JP4268568B2 - Optical head and optical information processing apparatus provided with optical head - Google Patents

Description

  The present invention relates to an optical head for optically writing and / or reading data on an optical information recording medium such as an optical disk having a plurality of information recording layers, and an optical information processing apparatus including such an optical head.

  Conventionally, various techniques for increasing the recording capacity of an optical disc have been developed. For example, by shortening the wavelength of the laser beam used for writing and reading data, or by increasing the numerical aperture (NA) of the objective lens that converges the laser beam on the optical disc, the recording density of the optical disc is improved, Techniques for increasing the recording capacity have been developed. In addition, a technique for increasing the recording capacity by providing a plurality of information recording layers on which data is written on one optical disc has been developed. According to the latter technique, it is possible to increase the recording capacity of the optical disk without changing the wavelength of the laser light source mounted on the optical head or the numerical aperture of the objective lens, and the digital versatile disk (DVD) or the like has already been achieved. Has been adopted as. For example, a single-sided dual-layer DVD has two information recording layers, and each layer is irradiated with a laser from the same direction to read data.

  When data is written to and / or read from an optical disc provided with two or more information recording layers in order to increase the recording capacity, the optical disc apparatus determines which information is recorded by the laser beam condensed by the objective lens. It is necessary to perform processing for determining whether or not a layer is in a converged state (so-called layer determination processing). For example, Patent Document 1 shows an example of a conventional technique related to layer discrimination processing. The conventional layer discrimination process will be described below with reference to FIGS.

  FIG. 19 shows a schematic configuration of the optical head 100 for performing the layer discrimination processing. The optical disc 107 has two information recording layers (layer 0 and layer 1). The information recording layers on the side far from the objective lens 106 of the optical head 100 are referred to as layer 0 and layer 1 in order.

  When the semiconductor laser 101 emits linearly polarized laser light, the diffraction grating 102 generates three beams, that is, a main beam and two sub-beams on both sides thereof. These beams are converted into substantially parallel light by the collimator lens 103, reflected by the beam splitter 104, and converted into circularly polarized light by the quarter wavelength plate 105. The light converted into the circularly polarized light is condensed on the layer 0 or the layer 1 through the substrate of the optical disk 107 by the objective lens 106. The diffraction grating 102 is adjusted for tracking control using a three-beam method.

  The laser light reflected at layer 0 or layer 1 of the optical disk 107 is transmitted again through the substrate, transmitted through the objective lens 106, converted into linearly polarized light different from the forward path by the quarter wavelength plate 105, and then the beam splitter 104. , Passes through the detection lens 108, and is collected on the photodetector 110. The photodetector 110 has a plurality of light receiving elements. Each light receiving element generates and outputs a light amount signal having a level corresponding to the amount of incident light.

  FIG. 20 shows an arrangement of five light receiving elements 110 a to 110 e provided in the photodetector 110. The photodetector 110 includes a four-divided light receiving element 110a that receives a main beam, light receiving elements 110b and 110c that receive a sub beam for detecting a tracking error signal, and light receiving elements 110d and 110e that receive the sub beam for layer discrimination. And have. The main beam of the laser beam reflected by the predetermined information recording layer of the optical disc 107 is formed as a focused spot m on the light receiving element 110a, and the two sub beams are formed as focused spots s on the light receiving elements 110b and 110c, respectively. Is done. The light receiving element 110b, the four-divided light receiving element 110a and the light receiving element 110c are arranged on a straight line in this order. The light receiving element 110d is disposed between the light receiving element 110b and the quadrant light receiving element 110a, and the light receiving element 110e is disposed on the opposite side of the quadrant light receiving element 110a with respect to the light receiving element 110c.

  FIG. 21 shows a position where the reflected light is incident on the photodetector 110 when the laser light focused by the objective lens is converged on the layer 0 of the optical disk 107. Condensed spots m0 and s0 by the main beam and the two sub beams reflected from the layer 0 are formed at the substantially central portions of the light receiving elements 110a, 110b, and 110c, respectively. At this time, the laser light reflected by the layer 1 at the same time forms other large condensing spots m1 and s1 with low light intensity. The center position of the focused spot m1 by the main beam reflected by the layer 1 is substantially equal to the center position of the focused spot m0 by the main beam reflected by the layer 0. On the other hand, the two condensing spots s1 by the sub-beams reflected by the layer 1 are formed in a state where the distance between the centers is enlarged as compared with the condensing spot s0 by the sub-beams reflected by the layer 0.

  FIG. 22 shows a position where the reflected light is incident on the photodetector 110 when the laser light focused by the objective lens is converged on the layer 1 of the optical disc 107. Condensed light condensing spots m1 and s1 formed by the main beam and two sub beams reflected from the layer 0 are formed at the substantially central portions of the light receiving elements 110a, 110b, and 110c, respectively. At this time, the laser beams reflected by the layer 0 at the same time form other large converging spots m0 and s0 with low light intensity. The center position of the focused spot m0 by the main beam reflected by the layer 0 is substantially equal to the center position of the focused spot m1 by the main beam reflected by the layer 1. On the other hand, the two condensing spots s0 by the sub-beams reflected by the layer 0 are formed in a state where the center distance is reduced as compared with the condensing spots s1 by the sub-beams reflected by the layer 1.

Here, the layer discrimination signal RD is
RD = (light quantity signal output from light receiving element 110d) − (light quantity signal output from light receiving element 110e)
Sought by. For example, when RD> 0, it can be determined that the focused spot is in a converged state in layer 0. When RD <0, it can be determined that the focused spot is in a converged state in layer 1.
Japanese Patent Laid-Open No. 9-259456

  However, since the above-described layer discrimination method is premised on the use of a sub beam by the three beam method, it cannot be applied to an optical head employing a one beam method without a sub beam or an optical information processing apparatus having such an optical head. . Since the 3-beam system is more complicated in configuration and processing than the 1-beam system, discrimination processing based on the 1-beam system with a simpler configuration is required. Further, according to the three-beam method, the light intensity of the sub-beam is small, so that the light intensity of the focused spot that must be detected is small, and the spread is relatively large. Therefore, it is difficult to obtain a sufficient S / N ratio.

  An object of the present invention is to provide an optical head capable of performing layer discrimination processing using a signal having a large S / N ratio without depending on a tracking error detection method, and optical information processing for mounting such an optical head Is to provide a device.

  An optical information processing apparatus according to the present invention radiates light from the second information recording layer side to an information recording medium in which a first information recording layer and a second information recording layer are laminated, and writes data and / or Read. The optical information processing apparatus generates a light amount signal in accordance with a light source that emits the light, a condensing optical system that condenses the light from the light source to form a focal point, and a light reception amount of at least one light receiving element. A light receiving portion, a detection optical system for guiding the first reflected light from the first information recording layer and the second reflected light from the second information recording layer to the light receiving portion, and a layer discrimination signal based on the light quantity signal. A processing circuit that generates and determines based on the layer determination signal whether the focal point is located in the vicinity of the first information recording layer or the second information recording layer of the loaded information recording medium; I have. The detection optical system includes an optical element that gives astigmatism to the first reflected light and the second reflected light. The light receiving unit includes an incident area of the second reflected light when the focal point is positioned in the vicinity of the first information recording layer, and the first reflecting unit when the focal point is positioned in the vicinity of the second information recording layer. A light-receiving element for discrimination arranged based on an incident area of one reflected light is included as the at least one light-receiving element.

  The light-receiving element for discrimination is arranged in a region where one of the first reflected light and the second reflected light is incident, out of the region of the light receiving unit where the first reflected light and the second reflected light are incident. Also good.

  Due to the astigmatism, the first reflected light and the second reflected light have a first axis and a second axis perpendicular to and orthogonal to the optical axis, respectively, and the second reflected light has the focal point When positioned near the first information recording layer, it converges before entering the light receiving unit with respect to the first axis, and the light receiving element for discrimination is aligned with the axis on the light receiving unit corresponding to the first axis. It may be arranged along.

  A plurality of the light-receiving elements for determination may be arranged at substantially symmetric positions with respect to the center of the optical axis.

  The light receiving unit receives a first reflected light when the focal point is located in the vicinity of the first information recording layer and a second reflected light when the focal point is located in the vicinity of the second information recording layer. A light receiving element, and the processing circuit generates a focus error signal based on a light amount signal corresponding to the amount of light received by the processing light receiving element, and further determines the focus position based on the focus error signal. May be.

  The light receiving unit includes at least one auxiliary light receiving element disposed along an axis on the light receiving unit corresponding to the second axis, and the second reflected light is about the second axis, When the focal point is located in the vicinity of the first information recording layer, it converges behind the light receiving unit, and the processing circuit further generates the layer determination signal based on the amount of light received by the auxiliary light receiving element. May be.

  The plurality of light receiving elements for determination are arranged at positions substantially symmetrical with respect to the center of the optical axis, and the plurality of auxiliary light receiving elements are arranged at positions substantially symmetrical with respect to the center of the optical axis. Also good.

  The processing circuit calculates the difference between the light quantity signal from the light receiving element for discrimination and the light quantity signal from the auxiliary light receiving element by the sum of the light quantity signal from the light receiving element for discrimination and the light quantity signal from the auxiliary light receiving element. The layer discrimination signal may be generated by division.

  The detection optical system converges the first reflected light in the vicinity of the optical element and converges the second reflected light on the light receiving unit when the focal point is located in the vicinity of the second information recording layer. Also good.

  When the focal point is located in the vicinity of the second information recording layer, the detection optical system converges the first reflected light before entering the optical element, and the second reflected light is reflected on the light receiving unit. It may be converged.

  The detection optical system includes a light-blocking portion that blocks a part of the light, and when the focal point is located in the vicinity of the second information recording layer, the first reflected light is converged in the vicinity of the light-blocking portion and the light reception is performed. The second reflected light may be converged on the light receiving part while blocking the incident on the part.

  The detection optical system includes a light shielding portion having an opening that shields a peripheral portion of light, and when the focal point is located in the vicinity of the first information recording layer, the peripheral portion of the second reflected light is shielded by the light shielding portion. The cross-sectional area of the light beam of the second reflected light incident on the light receiving unit may be further reduced.

  Information unique to each information recording layer is recorded in the first information recording layer and the second information recording layer, and the processing circuit acquires the unique information, and the focus is based on the unique information. The information recording layer in which is located may be specified and compared with the determination result to verify whether the determination result is accurate.

  Each of the first information recording layer and the second information recording layer has a plurality of information tracks in which the data is written, and each of the plurality of information tracks specifies a data position on the information recording medium. The processing circuit may acquire the address information as the unique information.

  As a result of verification, when it is determined that the focal point is located in the vicinity of an information recording layer different from the predetermined information recording layer, the processing circuit is in the vicinity of another information recording layer based on the layer determination signal. The position of the focal point may be changed.

  The information recording medium has (N + 1) (N: natural number) information recording layers, and the second information recording layer is an arbitrary layer up to the Nth layer as viewed from the light emitting side. The first information recording layer may be an information recording layer located deeper than the first information recording layer.

  The optical information processing apparatus according to the present invention can be loaded with a plurality of types of information recording media, and emits light to the loaded information recording media to write and / or read data. The type of the information recording medium differs depending on whether the information recording medium has a single information recording layer or a plurality of stacked information recording layers. The optical information processing device generates a light amount signal according to the amount of light received by at least one light receiving element, a light source that emits the light, a condensing optical system that condenses the light from the light source to form a focal point And a detection optical system for guiding reflected light from the information recording layer to the light receiving unit, and an information recording medium loaded based on the layer discrimination signal, generating a layer discrimination signal based on the light amount signal And a processing circuit for discriminating the type of the. The detection optical system includes an optical element that gives astigmatism to the reflected light, and the light receiving unit includes the first information recording layer and the second information recording layer when the information recording medium includes the first information recording layer and the second information recording layer. The incident area of the second reflected light when the focal point is located in the vicinity of the first information recording layer, and the incident area of the first reflected light when the focal point is located in the vicinity of the second information recording layer Is included as the at least one light receiving element.

  The processing circuit may determine the number of the information recording layers based on a level of the layer determination signal when the focal point is in the vicinity of the information recording layer of the loaded information recording medium.

  An optical head according to the present invention emits light from the second information recording layer side to an information recording medium in which a first information recording layer and a second information recording layer are laminated, and writes and / or reads data. Do. The optical head includes a light source that emits the light, a condensing optical system that condenses the light from the light source to form a focal point, and a light receiving unit that generates a light amount signal according to the amount of light received by at least one light receiving element. And a detection optical system for guiding the first reflected light from the first information recording layer and the second reflected light from the second information recording layer to the light receiving unit, and a layer discrimination signal based on the light quantity signal. A processing circuit for determining whether the focal point is located in the vicinity of the first information recording layer or the second information recording layer of the loaded information recording medium based on the layer determination signal. Yes. The detection optical system includes an optical element that gives astigmatism to the first reflected light and the second reflected light, and the light receiving unit has the focal point located in the vicinity of the first information recording layer. A light-receiving element for determination arranged based on the incident area of the second reflected light when and the incident area of the first reflected light when the focal point is located in the vicinity of the second information recording layer, As at least one light receiving element.

  The processing circuit according to the present invention radiates light from the second information recording layer side to the information recording medium in which the first information recording layer and the second information recording layer are laminated, and writes and / or reads data. Implemented on the device to do. The apparatus includes a light source that emits the light, a condensing optical system that condenses light from the light source to form a focal point, and a light receiving unit that generates a light amount signal according to the amount of light received by at least one light receiving element. The incident area of the second reflected light when the focal point is positioned in the vicinity of the first information recording layer, and the first when the focal point is positioned in the vicinity of the second information recording layer. A light-receiving part that includes a light-receiving element for discrimination arranged based on the incident area of the reflected light as the at least one light-receiving element, the first reflected light from the first information recording layer, and the second information recording layer An optical element that gives astigmatism to the second reflected light, and a detection optical system that guides the first reflected light and the second reflected light to the light receiving unit. The processing circuit generates a layer discrimination signal based on the light amount signal, and the focus is based on the layer discrimination signal, the first information recording layer and the second information recording layer of the information recording medium loaded. It is discriminated in the vicinity.

  According to the present invention, the layer discrimination signal is generated using the reflected light from a layer different from the information recording layer (layer) of the optical information recording medium on which the focal point is formed by the objective lens. The shape of the reflected light that is incident on the photodetector differs depending on the position of the focal point. Therefore, the layer on which the focal point is formed can be reliably identified based on the layer identification signal and further by considering the focus error signal. can do. Since the reflected light from the layer has sufficient intensity for detection, a layer discrimination signal can be generated with a high S / N ratio. This process does not require the use of a sub beam in the conventional three beam system. Therefore, according to the layer discrimination processing of the present invention, it can be realized using a one-beam optical head.

  Hereinafter, the present invention will be described with reference to the accompanying drawings. In the drawings, components having the same reference numerals have similar functions and configurations and perform similar operations. Prior to describing various embodiments of the present invention, first, an optical information recording medium on which information is recorded by the optical information processing apparatus according to the present invention and the recorded information is reproduced will be described. In this specification, an optical disk is described as an example of the optical information recording medium. However, the present invention can be applied to, for example, a card capable of optically reading data.

  FIG. 1A shows the appearance of the optical disc 1. The optical disc 1 is a disc-shaped recording medium such as a CD, a DVD, or a Blu-ray Disc (BD). The optical disc apparatus records information by irradiating one side of the optical disc 1 with light such as a laser, or reads the recorded information. Data is written in an information recording layer (hereinafter referred to as “layer”) formed of a phase change material or the like. More specifically, the layer has a plurality of information tracks (not shown) formed in a spiral shape, for example. Each information track is defined as a groove or valley element on the information surface and is given a separate address. Data is written to each information track.

  In the present invention, the number of layers is not limited to one, but two or more layers are stacked. FIG. 1B is a cross-sectional view of an optical disc 1 having two layers. In this figure, the light emitted from the layer 1 side is also shown for reference. This light is focused on layer 0. The layer depth of the optical disc 1 varies depending on the type of the optical disc 1. For example, in the BD, the layer 0 is provided at a depth of 100 μm when viewed from the surface on which light is emitted, and the layer 1 is provided at a shallow position of 25 μm. Each layer has a predetermined reflectance and reflects the received light. Note that there is a substrate that functions as a protective layer from the surface of the optical disc 1 on the light incident side to the layer 1. Next, FIG. 1C is a cross-sectional view of the optical disc 1 having (N + 1) layers (N: natural number). For example, each layer is provided at an interval of 25 μm. Other configurations are the same as those of the two-layer optical disk.

  Next, FIG. 1 (d) shows a TOC area 150 provided in layer 0. A TOC area 150 shown in FIG. 1 (d) is provided on the innermost periphery of layer 0. In the TOC area 150, TOC (Table Of Contents) indicating what information is recorded at which position of the optical disc 1 is shown. The TOC is a so-called “table of contents”, and when the optical disc apparatus accesses the optical disc 1, it is necessary to first read the TOC recorded in the TOC area 150. Therefore, in order to specify layer 0, the layer discrimination processing according to the present invention is important.

  Embodiments of an optical disk device according to the present invention will be described below. In the present specification, the optical disk 1 will be described as having two layers (layer 0 and layer 1).

(Embodiment 1)
FIG. 2 shows a configuration of the optical disc apparatus 51 according to the present embodiment. The optical disc device 51 emits light from the layer 1 side to the optical disc 1 and writes and / or reads data to and from the layer 0 and / or layer 1.

  The optical disk device 51 includes a semiconductor laser light source 2, a collimator lens 3, a beam splitter 4, a quarter wavelength plate 5, an objective lens 6, a detection lens 8, an anamorphic lens 9, a photodetector 10, A signal processing circuit 20, a servo control circuit 21, and an actuator coil 22 are included. The optical disk 1 is generally detachable and is not a component of the optical disk device 51, but is shown in FIG. 2 for explanation. The optical disk device 51 may include various hardware elements such as a spindle motor that rotates the optical disk 1, a modulation / demodulation circuit for writing and / or reading data, and an error correction circuit. Only the main components related to the present invention are described.

  A semiconductor laser light source 2 (hereinafter simply referred to as “light source 2”) emits a laser beam having a wavelength of 405 nm, for example. The collimating lens 3 converts the incident light into substantially parallel light and outputs it. The beam splitter 4 substantially reflects the polarization component of the laser light incident from the collimating lens 3 side, and substantially transmits the polarization component of the laser light incident from the quarter wavelength plate 5 side. The quarter wave plate 5 converts incident light from circular deflection to linear deflection, or from linear deflection to circular deflection. The objective lens 6 collects incident light to form a focal point.

  The detection lens 8 is provided to adjust the optical characteristics of light incident on the anamorphic lens 9. The anamorphic lens 9 is designed to generate astigmatism by giving different focal lengths to two orthogonal axes in order to perform focus control by a known astigmatism method. The photodetector 10 includes at least one light receiving element, and the light receiving element generates a light amount signal according to the amount of light received. FIG. 3 shows the arrangement of the light receiving elements of the photodetector 10 according to the present embodiment. The photodetector 10 has a plurality of light receiving elements 10a to 10h. The light receiving elements 10a to 10d receive light for generating a focus error signal. For reference, FIG. 3 shows a light beam 30 incident on the light receiving elements 10a to 10d. The light receiving elements 10a to 10d are also referred to as four-divided light receiving elements. The light receiving elements 10e to 10h are arranged at the four corners around the light receiving elements 10a to 10d, and receive light for generating a layer discrimination signal. The layer discriminating signal is used to discriminate which information recording layer the focus is on or in the vicinity (hereinafter referred to as only “near” including both).

  Note that while the FE signal described later is being detected, it can be assumed that the focal point is located “near” the layer corresponding to the FE signal. Alternatively, when the focal point is located within a range L in which focus control can be performed on the layer based on the FE signal, the focal point may be determined to be “near” the layer. For example, in the two-layer BD, the above-mentioned “range L” corresponds to a section defined by a position corresponding to the minimum value of the focus error signal and a position corresponding to the maximum value, and the width is about 1 to 5 μm. Furthermore, when the focal point is in the range L * wider than the above-described range L, it may be determined that the focal point is positioned “in the vicinity” of the layer. In the case of the two-layer BD, the above-described range L * is a range of ± 5 μm including the range L, that is, a range of 10 μm in width. In the two-layer BD, the interval between layers 0 and 1 (the interval corresponding to the zero cross point of the focus error signal) is 14 to 16 μm.

  Refer to FIG. 2 again. The signal processing circuit 20 and / or the servo control circuit 21 is a semiconductor integrated circuit that has been programmed in advance to perform the control described in this specification. The signal processing circuit 20 generates a focus error signal according to the light amount signal output from the photodetector 10, and generates a layer determination signal according to the light amount signal output from the photodetector 10. Then, based on the layer determination signal, or on the basis of the layer determination signal and the focus error signal, it is determined whether the focal point is located near layer 0 or layer 1 of the optical disc 1. In the discrimination process, a control signal for changing the position of the objective lens 6 is generated and output. After specifying the focus position, the signal processing circuit 20 continues to generate a focus error signal to perform normal data reading or writing operation, and further generates and outputs a tracking error signal. The servo control circuit 21 generates a drive signal based on these signals so that the focal point does not deviate from the desired layer, and applies the drive signal to the actuator coil 22. The actuator coil 22 changes the position of the objective lens 6 in a direction perpendicular to the optical disc 1 or in a direction parallel to the optical disc 1 according to the level of the drive signal.

  In the optical disc device 51, a condensing optical system is formed that condenses light from the light source 2 by the collimating lens 3 and the objective lens 6 to form a focal point. The objective lens 6, the detection lens 8, and the anamorphic lens 9 constitute a detection optical system for guiding the reflected light from the optical disc 1 to the light receiving unit 10. The beam splitter 4 and the quarter wave plate 5 can be regarded as a condensing optical system or a detection optical system. The light source 2, the condensing optical system, the detection optical system, and the photodetector 10 constitute an optical head. When the signal processing circuit 20 and the servo control circuit 21 are provided in the optical head, they become components of the optical head, but may be realized as an optical disk controller separate from the optical head. In this case, the optical head performs an optical detection process or the like to output a detection signal (light quantity signal), and the optical disk controller processes the light quantity signal output from the optical head.

  Next, the operation of the optical disc apparatus 51 will be described. First, linearly polarized laser light emitted from the light source 2 is converted into substantially parallel light by the collimator lens 3. Thereafter, the laser beam is reflected by the beam splitter 4, converted into circularly polarized light by the quarter-wave plate 5, and layer 0 or layer to be recorded / reproduced by the objective lens 6 over the substrate (protective layer) of the optical disc 1. 1 is condensed.

  The condensed laser light is reflected at layer 0 and layer 1. More specifically, when the laser beam is focused on the layer 1, the laser beam is reflected on the layer 1, and part of the laser beam is transmitted to the layer 0 and is reflected on the layer 0. The reason why a part of the laser light is transmitted to the layer 0 is that the layer 1 is configured to transmit light in order to realize reading and writing of data with respect to the layer 0. On the other hand, when the laser beam is focused on the layer 0, the laser beam is reflected at the layer 0 and a part thereof is reflected at the layer 1. The laser light reflected in each layer is transmitted again through the substrate of the optical disk 1 and the objective lens 6, converted into linearly polarized light different from the forward path by the quarter wavelength plate 5, and then transmitted through the beam splitter 4.

  The backward laser beam that has passed through the beam splitter 4 enters the anamorphic lens 9 through the detection lens 8. The anamorphic lens 9 gives astigmatism to incident light by making the lateral magnification on the second axis different from the lateral magnification on the first axis of incident light. Here, “first axis” and “second axis” are defined as two axes perpendicular to and perpendicular to the optical axis of the laser beam. As a result, the focal position of the laser beam differs with respect to the first axis and the second axis. The laser light exiting the anamorphic lens 9 enters the photodetector 10. The laser light to which astigmatism is given is focused on the near side (objective lens 6 side) and the far side (opposite side to the anamorphic lens 9 with respect to the photodetector 10) incident on the photodetector 10. In the following, the front side of the photodetector 10, the axial direction of the laser beam having a focal position before entering the photodetector 10 is the first axial direction, and the laser beam having the focal position on the far side of the photodetector 10 is The axial direction is the second axial direction. Of the laser light given astigmatism by the anamorphic lens 9, the light reflected from the layer where the focal point is located is adjusted so as to be a substantially circular focused spot on the light receiving elements 10a to 10d shown in FIG. ing. On the other hand, the first axis direction corresponds to the direction connecting the light receiving elements 10g and 10h in FIG. 3, and the second axis direction corresponds to the direction connecting the light receiving elements 10e and 10f.

  The photodetector 10 detects a laser beam in each light receiving element and generates a light amount signal corresponding to the light amount. The signal processing circuit 20 performs a calculation based on the level of the light quantity signal to generate a layer discrimination signal, and generates an error signal such as a focus error signal and a tracking error signal and an information signal representing data. The signal processing circuit 20 determines whether the focal point of the laser light is located near the layer 0 or the layer 1 of the loaded optical disc 1 based on at least the layer determination signal. The servo control circuit 21 supplies current to the actuator coil in accordance with the error signal, and drives the objective lens 6 in the focus direction and the tracking direction. As a result, the focal point formed on the layer of the optical disc 1 by the objective lens 6 can follow the information track formed on the layer.

Here, the focus error signal FE by the astigmatism method is
FE = (light quantity signal output from light receiving element 10a) + (light quantity signal output from light receiving element 10c)
-(Light amount signal output from light receiving element 10b)-(light amount signal output from light receiving element 10d)
Obtained by.

For example, the tracking error signal TE by the push-pull method is
TE = (light quantity signal output from light receiving element 10a) + (light quantity signal output from light receiving element 10d)
-(Light quantity signal output from light receiving element 10b)-(light quantity signal output from light receiving element 10c)
Obtained by.

  Next, the layer discrimination process according to the present embodiment will be described. The layer discrimination processing according to the present embodiment is intended to discriminate layer 0. The reason is that when the optical disc 1 is loaded in the optical disc apparatus 51, layer 0 must be specified in order to read data in the TOC area 150 (FIG. 1 (d)) of the optical disc 1. However, according to the layer discrimination process described below, it is possible to discriminate not only layer 0 but also layer 1.

  FIG. 4 shows paths of reflected light from the layer 0 (broken line) and reflected light from the layer 1 (solid line) when the focal point is located in the vicinity of the layer 0. In order to simplify the description, the path of incident light to the light source 1, the collimating lens 3, and the optical disc 1 is omitted. The information recording layer to be recorded and reproduced is layer 0.

  When the focal point formed by the objective lens 6 is in the vicinity of layer 0 of the optical disc 1, the reflected light from the layer 0 passes through the optical path indicated by the broken line, is given astigmatism by the anamorphic lens 9, and is supplied to the photodetector 10. Incident. At this time, the reflected light is focused on the photodetector 10. Since the astigmatism is given to the reflected light from the layer 0 by the anamorphic lens 9, it has different focal positions with respect to the first axis direction and the second axis direction. Accordingly, the focal position of the reflected light is not exactly one. However, when the entire reflected light is incident on the four-divided light receiving elements 10a to 10d and the distances to the respective focal positions are substantially equal from the four-divided light receiving elements, in this specification, “focus is set”. Or, it will be described as “convergent”.

  On the other hand, the reflected light (stray light) from the layer 1 passes through the optical path indicated by the solid line, is given astigmatism by the anamorphic lens 9, and enters the photodetector 10. This reflected light is incident on the photodetector 10 in a state having a wider range than the reflected light from the layer 0.

  FIG. 5 shows the shape of each reflected light incident on the photodetector 10 when the focal point of the laser light is in the vicinity of layer 0 of the optical disc 1. On the light receiving elements 10 a to 10 d on the photodetector 10, a condensed spot a <b> 0 is formed by the reflected light from the layer 0. At the same time, another large focused spot a1 having a low light intensity is formed by the reflected light (stray light) from the layer 1. It should be noted that the elliptical condensing spot a1 is received almost evenly by the light receiving elements 10e and 10f arranged along the second axis direction, but the light reception arranged along the first axis direction. This means that almost no laser light is incident on the element 10g and the light receiving element 10h. In other words, the light receiving element 10g and the light receiving element 10h are arranged along the first axis direction in a region where the reflected light from the layer 1 is not incident when the focal point is in the vicinity of the layer 0 of the optical disc 1.

  FIG. 6 shows the paths of the reflected light from the layer 0 (solid line) and the reflected light from the layer 1 (broken line) when the focal point is located in the vicinity of the layer 1.

  When the focal point formed by the objective lens 6 is in the vicinity of the layer 1 of the optical disc 1, the laser light reflected by the layer 1 passes through the optical path indicated by the broken line, is given astigmatism by the anamorphic lens 9, and the photodetector 10 is incident. Reflected light from the layer 1 (broken line) is focused on the photodetector 10.

  On the other hand, the laser light (stray light) reflected by the layer 0 passes through the optical path indicated by the solid line, converges in the vicinity of the anamorphic lens 9, and then enters the photodetector 10. The reflected light from the layer 0 (solid line) is incident on the photodetector 10 in a state having a wider range than the reflected light from the layer 1.

  FIG. 7 shows the shape of each reflected light incident on the photodetector 10 when the focus of the laser light is in the vicinity of layer 1 of the optical disc 1. On the light receiving elements 10 a to 10 d on the photodetector 10, a condensing spot b <b> 1 is formed by the laser light reflected from the layer 1. At the same time, another large focused spot b0 having a low light intensity is formed by the laser light (stray light) reflected by the layer 0. The condensing spot b0 is circular. The reason that the shape of the focused spot b0 is not elliptical like the focused spot a1 (FIG. 5) is that the astigmatism is hardly given to the reflected light from the layer 0 by the anamorphic lens 9. Therefore, a substantially circular condensing spot b0 is formed on the photodetector 10. Laser light is incident on the light receiving elements 10e to 10h substantially evenly (or with an approximately equal amount of light).

  Here, when FIG. 5 and FIG. 7 are compared, when the focal point exists in the layer 0, an elliptical condensing spot a1 (FIG. 5) is formed on the photodetector 10 by the reflected light from the layer 1. . At this time, the light receiving elements 10g and 10h substantially do not detect the light of the focused spot a1. On the other hand, when the focal point exists in the layer 1, a circular condensing spot b0 (FIG. 7) is formed on the photodetector 10 by the reflected light from the layer 0. At this time, the light receiving elements 10g and 10h detect the light at the focused spot b0. It can be said that the arrangement of the light receiving elements 10g and 10h is determined based on the difference in the incident area of reflected light from a layer different from the layer where the focal point exists (or the shape of the reflected light when incident). As will be described later, the light quantity signals from the light receiving elements 10g and 10h are necessary to generate the layer discrimination signal. Since the light receiving elements 10g and 10h are used for layer discrimination, they may be called discrimination light receiving elements in this specification.

  The arrangement of the light receiving elements 10g and 10h can be set under an ideal state, for example, before shipment of the optical disc device 51. Thereafter, when the user loads a new optical disc into the optical disc apparatus 51, the layer discrimination processing can be performed based on the unique characteristics of each optical disc.

Using the light receiving elements arranged as described above, the signal processing circuit 20 obtains the layer discrimination signal RD by the following calculation. That is, the layer discrimination signal RD according to the present embodiment is
RD = (light quantity signal output from light receiving element 10e) + (light quantity signal output from light receiving element 10f)
-(Light quantity signal output from light receiving element 10g)-(light quantity signal output from light receiving element 10h)
Can be obtained as The level of the light amount signal output from the light receiving elements 10g and 10h is substantially 0 in the example shown in FIG. 5, and takes a positive value larger than 0 in the example shown in FIG. As a result, in consideration of the relationship between the amount of light received by the light receiving element 10e and the light receiving element 10f, the level of the layer determination signal RD is larger than 0 in the example shown in FIG. 5 and substantially 0 in the example shown in FIG. Become.

  FIG. 8 shows the result of calculating the change of the focus error signal FE and the layer discrimination signal RD (vertical axis) with respect to the displacement amount (horizontal axis) of the objective lens 6.

  When the objective lens 6 is displaced, the focus error signal FE has a so-called S-shape that corresponds to the convergence state of the focus on the information recording layer when the focus approaches and leaves each layer. In the S-shaped range, the zero cross point of the focus error signal FE corresponds to the convergence position on each layer.

  As the objective lens 6 approaches the optical disk 1 from a position sufficiently away from the optical disk 1, the S-shape of layer 1 appears first in the focus error signal FE, and then the S-shape of layer 0 appears. However, this is a detection result under ideal conditions, and when the optical disc 1 is rotated in a state where the surface is shaken, it is determined which layer the resulting S-shaped shape is obtained from. Can not.

  Therefore, in the present embodiment, the above-described layer discrimination signal RD is used. The level of the layer discrimination signal RD is positive when the focus is in the vicinity of layer 0 (FIGS. 4 and 5), and is almost 0 when the focus is in the vicinity of layer 1 (FIGS. 6 and 7). It is. Near the zero cross point of the focus error signal FE, the focal point is located in the vicinity of layer 0 or layer 1. Then, the signal processing circuit 20 determines that the focus is in the vicinity of layer 0 if the level of the layer determination signal RD is positive near the zero cross point of the focus error signal FE, and the level of the layer determination signal RD is substantially equal. If it is 0, it can be determined that the focus is in the vicinity of layer 1. When the signal processing circuit 20 compares the focus error signal FE and the layer determination signal RD, it can be easily determined which layer the S-shape appearing in the waveform of the focus error signal FE is based on. By using the layer discrimination signal RD, it is possible to discriminate the layer on which the focus control is to be performed before the focus control is performed, so that the time from the so-called standby state at the time of starting the drive to the actual recording / reproduction can be greatly reduced. Can be shortened.

The calculation method for obtaining the above-described layer discrimination signal RD is an example. Explaining another calculation method, for example, it is preferable to perform layer discrimination based on a normalized layer discrimination signal RD obtained by the layer discrimination signal RD = Ra / Rb. here,
Ra = (light amount signal output from the light receiving element 10e) + (light amount signal output from the light receiving element 10f) − (light amount signal output from the light receiving element 10g) − (light amount signal output from the light receiving element 10h), and,
Rb = (light quantity signal output from the light receiving element 10e) + (light quantity signal output from the light receiving element 10f) + (light quantity signal output from the light receiving element 10g) + (light quantity signal output from the light receiving element 10h)
It is. By normalizing with the sum of the amounts of light received by the respective light receiving elements, a stable layer discrimination signal RD can be obtained without being affected by an offset due to a change in the reflectance of the optical disc 1 or the like.

Also, the layer discrimination signal RD is
RD = (light quantity signal output from light receiving element 10g) + (light quantity signal output from light receiving element 10h)
It can also be. FIG. 9 shows the waveform of the layer discrimination signal RD based only on the amount of light received by the light receiving elements 10g and 10h. Similarly in FIG. 9, when the focus is in the vicinity of layer 0 (FIGS. 4 and 5), it is positive, and when the focus is in the vicinity of layer 1 (FIGS. 6 and 7), it is almost zero. . Similarly, if the focus error signal FE and the layer determination signal RD are considered together, it is possible to easily determine which layer the S-shape appearing in the waveform of the focus error signal FE is based on.

  According to the above-described processing, the layer determination signal is generated using the reflected light from a layer different from the layer on which the focal point is formed by the objective lens 6. Since the shape of the reflected light that enters the photodetector 10 differs depending on the position of the focal point, the focal point is formed by the objective lens 6 based on the layer discrimination signal and further by considering the focus error signal. The layer can be reliably determined. In addition, since the reflected light from the layer has sufficient intensity to detect, the layer discrimination signal can be generated with a high S / N ratio.

  In the above-described processing, it is not necessary to use a sub beam in the conventional three beam system. Therefore, according to the layer discrimination processing of the present embodiment, it can be applied to a one-beam optical head. Of course, the above-described processing can be applied to the three-beam method.

(Embodiment 2)
FIG. 10 shows a configuration of the optical disc apparatus 52 according to the present embodiment. The optical disk device 52 originally includes the same components as the optical disk device 51 shown in FIG. 2, but some components are omitted as in FIG. The point that the optical head is constituted by the light source, the condensing optical system, the detection optical system, and the photodetector is the same as that of the first embodiment.

  The optical disk device 52 according to the present embodiment is different from the optical disk device 51 according to the first embodiment in that the optical disk device according to the present embodiment reflects light from the layer 0 when the focal point of the laser light is in the vicinity of the layer 1. That is, the light is configured to be focused before entering the anamorphic lens 9. The purpose is to make the reflected light from layer 1 when the focal point exists in layer 0 and the direction of astigmatism of the reflected light from layer 0 when the focal point exists in layer 1 to be different from each other. The purpose is to make the light incident on different regions of the photodetector 10. However, as in the first embodiment, it is only necessary to make a difference in the incident area, and therefore it is not necessary for the entire reflected light to be incident on a completely different area.

  Hereinafter, the optical disk device 52 will be described. Note that description of components having the same functions and configurations as those of the optical disc apparatus 51 of Embodiment 1 is omitted.

  The detection lens 8 in the present embodiment has a larger focal length than the detection lens 8 according to the first embodiment. As a result, the distance between the position where the reflected light from layer 0 converges and the position where the reflected light from layer 1 converges become larger. When the focus is on the layer 1, the reflected light from the layer 1 is adjusted so as to converge on the photodetector 10, so that the position at which the reflected light from the other layer 0 is focused is further detected. Close to. Thus, the reflected light from layer 0 is focused before adjusting the focal length of the detection lens 8 and / or placing the anamorphic lens 9 closer to the photodetector 10 and entering the anamorphic lens 9. Can be tied. On the other hand, it is necessary to give the anamorphic lens 9 a larger refractive power and give astigmatism equivalent to the anamorphic lens of Embodiment 1 to the incident light. The “refractive power” means an optical characteristic for forming a focal point closer to the lens. The refractive power can be increased by increasing the refractive index of the lens or decreasing the radius of curvature of the lens.

  FIG. 11 shows the shape of each reflected light incident on the photodetector 10. A condensing spot c0 is formed by the reflected light from layer 0 when the focal point formed by the objective lens 6 is in the vicinity of layer 1. On the other hand, the condensed spot c1 is formed by the reflected light from the layer 1 when the focal point is in the vicinity of the layer 0. The condensing spots c0 and c1 have different elliptical shapes in which the major axis and the minor axis are orthogonal to each other according to astigmatism provided by the anamorphic lens 9.

At this time, the layer discrimination signal RD is
RD = (light quantity signal output from light receiving element 10e) + (light quantity signal output from light receiving element 10f)
-(Light quantity signal output from light receiving element 10g)-(light quantity signal output from light receiving element 10h)
Obtained by. The sign of the layer discrimination signal RD is inverted near the convergence of the layer 1 and the convergence of the layer 0. As in the first embodiment, by comparing the focus error signal FE and the layer determination signal RD, it is possible to easily determine which layer the S-shape appearing in the waveform of the focus error signal FE is based on.

  According to the above-described embodiment, when the focal point is in the vicinity of layer 1, the configuration is such that the reflected light from layer 0 is converged by the detection lens 8 before reaching the anamorphic lens 9, so that the detection sensitivity is increased. can do.

  Here, the case where the reflected light from the layer 0 converges at a position after passing through the anamorphic lens 9 without using such a detection lens 8 will be considered. According to this configuration, the elliptical reflected light having the same major axis and minor axis directions is incident on the photodetector 10 due to astigmatism due to the anamorphic lens 9, and therefore, from the light receiving elements 10g and 10h for layer discrimination. It is not possible to perform layer discrimination using the light quantity signal. However, if the signal processing circuit 20 performs determination based on the following determination method, accurate layer determination processing is possible.

That is, the layer discrimination signal RD used at this time is obtained by the normalized layer discrimination signal RD = Ra / Rb. Here, Ra = (light amount signal output from light receiving element 10e) + (light amount signal output from light receiving element 10f) − (light amount signal output from light receiving element 10g) − (light amount signal output from light receiving element 10h) ),and,
Rb = (light quantity signal output from the light receiving element 10e) + (light quantity signal output from the light receiving element 10f) + (light quantity signal output from the light receiving element 10g) + (light quantity signal output from the light receiving element 10h)
It is. The possibility of erroneous detection can be reduced by using the normalized layer discrimination signal RD. At this time, the light incident on the light receiving element 10g and the light receiving element 10h is different between the case where the focal point exists in the vicinity of the layer 0 and the case where the focal point exists in the vicinity of the layer 1. Therefore, the level of the layer discrimination signal RD is also different in each case. For example, the level of the layer determination signal RD is greater when the focus is near layer 0 than when the focus is near layer 1. Therefore, a threshold value is defined between the level of the layer determination signal RD when the focus is in the vicinity of layer 0 and the level of the layer determination signal RD when the focus is in the vicinity of layer 1. Thus, the signal processing circuit 20 determines that the focus is in the vicinity of layer 0 if the level of the layer determination signal RD is equal to or greater than the threshold value near the zero cross point of the focus error signal FE, and the level of the layer determination signal RD is the threshold value. If it is below, it may be determined that the focus is in the vicinity of layer 1. By comparing the focus error signal FE and the layer determination signal RD, it is possible to easily determine which layer the S-shape appearing in the waveform of the focus error signal FE is based on.

  As described above, Embodiments 1 and 2 according to the present invention have been described on the assumption that the tracking error signal detection method uses the push-pull method. However, the present invention is not limited to the push-pull method, and can be applied to any tracking error signal detection method that can be combined with the astigmatism method, which is a focus error signal detection method.

  In addition, even for an optical disc having three or more layers as shown in FIG. 1C, the difference in the shape of the focused spot due to the laser light reflected by each layer is caused by astigmatism by the anamorphic lens. By detecting the difference in the amount of light, it is possible to determine in which layer the focused spot by the objective lens is converged.

(Embodiment 3)
FIG. 12A shows the configuration of the optical disc apparatus 53 according to the present embodiment. FIG. 12B is an enlarged view of the peripheral portion 60 of the anamorphic lens 9. The optical disk device 53 originally has the same components as the optical disk device 51 shown in FIG. 2, but some components are omitted as in FIG. The point that the optical head is constituted by the light source, the condensing optical system, the detection optical system, and the photodetector is the same as that of the first embodiment.

  As shown in FIG. 12B, the optical disc device 53 according to the present embodiment has a light shielding region 12 that blocks a part of light transmitted through the anamorphic lens 9 on the anamorphic lens 9. The detection lens 8 and the anamorphic lens 9 converge the reflected light from the layer 0 so as to almost converge on the anamorphic lens 9 (near the light shielding portion) when the focal point is located in the vicinity of the layer 1. The purpose is to converge the reflected light from the layer 0 in the vicinity of the light shielding portion so as not to enter the light receiving portion. The light shielding region 12 has a minimum size necessary for shielding only the reflected light from the layer 0 when the focal point is located in the vicinity of the layer 1.

  Hereinafter, the optical disk device 53 will be described. Note that description of components having the same functions and configurations as those of the optical disc apparatus 51 of Embodiment 1 is omitted.

  FIG. 13 shows the arrangement of the light receiving elements 10e of the photodetector 10 according to the present embodiment. The photodetector 10 has four divided light receiving elements 10a to 10d and four light receiving elements 10e. The light receiving elements 10a to 10d receive light for generating a focus error signal. The light receiving element 10e is disposed at the four corners of the periphery of the light receiving elements 10a to 10d, and receives light for generating a layer discrimination signal. That is, the light receiving element 10e is a light receiving element for discrimination. The laser beam given astigmatism by the anamorphic lens 9 is adjusted to be substantially circular on the light receiving elements 10a to 10d. For reference, FIG. 3 shows a light beam 40 incident on the light receiving elements 10a to 10d.

  FIG. 14 shows the shape of each reflected light incident on the photodetector 10 when the focus of the laser light is in the vicinity of layer 0 of the optical disc 1. On the light receiving elements 10a to 10d on the photodetector 10, a condensing spot d0 is formed by the laser light reflected from the layer 0. At the same time, the reflected light from the layer 1 forms a larger condensing spot d1 having an elliptical shape with a small light intensity. The laser light reflected by the layer 1 generally passes through the optical path shown by the solid line in FIG. 4 and is given astigmatism by the anamorphic lens 9.

  On the other hand, FIG. 15 shows the shape of each reflected light incident on the photodetector 10 when the focal point of the laser light is located near the layer 1 of the optical disc 1. On the light receiving elements 10 a to 10 d on the photodetector 10, a condensing spot e <b> 1 due to the reflected light from the layer 1 is formed. However, the laser beam reflected by the layer 0 is not incident on the photodetector 10. The reason is that the laser beam reflected by the layer 0 is almost converged on the anamorphic lens 9 in which the light shielding region 12 is formed and is shielded by the light shielding region 12. Therefore, only the condensing spot e <b> 1 due to the reflected light from the layer 1 is formed on the photodetector 10. By providing the light shielding region 12, not only the focused spot e1 but also a part of the focused spots d0 and d1 when the focal point of the laser beam is located in the vicinity of the layer 1 of the optical disc 1 is shielded. I can say that. However, there is no significant influence from the viewpoint of detecting the amount of light.

The layer discrimination signal RD according to this embodiment is
RD = (light quantity signal output from the light receiving element 10e)
As obtained. The “light quantity signal” referred to here may be the sum of the light quantity signals output from the four light receiving elements 10e, or may be a light quantity signal output from one light receiving element 10e.

  When the focal point is located in the vicinity of layer 0 (FIG. 14), the condensed spot d1 is formed by the reflected light from layer 1 and spreads on the light receiving element 10e, so that the layer determination signal RD shows a predetermined value. . However, when the focal point is located in the vicinity of layer 1 (FIG. 15), the layer determination signal RD is substantially zero. As a result, as in the first embodiment, the signal processing circuit 20 determines that the focus is in the vicinity of layer 0 if the level of the layer determination signal RD is positive near the zero-cross point of the focus error signal FE, and thus determines the layer. If the level of the signal RD is substantially 0, it may be determined that the focal point is in the vicinity of the layer 1.

(Embodiment 4)
FIG. 16A shows the configuration of the optical disc apparatus 54 according to the present embodiment. FIG. 16B is an enlarged view of the peripheral portion 70 of the anamorphic lens 9. The optical disk device 54 has essentially the same components as the optical disk device 51 shown in FIG. 2, but some components are omitted as in FIG. The point that the optical head is constituted by the light source, the condensing optical system, the detection optical system, and the photodetector is the same as that of the first embodiment.

  As shown in FIG. 16B, the optical disk device 53 according to the present embodiment has a ring-shaped aperture 13 on the anamorphic lens 9 that blocks a part of the light transmitted through the anamorphic lens 9. The detection lens 8 and the anamorphic lens 9 are configured to block the peripheral portion of the reflected light from the layer 1 by the aperture 13 when the focal point is located in the vicinity of the layer 0. The purpose of blocking the peripheral edge of the reflected light from the layer 1 is to make the cross-sectional area of the light beam when entering the photodetector 10 smaller. Thereby, on the photodetector 10, the cross-sectional area of the reflected light beam from the layer 0 when the focal point is located in the vicinity of the layer 1 and the interruption of the reflected light beam from the layer 1 when the focal point is located in the vicinity of the layer 0. Since the area can be made different, the difference can be used for the layer discrimination processing in the same manner as in the first to third embodiments.

  FIG. 17 shows the shape of each reflected light incident on the photodetector 10 when the focus of the laser light is in the vicinity of layer 1 of the optical disc 1. In the present embodiment, the arrangement of the light receiving elements of the photodetector 10 is the same as that in the third embodiment. On the light receiving elements 10 a to 10 d on the photodetector 10, a condensing spot f <b> 1 due to the reflected light from the layer 1 is formed. At the same time, another large focused spot f0 having a low light intensity is formed by the reflected light from the layer 0. The focused spot f0 is substantially circular. The focused spot f0 is substantially uniformly incident on any of the four light receiving elements 10e. In other words, they are arranged so as to fall within the range of the focused spot f0.

  The reason why the condensing spot f0 is circular will be described. The reflected light from the layer 0 converges in the vicinity of the anamorphic lens 9. Therefore, the astigmatism is not substantially given to the reflected light from the layer 0 by the anamorphic lens 9. Therefore, when the reflected light from the layer 0 is incident on the photodetector 10, it becomes a substantially circular shape instead of an elliptical shape.

  On the other hand, FIG. 18 shows the shape of each reflected light incident on the photodetector 10 when the focus of the laser light is in the vicinity of layer 0 of the optical disc 1. On the light receiving elements 10 a to 10 d on the photodetector 10, a condensing spot g <b> 0 due to reflected light from the layer 0 is formed. At the same time, the condensed spot g1 is formed by the reflected light from the layer 1.

  Here, the reflected light from the layer 1 enters the anamorphic lens 9 through the optical path indicated by the solid line in FIG. At this time, the outer peripheral portion of the reflected light is shielded by the ring-shaped aperture 13 provided in the anamorphic lens 9. As a result, the size of the focused spot g1 formed on the photodetector 10 by the reflected light from the layer 1 is smaller than the focused spot when the aperture 13 is not provided.

  It should be noted here that the light receiving element 10e is disposed outside the range in which the focused spot g1 extends. Therefore, the light receiving element 10e does not receive the focused spot g1. As a result, the light receiving element 10e detects the reflected light from the layer 0 when the focal point of the laser beam is near the layer 1 of the optical disc 1, but detects the layer when the focal point of the laser beam is near the layer 0 of the optical disc 1. It can be said that the reflected light from 1 is not detected. Therefore, the layer determination signal can be generated using the light amount signal output from the light receiving element 10e. That is, also in the present embodiment, the light receiving element 10e functions as a light receiving element for determination.

  Since the position where the light receiving element 10e is provided is determined in relation to the reflected light shielded by the aperture 13, it is also related to the size of the aperture 13. Explaining the relationship between the light receiving element 10e and the aperture 13, the aperture 13 shields only the outer peripheral portion of the condensing spot g1 reflected by the layer 1 and does not affect the other condensing spots f0, f1, and g0. Is selected. The light receiving element 10e is arranged on the photodetector 10 so as to detect only the focused spot f0 and not the focused spot g1.

The layer discrimination signal RD according to this embodiment is
RD = (light quantity signal output from the light receiving element 10e)
As obtained. The “light quantity signal” referred to here may be the sum of the light quantity signals output from the four light receiving elements 10e, or may be a light quantity signal output from one light receiving element 10e. In order to cope with the case where the position of the focused spot g1 is deviated, the light amount signal is zero when the level of each light amount signal of the four light receiving elements 10e is not more than a predetermined value. It is good.

  The level of the layer discrimination signal RD takes a positive value with respect to the above-described focused spot f0 (FIG. 17) and is substantially 0 with respect to the focused spot g1 (FIG. 18). As a result, the signal processing circuit 20 can determine that the focal point formed by the objective lens 6 exists in the vicinity of the layer 1 when the level of the layer determination signal RD is positive near the zero-cross point of the focus error signal FE. When the level of the determination signal RD is 0, it can be determined that the focal point formed by the objective lens 6 exists in the vicinity of layer 0. This is the same as in the first embodiment.

  In the above-described third and fourth embodiments, an example in which the focus error signal is detected by the astigmatism method has been described. As long as it is an optical system in which a light-shielding region is provided in the middle of the detection lens 8 and the light detector 10, it can be applied to any focus error signal detection method. In other words, when a servo signal detection system for a focus error signal, a tracking error signal, etc. and an information signal detection system are branched by a beam splitter, etc., a servo signal is detected by providing a light shielding area in the middle of the information signal detection system. A configuration independent of the system can be easily realized.

  In the third and fourth embodiments, the light receiving elements that generate the layer discrimination signals are arranged at the four corners around the light receiving element that detects the focus signal. However, this is an example, and the light receiving elements are converged according to the converged information recording layer. If the arrangement is such that the layer discrimination signal RD changes, the position and shape of the light receiving element for detecting the layer discrimination signal are arbitrary, and the present invention can be applied to either case.

  In each embodiment, astigmatism is given by the anamorphic lens 9, but astigmatism can also be given by an optical element other than the lens, for example, a diffraction grating or a reflection mirror. A so-called liquid crystal lens in which a liquid crystal material and an optical element (prism, lens, etc.) are combined can also be used as the “optical element”.

  After the layer having the focal point is determined by the layer determination process of each embodiment, a verification process for increasing the certainty of the determination can be performed. For example, since each information track of the optical disc 1 is given a unique address for specifying the data position on the optical disc, the optical disc apparatus uses the value of the address as unique information for specifying the layer. it can. Specifically, the optical disc apparatus performs tracking control on an arbitrary information track, and reads an arbitrary address of the information track. Then, based on the value of the read address, the layer having the address can be specified, and it can be verified whether or not it matches with the layer specified as a result of the discrimination process.

  Further, after it is determined that the layer in which the focus exists is layer 0, the optical head is sought to the innermost peripheral portion of the layer in order to read out the TOC area 150 shown in FIG. If it does not exist, it can be determined that the layer in which the focus exists was not layer 0. In that case, what is necessary is just to perform what is called an interlayer jump which changes the position of a focus to the other layer. Specifically, the signal processing circuit 20 may send a predetermined pulse to the focus control signal and drive the actuator coil 22 to move the position of the objective lens 6 in a direction perpendicular to the optical disc 1. At this time, the position of the other layer can be specified using the layer determination signal and / or the focus error signal.

  In this specification, the optical disk 1 is described on the premise that it is a two-layer disk having two layers. However, when an optical disk having three or more layers can be loaded in the optical disk apparatus, the number of layers is first specified. In addition, it is necessary to perform processing based on the number of layers. For example, when an optical disk is stored in a disk cartridge, information for specifying the number of layers may be described in the disk cartridge. In this case, the optical disc apparatus can specify the number of layers by reading the information.

  In some cases, an optical disc (single layer disc) having only one layer is loaded. In this case, the optical disk apparatus assumes that the loaded optical disk is a two-layer disk, changes the focus position, performs the layer determination processing according to the present invention, and, for example, a normalized layer determination signal RD = Ra Find / Rb. At this time, the arrangement of the light-receiving elements for determination is as described in the above embodiments. As a result of the layer discrimination process, the optical disc apparatus can obtain the layer discrimination signal RD regardless of whether a two-layer disc or a single-layer disc is loaded.

  However, regarding the waveform, the layer discrimination signal RD of the two-layer disc and the layer discrimination signal RD of the single-layer disc are greatly different. Specifically, the level of the layer discrimination signal when the two-layer disc is loaded changes to positive and zero (see, for example, FIG. 8). On the other hand, the level of the layer discrimination signal when a single-layer disc is loaded does not become 0 at the zero cross point of the focus error signal, but is always positive (high level). The reason why the level always becomes high is that the light reflected on the surface of the single-layer disc is detected by the light-receiving element for discrimination. Although the level of the light amount signal output from each discrimination light receiving element is small, the layer discrimination signal RD sufficient for detection can be obtained by performing the normalization processing of the layer discrimination signal. Even when a two-layer disc is loaded, the light reflected from the surface is detected by the light-receiving element for discrimination, but its influence can be ignored. This is because the intensity of the reflected light from each layer is sufficiently large.

  Therefore, the signal processing circuit 20 determines that the disc is a two-layer disc if the layer discriminating signal level is low in the vicinity of the zero cross point of the focus error signal, and if the focus is always high, the signal processing circuit 20 determines a single layer. You may judge that it is a disk. As a result, the signal processing circuit 20 can perform layer discrimination processing on the loaded optical disc to determine the number of layers and specify the type of the optical disc.

  The optical information processing apparatus incorporating the optical head of the present invention can identify at which layer the focal point of light is located or in the vicinity thereof at very high speed. Thereby, for example, an optical disc apparatus that shortens the time from start to start of data access, and a layer to be operated can be quickly and surely switched during data writing and / or reading operations to different layers. An optical disc device that can be used can be obtained.

(A) is a figure which shows the external appearance of the optical disk 1, (b) is sectional drawing of the optical disk 1 which has a layer of two layers, (c) is sectional drawing of the optical disk 1 which has a layer of (N + 1) layers. (D) is a diagram showing a TOC area 150 provided in layer 0. 1 is a diagram illustrating a configuration of an optical disc device 51 according to Embodiment 1. FIG. FIG. 3 is a diagram illustrating an arrangement of light receiving elements of the photodetector 10 according to the first embodiment. It is a figure which shows the path | route of the reflected light from a layer 0 (broken line) and the reflected light from a layer 1 (solid line) when a focus is located on the layer 0 or its vicinity. FIG. 3 is a diagram showing the shape of each reflected light incident on the photodetector 10 when the focal point of the laser light is in the vicinity of layer 0 of the optical disc 1. It is a figure which shows the path | route of the reflected light from a layer 0 (solid line) and the reflected light from a layer 1 (dashed line) when a focus is located on the layer 1 or its vicinity. FIG. 3 is a diagram showing the shape of each reflected light incident on the photodetector 10 when the focus of the laser light is in the vicinity of layer 1 of the optical disc 1. 6 is a graph showing a focus error signal FE and a layer discrimination signal RD (vertical axis). It is a figure which shows the waveform of the layer discrimination | determination signal RD based only on the light reception amount of the light receiving elements 10g and 10h. 6 is a diagram illustrating a configuration of an optical disc device 52 according to Embodiment 2. FIG. It is a figure which shows the shape of each reflected light which injected into the photodetector. (A) is a figure which shows the structure of the optical disk apparatus 53 by Embodiment 3, (b) is an enlarged view of the peripheral part 60 of the anamorphic lens 9. FIG. It is a figure which shows arrangement | positioning of the light receiving element 10e of the photodetector 10 by Embodiment 3. FIG. FIG. 3 is a diagram showing the shape of each reflected light incident on the photodetector 10 when the focal point of the laser light is in the vicinity of layer 0 of the optical disc 1. FIG. 3 is a diagram showing the shape of each reflected light incident on the photodetector 10 when the focal point of the laser light is positioned near the layer 1 of the optical disc 1. (A) is a figure which shows the structure of the optical disk apparatus 54 by Embodiment 4, (b) is an enlarged view of the peripheral part 70 of the anamorphic lens 9. FIG. 3 is a diagram showing the shape of each reflected light incident on the photodetector 10 when the focal point of the laser light is in the vicinity of layer 1 of the optical disc 1. FIG. FIG. 3 is a diagram showing the shape of each reflected light incident on the photodetector 10 when the focal point of the laser light is in the vicinity of layer 0 of the optical disc 1. It is a figure which shows schematic structure of the optical head 100 for performing a layer discrimination | determination process. It is a figure which shows arrangement | positioning of the five light receiving elements 110a-110e provided in the photodetector 110. FIG. FIG. 4 is a diagram illustrating a position where reflected light is incident on a photodetector 110 when laser light focused by an objective lens is converged on layer 0 of an optical disc 107. FIG. 4 is a diagram illustrating a position where reflected light is incident on a photodetector 110 when the laser light focused by the objective lens is converged on layer 1 of the optical disc 107.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Optical disk 2 Semiconductor laser light source 3 Collimating lens 4 Beam splitter 5 1/4 wavelength plate 6 Objective lens 7 Optical disk 8 Detection lens 9 Anamorphic lens 10 Photo detector 12 Light-shielding area 13 Aperture 20 Signal processing circuit 21 Servo control circuit 22 Actuator coil 51 54 optical disk device

Claims (22)

An optical information processing apparatus for writing and / or reading data on an information recording medium in which at least a first information recording layer and a second information recording layer are laminated,
A light source that emits light;
A condensing optical system for condensing light from the light source to form a focal point;
A light receiving unit that generates a light amount signal according to the amount of light received by at least one light receiving element;
A detection optical system for guiding the first reflected light from the first information recording layer and the second reflected light from the second information recording layer to the light receiving unit;
A layer determination signal is generated based on the light amount signal, and the focus is selected from the first information recording layer and the second information recording layer of the loaded information recording medium based on the layer determination signal. And a processing circuit for determining whether it is located in the vicinity of the information recording layer,
The light receiving unit, viewed contains a discrimination light receiving element arranged on the basis of the incident area of the reflected light from the information recording layer other than the information recording layer in which the focal point is located near, as said at least one light receiving element,
The light receiving unit includes an incident area of the second reflected light when the focal point is located in the vicinity of the first information recording layer, and the focal point is located in the vicinity of the second information recording layer. look including the discrimination light receiving element arranged on the basis of the incidence region of the first reflected light, as said at least one light receiving element,
The detection optical system includes an optical element that gives astigmatism to reflected light from the information recording medium,
When the focal point is located in the vicinity of the second information recording layer, the first reflected light is converged in the vicinity of the optical element, and the second reflected light is converged on the light receiving unit, whereby the first reflected light is converged. An optical information processing apparatus in which reflected light forms a substantially circular spot on the light receiving unit . Writing data and / or data on the first information recording medium having a single information recording layer , or the second information recording medium in which at least the first information recording layer and the second information recording layer are laminated An optical information processing apparatus that performs reading,
A light source that emits light;
A condensing optical system for condensing light from the light source to form a focal point;
A light receiving unit that generates a light amount signal according to the amount of light received by at least one light receiving element;
A detecting optical system for guiding the second light reflected from the first reflection light and the second information recording layer from the first information recording layer to the light receiving portion when said second information recording medium is loaded,
A processing circuit for generating a recording medium determination signal based on the light amount signal and determining a type of the information recording medium loaded based on the recording medium determination signal;
The light receiving unit has an incident area of the second reflected light when the second information recording medium is loaded and the focal point is located in the vicinity of the first information recording layer, and the focal point is It looks including the discrimination light receiving element arranged on the basis of the incidence region of the first reflected light when positioned in the vicinity of the second information recording layer, as said at least one light receiving element,
The detection optical system includes an optical element that gives astigmatism to reflected light from the first information recording medium and reflected light from the second information recording medium,
When the focal point is located in the vicinity of the second information recording layer, the first reflected light is converged in the vicinity of the optical element, and the second reflected light is converged on the light receiving unit, whereby the first reflected light is converged. An optical information processing apparatus in which reflected light forms a substantially circular spot on the light receiving unit . The light-receiving element for discrimination is disposed in a region where one of the first reflected light and the second reflected light is incident, out of the region of the light receiving unit where the first reflected light and the second reflected light are incident. The optical information processing apparatus according to claim 1 or 2 . Due to the astigmatism, the first reflected light and the second reflected light have a first axis and a second axis perpendicular to and orthogonal to the optical axis, respectively, and the second reflected light has the focal point Before being incident on the light receiving unit with respect to the first axis when located in the vicinity of the first information recording layer,
The optical information processing apparatus according to claim 3 , wherein the light-receiving element for determination is arranged along an axis on the light-receiving unit corresponding to the first axis. The optical information processing apparatus according to claim 4 , wherein a plurality of the determination light receiving elements are arranged at positions substantially symmetrical with respect to a center of the optical axis. The light receiving unit receives a first reflected light when the focal point is located in the vicinity of the first information recording layer and a second reflected light when the focal point is located in the vicinity of the second information recording layer. A light receiving element for
The processing circuit generates a focus error signal based on the light quantity signal corresponding to the received light amount of the processing light-receiving element, further determine the position of the focal point based on the focus error signal, according to claim 3 Optical information processing device. The light receiving unit has at least one auxiliary light receiving element disposed along an axis on the light receiving unit corresponding to the second axis,
Regarding the second axis, the second reflected light converges on the back side of the light receiving unit when the focal point is located in the vicinity of the first information recording layer,
The optical information processing apparatus according to claim 4 , wherein the processing circuit further generates the layer discrimination signal based on a light reception amount of the auxiliary light receiving element. The plurality of light-receiving elements for determination are arranged at positions substantially symmetrical with respect to the center of the optical axis, and the plurality of auxiliary light-receiving elements are arranged at positions substantially symmetrical with respect to the center of the optical axis. The optical information processing apparatus according to claim 7 . The processing circuit calculates the difference between the light quantity signal from the light receiving element for discrimination and the light quantity signal from the auxiliary light receiving element by the sum of the light quantity signal from the light receiving element for discrimination and the light quantity signal from the auxiliary light receiving element. The optical information processing apparatus according to claim 7 , wherein the layer discrimination signal is generated by division. The detection optical system includes a light blocking unit that blocks a part of the light,
When the focal point is located in the vicinity of the second information recording layer, the first reflected light is converged in the vicinity of the light shielding unit to block the incident on the light receiving unit, and the second reflected light is transmitted to the light receiving unit. The optical information processing apparatus according to claim 1 , wherein the optical information processing apparatus converges above. The detection optical system includes a light shielding portion having an opening that shields a peripheral portion of light,
When the focal point is located in the vicinity of the first information recording layer, the peripheral portion of the second reflected light is blocked by the light shielding portion, and the cross-sectional area of the light beam of the second reflected light incident on the light receiving portion is made smaller. The optical information processing apparatus according to claim 1 or 2 . Information specific to each information recording layer is recorded in the first information recording layer and the second information recording layer,
The processing circuit acquires the unique information, identifies an information recording layer where the focal point is located based on the unique information, and verifies whether the determination result is accurate by comparing with the determination result The optical information processing apparatus according to claim 1 or 2 . Each of the first information recording layer and the second information recording layer has a plurality of information tracks in which the data is written, and each of the plurality of information tracks specifies a data position on the information recording medium. With a unique address,
The optical information processing apparatus according to claim 12 , wherein the processing circuit acquires the address information as the unique information. As a result of verification, when it is determined that the focal point is located in the vicinity of an information recording layer different from the predetermined information recording layer, the processing circuit is in the vicinity of another information recording layer based on the layer determination signal. The optical information processing apparatus according to claim 12 , wherein the focal position is changed. The information recording medium has N + 1 (N: natural number) information recording layers, and the second information recording layer is an arbitrary layer up to the Nth layer as viewed from the light emitting side. , the first information recording layer is a recording layer existing at a position deeper than the second information recording layer, optical information processing apparatus according to claim 1 or 2. An optical information processing apparatus for further writing and / or reading data on a third information medium in which a plurality of information recording layers different in number from the second information medium are laminated,
Information recording in which the focal point is located in the vicinity when the focal point is located in the vicinity of any one of the plurality of information recording layers of the third information medium when the third information recording medium is loaded The optical information processing apparatus according to claim 2 , wherein a light-receiving element for discrimination arranged based on an incident region of reflected light from an information recording layer other than the layer is included as the at least one light-receiving element. The processing circuitry, based on the level of the layer discrimination signal when the focus exists in the vicinity of the information recording layer of the loaded information recording medium, to determine the number of the information recording layer, according to claim 2 Optical information processing equipment. The light receiving unit reflects reflected light from the surface of the first information recording medium when the first information recording medium is loaded and the focal point is located in the vicinity of the single information recording layer. The optical information processing apparatus according to claim 2 , comprising: a light-receiving element for determination arranged based on an incident region as the at least one light-receiving element. An optical head for writing and / or reading data on an information recording medium in which at least a first information recording layer and a second information recording layer are laminated,
A light source that emits light;
A condensing optical system for condensing light from the light source to form a focal point;
A light receiving unit that generates a light amount signal according to the amount of light received by at least one light receiving element;
A detection optical system for guiding the first reflected light from the first information recording layer and the second reflected light from the second information recording layer to the light receiving unit;
A layer determination signal is generated based on the light amount signal, and the focus is selected from the first information recording layer and the second information recording layer of the loaded information recording medium based on the layer determination signal. And a processing circuit for determining whether it is located in the vicinity of the information recording layer,
The light receiving unit, viewed contains a discrimination light receiving element arranged on the basis of the incident area of the reflected light from the information recording layer other than the information recording layer in which the focal point is located near, as said at least one light receiving element,
The light receiving unit includes an incident area of the second reflected light when the focal point is located in the vicinity of the first information recording layer, and the focal point is located in the vicinity of the second information recording layer. look including the discrimination light receiving element arranged on the basis of the incidence region of the first reflected light, as said at least one light receiving element,
The detection optical system includes an optical element that gives astigmatism to reflected light from the information recording medium,
When the focal point is located in the vicinity of the second information recording layer, the first reflected light is converged in the vicinity of the optical element, and the second reflected light is converged on the light receiving unit, whereby the first reflected light is converged. An optical head in which reflected light forms a substantially circular spot on the light receiving portion . Writing data and / or data on the first information recording medium having a single information recording layer , or the second information recording medium in which at least the first information recording layer and the second information recording layer are laminated An optical head for reading,
A light source that emits light;
A condensing optical system for condensing light from the light source to form a focal point;
A light receiving unit that generates a light amount signal according to the amount of light received by at least one light receiving element;
A detecting optical system for guiding the second light reflected from the first reflection light and the second information recording layer from the first information recording layer to the light receiving portion when said second information recording medium is loaded,
A processing circuit for generating a recording medium determination signal based on the light amount signal and determining a type of the information recording medium loaded based on the recording medium determination signal;
The light receiving section is an incident area of reflected light from the single information recording layer when the first information recording medium is loaded and the focal point is located in the vicinity of the single information recording layer. And when the second information recording medium is loaded, the second reflected light incident area when the focal point is located in the vicinity of the first information recording layer, and the focal point is the second information recording layer. It looks including the discrimination light receiving element arranged on the basis of the incidence region of the first reflected light when positioned in the vicinity of the information recording layer, as said at least one light receiving element,
The detection optical system includes an optical element that gives astigmatism to reflected light from the first information recording medium and reflected light from the second information recording medium,
When the focal point is located in the vicinity of the second information recording layer, the first reflected light is converged in the vicinity of the optical element, and the second reflected light is converged on the light receiving unit. The optical head in which the first reflected light forms a substantially circular spot on the light receiving part . A processing circuit mounted on a device for writing and / or reading data on an information recording medium in which at least a first information recording layer and a second information recording layer are laminated,
The device is
A light source that emits light;
A condensing optical system for condensing light from the light source to form a focal point;
A light receiving unit that generates a light amount signal according to the amount of light received by at least one light receiving element, and is arranged based on an incident region of reflected light from an information recording layer other than the information recording layer in the vicinity of the focal point A light receiving unit including a light receiving element for determination as the at least one light receiving element;
A detection optical system that guides the first reflected light from the first information recording layer and the second reflected light from the second information recording layer to the light receiving unit, and
The light receiving unit includes an incident area of the second reflected light when the focal point is located in the vicinity of the first information recording layer, and the focal point is located in the vicinity of the second information recording layer. A light-receiving element for discrimination arranged based on the incident area of the first reflected light, as the at least one light-receiving element;
The detection optical system includes an optical element that gives astigmatism to reflected light from the information recording medium,
When the focal point is located in the vicinity of the second information recording layer, the first reflected light is converged in the vicinity of the optical element, and the second reflected light is converged on the light receiving unit, whereby the first reflected light is converged. The reflected light forms a substantially circular spot on the light receiving part,
A layer determination signal is generated based on the light amount signal, and the focus is selected from the first information recording layer and the second information recording layer of the loaded information recording medium based on the layer determination signal. A processing circuit that determines whether or not it is located in the vicinity of the information recording layer. Writing data and / or data on the first information recording medium having a single information recording layer , or the second information recording medium in which at least the first information recording layer and the second information recording layer are laminated A processing circuit implemented in a device that performs reading,
The device is
A light source that emits light;
A condensing optical system for condensing light from the light source to form a focal point;
A light receiving unit that generates a light amount signal according to the amount of light received by at least one light receiving element, wherein the focal point is positioned in the vicinity of the single information recording layer when the first information recording medium is loaded. When the incident area of the reflected light from the single information recording layer and the focal point when the second information recording medium is loaded are positioned in the vicinity of the first information recording layer A light receiving element for discrimination arranged based on the incident area of the second reflected light and the incident area of the first reflected light when the focal point is located in the vicinity of the second information recording layer. A light receiving portion including two light receiving elements;
Wherein when the second information recording medium is loaded and a detecting optical system for guiding the second light reflected from the first reflection light and the second information recording layer from the first information recording layer to the light receiving portion And
The detection optical system includes an optical element that gives astigmatism to reflected light from the first information recording medium and reflected light from the second information recording medium,
When the focal point is located in the vicinity of the second information recording layer, the first reflected light is converged in the vicinity of the optical element, and the second reflected light is converged on the light receiving unit, whereby the first reflected light is converged. The reflected light forms a substantially circular spot on the light receiving part,
A processing circuit that generates a recording medium discrimination signal based on the light amount signal and discriminates the type of the information recording medium loaded based on the recording medium discrimination signal.