JPH04238123A - Optical disk device - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an improvement in a recording and reproducing method in an optical disc device.

0002

2. Description of the Related Art In order to improve the recording density of optical discs, various methods have been developed to increase the track density. One example is simply increasing track density. Another method is to record data not only on the tracks but also between the tracks, unlike the conventional method of writing information signals only on the tracks. When these methods are used, data signals recorded on adjacent tracks are mixed in when reproducing data on a target track, making it difficult to accurately reproduce data on a desired track. Therefore, OPTICAL DATA S
TORAGE, 1990, CONFERENCE
As shown in DIGEST, pages 18 to 21, three laser beams are emitted from a semiconductor laser, and after reproducing the data of three adjacent tracks with these beams, the three signals corresponding to each are added together. A method was devised to eliminate the influence of information signals mixed in from adjacent tracks.

0003

[Problems to be Solved by the Invention] However, the above-mentioned conventional methods have had the following problems. In a laser light source such as a semiconductor laser, emitting three laser beams is more complicated and difficult than emitting one laser beam. In addition, in order to accurately irradiate the three laser beams onto adjacent tracks with a deviation of 0.5 to 0.8 μm, it is necessary to align the three laser light sources and the position of the optical components of the laser light source group. The alignment had to be done extremely precisely. Furthermore, since it is impossible to make the characteristics of the three laser light sources exactly the same, it is impossible to connect the three laser beam focuses on the track without aberration and reproduce recorded information in the same state. Therefore, even if reproduced signals of adjacent tracks are obtained from the three beams, the signals of the adjacent tracks cannot be sufficiently removed because the reproduction conditions are different. Furthermore, if a distance is required for the arrangement of the laser light sources, it is difficult to arrange three laser beam focuses on the same radius, so as shown in FIG. Focuses 41 and 43 that illuminate adjacent tracks 44 and 45 were sometimes placed at positions shifted to opposite sides in the circumferential direction with respect to center 40 . However, in this case, there will be a time difference between the information signals reproduced by the three laser beam focal points, which is equal to the time it takes for the disk to move the radial distance between the focal points. In order to compensate for this time difference, it was necessary to add a delay circuit to the signal path or to use a latch circuit to match the timing. Furthermore, it was necessary to delicately adjust the amount of delay and timing to accommodate slight variations in radial distance.

[0004] Therefore, the present invention significantly eliminates the complexity of the light source, the reduction in yield, the difficulty in alignment in the process, the increase in manufacturing time and cost caused by these, and the reduction in the ability to remove adjacent track signals. It is an object of the present invention to provide an optical disc device in which the configuration and adjustment of an information signal reproducing circuit are simplified.

[0005]

[Means for Solving the Problems] The present invention provides an optical disc device that includes a laser light source that emits a laser beam, a laser beam from the laser light source that is focused on a track on an optical disc, and a reflected light from the disc that is converted into an optical disc. an optical device that guides the laser beam to a detector; and a hologram element or a diffraction grating that is included in the optical device and provided in a path from the laser light source to an objective lens that focuses the laser beam onto a disk, The 0th-order light of the laser beam that has passed through the element or the diffraction grating is focused on a track on which data is recorded/reproduced, and the +1st-order light is focused on a track adjacent to the track irradiated by the focus of the 0th-order light, The −1st order light is focused on a track on the opposite side of the track irradiated by the 0th order light from the track irradiated by the +1st order light and adjacent to the track irradiated by the 0th order light, and detects the information signals recorded on the tracks included in the 0th-order light, +1st-order light, and -1st-order light individually to create three systems of signals, and then applies appropriate coefficients to the three systems of signals. It is characterized by having a signal processing circuit that multiplies and adds signals.

[0006]

[Operation] According to the configuration of the present invention, the laser beam emitted from the laser light source is diffracted by the hologram element or diffraction grating placed on the path to the objective lens, and the 0th-order light is divided into the main beam, the +1st-order light, and the -1st-order light. The primary light is changed into three beams as sub-beams, and the beams reflected by the disk and returned are introduced into a photodetector to obtain three information reproduction outputs. Further, by multiplying these three signals by a coefficient and adding them to cancel out the mixed signal components from the adjacent tracks, it is possible to obtain an information reproduction output that is not affected by the adjacent track signals. Furthermore, since at least one laser light source is required, the configuration of the disk device and the vicinity of the laser light source can be simplified.

[0007]

EXAMPLES The present invention will be explained based on examples.

FIG. 1 is a schematic diagram showing an optical path and a reproduction signal path of a disk device according to the present invention.

The light emitted from the semiconductor laser 1 is changed from radial to parallel light by a collimator lens 2. The hologram element 3 splits the laser beam into 0th-order light, +1st-order light, and -1st-order light. Of these, the zero-order light is the main beam, has the strongest light intensity, and travels straight toward the disk. +1st order light and -
The primary light is a secondary beam whose light intensity is weaker than the main beam.
Diffraction bends the path. The three beams are condensed through an objective lens 5 and focused onto a disk 6. At this time, since the +1st order light and -1st order light exist on both sides of the 0th order light, the 0th order light is the target track, the +1st order light and the -1st order light are adjacent to the 0th order light, and are opposite to each other. Focus on the side track. Therefore, the three beams receive polarization according to the information signals of the three adjacent tracks with the zero-order light as the center, and return to the objective lens 5. At this time, as shown in FIG. 4, the performance of the hologram element and the installation location and direction should be selected so that adjacent focal points 47 and 48 are arranged on the same radius around the center spot 46, as shown in FIG. can. Therefore, the above-mentioned time difference does not occur between the information signals reproduced by the three focal points. The group of light rays is partially reflected by the polarizing beam splitter 4 and has its optical path bent, is converged by the condensing lens 7, is further bent by the direction changed to an information signal by the Wollaston prism 8, and is sent to the photodetector 9. incident. The photodetector 9 is composed of a six-divided photodiode, which is divided into three parts in the vertical direction as shown in the figure, and further divided into two parts in the direction perpendicular to the plane of the paper. Of the beams reflected from the disk and incident on the photodetector 9, the 0th order light enters the central part 9a of the vertically divided parts, and the beams corresponding to +1st order light and -1st order light enter the upper part 9a. and the lower photodetector (9b and 9c, respectively)
incident on . 9a, 9b, and 9c are further divided into two as described above, and since an information reproduction signal with reversed polarity enters each of the two divided photodiodes, it is necessary to find the difference between the two photodiode output signals. Thus, three systems of information signals picked up by each beam on the track are obtained. Although the subsequent steps can be implemented using either an analog circuit or a digital circuit, in this embodiment, an example of a digital circuit will be described. The analog playback outputs of the three systems are converted into digital values by an A/D converter 11, and passed through a filter 12, which will be described later, to become playback outputs from which the effects of adjacent tracks have been removed.

Next, the operation of the filter 12 will be explained. A/
The digital signal data of the zero-order optical reproduction signal outputted by the D converter 11 is multiplied by a coefficient a0 in a multiplier 27. The latch circuit 25 and the latch circuit 26 respectively hold digital data from the previous A/D conversion, and the multiplier 28 and the multiplier 29 similarly hold the coefficient a1,
It can be multiplied by a2. By adding the outputs of these three multipliers, the output waveform becomes one with a good S/N ratio and no distortion.

The +1st-order light and the -1st-order light are processed in the same way, and the signals of all three systems become sharp signals with a good S/N ratio.

Thereafter, the signals of the three systems enter an adder 35 and are added together. By this addition, adjacent track signal components included in the zero-order light cancel each other out, leaving only the information signal component of the track corresponding to the zero-order light. That is,
The signal components on the track corresponding to the +1st order light and -1st order light included in the 0th order light can be canceled by the signal components included in the +1st order light and -1st order light.

The present invention is effective and can be applied even if the laser beam focuses are not arranged on the same radius as shown in FIG.

[0014]

As described above, the present invention eliminates the need to use a laser light source capable of emitting three beams by inserting a hologram element or a diffraction grating into the laser light path between the laser light source and the objective lens. did. This simplifies the laser light source and the disk device, making it possible to easily assemble them in the manufacturing process, making it possible to significantly reduce time and costs. Furthermore, since the laser beams are generated from the same light source, the beam characteristics are uniform and have the same information signal reproduction characteristics, so that mixed signals from adjacent tracks can be effectively removed.

[Brief explanation of the drawing]

FIG. 1 is a schematic diagram of a laser beam path and a reproduction signal processing circuit of an optical disc device of the present invention.

FIG. 2 is a block diagram showing the configuration of a filter of the optical disc device of the present invention.

FIG. 3 is a schematic diagram showing the arrangement of a laser beam focus that irradiates a track in a conventional optical disc device.

FIG. 4 is a schematic diagram showing the arrangement of a laser beam focus that irradiates a track in the optical disc device of the present invention.

Claims (1)

[Claims] 1. An optical disc device, comprising: a laser light source that emits a laser beam; an optical device that focuses the laser beam from the laser light source onto a track on an optical disc and guides reflected light from the disc to a photodetector; The optical device includes a hologram element or a diffraction grating that is included in the optical device and is provided in a path from the laser light source to an objective lens that focuses the laser beam onto a disk, and the hologram element or the diffraction grating that passes through the hologram element or the diffraction grating. The 0th order light of the laser beam is focused on a track where data is recorded/reproduced, the +1st order light is focused on a track adjacent to the track irradiated by the focus of the 0th order light, and the -1st order light is focused on the track adjacent to the track irradiated by the focus of the 0th order light. The light is focused on a track opposite to the track irradiated with the +1st order light and adjacent to the track irradiated with the 0th order light, and the photodetector collects the 0th order light and the +1st order light. ,
- Detect the information signals recorded on the tracks included in the primary light individually to create three systems of signals, and
An optical disc device characterized by having a signal processing circuit that multiplies system signals by appropriate coefficients and adds them together.