JP4641189B2 - Information playback device - Google Patents

Description

  The present invention relates to an information recording medium such as an optical disk and an optical card.

  In recent years, optical disks have been widely used as means for recording and reproducing data such as video data, audio data, and computer data. A high-density recording disk called a DVD (Digital Versatile Disc) has been put into practical use. This DVD includes a multilayer disc having a laminated structure having a plurality of recording layers that can be read from one side of the disc. A dual-layer disc having two recording layers on one side has been put to practical use as a read-only disc.

  As shown in FIG. 1, a DVD read-only dual-layer disc includes a first recording layer closer to the light incident side as viewed from the reading side, that is, a shallow recording layer, and a deeper second recording layer. In a dual-layer disc, the signal of either the shallow recording layer or the deep recording layer can be read from one side of the disc only by moving the focus of the reproducing light beam (hereinafter referred to as focus jump). The shallow recording layer is made a semi-transparent film so that the light beam can be transmitted through the shallow recording layer and the signal of the deep recording layer can be read, and the film thickness and material are selected. A reflective film is used for the deep recording layer. In order to separate these between the shallow recording layer and the deep recording layer with a certain thickness, a light-transmitting spacer layer having a high transmittance at the wavelength of light is provided.

  In the DVD standard, as shown in FIG. 2, the thickness of the transparent cover layer on the recording layer of a single-layer disc having only one recording layer is 600 μm. In contrast, in the case of a dual-layer disc, the positions of the two recording layers are 570 μm and 630 μm from the incident side surface, that is, the first and second layers above and below the recording layer depth of 600 μm of a single-layer DVD. It is configured to place. In this way, the distribution with the center of the thickness of the single-layer recording layer is performed on the two-layer disc is that the objective lens having a relatively small numerical aperture of 0.6 of the pickup optical system for signal recording / reproducing in the DVD standard is 600 μm thick. Even if this low numerical aperture objective lens is used, the signal deviation is greatly affected by the depth deviation of the first and second layers of about ± 30 μm from the single-layer recording layer. Adopted because it does not reach. At this time, a wavefront aberration occurs in the reading light beam due to a 30 μm thickness shift of the recording layer. However, when the numerical aperture is about 0.6, the amount of wavefront aberration is small, which is not a problem.

  A program such as a movie for a long time that does not fit in the first recording layer of a two-layer disc is reproduced over the second recording layer. In addition, the DVD standard defines a single-sided signal reproduction method called an opposite track path method in which two layers are reproduced continuously. This is to reproduce a recording layer having a depth of 570 μm from the inner periphery to the outer periphery, focus jump to the recording layer having a depth of 630 μm on the outer periphery, and reproduce the signal from the outer periphery toward the inner periphery. Is to do. At this time, by reading the information area representing the disc contents recorded on the 570 μm layer, the apparatus side can detect the title of the DVD, the program recording time, or that the two-layer disc is of the opposite track path system. .

  On the other hand, higher density is required for next-generation optical discs as the amount of information increases. To increase the density, it is conceivable to increase the numerical aperture of the objective lens to 0.8 or more. When such a high numerical aperture objective lens is used, the amount of wavefront aberration due to an error in the cover layer thickness on the recording layer is increased to make signal reading impossible, and two-layer recording of the next generation optical disc is performed. A layer structure cannot be easily reproduced. For this reason, it can be considered that an optical system capable of adjusting the amount of wavefront aberration is incorporated in the pickup to compensate for the occurrence of wavefront aberration according to the depth of the recording layer.

  When reading next-generation single-layer discs and multi-layer discs such as double-layer discs in an optical system that compensates for wavefront aberration while maintaining compatibility, there is a difference in the cover layer thickness corresponding to the depth between the recording layers. Therefore, it has been necessary to focus on the recording layer while correcting the wavefront aberration of the light beam to search for lead-in information. For this reason, when a dual-layer disc is reproduced immediately after the single-layer disc is reproduced, there is a problem that it takes a long time to start the reproduction. In addition, when the numerical aperture is large, the tolerance for the tilt of the disk increases significantly as the cover layer thickness increases. It was necessary to improve and produce.

The present invention has been made in view of such circumstances, and multilayer information recording that enables quick data reproduction even when information is recorded and reproduced using an objective lens having a large numerical aperture of 0.8 or more. An object of the present invention is to provide an information reproducing apparatus capable of reproducing any information on a single-layer information recording medium compatible with the medium.

The information reproducing apparatus according to claim 1 , further comprising: a cover layer on the light incident side recording layer having a single recording layer and having a refractive index n and having a thickness t, and the optical recording from the light incident side surface of the recording layer. A single-layer information recording medium having a distance d1 = n × t, and is compatible with the single-layer information recording medium in the same standard, and the first recording layer and the second recording layer from the light incident side surface In which the optical distance from the light incident side surface of the second recording layer can reproduce any information on the two- layer information recording medium equal to d1 , An objective lens having a numerical aperture and generating a light spot of the light beam , loading means for loading the single-layer information recording medium or the two- layer information recording medium, and a wavefront for correcting the amount of wavefront aberration of the light beam An aberration correction unit, and the loading unit stores the single-layer information recording medium. When filled, the wavefront aberration correcting means minimizes the amount of wavefront aberration of the light beam when the focused spot is connected at a position away from the light incident surface of the single-layer information recording medium by the optical distance d1. When the two-layer information recording medium is loaded by the loading means, the wavefront aberration correcting means connects the focused spot at a position away from the light incident surface of the two-layer information recording medium by the optical distance d1. In this case, the amount of wavefront aberration of the light beam is minimized .

BEST MODE FOR CARRYING OUT THE INVENTION

  Next, embodiments of the present invention will be described with reference to the drawings.

<Double-layer disc>
An example of the multilayer disk of the first embodiment of the present invention is a two-layer disk having a two-layer structure of recording layers L1 and L2, for example, as shown in FIG. This is a reproduction compatibility with a single-layer disc (FIG. 4) reproduced or recorded through a cover layer on the light incident side recording layer having a predetermined refractive index n and having a predetermined refractive index n. Alternatively, it is a dual-layer disc having recording compatibility.

  Of the recording layers of such a two-layer disc, the deepest recording layer, that is, the recording layer at the deepest position from the light incident side is covered with a cover layer having a thickness in which the optical distance d1 has a relationship of d1 = n × t. .

  Further, the shallow recording layer other than the deepest recording layer is covered with a cover layer having a thickness in which the optical distance d2 has a relationship of d2 <n × t. Such a two-layer disc includes a deepest recording layer formed at an optical distance d1 satisfying the formula d1 = n × t and a shallow recording layer formed at an optical distance d2 satisfying the formula d2 <n × t.

  In this double-layer disc, since the deepest recording layer having an optical distance d1 is disposed at the same optical path thickness as the recording layer of the single-layer disc, the single-layer disc is adapted to minimize the wavefront aberration. Even with the pickup, it is possible to reproduce the information of the deepest recording layer having the optical distance d1 without searching for the position of the shallow recording layer of the multilayer disc. In addition, since the optical distance d2 is set shorter than d1, the tolerance of the disc tilt when recording / reproducing on this shallow recording layer is not stricter than that of a single-layer disc, and is flatter than that of a single-layer disc. There is no need to improve.

  In a two-layer disc, information of contents that are supposed to be reproduced in a predetermined order over two layers is recorded, and the order is recorded so that a recording layer with a shallow optical distance d2 is reproduced before the deepest recording layer. obtain. That is, physical address information can be sequentially recorded from the shallow recording layer to the deepest recording layer in order from the light incident side.

  Further, in a two-layer disc, signal reproduction may be in the order starting from the inner periphery to the outer periphery of the optical distance d2 surface and continuing from the outer periphery of the optical distance d1 surface to the inner peripheral direction. Also, physical address information can be recorded sequentially from the inner circumference to the outer circumference of the deepest recording layer.

  With this configuration, when reproducing a program for a time exceeding the recording limit of one shallow recording layer, the recording was performed on the deepest recording layer after the reproduction of the shallow recording layer having a large disc tilt tolerance was completed. Since the remaining information is reproduced, it is possible to increase the tolerance of the average disc tilt.

  In the two-layer disc, predetermined content information regarding all the contents of the two layers can be further recorded in the deepest recording layer having the optical distance d1. The signal reproducing apparatus first reads predetermined information indicating the title of the two-layer disc, the program recording time, or the opposite track path method at the deepest recording layer at the optical distance d1, and then the optical disc. The signal reproduction can be continued after jumping the focus position to the inner periphery of the shallow recording layer of the distance d2. For each recording layer in the depth order from the deepest recording layer to the shallow recording layer, the physical address information may be sequentially recorded alternately in the forward direction from the inner periphery to the outer periphery and in the reverse direction from the outer periphery to the inner periphery.

  By using a disc on which information is recorded with such a configuration, it is possible to read predetermined information indicating the contents of the disc over two layers in the same wavefront aberration correction state as that of the single-layer disc. The reproducing apparatus can know that it is a layered disc without searching for the position of the recording layer with the wavefront aberration correcting apparatus, and can quickly start reproduction. Therefore, according to the present invention, when the adjacent recording layers are continuously reproduced from the shallow recording layer, the reproduction surface of those recording layers can be smoothly transferred.

  This information may be recorded as pits on the inner periphery of the deepest recording layer, or may be called a PEP in which a barcode or pits are used to form a barcode. Alternatively, it may be a wavefront aberration correction signal in a region in which a signal used to detect the wavefront aberration is recorded.

  In addition, the numerical aperture of the objective lens that generates the condensed spot is selected to be 0.8 or more, and the objective lens is designed to minimize the amount of wavefront aberration when the spot is formed through the optical distance d1. .

  In the above example, a description has been given of a two-layer disc. However, even if there are three or more layers, the same configuration is possible, and it is also possible to provide other recording layers that do not satisfy this condition. is there. Although the recording density is not described, the two recording layers may have the same recording density, or the recording density may be different for each recording layer.

  In the above example, the thickness of the cover layer is described assuming that the optical path lengths are equal. However, this can of course be realized with the same thickness by a material having the same refractive index, and a material having a different refractive index. Also, the product of refractive index and thickness, that is, the optical thickness (distance) may be made equal. Moreover, when the refractive index of the substance (spacer) with which the layers are filled is different, it is possible to set to an equivalent optical path length by performing sequential calculation.

  For example, the refractive index of the light incident side cover layer of the two-layer disc is nC and the thickness is tC, the refractive index of the shallow recording layer L1 is nL1 and the thickness is tL1, and the refractive index of the spacer layer between the recording layers L1 and L2 is When nS and thickness are tS, the light incident on the shallow recording layer L1 so that the optical distance d1 from the light incident side surface of the deepest recording layer L2 satisfies d1 = n × t = nC × tC + nL1 × tL1 + nS × tS. The optical distance d2 from the side surface is designed to satisfy d2 = nC × tC <n × t.

Each of the recording layers L1 and L2 has a laminated structure including a recording layer made of a phase change material such as Ag—In—Sb—Te and a glassy protective layer such as ZnS—SiO ₂ sandwiching the recording layer. In the case of an optical disc in which data can be recorded or erased or rewritten by a light beam using a recording layer of phase change material, a rewritable area in which data can be rewritten or recorded or erased, and address, recording timing, etc. as sequential physical address information Each recording layer may be provided with a pre-pit area in which a row of embossed pits for carrying the above information is provided in advance. Although an example of a rewritable double-layer disc using a phase change material has been described, the recording layer material of the present invention is not limited to a phase change material, and a write-once type dye material can be used. It can also be configured as a playback-only disc.

  In addition to the above conditions, the reproduction and recording compatibility single-layer and multi-layer discs are common in the disc diameter, overall disc thickness, track pitch, shortest pitch length, warp angle, birefringence, format, and the like. For example, these may be a CAV (constant angular velocity) or CLV (constant linear velocity) method. Further, it may be a zone CAV or CLV multi-layer disc in which CAV and CLV are combined. In addition, convex groove tracks and concave land tracks are alternately formed spirally or concentrically on each recording layer of the multilayer disc. Each groove track may be wobbled at a frequency corresponding to the rotational speed of the multilayer disk.

<Recording and playback device>
When recording data on a multi-layer disc, the prepit area and the rewritable area of the recording layer are scanned with low-intensity reproducing light beam irradiation (reading power) to detect land prepits and groove prepits in the prepit area. Thus, while recognizing the position on the track to be recorded, a high intensity recording light beam (writing power) modulated according to the data is condensed and irradiated onto the rewritable area of the track.

  FIG. 5 is a block diagram showing the configuration of the recording / reproducing apparatus of the present invention.

  The optical pickup 21 includes an optical system including a condenser lens, a beam splitter, an objective lens, and the like, and a semiconductor laser as a light source, a photodetector, an objective lens actuator, and the like. The objective lens 21a has a numerical aperture of 0.8 or more and generates a light spot on the recording layer. The objective lens 21a minimizes the amount of wavefront aberration of a light beam when a converging spot is formed at an optical distance d1 away from the surface when either compatible single-layer or multi-layer disc is loaded at a normal position. And a lens group. The optical pickup 21 includes wavefront aberration correction means 21b that varies the amount of wavefront aberration included in the focused spot.

  The optical pickup 21 irradiates the multilayer disc 1 with a light beam as recording light or readout light, and detects a reflected light beam from the recording layer of the optical disc, and tracks and prepits formed on the multilayer disc 1 or A photodetector that reads a signal corresponding to the recording mark as a change in reflectance is provided. The servo circuit 20 includes a focus servo circuit and a tracking servo circuit. Based on a control signal from the optical pickup 21 and a control command from the control unit (CPU) 26, servo control and reproduction position (radius) of the focus and tracking of the pickup. Position) control, spindle motor speed control, etc. When the multilayer disk of the above example, for example, a two-layer disk is loaded, the light beam is irradiated first on the deepest recording layer L2 having the optical distance d1, the initial focus servo is executed, and the light beam is emitted from the multilayer disk. Tracking servo control and focus servo control are performed on the objective lens so as to accurately focus on the recording layer. The focus servo circuit also executes focus servo for jumping the focus position to the recording layer L1 having a shallow optical distance d2 after execution of the initial focus servo.

  A read signal (RF signal) output from the optical pickup 21 is amplified by an amplifier circuit and supplied to a pre-address decoder 23 and a decoder 43.

  The pre-address decoder 23 extracts the bripit and wobble signals, and the internal synchronous clock and timing signal generation circuit generates a clock signal and timing signal synchronized with the rotation of the multilayer disk 1. The timing signal represents a position on the current disc such as a pre-pit area or writable area where a light beam is recorded (reproduced), a land track, or a groove track. The pre-address decoder 23 reads the address information from the signal read from the emboss pits in the pre-pit area of the disc by the pickup, and sends the address information and timing signal to the CPU 26. The pre-address decoder 23 includes a circuit for detecting a rewritable area and a pre-pit area of the multilayer disc.

  The CPU 26 detects the position of the prepit area of the recording layer from these signals. The CPU 26 has a built-in or connected storage device for storing necessary data and the like. Based on the supplied signal, the CPU 26 controls the entire apparatus. The CPU 26 reads the address information from the pre-address decoder 23 and sends a control command to the recording control circuit 36 and the servo circuit 20, thereby controlling the recording / reproducing operation to a predetermined address.

  The recording control circuit 36 controls the laser power of the pickup in accordance with each state such as recording, erasing and reproduction based on the control command from the CPU 26 and the timing signal from the pre-address decoder 23. In the recording state, information on the disk is recorded by modulating the power of the pickup laser based on the signal from the encoder 27. In the playback state (when data in the rewritable area is played back or when address information in the pre-pit area is played back), the read power is controlled to be kept at a weak and constant power so that the information recorded on the disc is not erased. .

  The encoder 27 performs processing such as adding a parity code for error correction to the data to be recorded and converting the data into an RLL code (Run Length Limited code), for example, to obtain a signal suitable for recording on the multilayer disk 1. Convert (encode). The converted signal is sent from the encoder 27 to the recording control circuit 36.

  The decoder 43 performs reverse processing (demodulation of RLL code, error correction, etc.) of processing performed by the encoder from the signal read from the rewritable area of the disk, and restores the original recorded data.

FIG. 3 is a schematic sectional view of a two-layer disc. 1 is a schematic cross-sectional view of a single layer disc. 1 is a schematic cross-sectional view of a two-layer disc according to the present invention. 1 is a schematic cross-sectional view of a single-layer disc compatible with a dual-layer disc of the present invention. BRIEF DESCRIPTION OF THE DRAWINGS The schematic block diagram explaining the recording / reproducing apparatus by this invention.

Explanation of symbols

1 Multi-layer disc 20 Servo circuit 21 Optical pickup 23 Pre-address decoder 26 Control unit (CPU)
27 Encoder 36 Recording control circuit 43 Decoder

Claims (3)

A single recording layer having a cover layer on the light incident side recording layer of thickness t having a refractive index n, and an optical distance from the light incident side surface of the recording layer being d1 = n × t. The layer information recording medium and the single layer information recording medium are reproduction compatible with the same standard, and have a first recording layer and a second recording layer in order from the light incident side surface. An information reproducing apparatus capable of reproducing any information of a two- layer information recording medium having an optical distance from the light incident side surface of the layer equal to the d1 .
An objective lens having a numerical aperture greater than or equal to 0.8 and producing a focused spot of the light beam;
Loading means for loading the single-layer information recording medium or the two- layer information recording medium;
Wavefront aberration correction means for correcting the amount of wavefront aberration of the light beam,
When the single-layer information recording medium is loaded by the loading means, the wavefront aberration correcting means connects the focused spot at a position away from the light incident surface of the single-layer information recording medium by the optical distance d1. , Minimizing the amount of wavefront aberration of the light beam,
When the two-layer information recording medium is loaded by the loading means, the wavefront aberration correcting means connects the focused spot at a position away from the light incident surface of the two-layer information recording medium by the optical distance d1. An information reproducing apparatus that minimizes the amount of wavefront aberration of the light beam . 2. The information reproducing apparatus according to claim 1 , further comprising a focus servo unit that performs an initial focus servo on the second recording layer when the two-layer information recording medium is loaded by the loading unit. 3. The information reproduction according to claim 2 , wherein the focus servo means executes focus servo for jumping a focus position from the second recording layer to the first recording layer after execution of the initial focus servo. apparatus.

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