JPH0668474A - Optical recording medium and its reproducing device - Google Patents

Abstract

PURPOSE:To record two different kinds of information on two tracks with different recording density on an optical disk and to reproduce selectively or simultaneously the two different kinds of information from the optical disk. CONSTITUTION:Laser beams of two different kinds of wavelength outputted from a laser 101 using an SHG element are converged on an objective lens 109, and a pit 201 of low recording density and a pit 202 of high recording density recorded alternately on the tracks of the optical disk are irradiated with the beams, and signals can be reproduced by detecting reflected light by a first photodetector 111 and a second photodetector 116.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical recording medium such as a video disc and a compact disc and an optical reproducing device.

[0002]

2. Description of the Related Art There is known an optical reproducing apparatus for recording information on a disc surface by pits, irradiating the pits with laser light, and taking reflected light to reproduce the information.

In this apparatus, information is reproduced by utilizing interference and analysis of light, and the size of a pit for obtaining a good reproduced signal depends on the laser wavelength and the objective lens. Equations 1 and 2 below show the relational expressions.

[0004]

[Equation 1]

D: Beam converging diameter λ: Laser wavelength K: Coefficient NA: Numerical aperture of objective lens

[0006]

[Equation 2]

T: Depth of pit n: Refractive index λ: Laser wavelength By the way, in order to increase the density of the optical disc, it is necessary to shorten the wavelength of the semiconductor laser as understood from the above relational expression. Currently, research is being conducted to generate blue laser light having a shorter wavelength than red. If a blue laser can be made, the recording density will be improved by 4 times compared to a red laser.
It is considered to be a promising light source for HDTV optical discs.
When a red laser is used, an image for HDTV can be recorded on the optical disk for HDTV for only one hour, but with a blue laser, recording for four hours is possible.

As one means for generating laser light in the blue region, an SHG element (Second Harmoni) is used.
c Generator). This is an 860nm band semiconductor laser that is at a practical level.
This is a method of irradiating an HG element and generating a second harmonic corresponding to blue light (wavelength 430 nm) by a non-linear optical effect. Currently, as an SHG element, research and development is being carried out on a bulk crystal and an optical waveguide.

From the SHG element, a fundamental wave is emitted in addition to the second harmonic. Further, with the increasing density of optical discs, there are many cases where two different types of information such as computer information and video information are simultaneously reproduced.

[0010]

Therefore, according to the present invention, S
By utilizing the fundamental wave and the second harmonic emitted from the laser using the HG element, it is possible to reproduce two tracks having different recording densities, and the second fundamental wave is used to generate the second fundamental wave. By using this technology, it will be possible to increase the density of optical disks.

[0011]

DISCLOSURE OF THE INVENTION According to the present invention, in an optical recording medium in which information is recorded in a plurality of tracks arranged on a medium by a pit row, tracks having different recording density of information pits are recorded alternately. The first feature is that the structure is arranged.

Further, according to the present invention, in an optical recording / reproducing apparatus for detecting information on an optical recording medium according to claim 1 by irradiating a laser beam, a laser light source for emitting a laser beam having a fundamental wave and a harmonic wave, A first optical for detecting information by irradiating a track having a lower recording density of information pits on the optical recording medium of claim 1 with a laser beam of a fundamental wave having a longer wavelength emitted from the laser light source. Means for detecting information by irradiating a track having a higher recording density of information pits on the optical recording medium according to claim 1 with a laser beam of a higher harmonic of a shorter wavelength emitted from the laser light source. The second feature is that the optical device has two optical means.

[0013]

According to the first feature, since tracks having different recording densities of information pits are alternately recorded on the optical recording medium, the influence of interference between adjacent tracks is small when information is detected.

According to the second feature, one laser light source detects the information pits of the two tracks on the optical recording medium of the first feature independently without affecting each other.

[0015]

An embodiment of the present invention will be described with reference to the drawings.
FIG. 1 shows an optical disk reproducing apparatus for reproducing an optical disk. FIG. 2 shows an optical disk used in the present invention. 201 low density recording pits and 20 pits are formed on the substrate of the optical disc.
Two high-density recording pits are alternately recorded for each track. The pitch of the track on which the low-density pits 201 are recorded is half the pitch of the track on which the high-density pits 202 are recorded. Further, in the optical disc of FIG. 2, the depth of the pits 201 for low density recording is small so that the influence of interference of adjacent tracks is small.
It is set deeper than the depth of 02.

In FIG. 1, reference numeral 100 denotes an optical disk used in the present invention, which corresponds to FIG. 101 is the fundamental wave and the second
A laser using an SHG element that outputs harmonics (generally, the output of the fundamental wave using the SHG element is extremely larger than the output of the second harmonic wave, but a filter may be provided on the output surface of the fundamental wave or resonance may occur. The output of the fundamental wave and the second harmonic can be approximated by devising the coating of the end face of the vessel.), 102 is the optical path of the fundamental wave (shown by the broken line), 10
Reference numeral 3 is an optical path of the second fundamental wave (illustrated by a solid line). The wavelength of the second harmonic is half the fundamental wave. Reference numeral 104 is a first dichroic mirror for separating the optical paths of the fundamental wave 102 and the second harmonic wave 103, and 105 is the optical path 102 of the fundamental wave.
Is a first polarization beam splitter, 107 is a first quarter-wave plate, and 108 is a reflected light of the fundamental wave 102 and the second harmonic wave 103 from the optical disk. A second dichroic mirror 109 for separating the optical path is a fundamental wave 102 and a second harmonic wave 1
03 is an objective lens that focuses light onto the optical disc 100.
The objective lens 109 irradiates the second harmonic 103 to the high density recording pits 202 of the optical disc 100, and the fundamental wave 102 to the low density recording pits 201 of the optical disc 100.
To irradiate. 110 is the fundamental wave 1 from the optical disc 100
The first photodetector for detecting the reflected light of 02, 111 is the second
A second collimator lens provided in the harmonic optical path 103, 112 a second polarization beam splitter, 113 a second quarter-wave plate, 114 a second harmonic 103 from the optical disc 100. It is the 2nd photodetector which detects the reflected light of.

Next, the operation of the optical disc reproducing apparatus of FIG. 1 for reproducing the optical disc 100 will be described. Laser 1
The laser beam of the fundamental wave 102 and the second harmonic wave 103 is output from 00. The output laser beam is dispersed by the first dichroic mirror 104. The separated fundamental wave 102 is the first collimator lens 10
5, through the first polarization beam splitter 106, the first quarter-wave plate 107, and the second dichroic mirror 108, the light is condensed by the objective lens and formed into the low density recording pits 201 on the optical disc 100. Is irradiated. Further, the separated second harmonic 103 is supplied to the second collimator lens 11
1, second polarization beam splitter 112, second quarter-wave plate 113, second dichroic mirror 108
Through the objective lens 109, and the optical disc 10
The high density recording pits 202 above 0 are irradiated.

The laser beams of the fundamental wave 102 and the second harmonic wave 103, which are simultaneously applied to the low density recording pits 201 and the high density recording pits 202 on the optical disc 100, are reflected respectively, and are reflected by the objective lens 109 to the second dichroic. -Reach Mira-108. At this time, the objective lens 10
The fundamental wave 102 focused by 9 and applied to the optical disc 100 is also applied to the high density recording pit 202 because of the large focused spot diameter.
Is sufficiently shallower than the depth of the pits 201 for low-density recording, the optical disc 100 is
The fundamental wave 102 reflected from does not include an interference component due to the high density pits 202. Further, since the second harmonic wave 103 focused on the optical disc 100 by the objective lens 109 has a small focused spot diameter, it is focused only on the high density pits 202 and is not affected by the low density pits 201. Therefore, each reflected light is not affected by adjacent tracks and can be used as a good detection signal.

Next, the second dichroic mirror 108
In, the light is split into the second harmonic wave 102 and the fundamental wave 103 according to the wavelength of light. The separated fundamental wave 102 is the first
The signal detected by the photodetector 110 is sent to the decoder circuit for signal reproduction. Further, the separated second harmonic 103 is also detected by the second photodetector 114, and the detected signal is sent to the decoder circuit for signal reproduction at the same time as the signal detected by the first photodetector 110. .

Thus, the optical disc reproducing apparatus of FIG. 1 can simultaneously reproduce the data of two tracks on the optical disc 100.

Simultaneous reproduction is a case where information is mutually related in different density recording (for example, image information and audio information related thereto). When the two pieces of information are unrelated to each other, the information is selectively reproduced.

The optical disk of FIG. 2 used in the above embodiment is cut by, for example, the 2-beam type cutting apparatus shown in FIG. Reference numerals 301 and 302 denote laser devices having different wavelengths, and the laser output of the laser device 301 is used to record high density pits 202. In addition, the laser output of the laser device 302 is low density pits 2.
Used to record 01. Laser device 301,
The laser output of 302 is sent to the optical modulators 303 and 304, and is optically modulated according to the signal from the encoder circuit 305. The outputs from the optical modulators 303 and 304 are combined by the polarization beam splitter 306, and the recording head 307
Sent to. The recording head 307 is a light modulator 303, 30.
According to the output of No. 4, the high density pits 202 and the low density pits 201 as shown in FIG.

[0023]

According to the present invention, by alternately recording tracks of pits having different recording densities on an optical disk, the influence of interference of adjacent tracks can be reduced when information is detected, so that a good reproduction signal can be obtained. You can Also,
Since two tracks with different recording densities on the optical disk can be reproduced at the same time, the data transfer rate can be improved. Further, it is possible to selectively reproduce two different types of information on the disc.

[Brief description of drawings]

FIG. 1 shows an embodiment of an optical disc reproducing apparatus of the present invention.

FIG. 2 is an embodiment of the optical disc of the present invention.

FIG. 3 is an embodiment of an optical disc cutting apparatus for producing an optical disc of the present invention.

[Explanation of symbols]

 100 optical disk 101 laser 104 first dichroic mirror 105 second dichroic mirror 109 objective lens 111 first photodetector 116 second photodetector 201 pit for low density recording 202 pit for high density recording

Continuation of front page (51) Int.Cl. ⁵ Identification number Internal reference number FI Technical indication location G11B 7/24 561 7215-5D (72) Inventor Hitoshi Terasaki 2-18 Keiyohondori, Moriguchi-shi, Osaka Sanyo Denki Within the corporation

Claims (2)

[Claims] 1. An optical recording medium in which a plurality of information are recorded in a pit row on a plurality of spiral or concentric tracks arranged on the medium, and the recording density of the information pits is on each track. An optical recording medium characterized in that they have mutually different structures. 2. An optical reproducing apparatus for detecting a signal on an optical recording medium in which information is recorded by a pit train by irradiating laser light, and a laser light source for emitting fundamental and harmonic laser light, First optical means for detecting a signal by irradiating an information pit on an optical recording medium with a fundamental wave light emitted from the laser light source, and detecting a signal by irradiating a harmonic wave emitted from the laser light source Second optical means and optical selecting means for selectively or simultaneously deriving the first optical means or the second optical means based on the recording density of information pits on the optical recording medium are arranged. Optical playback device.