JP2786909B2 - Optical playback device - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to an optical reproducing apparatus for reading recorded information from an optical recording medium such as a video disk and a compact disk.

[Prior Art] A video disk and a compact disk for reproducing video and audio information using a laser beam are known.

As one of the video discs, there is a high-definition video disc which records a signal obtained by FM-modulating a MUSE signal obtained by band-compressing a high-definition image using a TCI multiplexed sub-Nyquist encoding method.

Since the bandwidth of the MUSE signal recorded on the high-definition video disc is about twice the bandwidth of the NTSC signal recorded on the current video disc, the rotation speed of the high-definition video disc is about twice that of the NTSC video disc. Therefore, the disc playback time is half that of NTSC video discs (one side
30 minutes).

In order to increase the disk reproduction time, it is necessary to increase the recording density. That is, it is necessary to reduce the size of a recording signal unit called a pit. However, even if the recording density of the recording medium increases, if the resolution of the reproducing optical system for reading out the pit information is low, the reproduction cannot be performed sufficiently.

The diameter of the signal readout beam of the reproduction optical system is given by the beam diameter =
If d, numerical aperture of the objective lens = NA, and reproduction light wavelength = λ, then the relational expression of d∝λ / NA is obtained, and the video diameter d is reduced (shorter).
A possible method is to shorten the wavelength λ of the reproduction light.

Currently, a laser beam of λ = 780 nm is used to play NTSC video discs and compact discs.
780n for the purpose of reducing the beam diameter d
Semiconductor lasers having a wavelength shorter than m are under development, and semiconductor lasers having a wavelength of 670 to 680 nm are currently on the market.
In addition, there are 632.8 nm He-Ne laser and laser light using the second harmonic of 400 to 550 nm, and the use of a short-wavelength light source to reproduce signal pits in a high-density recording medium. Becomes possible.

[Problems to be Solved by the Invention] By using a laser beam having a short wavelength, it is possible to reproduce a high-density recording disk with small pits. However, when reproducing a disk having pits of a normal size manufactured for a conventional laser beam having a long wavelength with a short-wavelength laser beam, the diffraction of the short-wavelength laser beam by the pits is reduced, and the reproduction signal is reduced. Cannot be sufficiently obtained, and good reproduction cannot be performed. That is, a pickup for a high-density recording disk having a short-wavelength laser beam cannot be used for reproducing a disk recorded at a normal density.

Therefore, an object of the present invention is to provide an optical reproducing apparatus that can read out pit information from both high-density and normal-density recording disks with a single pickup.

[Means for Solving the Problems] In the optical reproducing apparatus according to claim 1, pits are indicated from recording media having different recording densities by a laser beam having a wavelength suitable for reproducing a recording medium having a high recording density. In an optical reproducing apparatus that reads and reproduces information, the recording medium is irradiated with the laser light, and an optical pickup having an objective lens that detects reflected light thereof, according to a recording density of the recording medium, An offset setting circuit for setting an offset amount for switching a beam diameter of a laser beam applied to the recording medium; and an output of the offset setting circuit and a focus error signal from the optical pickup. And a focus servo circuit for controlling the objective lens.

3. An optical reproducing apparatus according to claim 2, wherein information represented by pits is read from a recording medium having a different recording density and reproduced by a laser beam having a wavelength suitable for reproducing a recording medium having a high recording density. In the apparatus, a detecting means for detecting a recording density of the recording medium, and an offset setting circuit for setting an offset amount for switching a beam diameter of the laser light applied to the recording medium according to an output of the detecting means. An optical pickup having an objective lens for irradiating the recording medium with the laser light and detecting the reflected light, and a beam diameter of the laser light irradiating the recording medium according to the recording density of the recording medium An offset setting circuit for setting an offset amount for switching the output, an output of the offset setting circuit, and a signal from the optical pickup. On the basis of the Kasuera signal,
A focus servo circuit for controlling the objective lens in the pickup.

[Operation] In the first aspect, when reproducing a recording medium having a high recording density with a short-wavelength laser light pickup, the pit is irradiated with laser light in a focused state, and reading and reproducing are performed. When reproducing a recording medium having a normal recording density, that is, a recording medium having a large pit, an offset is set for the focus servo circuit, and the pit is irradiated with laser light in a state slightly out of focus. By irradiating the pit with a beam that is not sufficiently narrowed in this way,
Large pits are no longer irradiated with a beam having a small diameter, and diffraction due to pits occurs. As a result, even if the recording medium is high-density recording or normal-density recording, good reproduction is possible. Can be done.

In Claim 2, information on whether the recording medium is high-density recording or normal-density recording is obtained by detecting means for detecting the recording density of the recording medium, the recording density of the recording medium is determined, and a short-wavelength laser light pickup is performed. When reproducing a recording medium with a high recording density by irradiating the pit with laser light in a focused state,
Read and reproduce. A recording medium with a normal recording density, ie,
When reproducing a recording medium having large pits, an offset is set for the focus servo circuit, and the pits are irradiated with laser light slightly out of focus. By irradiating the pit with a beam that is not sufficiently narrowed as described above, a beam having a small diameter is not irradiated to a large pit, and diffraction due to the pit occurs. Can be reproduced satisfactorily regardless of whether the recording is a high density recording or a normal density recording.

[Examples] The present invention will be specifically described based on drawings showing examples.

FIG. 1 is an overall configuration diagram showing an optical reproducing apparatus according to an embodiment of the present invention, FIG. 2 is an enlarged explanatory view of a pit portion of a disk in the optical reproducing apparatus according to the embodiment of the present invention,
FIG. 3 is an explanatory view showing an outline of a focus servo operation in the optical reproducing apparatus according to the embodiment of the present invention.

In FIG. 3, a laser beam 1 is focused by an objective lens 2 on a pit 4 formed on a disk 3 as a recording medium. The objective lens 2 is provided with a coil 5, controls a current flowing through the coil 5, drives the objective lens 2 by the magnetic action of the coil 5 and the magnet 6, and performs focus servo.

In FIG. 2, in the case of a disc 3 on which a MUSE signal which is a high-definition television signal is recorded, for example, a disc 3 having a reproduction time of 20 to 30 minutes on one side generally has a linear velocity of 18 to 21 m / s. ing. On the other hand, a high-density recording disk 3 with a single-sided reproduction time of 45 to 60 minutes to increase the reproduction time
Has a linear velocity of 14 to 17 m / s. Then, in the low linear velocity disk 3 of 45 to 60 minutes, small pits 4 are formed as much as the linear velocity becomes slow. Therefore, in order to reproduce the low linear velocity disk 3, it is necessary to narrow down the light.

FIG. 2 (a) is an explanatory diagram in the case where the pits 4a of the disk 3 of normal density recording having a high linear velocity are reproduced by the laser light 1a having a long wavelength (600 to 830 nm). The laser beam 1a focused by the objective lens 2 is sufficiently larger than the pits 4a for high-density recording for information recording, and the amount of reflected light changes due to diffraction by the pits 4a, which is detected as a signal. When the normal density recording disk 3 is reproduced, the reading is performed at the in-focus position so that the focus error signal becomes zero.

FIG. 2 (b) shows a case where a laser beam 1 having a short wavelength (400 to 600 nm) is used as a pickup for low linear velocity high density recording, and pits 4 of a high density recording disk 3 are reproduced by the laser beam 1. FIG. The laser beam 1 narrowed down by the objective lens 2 is sufficiently larger than the pits 4 for high-density recording for information recording, and the amount of reflected light changes due to diffraction by the pits 4 and is detected as a signal. It should be noted that, even when reproducing the high-density recording disk 3, reading is performed at the in-focus position so that the focus error signal becomes zero.

FIG. 2 (c) shows a case where a laser beam 1 having a short wavelength (400 to 600 nm) is used as a pickup for low linear velocity high density recording, and pits 4a of a disk 3 for normal density recording are reproduced with the laser beam 1. FIG. At this time, when the normal density recording disk 3 is reproduced, it is assumed that the reading is performed at the in-focus position so that the focus error signal becomes zero. When a disk 3 having a large pit 4a is reproduced at a high linear velocity with the short-wavelength laser light 1, the thickness of the disk 3 increases, and the diameter of the pit 4a and the beam diameter become almost the same. The change in the amount of reflected light due to the presence or absence is small, and good reproduction cannot be performed.

FIG. 2 (d) shows a case in which a laser beam 1 having a short wavelength (400 to 600 nm) is used as a pickup for low linear velocity and high density recording, and pits 4a of a disk 3 for normal speed recording are reproduced by the laser beam 1. FIG. At this time, when the normal density recording disc 3 is reproduced, an offset is added to the focus error signal so that the focus error signal in this state becomes zero, and reading is performed at a predetermined distance from the in-focus position. Shall be performed. That is, when the pit 4a is irradiated with the laser beam 1 deviated from the in-focus position state by applying an offset to the focus servo circuit 13 (see FIG. 1), diffraction occurs due to the pit 4a, and the amount of reflected light changes. And good reproduction can be performed.

FIG. 1 shows a book for reading from a high-density recording and normal-density recording disk 3 using a laser beam 1 of a short wavelength (400 to 600 nm) as a pickup for low linear velocity and high density recording shown in FIG. 1 shows a configuration of an optical reproducing apparatus according to an embodiment of the present invention.

In the figure, a disc 3 is picked up by a pickup 10 including a laser light source of a short wavelength (400 to 600 nm), an objective lens 2 and the like.
Is read out and reproduced by the reproduction circuit 11. This reproduced signal is applied to the video demodulation circuit 12,
Demodulated into a video signal. On the other hand, the reproduction signal reproduced by the reproduction circuit 11 also includes a focus error signal, as is well known, and this reproduction signal is applied to the focus servo circuit 13 to perform focus servo control. The focus servo circuit 13 includes an offset setting circuit 14, and an offset is set according to the recording density of the disk 3.

Focus servo by the focus servo circuit 13
For example, an astigmatism focus servo known in the technical field such as Japanese Patent Publication No. 60-48949 (H04N5 / 84) can be used. Then, when reproducing the disc 3 of the normal density recording,
An offset is added to the focus error signal output from the four-segment photosensor in a state where the beam diameter for irradiating the pit 4 is not sufficiently focused without being in the focused state, so that the focus error signal in this state becomes zero. That is, a signal indicating a focused state is obtained.

The recording density can be determined, for example, by detecting a linear velocity. For example, a control track is provided on the innermost peripheral portion of the disk 3, linear velocity information is written in the control track, and the linear velocity information is read out by the linear velocity determining circuit 15.
The offset can be controlled based on the output of the linear velocity determination circuit 15.

Alternatively, since the information recorded on the disc 3 is recorded at a constant linear velocity, the pickup is set at a predetermined radial position to reproduce the signal, and the discrimination is made by paying attention to the rotation speed of the disc 3 at that time. May be. That is, a pilot signal for disk rotation control is recorded at a specific radius position on the inner circumference of the disk 3, the disk 3 is rotated at the start of the reproducing operation, and the pilot signal separation circuit 16 first detects the pilot signal. The motor rotation control circuit 17 is driven based on the pilot signal. The output of the motor rotation control circuit 17 controls the spindle motor 18 to obtain a predetermined line connection. At this time, the FG pulse generated according to the rotation of the spindle motor 18 may be counted by the linear velocity determining circuit 15 to determine the linear velocity.

[Effects of the Invention] As described above, the optical reproducing apparatus according to claim 1 irradiates a recording medium with a laser beam and detects an reflected light of the recording medium. An offset setting circuit for setting an offset amount for switching a beam diameter of a laser beam applied to the recording medium in accordance with a recording density; and an output of the offset setting circuit and a focus error signal from an optical pickup. A focus servo circuit for controlling the objective lens in the pickup, and when reproducing at a high recording density, irradiating the pits of the recording medium with a laser beam in a focused state to perform reading and reproducing. Do. When reproducing a recording medium of normal recording density with large pits,
An offset is set for the focus servo circuit, and the pits are irradiated with laser light slightly out of focus, and large pits are no longer irradiated with a beam with a small diameter. Occurs, even if the recording medium is high-density recording, even if it is normal density recording,
Good reproduction can be performed.

Therefore, the information written on the recording medium can be reproduced satisfactorily on both the high-density and normal-density recording disks by one pickup.

An optical reproducing apparatus according to claim 2, wherein an offset setting circuit that sets an offset amount for switching a beam diameter of a laser beam applied to the recording medium in accordance with an output of a detection unit that detects a recording density of the recording medium. An optical pickup having an objective lens for irradiating the recording medium with the laser light and detecting the reflected light, and a beam diameter of the laser light irradiating the recording medium according to the recording density of the recording medium An offset setting circuit for setting an offset amount for switching between the two, and a focus servo circuit for controlling an objective lens in the pickup based on an output of the offset setting circuit and a focus error signal from an optical pickup. Information about whether the recording medium is high-density recording or normal-density recording is obtained by detecting means for detecting the recording density of the recording medium. Determines the recording density of the recording medium,
When reproducing a recording medium having a high recording density with a short-wavelength laser light pickup, a pit is irradiated with laser light in a focused state, and reading and reproduction are performed. When reproducing a recording medium with normal recording density with large pits, set the offset to the focus servo circuit, irradiate the pits with laser light slightly out of focus, and not sufficiently narrow down the pits. By irradiating the pit with a beam of pits, a beam of a small diameter is not irradiated to a large pit, and diffraction by the pit occurs. As a result, even if the recording medium is a high-density recording, Even in the case of density recording, good reproduction can be performed.

Therefore, the information written on the recording medium can be reproduced satisfactorily on both the high-density and normal-density recording disks by one pickup.

[Brief description of the drawings]

FIG. 1 is an overall configuration diagram showing an optical reproducing apparatus according to an embodiment of the present invention, FIG. 2 is an enlarged explanatory view of a pit portion of a disk in the optical reproducing apparatus according to the embodiment of the present invention, and FIG. FIG. 4 is an explanatory diagram showing an outline of a focus servo operation in the optical reproducing device according to the embodiment of the present invention. In the figure, 1 is a laser beam, 3 is a disk, 4 is a pit, 10 is a pickup, 13 is a focus servo circuit, and 14 is an offset setting circuit.

──────────────────────────────────────────────────続 き Continuation of front page (56) References JP-A-63-266639 (JP, A) JP-A-63-209030 (JP, A) JP-A-61-50225 (JP, A) JP-A-59-50 77606 (JP, A) JP-A-61-139939 (JP, A) (58) Fields investigated (Int. Cl. ⁶ , DB name) G11B 7/09 G11B 7/08

Claims (2)

(57) [Claims] 1. An optical reproducing apparatus for reading and reproducing information indicated by pits from recording media having different recording densities by using a laser beam having a wavelength suitable for reproducing a recording medium having a high recording density, wherein: An optical pickup having an objective lens for irradiating the laser light and detecting the reflected light, and for switching a beam diameter of the laser light applied to the recording medium according to the recording density of the recording medium. An offset setting circuit that sets an offset amount; and a focus servo circuit that controls an objective lens in the pickup based on an output of the offset setting circuit and a focus error signal from the optical pickup. Characteristic optical playback device. 2. An optical reproducing apparatus for reading and reproducing information indicated by pits from recording media having different recording densities by using a laser beam having a wavelength suitable for reproducing a recording medium having a high recording density, wherein: Detecting means for detecting the recording density of the laser beam; an offset setting circuit for setting an offset amount for switching a beam diameter of the laser beam applied to the recording medium in accordance with an output of the detecting means; An optical pickup having an objective lens for irradiating a laser beam and detecting a reflected light thereof; and an offset amount for switching a beam diameter of the laser beam irradiating the recording medium according to the recording density of the recording medium. An offset setting circuit for setting an output of the offset setting circuit and a focus error signal from the optical pickup. Based on an optical reproducing apparatus characterized by comprising a focus servo circuit which controls the objective lens in the pickup.