JP2503006B2 - Semiconductor laser drive device in optical recording / reproducing apparatus - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Outline] The present invention is designed to generate a specified read power even when a semiconductor laser is deteriorated in a semiconductor laser drive circuit of an optical recording / reproducing apparatus (hereinafter referred to as an optical disk apparatus). In addition to the photodetector for the first control means for controlling the read power level, a second photodetector for controlling the write power level is provided to control the write power to a specified value.

[Industrial applications]

The present invention relates to an optical disk device, and more particularly to a driving device for a semiconductor laser that serves as a light source.

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 that is ten and several times higher than a conventionally used magnetic disk device or the like.

In addition, for recording data on the optical disk device, for example, a strong laser light amount (5-10 mW equivalent light amount) emitted from a semiconductor laser (hereinafter abbreviated as LD of laser diode) is recorded on a recording film on the optical disk medium. It is performed by irradiating a light beam as a light power level and making holes (pits) by its thermal reaction (however, there is also a method of changing the crystalline state of the recording film).

On the other hand, the data written on the optical recording medium is obtained by irradiating the recording film with a weak laser beam emitted from the LD (a light amount equivalent to about 1 mW, which is called a read power level) as a light beam. It can be read by reflected light.

In order to obtain a more stable write power level and read power level for the LD emission amount used in this way, the LD emission amount is monitored by a photodetector (hereinafter abbreviated as PD of photodiode). Then, the light emission power of the LD is controlled by the monitor current.

Further, the LD has its own characteristic, and in order to be used for an optical disc, adjustment is made corresponding to the characteristic, and it is set so that a substantially constant write power level and read power level can be obtained. .

Therefore, it is desired that the power of the LD be able to emit the specified power even if the LD itself deteriorates.

[Conventional technology]

FIG. 4 shows a block diagram of a conventional LD drive circuit. In the figure, reference numeral 1 denotes an LD unit, which monitors a light emitting amount from an LD that emits a read power level (a light amount corresponding to about 1 mW) and a write power level (a light amount corresponding to about 5 to 10 mW) by a drive current. And PD.

Reference numeral 2 denotes a PD current adjusting unit, which includes a variable resistor RV1 for adjusting the monitor current flowing in the PD to a predetermined voltage value at the time of initial setting.

Reference numeral 3 is a read power level detector, which is an operational amplifier
It is composed of 31 and 32, fixed resistors R1 and R2, and capacitor C1, and detects the PD voltage taken out from the PD current adjusting unit 2 and sets it in the digital / analog (hereinafter abbreviated as D / A) converter 4. It has the function of setting and outputting a voltage equivalent to the read power level.

The D / A converter 4 is preset by an arithmetic circuit (not shown) so that the output power of the LD becomes the PD voltage indicating the read power level.

Reference numeral 5 is a read power level current adjusting unit, which is composed of a transistor TR1, a loop L, and a fixed resistor R3, and has a function of adjusting the drive current so that the LD emits light at the read power level.

The first automatic control means configured in FIG. 1 includes an LD unit, a PD current adjusting unit 2, a read power detecting unit 3, and a D / A.
It is composed of a converter 4 and a read power level current adjusting section 5.

A write power level current adjusting unit 6 has a function of adjusting the drive current so that the LD emits light at the write power level.

Reference numeral 7 denotes a D / A converter, which is set in advance by an arithmetic circuit (not shown) so that the output power of the LD becomes the PD voltage indicating the write power level.

A write power level setting unit 8 is composed of a transistor TR4 and a fixed resistor R5, and controls the write power level current adjusting unit 6 so that the LD outputs the write power level set in the D / A converter 7. It has a function to set.

9 is a write power level current subtraction unit setting unit,
Composed of a transistor TR5 and a variable resistor RV2. The output from the D / A converter 7 causes a write power level current subtraction unit.
Has the function of setting 10.

Reference numeral 10 is a write power level current subtraction unit, which is composed of two transistors TR6, TR7, and a fixed resistor R6, and is used to subtract the write power level current from the PD current in which the write power level current is superimposed on the read power level current. Has a pulling function.

Reference numeral 11 denotes a shift unit, which is composed of a logical product circuit AND, two Zener diodes D1 and D2, and resistors R7 and R8, so that the write power level is shifted according to write data (hereinafter abbreviated as write data). In addition, it has a function of adjusting the bias of each of the transistors TR2, TR3, TR6, TR7 of the write power level current adjusting unit 6 and the write power level current subtracting unit 10.

The second automatic control means configured in FIG. 1 includes a write power level current adjusting section, a D / A converter 7, a write power level setting section 8, a write power level current subtraction section setting section 9, a write power level current subtraction section. It is composed of a unit 10, a shift unit 11, and the like.

FIG. 5 is a diagram for explaining the relationship between the drive current of the laser diode and the light emission amount. In the figure, the vertical axis represents the LD light emission amount (in units of mW), the horizontal axis represents the applied current to the LD (ILD), the symbol (a) is the LD characteristic curve, the symbol (b) is the write power level point, and the symbol ( c) is a read power level point, symbol W is a current level flowing in the LD at the time of writing data, and symbol R is a current level flowing in the LD at the time of reading data.

FIG. 6 is a diagram for explaining the monitor voltage, and shows the waveform of the PD voltage obtained by monitoring the amount of light emitted from the LD with the PD. 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 characteristics, and if there are large fluctuations in the write power level and read power level output by the LD, it will adversely affect the data quality and so on. So that the write power level and read power level of
Initialize the PD current adjustment unit 2.

That is, with a power meter calibrated in a completed state as an optical head not shown, a synchroscope, etc., the output voltage of the PD when the LD emits light with a constant power, the variable resistor RV1 Adjust and lock the variable resistor RV1 to fix the current state.

Further, the circuit shown in FIG. 4 automatically controls the PD voltage when the PD is monitored to a read power level when the LD power changes and the output power fluctuates due to, for example, deterioration of the LD or a change in ambient temperature. are doing.

Therefore, if there is a component of the write power level, the write power level equivalent portion is removed by the write power level current subtraction unit 10, and the light emission power is adjusted based on the set value set in the D / A converters 4 and 7. Has the function of automatic adjustment.

Even when this automatic adjustment function is set according to a predetermined function, adjustment is performed by the variable resistor RV2 in the write power level current subtraction unit setting unit 9, and the variable resistor RV2 is locked to fix the state at that time. is necessary.

[Problems to be solved by the invention]

In the conventional LD drive circuit, when the characteristics of the LD change due to aging, that is, when the differential efficiency changes, the read power level is automatically controlled to a constant value in the read mode, but in the recording mode, the LD is preset at the time of initial setting. Since only a predetermined constant write current is superposed, there is a drawback that a predetermined write power level is not generated.

In FIG. 7, the horizontal axis represents current and the vertical axis represents light amount (power). I _R0 represents the LD read current by the automatic control means.
The power at this time is P _R. I _W0 is the write current and the power is P _W0 . When LD deteriorates I _R1 by automatic control means
The current can flow. Since the write current I _W1 is equal to I _W0 , the output power is P _W1 , which is less than the specified power P _W0 . That is, when the LD deteriorates, the predetermined write power level is not generated.

The present invention has been made in view of the above-mentioned conventional drawbacks.
It is an object of the present invention to provide a semiconductor laser driving device in an optical recording / reproducing device that generates a predetermined write power level regardless of the deterioration of the above.

[Means for solving problems]

As shown in the principle diagram of FIG. 1, the semiconductor laser driving device in the optical recording / reproducing apparatus of the present invention is provided with an optical system 12 for irradiating the optical disk with the emitted light of the semiconductor laser LD having a photodetector PD for monitoring, First automatic control means 13 for controlling the emitted light to a predetermined read power level by the output of the monitor photodetector PD, and a write current preset to the semiconductor laser drive current corresponding to the read power level. And a second automatic control means 14 for controlling the write power level by superimposing the same on a semiconductor laser driving device in an optical recording / reproducing apparatus, the second monitor photodetector for monitoring the write power level. A PD2 is provided in the optical system 12, and a write power level and a target write power level that are calibrated in advance corresponding to the output of the second monitor photodetector PD2 are provided. The arithmetic circuit 15 is provided for calculating a difference between adopts a configuration for automatically controlling the write current by the output of the arithmetic circuit 15.

[Action]

While being emitted from the semiconductor laser LD and passing through the optical system 12, a part thereof is extracted by a beam splitter or the like and made incident on the second monitor photodetector PD2, and the second monitor photodetector PD2 writes the light. The second control means 14 outputs the output of a calculation circuit 15 that detects only the level and calculates the difference between the write power level calibrated in advance corresponding to the photoelectrically converted output and the target write power level.
It is possible to generate a specified write power by controlling.

〔Example〕

Embodiments of the present invention will be described in detail below with reference to the drawings. In addition,
In order to make the description of the configuration and operation easier to understand, the same parts are denoted by the same reference numerals throughout the drawings, and the duplicated description thereof will be omitted.

FIG. 2 shows a block diagram of an optical system according to an embodiment of the present invention. In the figure, 1 is an LD unit, which is a semiconductor laser
It is composed of an LD and a photodetector PD for monitoring. The optical system 12 in FIG. 1 is composed of a collimator lens 12a, a perfect circle correction prism 12b, and a beam splitter 12c in this figure.

PD2 represents a second monitor photodetector that detects light partially reflected by the beam splitter 12c. In this way, separately from the monitor photodetector PD that monitors the backward light of the semiconductor laser LD, the emitted light of the semiconductor laser LD is extracted and monitored in the middle of the optical system.

FIG. 3 is a configuration diagram of an LD drive circuit according to a specific embodiment of the present invention. In the figure, PD2 is a second monitor photodetector, and a resistor R9 connected in series with it converts the output of the second monitor photodetector PD2 into a voltage. The converted voltage is input to the arithmetic circuit 15 via the A / D converter 16.
In addition, the voltage conversion output of the conventional monitor photodetector PD is A / D
Input to the arithmetic circuit 15 via the converter 17.

The arithmetic circuit 15 selects the write level from the output signal of the A / D converter 16 and calculates the difference between the write power level calibrated in advance corresponding to the write level and the target write power level stored in advance, The correction value
It is added to the input side of the D / A converter 7 and output. Also, D
A / D converter 1 when the output of A / A converter 7 is corrected
The D / A converter 18 is controlled so that the output value of 7 becomes the same as the value stored in advance.

〔The invention's effect〕

As described in detail above, according to the driving method of the semiconductor laser of the present invention, it is possible to generate a predetermined recording power even if the LD deteriorates due to aging and the differential efficiency decreases.

[Brief description of drawings]

FIG. 1 is a principle diagram of the present invention, FIG. 2 is a configuration diagram of an optical system according to one embodiment of the present invention, FIG. 3 is a configuration diagram of an LD drive circuit according to one embodiment of the present invention, and FIG. 5 is a configuration diagram of the LD drive circuit of FIG. 5, FIG. 5 is a diagram illustrating the relationship between the drive current of the laser diode and the light emission amount, FIG. 6 is a diagram illustrating the monitor voltage, and FIG. The figure is shown. In FIG. 1, 12 is an optical system, 13 is a first automatic control means, 14 is a second automatic control means, 15 is an arithmetic circuit, LD is a semiconductor laser, PD is a monitor photodetector, and PD2 is a second. The respective photodetectors for monitoring are shown.

Claims (1)

(57) [Claims] 1. An optical system for irradiating an optical disc with emitted light of a semiconductor laser having a monitor photodetector, and controlling the emitted light to a predetermined read power level by the output of the monitor photodetector. And an automatic recording means for controlling the write power level by superposing a preset write current on the semiconductor laser drive current corresponding to the read power level. In the semiconductor laser driving device of the reproducing device, a second monitor photodetector for monitoring the write power level is provided in the optical system, and the second monitor photodetector is calibrated in advance in accordance with the output of the second monitor photodetector. Providing an arithmetic circuit for calculating the difference between the write power level and the target write power level, and automatically controlling the write current by the output of the arithmetic circuit. A semiconductor laser drive device in an optical recording / reproducing device characterized by the above.