JPH03102656A - Multi-beam optical disk device - Google Patents

Abstract

PURPOSE:To attain automatic control so that an optical output of each laser diode is an optimum value by utilizing the result of measurement of an optical output of one of plural light beams from a multi-beam optical head so as to adjust the optical output of each laser diode. CONSTITUTION:Outputs of all beams are set by a microcomputer 1 so that they are well arranged to be a constant value. The relation between an optical output of a laser diode and a current at a specific reference temperature T0 is obtained in advance in the setting, the relation is corrected at the operating temperature so as to keep the optical outputs of all laser diodes to be constant. In this case, each one light beam of multi-beam laser arrays is left and other beams are extinguished momentarily to read the current of a monitor photodiode 10 at that time thereby obtaining the operating characteristic of the laser diode. Thus, the light power is accurately controlled for each beam according to the temperature of the laser diode of the multi-beam optical disk device, the temperature of the disk and the recording radius or the like.

Description

DETAILED DESCRIPTION OF THE INVENTION (1) Technical field to which the invention pertains The present invention relates to a multi-beam optical disc device using multiple Q lasers, and particularly to a device for automatically controlling the optical output of each light beam. It is.

(2) Prior art and its problems As a device for recording and reproducing information by irradiating a disk-shaped recording medium with a laser beam, there is a magneto-optical disk system that uses magneto-optics, as well as disk drilling, deformation, refractive index changes, etc. There are devices based on an optical disk system that utilizes , and these devices are collectively called optical disk devices. In the magneto-optical disk method, a magneto-optical disk is first irradiated with a laser beam in the form of a spot.The temperature of the irradiated area rises to near the Curie point, and the magnetization is reversed by a weak external magnetic field, forming a spont-shaped magnetic domain. However, since the disk is rotating, the temperature of the magnetic domain quickly returns to room temperature, and the reversed magnetic domain remains unchanged. During playback, a laser beam with a lower power than during recording is irradiated onto the recording surface of the disk, and the direction of magnetization in the area irradiated with the laser beam is detected from the rotation direction of the polarization plane of reflected or transmitted light. information can be played back.

In the optical recording method, an optical disk is irradiated with a strong laser beam in the form of a spot, and information is recorded by deforming and altering only the portion irradiated with the laser beam. During playback, a weak laser beam that does not deform or alter the optical disk is irradiated onto the optical disk in a slit shape, and the intensity of the transmitted or reflected light from the area irradiated with the laser beam is detected. Regenerate information by

In recording and reproducing devices using these magneto-optical disks and optical disks, one method of increasing the transfer speed is to record in parallel on a plurality of tracks using a plurality of light beam spots. To obtain multiple laser beams, a semiconductor laser array (abbreviated as a laser array) is used, which is a monolithic integration of multiple semiconductor lasers with the same oscillation wavelength in a mutually independent manner. A typical example of this is an independently modulated laser diode, which is made by integrating a plurality of semiconductor lasers independently of each other. 5 in one laser array
Since a plurality of semiconductor lasers are arranged at a pitch of 0 to 300n, it is difficult to independently monitor the optical output of each laser. Although products that solve this problem are being developed, the ones that are currently in practical use only monitor the optical output using a single photodiode mounted within the laser array. Therefore, although it is possible to monitor the optical output of the entire laser array, it is not easy to separately measure the optical output of each semiconductor laser and control the optical output individually.

However, when recording with an optical disc device. The optical output of the laser must take different values during erasing and reproducing. For this purpose, the following conditions are necessary. ■Especially accurate light output is required during recording, so the output of each light beam must be precisely controlled. ■The optical output vs. forward current characteristic of a laser diode is temperature dependent; even if the current value is the same, the higher the temperature, the lower the optical output, and the lower the temperature, the stronger the optical output, so corrections are needed for this purpose. is necessary.

■Magneto-optical disks record and erase data near the Curie point of the disk temperature, so the optical output must be corrected depending on the disk temperature. ■When recording or erasing, if the disk rotates in one motion, it must be corrected so that the optical output increases toward the outer periphery.

In this case, it is of course desirable to adjust the optical output of each laser for each recording track. However, as mentioned above, currently there is only one laser array in one laser array.
Since only one optical output monitor element is mounted,
It was not possible to individually adjust the optical output of each laser element. It is possible to measure by lighting up each laser diode in the laser array, but focusing servo. ``This method cannot be used because the tracking servo has come off. In addition, the interval between laser elements in the laser array (array pitch) is 50 to 30, as described above.
It is extremely narrow at about 0n, and thermal interaction (crosstalk) occurs between each laser diode element.

For this reason, the difference between when all the laser diodes in the laser array are turned on and when only l laser diodes are turned on is for each laser diode.
Their light output vs. forward current characteristic curves will be different, so even if they are turned on one by one and adjusted to the optimum value, in actual use where all of them are turned on, it is not necessarily the case that the individual beams are The disadvantage is that the optical output of the optical system is not the optimum value.

(3) Purpose of the Invention The purpose of the present invention is to monitor the individual light outputs of a plurality of laser elements during play in use when there is only one optical output monitor element in a semiconductor laser array used in a multi-beam optical disk device. The relationship between output and forward current is measured separately, and the temperature of the laser array is determined based on that relationship.
Disc temperature. Another object of the present invention is to provide a method for individually controlling the optical output of each laser element depending on the radius of the recording track.

(4) Structure of the invention (4-1) Characteristics of the invention and differences from conventional technology The present invention has the following features:
In a multi-beam optical disk device, the optical output of each of the multiple light beams from the multi-beam optical head is measured by the means shown below, and the measurement results are used to determine the light output of each laser diode in the laser array. The most important feature is that the output is automatically controlled to the optimum values for playback, recording, and erasing. When measuring the optical output of each light beam from the optical head, all but one of all the laser diodes in the laser array are turned off momentarily, and during that period the photodiodes in the laser array are The optical output power of the lit laser diode is measured by measuring the current. Also, at that time, the current flowing through the lit laser diode is determined. This is performed sequentially for all laser diodes in the laser array. Cutting off all but one of the plurality of light beams from the laser array will have a fatal effect on the focusing servo and tracking servo, so it cannot be done during signal reproduction or recording/erasing. Therefore, perform the above measurements while loading the disk or when turning on the power to the disk drive. Using these measurement results, the optical output of each laser diode is automatically controlled to the optimal value during reproduction, recording, and erasing.

The case of magneto-optical recording where the rotational speed of the disk is constant is as follows.

(2) Correcting changes in optical output due to temperature changes of the laser diode during reproduction so that a constant optical output, for example 2 m-, is always obtained.

(2) During recording The optical output of the laser diode required during recording requires higher output as you move toward the outer periphery of the disk when the rotational speed of the disk is constant, but the optimum optical output changes depending on the temperature of the disk. This is because if the temperature of the disk is close to the Curie point, the optical output of the laser diode must be reduced, and if the temperature is far from the Chierie point, the optical output must be increased.

The optimum optical output for recording at each radial position around the reference temperature is determined in advance, and the optical output for recording is corrected according to the disc temperature when actually recording.

In addition, the optical output vs. forward current characteristics of the laser diode are
Since it also changes depending on the temperature of the laser diode, correction is made for this variation.

(2) At the time of erasing, a light output with a stronger intensity, for example 130%, than the optimum light output during recording at each radial position is obtained.

In the CLV method, where the rotational speed is not constant and the linear velocity is kept constant by decreasing the rotational speed of the disk as the recording track approaches the outer periphery of the disk, the correction based on the radius of the recording position of the disk in the above item (2) is not necessary. do not. Further, optical disks other than magneto-optical disks do not necessarily require correction based on the temperature of the disk.

(4-2) Example Below, the recording area of the disk is divided into two parts, inner and outer, and 4-beam laser arrays are used for the inner and outer peripheries, respectively, and 8 beams are used for parallel recording. An 8-beam magneto-optical disk device that performs parallel playback to increase transfer speed will be described. 4
One monitor photodiode is mounted within the laser array of the beam, and it is not possible to measure the optical output of the four laser diodes separately, so remove the laser diode you want to measure among the four laser diodes. By momentarily turning off the other three laser diodes and reading the current of the monitoring photodiode during that period, the optical output of the laser diode to be measured and the current flowing through the laser diode are measured. The reason why four laser diodes are not lit one by one for measurement is because there is thermal interaction between each laser diode element in the laser array, so if all the laser diodes in the laser array are lit This is because the optical output vs. forward current characteristic curve of each laser diode is different between the case where only one laser diode is turned on and the case where only one laser diode is turned on. This characteristic curve cannot be determined if the focusing servo or tracking servo is engaged, so the characteristic curve is determined by measuring with both of these servos not operating.

Figure 1 shows the configuration of the measurement circuit and control circuit for controlling the laser diode. In Figure 1, 1 is a microcomputer, 2 is a CPU, 3 is a ROM, and 4 is an RA.
M, 5-1.5-2.5-3 is an A/D converter, 6-1.
6-2 is a laser array drive circuit, 7 is an optical head, 8-1
is a laser array for the inner circumference, 8-2 is a laser array for the outer circumference,
9-L 9-2. - 9-8 are laser diodes for channel 1, channel 2, ..., channel 8, respectively, 10-1 and 10-2 are monitor diodes, and 11-
1. A temperature sensor 11-2 measures the temperature of the laser array. A temperature sensor 12 measures the temperature of the optical disc. 13 is a changeover switch.

The output of the laser diode is divided into bottom power required for reproduction and peak power required for recording/erasing.

FIG. 2 shows an example of laser diode output settings. The radius of the innermost circumference of the recording portion of a magneto-optical disk having a diameter of 130+n+a is 30 mm, and the radius of the outermost circumference is 60 mm. The bottom power is set to 2 m, which is the same when reproducing the inner circumferential portion of the optical disc and when reproducing the outer circumferential portion. The beak power is 5 mW when recording at a point with a radius of 30 mm on the optical disc. Radius 601II [9m when recorded at point I1
This is an example where W4 is set.

(Correction of optical output according to disk radius) The above-mentioned beak power values and their intermediate values are stored in the microcomputer 1 along with their corresponding track addresses.
It is recorded in ROM3 inside. When recording or erasing,
The light beam output value corresponding to the address of each track is read from the ROM 3 and given to the laser array drive circuit 6-1 through the CPU 2, and a predetermined current is passed through each laser diode to generate light suitable for that radial position. Irradiates the output beam onto the disk.

(Measurement of forward current and optical output when using each laser diode) In the case of the multi-beam optical disk device of this example, all optical beam outputs from the multi-beam optical head are set to the same output. If this is not done, the reproduced outputs will be uneven for each beam, causing a problem. Therefore, the microcomputer 1 shown in FIG. In setting, the relationship between the optical output and current of the laser diode at a specific reference temperature T0 is determined in advance, and during use, correction is performed according to the temperature at that time to keep the optical output of all laser diodes constant. The right side of the flowchart in FIG. 3 shows the procedure for determining the characteristics of each laser diode during use.

In this embodiment, four-beam laser arrays 8-1 and 8-2
First, all four diodes 11 to 9-4 in the laser array 8-1 are turned on, and then the other three laser diodes are turned on, leaving only the laser diode 9-1 for channel 1. The diodes 92 to 9-4 are momentarily turned off. The current of the monitor photodiode 10-1 at that time is A
/D converter 5-1 converts it into a digital quantity, and microcomputer 1 outputs the signal to laser diode 9 of channel 1.
-Measure the output of -1. Channel 1 is controlled by driving the laser array drive circuit 6-1 based on the measurement results.
The optical output of the laser diode 9-1 is
Adjust to mW. Channel 1 laser beam output is 2n
After setting to +I/4, the light beam output from each of the laser diodes 9-2 to 9-8 is adjusted and set to 2 mW for channel 2, then channel 3, and then channel 8.

Subsequently, a peak power of 4 mW is set using the same procedure. The same procedure is performed for the 11th section of the output power of 7m-1 and 9h. Save each set current value.

Next, the slope coefficient Kll of the optical output versus forward current of the laser diode when the optical output is bottom power is determined. Similarly, the slope coefficient K a of the optical output of the laser diode versus the forward current at the optical output of the beak power is determined. An example of this is shown in FIG.

By repeating the above procedure from the first channel to the eighth channel, the characteristic curve of each laser diode at the reference temperature T0 is determined. FIG. 4 shows an example of this, where ■ at temperature T0. is the forward current at the optical output P0, and 10 is the current value at the intersection with the horizontal axis of a line obtained by linearly extending the characteristic curve, which is called the threshold current.

The slope coefficient K0 of the optical output vs. forward current characteristic curve obtained as described above is stored in the microcomputer 1, and is used in the optical output correction at the temperature TI, which will be described below. Also, the disk temperature at this time is saved as the reference temperature TI.

(Correction of optical output due to laser diode temperature) The optical output vs. forward current characteristic of a laser diode varies depending on the temperature of the laser diode.
When used for erasing, it is necessary to compensate for fluctuations in optical output due to the temperature of the laser diode at that time.

The temperature of the laser diode is measured by a temperature sensor 11-1 for the inner laser array and a temperature sensor 11-2 for the outer laser array.
3. The data is taken into the microcomputer 1 through the A/D converter 5-3. FIG. 4 shows changes in the characteristic curve at temperature T1 and at temperature TY. In this case, the optical output is P
a (mW), the set value of the forward current is the temperature T
. It must be I0 when the temperature is TI, and h when the temperature TI is.

When the temperature of the laser diode 9-1 is Tt, the light beam output P0 from the laser diode 9-1 is Pa-K+X(r+t+) according to FIG. 4. Therefore, the forward current I1 of the laser diode 9-1 is I l= l l + P o/ K r where K,
, i, changes depending on the temperature. That is, T o <
As T I, K1=Ko+C+(To T+) i1=i0+cz(To T+) However, K1: Temperature T. of the laser diode. Slope coefficient K0 at laser diode temperature T0: Slope coefficient 10 at laser diode temperature T0: Threshold at laser diode temperature T0 Value at the point where the extension of the straight line of the characteristic curve intersects the horizontal axis with current 11: Laser Threshold current value C1 at diode temperature TI: Temperature coefficient of slope coefficient C2: Temperature coefficient of threshold current Temperature coefficient C,,C, is determined in advance for the laser diode alone. A flowchart for correcting the optical output according to the temperature of the laser diode, which is stored in the microcomputer 1, is shown on the left side of FIG. The current value h is determined by the CPU 2, and the laser array drive circuit 6-
1, a forward current 1 flows through the laser diode 9-1, resulting in an optical output P. obtain. The CPU 2 switches the laser diodes 9-2, 9-3 one after another, repeats the same operation as in 9-1, and the optical output of all laser diodes reaches P.
It is unified to 0. Reference temperature T. K. in ．． i. K. at any temperature T, based on ．． i. However, in order to reduce the prediction error at that time, when the temperature changes by 10°C or more, the characteristics of the laser diode are measured again using that temperature as the reference temperature.

(Correction of optical output according to the temperature of the disk) In the case of recording or erasing, it is necessary to correct the optical output according to the temperature of the disk. If the temperature of the optical disk before projecting the light beam is close to the Curie temperature, the beam output is decreased, and the beam output is increased as the distance from the Curie temperature increases.

The optimum optical output PII for recording or erasing at each radial position at the reference temperature Tu of the disk is determined in advance and stored in the microcomputer 1. Actually recorded/
When erasing data, the disk temperature T is measured by the disk temperature sensor 12, and the temperature Tl is sent to the microcomputer l through the changeover switch 13 and the A/D converter 5-3.
Take in the value of l. The recording output after correction based on the disc temperature is P1, the Curie temperature is Tl, and the current temperature is T.
D, then Pl=PK(Tc-TO)/(Te-T.
) FIG. 6 is a flowchart showing the correction of the recording/erasing output due to the disc temperature change described above. In the example shown in Fig. 6, the temperature of the disk is measured every time the track radius changes by 0.4 mm+, but it is not always necessary to measure the temperature of the disk by 0.4 mm+.
It does not have to be mm.

Although the embodiments of magneto-optical disks have been described above, the present invention can also be applied to optical disks that do not use magnetism by omitting some of the above-mentioned means.

Further, the present invention provides a method for each laser element in one semiconductor laser array. It can also be applied to control the laser output of a multi-beam optical disk device used for erasing, recording, and reproducing, respectively.

(5) Effects of the Invention As explained in detail above, the present invention is capable of controlling the optical power of a multi-beam optical head by heating each of the light beams of a multi-beam laser array one by one and instantly turning off the other beams. By reading the current of the monitoring photodiode at that time, the characteristics of the laser diode during use can be obtained. From this, the characteristics of the laser diode during use can be obtained. This allows for precise control of optical power. Therefore, extremely good recording and reproduction characteristics can be obtained.

[Brief explanation of drawings]

Figure 1 is a configuration diagram of a measurement circuit and control circuit for controlling a laser diode, Figure 2 is a characteristic diagram showing an example of laser diode output setting, and Figure 3 is a flowchart showing the procedure for setting the laser diode optical output. , Figure 4 is a temperature characteristic diagram of the optical output vs. forward current characteristic curve of the laser diode, Figure 5 is a diagram of the optical output vs. forward current characteristic curve of the laser diode, and Figure 6 is the optical output correction of the laser diode depending on the disk temperature. It is a flowchart which shows the procedure. 1...Microcomputer, 2...CP/U
13...ROM, 4...RAM, 5-1
．． 5-2.5-3...A/D converter, 6-1.6
-2... Laser array drive circuit, 7... Optical head, 8-l... Inner circumferential laser array, 8-2...
- Laser array for outer periphery, 9-1. 9-2,...
9-8... Laser diode, 10-1. 10-
2...Monitor diode, 11-1. 11-2.
12... Temperature sensor, 13... Changeover switch. ((1) Figure 5(b) Figure 6

Claims (1)

[Claims] (1) One or more semiconductor laser arrays each having a plurality of independently drivable laser diodes and one optical output monitor element, and when all the laser diodes in the laser array are turned on, one laser The other laser beams are turned off, leaving only the beam, and at that time, the output of the optical output monitor element is compared with a reference value, and the optical output of the one laser diode that was lit reaches a predetermined value. The control is performed sequentially for each of the laser diodes, and the characteristics of the optical output versus forward current of each laser diode are determined, and the output of all laser diodes reaches a predetermined value when all beams are turned on. A multi-beam optical disc device configured to maintain