through the photodiode PD. A current subtraction unit 200 that outputs a value obtained by subtracting a constant output from the constant switch circuit 100 from a value, an adjustment unit 210 that outputs a value according to the difference between the target value and the output of the current subtraction unit 200, and an adjustment unit 210 The variable current source 220 outputs a current according to the output of the high frequency superimposing circuit section 400.

The sum of the current output from the current switch circuit 310 and the current output from the variable current source 220 flows through the laser diode LD.

In the read mode, the high frequency superimposition circuit section 400 outputs a high frequency pulsed current switch switching instruction signal, and also outputs a constant switch switching instruction signal indicating that a constant of zero should be output, and erases. /Write mode and if there is erase/write data, outputs a current switch switching instruction signal that instructs that the current of the basic current source 300 should flow to the laser diode LD, and also outputs a predetermined constant. It is configured to output a constant switch switching instruction signal indicating what to do.

[Function] In the erase/write mode, the basic current source 300 flows the current necessary for the laser diode to emit light of, for example, 7 mW, and the constant switch circuit 100 causes the laser diode LD to emit light of 7 mW. It outputs a constant corresponding to the value of the current flowing through the photodiode PD when this happens. In erase/write mode and in erase/write mode.
When the data is l, the current output from the basic current source 300 flows through the laser diode LD. When the laser diode LD emits light of 7 mW, the output of the current subtraction section 200 becomes zero. For example, the target value is 1mW
Therefore, the adjustment unit 210 outputs a value indicating that the current should be increased. The current output from variable current source 220 also flows through laser diode LD. Variable current source 2
With an additional current of 20, the laser diode LD always emits 8 mW.

In the read mode, the basic current source 300 flows a current necessary for the laser diode to emit light of, for example, 2 mW, and a high frequency pulsed current switch switching instruction signal is given to the t-current switch circuit 310, which switches the constant switch. Circuit 100 outputs a constant of zero. In read mode,
The laser diode LD operates so that the average amount of light emitted is 1 mW.

〔Example〕

FIG. 2 is a block diagram of one embodiment of the present invention.

In the figure, 1 to 3 are D/A converters, and 4 is an A/A converter.
/D converter, 5 to 8 are level shift circuits, 1
0 to 16 are transistors, 17 is a current-voltage converter,
1 is an error integrator, 19 is a switch, R1 to R4 are resistors, LD is a laser diode, and PD is a photodiode. I th : Current at the point where the laser starts emitting light (threshold power) II : Current at the point equivalent to the read power (1 mW
) ■2: Current for high frequency superimposition (2mW) ■, Nirite・
Current equivalent to power (8mW) ■'l: Monitor current during read power emission ■'2mv
aj Average value of monitor current for high frequency superimposition) '3 Knee 7 (
The monitor current for each power is shown.

The microprocessor applies digital signals to the inputs of D/A converters 1-3. A/D converter 4
The digital output of is captured by the microprocessor. Level shift circuits 5 to 8 may be considered to correspond to voltage dividers.

The D/A converter 3 is set so that the transistor 10 flows a monitor current of 1/3171. I'3
1'l is a current flowing through the photodiode PD when the laser diode emits light of 7 mW, for example, and is hereinafter expressed as I(2). transistors 11 and 1
2 constitutes a changeover switch. When the signal a' is at a high level and the signal bo is at a low level, the transistor 11 is turned on, and when the signal a is at a low level and the signal bo is at a high level, the transistor 12 is turned on. When the transistor 12 is on, the sum of (2) and the current flowing out from the current-voltage converter 17 flows into the photodiode PD.

Photo diode PD receives part of the light emitted from laser diode LD.

The current-voltage converter 17 converts the current flowing through the photodiode PD into a voltage when the transistor 12 is off, and subtracts I (k) from the current flowing through the photodiode PD when the transistor 12 is on. Convert the value to voltage. The output of the current-voltage converter 17 is sent to the microprocessor via the A/D converter 4. Further, the output of the current-voltage converter 17 is applied to one input terminal of the error integrator 19 . The input terminal of the error integrator 18 receives a photo signal when the laser diode emits light of 1 mW.
A value (target value) obtained by converting the current flowing through the diode PD into a voltage is applied. A proportional element may be added to the error integrator 18. The output of error integrator 18 is applied to the base of transistor 13 via switch 19 and level shift circuit 8.

The switch 19 is turned on when performing APC;
It is turned off when not performed. The current flowing through transistor 13 is supplied to laser diode LD. The sum of the current flowing through the transistor 13 and the current flowing through the transistor 15 flows through the laser diode LD.

When writing data to an optical disk, a digital value is applied to the DAC 2 to cause the laser diode LD to emit 7 mW, and when reading data from the optical disk, a digital value is applied to the DAC 2 to cause the laser diode LD to emit 2 mW. A digital value is applied to DAC2. D.A.
The output of C2 is applied to the base of transistor 14 via level shift circuit 6. transistors 15 and 1
Reference numeral 6 constitutes a changeover switch, in which a transistor 15 is turned on when the signal a is at a low level and a signal is at a high level, and a transistor 16 is turned on when the signal a is at a high level and the signal is at a low level. When transistor 15 is on, the current flowing through transistor 14 is supplied to laser diode LD.

FIG. 3 is a diagram showing an example of the configuration of a high frequency superimposing circuit section used in the present invention, and FIG. 4 is a diagram showing waveforms of the high frequency superimposing circuit section. In the figure, G1 to G4 indicate gates, and Sl to S indicate signal waveforms, respectively.

When the erase/write data is 1 and the erase/write gate is 1, the signal bo is O1, the signal a'' is 1, the signal O2 is 0, and the erase/write data is O and When the erase/write gate is 1, the signal bo becomes 1. The signal a' becomes O1. The signal a becomes 1. The signal a becomes 0.

When the erase/write data is 1 and the erase/write gate is O, the signal bo is 1. Signal a' becomes O, and signals S and a invert their states at regular intervals. The same applies when the erase/write data is O and the erase/write gate is O. Figure 4 shows the waveforms of each part.

FIG. 5 is a diagram showing the LD current, its output power, and the modulation status by write data.

If the write gate is 1 and the write data is 1, then
Transistor 14 conducts a current corresponding to 7 mW, and this current corresponding to 7 mW flows through transistor 15 to laser diode LD. When the write gate is 1 and the write data is 1, a current 1 (k) corresponding to 7 mW flows out from the transistor 10 and is supplied to the photodiode PD via the transistor 12.
Assuming that the photodiode PD is passing a current corresponding to a light emission amount of 7 mW, the current flowing out from the current-voltage converter 17 becomes zero. Since zero is input to one input terminal of the error integrator 18 and a target value of 1 mW is input to the tenth input terminal, the error integrator 18 instructs the transistor 13 to increase the current, Ultimately, the transistor 13 flows a current corresponding to the amount of light emission of 1 mW.

If the write gate is 1 and the write data is 0,
Transistor 14 flows a current equivalent to 7 mW, and this current equivalent to 7 mW flows through transistor 16 and resistor R.
4 and flows to ground.

If the write gate is 1 and the write data is O, then
A current I corresponding to 7 mW flows out of the transistor 10
Since (b) flows to the ground via the transistor 11, assuming that the amount of light emitted from the photodiode PD is zero, the current flowing out from the current-voltage converter 17 becomes zero.

Since zero is input to one input terminal of the error integrator 18 and a target value of 1 mW is input to the tenth input terminal, the error integrator 18 outputs a signal from the transistor 13 that indicates that the current should be increased.
Finally, the transistor 13 flows a current corresponding to the amount of light emission of 1 mW.

If the write gate is 0, transistor 14 is 2
A current corresponding to mW is applied. Signal a and signal S alternately turn on and off, but when signal a is on, 2mW
A current corresponding to is supplied to the laser diode LD. When the write gate is at O, the current flowing out of transistor 10 flows through transistor 11 to ground.

Assuming that the amount of light emitted from the photodiode PD is 2 mW, the current flowing out from the current-voltage converter 17 is equivalent to 2 mW. Since a voltage equivalent to 2 mW is input to one input terminal of the error integrator 18 and a target value of 1 mW is input to the tenth input terminal, the error integrator 18 instructs the transistor 13 to reduce the current. do. transistor 13
The current flowing through the laser diode LD is adjusted so that the average light emission amount of the laser diode LD is 1 mW.

FIG. 6 is a diagram illustrating the output power of the LD when high frequency is superimposed. When high frequency is superimposed (read), APC is applied to the average value, and as shown in Figure 6, even if the oscillation duty changes, the APC circuit automatically controls the average power to 1 mW. be done.

FIG. 7 is a diagram showing the flow of processing by the microprocessor.

■Reset all DACs 1 to 3.

■ Cut the APC loop and connect the light emission adjustment system.

■ Set E/WGT=1 and E/WDT=1. Transistor 15 turns on.

■ Check whether the LD has started emitting light or not. If NO, proceed to ■; if YES, proceed to ■.

■ Add 1 to DAC1. Return to ■.

■ Check whether the light emission amount of the LD is 2 mW or not. If NO, proceed to ■; if YES, proceed to ■.

■ Add 1 to DAC2. Return to ■.

■ Set DAC2 in register R1 (register in the microprocessor) and reset DAC2.

■ Check whether the LD's light emission amount is at the read power (1mW). If No, proceed to [phase], if YES, proceed to ■
Proceed to.

[Phase] Add 1 to DAC1. Return to ■.

■ Check whether the amount of light emitted from the LD is at the light power (8mW). If NO, proceed to @; if YES, proceed to ■.

@Add 1 to DAC2. Return to ■.

@ Set DAC2 to R2 (register in the microprocessor).

Q　Reset DAC2 and 1.

@ Set E/WGT=0, E/WDT=0.

[Phase] Turn on APC.

■ The output of the current-voltage converter 17 is read power (1 m
Check whether W) is indicated, and if NO, proceed to ■; if YES, proceed to [Phase].

■ Add 1 to DACl. Return to ■.

■ Remove R2 and set it to AC2.

[Phase] Set E/WGT=l, E/WDT=1.

■ The output of the current-voltage converter 17 is read power (1 m
Check whether W) is indicated, and if No, proceed to @; if YES, proceed to [phase].

@Add 1 to DAC3. Return to ■.

@Set R1 to DAC2.

@ Set E/WGT=OS'E/WDT=o.

@Check whether E/WGT (erase/write gate) is at high level. If YES, proceed to [phase].

@Set R2 to DAC2.

@Check whether E/WGT is at a low level. If YES, proceed to [phase].

@Set R1 to DAC2. Proceed to @.

FIG. 8 is a diagram showing a second embodiment of the present invention.

In the figure, 2-1 and 2-2 are D/A converters;
1 and 22 indicate switches, and 23 indicates an inversion gate, respectively.

In the embodiment shown in FIG. 8, the value of register R1 is preset in the D/A converter 2-1, the value of register R2 is preset in the D/A converter 2-2, and the value of register R2 is preset in the D/A converter 2-2.
/WGT=O, turn on the switch 21 and turn on the E/W
When GT=1, switch 22 is turned on. The rest of the structure is the same as the embodiment shown in FIG. According to the embodiment shown in FIG. 8, it is possible to switch from read mode to erase/write mode or from erase/write mode to read mode at high speed.

FIG. 9 is a diagram showing an example of the LD unit. Figure 9 (a
), the cathode of the laser diode LD and the photo-
It is connected to the anode of the diode, and the connection point is grounded. Further, in FIG. 9(b), the cathode of the photodiode PD and the anode of the laser diode LD are connected, and the connection point is grounded. In the embodiment shown in FIG. 2, the LD unit shown in FIG. 9(a) is used.

FIG. 10 is a diagram showing an example of a circuit on the LD current supply side when the LD unit of FIG. 9(b) is used. In the figure, 14' to 16'' indicate transistors, respectively. In this example, NPN type transistors are used as the transistors 14' to 16'.

The circuit on the PD current detection side is similarly configured using NPN transistors. In addition, the lead shown in this example
The power write power and high frequency superimposition power are shown as examples, and the functions of the present invention will not be impaired even if the values are changed.

[Effect of the invention] As is clear from the above explanation, according to the present invention, AP
Under the condition where C is applied, high frequency superimposition during write emission and reading becomes possible, and stable laser control becomes possible.

[Brief Description of the Drawings] Fig. 1 is a diagram explaining the principle of the present invention, Fig. 2 is a block diagram showing a first embodiment of the invention, Fig. 3 is a diagram showing an example of the configuration of a high frequency superimposing circuit section, Figure 4 shows the waveform of the high frequency superimposition circuit section, and Figure 5 shows the LD current, its output power, and the light output power.
6 is a diagram showing the output power of the LD when high frequency is superimposed, FIG. 7 is a diagram showing the processing flow of the microprocessor, and FIG. 8 is a diagram showing the process flow of the microprocessor. FIG. 9 is a diagram showing an example of an LD unit, and FIG. 10 is a diagram showing important parts of a third embodiment of the present invention. ■ or 3...D/A converter, 4...A/D converter, 5 or 8...level shift circuit, 10
16...Transistor, 17...Current voltage converter, 18...Error integrator, 19...Switch, R
1 to R4...resistance, LD...laser diode, PD...photo diode.

Claims (1)

[Claims] A laser diode (LD), a photodiode (PD) that flows a current according to the amount of light emitted by the laser diode (LD), and a photodiode (PD) that outputs a predetermined current value in a read mode and performs a write operation. - A basic current source (300) that outputs a current of another predetermined value in the mode, and a current switch circuit (300) that causes the current output from the basic current source to flow through the laser diode (LD) in response to a current switch switching instruction signal. 310), a constant switch circuit (100) that outputs a constant of a predetermined value or a constant of zero according to a constant switch switching signal, and an output of the constant switch circuit (100) from the current value flowing through the photodiode (PD). a current subtraction unit (200) that outputs a value obtained by subtracting a constant; an adjustment unit (210) that outputs a value according to the difference between the target value and the output of the current subtraction unit; and an output of the adjustment unit (210). A variable current source (220) that outputs a current according to In the read mode, the high frequency superimposition circuit section (400) outputs a high frequency pulsed current switch switching instruction signal, and also outputs a zero current switch switching instruction signal. Outputs a constant switch switching instruction signal indicating that a constant should be output, and when in erase/write mode and there is erase/write data, the current of the basic current source (300) is transferred to the laser diode (LD). A laser diode characterized in that the laser diode is configured to output a current switch switching instruction signal indicating that a current should be outputted at a constant value, and a constant switch switching instruction signal indicating that a predetermined constant should be outputted. control method.