JP2008097701A - Optical disk unit, disk tilt correction method and optical disk - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To reliably correct a tilt of an optical disk which records a hologram for representing information with a simple configuration. <P>SOLUTION: Tilt correction is carried out by recording in advance volume hologram Hv in an optical disk 100 for storing a hologram-used record mark RM in a disc volume recording medium, and producing a tilt error signal based on a reproducing light from the volume hologram Hv to correct the tilt of the optical disk 100 without separately installing a means for detecting tilt. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to an optical disc device, a disc tilt correction method, and an optical disc, and is suitable for application to, for example, a standing wave recording type optical disc device.

  2. Description of the Related Art Conventionally, in an optical disc apparatus, a light beam is irradiated onto an optical disc such as a CD (Compact Disc), a DVD (Digital Versatile Disc), and a Blu-ray Disc (registered trademark, hereinafter referred to as BD), and the reflected light is read. Thus, information that can be reproduced is widely used.

  In such a conventional optical disc apparatus, information is recorded by irradiating the optical disc with a light beam to change the local reflectance of the optical disc.

  For this optical disc, the size of the light spot formed on the optical disc is given by approximately λ / NA (λ: wavelength of the light beam, NA: numerical aperture), and the resolution is also known to be proportional to this value. It has been. For example, Non-Patent Document 1 shows details of a BD that can record data of approximately 25 [GB] on an optical disk having a diameter of 120 [mm].

  By the way, various kinds of information such as various contents such as music contents and video contents, or various data for computers are recorded on the optical disc. In particular, in recent years, the amount of information has increased due to higher definition of video and higher sound quality of music, and an increase in the number of contents to be recorded on one optical disc has been demanded. It is requested.

  In view of this, there has also been proposed a method of increasing the recording capacity of one optical disc by overlapping recording layers in one optical disc (see, for example, Non-Patent Document 2).

  On the other hand, an optical disk apparatus using a hologram has been proposed as a method for recording information on the optical disk (see, for example, Non-Patent Document 3).

  For example, as shown in FIG. 1, the optical disk apparatus 1 condenses a light beam from an optical head 7 once in an optical disk 8 made of a photopolymer whose refractive index changes depending on the intensity of the irradiated light. By using the reflection device 9 provided on the back side (lower side in FIG. 1), the light beam is once again condensed at the same focal position from the opposite direction.

  The optical disc apparatus 1 emits a light beam composed of laser light from a laser 2, modulates the light wave by an acousto-optic modulator 3, and converts it into parallel light by a collimator lens 4. Subsequently, the light beam passes through the polarization beam splitter 5, is converted from linearly polarized light to circularly polarized light by the quarter wavelength plate 6, and then enters the optical head 7.

  The optical head 7 is adapted to record and reproduce information. The optical head reflects a light beam by a mirror 7A, condenses it by an objective lens 7B, and is rotated by a spindle motor (not shown). 8 is irradiated.

  At this time, the light beam is once focused inside the optical disc 8, then reflected by the reflecting device 9 disposed on the back side of the optical disc 8, and from the back side of the optical disc 8 to the same focal point inside the optical disc 8. Focused. Incidentally, the reflection device 9 includes a condenser lens 9A, a shutter 9B, a condenser lens 9C, and a reflection mirror 9D.

  As a result, as shown in FIG. 2 (A), a standing wave is generated at the focal position of the light beam, and the light spot size is formed in a shape in which two cones are bonded together on the bottom surfaces. A recording mark RM composed of a small hologram is formed. Thus, the recording mark RM is recorded as information.

  When a plurality of recording marks RM are recorded in the optical disk 8, the optical disk apparatus 1 rotates the optical disk 8 and arranges the recording marks RM along a concentric or spiral track to form one mark recording layer. And by adjusting the focal position of the light beam, each recording mark RM can be recorded so that a plurality of mark recording layers are stacked.

  As a result, the optical disc 8 has a multilayer structure having a plurality of mark recording layers therein. For example, in the optical disc 8, as shown in FIG. 2B, the distance (mark pitch) p1 between the recording marks RM is 1.5 [μm], the distance between tracks (track pitch) p2 is 2 [μm], and the interlayer The distance p3 is 22.5 [μm].

  Further, when reproducing information from the disc 8 on which the recording mark RM is recorded, the optical disc apparatus 1 closes the shutter 9B of the reflection device 9 so that the light beam is not irradiated from the back side of the optical disc 8.

  At this time, the optical disc apparatus 1 irradiates the recording mark RM in the optical disc 8 with the optical beam by the optical head 7 and causes the reproducing light beam generated from the recording mark RM to enter the optical head 7. The reproduction light beam is converted from circularly polarized light to linearly polarized light by the quarter wavelength plate 6 and reflected by the polarizing beam splitter 5. Further, the reproduction light beam is condensed by the condenser lens 10 and irradiated to the photodetector 12 through the pinhole 11.

At this time, the optical disc apparatus 1 detects the light amount of the reproduction light beam by the photodetector 12 and reproduces information based on the detection result.
Y. Kasami, Y. Kuroda, K. Seo, O. Kawakubo, S. Takagawa, M. Ono, and M. Yamada, Jpn. J. Appl. Phys., 39, 756 (2000) I. Ichimura et al, Technical Digest of ISOM'04, pp52, Oct. 11-15, 2005, JejuKorea RR Mcleod er al., “Microholographicmultilayer optical disk data storage,” Appl. Opt., Vol. 44, 2005, pp3197

  When reproducing the recording mark RM composed of the above-mentioned micro hologram, the wavefront of the light beam to be irradiated coincides with the wavefront of the light beam when the recording mark RM is recorded (that is, coincident with the grating of the microhologram). The maximum amount of reproduction light is obtained.

  For this reason, when the optical disc is tilted, there is a problem that the wavefront of the light beam is distorted due to the aberration generated thereby, and the amount of the reproduction light from the recording mark RM is reduced and a good reproduction signal cannot be obtained.

  Especially in an optical disc that performs multi-layer recording, the depth of each recording layer (distance from the disc surface to the recording layer) differs greatly, so that wavefront distortion is more sensitive than single-layer recording and dual-layer recording discs. For this reason, there is a problem that an allowable amount with respect to tilt becomes small.

  The present invention has been made in view of the above points, and an optical disc apparatus and disc tilt correction capable of more reliably recording and reproducing information with a simple configuration with respect to an optical disc for recording a hologram representing information. The method and the optical disc are to be proposed.

  In order to solve such a problem, in the optical disc apparatus of the present invention, in the optical disc apparatus corresponding to the optical disc for recording the recording mark using the hologram in the disc-shaped volume type recording medium, the volume hologram recorded in advance on the optical disc is recorded. A plane wave irradiating means for irradiating a light beam composed of a plane wave; a light receiving means for receiving a reproduction light generated from the volume hologram by irradiating the volume hologram with the plane wave; Tilt error signal generating means for generating a tilt error signal indicating the tilt of the optical disk from the signal and tilt correction means for correcting the tilt of the optical disk based on the tilt error signal are provided.

  By generating a tilt error signal based on the reproduction light from the volume hologram recorded in advance on the optical disc and correcting the tilt of the optical disc, the tilt can be corrected without providing a separate tilt detecting means, and the information can be more reliably stored. Recording and playback can be performed.

  As a volume hologram, when the optical disk is tilted in a predetermined direction, the first volume hologram formed so that the amount of received light in the first light receiving region of the light receiving means is maximized, and the optical disk is tilted in the direction opposite to the predetermined direction. A second volume hologram formed to maximize the amount of light received in the second light receiving region of the light receiving means is sometimes formed, and the first light receiving signal generated by the first light receiving region and the second light receiving By generating a tilt error signal using the difference between the second received light signals generated by the area, an S-shaped tilt error signal with good signal characteristics before and after the disc tilt as the control target point is zero. The tilt of the optical disc can be corrected more reliably.

  In the disc tilt correction method of the present invention, in the disc tilt correction method of an optical disc apparatus corresponding to an optical disc that records a recording mark using a hologram in a disc-shaped volume recording medium, the volume recorded in advance on the optical disc A first control step of irradiating the hologram with a light beam of a plane wave, receiving the reproduction light generated from the volume hologram by irradiating the volume hologram with the plane wave, and generating a received light signal corresponding to the amount of received light; There is provided a second control step for generating a tilt error signal indicating the tilt of the optical disc from the received light signal, and a third control step for correcting the tilt of the optical disc based on the tilt error signal.

  By generating a tilt error signal based on the reproduction light from the volume hologram recorded in advance on the optical disc and correcting the tilt of the optical disc, the tilt can be corrected without providing a separate tilt detecting means, and the information can be more reliably stored. Recording and playback can be performed.

  Further, in the optical disc of the present invention, in an optical disc corresponding to an optical disc that records a recording mark using a hologram in a disc-shaped volume recording medium, the amount of reproduced light is maximized when the optical disc is tilted in a predetermined direction. The formed first volume hologram and the second volume hologram formed so that the reproduction light quantity is maximized when the optical disc is tilted in the direction opposite to the predetermined direction are provided.

  By providing the optical disk with the first volume hologram and the second volume hologram angle-multiplexed, a tilt error signal can be generated based on the reproduction light from the volume hologram to correct the tilt of the optical disk. .

  According to the present invention, a volume hologram is recorded in advance on an optical disk that records a recording mark using a hologram in a volume type recording medium, and a tilt error signal is generated based on the amount of light reproduced from the volume hologram. By correcting the tilt of the optical disc and correcting the tilt without providing a separate tilt detecting means, the optical disc apparatus and the disc tilt correcting method can record and reproduce information more reliably with a simple configuration. And an optical disc can be realized.

  Hereinafter, an embodiment of the present invention will be described in detail with reference to the drawings.

(1) Configuration of Optical Disc First, the optical disc 100 used as an information recording medium in the present invention will be described. As shown in the external view in FIG. 3A, the optical disc 100 as a whole is formed in a disk shape having a diameter of about 120 [mm], similar to the conventional CD, DVD and BD, and has a hole 100H at the center. Is formed.

  Further, as shown in the cross-sectional view of FIG. 3B, the optical disc 100 has a recording layer 101 for recording information in the center, and the recording layer 101 is sandwiched from both sides by the substrates 102 and 103. It is configured.

  Incidentally, the thickness t1 of the recording layer 101 is about 0.3 [mm], and the thicknesses t2 and t3 of the substrates 102 and 103 are both about 0.6 [mm].

  The substrates 102 and 103 are made of, for example, a material such as polycarbonate or glass, and both of them transmit light incident from one surface to the opposite surface with high transmittance. Further, the substrates 102 and 103 have a certain degree of strength and play a role of protecting the recording layer 101.

  Similar to the optical disc 8 (FIG. 1), the recording layer 101 is made of a photopolymer whose refractive index changes depending on the intensity of irradiated light, and responds to a blue light beam having a wavelength of 405 [nm]. As shown in FIG. 3B, when two blue light beams Lb1 and Lb2 having relatively strong intensities interfere in the recording layer 101, a standing wave is generated in the recording layer 101. Thus, an interference pattern having properties as a hologram as shown in FIG. 2A is formed.

  The optical disc 100 also has a reflection / transmission film 104 at the boundary surface between the recording layer 101 and the substrate 102. The reflection / transmission film 104 is made of a dielectric multilayer film or the like, and transmits the blue light beams Lb1 and Lb2 having a wavelength of 405 [nm] and the blue reproduction light beam Lb3 and reflects a red light beam having a wavelength of 660 [nm]. It has wavelength selectivity.

  The reflection / transmission film 104 forms a tracking servo guide groove. Specifically, a spiral track is formed by lands and grooves similar to a general BD-R (Recordable) disk. Yes. This track is recognized by being divided into predetermined recording units (referred to as sectors), and information is written or reproduced in units of sectors during recording or reproduction.

  Note that pits or the like may be formed in the reflective / transmissive film 104 (that is, the boundary surface between the recording layer 101 and the substrate 102) instead of the guide grooves, or the guide grooves and pits may be combined.

  When the red light beam Lr1 is irradiated from the substrate 102 side, the reflection / transmission film 104 reflects this toward the substrate 102 side. Hereinafter, the light beam reflected at this time is referred to as a red reflected light beam Lr2.

  This red reflected light beam Lr2 is used for, for example, adjusting the focal point Fr of the red light beam Lr1 collected by a predetermined objective lens OL1 to a target track (hereinafter referred to as a target track) in an optical disc apparatus. It is assumed that the objective lens OL1 is used for position control (that is, focus control and tracking control).

  In the following, the surface on the substrate 102 side of the optical disc 100 is referred to as a guide surface 100A, and the surface on the substrate 103 side of the optical disc 100 is referred to as a recording light irradiation surface 100B.

  In practice, when information is recorded on the optical disc 100, as shown in FIG. 3B, the red light beam Lr1 is collected by the position-controlled objective lens OL1, and the target track of the reflective / transmissive film 104 is recorded. (Hereinafter referred to as the target track).

  Further, the blue light beam Lb1 that shares the optical axis Lx with the red light beam Lr1 and is collected by the objective lens OL1 passes through the substrate 102 and the reflective / transmissive film 104, and is behind the desired track in the recording layer 101. In other words, it is focused on a position corresponding to the substrate 102 side. At this time, the focal point Fb1 of the blue light beam Lb1 is located farther than the focal point Fr on the common optical axis Lx with reference to the objective lens OL1.

  Further, the blue light beam Lb2 having the same wavelength as that of the blue light beam Lb1 and sharing the optical axis Lx has an optical characteristic equivalent to that of the objective lens OL1 from the opposite side of the blue light beam Lb1 (that is, the substrate 103 side). The light is condensed and irradiated by the lens OL2. At this time, the focal point Fb2 of the blue light beam Lb2 is set to the same position as the focal point Fb1 of the blue light beam Lb1 by controlling the position of the objective lens OL2.

  As a result, a recording mark RM having a relatively small interference pattern is recorded on the optical disc 100 at the positions of the focal points Fb1 and Fb2 corresponding to the back side of the target track in the recording layer 101.

  At this time, in the recording layer 101, the recording marks RM are formed in the portions where the blue light beams Lb1 and Lb2 of the convergent light, which are both spherical waves, are overlapped and have a predetermined intensity or more. For this reason, as shown in FIG. 2 (A), the recording mark RM generally has a shape in which two cones are bonded to each other at the bottom surfaces, and a central portion (a portion where the bottom surfaces are bonded together). Is slightly constricted.

  Incidentally, with respect to the recording mark RM, the diameter RMr of the constricted portion at the center is expressed as follows when the wavelengths of the blue light beams Lb1 and Lb2 are λ [m] and the numerical apertures of the objective lenses OL1 and OL2 are NA (1) ).

  Further, the height RMh of the recording mark RM can be obtained by the following equation (2), where n is the refractive index of the objective lenses OL1 and OL2.

  For example, when the wavelength λ is 405 [nm], the numerical aperture NA is 0.5, and the refractive index n is 1.5, the diameter RMr = 0.97 [μm] from the formula (1) and the height from the formula (2). RMh = 9.72 [μm].

  Further, the optical disc 100 is designed such that the thickness t1 (= 0.3 [mm]) of the recording layer 101 is sufficiently larger than the height RMh of the recording mark RM. For this reason, the optical disc 100 records the recording mark RM while switching the distance from the recording reflective film 104 in the recording layer 101 (hereinafter referred to as depth), as shown in FIG. In addition, it is possible to perform multilayer recording in which a plurality of mark recording layers are stacked in the thickness direction of the optical disc 100.

  In this case, the depth of the recording mark RM is changed by adjusting the depths of the focal points Fb1 and Fb2 of the blue light beams Lb1 and Lb2 in the recording layer 101 of the optical disc 100. For example, in the optical disc 100, when the distance p3 between the mark recording layers is set to about 15 [μm] in consideration of the mutual interference between the recording marks RM, about 20 mark recording layers are formed in the recording layer 101. can do.

  On the other hand, when the information is reproduced, the optical disc 100 is focused on the target track of the reflection / transmission film 104 so that the red light beam Lr1 collected by the objective lens OL1 is focused as when the information is recorded. The position of the objective lens OL1 is controlled.

  Further, in the optical disc 100, the focal point Fb1 of the blue light beam Lb1 transmitted through the substrate 102 and the reflective / transmissive film 104 through the same objective lens OL1 corresponds to the “back side” of the target track in the recording layer 101, and the target depth. (Hereinafter, this is referred to as a target mark position).

  At this time, the recording mark RM recorded at the position of the focal point Fb1 generates a blue reproduction light beam Lb3 from the recording mark RM recorded at the target mark position due to the property as a hologram. The blue reproduction light beam Lb3 has optical characteristics equivalent to those of the blue light beam Lb2 irradiated during recording of the recording mark RM, and is in the same direction as the blue light beam Lb2, that is, from the recording layer 101 to the substrate 102. It will proceed while diverging to the side.

  As described above, when information is recorded on the optical disc 100, the focal points Fb1 and Fb2 overlap in the recording layer 101 by using the red light beam Lr1 for position control and the blue light beams Lb1 and Lb2 for information recording. The recording mark RM is formed as the information at the position, that is, the target mark position on the back side of the target track and the target depth in the reflective / transmissive film 104.

  Further, when recorded information is reproduced, the optical disc 100 is recorded at the position of the focal point Fb1, that is, the target mark position by using the red light beam Lr1 for position control and the blue light beam Lb1 for information reproduction. A blue reproduction light beam Lb3 is generated from the recorded mark RM.

  In this manner, in the optical disc 100, the recording mark RM is recorded on the virtual track in the recording layer 101 by the positioning control based on the track formed on the reflective / transmissive film 104.

  In addition to this configuration, a tilt detection hologram (not shown) for detecting the tilt of the optical disc 100 and performing tilt correction is recorded on the optical disc 100, as will be described in detail later.

(2) Configuration of Optical Disc Device Next, the optical disc device 20 corresponding to the optical disc 100 described above will be described. As shown in FIG. 4, the optical disc apparatus 20 is configured to perform overall control by a control unit 21.

  The control unit 21 is mainly configured by a CPU (Central Processing Unit) (not shown), reads various programs such as a basic program and an information recording program from a ROM (Read Only Memory) (not shown), and stores them in a RAM (Random) (not shown). Various processes such as an information recording process are executed by expanding in (Access Memory).

  For example, when the control unit 21 receives an information recording command, recording information, and recording address information from an external device (not shown) with the optical disc 100 loaded, the control unit 21 supplies the driving command and recording address information to the driving control unit 22. The recording information is supplied to the signal processing unit 23. Incidentally, the recording address information is information indicating an address at which the recording information is to be recorded among the addresses given to the recording layer 101 of the optical disc 100.

  The drive control unit 22 drives and controls the spindle motor 24 in accordance with the drive command, thereby rotating the optical disc 100 held via a chuck (not shown) at a predetermined rotational speed and drivingly controlling the sled motor 25. Thus, the optical pickup 26 is moved along the movement axes 25A and 25B to a position corresponding to the recording address information in the radial direction of the optical disc 100 (that is, the inner circumferential direction or the outer circumferential direction).

  The signal processing unit 23 generates a recording signal by performing various signal processing such as predetermined encoding processing and modulation processing on the supplied recording information, and supplies the recording signal to the optical pickup 26.

  As shown in FIG. 5, the optical pickup 26 has a substantially U-shaped side surface. As shown in FIG. 3B, the optical pickup 26 irradiates the optical disc 100 with a light beam focused on both sides. Has been made to get.

  The optical pickup 26 performs focus control and tracking control based on the control of the drive control unit 22 (FIG. 4), so that a track indicated by recording address information in the recording layer 101 of the optical disc 100 (hereinafter referred to as a target track). The recording mark RM corresponding to the recording signal from the signal processing unit 23 is recorded.

  When the control unit 21 receives, for example, an information reproduction command and reproduction address information indicating the address of the recording information from an external device (not shown), the control unit 21 supplies the drive command to the drive control unit 22 and also reproduces the reproduction processing command. Is supplied to the signal processing unit 23.

  As in the case of recording information, the drive control unit 22 controls the spindle motor 24 to rotate the optical disc 100 at a predetermined rotational speed, and controls the sled motor 25 to control the optical pickup 26 for reproduction addressing. Move to a position corresponding to the information.

  The optical pickup 26 performs focus control and tracking control based on the control of the drive control unit 22 (FIG. 4), so that the light beam is applied to the track (that is, the target track) indicated by the reproduction address information in the recording layer 101 of the optical disc 100. Are irradiated with a light beam having a predetermined light amount. At this time, the optical pickup 26 detects a reproduction light beam generated from the recording mark RM of the recording layer 101 in the optical disc 100, and supplies a detection signal corresponding to the amount of light to the signal processing unit 23 (details will be described later).

  The signal processing unit 23 generates reproduction information by performing various signal processing such as predetermined demodulation processing and decoding processing on the supplied detection signal, and supplies the reproduction information to the control unit 21. In response to this, the control unit 21 sends the reproduction information to an external device (not shown).

  As described above, the optical disc apparatus 20 controls the optical pickup 26 by the control unit 21 to record information on the target track in the recording layer 101 of the optical disc 100 and reproduce information from the target track. .

(3) Configuration of Optical Pickup Next, the configuration of the optical pickup 26 will be described. As schematically shown in FIG. 6, the optical pickup 26 is provided with a large number of optical components, and is roughly divided into a guide surface position control optical system 30, a guide surface information optical system 50, and a recording light irradiation surface optical system 70. And a tilt detection optical system 90. Note that the configuration of the tilt detection optical system 90 will be described together when the tilt correction using the tilt detection optical system 90 is described.

(3-1) Configuration of Guide Surface Red Optical System The guide surface position control optical system 30 irradiates the guide surface 100A of the optical disc 100 with the red light beam Lr1, and the red light beam Lr1 is reflected by the optical disc 100. The red reflected light beam Lr2 is received.

  In FIG. 7, the laser diode 31 of the guide surface position control optical system 30 can emit red laser light having a wavelength of about 660 [nm]. In practice, the laser diode 31 emits a red light beam Lr1 having a predetermined amount of light, which is a divergent light, based on the control of the control unit 21 (FIG. 4) and makes it incident on the collimator lens 32. The collimator lens 32 converts the red light beam Lr1 from diverging light to parallel light and makes it incident on the non-polarizing beam splitter 34 via the slit 33. In FIG. 7, the tilt detection optical system 90 (FIG. 6) is omitted.

  The non-polarizing beam splitter 34 transmits the red light beam Lr1 at a rate of about 50% on the reflection / transmission surface 34A and makes it incident on the correction lens 35. The correction lenses 35 and 36 cause the red light beam Lr1 to diverge once and then converge to enter the dichroic prism 37.

  The reflection / transmission surface 37S of the dichroic prism 37 has so-called wavelength selectivity in which the transmittance and the reflectance differ depending on the wavelength of the light beam, and transmits the red light beam at a rate of approximately 100%. Is reflected at a rate of almost 100%. Therefore, the dichroic prism 37 transmits the red light beam Lr1 through the reflection / transmission surface 37S and makes it incident on the objective lens 38.

  The objective lens 38 condenses the red light beam Lr1 and irradiates it toward the guide surface 100A of the optical disc 100. At this time, as shown in FIG. 3B, the red light beam Lr1 is transmitted through the substrate 102 and reflected by the reflective / transmissive film 104, and becomes a red reflected light beam Lr2 that goes in the opposite direction to the red light beam Lr1.

  The objective lens 38 is designed to be optimized for the blue light beam Lb1, and the red light beam Lr1 has a numerical aperture (NA) depending on the optical distance between the slit 33 and the correction lenses 35 and 36. : Numerical Aperture) acts as a condenser lens with 0.41.

  Thereafter, the red reflected light beam Lr2 is sequentially transmitted through the objective lens 38, the dichroic prism 37, and the correction lenses 36 and 35 to be converted into parallel light, and then incident on the non-polarized beam splitter 34.

  The non-polarizing beam splitter 34 irradiates the mirror 40 by reflecting the red reflected light beam Lr2 at a ratio of about 50%, and reflects the red reflected light beam Lr2 again by the mirror 40, and then collects the condensing lens 41. To enter.

  The condensing lens 41 converges the red reflected light beam Lr2 and gives astigmatism by the cylindrical lens 42, and then irradiates the photodetector 43 with the red reflected light beam Lr2.

  By the way, in the optical disc apparatus 20, since there is a possibility that surface blurring or the like occurs in the rotating optical disc 100, the relative position of the target track with respect to the guide surface position control optical system 30 may vary.

  Therefore, in order for the guide surface position control optical system 30 to cause the focal point Fr (FIG. 3B) of the red light beam Lr1 to follow the target track, the focal point Fr is in the proximity direction or the separation direction with respect to the optical disc 100. In addition, it is necessary to move the optical disc 100 in the tracking direction which is the inner peripheral side direction or the outer peripheral side direction.

  Therefore, the objective lens 38 can be driven in the biaxial direction of the focus direction and the tracking direction by the biaxial actuator 38A.

  In the guide surface position control optical system 30 (FIG. 7), the focusing state when the red light beam Lr1 is collected by the objective lens 38 and applied to the reflective / transmissive film 104 of the optical disc 100 is red by the condenser lens 41. The optical positions of the various optical components are adjusted so that the reflected light beam Lr2 is collected and reflected in the focused state when the photodetector 43 is irradiated.

  As shown in FIG. 8, the photodetector 43 has four detection areas 43A, 43B, 43C, and 43D that are divided in a lattice pattern on the surface irradiated with the red reflected light beam Lr2. Incidentally, the direction (vertical direction in the figure) indicated by the arrow a1 corresponds to the traveling direction of the track when the red light beam Lr1 is irradiated onto the reflective / transmissive film 104 (FIG. 3).

  The photodetector 43 detects a part of the red reflected light beam Lr2 by the detection regions 43A, 43B, 43C, and 43D, respectively, and generates detection signals SDAr, SDBr, SDCr, and SDDr according to the detected light amount, respectively. These are sent to the signal processing unit 23 (FIG. 4).

  The signal processing unit 23 performs focus control by a so-called astigmatism method, calculates a focus error signal SFEr according to the following equation (3), and supplies this to the drive control unit 22.

  The focus error signal SFEr represents the amount of deviation between the focal point Fr of the red light beam Lr1 and the reflection / transmission film 104 of the optical disc 100.

  The signal processing unit 23 performs tracking control by a so-called push-pull method, calculates a tracking error signal STEr according to the following equation (4), and supplies the tracking error signal STer to the drive control unit 22.

  This tracking error signal STEr represents the amount of deviation between the focal point Fr of the red light beam Lr1 and the target track in the reflection / transmission film 104 of the optical disc 100.

  The drive control unit 22 generates a focus drive signal SFDr based on the focus error signal SFEr, and supplies the focus drive signal SFDr to the biaxial actuator 38A, whereby the red light beam Lr1 is applied to the reflective / transmissive film 104 of the optical disc 100. The objective lens 38 is feedback-controlled (that is, focus control) so as to be focused.

  Further, the drive control unit 22 generates a tracking drive signal STDr based on the tracking error signal STEr and supplies the tracking drive signal STDr to the biaxial actuator 38A, whereby the red light beam Lr1 is reflected and transmitted by the reflective / transmissive film 104 of the optical disc 100. The objective lens 38 is feedback-controlled (that is, tracking control) so as to focus on the target track.

  As described above, the guide surface position control optical system 30 irradiates the reflection / transmission film 104 of the optical disc 100 with the red light beam Lr1 and supplies the signal processing unit 23 with the light reception result of the red reflection light beam Lr2 that is the reflection light. Has been made. In response to this, the drive control unit 22 performs focus control and tracking control of the objective lens 38 so that the red light beam Lr1 is focused on the target track of the reflection / transmission film 104.

(3-2) Configuration of Guide Surface Blue Optical System The guide surface information optical system 50 is configured to irradiate the guide surface 100A of the optical disc 100 with the blue light beam Lb1 and is incident from the optical disc 100. The blue light beam Lb2 or the blue reproduction light beam Lb3 is received.

(3-2-1) Irradiation of Blue Light Beam In FIG. 9, the laser diode 51 of the guide surface information optical system 50 is configured to emit blue laser light having a wavelength of about 405 [nm]. In practice, the laser diode 51 emits a blue light beam Lb0 made of divergent light based on the control of the control unit 21 (FIG. 4) and makes it incident on the collimator lens 52. The collimator lens 52 converts the blue light beam Lb0 from diverging light into parallel light and makes it incident on the half-wave plate 53. In FIG. 9, the tilt detection optical system 90 (FIG. 6) is omitted.

  At this time, the blue light beam Lb0 is incident on the surface 55A of the polarization beam splitter 55 after the polarization direction is rotated by a predetermined angle by the half-wave plate 53 and the intensity distribution is shaped by the anamorphic prism 54.

  The polarization beam splitter 55 reflects or transmits the light beam on the reflection / transmission surface 55S at a different rate depending on the polarization direction of the light beam. For example, the reflection / transmission surface 55S reflects a p-polarized light beam at a rate of approximately 50%, transmits the remaining 50%, and transmits an s-polarized light beam at a rate of approximately 100%.

  Actually, the polarization beam splitter 55 reflects the p-polarized blue light beam Lb0 at a rate of about 50% by the reflection / transmission surface 55S, and makes it incident on the quarter-wave plate 56 from the surface 55B, and the remaining 50 % Is transmitted and is incident on the shutter 71 from the surface 55D. Hereinafter, the blue light beam reflected by the reflection / transmission surface 55S is referred to as a blue light beam Lb1, and the blue light beam transmitted through the reflection / transmission surface 55S is referred to as a blue light beam Lb2.

  The quarter-wave plate 56 converts the blue light beam Lb1 from linearly polarized light to circularly polarized light and irradiates the movable mirror 57, and is reflected by the movable mirror 57 to convert the blue light beam Lb1 from circularly polarized light to linearly polarized light. Then, the light is again incident on the surface 55B of the polarization beam splitter 55.

  At this time, the blue light beam Lb1 is converted from p-polarized light to left-circularly polarized light by, for example, the quarter-wave plate 56, converted from left-circularly polarized light to right-circularly polarized light when reflected by the movable mirror 57, and then 1 again. / 4 wavelength plate 56 converts right circularly polarized light into s polarized light. That is, the polarization direction of the blue light beam Lb1 differs between when it is emitted from the surface 55B and when it is incident on the surface 55B after being reflected by the movable mirror 57.

  The polarization beam splitter 55 transmits the blue light beam Lb1 as it is through the reflection / transmission surface 55S according to the polarization direction (s-polarization) of the blue light beam Lb1 incident from the surface 55B, and passes from the surface 55C to the polarization beam splitter 58. It is made to enter.

  As a result, the guide surface information optical system 50 extends the optical path length of the blue light beam Lb1 by the polarizing beam splitter 55, the quarter wavelength plate 56, and the movable mirror 57.

  The reflection / transmission surface 55S of the polarizing beam splitter 58 reflects, for example, a p-polarized light beam at a rate of about 100% and transmits an s-polarized light beam at a rate of about 100%. In practice, the polarization beam splitter 58 transmits the blue light beam Lb1 as it is through the reflection / transmission surface 58S, and converts it from linearly polarized light (s-polarized light) to circularly polarized light (right circularly polarized light) by the quarter wavelength plate 59. Then, the light is incident on the relay lens 60.

  The relay lens 60 converts the blue light beam Lb1 from parallel light into convergent light by the movable lens 61, converts the blue light beam Lb1 that has become divergent light after convergence into the convergent light again by the fixed lens 62, and the dichroic prism. 37 is incident.

  Here, the movable lens 61 is moved in the optical axis direction of the blue light beam Lb1 by the actuator 61A. In practice, the relay lens 60 can change the convergence state of the blue light beam Lb1 emitted from the fixed lens 62 by moving the movable lens 61 by the actuator 61A based on the control of the control unit 21 (FIG. 4). Has been made.

  The dichroic prism 37 reflects the blue light beam Lb1 by the reflection / transmission surface 37S in accordance with the wavelength of the blue light beam Lb1, and makes it incident on the objective lens 38. Incidentally, when the blue light beam Lb1 is reflected on the reflection / transmission surface 37S, the polarization direction of the circularly polarized light is inverted, and is converted from, for example, right circularly polarized light to left circularly polarized light.

  The objective lens 38 condenses the blue light beam Lb1 and irradiates the guide surface 100A of the optical disc 100 with it. Incidentally, the objective lens 38 acts as a condensing lens having a numerical aperture (NA) of 0.5 with respect to the blue light beam Lb1 due to the optical distance to the relay lens 60 and the like.

  At this time, the blue light beam Lb1 passes through the substrate 102 and the reflective / transmissive film 104 and is focused in the recording layer 101, as shown in FIG. 3B. Here, the position of the focal point Fb1 of the blue light beam Lb1 is determined by a convergence state when the blue light beam Lb1 is emitted from the fixed lens 62 of the relay lens 60. That is, the focal point Fb1 moves to the guide surface 100A side or the recording light irradiation surface 100B side in the recording layer 101 according to the position of the movable lens 61.

  Specifically, the guide surface information optical system 50 is designed so that the moving distance of the movable lens 61 and the moving distance of the focal point Fb1 of the blue light beam Lb1 are substantially proportional to each other. ], The focal point Fb1 of the blue light beam Lb1 is moved by 30 [μm].

  In practice, the guide surface information optical system 50 is controlled by the control unit 21 (FIG. 4) to control the position of the movable lens 61, whereby the focal point Fb1 of the blue light beam Lb1 in the recording layer 101 of the optical disc 100 (FIG. 3 (FIG. 3)). The depth d1 of B)) (that is, the distance from the reflective / transmissive film 104) is adjusted.

  The blue light beam Lb1 becomes divergent light after converging to the focal point Fb1, passes through the recording layer 101 and the substrate 103, is emitted from the recording light irradiation surface 100B, and enters the objective lens 79 (details will be described later).

  Thus, the guide surface information optical system 50 irradiates the blue light beam Lb1 from the guide surface 100A side of the optical disc 100 to position the focal point Fb1 of the blue light beam Lb1 in the recording layer 101, and further moves the relay lens 60 at the movable position. Depending on the position of the lens 61, the depth d1 of the focal point Fb1 is adjusted.

(3-2-2) Reception of Blue Light Beam By the way, the optical disc 100 transmits the blue light beam Lb2 irradiated to the recording light irradiation surface 100B from the objective lens 79 of the recording light irradiation surface optical system 70, and from the guide surface 100A. The light is emitted as diverging light (details will be described later). Incidentally, the blue light beam Lb2 is circularly polarized (for example, right circularly polarized).

  At this time, in the guide surface information optical system 50, as shown in FIG. 10, after the blue light beam Lb2 is converged to some extent by the objective lens 38, it is reflected by the dichroic prism 37 and enters the relay lens 60. Incidentally, when the blue light beam Lb2 is reflected by the reflection / transmission surface 37S, the polarization direction of the circularly polarized light is inverted, and is converted from, for example, right circularly polarized light to left circularly polarized light. In FIG. 10, the tilt detection optical system 90 (FIG. 6) is omitted.

  Subsequently, the blue light beam Lb2 is converted into parallel light by the fixed lens 62 and the movable lens 61 of the relay lens 60, and further converted from circularly polarized light (left circularly polarized light) to linearly polarized light (p polarized light) by the quarter wavelength plate 59. Then, the light enters the polarization beam splitter 58.

  The polarization beam splitter 58 reflects the blue light beam Lb2 according to the polarization direction of the blue light beam Lb2 and makes it incident on the condenser lens 63. The condensing lens 63 condenses the blue light beam Lb2 and irradiates the photodetector 64 with it.

  Incidentally, each optical component in the guide surface information optical system 50 is arranged so that the blue light beam Lb2 is focused on the photodetector 64.

  The photodetector 64 detects the light amount of the blue light beam Lb2, generates a reproduction detection signal SDp according to the light amount detected at this time, and supplies this to the signal processing unit 23 (FIG. 4).

  However, the reproduction detection signal SDp generated by the photodetector 64 according to the amount of the blue light beam Lb2 at this time has no particular application. For this reason, the signal processing unit 23 (FIG. 4) is not particularly subjected to signal processing although the reproduction detection signal SDp is supplied.

  On the other hand, when the recording mark RM is recorded on the recording layer 101, the optical disc 100 has the characteristics as a hologram when the focal point Fb1 of the blue light beam Lb1 is focused on the recording mark RM as described above. The blue reproduction light beam Lb3 is generated from the recording mark RM.

  This blue reproduction light beam Lb3 is a reproduction of the light beam irradiated in addition to the blue light beam Lb1 when the recording mark RM is recorded, that is, the blue light beam Lb2, on the principle of hologram. Therefore, the blue reproduction light beam Lb3 is finally irradiated on the photodetector 64 by passing through the same optical path as the blue light beam Lb2 in the guide surface information optical system 50.

  Here, each optical component in the guide surface information optical system 50 is arranged so that the blue light beam Lb2 is focused on the photodetector 64 as described above. For this reason, the blue reproduction light beam Lb3 is focused on the photodetector 64 in the same manner as the blue light beam Lb2.

  The photodetector 64 detects the light amount of the blue light beam Lb3, generates a reproduction detection signal SDp according to the light amount detected at this time, and supplies it to the signal processing unit 23 (FIG. 4).

  In this case, the reproduction detection signal SDp represents information recorded on the optical disc 100. Therefore, the signal processing unit 23 generates reproduction information by performing predetermined demodulation processing, decoding processing, and the like on the reproduction detection signal SDp, and supplies the reproduction information to the control unit 21.

  As described above, the guide surface information optical system 50 receives the blue light beam Lb2 or the blue reproduction light beam Lb3 incident on the objective lens 38 from the guide surface 100A of the optical disc 100, and supplies the light reception result to the signal processing unit 23. It is made like that.

(3-3) Configuration of Recording Light Irradiation Surface Optical System The recording light irradiation surface optical system 70 (FIG. 6) irradiates the recording light irradiation surface 100B of the optical disc 100 with the blue light beam Lb2. Further, the blue light beam Lb1 irradiated from the guide surface information optical system 50 and transmitted through the optical disc 100 is received.

(3-3-1) Irradiation of Blue Light Beam In FIG. 10, as described above, the polarization beam splitter 55 of the guide surface information optical system 50 applies approximately 50% of the blue light beam Lb0 that is p-polarized light on the reflection / transmission surface 55S. And is incident on the shutter 71 from the surface 55D as a blue light beam Lb2.

  The shutter 71 is configured to block or transmit the blue light beam Lb2 based on the control of the control unit 21 (FIG. 4). When the shutter 71 transmits the blue light beam Lb2, the shutter 71 enters the polarization beam splitter 72.

  The reflection / transmission surface 72S of the polarization beam splitter 72 transmits, for example, a p-polarized light beam at a rate of about 100% and reflects an s-polarized light beam at a rate of about 100%. In practice, the polarization beam splitter 72 transmits the p-polarized blue light beam Lb2 as it is, reflects it by the mirror 73, and then converts it from linearly polarized light (p-polarized light) to circularly polarized light (left-circularly polarized light) by the quarter wavelength plate 74. ) And then incident on the relay lens 75.

  The relay lens 75 is configured in the same manner as the relay lens 60, and includes a movable lens 76, an actuator 76A, and a fixed lens 77 corresponding to the movable lens 61, the actuator 61A, and the fixed lens 62, respectively.

  The relay lens 75 converts the blue light beam Lb2 from parallel light to convergent light by the movable lens 76, converts the blue light beam Lb2 that has become divergent light after convergence into the convergent light again by the fixed lens 77, and the galvanometer mirror 78. To enter.

  Similarly to the relay lens 60, the relay lens 75 moves the movable lens 76 by the actuator 76 </ b> A based on the control of the control unit 21 (FIG. 4), thereby changing the convergence state of the blue light beam Lb <b> 2 emitted from the fixed lens 77. It can be changed.

  The galvanometer mirror 78 reflects the blue light beam Lb2 and makes it incident on the objective lens 79. Incidentally, when the blue light beam Lb2 is reflected, the polarization direction of the circularly polarized light is reversed, and is converted from, for example, left circularly polarized light to right circularly polarized light.

  The galvanometer mirror 78 can change the angle of the reflecting surface 78A, and the traveling direction of the blue light beam Lb2 is adjusted by adjusting the angle of the reflecting surface 78A according to the control of the control unit 21 (FIG. 4). It can be adjusted.

  The objective lens 79 is configured integrally with the biaxial actuator 79A. Like the objective lens 38, the objective lens 79 is integrated with the focus direction which is the approaching or separating direction of the optical disc 100 and the inner circumference of the optical disc 100. The optical disc 100 can be driven in two axial directions, a tracking direction which is a lateral direction or an outer peripheral side direction, and a radial tilt which tilts the optical axis in the radial direction (radial direction) of the optical disc 100.

  The objective lens 79 condenses the blue light beam Lb2 and irradiates the recording light irradiation surface 100B of the optical disc 100. This objective lens has the same optical characteristics as the objective lens 38, and the numerical aperture (NA) of the blue light beam Lb2 is 0.5 because of the optical distance to the relay lens 75 and the like. It will act as a condenser lens.

  At this time, the blue light beam Lb2 is transmitted through the substrate 103 and focused into the recording layer 101 as shown in FIG. Here, the position of the focal point Fb <b> 2 of the blue light beam Lb <b> 2 is determined by the convergence state when it is emitted from the fixed lens 77 of the relay lens 75. That is, the focal point Fb2 moves to the guide surface 100A side or the recording light irradiation surface 100B side in the recording layer 101 according to the position of the movable lens 76, like the focal point Fb1 of the blue light beam Lb1.

  Specifically, like the guide surface information optical system 50, the recording light irradiation surface optical system 70 is designed so that the moving distance of the movable lens 76 and the moving distance of the focal point Fb2 of the blue light beam Lb2 are substantially proportional. For example, when the movable lens 76 is moved by 1 [mm], the focal point Fb2 of the blue light beam Lb2 is moved by 30 [μm].

  In practice, the recording light irradiation surface optical system 70 controls the recording of the optical disk 100 by controlling the position of the movable lens 61 in the relay lens 75 together with the position of the movable lens 61 in the relay lens 60 by the control unit 21 (FIG. 4). The depth d2 of the focal point Fb2 (FIG. 3B) of the blue light beam Lb2 in the layer 101 is adjusted.

  At this time, in the optical disc apparatus 20, the objective lens 38 in the recording layer 101 when the control unit 21 (FIG. 4) assumes that no surface blur or the like has occurred in the optical disc 100 (that is, in an ideal state). The focal point Fb2 of the blue light beam Lb2 when the objective lens 79 is at the reference position is aligned with the focal point Fb1 of the blue light beam Lb1 when it is at the reference position.

  The blue light beam Lb2 is focused at the focal point Fb2, and then passes through the recording layer 101, the reflective / transmissive film 104 and the substrate 102 while diverging, is emitted from the guide surface 100A, and is incident on the objective lens 38. ing.

  As described above, the recording light irradiation surface optical system 70 irradiates the blue light beam Lb2 from the recording light irradiation surface 100B side of the optical disc 100 to position the focal point Fb2 of the blue light beam Lb2 in the recording layer 101, and further relays the relay lens. The depth d2 of the focal point Fb2 is adjusted according to the position of the movable lens 76 at 75.

(3-3-2) Reception of Blue Light Beam By the way, the blue light beam Lb1 irradiated from the objective lens 38 of the guide surface information optical system 50 (FIG. 9) is transmitted into the recording layer 101 of the optical disc 100 as described above. , Once converged, becomes divergent light and enters the objective lens 79.

  At this time, in the recording light irradiation surface optical system 70, the blue light beam Lb 1 is converged to some extent by the objective lens 79, then reflected by the galvanometer mirror 78 and incident on the relay lens 75. Incidentally, when the blue light beam Lb1 is reflected by the reflecting surface 78S, the polarization direction of the circularly polarized light is inverted, and is converted from, for example, left circularly polarized light to right circularly polarized light.

  Subsequently, the blue light beam Lb1 is converted into parallel light by the fixed lens 62 and the movable lens 61 of the relay lens 75, and further converted from circularly polarized light (right circularly polarized light) to linearly polarized light (s polarized light) by the quarter wavelength plate 74. After being reflected by the mirror 73, the light is incident on the polarization beam splitter 72.

  The polarization beam splitter 72 reflects the blue light beam Lb1 according to the polarization direction of the blue light beam Lb1 and makes it incident on the condenser lens 80. The condensing lens 80 converges the blue light beam Lb1 and gives astigmatism by the cylindrical lens 81, and then irradiates the photodetector 82 with the blue light beam Lb1.

  However, the optical disc 100 may actually cause a surface blur or the like. For this reason, as described above, the objective lens 38 is subjected to focus control and tracking control by the guide surface position control optical system 30, the drive control unit 22 (FIG. 4), and the like.

  At this time, since the focal point Fb1 of the blue light beam Lb1 moves with the movement of the objective lens 38, the focal point Fb2 is shifted from the position of the focal point Fb2 in the blue light beam Lb2 when the objective lens 79 is at the reference position. .

  Therefore, in the recording light irradiation surface optical system 70, the amount of deviation of the focal point Fb2 of the blue light beam Lb2 from the focal point Fb1 of the blue light beam Lb1 in the recording layer 101 is condensed by the condensing lens 80 so that the blue light beam Lb1 is condensed. The optical positions of the various optical components are adjusted so as to be reflected in the irradiation state at the time of irradiation.

  As shown in FIG. 11, the photodetector 82 has four detection regions 82A, 82B, 82C, and 82D that are divided in a lattice pattern on the surface irradiated with the blue light beam Lb1, as with the photodetector 43. . Incidentally, the direction indicated by the arrow a2 (the horizontal direction in the figure) corresponds to the track traveling direction in the reflective / transmissive film 104 (FIG. 3) when the blue light beam Lb1 is irradiated.

  The photodetector 82 detects a part of the blue light beam Lb1 by the detection areas 82A, 82B, 82C, and 82D, respectively, generates detection signals SDAb, SDBb, SDCb, and SDDb according to the detected light amount, respectively. Is sent to the signal processing unit 23 (FIG. 4).

  The signal processing unit 23 performs focus control by a so-called astigmatism method, calculates a focus error signal SFEb according to the following equation (5), and supplies this to the drive control unit 22.

  This focus error signal SFEb represents the amount of shift in the focus direction between the focal point Fb1 of the blue light beam Lb1 and the focal point Fb2 of the blue light beam Lb2.

  The signal processing unit 23 performs tracking control using a push-pull signal, calculates a tracking error signal STEb according to the following equation (6), and supplies the tracking error signal STEb to the drive control unit 22.

  The tracking error signal STEb represents the amount of deviation in the tracking direction between the focal point Fb1 of the blue light beam Lb1 and the focal point Fb2 of the blue light beam Lb2.

  Further, the signal processing unit 23 generates a tangential error signal necessary for tangential control. This tangential control is control for moving the focal point Fb2 of the blue light beam Lb2 to the target position in the tangential direction (that is, the tangential direction of the track).

  Specifically, the signal processing unit 23 performs tangential control using a push-pull signal, calculates a tangential error signal SNEb according to the following equation (7), and sends this to the drive control unit 22. Supply.

  The tangential error signal SNEb represents the amount of deviation in the tangential direction between the focal point Fb1 of the blue light beam Lb1 and the focal point Fb2 of the blue light beam Lb2.

  In response to this, the drive control unit 22 generates a focus drive signal SFDb based on the focus error signal SFEb, and supplies the focus drive signal SFDb to the biaxial actuator 79A, whereby the blue light beam Lb1 is focused on the focus Fb1. The focus of the objective lens 79 is controlled so as to reduce the shift amount of the light beam Lb2 with respect to the focus direction of the focus Fb2.

  Further, the drive control unit 22 generates a tracking drive signal STDb based on the tracking error signal STEb, and supplies the tracking drive signal STDb to the biaxial actuator 79A, whereby the blue light beam Lb2 with respect to the focal point Fb1 of the blue light beam Lb1. The objective lens 79 is subjected to tracking control so as to reduce the amount of deviation of the focal point Fb2 in the tracking direction.

  Further, the drive control unit 22 generates a tangential drive signal SNDb based on the tangential error signal SNEb, and supplies the tangential drive signal SNDb to the galvanometer mirror 78, whereby blue light with respect to the focal point Fb1 of the blue light beam Lb1. Tangential control is performed by adjusting the angle of the reflecting surface 78A of the galvanometer mirror 78 so as to reduce the amount of deviation of the focal point Fb2 of the beam Lb2 in the tangential direction.

  As described above, the recording light irradiation surface optical system 70 receives the blue light beam Lb1 incident on the objective lens 79 from the recording light irradiation surface 100B of the optical disc 100 and supplies the light reception result to the signal processing unit 23. ing. In response to this, the drive control unit 22 performs focus control and tracking control of the objective lens 79 and tangential control by the galvanometer mirror 78 so that the focus Fb2 of the blue light beam Lb2 is aligned with the focus Fb1 of the blue light beam Lb1. Has been made.

(3-4) Adjustment of Optical Path Length By the way, as described above, the optical pickup 26 of the optical disc apparatus 20 records the blue light beam Lb1 from the blue light beam Lb0 by the polarization beam splitter 55 (FIG. 9), as described above. By separating Lb2 and causing the blue light beams Lb1 and Lb2 to interfere with each other in the recording layer 101 of the optical disc 100, the recording mark RM is recorded at the target mark position in the recording layer 101.

  The laser diode 51 that emits the blue light beam Lb0 has a recording mark RM as a hologram correctly recorded on the recording layer 101 of the optical disc 100 in accordance with general hologram forming conditions. The length needs to be equal to or larger than the hologram size (that is, the height RMh of the recording mark RM).

  In practice, in the laser diode 51, like a general laser diode, the coherent length is a value obtained by multiplying the length of a resonator (not shown) provided in the laser diode 51 by the refractive index of the resonator. Therefore, it is considered to be approximately 100 [μm] to 1 [mm].

  On the other hand, in the optical pickup 26, the blue light beam Lb1 passes through the optical path in the guide surface information optical system 50 (FIG. 9) and is irradiated from the guide surface 100A side of the optical disc 100, and the blue light beam Lb2 is irradiated with the recording light irradiation surface. The light passes through the optical path in the optical system 70 (FIG. 10) and is irradiated from the recording light irradiation surface 100B side of the optical disc 100. That is, in the optical pickup 26, since the optical paths of the blue light beams Lb1 and Lb2 are different from each other, a difference occurs in the optical path length (that is, the length of the optical path from the laser diode 51 to the target mark position).

  Further, in the optical pickup 26, as described above, the depth of the target mark position (target depth) in the recording layer 101 of the optical disc 100 is adjusted by adjusting the positions of the movable lenses 61 and 76 in the relay lenses 60 and 75. It has been made to change. At this time, the optical pickup 26 changes the optical path lengths of the blue light beams Lb1 and Lb2 by changing the depth of the target mark position.

  However, in order to form an interference pattern in the optical pickup 26, the difference in optical path length between the blue light beams Lb1 and Lb2 is reduced from the coherent length (ie, approximately 100 [μm] to 1 [mm] depending on the general hologram forming conditions. ]) It needs to be as follows.

  Therefore, the control unit 21 (FIG. 4) adjusts the optical path length of the blue light beam Lb1 by controlling the position of the movable mirror 57. In this case, the control unit 21 uses the relationship between the position of the movable lens 61 in the relay lens 60 and the depth of the target mark position, and moves the movable mirror 57 in accordance with the position of the movable lens 61, thereby the blue color. The optical path length of the light beam Lb1 is changed.

  As a result, the optical pickup 26 can suppress the difference in optical path length between the blue light beams Lb1 and Lb2 to be equal to or less than the coherent length, and can record the recording mark RM made of a good hologram at the target mark position in the recording layer 101. Can do.

  As described above, the control unit 21 of the optical disc apparatus 20 controls the position of the movable mirror 57, thereby suppressing the difference in optical path length between the blue light beams Lb1 and Lb2 in the optical pickup 26 to be equal to or less than the coherent length. A good recording mark RM can be recorded at a target mark position in 100 recording layers 101.

(4) Recording and Reproducing Information (4-1) Recording Information on Optical Disc When recording information on the optical disc 100, the control unit 21 (FIG. 4) of the optical disc apparatus 20 is an external device (not shown) as described above. When the information recording command, the recording information, and the recording address information are received, the driving command and the recording address information are supplied to the drive control unit 22 and the recording information is supplied to the signal processing unit 23.

  At this time, the drive controller 22 causes the guide surface position control optical system 30 (FIG. 7) of the optical pickup 26 to irradiate the red light beam Lr1 from the guide surface 100A side of the optical disc 100, and the reflected red light beam Lr2 as the reflected light. Based on this detection result, focus control and tracking control (that is, position control) of the objective lens 38 are performed to cause the focus Fr of the red light beam Lr1 to follow the target track corresponding to the recording address information.

  Further, the control unit 21 causes the guide surface information optical system 50 (FIG. 9) to irradiate the blue light beam Lb1 from the guide surface 100A side of the optical disc 100. At this time, the focal point Fb1 of the blue light beam Lb1 is focused by the position-controlled objective lens 38, thereby being positioned behind the target track.

  Further, the control unit 21 adjusts the position of the movable lens 61 in the relay lens 60 to adjust the depth d1 of the focal point Fb1 (FIG. 3B) to the target depth. As a result, the focal point Fb1 of the blue light beam Lb1 is adjusted to the target mark position.

On the other hand, the control unit 21 controls the shutter 71 of the recording light irradiation surface optical system 70 (FIG. 10) to transmit the blue light beam Lb2, and irradiates the blue light beam Lb2 from the recording light irradiation surface 100B side of the optical disc 100. Let

  The control unit 21 adjusts the depth d2 of the blue light beam Lb2 (FIG. 3B) by adjusting the position of the movable lens 76 in the relay lens 75 according to the position of the movable lens 61 in the relay lens 60. To do. As a result, the depth d2 of the focal point Fb2 of the blue light beam Lb2 is adjusted to the depth d1 of the focal point Fb1 in the blue light beam Lb1 when it is assumed that no surface blur has occurred in the optical disc 100.

  Further, the control unit 21 causes the recording light irradiation surface optical system 70 to detect the blue light beam Lb1 via the objective lenses 38 and 79, and based on the detection result, the drive control unit 22 performs focus control and tracking of the objective lens 79. Control and radial control (that is, position control) of the galvanometer mirror 78 are performed.

  As a result, the focal point Fb2 of the blue light beam Lb2 is adjusted to the position of the focal point Fb1 in the blue light beam Lb1, that is, the target mark position.

  In addition, the control unit 21 adjusts the position of the movable mirror 57 according to the position of the movable lens 61 in the relay lens 60, and suppresses the difference in optical path length between the blue light beams Lb1 and Lb2 to be equal to or less than the coherent length.

  Thus, the control unit 21 of the optical disc apparatus 20 can form a good recording mark RM at the target mark position in the recording layer 101 of the optical disc 100.

  By the way, the signal processing unit 23 (FIG. 4) generates a recording signal representing binary data having a value “0” or “1” based on recording information supplied from an external device (not shown) or the like. In response to this, the laser diode 51 emits the blue light beam Lb0 when the recording signal has the value “1”, for example, and does not emit the blue light beam Lb0 when the recording signal has the value “0”. .

  As a result, the optical disc apparatus 20 forms the recording mark RM at the target mark position in the recording layer 101 of the optical disc 100 when the recording signal has the value “1”, and at the target mark position when the recording signal has the value “0”. Since the recording mark RM is not formed, the value “1” or “0” of the recording signal can be recorded at the target mark position depending on the presence or absence of the recording mark RM. The recording layer 101 can be recorded.

(4-2) Reproduction of Information from Optical Disc When reproducing information from the optical disc 100, the control unit 21 (FIG. 4) of the optical disc apparatus 20 is red by the guide surface position control optical system 30 (FIG. 7) of the optical pickup 26. A light beam Lr1 is irradiated from the guide surface 100A side of the optical disc 100, and based on the detection result of the reflected red light beam Lr2, the drive control unit 22 performs focus control and tracking control (that is, position control) of the objective lens 38. ).

  Further, the control unit 21 causes the guide surface information optical system 50 (FIG. 9) to irradiate the blue light beam Lb1 from the guide surface 100A side of the optical disc 100. At this time, the focal point Fb1 of the blue light beam Lb1 is focused by the position-controlled objective lens 38, thereby being positioned behind the target track.

  Incidentally, the control unit 21 is configured to prevent erroneous erasure of the recording mark RM by the blue light beam Lb1 by suppressing the emission power of the laser diode 51 during reproduction.

  Further, the control unit 21 adjusts the position of the movable lens 61 in the relay lens 60 to adjust the depth d1 of the focal point Fb1 (FIG. 3B) to the target depth. As a result, the focal point Fb1 of the blue light beam Lb1 is adjusted to the target mark position.

  On the other hand, the control unit 21 controls the shutter 71 of the recording light irradiation surface optical system 70 (FIG. 10) to block the blue light beam Lb2, so that the optical disk 100 is not irradiated with the blue light beam Lb2.

  That is, the optical pickup 26 irradiates the recording mark RM recorded at the target mark position in the recording layer 101 of the optical disc 100 with only the blue light beam Lb1 as so-called reference light. In response to this, the recording mark RM acts as a hologram, and generates a blue reproduction light beam Lb3 as so-called reproduction light toward the guide surface 101A. At this time, the guide surface information optical system 50 detects the blue reproduction light beam Lb3 and generates a detection signal corresponding to the detection result.

  Thus, the control unit 21 of the optical disc apparatus 20 generates the blue reproduction light beam Lb3 from the recording mark RM recorded at the target mark position in the recording layer 101 of the optical disc 100, and receives the blue reproduction light beam Lb3. It is possible to detect that it is recorded.

  Here, when the recording mark RM is not recorded at the target mark position, the optical disk device 20 does not generate the blue reproduction light beam Lb3 from the target mark position. A detection signal indicating that the beam Lb3 has not been received is generated.

  In response to this, the signal processing unit 22 recognizes whether the blue reproduction light beam Lb3 is detected based on the detection signal as a value “1” or “0”, and generates reproduction information based on the recognition result. To do.

  Thereby, in the optical disc apparatus 20, when the recording mark RM is formed at the target mark position in the recording layer 101 of the optical disc 100, the blue reproduction light beam Lb3 is received, and the recording mark RM is formed at the target mark position. By not receiving the blue reproduction light beam Lb3 when there is not, it is possible to recognize whether the value “1” or “0” is recorded at the target mark position, and as a result, recording is performed on the recording layer 101 of the optical disc 100. Information can be reproduced.

(5) Tilt correction of optical disc according to the present invention As described above, the optical disc apparatus 20 of the present invention forms a standing wave in the recording layer 101 by the blue light beams Lb1 and Lb2 during recording, thereby forming the recording mark RM. During recording and reproduction, a reproduction detection signal SDp is obtained by irradiating the recording mark RM with the blue light beam Lb1 to generate the blue reproduction light beam Lb3.

  Here, when recording and reproducing the recording mark RM, it is necessary to strictly correct the aberration caused by the thickness of the cover layer. However, when the optical disc is tilted, the wavefront of the light beam is affected by the tilt. Distortion occurs, and the above-described aberration cannot be corrected. In particular, in optical discs that perform multi-layer recording, the depth of each recording layer (distance from the disc surface to the recording layer) differs greatly, so wavefront distortion is more sensitive than single-layer recording and dual-layer recording discs. For this reason, there is a problem that an allowable amount with respect to tilt becomes small.

  In order to cope with such a problem, in the optical disc apparatus 20 of the present invention, a volume hologram for tilt detection is recorded on the optical disc 100 in advance, and reproduction light from the volume hologram for tilt detection is recorded at the time of data recording and reproduction. The amount of tilt of the optical disc 100 is detected based on the above, and the irradiation angle of the blue light beams Lb1 and Lb2 to the optical disc 100 is controlled based on the detection result.

(5-1) Principle of tilt correction using volume hologram First, the principle of tilt correction using the volume hologram of the present invention will be described with reference to FIG. As shown in FIG. 12A, the reference surface (for example, the surface) of the optical disc 100 is irradiated with two plane waves Lf1 and Lf2 made of laser light as recording light as shown in the figure to produce a tilt detection hologram Hv. Suppose you record. As the plane waves Lf1 and Lf2, for example, a blue laser having the same wavelength 405 [nm] as the blue light beams Lb1 and Lb2 is used so that the recording layer 101 of the optical disc 100 reacts to change the refractive index. As long as the tilt detection hologram Hv can be formed on the recording layer 101, laser light of other wavelengths may be used.

  The position for recording the tilt detection hologram Hv may overlap the recording mark RM made of a minute hologram. However, in order to avoid the deterioration of the reproduction signal from the recording mark RM as much as possible, the position for tilt detection is used. It is desirable that the hologram Hv and the recording mark RM are recorded in separate areas.

  When one of the plane waves Lf1 and Lf2 is irradiated onto the tilt detection hologram Hv recorded on the optical disc 100 in this way, a plane wave is generated from the tilt detection hologram Hv. For example, as shown in FIG. 12B, when the plane wave Lf1 is irradiated, the reproduction light Lf3 composed of the plane wave is generated.

  The reproduction light intensity (that is, the hologram diffraction efficiency) of the reproduction light Lf3 becomes maximum when the incident angle of the plane wave Lf1 at the time of recording and the plane wave Lf1 at the time of reproduction coincides with the optical disc 100, and the reproduction depends on the difference between these angles. The light intensity decreases monotonously. In particular, it is known that when the difference in the incident angle of the plane wave occurs in the in-track direction (the plane direction in which the plane waves Lf1 and Lf2 are stretched), the reproduction light intensity rapidly decreases.

  Therefore, if the tilt of the optical disc 100 is controlled so as to keep the reproduction light intensity from the tilt detection hologram Hv at a maximum, the attitude of the optical disc 100 with respect to the plane wave Lf1 when the tilt detection hologram Hv is recorded can be accurately reproduced. Thus, the tilt of the optical disc 100 can be corrected.

  In general, in an optical disc manufactured by injection molding of plastic such as polycarbonate, there is often a problem in that the disc is warped in the radial direction (radial direction). On the other hand, there is little warping that causes a problem in the tangential direction (rotation direction) of the disk. Therefore, in a flat state where the optical disc 100 is not warped, if the tilt detection hologram Hv is recorded with the in-track direction coincident with the radial direction of the disc, the reproduction light from the tilt detection hologram Hv is recorded. The recording mark RM can be recorded and reproduced while maintaining the optical disc 100 in an ideal posture based on the reproduction light intensity of Lf3.

  In order to record the tilt detection hologram Hv on the flat optical disc 100, it is desirable to perform it at the earliest possible time before the influence of stress remaining in the disc, moisture absorption, or the like occurs. For this reason, when the optical disc 100 is first mounted on the optical disc apparatus 20, the optical disc apparatus 20 may record the tilt detection hologram Hv. However, the tilt detection hologram Hv is recorded when the optical disc 100 is manufactured. Is ideal.

  The concept of tilt correction using such a tilt detection hologram Hv is shown in FIG. Three tilt detection holograms Hv 1, Hv 2, and Hv 3 arranged in the radial direction of the optical disc 100 are recorded at two positions symmetrical with respect to the center of the optical disc 100. Then, a plane wave Lf1 is irradiated to the tilt detection hologram Hv (here, Hv2) in the vicinity of the recording mark RM to be recorded or reproduced, and based on the signal level of the reproduction light Lf3 generated from the tilt detection hologram Hv2. If the attitude of the optical disc 100 is controlled, even if a warp occurs in the radial direction of the optical disc 100 after recording the tilt detection hologram Hv, the recording mark RM can be recorded and reproduced locally in the vicinity of each tilt detection hologram Hv. On the other hand, an optimal disk posture can be realized.

  The number of tilt detection holograms Hv provided on the optical disc 100 may be arbitrarily determined, but the tilt correction can be performed with finer accuracy as the number increases. However, if the number of tilt detection holograms Hv is increased, the area for recording the recording marks RM decreases, and the recording density of the entire optical disc 100 decreases.

  Next, a control error of tilt correction of the optical disc 100 using the tilt detection hologram Hv composed of the volume hologram described above will be considered. When the disc incidence angle difference Δθ in the in-track direction of the plane wave Lf1 during recording and reproduction reaches a certain value, the diffraction efficiency of the volume hologram becomes completely zero (that is, the light quantity of the reproduction light Lf3 becomes zero). At this time, the value of Δθ is obtained by the following equation (8).

  Here, λ is the recording / reproducing wavelength, L is the disc thickness, and θ is the disc incident angle of the plane wave Lf1 during recording. For example, when λ = 407 [nm], L = 1 [mm], and θ = 45 °, Δθ = 0.016 °.

  Therefore, the tilt correction method described above makes it possible to keep the tilt error in the disk radial direction within 0.016 °. Thereby, the laser beam for recording and reproducing the recording mark RM is always incident on the optical disc 100 at an angle of 90 ± 0.016 °. It can be said that this error is sufficiently small for a minute hologram recording / reproducing system having a recording medium tilt tolerance equivalent to that of a conventional optical disk system.

  In the above, the method of controlling the disk attitude so that the reproduction light intensity from the tilt detection hologram Hv maintains the maximum value as the principle of tilt correction by the volume hologram has been described. In this case, the recording mark RM is recorded or reproduced. However, it is difficult to control the posture in real time. Therefore, when the optical disc 100 is mounted on the optical disc 20, the radial tilt amount at each radial position is measured based on the reproduction light intensity of each tilt detection hologram Hv, and between the tilt detection holograms Hv. The radial tilt amount is obtained by linear interpolation from the measured radial tilt amount, and the radial tilt amount at each radial position is stored as a function of the radial position. At the time of recording and reproduction, the disk attitude may be controlled based on the stored value.

(5-2) Tilt Correction of Optical Disc in Optical Disc Device of Present Invention Next, a tilt correction method of the optical disc 100 actually used in the optical disc device 20 of the present invention will be described in detail. In this case, each tilt detection hologram Hv is angle-multiplexed and recorded so that the attitude control of the optical disc 100 can be performed in real time while recording or reproducing the recording mark RM.

  That is, as shown in FIG. 14, when the tilt detection hologram Hv is recorded on the optical disc 100, the disc incident angles of the two plane waves Lf1 and Lf2 are always kept the same with respect to the disc surface normal, The tilt detection hologram Hv is recorded by changing both in the in-track direction (that is, in the radial direction) by ± Δθ. Therefore, the disc incident angles of the plane waves Lf1 and Lf2 at a certain time are θ, the disc incident angles at a certain time are θ + Δθ, and the disc incident angles at a certain time are θ−Δθ, respectively.

  Thus, the optical disc 100 is formed with a tilt detection hologram Hva formed with a plane wave with an incident angle θ + Δθ, a tilt detection hologram Hvb formed with a plane wave with an incident angle θ−Δθ, and a plane wave with an incident angle θ. The tilt detection hologram Hvc is angularly multiplexed in the radial direction and recorded. Note that Δθ, which is the deflection angle of the plane waves Lf1 and Lf2, is obtained when a reproduction signal is obtained from the tilt detection hologram Hv in a state where the disk incident angle of the plane wave Lf1 continuously changes as shown in FIG. It is necessary to set so that there is no state in which the reproduction light intensity becomes zero. Specifically, it is desirable that the angle selectivity of the tilt detection hologram Hv is not higher than that.

  With respect to the optical disc 100 on which the tilt detection hologram Hv is angle-multiplexed recorded in this way, the optical disc apparatus 20 detects the tilt amount by the tilt detection optical system 90 shown in FIG. In other words, the laser diode 91 of the tilt detection optical system 90 can emit laser light having the same wavelength as that used when forming the tilt detection hologram Hv. The tilt detection optical system 90 converts the laser light, which is the divergent light emitted from the laser diode 91, into parallel light by the collimator lens 92 and irradiates the optical disc 100 as a plane wave Lf1. The tilt detection optical system 90 irradiates the two-detector 93 for tilt detection with the reproduction light Lf3 generated by irradiating the tilt detection hologram Hv with the plane wave Lf1.

  The two-divided photodetector 93 is divided into two light receiving surfaces, a first light receiving surface 93A and a second light receiving surface 93B, and generates detection signals STa and STb in accordance with the detected light amounts, respectively. It supplies to the part 23 (FIG. 4). This two-divided photodetector 93 is obtained from a tilt detection hologram Hva formed by a plane wave having an incident angle θ + Δθ in a state where the incident angle of the plane wave Lf1 with respect to the optical disc 100 in the reference posture (that is, a state where no tilt is generated) is θ. The reproduction light Lf2a is received by the first light receiving surface 93A, and the reproduction light Lf2b from the tilt detection hologram Hvb formed by the plane wave having the incident angle θ−Δθ is received by the second light receiving surface 93B, and further incident. The position is determined so that the reproduction light Lf2c from the tilt detecting hologram Hvc formed by the plane wave of the angle θ is received in the dead zone at the boundary between the first light receiving surface 93A and the second light receiving surface 93B.

  When the incident angle of the plane wave Lf1 with respect to the optical disc 100 changes from θ, the irradiation light amounts of the reproduction light Lf2a, reproduction light Lf2b, and reproduction light Lf2c to the two-divided photodetector 93 change, but the respective irradiation positions hardly change.

  Based on the following equation (9), the signal processing unit 23 subtracts the detection signal STb based on the received light amount of the first light receiving surface 93A from the detected signal STb based on the received light amount of the second light receiving surface 93B, and tilts it. An error signal STLEr is generated.

  FIG. 16 shows the value of the tilt error signal STLEr corresponding to the change in the incident angle of the plane wave Lf1 with respect to the optical disc 100. The radial error does not occur in the optical disc 100 and the tilt error signal STLEr is in the state where the incident angle of the plane wave Lf1 is θ. The value is 0 and exhibits an S-shaped curve that changes substantially linearly in the range before and after (± Δθ). In this range, the tilt error signal STLEr represents the radial tilt amount of the optical disc 100.

  Then, by tilting the optical disc 100 so that the value of the tilt error signal STLEr becomes 0 (that is, keeping the incident angle of the plane wave Lf1 with respect to the optical disc 100 at θ), the radial tilt generated in the optical disc 100 is corrected and recorded. The incident angle of the blue light beam Lb1 (also Lb2 at the time of recording) at the position where the mark RM is recorded or reproduced can be maintained correctly.

  Next, a specific method for tilting the optical disc 100 by the optical disc apparatus 20 will be described. As shown in FIG. 4, the spindle motor 24 of the optical pickup 20 is mounted on a gonio stage 24 </ b> A that tilts the spindle motor 24 in two orthogonal directions in accordance with a tilt control signal from the drive control unit 22.

  The drive control unit 22 generates a tilt control signal based on the tilt error signal STLEr and drives the gonio stage 24A, thereby correcting the radial tilt of the optical disc 100 and always performing recording or reproduction in an appropriate state. .

(6) Operation and Effect In the configuration described above, the tilt detection hologram Hv made of a volume hologram is recorded in an angle-multiplexed manner in the radial direction on the optical disc 100 that records the recording mark RM made of a minute hologram.

  The optical disk device 20 irradiates a plane wave Lf1 in the vicinity of the recording mark RM during recording and reproduction with respect to the optical disk 100, and based on the light quantity of the reproduction light Lf3 emitted from the tilt detection hologram Hv by the plane wave Lf1, A tilt error signal STLEr indicating the tilt amount is generated.

  Then, the optical disc apparatus 20 controls the gonio stage 24A in accordance with the tilt error signal STLEr to tilt the optical disc 100, thereby eliminating the influence of the tilt of the optical disc 100 at the recording and reproduction positions of the recording mark RM. The recording mark RM can be recorded in a good state, and a good reproduction detection signal SDp can be obtained from the recording mark RM by eliminating the influence of tilt even during reproduction.

  In particular, the reproduction light Lf3 from the angle-detected hologram Hv for tilt detection is received by the two-divided photodetector 93, and the difference between the detection signals STa and STb obtained from the first light receiving surface 93A and the second light receiving surface 93B, respectively. By generating the tilt error signal STLEr, it is possible to generate the S-shaped tilt error signal STLEr with good signal characteristics before and after the disc tilt, which is the control target point, is 0, and more reliably the optical disc 100. The tilt can be corrected.

  Since the recording and reproducing performance of the optical disk device 20 can be improved by correcting the tilt of the optical disk 100, the recording density of the optical disk 100 and the recording / reproducing speed are improved accordingly. The performance of the device 100 can be further improved.

  According to the above configuration, the tilt amount of the optical disc 100 is detected from the tilt detection hologram Hv recorded on the optical disc 100, and the tilt of the optical disc 100 is corrected according to the detected amount. The recording marks can be recorded and reproduced with certainty on the optical disc 100 without providing the recording medium.

(7) Other Embodiments In the above-described embodiment, when the tilt detection hologram Hv is recorded on the optical disc 100, the in-track directions Dint (FIG. 12A) of the plane waves Lf1 and Lf2 are applied to the optical disc 100. The tilt detection hologram Hv is angle-multiplexed and recorded in the radial direction so as to coincide with the radial direction, and the radial tilt of the optical disc 100 is corrected according to the tilt error signal STLEr based on the tilt detection hologram Hv. However, the present invention is not limited to this, and as shown in FIG. 17, the in-track direction Dint of the plane waves Lf1 and Lf2 is made to coincide with the rotation direction of the optical disc 100 (that is, the tangential direction). Hologram Hv is angle-multiplexed in the tangential direction and recorded. The tangential tilt of the optical disc 100 is corrected in accordance with the tilt error signal STLEr based on the tilt detection hologram Hv, and the tilt detection hologram Hv is angle-multiplexed in both the radial direction and the tangential direction. In this case, both the radial tilt and the tangential tilt of the optical disc 100 may be corrected according to the tilt error signal STLEr based on the tilt detection hologram Hv.

  In the above-described embodiment, the two-divided photodetector 93 is used as the light receiving means for receiving the reproduction light from the tilt detecting hologram Hv and detecting the tilt. However, the present invention is not limited to this. The tilt may be detected by receiving reproduction light from the tilt detecting hologram Hv using various other light receiving elements.

  As such a light detector for tilt detection, for example, an optical position sensor (hereinafter referred to as PSD) or a one-dimensional CCD (Charge Coupled Device) can be used. This PSD is a sensor that can determine the position of the center of gravity of the light amount of a light spot, and a material that generates a voltage corresponding to the amount of received light is uniformly applied to the light receiving surface thereof. When light is incident on the light receiving surface of the PSD, a voltage is generated at the irradiation position, and the potential at a location away from the irradiation position is decreased by the resistance of the light receiving surface material. The voltage ratio at both ends changes, whereby the position of the center of gravity of the light amount of the spot can be obtained as a voltage. In this way, the voltage output from the PSD is used as the tilt error signal STLEr, and the optical disc 100 is tilted so that the value of the tilt error signal STLEr coincides with the value when the optical disc 100 has no radial tilt. Thus, the tilt generated in the optical disc 100 can be corrected.

  In the above-described embodiment, the tilt of the optical disc 100 is corrected by tilting the entire optical disc 100 according to the tilt error signal STLEr based on the tilt detection hologram Hv. However, the present invention is not limited to this, and the irradiation angle of the recording light or the reference light to the optical disc 100 may be changed while the angle of the optical disc 100 is fixed. As a method for changing the irradiation angle, various methods such as a method of tilting the objective lens and a wavefront control using a spatial phase control element after shaping an intensity distribution using an anamorphic lens can be applied.

  In the above-described embodiment, the case where the present invention is applied to the optical disc apparatus 20 using a double-sided irradiation type hologram that irradiates light beams from both sides of the optical disc 100 to form a standing wave has been described. The present invention is not limited to this, and the present invention can also be applied to an optical disk apparatus using a single-sided irradiation type hologram in which an irradiated light beam is reflected by a reflective film provided on the optical disk to form a standing wave.

  In the above-described embodiment, the recording beam RM is formed by using a light beam for controlling the position of the objective lens 38 (referred to as a position control light beam) as a red light beam having a wavelength of about 660 [nm]. The case where the light beam for this purpose (referred to as the recording light beam) is a blue light beam having a wavelength of about 405 [nm] has been described, but the present invention is not limited to this, and the position control light beam and the recording light Each beam may have an arbitrary wavelength.

  In the above-described embodiment, the case where the tilt detection hologram Hv composed of a volume hologram is recorded by the interference of the two plane waves Lf1 and Lf2 is described. However, the present invention is not limited to this, and the interference between the plane wave and the spherical wave is performed. The tilt detection hologram Hv formed of a volume hologram may be recorded by the method, and the tilt detection hologram Hv may be reproduced by a plane wave. As the spherical wave in this case, any one of the blue light beams Lb1 and Lb2 that are spherical waves for recording the recording mark RM may be used.

  For example, as shown in FIG. 18, a tilt detection hologram Hv is recorded in advance on the optical disc 100 by the interference of the plane wave Lf1 and the blue light beam Lb1, and the optical disc 100 is recorded and reproduced with respect to the optical disc 100. The tilt detection hologram Hv may be reproduced by irradiating the plane wave Lf1. When the tilt detection hologram Hv is recorded on the optical disc 100, the above-described angle hologram recording of the volume hologram can be performed by changing the incident angle of the blue light beam Lb1 with, for example, a galvanometer mirror.

  Furthermore, in the above-described embodiment, a case where the present invention is applied to the optical disc 100 and the optical disc apparatus 20 that record the recording mark RM made of a minute hologram by causing the blue light beams Lb1 and Lb2 made of two spherical waves to interfere with each other. As described above, the present invention is not limited to this, and can be applied to an optical disc and an optical disc apparatus using various other holograms.

  For example, in recent years, a hologram is recorded in advance on the entire recording layer of an optical disk using opposed plane waves, and information is recorded by destroying the hologram by focusing the laser beam on the focal position of the spherical wave. Type optical disks and optical disk devices have been proposed (RR McLeod, AJ Daiber, ME McDonald, SL Sochava, T. Honda, TL Robertson, T. Slagle, L. Hesselink, Technical Digest of ISOM / ODS, MB1, (2005 )), The present invention is also applicable to this type of optical disc and optical disc apparatus.

  As described above, in a negative type optical disc, a hologram formed by plane waves is formed on the entire recording layer, so that the hologram is irradiated with plane waves and the tilt of the optical disc is corrected based on the amount of reproduced light. Can do.

  The present invention can be used in an optical disc apparatus that records a large amount of music content, video content, or various data on an optical disc as a recording medium.

It is a basic diagram which shows the structure of the conventional standing wave recording-type optical disk apparatus. It is a basic diagram which shows the mode of formation of a hologram. It is a basic diagram which shows the structure of the optical disk by one Embodiment of this invention. 1 is a schematic diagram illustrating a configuration of an optical disc device according to an embodiment of the present invention. It is a basic diagram which shows the external appearance structure of an optical pick-up. It is a basic diagram which shows the structure of an optical pick-up. It is a basic diagram which shows the optical path of a red light beam. It is a basic diagram which shows the structure of the detection area | region in a photodetector. It is a basic diagram which shows the optical path (1) of a blue light beam. It is a basic diagram which shows the optical path (2) of a blue light beam. It is a basic diagram which shows the structure of the detection area | region in a photodetector. It is a basic diagram with which it uses for description about recording and reproduction | regeneration of the volume hologram with respect to an optical disk. It is a basic diagram which shows the concept of the tilt correction using a volume hologram. It is an approximate line figure used for explanation about angle multiplexing recording of a hologram for tilt detection. It is a characteristic curve figure which shows the reproduction light intensity distribution of a volume hologram. It is a characteristic curve figure which shows a tilt error signal. It is an approximate line figure used for explanation about angle multiplexing recording of a hologram for tilt detection of other embodiments. It is a basic diagram which shows the recording of the volume hologram of other embodiment.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 20 ... Optical disk apparatus, 21 ... Control part, 22 ... Drive control part, 23 ... Signal processing part, 26 ... Optical pick-up, 30 ... Guide surface position control optical system, 31, 51 ... Laser diode, 37, 55, 58, 72 ... Polarizing beam splitter, 38, 79 ... Objective lens, 38A, 79A ... Actuator, 43, 64, 82 ... Photo detector, 50 ... Guide surface information optical system, 56 ... 1 / 4 wavelength plate, 57 ... movable mirror, 60, 75 ... relay lens, 61, 76 ... movable lens, 70 ... recording light irradiation surface optical system, 71 ... shutter, 78 ... galvanometer mirror, 90 ... ... Tilt detection optical system, 100 ... optical disc, 101 ... recording layer, 102, 103 ... substrate, 104 ... reflection / transmission film, Lr1 ... red light beam, Lr2 ... red reflected light beam Lb0, Lb1, Lb2 ...... blue light beam, Lb3 ...... blue reproduction light beam, Fr, Fb1, Fb2 ...... focus, RM ...... recording mark.

Claims (9)

In an optical disc apparatus corresponding to an optical disc for recording a recording mark using a hologram in a disc-shaped volume type recording medium,
Plane wave irradiation means for irradiating a volume hologram pre-recorded on the optical disc with a light beam of plane wave;
A light receiving means for receiving a reproduction light generated from the volume hologram by irradiating the volume hologram with the plane wave, and generating a light reception signal corresponding to the amount of received light;
A tilt error signal generating means for generating a tilt error signal indicating the tilt of the optical disc from the received light signal;
An optical disc apparatus comprising: tilt correction means for correcting the tilt of the optical disc based on the tilt error signal. The volume hologram includes a first volume hologram formed so that the amount of reproduction light is maximized when the optical disc is tilted in a predetermined direction, and the amount of reproduction light when the optical disc is tilted in a direction opposite to the predetermined direction. The optical disk device according to claim 1, further comprising: a second volume hologram formed so as to be maximized. The light receiving means includes a first light receiving region formed to receive the reproduction light from the first volume hologram, and a second light reception formed to receive the reproduction light from the second volume hologram. And having an area
The tilt error signal generation unit generates the tilt error signal using a difference between the first light reception signal generated by the first light reception region and the second light reception signal generated by the second light reception region. The optical disk apparatus according to claim 2, wherein The recording mark is a micro-hologram formed by irradiating the first and second spherical wave lights at the same focal position to form a standing wave. Optical disk device. The optical disk apparatus according to claim 4, wherein the volume hologram is formed by irradiating and interfering with first plane wave light and second plane wave light. The optical disk apparatus according to claim 4, wherein the volume hologram is formed by irradiating and interfering with plane wave light and the first spherical wave light. The optical disc apparatus according to claim 1, wherein the recording mark is formed by destroying the volume hologram formed in the optical disc. In a disc tilt correction method of an optical disc apparatus corresponding to an optical disc for recording a recording mark using a hologram in a disc-shaped volume recording medium,
A volume hologram recorded in advance on the optical disc is irradiated with a light beam having a plane wave, and the volume hologram is irradiated with the plane wave to receive reproduction light generated from the volume hologram, and according to the amount of received light. A first control step for generating a received light signal;
A second control step of generating a tilt error signal indicating the tilt of the optical disc from the light reception signal;
A disc tilt correction method comprising: a third control step of correcting the tilt of the optical disc based on the tilt error signal. In an optical disc corresponding to an optical disc for recording a recording mark using a hologram in a disc-shaped volume type recording medium,
A first volume hologram formed so that the amount of reproduced light is maximized when the optical disc is tilted in a predetermined direction;
An optical disc comprising: a second volume hologram formed so that a reproduction light amount is maximized when the optical disc is tilted in a direction opposite to the predetermined direction.

Images