JPH05101414A - Optical disk recording and reproducing method and photodetector - Google Patents

Abstract

PURPOSE:To provide a control method for keeping displacement of plural semiconductor laser beams on an optical disk small even when their light emitting positions are slightly shifted and their wavelengths are slightly different and a photodetector for this purpose. CONSTITUTION:A semiconductor laser manufactured with plural, for example, two laser chips on one substrate at the same time is used, and they are focused on the disk by the same optical system. Two photodetecting parts for independently receiving reflected light of two lasers respectively is provided, and these photodetecting parts are divided into four respectively to be 11-14 and 15-18, where a control signal is obtained independently from each reflected light, and these signals are synthesized to make a signal for actually controlling a laser spot. By this method, even when plural semiconductor lasers are slightly dislocated and the wavelengths of the plural semiconductor lasers are slightly different, displacement of their individual spots can be kept small, and hence deterioration of a regenerative signal from plural spots can be diminished to the utmost.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical disk recording / reproducing method for recording or reproducing information on an optical disk and a photodetector useful for the same.

[0002]

2. Description of the Related Art A plurality of laser beams are used to improve a transfer rate when recording or reproducing information on an optical disk. A plurality of laser beams are simultaneously radiated onto the optical disc to squeeze, and a plurality of reflected lights thereof are received by separate photodetectors and reproduced independently. The signal from the photodetector is used not only for reproducing the recording signal, but also for producing a focus control signal and a tracking control signal to accurately irradiate the laser spot on the disc.
One of a plurality of photodetectors is used for the control.

To generate a plurality of laser beams,
If a chip in which a plurality of semiconductor lasers are simultaneously manufactured on one substrate is used, the configuration of the optical system is the same as the case of using one semiconductor laser, and it is stable against temperature changes and changes over time.

[0004]

When a plurality of semiconductor lasers are formed on one chip, they can be formed at predetermined positions to some extent, but it is still necessary to allow a slight positional deviation, and the laser beam is directed onto the optical disk. The spot position narrowed down to is slightly different from the predetermined position. Also, it must be allowed that the wavelengths of the plurality of semiconductor lasers are slightly different. In general, an objective lens has chromatic aberration, and a difference in wavelength also causes a positional shift in which a laser beam is focused on an optical disc. If only one laser beam is used for control, the spot of the laser beam used for the control can be accurately controlled for focus and tracking, but other spots will be displaced from a predetermined position.

[0005]

A photodetector for independently receiving reflected light of a plurality of laser beams is provided, and each of the photodetector is divided into four parts, and a focus control signal and a focus control signal are provided independently of each reflected light. Obtain a tracking control signal. A control signal for a laser spot is created by combining signals from a plurality of laser beams.

[0006]

[Function] Even if the positional relationship of the laser spots focused on the optical disk is slightly deviated due to the slight misalignment of the plural semiconductor lasers and the slight difference in the wavelengths of the plural semiconductor lasers, the signals from the respective laser beams are Since the control signals are combined by using them, even if complete control is not possible for each of the multiple spots, the positional deviation of each spot can be made small, and the deterioration of the reproduced signal from multiple spots is small. I can keep it.

[0007]

EXAMPLE FIG. 1 shows the configuration of an optical system using the optical disk recording method of the present invention. Reference numerals 1 and 2 denote semiconductor lasers, the laser beams of which pass through a polarization beam splitter 3 and a quarter wavelength plate 4 to be collimated by a collimator lens 5 and are focused on an optical disk 7 by an objective lens 6.

The reflected light passes through the objective lens 6, the collimator lens 5 and the quarter-wave plate 4 again, is reflected by the polarization beam splitter 3, and passes through the cylindrical lens 8 to be given astigmatism. And is irradiated onto the photodetector 9.

Although the semiconductor lasers 1 and 2 are shown separately in the figure, they are constructed on one chip. In this embodiment, the case where two laser beams are used has been shown, but the same applies to the case where three or more laser beams are used.

FIG. 2 shows the shape of an embodiment of the photodetector of the present invention and the reflected light radiated thereon. The photodetector is divided into two parts, each of which is irradiated with the reflected light of an individual laser beam. Each part is divided into four in a cross shape, and the respective reflected lights simultaneously produce a focus control signal due to astigmatism. The sum of the signals from the photodetectors 11 and 13 minus the sum of the signals from 12 and 14 gives the first focus control signal, and from the sum of the signals from the photodetectors 15 and 16, 16, Subtracting the sum of the 18 signals gives the second focus control signal.

If only the first focus control signal is used for control, one laser beam can accurately irradiate the most narrowed spot on the optical disc, but the position shift of the light emitting point and the slight difference in wavelength are caused. If the two spot positions deviate from the predetermined positional relationship, the spot position of the other laser beam deviates from the optical disk surface, and the quality of the recording or reproducing signal deteriorates.

However, if the sum signal of the first and second focus control signals is used as a signal for actually controlling the focus of the laser beam, it is not possible to control both of the two laser beams to the exact focus position at the same time. However, both of the two laser beams can be simultaneously focused on the optical disc within a small error range, and the deterioration of the recording or reproducing signal can be kept small.

Next, the tracking control will be described. FIG. 3 shows a case where two adjacent laser spots are irradiated onto adjacent grooves on an optical disk having a groove 19 formed on a flat plate to record / reproduce information signals, and a laser spot arrangement diagram thereof is shown.

The respective reflected lights are applied to the photodetector as shown in FIG. A push-pull tracking signal is generated from these photodetectors. The sum of the photodetectors 11 and 12 minus the sum of 13 and 14 gives the first tracking signal, and the sum of the photodetectors 15 and 16
Subtracting the sum of 17 and 18 also gives the second tracking signal.

If control is performed using only the first tracking signal, one laser spot can accurately track the groove 19, but if the light emitting point deviates from the predetermined position, then 2
The distance between the two spots is different from the predetermined value, and the other laser spot is displaced from the adjacent groove to deteriorate the quality of the recording or reproducing signal.

However, similarly to the focus control, if the sum signal of the first and second tracking signals is used as a signal for actually controlling the tracking of the laser spot, both of the two laser spots can be accurately and exactly on the groove 19. Even if tracking control cannot be performed, both of the two laser spots can be simultaneously tracked on the groove within a small error range, and the deterioration of the recording or reproduction signal can be kept small.

To reproduce the recorded signal, the photodetectors 11 and 1 are used.
The sum signal of 2, 13, and 14 is the first reproduction signal, and the sum signal of the photodetectors 15, 16, 17, and 18 is the second reproduction signal. Since they can be played independently at the same time, the transfer rate can be doubled.

FIG. 4 shows the laser spot arrangement on the V-groove disk. The case where two spots are tracked on the adjacent slope of the V groove 20 to record / reproduce an information signal is shown, and the reflected light thereof is also applied to the photodetector as shown in FIG. A tracking method is provided in Japanese Patent Publication No. 3-9538, so that method will be briefly described.

If the depth of the V groove is changed every other rotation at a constant low frequency f, the ridge line portion of the V groove meanders at the frequency f. The push-pull tracking signal from the laser spot contains a component that changes at the frequency f. The two spots can simultaneously track adjacent slopes so that their components are equal for the two spots.

A method of achieving this method by using the photodetector of FIG. 2 will be described. From the sum of the photo detectors 11 and 12, 13,
The component of the frequency f is extracted from the first tracking signal obtained by subtracting the sum of 14 to obtain the first signal. Light detector 1
The component of frequency f is extracted from the second tracking signal obtained by subtracting the sum of 17 and 18 from the sum of 5 and 16, and is used as the second signal. Tracking control may be performed so that the first and second signal amplitudes become equal to each other. In this case, unlike the example of the flat disk in FIG. 3, the sum signal of the two control signals is not created, but the tracking control signal for actually controlling the laser beam is obtained from the two laser beams. Since it is made using signals, the object of the present invention can be achieved as well.

The V-groove disk is a disk whose track pitch is narrowed to increase the density. However, in order to suppress crosstalk, it is necessary to optimize the light receiving region of reflected light. However, in reproducing a digital signal, a reproduced signal of good quality can be obtained even if all the reflected light is received. The reproduction of the recording signal on the slope of the V groove is also performed by the photodetectors 11 and 1 as in the flat disk.
The sum signal of 2, 13, and 14 is the first reproduction signal, and the sum signal of the photodetectors 15, 16, 17, and 18 is the second reproduction signal. Since they can be played independently at the same time, the transfer rate can be doubled.

[0022]

EFFECTS OF THE INVENTION A plurality of semiconductor lasers are squeezed on a disk, and a photo-detecting section for individually receiving reflected light is provided. The photodetector is divided into four parts, each of which produces a control signal independently from the reflected light and combines them to create a signal that actually controls the laser spot. Even if the deviation occurs, the positional deviation of each laser spot can be kept small.

[Brief description of drawings]

FIG. 1 is a configuration diagram of an optical system of an optical disc device using an optical disc recording / reproducing method of the present invention.

2 is a configuration diagram of an embodiment of a photodetector of the present invention used in the optical disk device of FIG.

FIG. 3 is a layout diagram of laser spots on a flat disk in the apparatus of the embodiment.

FIG. 4 is a layout diagram of laser spots on a V-groove disk in the apparatus of the embodiment.

[Explanation of symbols]

 1, 2 Semiconductor laser 3 Polarization beam splitter 4 Quarter wave plate 5 Collimator lens 6 Objective lens 7 Optical disk 8 Cylindrical lens 9 Photodetector 11-18 Photodetector 19 Groove 20 V groove

Claims (2)

[Claims] 1. A method of irradiating a plurality of laser beams onto an optical disk, receiving the reflected light from the optical disc by a photodetector, and recording or reproducing a signal, the reflected light of each of the plurality of laser beams is recorded. An optical disk recording / reproducing method, characterized in that light is received by respective separate photodetectors, and the photodetectors are each divided into four parts, and a control signal is created using signals from reflected lights of a plurality of laser beams. 2. A photodetector comprising a plurality of parts, each of which is divided into four parts.