JP2650185B2 - Laser control method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical disk apparatus for optically writing / reading data, and more particularly to a laser control method for controlling a laser beam emitted from a laser diode to be constant. An optical disk device, which is expected as a large-capacity external storage device for an information processing device, can perform a high-density recording which is ten and several times higher than a conventionally used magnetic disk device or the like.

For recording data on an optical disk device, for example, a strong laser light amount (a light amount corresponding to 5 to 10 mW, which is called a write power level) emitted from a laser diode on a recording film on an optical disk medium is used as a light beam. Irradiation is performed by making holes (pits) or changing the crystalline state of the recording film by the thermal reaction.

On the other hand, data written on an optical recording medium is a weak laser beam (about 1 mW) emitted from a laser diode.
(This is called a read power level with a considerable amount of light.) As a light beam, the reflected light amount can be read by irradiating the recording film with the light beam. The light emission amount of the laser diode is monitored by the photodiode so that the light emission amount of the laser diode used in this way can be obtained as a more stable write power level and read power level,
The emission power of the laser diode is controlled by the monitor current.

[0004] Further, a laser diode has specific characteristics, and in order to use the laser diode for an optical disk device, an adjustment corresponding to the specific characteristics is performed so that a substantially constant write power level and read power level can be obtained. Is set to It is expected that such a setting and control to obtain a constant write power level and read power level at all times can be realized by a simple control method.

[0005]

2. Description of the Related Art FIG. 3 is a block diagram illustrating a conventional example, FIG. 4 is a diagram illustrating a relationship between a drive current of a laser diode and a light emission amount, and FIG. 5 is a diagram illustrating a monitor voltage. FIG. 3 shows a circuit for controlling the driving of the laser diode unit 1 of the optical disk device. This circuit diagram shows a read power level (light amount of about 1 mW) and a write power level (light amount of about 5 to 10 mW) according to the drive current. ) Laser diode (hereinafter referred to as LD)
And an LD unit 1 comprising a photodiode (hereinafter referred to as PD) for monitoring the amount of light emitted from the LD, and a variable resistor RV1 for adjusting at the time of initial setting the monitor current flowing through the PD to a predetermined voltage value. The PD current adjusting unit 2 includes an operational amplifier 31, fixed resistors R1 and R2, and a capacitor C1.
The read power level detector 3, which sets and outputs a voltage corresponding to the read power level set in the analog (hereinafter referred to as D / A) converter 4, so that the output power of the LD becomes the PD voltage indicating the read power level. , A D / A converter 4, a transistor TR 1, and a wire ring L, which are preset by a microprocessor (not shown).
A read power level current adjusting section 5 for adjusting the drive current so that the LD emits the read power level, and two transistors TR2, TR3;
A write power level current adjusting unit 6 which comprises a fixed resistor R3 and adjusts a drive current so as to emit light of a write power level from the LD. The micro power is previously adjusted so that the output power of the LD becomes a PD voltage indicating the write power level. The D / A converter 7 includes a D / A converter 7 set by a processor (not shown), a transistor TR4, and a fixed resistor R5. The write power level set in the D / A converter 7 is written so that the LD outputs the write power level. It comprises a write power level setting section 8 for setting a write power level current adjusting section 6 so that the LD outputs a power level, a transistor TR5, and a variable resistor RV2. The write power level current subtraction setting unit 9 for setting the subtraction unit 10 A write power level current subtracting unit 10 for subtracting the write power level current from the PD current in which the write power level current is superimposed on the read power level current; The transistors TR2 and TR2 of the write power level current adjustment unit 6 and the write power level current subtraction unit 10 include two zener diodes D1 and D2 so that the write power level is shifted according to write data (hereinafter, referred to as write data). And a level shift unit 11 for adjusting biases of 3, 6, and 7.

For example, a current flowing through an LD during data writing has a pulse waveform as shown in FIG. 4 and is applied.
In FIG. 4, the vertical axis represents the light emission amount of the LD (in units of mW), the horizontal axis represents the applied current (ILD) to the LD, the symbol (a) represents the characteristic curve of the LD, and the symbol (b) represents the write power level point. , Code (c) is the read power level point, W is the current level flowing through the LD when writing data, and code R is L when reading data.
The current level flowing through D is shown.

At this time, the amount of light emitted from the LD is
Has a waveform shown in FIG. That is, a pulse waveform of the write power level (b) 'is superimposed on the read power level (c)'. On the other hand, each LD has its own characteristic, and if there is a large change in the write power level and the read power level output by the LD, the data quality is adversely affected. Initial setting is performed by the PD current adjustment unit 2 so that a substantially constant write power level and read power level can always be obtained.

That is, when the LD emits light with a constant power by a power meter, a synchroscope, or the like, which is completed as an optical head (not shown), the PD
Is adjusted by the variable resistor RV1 so as to have a constant value, and the variable resistor RV1 is locked so as to fix the output voltage at that time. The circuit shown in FIG. 3 automatically controls the PD voltage at the time of monitoring by the PD to the read power level when the output power fluctuates due to a change in LD characteristics due to, for example, deterioration of the LD or fluctuation of the ambient temperature. ing.

For this purpose, if there is a write power level component, the write power level equivalent is removed by the write power level current subtraction unit 10 and the set values set in the D / A converters 4 and 7 are used as a reference. To automatically adjust the light emission power. Even when this automatic adjustment function is set as a predetermined function, the step of adjusting the variable resistor RV2 in the write power level current subtraction section setting section 9 and locking the variable resistor RV2 to fix the state at that time is included. Will be needed.

For this reason, in the conventional example shown in FIG. 3, it is difficult to automate these tests (tests for each printed board), which is a factor that hinders reduction in test man-hours and cost reduction, and changes the LD unit 1. However, there is a problem that it cannot be easily performed.

[0011]

According to the present invention, in a laser control method, a first step of detecting a value corresponding to a light emission power of a laser diode via an output of a photodiode, and reading the value into the laser diode. Power emission, a first instruction value corresponding to the read power level current is determined so that the detection means detects a first detection value corresponding to the read power level, and the laser diode emits write power. The second detection value corresponding to the current of the write power level is determined so that the detection means detects the second detection value corresponding to the write power level, and the first detection value and the second detection value are determined. A second step of determining a subtraction amount corresponding to a difference from the second detection value;
A third step of supplying a read power level current to the read power current supply means with the first instruction value at the time of read power emission, and a write power current supply of the second instruction value at the time of write power emission. A fourth step of supplying a current of a write power level to the means; and, at the time of write power emission, subtracting the subtraction amount from the detection value of the detection means, and converting the detection value of the detection means at the time of write power emission to the read power level. A fifth step of normalizing to a corresponding detection value and a sixth step of controlling the emission power of the laser diode based on the normalized detection value at the time of light power emission are at least included. And

Further, the second step is performed at the time of starting the apparatus or when replacing the optical storage medium. Further, when changing the write power level, the second instruction value and the subtraction amount are both changed. Further, when the first instruction value, the second instruction value, or the subtraction amount is determined by the light power emission, the determination is performed in an off-focus state or a defocus state.

Further, in the second step, after the first instruction value is determined, the second instruction value is determined, and finally the subtraction amount is determined. FIG. 1 shows a block diagram illustrating the principle of the present invention. The block diagram of the present principle is the functional blocks 1 to 11 described in FIG.
The PD current / voltage conversion unit 12 converts the current flowing through the PD into a voltage at a predetermined conversion ratio instead of the PD current adjustment unit 2 (excluding the PD current adjustment unit 2).
And a PD voltage between the PD current / voltage converter 12 and the read power level detector 3 and whose output (output to a microprocessor not shown) value of the A / D converter 16 indicates the read power level To D / A converter 4
Is set, the analog switch 13 that turns off the output of the PD current / voltage converter 12 to stop the functions such as the read power level detection 3 and the like, and the output value of the A / D converter 16 indicates the read power level. Of the D / A converter and the write power level setting unit 8 and the write power level current subtraction unit setting unit 17 which determine a value determined by the microprocessor (not shown) so as to obtain a proper PD voltage value. An analog switch for turning on the operation of the write power level current subtraction section setting section 17 while the output value of the A / D converter 16 indicates the PD voltage indicating the read power level. , An A / D converter 16 for setting the PD voltage at that time and notifying the microprocessor of the PD voltage is additionally provided.

The first auto power control is performed by the read power level detection 3 and the read power level current adjustment unit 5, and the second auto power control is performed by the write power level setting unit 8 and the write power level current subtraction unit setting unit 17. Power control shall be formed. With the above-described configuration, the laser diode is supplied to a laser control circuit (first and second auto power control) for controlling the amount of laser light emitted from each LD having a specific characteristic curve to be always constant. When the unit is initially set, a plurality of resistor groups are set so as to have a predetermined ratio by a dip switch or the like, and a D / D having a set value such that a PD voltage at the time of light power emission indicates a read power level is set. By automatically and easily controlling the subtraction of the write power level current by the A converter, automation of the test of the laser control circuit, reduction of test man-hours and cost reduction, and control of the control by the laser control circuit are realized. Automation can be further promoted.

In the second step, the first instruction value, the second instruction value, and the subtraction amount are each determined while monitoring with a photodiode, so that the emission power can be adjusted with higher accuracy. Can be performed. In addition, when the first instruction value, the second instruction value, and the subtraction amount are determined by the write power emission, an erroneous recording on the optical storage medium can be performed by setting the optical disk in an off-focus state or a defocus state. Alternatively, erroneous erasure can be prevented.

Further, the setting of the first instruction value, the second instruction value, and the subtraction amount is performed at the time of starting the apparatus or at the time of exchanging the medium.
It is possible to control the amount of laser light corresponding to the influence of a temperature change or the like.

[0017]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, the gist of the present invention will be specifically described with reference to an embodiment shown in FIG. FIG. 2 is a block diagram illustrating an embodiment of the present invention. Note that the same reference numerals indicate the same objects throughout the drawings. The PD current / voltage converter 12 in the present embodiment includes fixed resistors R9 to R13 for converting the PD current into a voltage at a predetermined ratio, and fixed resistors R9 to R13.
A switch 21 (for example, a dip switch, a shotper, an analog switch, etc., but a dip switch is used in this embodiment) for short-circuiting 9 to R13.

The fixed resistor R of the PD current / voltage converter 12
9 to R13 are set at the time of design. The setting of the switch 21 is performed at the time of assembling and testing the device.
That is, as described above, the light emission power of the LD and the PD current are equal to the LD current.
Since each unit 1 is different, it cannot be used as it is because there are many errors. Therefore, the characteristic data at this time is measured in advance, and based on the characteristic data, the output voltage of the PD (the value set in the A / D converter 16 after A / D conversion) when the light is emitted at a constant power is constant. The switches 21 determine the resistance values of the fixed resistors R9 to R13 which are weighted in advance so as to have the values.

As a result, the relationship between the light emission power of the LD and the PD voltage is determined, for example, such that the light emission power of 1 mW is the PD voltage of 0.5 V. Also, the emission power and P
Since the D voltage is in a 1: 1 proportional relationship, if the light emission power changes, a PD voltage corresponding thereto can be obtained. The above is the contents to be processed before product shipment, but the following processing is performed at the time of use on the user side, for example, when the power is turned on or the optical disk is replaced.

A first auto power control (hereinafter referred to as APC) having a function of automatically adjusting the light emission power of the LD by feedback of the read power level.
When the processing portion (for example, the read power level detection unit or the read power level current adjustment unit 5) changes, ie, the light emission power of the LD changes due to a rise in temperature or the like (changes as indicated by the dotted line in FIG. 5), the change (The dotted line in FIG. 5 functions to return to the solid line.) The function of the first APC processing portion is turned off by the analog switch 13.

The analog switch 13 is turned on / off under the control of a microprocessor (not shown). Further, while the function of the first APC processing section is turned off in the analog switch 13, the A / D converter 1
The D / A converter 4 is set so that 6 becomes a PD voltage indicating a specified power (about 1 mW) at the time of reading. D / A
The set value of the converter 4 is supplied to the base of the transistor TR1 via the operational amplifier 31 operating as a voltage follower. Thereby, the transistor TR1
Is turned on, and the emitter voltage and the voltage VEE1 (VEE1
2 also indicates a supply voltage), and the current determined by the fixed resistor R3 is supplied to the LD, whereby the first APC process is performed.

Next, the operation of adjusting the light emission power of the LD at the write power level will be described. In this case, since a power level at which data can be written is output, defocusing is performed to the extent that data writing cannot be performed. Since light emission at the time of data writing is pulse-modulated as shown in FIG. 4, the PD voltage is determined by the ratio of the duty cycle of the pulse. For example, in the case of pulse emission of 10 mW and a duty of 50% (however, read power 1 mW, 0.5 V
/ MW), [{10mW-1mW / 2} + 1mW] × 0.5-2.75V.

Therefore, in the state where the writing light emitting operation is performed,
Turn off the analog switch 15 and set the A / D converter 1
The value of the D / A converter 7 is set by a microprocessor (not shown) in a state where the writing light emission operation is performed so that the output of 6 becomes this value. When the write power is changed, a value calculated by the above equation is used according to the write power.

Next, the write power level current subtracting section 10 for subtracting the PD current corresponding to the light power level light emission is operated. That is, the analog switch 15 is turned on (that is, the second APC including the write power level current subtractor setting unit 17 and the like is turned on), and the set value of the D / A converter 14 is changed to the value of the A / D converter 16. Indicates the PD voltage of the read power level. In the case of the present embodiment, this voltage value is 0.5V.

Finally, the first APC processing part is turned on,
The set value of the D / A converter 4 is adjusted again so that the output value of the A / D converter 16 becomes the read power level 0.5V.

[0026]

According to the present invention as described above, the automation of the test of the laser control device, the reduction in the number of test steps and the cost can be facilitated, and the replacement of the LD unit can be facilitated. Further, by using the laser control method of the present invention, there is an effect that the specified emission power can always be obtained accurately.

[Brief description of the drawings]

FIG. 1 is a block diagram illustrating the principle of the present invention.

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

FIG. 3 is a block diagram illustrating a conventional example.

FIG. 4 is a diagram illustrating a relationship between a drive current of a laser diode and a light emission amount.

FIG. 5 is a diagram illustrating a monitor voltage.

[Explanation of symbols]

 Reference Signs List 1 LD unit 2 PD current adjustment unit 3 Read power level detection unit 4, 7, 14 D / A converter 5 Read power level current adjustment unit 6 Write power level current adjustment unit 8 Write power level setting unit 9, 17 Write power level current Subtractor setting unit 10 Write power level current subtractor 11 Level shifter 12 PD current / voltage converter 13, 15 Analog switch 16 A / D converter 21 Switch 31 Operational amplifier

Claims (5)

(57) [Claims] 1. A first step in which detection means detects a value corresponding to the light emission power of a laser diode via an output of a photodiode, causing the laser diode to emit read power, and the detection means setting a read power level. The first instruction value corresponding to the current of the read power level is determined so as to detect the first detection value corresponding to, and the laser diode emits the write power, and the detecting means corresponds to the write power level. A second instruction value corresponding to the current of the write power level is determined so as to detect a second detection value, and a subtraction amount corresponding to a difference between the first detection value and the second detection value is determined. A second step of determining, and a third step of supplying a read power level current to the read power current supply means with the first instruction value when the read power is emitted. A fourth step of supplying a write power level current to the write power current supply means with the second instruction value at the time of light power emission; and the subtraction amount from the detection value of the detection means at the time of light power emission. A fifth step of normalizing a detection value of the detection means at the time of write power emission to a detection value corresponding to a read power level; and, at the time of write power emission, of a laser diode based on the normalized detection value. A laser control method comprising at least a sixth step of controlling light emission power. 2. The laser control method according to claim 1, wherein the second step is performed at the time of starting up the apparatus or replacing the optical storage medium. 3. The laser control according to claim 1, wherein when the write power level is changed in the second step, both the second instruction value and the subtraction amount are changed. Method. 4. In the second step, when the first instruction value, the second instruction value, or the subtraction amount is determined by the light power emission, the determination is performed in an off-focus state or a defocus state. 4. The laser control method according to claim 1, wherein: 5. The method according to claim 1, wherein in the second step, after the first instruction value is determined, the second instruction value is determined, and finally the subtraction amount is determined. Laser control method.