JP4784473B2 - Optical disc apparatus, disc tilt correction method, and optical disc - Google Patents

Description

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

  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, Jeju Korea RR Mcleod er al., “Microholographic multilayer 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, 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, since the depth of each recording layer (distance from the disc surface to the recording layer) is greatly different, there are many factors that cause wavefront distortion compared to a single-layer recording or a dual-layer recording disc, For this reason, there is a problem that an allowable amount with respect to tilt is reduced.

  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 this problem, the optical disc apparatus of the present invention is a micro hologram formed corresponding to information recorded on an optical disc in a data area provided in a predetermined sector which is a divided recording unit inside a track. In the tilt servo area provided in the sector, in the tilt servo area, the first tilt detection micro hologram formed in advance so that the amplitude of the reproduction signal is maximized when the optical disk is tilted in a predetermined direction, and in the tilt servo area A second tilt detection micro-hologram formed in advance so that the amplitude of the reproduction signal is maximized when the optical disk is tilted in the reverse direction of the predetermined direction, and the first tilt detection micro-hologram and the second tilt Each detection hologram is tilted in the opposite direction with respect to the reference plane of the optical disk. Irradiating means for irradiating a light beam to the optical disc is a recording mark formed on the optical disc, the first tilt detection micro hologram and the second tilt is reflected by the detection micro-hologram light beam received to the reproduction signal , A first reproduction signal amplitude based on the light beam reflected by the first tilt detection micro-hologram, and a second light beam based on the light beam reflected by the second tilt detection micro-hologram. A tilt error signal generating means for generating a tilt error signal indicating the tilt of the optical disc using a difference from the amplitude of the reproduction signal of the optical disc, and a tilt correcting means for correcting the tilt of the optical disc based on the tilt error signal. did.

  By correcting the tilt of the optical disc by generating a tilt error signal based on the reflected light from the minute hologram for tilt detection recorded in advance on the optical disc, the tilt can be corrected without providing a separate tilt detecting means such as a tilt sensor. Thus, information can be recorded and reproduced more reliably.

  Then, as the tilt detection micro-hologram, the first tilt detection micro-hologram formed so that the amplitude of the reproduction signal is maximized when the optical disc is tilted in a predetermined direction, and the optical disc is reproduced when the optical disc is tilted in the reverse direction of the predetermined direction. The second tilt detection micro-hologram formed so as to maximize the signal amplitude is recorded, and the amplitude of the first reproduction signal based on the light beam reflected by the first tilt detection micro-hologram By generating the tilt error signal using the difference from the amplitude of the second reproduction signal based on the light beam reflected by the second tilt detection micro-hologram, the disc tilt as the control target point is zero. S-shaped tilt error signal with good signal characteristics before and after the state can be generated, and the tilt of the optical disc can be corrected more reliably. That.

In the disc tilt correction method of the present invention , a recording mark made of a minute hologram formed corresponding to information recorded on an optical disc in a data area provided in a predetermined sector which is a divided recording unit inside a track. In the tilt servo area provided in the sector, the first minute hologram for tilt detection that is formed in advance so that the amplitude of the reproduction signal is maximized when the optical disk is tilted in a predetermined direction, and the optical disk in the tilt servo area. A second tilt detection micro-hologram formed in advance so that the amplitude of the reproduction signal is maximized when tilted in the reverse direction of the predetermined direction, and the first tilt detection micro-hologram and the second tilt detection micro-hologram. An optical device in which the holograms are inclined in the opposite direction with respect to the reference plane of the optical disc. A first control step of irradiating a light beam to the disk, and receives the recording mark formed on the optical disc, the light beam reflected by the first tilt detection micro hologram and the second tilt detection micro hologram reproduction A second control step for generating a signal, an amplitude of the first reproduction signal based on the light beam reflected by the first tilt detection micro-hologram, and a light beam reflected by the second tilt detection micro-hologram A third control step for generating a tilt error signal indicating the tilt of the optical disc using the difference from the amplitude of the second reproduction signal based on the fourth control, and a fourth control for correcting the tilt of the optical disc based on the tilt error signal Steps.

  By correcting the tilt of the optical disk by generating a tilt error signal based on the reflected light from the minute hologram for tilt detection recorded in advance on the optical disk, the tilt can be corrected without providing a separate detecting means such as a tilt sensor. Thus, information can be recorded and reproduced more reliably.

In the optical disc of the present invention, in a data area provided in a predetermined sector which is a divided recording unit inside the track, a recording mark made up of a minute hologram formed corresponding to information recorded on the optical disc, and the sector In the tilt servo area, the first fine hologram for tilt detection formed in advance so that the amplitude of the reproduction signal is maximized when the optical disk is tilted in the predetermined direction , and the optical disk is moved in the predetermined direction in the tilt servo area. A second tilt detection micro-hologram formed in advance so that the amplitude of the reproduction signal is maximized when tilted in the reverse direction, and the first tilt detection micro-hologram and the second tilt detection micro-hologram are: Each of them is formed to be inclined in the opposite direction with respect to the reference surface of the optical disk .

  By recording a tilt detection micro-hologram on the optical disc in advance, a tilt error signal can be generated based on the reflected light from the tilt detection micro-hologram to correct the tilt of the optical disc.

  According to the present invention, a tilt detection micro-hologram is recorded in advance on an optical disk that records a micro-hologram in a disk-shaped volume recording medium, and tilt is performed based on reflected light from the tilt detection micro-hologram. An optical disc apparatus that corrects tilt without providing a separate tilt detector by generating an error signal and correcting tilt of the optical disc, and can record and reproduce information more reliably with a simple configuration. A disc tilt correction method 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. (i.e. the substrate 103 side) is focused at a position corresponding to. 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 which are both converged light overlap and become equal to or higher than the predetermined intensity. 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) ).

The height RMh of the recording mark RM can be obtained by the following equation (2), where n is the refractive index of the recording layer 101 .

  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.

(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. It is comprised by.

(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.

  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 controller 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.

  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 in accordance with 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.

  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 detection of the 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 and records the recording mark RM during recording. 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, the recording mark RM formed on the optical disc 100 by the optical disc apparatus 20 is a micro-hologram as described above, and has a feature that the angle dependency is extremely high. That is, when the recording mark RM is irradiated with the light beam with the irradiation angle θ as shown in FIG. 12A, the signal amplitude W of the reproduction detection signal SDp shows a change as shown in FIG. Therefore, the irradiation angle θ with respect to the recording mark RM, that is, the tilt amount of the optical disc can be recognized based on the reproduction signal amplitude W from the recording mark RM.

  The optical disk device 20 of the present invention utilizes such angle dependency of a minute hologram, records a minute hologram for tilt detection on the optical disk 100 in advance, and reproduces a reproduction signal from the minute hologram at the time of data recording and reproduction. The tilt amount of the optical disc 100 is detected based on the amplitude W, and the irradiation angle of the blue light beams Lb1 and Lb2 on the optical disc 100 is controlled based on the detection result.

  However, when detecting the amount of tilt using such a single minute hologram, it is necessary to perform servo control so as to maintain the maximum value of the reproduction signal amplitude W (so-called maximum value detection), and detection at the optimum point. Since the sensitivity is zero, learning control is required, and it is difficult to increase the control accuracy and time constant.

  Therefore, in the optical disc apparatus 20 of the present invention, the tilt amount of the optical disc 100 is detected more easily and reliably by using two types of micro holograms for tilt detection.

  That is, as shown in FIG. 13, in each sector Sec of the track formed on the recording layer 101 of the optical disc 100, a tilt servo area Ta for detecting the tilt amount of the optical disc 100 is provided at the head, and the tilt servo The area behind the area Ta is defined as a data area Da for recording the recording mark RM.

  The tilt servo area Ta is further divided into two, a plus pattern area Ta1 and a minus pattern area Ta2. In the plus pattern area Ta1 and the minus pattern area Ta2, a plurality of plus tilt marks TM1 and minus tilt marks TM2 are recorded in advance when the optical disc 100 is manufactured.

  The tilt mark TM (plus tilt mark TM1 and minus tilt mark TM2) is a minute hologram for tilt detection formed by the same recording method as the recording mark RM, and can be detected by the optical disc apparatus 20, but the optical disc 100 The recording mark RM differs from the recording mark RM in that it is recorded with a predetermined tilt angle (referred to as an azimuth angle) with respect to the disk surface as the reference surface.

  That is, the recording mark RM for data recording is formed by irradiating the blue light beams Lb1 and Lb2 perpendicularly to the surface of the optical disc 100 during recording (irradiation angle 0 °), and the irradiation angle 0 during reproduction. Whereas the blue light beam Lb1 is irradiated at an angle, as shown in FIG. 14A, the plus tilt mark TM1 and the minus tilt mark TM2 each have a + radial azimuth angle with respect to the radial direction (radial direction) of the optical disc. And -radial azimuth angles.

  As described above, since the micro hologram has angle dependency, the plus tilt mark TM1 and the minus tilt mark TM2 can be regarded as having optical characteristics in the respective azimuth angle directions.

  When the light beam is irradiated with the irradiation angle θ on the plus tilt mark TM1 and the minus tilt mark TM2 having such a radial azimuth angle, the reproduction signal amplitude W1 and the reproduction signal amplitude W2 are shown in FIG. ).

  Then, in both recording and reproduction, the difference between the reproduction signal amplitude W1 and the reproduction signal amplitude W2 sequentially obtained from the tilt servo area Ta is calculated using the following equation (8), whereby the optical disc 100 which is the optimum point is calculated. It is possible to obtain a tilt error signal ETL indicating a change in an S-shaped curve having a value of 0 when the amount of tilt in the radial direction is zero.

  For example, when the optical disc 100 has a positive tilt, the reproduction detection signal SDp has a waveform as shown in FIG. 12, and the reproduction signal amplitude W1 from the plus tilt mark TM1 is the reproduction signal amplitude from the minus tilt mark TM2. A value larger than W2 is shown. If the tilt error signal ETL is generated from the reproduction signal amplitude W1 and the reproduction signal amplitude W2, and the irradiation angle of the blue light beam Lb1 on the optical disc 100 is controlled so that the tilt error signal ETL becomes zero, it is always ideal. The optical disc 100 can be recorded and reproduced with dimensions.

  In order to control the irradiation angle of the light beam with respect to the optical disc 100, a method of tilting the entire optical disc 100 together with the spindle motor 24 is reliable and easy. That is, 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 control unit 21 detects the head position of the sector Sec based on the reproduction detection signal SDp, samples and holds the reproduction signal amplitude W1 and the reproduction signal amplitude W2, and then indicates the tilt amount of the optical disc 100 using Expression ( 8 ). A tilt error signal ETL is generated and supplied to the drive control unit 22. As shown in FIG. 15, since the tilt servo areas Ta are distributed in the circumferential direction of the optical disc 100, the tilt error signal ETL is generated a plurality of times for one rotation of the optical disc 100. The drive control unit 22 generates a tilt control signal based on the tilt error signal ETL and drives the goniostage 24A, thereby correcting the tilt of the optical disc 100 and always performing recording or reproduction in an appropriate state.

  When manufacturing the optical disc 100, as a method of writing the plus tilt mark TM1 and the minus tilt mark TM2 with the azimuth angle described above, the optical disc 100 may be tilted using the gonio stage described above. You may make it irradiate a light beam with a suitable azimuth angle in the state which fixed the angle.

(6) Operation and Effect In the above configuration, with respect to the optical disc 100 used in the optical disc apparatus 20, the plus tilt mark TM1 having a positive azimuth angle having optical characteristics in different directions at the head region of each sector, and A minus tilt mark TM2 having a minus azimuth angle is recorded in advance.

  When recording or reproducing the optical disc 100 having the tilt servo area Ta for tilt detection, the control unit 21 of the optical disc apparatus 20 reproduces the plus tilt mark TM1 and the minus tilt mark TM2 of the tilt servo area Ta. From the difference between the reproduction signal amplitudes W1 and W2 of the detection signal SDp, a tilt error signal ETL indicating the tilt amount of the optical disc 100 at the light beam irradiation position is generated.

  Then, the control unit 21 of the optical disc apparatus 20 corrects the tilt of the optical disc 100 based on the tilt error signal ETL, thereby eliminating the influence of the tilt during recording and recording the recording mark RM in a good recording state. In addition, it is possible to obtain an excellent reproduction detection signal SDp from the recording mark RM by eliminating the influence of tilt even during reproduction.

  In particular, by taking the difference between the reproduction signal amplitudes W1 and W2 of the reproduction detection signal SDp obtained by reproducing the plus tilt mark TM1 and the minus tilt mark TM2, before and after the disc tilt that is the control target point is zero. An S-shaped tilt error signal ETL with good signal characteristics can be generated, and the tilt of the optical disc 100 can be more reliably 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 servo area Ta provided on the optical disc 100, and the tilt of the optical disc 100 is corrected accordingly. Without providing, recording marks can be reliably recorded and reproduced on the optical disc 100.

(7) Other Embodiments In the above-described embodiment, the tilt servo area Ta is provided at the head of each sector sec. However, the present invention is not limited to this, and the tilt of the optical disc 100 is appropriately adjusted. The number of tilt servo areas Ta may be increased or decreased as appropriate within the detectable range.

  For example, tilt servo areas Ta are provided in three tracks on the inner and outer circumferences of the optical disc 100 and in the middle thereof, and the tilt error signal ETL is generated using the reproduction signal amplitudes W1 and W2 from the tilt servo areas Ta. In this way, the tilt of the optical disc 100 can be corrected.

  In the above-described embodiment, plus tilt mark TM1 and minus tilt mark TM2 having radial azimuth angles of + and-, respectively, are recorded in the tilt servo area Ta of the optical disc 100, and the plus tilt mark TM1 and minus tilt mark TM1 are recorded. Although the radial tilt of the optical disc 100 is corrected based on the mark TM2, the present invention is not limited to this, and two tilt marks each having a radial angle in the tangential direction of + and − are provided in the tilt servo area Ta. The tangential tilt of the optical disc 100 is corrected based on the tilt mark, and both the radial tilt and the tangential tilt are corrected by using these tilt marks together. Also good.

  In the above-described embodiment, the optical disc 100 is tilted according to the azimuth angle of the recording mark RM, so that the azimuth angle is given to the recording mark RM and the reference light is irradiated according to the azimuth angle of the recording mark RM. However, the present invention is not limited to this, and the irradiation angle of the recording light or the reference light on 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.

  Further, in the above-described embodiment, the case where the present invention is applied to the optical disk apparatus 20 using the double-sided irradiation type hologram that irradiates light beams from both surfaces of the optical disk 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. As a method for recording information on the optical disc 100, in addition to the above-described micro-hologram, various other methods such as a mark for recording information by changing the reflectance can be used.

  Further, in the above-described embodiment, a 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.

  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 an approximate line figure used for explanation of angle dependence of a minute hologram. It is an approximate line figure used for explanation of arrangement of a tilt mark, and reproduction signal amplitude. It is an approximate line figure used for explanation of a tilt mark and reproduction signal amplitude. It is an approximate line figure used for explanation of distributed arrangement of a tilt servo area.

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, 100 ... ... optical disc, 101 ... recording layer, 102, 103 ... substrate, 104 ... reflective / transmissive 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 (5)

In a data area provided in a predetermined sector which is a divided recording unit inside the track, a recording mark made of a micro hologram formed corresponding to information recorded on the optical disc, and a tilt servo area provided in the sector In the first tilt detection micro-hologram formed in advance so that the amplitude of the reproduction signal is maximized when the optical disc is tilted in a predetermined direction, and the tilt servo area, the optical disc is in a direction opposite to the predetermined direction. A second tilt detection micro-hologram formed in advance so that the amplitude of the reproduction signal is maximized when tilted, and the first tilt detection micro-hologram and the second tilt detection micro-hologram are respectively light to the optical disc is formed to be inclined in opposite directions with respect to the reference surface of the optical disk Irradiating means for irradiating a beam over,
A light receiving means for receiving the light beam reflected by the recording mark formed on the optical disc, the first tilt detecting micro-hologram, and the second tilt detecting micro-hologram and generating a reproduction signal;
The amplitude of the first reproduction signal based on the light beam reflected by the first tilt detection micro-hologram and the second reproduction signal based on the light beam reflected by the second tilt detection micro-hologram. Tilt error signal generation means for generating a tilt error signal indicating the tilt of the optical disc using the difference between the amplitude of the optical disc,
Tilt correction means for correcting the tilt of the optical disc based on the tilt error signal;
An optical disc apparatus having The minute hologram for tilt detection is provided at a plurality of positions in the radial direction of the optical disc.
The optical disc apparatus according to claim 1. The tilt detection micro hologram is provided at the beginning of each said sector of the optical disk
The optical disc apparatus according to claim 1. In a data area provided in a predetermined sector which is a divided recording unit inside the track, a recording mark made of a micro hologram formed corresponding to information recorded on the optical disc, and a tilt servo area provided in the sector In the first tilt detection micro-hologram formed in advance so that the amplitude of the reproduction signal is maximized when the optical disc is tilted in a predetermined direction, and the tilt servo area, the optical disc is in a direction opposite to the predetermined direction. A second tilt detection micro-hologram formed in advance so that the amplitude of the reproduction signal is maximized when tilted, and the first tilt detection micro-hologram and the second tilt detection micro-hologram are respectively The optical disk is tilted in the opposite direction with respect to the reference plane of the optical disk and A first control step of irradiating over beam,
A second control step of generating a reproduction signal by receiving the light beam reflected by the recording mark, the first tilt detecting micro-hologram and the second tilt detecting micro-hologram formed on the optical disc; When,
The amplitude of the first reproduction signal based on the light beam reflected by the first tilt detection micro-hologram and the second reproduction signal based on the light beam reflected by the second tilt detection micro-hologram. A third control step for generating a tilt error signal indicating the tilt of the optical disc using a difference from the amplitude of the optical disc;
A disc tilt correction method comprising: a fourth control step of correcting the tilt of the optical disc based on the tilt error signal. In a data area provided in a predetermined sector which is a divided recording unit inside the track, a recording mark made of a micro hologram formed corresponding to information recorded on the optical disc;
A first tilt detection micro-hologram formed in advance so that the amplitude of a reproduction signal is maximized when the optical disc is tilted in a predetermined direction in a tilt servo area provided in the sector ;
In the tilt servo area, a second hologram for detecting tilt that is formed in advance so that the amplitude of the reproduction signal is maximized when the optical disk is tilted in the direction opposite to the predetermined direction.
Have
The first tilt detection micro-hologram and the second tilt detection micro-hologram are each formed by tilting in the opposite direction with respect to the reference surface of the optical disk.

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