JP2008097754A - Optical disk device, focal position control method, and volume type recording medium - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To improve recording and reproducing accuracy of information. <P>SOLUTION: Red light beams Lr1 and Lr2 are focused to target tracks of reflection transmission films 104 and 105 disposed on both surfaces of a recording layer 101 of an optical disk 100, and a distance t11 and a distance t12 are calculated by using a ratio m corresponding to the number of a mark recording layer ought to record a recording mark M are calculated. A space between the focal point Fr1 of the red light beam Lr1 and the focal point Fb1 of the blue light beam Lb1 is adjusted to the distance dt11 by moving a movable lens 61 and a space between the focal point Fr2 of the red light beam Lr2 and the focal point Fr2 of the blue light beam Lb2 is adjusted to the distance t12 by moving a movable lens 96, and thereby the focal point Fr1 and the focal point Fr2 can be aligned with the target position with good accuracy. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to an optical disc device, a focal position control method, and a volume type recording medium, and is suitable for application to an optical disc device that records a hologram on an optical disc, 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.

There has also been proposed an optical disc apparatus that uses different types of light beams for objective lens position control and information recording / reproduction (see, for example, Patent Document 1).
Y. Kasami, Y. Kuroda, K. Seo, O. Kawakubo, S. Takagawa, M. Ono, and M. Yamada, Jpn. J. Appl. Phys., 39,756 (2000) I. Ichimura et al, Technical Digest of ISOM'04, pp52, Oct. 11-15, 2005, JejuKorea RR McLeod et al., “Microholographic multilayer optical disk data storage,” Appl. Opt., Vol. 44, 2005, pp3197 JP 2004-265472 A (FIG. 2)

  By the way, it is conceivable to record and reproduce information by using an optical disc 18 as shown in FIG.

  The optical disc 18 has a configuration in which the recording layer 18C is sandwiched between the substrates 18A and 18D, and further includes a reflective / transmissive film 18B having a wavelength selectivity and a track formed between the substrate 18A and the recording layer 18C. ing. The reflection / transmission film 18B reflects the position control light beam L1 having a predetermined wavelength irradiated from the optical disc device 15 through the objective lens 16, and also records and reproduces the light beam L2 having a wavelength different from that of the position control light beam L1. It is designed to be transparent.

  By utilizing this, the optical disc device 15 detects return light reflected by the position control light beam L1 at the reflection / transmission film 18B, and position control such as focus control and tracking control of the objective lens 16 according to the detection result. The position control light beam L1 is focused on the desired track of the reflective / transmissive film 18B. The optical disk device 15 controls the position of the objective lens 17 in conjunction with the objective lens 16.

  In this state, the optical disc apparatus 15 focuses the recording / reproducing light beam L2 on the desired position U1 in the recording layer 18C via the objective lens 16, and further records the recording light beam L3 on the desired position via the objective lens 17 during recording. By focusing on U1, information (that is, recording mark RM, etc.) is recorded or reproduced at the desired position U1.

  By the way, in the optical disk device 15, the optical disk 18 may have an inclination (so-called skew) with respect to the optical disk device 15 due to factors such as warpage and surface blurring of the optical disk 18.

  In this case, as shown in FIG. 4 corresponding to FIG. 3, even if the optical disc apparatus 15 focuses the position control light beam L1 on the desired track of the reflection / transmission film 18B, the recording / reproducing light beam L2 is moved into the recording layer 18C. In this case, information (record mark RM, etc.) cannot be recorded at the desired position U1, or information at the desired position U1 cannot be reproduced. .

  As described above, the optical disk device 15 has a problem that the information recording / reproducing accuracy may be lowered when the optical disk 18 is tilted.

  The present invention has been made in consideration of the above points, and an object of the present invention is to propose an optical disc apparatus, a focus position control method, and a volume type recording medium that can improve information recording / reproducing accuracy.

  In order to solve such a problem, in the optical disc apparatus of the present invention, the first and second lights emitted from the same light source are respectively irradiated from both sides of the disc-shaped volume type recording medium so as to have the same focal position. In the optical disc apparatus that records the standing wave as a recording mark or irradiates the focal position with the first light from one surface of the volume recording medium and reproduces the recording mark, a position detection pattern provided on the volume recording medium The first position detection light is irradiated to the first reflection layer among the plurality of reflection layers formed with the first position detection light on the first reflection layer based on the reflected light. First position control means for focusing on one target position, and the second position detection light is irradiated to the second reflection layer among the plurality of reflection layers, and the second position detection light is applied based on the reflected light. Position detection light is applied to the second reflective layer Based on the second position control means for focusing on the second target position corresponding to the first target position, the position control result by the first position control means and the position control result by the second position control means, Focus position setting means for setting the focus positions of the first and second lights with reference to an imaginary line connecting the first and second target positions in the volume type recording medium is provided.

  As a result, the optical disc apparatus of the present invention can reliably recognize the first and second target positions that serve as indices for determining the focal positions of the first and second lights. By using the virtual line connecting the target positions as a reference, the focal positions of the first and second lights can be adjusted to the desired position reliably and accurately.

  In the focal position control method of the present invention, the first and second lights emitted from the same light source are respectively irradiated from both sides of the disk-shaped volume recording medium so as to have the same focal position. In a focus position control method for recording a wave as a record mark or irradiating the focus position with the first light from one surface of the volume type recording medium and reproducing the record mark, the position detection provided on the volume type recording medium The first position detection light is irradiated to the first reflection layer among the plurality of reflection layers on which the pattern is formed, and the first position detection light is applied to the first reflection layer based on the reflection light. A first position control step for focusing on the first target position; and the second position detection light is irradiated to the second reflective layer among the plurality of reflective layers, and the second position detection light is applied based on the reflected light. The position detection light of the first reflection layer in the second reflection layer Volume type recording based on the second position control step for focusing on the second target position corresponding to the target position, the position control result by the first position control step, and the position control result by the second position control step And a focal position setting step for setting the focal positions of the first and second lights with reference to an imaginary line connecting the first and second target positions in the medium.

  Thereby, in the focus position control method of this invention, the 1st and 2nd target position used as the parameter | index at the time of determining the focus position of 1st and 2nd light can be recognized reliably, and the said 1st and 2nd By using the virtual line connecting the two target positions as a reference, the focal positions of the first and second lights can be reliably and accurately adjusted to the desired positions.

  Furthermore, in the volume type recording medium of the present invention, in the volume type recording medium provided with a recording layer for recording standing waves generated by the first and second lights irradiated from both sides, the position detection pattern is A first reflection layer for focusing the first position detection light on the first target position on the position detection pattern and a position detection pattern corresponding to the first reflection layer are formed. A second reflective layer for focusing the second position detection light on the second target position corresponding to the first target position on the position detection pattern, and the recording layer is a volume type recording The recording position of the standing wave is determined with reference to an imaginary line connecting the first and second target positions in the medium.

  As a result, in the volume type recording medium of the present invention, the first and second target positions that serve as indices for determining the focal positions of the first and second lights can be reliably recognized. By using the virtual line connecting the two target positions as a reference, the first and second lights can be reliably and accurately focused on the desired position.

  According to the present invention, it is possible to reliably recognize the first and second target positions that serve as indices for determining the focal positions of the first and second lights, and to determine the first and second target positions. By using the connecting virtual line as a reference, it is possible to accurately adjust the focal positions of the first and second lights to a desired position, thus realizing an optical disc apparatus and a focal position control method capable of improving information recording / reproducing accuracy. it can.

  Further, according to the present invention, the first and second target positions can be reliably recognized as indices for determining the focal positions of the first and second lights. By using the virtual line connecting the two as a reference, the first and second lights can be focused on the desired position reliably and accurately, and thus a volume type recording medium capable of improving the information recording / reproducing accuracy 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 embodiment will be described. As shown in the external view in FIG. 5A, 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.

  5B, the optical disc 100 has a recording layer 101 for recording information at the center, and the recording layer 101 is sandwiched from both sides by the substrates 102 and 103. As shown in FIG. 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.

  Incidentally, the optical disc 100 has a substantially symmetric structure with the recording layer 101 as the center in the thickness direction, and consideration is given to suppressing the occurrence of warpage, distortion, etc. due to secular change as a whole. In addition, about the surface of the board | substrates 102 and 103, unnecessary reflection may be made to be prevented by anti-reflective coating.

  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 the irradiated light, and responds to a blue light beam having a wavelength of about 405 [nm]. . As shown in FIG. 5B, 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.

  Further, the recording layer 101 has a refractive index equivalent to that of the substrates 102 and 103 with respect to a blue light beam having a wavelength of 405 [nm], and the blue light is reflected at the boundary surface between the recording layer 101 and the substrate 103. The beam is hardly refracted.

  The optical disc 100 has reflection / transmission films 104 and 105 as reflection layers on the boundary surface between the recording layer 101 and the substrate 102 and on the boundary surface between the recording layer 101 and the substrate 103, respectively. Each of the reflection / transmission films 104 and 105 is a dielectric multilayer film or the like, and transmits the blue light beams Lb1 and Lb2 and the blue reproduction light beam Lb3 having a wavelength of 405 [nm] and red having a wavelength of 660 [nm]. It has wavelength selectivity such as reflecting a light beam.

  The reflection / transmission films 104 and 105 form guide grooves as position detection patterns used for tracking servo and focus servo. Specifically, the reflection / transmission films 104 and 105 are the same as those of a general BD-R (Recordable) disk or the like. A spiral track is formed by the land and the groove. This track is given an address consisting of a series of numbers for each predetermined recording unit, and the track on which information is recorded or reproduced can be specified by the address.

  Further, the tracks formed on the reflective / transmissive films 104 and 105 are assigned the same address at corresponding positions in the thickness direction of the optical disc 100.

  Note that pits or the like are formed instead of the guide grooves on the reflection / transmission films 104 and 105 (that is, the boundary surface between the recording layer 101 and the substrate 102 and the boundary surface between the recording layer 101 and the substrate 103), or It may be combined with pits or the like. In short, it is sufficient that the address can be recognized by the light beam.

  The reflection / transmission film 104 reflects the red light beam Lr1 as the first position detection light from the substrate 102 side to the substrate 102 side. Hereinafter, the light beam reflected at this time is referred to as a red reflected light beam Lr1e.

  The red reflected light beam Lr1e is, for example, a red light beam Lr1 collected by a predetermined objective lens OL1 with respect to a target track (corresponding to a target guide position, hereinafter referred to as a target track) in an optical disc apparatus. It is assumed that it is used for position control (that is, focus control and tracking control) of the objective lens OL1 for adjusting the focal point Fr1.

  Further, when the red light beam Lr2 as the second position detection light is irradiated from the substrate 103 side, the reflection / transmission film 105 reflects this toward the substrate 103 side. Hereinafter, the light beam reflected at this time is referred to as a red reflected light beam Lr2e.

  Similar to the red reflected light beam Lr1e, the red reflected light beam Lr2e is used for position control for adjusting the focus Fr2 of the red light beam Lr2 collected by the predetermined objective lens OL2 with respect to the target track. Assumed.

  In the following, the surface on the substrate 102 side of the optical disc 100 is referred to as a first surface 100A, and the surface on the substrate 103 side of the optical disc 100 is referred to as a second surface 100B.

  In practice, when information is recorded on the optical disc 100, as shown in FIG. 5B, the red light beam Lr1 is condensed by the position-controlled objective lens OL1, and the first target in the reflective / transmissive film 104 is collected. In addition to being focused on the target track as the position, the red light beam Lr2 is condensed by the position-controlled objective lens OL2, and focused on the target track as the second target position in the reflective / transmissive film 105.

  Further, the blue light beam Lb1 that shares the optical axis Lx with the red light beam Lr1 and is condensed by the objective lens OL1 passes through the substrate 102 and the reflective / transmissive film 104, and is behind the target track in the recording layer 101 ( That is, it is focused on the substrate 102 side. At this time, the focal point Fb1 of the blue light beam Lb1 is located farther than the focal point Fr1 on the common optical axis Lx with reference to the objective lens OL1.

  Further, the blue light beam Lb2 having the same wavelength as 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 side of the substrate 103 opposite to the blue light beam Lb1. The light is condensed and irradiated by 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, in the optical disc 100, the focal points Fb1 and Fb2 can be positioned between the target track of the reflection / transmission film 104 and the target track of the reflection / transmission film 105 in the recording layer 101, and thereby a relatively small interference pattern. A recording mark RM is recorded.

  At this time, in the recording layer 101, the blue light beams Lb1 and Lb2 which are both converged light are overlapped, and a standing wave is generated in a portion where the intensity is not less than a predetermined intensity, so that a recording mark RM is formed. For this reason, as shown in FIG. 2 (A), the recording mark RM generally has a shape in which two cones are bonded to each other at the bottom surfaces, and a central portion (a portion where the bottom surfaces are bonded together). Is slightly constricted.

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

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

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

  Further, the optical disc 100 is designed such that the thickness t1 (= 0.3 [mm]) of the recording layer 101 is sufficiently larger than the height RMh of the recording mark RM. For this reason, the optical disc 100 is shown in FIG. 2B by recording the recording mark RM while switching the distance from the recording reflective film 104 in the recording layer 101 (hereinafter referred to as depth d). As described above, 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, in the recording layer 101 of the optical disc 100, the depth d 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. 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. The distance p3 may be set to various values other than about 15 [μm] in consideration of the mutual interference between the recording marks RM.

  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.

  The optical disk 100 is configured such that the position of the objective lens OL2 is controlled so that the red light beam Lr2 collected by the objective lens OL2 is focused on the target track of the reflective / transmissive film 105.

  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. (Which corresponds to the target recording position, hereinafter referred to as the 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, the optical disc 100 uses the red light beams Lr1 and Lr2 for position control and the blue light beams Lb1 and Lb2 for information recording when information is recorded, so that the focal points Fb1 and Fb2 in the recording layer 101 are used. The recording mark RM is formed as the information at a position where the two overlap each other, that is, a target mark position having a target depth between the target track of the reflective / transmissive film 104 and the target track of the reflective / transmissive film 105.

  Further, when recorded information is reproduced, the optical disc 100 uses the red light beams Lr1 and Lr2 for position control and the blue light beam Lb1 for information reproduction, so that the position of the focus Fb1, that is, the target mark position. A blue reproduction light beam Lb3 is generated from the recorded recording mark RM.

(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. 6, 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 indicates the address where the recording information should be recorded among the addresses given to the reflective / transmissive films 104 and 105 of the optical disc 100, and the layer number of the mark recording layer forming the multilayer structure (that is, the reflective / transmissive film 104). It is the information which shows how many layers it counts from.

  Similarly to the control unit 21, the drive control unit 22 is mainly configured by a CPU (not shown), reads various programs such as a tracking control program from a ROM (not shown), and develops them in a RAM (not shown), thereby tracking control. Various processes such as processes are executed.

  The drive control unit 22 drives and controls the spindle motor 24 in accordance with the drive command to rotate the optical disc 100 at a predetermined rotation speed, and controls the sled motor 25 to drive the optical pickup 26 with the moving shafts 25A and 25B. Are moved 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. 7, the optical pickup 26 has a substantially U-shaped side surface. As shown in FIG. 5B, 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. 6), thereby aligning the irradiation position of the light beam with the target track in the recording layer 101 of the optical disc 100, and the signal processing unit 23. The recording mark RM is recorded in accordance with the recording signal from (details will be described later).

  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. 6), so that the optical 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 the 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. 8, the optical pickup 26 is provided with a large number of optical components, and is roughly divided into a first surface position control optical system 30, a first surface information optical system 50, and a second surface position control. An optical system 70 and a second surface information optical system 90 are included.

(3-1) Configuration of First Surface Position Control Optical System The first surface position control optical system 30 irradiates the first surface 100A of the optical disc 100 with the red light beam Lr1, and the optical disc 100 causes the red light beam to be emitted. A red reflected light beam Lr1e formed by reflecting Lr1 is received.

  In FIG. 9, the laser diode 31 of the first 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. 6) 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 first surface 100A of the optical disc 100. At this time, as shown in FIG. 5B, 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 Lr1e that travels 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 Lr1e (FIG. 9) is sequentially transmitted through the objective lens 38, the dichroic prism 37, and the correction lenses 36 and 35 to become parallel light, and then enters the non-polarizing beam splitter 34.

  The non-polarizing beam splitter 34 irradiates the mirror 40 by reflecting the red reflected light beam Lr1e at a ratio of about 50%, and reflects the red reflected light beam Lr1e again by the mirror 40, and then collects the condensing lens 41. To enter.

  The condensing lens 41 converges the red reflected light beam Lr1e and irradiates the photodetector 43 with the red reflected light beam Lr1e after giving astigmatism by the cylindrical lens.

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

  Therefore, in order to make the focus Fr1 (FIG. 5B) of the red light beam Lr1 follow the target track in the first surface position control optical system 30, the focus Fr1 is a focus direction that is in the proximity direction or the separation direction with respect to the optical disc 100. It is necessary to move in the tracking direction which is the direction of the optical disk 100 and the direction of the inner circumference or the outer circumference of the optical disc 100.

  Further, as will be described later, the optical disc apparatus 20 preferably makes the red light beam Lr1 incident on the optical disc 100 substantially perpendicularly.

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

  Further, in the first surface position control optical system 30 (FIG. 9), the focusing state when the red light beam Lr1 is collected by the objective lens 38 and is applied to the reflective / transmissive film 104 of the optical disc 100 is changed by the collecting lens 41. The optical positions of the various optical components are adjusted so that the red reflected light beam Lr1e is reflected and reflected in the focused state when the photodetector 43 is irradiated.

  As shown in FIG. 10, 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 Lr1e. 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. 5B).

  The photodetector 43 detects a part of the red reflected light beam Lr1e by the detection areas 43A, 43B, 43C, and 43D, respectively, and generates detection signals SD1A, SD1B, SD1C, and SD1D according to the detected light amount, respectively. These are sent to the signal processing unit 23 (FIG. 6).

  The signal processing unit 23 performs focus control by a so-called astigmatism method, calculates a focus error signal SFE1 according to the following equation (3), and supplies this to the drive control unit 22.

  The focus error signal SFE1 represents the amount of deviation between the focal point Fr1 of the red light beam Lr1 and the reflective / transmissive film 104 of the optical disc 100.

  The signal processing unit 23 performs tracking control by a so-called push-pull method. The signal processing unit 23 calculates a tracking error signal STE1 according to the following equation (4) and supplies the tracking error signal STE1 to the drive control unit 22.

  The tracking error signal STE1 represents the amount of deviation between the focal point Fr1 of the red light beam Lr1 and the target track in the reflective / transmissive film 104 of the optical disc 100.

  Further, the signal processing unit 23 generates a tilt error signal SLE1 indicating the magnitude of the tilt (also referred to as skew or tilt) of the optical disc 100 based on the detection signals SD1A, SD1B, SD1C, and SD1D, and generates the tilt error signal SLE1. To supply.

  Incidentally, the signal processing unit 23 generates the reproduction RF signal SRF1 by adding all the detection signals SD1A, SD1B, SD1C, and SD1D, and sends this to the drive control unit 22 and the control unit 21. In response to this, the drive control unit 22 and the control unit 21 can recognize the address of the track where the focal point Fr1 of the red light beam Lr1 is located.

  The drive control unit 22 generates a focus drive signal SFD1 based on the focus error signal SFE1, and supplies the focus drive signal SFD1 to the triaxial 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 STD1 based on the tracking error signal STE1, and supplies the tracking drive signal STD1 to the triaxial 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.

  Further, the drive control unit 22 generates a tilt drive signal SLD1 based on the tilt error signal SLER1, and supplies the tilt drive signal SLD1 to the triaxial actuator 38A, whereby the red light beam Lr1 is substantially perpendicular to the optical disc 100. The objective lens 38 is feedback-controlled (that is, tilt control) so as to be incident on.

  Thus, the first 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 light reception result of the red reflection light beam Lr1e, which is the reflected light, to the signal processing unit 23. It is made like that. In response to this, the drive control unit 22 performs focus control and tracking control of the objective lens 38 so as to focus the red light beam Lr1 on the target track of the reflection / transmission film 104, and further performs tilt control. ing.

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

(3-2-1) Irradiation with Blue Light Beam In FIG. 11, the laser diode 51 of the first 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. 6) 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 according to the polarization direction (s-polarization) of the blue light beam Lb1 incident from the surface 55B, and passes from the surface 55C to the polarization beam splitter 58. It is made to enter.

  As a result, the first 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 drive control unit 22 (FIG. 6). It is made like that.

  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 first 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. 5B. 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 first surface 100A side or the second surface 100B side in the recording layer 101 according to the position of the movable lens 61.

  Specifically, the first 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. mm], the focal point Fb1 of the blue light beam Lb1 is moved by 30 [μm].

  In practice, in the first surface information optical system 50, the position of the movable lens 61 is controlled by the drive control unit 22 (FIG. 6), so that the focal point Fb1 (FIG. 6) of the blue light beam Lb1 in the recording layer 101 of the optical disc 100 is obtained. 5 (B)), the depth d1 (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 second surface 100B, and enters the objective lens 78.

  In this way, the first surface information optical system 50 irradiates the blue light beam Lb1 from the first 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, the relay lens 60. The depth d1 of the focal point Fb1 is adjusted according to the position of the movable lens 61 in FIG.

(3-2-2) Reception of Blue Light Beam By the way, the optical disc 100 transmits the blue light beam Lb2 irradiated from the objective lens 78 to the second surface 100B and emits it as divergent light from the first surface 100A. (Details will be described later). Incidentally, the blue light beam Lb2 is circularly polarized (for example, right circularly polarized).

  At this time, in the first surface information optical system 50, as shown in FIG. 12, 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 1st surface information optical system 50 is arrange | positioned so that the blue light beam Lb2 may focus on the photodetector 64. FIG.

  The photodetector 64 detects the amount of light of the blue light beam Lb2, generates a reproduction detection signal SDp according to the amount of light detected at this time, and supplies this to the signal processing unit 23 (FIG. 6).

  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. Therefore, the signal processing unit 23 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 passes through the same optical path as the blue light beam Lb2 in the first surface information optical system 50, and is finally irradiated to the photodetector 64.

  Here, each optical component in the first 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 this to the signal processing unit 23 (FIG. 6).

  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.

  Thus, the first 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 first surface 100A of the optical disc 100, and the light reception result is sent to the signal processing unit 23. It is made to supply.

(3-3) Configuration of Second Surface Position Control Optical System The second surface position control optical system 70 (FIG. 8) has a symmetric configuration with the first surface position control optical system 30 with the optical disc 100 interposed therebetween. In addition, the second surface 100B of the optical disc 100 is irradiated with a red light beam Lr2, and the red reflected light beam Lr2e formed by reflecting the red light beam Lr2 by the optical disc 100 is received.

  In FIG. 13, the second surface position control optical system 70 includes a laser diode 31 of the first surface position control optical system 30, a collimator lens 32, a slit 33, a non-polarizing beam splitter 34, correction lenses 35 and 36, a dichroic prism 37, Laser diode 71, collimator lens 72, slit 73, non-polarizing beam splitter 74, correction lenses 75 and 76, dichroic having the same configuration as objective lens 38, mirror 40, condenser lens 41, cylindrical lens 42 and photodetector 43, respectively. A prism 77, an objective lens 78, a mirror 80, a condenser lens 81, a cylindrical lens 82, and a photodetector 83 are included.

  Similarly to the objective lens 38, the objective lens 78 can be driven in a triaxial direction including a focus direction, a tracking direction, and a tilt direction by a triaxial actuator 78A.

  With this configuration, the second surface position control optical system 70 irradiates the second surface 100B of the optical disc 100 with a red light beam Lr2 having a wavelength of about 660 [nm] similar to the red light beam Lr1. . At this time, as shown in FIG. 5B, the red light beam Lr2 is transmitted through the substrate 103 and reflected by the reflective / transmissive film 105 to become a red reflected light beam Lr2e that travels in the opposite direction to the red light beam Lr2.

  The red reflected light beam Lr2e (FIG. 13) is sequentially transmitted through the objective lens 78, the dichroic prism 77, and the correction lenses 76 and 75 into parallel light, and then reflected by the non-polarizing beam splitter 74 at a rate of about 50%. Then, it is reflected again by the mirror 80 and enters the condenser lens 81.

  The condensing lens 81 converges the red reflected light beam Lr2e, gives astigmatism by the cylindrical lens 82, and irradiates the photodetector 83 with the red reflected light beam Lr2e.

  As shown in FIG. 14 corresponding to FIG. 10, the photodetector 83 has four detection areas 83A, 83B, 83C, and 83D divided in a lattice pattern on the surface irradiated with the red reflected light beam Lr2e. Yes. Incidentally, the direction (vertical direction in the figure) indicated by the arrow a2 corresponds to the traveling direction of the track when the red light beam Lr2 is irradiated onto the reflective / transmissive film 105 (FIG. 5B).

  The photodetector 83 detects a part of the red reflected light beam Lr2e by the detection areas 83A, 83B, 83C, and 83D, respectively, and generates detection signals SD2A, SD2B, SD2C, and SD2D according to the detected light amount, respectively. These are sent to the signal processing unit 23 (FIG. 6).

  The signal processing unit 23 performs focus control by a so-called astigmatism method, calculates a focus error signal SFE2 according to the following equation (5), and supplies this to the drive control unit 22.

  The focus error signal SFE2 represents the amount of deviation between the focal point Fr2 of the red light beam Lr2 and the reflective / transmissive film 105 of the optical disc 100.

  The signal processing unit 23 performs tracking control by a so-called push-pull method. The signal processing unit 23 calculates the tracking error signal STE2 according to the following equation (6) and supplies the tracking error signal STE2 to the drive control unit 22.

  This tracking error signal STE2 represents the amount of deviation between the focal point Fr2 of the red light beam Lr2 and the target track in the reflective / transmissive film 105 of the optical disc 100.

  Further, the signal processing unit 23 generates a tilt error signal SLE2 indicating the magnitude of the tilt (also referred to as skew or tilt) of the optical disc 100 based on the detection signals SD2A, SD2B, SD2C, and SD2D, and this is generated as a drive control unit 22. To supply.

  Incidentally, the signal processing unit 23 generates the reproduction RF signal SRF2 by adding all the detection signals SD2A, SD2B, SD2C, and SD2D as in the case of the first surface position control optical system 30, and generates the reproduction RF signal SRF2. The data is sent to the control unit 21. In response to this, the drive control unit 22 and the control unit 21 can recognize the address of the track where the focal point Fr2 of the red light beam Lr2 is located.

  The drive control unit 22 generates a focus drive signal SFD2 based on the focus error signal SFE2, and supplies the focus drive signal SFD2 to the triaxial actuator 78A, whereby the red light beam Lr2 is applied to the reflective / transmissive film 105 of the optical disc 100. The objective lens 78 is feedback-controlled (that is, focus control) so as to be focused.

  Further, the drive control unit 22 generates a tracking drive signal STD2 based on the tracking error signal STE2, and supplies the tracking drive signal STD2 to the triaxial actuator 78A, so that the red light beam Lr2 is reflected / transmitted film 105 of the optical disc 100. The objective lens 78 is feedback-controlled (that is, tracking control) so as to focus on the target track.

  Further, the drive control unit 22 generates a tilt drive signal SLD2 based on the tilt error signal SLE2, and supplies the tilt drive signal SLD2 to the triaxial actuator 78A, so that the red light beam Lr2 is substantially perpendicular to the optical disc 100. The objective lens 78 is feedback-controlled (that is, tilt control) so as to be incident on.

  As described above, the second surface position control optical system 70 irradiates the reflection / transmission film 105 of the optical disc 100 with the red light beam Lr2 symmetrically with the first surface position control optical system 30, and the red reflected light beam which is the reflected light. The light reception result of Lr2e is supplied to the signal processing unit 23. In response to this, the drive control unit 22 performs focus control and tracking control of the objective lens 78 so as to focus the red light beam Lr2 on the target track of the reflection / transmission film 105, and further performs tilt control. ing.

(3-4) Configuration of Second Surface Information Optical System The second surface information optical system 90 (FIG. 8) irradiates the second surface 100B of the optical disc 100 with the blue light beam Lb2.

  In FIG. 13, the polarization beam splitter 55 of the first surface information optical system 50 transmits the blue light beam Lb0 of p-polarized light at a rate of about 50% on the reflection / transmission surface 55S, as described above, and transmits this blue light beam. Lb2 is incident on the shutter 91 from the surface 55D.

  The shutter 91 is configured to block or transmit the blue light beam Lb2 based on the control of the control unit 21 (FIG. 6). When the blue light beam Lb2 is transmitted, the shutter 91 is reflected by the mirror 93, and then 1 After being converted from linearly polarized light (p-polarized light) into circularly polarized light (left-handed circularly polarized light) by the / 4 wavelength plate 94, the light is incident on the relay lens 95.

  Incidentally, as the shutter 71, for example, a mechanical shutter that blocks or transmits the blue light beam Lb2 by mechanically moving a blocking plate that blocks the blue light beam Lb2, or a blue shutter that changes the voltage applied to the liquid crystal panel. A liquid crystal shutter or the like that blocks or transmits the light beam Lb2 can be used.

  The relay lens 95 is configured in the same manner as the relay lens 60, and includes a movable lens 96, an actuator 96A, and a fixed lens 97 corresponding to the movable lens 61, the actuator 61A, and the fixed lens 62, respectively.

  The relay lens 95 converts the blue light beam Lb2 from parallel light into convergent light by the movable lens 96, converts the blue light beam Lb2 that has become divergent light after convergence into the convergent light again by the fixed lens 97, and the dichroic prism. 77 is incident.

  Similarly to the relay lens 60, the relay lens 95 moves the movable lens 96 by the actuator 96A based on the control of the drive control unit 22 (FIG. 6), so that the blue light beam Lb2 emitted from the fixed lens 97 is converged. Can be changed.

  The dichroic prism 77 reflects the blue light beam Lb2 according to the wavelength and makes it incident on the objective lens 78. 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 objective lens 78 condenses the blue light beam Lb2 and irradiates the second surface 100B of the optical disc 100 with it. At this time, the blue light beam Lb2 passes through the substrate 103 and the reflective / transmissive film 105 and is focused in 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 97 of the relay lens 95. That is, the focal point Fb2 moves to the first surface 100A side or the second surface 100B side in the recording layer 101 according to the position of the movable lens 96, like the focal point Fb1 of the blue light beam Lb1.

  Specifically, like the first surface information optical system 50, the second surface information optical system 90 is designed so that the moving distance of the movable lens 96 and the moving distance of the focal point Fb2 of the blue light beam Lb2 are substantially proportional. For example, when the movable lens 96 is moved by 1 [mm], the focal point Fb2 of the blue light beam Lb2 is moved by 30 [μm].

  In practice, the second surface information optical system 90 controls the position of the movable lens 96 in the relay lens 95 together with the position of the movable lens 61 in the relay lens 60 by the control unit 21 (FIG. 6). The depth d2 of the focal point Fb2 (FIG. 10) of the blue light beam Lb2 in the layer 101 is adjusted.

  At this time, in the optical disc apparatus 20, when it is assumed that surface blurring or the like has not occurred in the optical disc 100 by the control of the control unit 21 (FIG. 6) (that is, in an ideal state), the blue color is recorded in the recording layer 101. The focal point Fb1 of the light beam Lb1 and the focal point Fb2 of the blue light beam Lb2 are positioned at the target mark 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, and is emitted from the first surface 100A and incident on the objective lens 38. Has been made.

  In this way, the second surface information optical system 90 irradiates the blue light beam Lb2 from the second 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, the relay lens 95. The depth d2 of the focal point Fb2 is adjusted according to the position of the movable lens 96 in FIG.

(3-5) 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 to the blue light beam Lb1 by the polarization beam splitter 55 (FIG. 12) 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 first surface information optical system 50 (FIG. 12), is irradiated from the first surface 100A side of the optical disc 100, and the blue light beam Lb2 is second. The light is irradiated from the second surface 100B side of the optical disc 100 through the optical path in the surface optical system 70 (FIG. 13). 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 drive control unit 22 (FIG. 6) adjusts the optical path length of the blue light beam Lb1 by controlling the position of the movable mirror 57. In this case, the drive control unit 22 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 according to the position of the movable lens 61, thereby The optical path length of the blue 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 drive control unit 22 of the optical disc apparatus 20 controls the position of the movable mirror 57 to suppress the difference in optical path length between the blue light beams Lb1 and Lb2 in the optical pickup 26 to a coherent length or less. A good recording mark RM can be recorded at a target mark position in the recording layer 101 of the optical disc 100.

(4) Recording and Reproducing Information Next, a case where information is recorded on the optical disc 100 by the optical disc apparatus 20 and a case where information is reproduced from the optical disc 100 will be described in detail.

(4-1) Recording of Information on Optical Disc First, a configuration in which a part of the optical disc apparatus 20 in the case of recording information on the optical disc 100 is extracted is assigned the same reference numerals at the corresponding points in FIGS. As shown in FIG.

  When recording information on the optical disc 100, the control unit 21 of the optical disc apparatus 20 receives the information recording command, the recording information, and the recording address information from an external device (not shown) or the like as described above. The address information is supplied to the drive control unit 22 and the recording information is supplied to the signal processing unit 23.

  Further, the control unit 21 causes the first surface position control optical system 30 (FIG. 9) of the optical pickup 26 to irradiate the red light beam Lr1 from the first surface 100A side of the optical disc 100. At this time, the signal processing unit 23 generates the reproduction RF signal SRF1 and the focus error signal SFE1 based on the detection result of the red reflected light beam Lr1e by the photodetector 43, and sends them to the control unit 21 and the drive control unit 22.

  Further, the control unit 21 causes the second surface position control optical system 70 (FIG. 13) of the optical pickup 26 to irradiate the red light beam Lr2 from the second surface 100B side of the optical disc 100. At this time, the signal processing unit 23 generates the reproduction RF signal SRF2 and the focus error signal SFE2 based on the detection result of the red reflected light beam Lr2e by the photodetector 83, and sends them to the control unit 21 and the drive control unit 22.

  In addition, the control unit 21 causes the first surface information optical system 50 (FIG. 11) to irradiate the blue light beam Lb1 from the first surface 100A side of the optical disc 100 through the objective lens 38, and also controls the shutter 91 to control the blue color. After transmitting the light beam Lb2, the second surface information optical system 90 (FIG. 12) irradiates the blue light beam Lb2 from the second surface 100B side of the optical disc 100 through the objective lens 78.

  In the address calculation unit 21A of the control unit 21, the focal point Fr1 of the red light beam Lr1 and the focal point Fr2 of the red light beam Lr2 are actually located based on the reproduction RF signals SRF1 and SRF2 supplied from the signal processing unit 23. The track address is calculated and sent to the recording layer position calculation unit 21B.

  The address calculation unit 21A also determines the current address based on the focus error signals SFE1 and SFE2 supplied from the signal processing unit 23 and the position information regarding the focus direction of the objective lenses 38 and 78 supplied from the drive control unit 22. The thickness t1 of the recording layer 101 of the optical disc 100 is calculated and supplied to the recording layer position calculation unit 21B.

  The recording layer position calculation unit 21B determines the number i of the mark recording layer on which the recording mark RM is to be recorded, based on the recording address information from the external device (not shown) and the current address information, and uses this as the layer number. It supplies to the offset determination part 21C.

  As shown in FIG. 16, in the recording layer 101 of the optical disc 100, the distance between the reflective / transmissive film 104 side and the reflective / transmissive film 105 side is internally divided into m: (1-m) by the i-th mark recording layer. In this case, the position of the i-th mark recording layer can be expressed using a ratio m (where 0 ≦ m ≦ 1).

  On the other hand, in the recording layer 101, in consideration of the transmittance of the blue light beams Lb1 and Lb2 and the characteristics of the recording material, the intervals between the mark recording layers are not equal. It is considered that a better recording mark RM can be formed by changing the interval between the vicinity.

  Incidentally, when the interval is changed, specifically, the vicinity of the center is made narrower than the vicinity of the reflection / transmission films 104 and 105 according to the characteristics of the material constituting the recording layer 101 or the like. It is envisaged to widen.

  Therefore, in the optical disc apparatus 20 (FIG. 15), the ratio m is set at unequal intervals for each number i of the mark recording layer, and the correspondence between the number i of the mark recording layer and the ratio m is stored in advance as a ratio table TBL. 21D is stored.

  In practice, the layer offset determination unit 21C reads the ratio m corresponding to the mark recording layer number i from the table TBL of the storage unit 21D, and calculates the ratio m, the thickness t1 of the recording layer 101, and the total number N of mark recording layers. The distance t11 and the distance t12 are calculated according to the following equations (7) and (8), and are supplied to the drive control unit 22.

  The drive control unit 22 generates the first surface movable lens drive signal SDL1 having a voltage corresponding to the distance t11, and supplies the first surface movable lens drive signal SDL1 to the actuator 61A of the movable lens 61, thereby driving the movable lens 61 to generate red light. The distance between the focal point Fr1 of the beam Lr1 and the focal point Fb1 of the blue light beam Lb1 is adjusted to a distance t11 (FIG. 16).

  Similarly, the drive control unit 22 (FIG. 15) generates the second surface movable lens drive signal SDL2 having a voltage corresponding to the distance t12, and supplies the second surface movable lens drive signal SDL2 to the actuator 96A of the movable lens 96, thereby causing the movable lens 96 to move. The distance between the focal point Fr2 of the red light beam Lr2 and the focal point Fb2 of the blue light beam Lb2 is adjusted to a distance t12 (FIG. 16).

  In addition, the drive control unit 22 performs focus control and tracking control of the objective lens 38 by the first surface position control optical system 30 (FIG. 9) of the optical pickup 26, so that the focal point Fr1 of the red light beam Lr1 is reflected and transmissive film 104. Follow the target track above.

  At this time, the drive control unit 22 adjusts the distance between the focal point Fb1 of the red light beam Lr1 and the focal point Fb1 of the blue light beam Lb1 by the movable lens 61 of the relay lens 60 to the distance t11. Can be adjusted to the position.

  Further, the drive control unit 22 performs the focus control and tracking control of the objective lens 78 by the second surface position control optical system 70 (FIG. 13) of the optical pickup 26, so that the focal point Fr2 of the red light beam Lr2 is reflected and transmissive film 105. Follow the target track above.

  At this time, the drive control unit 22 adjusts the distance between the focal point Fr2 of the red light beam Lr2 and the focal point Fb2 of the blue light beam Lb2 to the distance t12 by the movable lens 96 of the relay lens 95. The focal point Fb2 can also be adjusted to 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.

  As a result, the control unit 21 of the optical disc apparatus 20 can adjust the focal points Fb1 and Fb2 of the blue light beams Lb1 and Lb2 to the target mark position in the recording layer 101 of the optical disc 100, thereby forming a good recording mark RM. Can do.

  At this time, the control unit 21 of the optical disc apparatus 20 uses the target track on the reflective / transmissive films 104 and 105 as an index, and divides the imaginary line connecting the two into a ratio m: (1-m). The position can be recognized with high accuracy.

  By the way, in the optical disc apparatus 20, when the optical disc 100 is warped, surface shake, or the like, the optical disc 100 has an inclination (so-called skew) with respect to the optical disc apparatus 20.

  In this case, as shown in FIG. 17A, if the focal point Fr1 of the red light beam Lr1 and the focal point Fr2 of the red light beam Lr2 are aligned with the target tracks of the reflective / transmissive films 104 and 105, respectively, the focal point of the blue light beam Lb1. Neither Fb1 nor the focal point Fb2 of the blue light beam Lb2 can be adjusted to the target mark position.

  Therefore, the optical disk apparatus 20 performs the above-described tilt control on the objective lenses 38 and 78 by the drive control unit 22, respectively, and as shown in FIG. 17B, the optical axes Lx1 and Lx1 of the red light beams Lr1 and Lr2. Lx2 can be maintained perpendicular to the optical disc 100, respectively.

  Further, as described above, the reflection / transmission films 104 and 105 of the optical disc 100 are assigned the same addresses at the corresponding positions in the thickness direction of the optical disc 100 with respect to the tracks. As a result, the optical disc apparatus 20 can adjust both the focal point Fb1 of the blue light beam Lb1 and the focal point Fb2 of the blue light beam Lb2 to the target mark position even if the optical disc 100 has an inclination.

  Incidentally, the signal processing unit 23 (FIG. 6) generates a recording signal representing binary data of, for example, 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 Next, FIG. 18 corresponding to FIG. 15 shows a configuration in which a part of the optical disc apparatus 20 in the case of reproducing information from the optical disc 100 is extracted.

  When reproducing information from the optical disc 100, the control unit 21 of the optical disc apparatus 20 receives the information reproduction command and reproduction address information from an external device (not shown) or the like as described above, and then outputs the drive command and reproduction address information. This is supplied to the drive control unit 22.

  Similarly to the time of information recording, the control unit 21 causes the first surface position control optical system 30 (FIG. 9) of the optical pickup 26 to irradiate the red light beam Lr1 from the first surface 100A side of the optical disc 100 and the optical pickup. 26, the red light beam Lr2 is irradiated from the second surface 100B side of the optical disc 100 by the second surface position control optical system 70 (FIG. 13).

  At this time, the signal processing unit 23 outputs the reproduction RF signals SRF1 and SRF2 and the focus error signals SFE1 and SFE2 based on the detection result of the red reflected light beam Lr1e by the photodetector 43 and the detection result of the red reflected light beam Lr2e by the photodetector 83. These are generated and sent to the control unit 21 and the drive control unit 22.

  Further, the control unit 21 irradiates the blue light beam Lb1 from the first surface 100A side of the optical disc 100 by the first surface information optical system 50 (FIG. 12). On the other hand, unlike the information recording, the control unit 21 controls the shutter 91 to block the blue light beam Lb2 so that the optical disk 100 is not irradiated with the blue light beam Lb2.

  At this time, the address calculation unit 21A of the control unit 21 calculates the address of the track where the focal point Fr1 of the red light beam Lr1 and the focal point Fr2 of the red light beam Lr2 are actually located based on the reproduction RF signals SRF1 and SRF2. Further, the thickness t1 of the recording layer 101 of the optical disc 100 at the current address is calculated, and these are supplied to the recording layer position calculation unit 21B.

  The recording layer position calculation unit 21B should reproduce (namely, focus Fb1 and Fb2 of the blue light beams Lb1 and Lb2) based on reproduction address information from the external device (not shown) and current address information. The number i of the mark recording layer is determined and supplied to the layer offset determining unit 21C.

  The layer offset determination unit 21C reads the ratio m corresponding to the mark recording layer number i from the table TBL of the storage unit 21D, and records the ratio m, the thickness t1 of the recording layer 101, and the mark recording layer as in the information recording. Using the total number N, the partial thickness t11 is calculated according to the above-described equation (7), and this is supplied to the drive control unit 22.

  The drive control unit 22 generates the first surface movable lens drive signal SDL1 having a voltage corresponding to the distance t11 and supplies the first surface movable lens drive signal SDL1 to the actuator 61A of the movable lens 61, thereby, as shown in FIG. 19, the red light beam Lr1. The distance between the focal point Fr1 and the focal point Fb1 of the blue light beam Lb1 is adjusted to the distance t11.

  In addition, the drive control unit 22 performs focus control and tracking control of the objective lens 38 by the first surface position control optical system 30 (FIG. 9) of the optical pickup 26, so that the focal point Fr1 of the red light beam Lr1 is reflected and transmissive film 104. Follow the target track above.

  At this time, the drive control unit 22 adjusts the distance between the focal point Fb1 of the red light beam Lr1 and the focal point Fb1 of the blue light beam Lb1 by the movable lens 61 of the relay lens 60 to the distance t11. Can be adjusted to the position.

  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. Accordingly, the recording mark RM acts as a hologram and generates a blue reproduction light beam Lb3 as so-called reproduction light toward the first surface 100A. At this time, the first surface information optical system 50 detects the blue reproduction light beam Lb3 and generates a detection signal corresponding to the detection result.

  In this case, unlike the recording, the optical disc device 20 does not irradiate the focus Fb2 of the blue light beam Lb2 to the target mark position, but adjusts the focus Fb1 of the blue light beam Lb1 to the target mark position. Lr2 is focused on the target track of the reflective / transmissive film 105.

  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.

  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.

  By the way, in the optical disk device 20, when the recording mark RM is not recorded at the target mark position, the blue reproduction light beam Lb3 is not generated 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.

  Incidentally, when the optical disc 100 is warped, surface-blurred, etc. and the optical disc 100 is inclined with respect to the optical disc device 20, the objective lenses 38 and 78 are respectively tilted as in the case of information recording. It is made to control.

  As a result, the optical disc apparatus 20 can maintain the optical axis Lx1 of the red light beam Lr1 perpendicular to the optical disc 100 as in the case shown in FIG. 17B, and the focal point Fb1 of the blue light beam Lb1 is targeted. It can be correctly aligned with the mark position.

(5) Operation and Effect In the above configuration, the optical disc apparatus 20 records information on the first surface and the second surface when recording information on the optical disc 100 in which the reflective / transmissive films 104 and 105 are provided on both surfaces of the recording layer 101, respectively. Focus control and tracking control of the objective lenses 38 and 78 are performed based on the detection results of the red reflected light beams Lr1e and Lr2e irradiated with the red light beams Lr1 and Lr2, and the focal points Fr1 and Fr2 are set as target tracks, respectively. The optical axes Lx1 and Lx2 are made to be substantially perpendicular to the optical disc 100 by following them and performing tilt control.

  Further, the optical disc apparatus 20 reads the ratio m corresponding to the number i of the mark recording layer on which the recording mark RM is to be recorded from the table TBL of the storage unit 21D, and sets the distance t11 and the distance t12 according to the expressions (7) and (8). The distance between the focal point Fr1 of the red light beam Lr1 and the focal point Fb1 of the blue light beam Lb1 is adjusted to the distance t11 by moving the movable lens 61 and the movable lens 96 in accordance with the calculation, and the red light beam Lr2 The distance between the focal point Fr2 and the focal point Fb2 of the blue light beam Lb2 is adjusted to the distance t12.

  As a result, the optical disc apparatus 20 can adjust the focus Fb1 of the blue light beam Lb1 and the focus Fb2 of the blue light beam Lb2 to the target mark position, and can record the recording mark RM at the target mark position.

  In particular, the optical disc apparatus 20 uses the two points of the target track on the reflection / transmission film 104 and the target track on the reflection / transmission film 105 as indices, and divides the imaginary line connecting them at a ratio m: (1-m). Since the target mark position can be determined, even if the optical disc 100 has an inclination with respect to the optical disc apparatus 20, the focal point Fb1 of the blue light beam Lb1 and the focal point Fb2 of the blue light beam Lb2 are both the target mark position. Can be accurately matched to.

  In this case, since the optical disk apparatus 20 uses two target tracks as an index, for example, the red light beam Lr1 is irradiated to the reflective / transmissive film 104 of the optical disk on which the reflective / transmissive film 105 is not provided, and the target track is aligned. Compared with the case where the target mark position is determined by the position of the movable lens 61 (that is, when the index is one place), the focus Fb1 and the focus Fb2 can be made to coincide with the target mark position with high accuracy. .

  Further, when the optical disk apparatus 20 uses the target track on the reflection / transmission film 104 and the target track on the reflection / transmission film 105 as an index, the optical disk device 20 actually uses the actual state of the recording layer 101 in the target track based on the driving state of the objective lenses 38 and 78. Since the thickness t1 can be calculated, even if the manufacturing quality of the optical disc 100 is poor and the thickness of the recording layer 101 is not uniform, a plurality of marks are provided in the recording layer 101 at an appropriate interval ratio. A recording layer can be formed.

  On the other hand, when reproducing information from the optical disc 100, the optical disc device 20 irradiates the first and second surfaces with the red light beams Lr1 and Lr2, respectively, and the detection results of the reflected red reflected light beams Lr1e and Lr2e. Based on this, focus control, tracking control and tilt control of the objective lenses 38 and 78 are performed.

  Further, the optical disc apparatus 20 reads the ratio m corresponding to the number i of the mark recording layer on which the recording mark RM to be read is recorded from the table TBL of the storage unit 21D, calculates the distance t11 according to the equation (7), Accordingly, the distance between the focal point Fr1 of the red light beam Lr1 and the focal point Fb1 of the blue light beam Lb1 is adjusted to the distance t11 by moving the movable lens 61 accordingly.

  As a result, the optical disk apparatus 20 can adjust the focal point Fb1 of the blue light beam Lb1 to the target mark position, and generate the reproduced blue light beam Lb3 as the reproduced light from the recording mark RM recorded at the target mark position. Can do.

  Even at the time of reproduction, the optical disc apparatus 20 can determine the target mark position by dividing the two target tracks by a ratio m: (1-m) using two target tracks as indices as in the recording. Even if the optical disc 100 is inclined with respect to the optical disc apparatus 20, the focal point Fb1 of the blue light beam Lb1 can be adjusted to the target mark position with high accuracy.

  According to the above configuration, the optical disc apparatus 20 focuses the red light beams Lr1 and Lr2 on the target tracks of the reflection / transmission films 104 and 105 provided on both surfaces of the recording layer 101 of the optical disc 100, and also records the recording marks RM. The distance t11 and the distance t12 are calculated by using the ratio m corresponding to the number i of the mark recording layer to record, and the movable lens 61 is moved so that the focal point Fr1 of the red light beam Lr1 and the focal point Fb1 of the blue light beam Lb1 Is adjusted to the distance t11, and the movable lens 96 is moved so that the distance between the focal point Fr2 of the red light beam Lr2 and the focal point Fb2 of the blue light beam Lb2 is adjusted to the distance t12. The focal point Fb2 can be accurately adjusted to the target mark position.

(6) Other Embodiments In the above-described embodiment, the case where the reflection / transmission films 104 and 105 having tracks formed on both surfaces of the recording layer 101 of the optical disc 100 is described. However, the present invention is not limited to this, and three or more reflective / transmissive films may be provided in the recording layer 101 including both surfaces.

  For example, in FIG. 20 corresponding to FIG. 16, in addition to the configuration of the optical disc 100, the optical disc 110 is provided with a reflection / transmission film 116 at the central portion of the recording layer 101. In this case, the optical disc apparatus 20 focuses the red light beam Lr1 on the reflective / transmissive film 104 and the red light when the portion of the recording layer 101 sandwiched between the reflective / transmissive films 104 and 116 is the target mark position. The beam Lr2 may be focused on the reflection / transmission film 116. When the portion of the recording layer 101 sandwiched between the reflection / transmission films 116 and 105 is set as the target mark position, the red light beam Lr1 is reflected. What is necessary is to focus the transmissive film 116 and focus the red light beam Lr2 on the reflective transmissive film 105. In this case, regarding the reflective / transmissive films 104, 105, and 116, the reflectance (or transmittance) of the red light beams Lr1 and Lr2 may be adjusted as appropriate.

  In the optical disc 110, two or more mark recording layers can be formed on the recording layer 101 between the reflection / transmission films 104 and 116 and between the reflection / transmission films 116 and 105, respectively.

  Incidentally, the position of the reflection / transmission film in the recording layer is not necessarily provided on both surfaces of the recording layer. For example, the reflection / transmission film may be provided near the center by a predetermined distance from both surfaces of the recording layer.

  In the above-described embodiment, the case where the red light beam Lr1 and the red light beam Lr2 are irradiated from both surfaces of the optical disc 100 has been described. However, the present invention is not limited to this, and the red light beam Lr1 and red light beam Lr2 are emitted from one surface of the optical disc 100. You may make it irradiate both light beam Lr1 and Lr2.

  For example, in FIG. 21 corresponding to FIG. 16, the reflection / transmission film 124 of the optical disc 120 reflects and transmits the red light beam at a rate of about 50%. In this case, the optical disk device 20 adjusts the polarization directions of the red light beams Lr3 and Lr4 to be different from each other by using optical elements such as various wavelength plates, and for example, the objective lens 38 based on the reflected light of the red light beam Lr3. The position of the movable lens (not shown) is moved to change the convergence state of the red light beam Lr4 in the same manner as the blue light beam Lb1, thereby focusing the red light beam Lr4 on the reflective / transmissive film 125, The local thickness t1 of the recording layer 101 may be calculated based on the position of the movable lens at this time.

  Incidentally, regarding the position control of the objective lens 78 at this time, for example, the focus error signal SFE and the tracking error signal STE when the position control of the objective lens 38 is performed based on the reflected light of the red light beam Lr3 are appropriately converted. Thus, the position of the objective lens 78 may be controlled.

  Further, in the above-described embodiment, the case where the red light beams Lr1 and Lr2 having the same wavelength are irradiated from both surfaces of the optical disc 100 and the positions of the objective lenses 38 and 78 are controlled based on the reflected light will be described. However, the present invention is not limited to this, and light beams having different wavelengths may be irradiated from both surfaces or one surface of the optical disc 100, and the positions of the objective lenses 38 and 78 may be controlled based on the reflected light. .

  For example, in FIG. 22 corresponding to FIG. 16, the reflective / transmissive film 135 of the optical disk 130 has wavelength selectivity that reflects the green light beam Lg1 and transmits the blue light beams Lb1 and Lb2 (shown by broken lines). Yes. Further, the reflection / transmission film 104 has a wavelength selectivity that reflects the red light beam Lr1 and transmits the green light beam Lg1 and the blue light beams Lb1 and Lb2.

  In this case, the optical disk device 20 may perform mixing of each light beam into the same optical path or separation into different optical paths by using, for example, a dichroic prism (not shown) corresponding to each wavelength. The position of the objective lens 38 is controlled based on the reflected light of the light beam Lr1, and the convergence state of the green light beam Lg1 is changed in the same manner as the blue light beam Lb1 by moving the position of a movable lens (not shown). The beam Lg1 may be focused on the reflective / transmissive film 135, and the local thickness t1 of the recording layer 101 may be calculated based on the position of the movable lens at this time.

  Further, in the above-described embodiment, the thickness t1 (FIG. 16) of the recording layer 101 is obtained by both the first surface position control optical system 30 and the second surface position control optical system 90 at the time of recording and reproducing information ( Although the case where the distance t11 is calculated according to the equation 7) has been described, the present invention is not limited to this. For example, when recording information, the first surface position control optical system is not used without using the second surface position control optical system 90. 30, the position of the objective lens 38 may be controlled, and the focus error signal SFE1, the tracking error signal STE1, and the like at this time may be appropriately converted to control the position of the objective lens 78. In this case, the distances t11 and t12 are calculated using the specified value of the thickness t1 according to the standard or the like, and the focal points Fb1 and Fb2 of the blue light beams Lb1 and Lb2 are adjusted to the target mark position.

  For information reproduction, for example, first, the position of the objective lens 38 is controlled only by the first surface position control optical system 30, the distance t11 is calculated using the specified value of the thickness t1, and the recording mark at the target mark position is calculated. The focus Fb1 of the blue light beam Lb1 is aligned with the RM to try to detect the reproduction light, and the second surface position control optical system 90 is also used for the first time when the reproduction light is not successfully detected. An actual measurement value of the length t1 may be obtained and the distance t11 may be calculated according to the equation (7).

  Further, in the above-described embodiment, a light beam for controlling the positions of the objective lenses 38 and 78 (referred to as a position control light beam) is a red light beam having a wavelength of about 660 [nm], and the recording mark RM is used as the recording mark RM. Although the case where the light beam for forming (referred to as a recording light beam) is a blue light beam having a wavelength of about 405 [nm] has been described, the present invention is not limited to this, and the position control light beam and The recording light beam may have an arbitrary wavelength.

  In this case, the reflection / transmission films 104 and 105 may have a property of reflecting the position control light beam according to the wavelength and transmitting the recording light beam according to the wavelength. The recording layer 101 may be any material that responds to the wavelength of the recording light beam.

  Incidentally, when the wavelength of the recording light beam is changed, the size of the recording mark RM changes as shown in the above formulas (1) and (2), so the distance p1 between the recording marks RM and the distance between the tracks. It is preferable to appropriately change p2 and the distance p3 between the mark recording layers.

  Alternatively, the position control light beam and the recording light beam may have the same wavelength. In this case, the reflection / transmission films 104 and 105 of the optical disc 100 may reflect (transmit) the position control light beam and the recording light beam at a predetermined ratio without wavelength selectivity.

  Furthermore, in the above-described embodiment, the case where the optical axes of the red light beam Lr1 and the blue light beam Lb1 are matched and the optical axes of the red light beam Lr2 and the blue light beam Lb2 are matched is described. The present invention is not limited to this. For example, the optical axes of the red light beam Lr1 and the blue light beam Lb1 may be shifted from each other by a predetermined interval, or may be shifted from each other by a predetermined angle. In this case, regarding the blue light beam Lb2, a good recording mark RM can be formed by advancing the optical axes common to the blue light beam Lb1 from opposite directions.

  Further, in the above-described embodiment, a so-called positive type is formed in which a recording mark RM representing an information value “0” or “1” is recorded by newly forming a small hologram in the recording layer 101 of the optical disc 100. Although the case where recording is performed has been described, the present invention is not limited to this, and for example, a hologram that covers almost the entire surface of the optical disc 100 is formed in layers at predetermined intervals in advance in the recording layer 101 of the optical disc 100. The information value “0” or “1” is recorded by destroying (erasing) the hologram at the target mark position by focusing the blue light beams Lb1 and Lb2 having a predetermined intensity on the target mark position. Negative recording may be performed.

  Further, in the above-described embodiment, the diameter of the optical disk 100 is about 120 [mm], 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 about 0.0. Although the case of 6 mm is described, the present invention is not limited to this, and other values may be used. In this case, after considering the thickness of the recording layer 101 and the substrates 102 and 103, the refractive index of each material, and the like, the optical characteristics of each optical component and the like so that the blue light beams Lb1 and Lb2 are focused on the target mark position. What is necessary is just to set arrangement | positioning.

  Furthermore, in the above-described embodiment, the first surface position control optical system 30 as the first position control means, the signal processing unit 23, the drive control unit 22, and the second surface position control as the second position control means. The optical system 70, the signal processing unit 23, the drive control unit 22, the relay lenses 60 and 95 as focus position setting means, the signal processing unit 23, the control unit 21, and the drive control unit 22 constitute an optical disc apparatus 20 as an optical disc apparatus. However, the present invention is not limited to this, and the first position control means, the second position control means, and the focus position setting means having other various circuit configurations constitute an optical disc apparatus. Anyway.

  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 mode of irradiation of the light beam to the conventional optical disk. It is a basic diagram which shows the mode of irradiation of the light beam when an optical disk inclines. 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 the red light beam in a 1st surface. 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 optical path of the red light beam in a 2nd surface. 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 mode of the recording of the information in an optical disk device. It is a basic diagram with which it uses for description of irradiation of the optical beam to the optical disk at the time of recording. It is an approximate line figure used for explanation of amendment of tilt. It is a basic diagram which shows the mode of the reproduction | regeneration of information in an optical disk apparatus. It is a basic diagram with which it uses for description of irradiation of the optical beam to the optical disk at the time of reproduction | regeneration. It is a basic diagram with which it uses for description of irradiation (1) of the light beam to the optical disk in other embodiment. It is a basic diagram with which it uses for description of irradiation (2) of the light beam to the optical disk in other embodiment. It is a basic diagram with which it uses for description of irradiation (3) of the light beam to the optical disk in other embodiment.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 20 ... Optical disk apparatus, 21 ... Control part, 21A ... Address calculation part, 21B ... Recording layer position calculation part, 22C ... Layer offset determination part, 22D ... Storage part, 22 ... Drive control part, 23 …… Signal processing unit 26 …… Optical pickup 30 …… First surface position control optical system 31, 51, 71 ...... Laser diode 37, 55, 58, 77 ...... Polarized beam splitter 38, 78. ... Objective lens, 38A, 78A ... Triaxial actuator, 43, 64, 83 ... Photo detector, 50 ... First surface information optical system, 60, 95 ... Relay lens, 61, 96 ... Movable lens, 61A, 96A ... Actuator, 70 ... Second surface position control optical system, 90 ... Second surface information optical system, 91 ... Shutter, 100 ... Optical disc, 101 ... Recording layer, 102, 103 ... Substrate, 104, 105 ... Reflective / transmissive film, Lr1, Lr2 ... Red light beam, Lr1e, Lr2e ... Red reflected light beam, Lb0, Lb1, Lb2 ... Blue light beam, Lb3 ... Blue reproduction light beam, Fr1, Fr2, Fb1, Fb2: Focus, RM: Recording mark.

Claims (17)

The standing wave is recorded as a recording mark by irradiating the first and second light emitted from the same light source so as to have the same focal position from both sides of the disk-shaped volume recording medium, or the volume In an optical disc apparatus for reproducing the recording mark by irradiating the first light from one surface of the mold recording medium to the focal position,
Of the plurality of reflective layers provided on the volume type recording medium and formed with the position detection pattern, the first reflective layer is irradiated with the first position detection light, and the first position detection light is applied based on the reflected light. First position control means for focusing position detection light on a first target position in the first reflective layer;
The second position detection light is irradiated to the second reflection layer among the plurality of reflection layers, and the second position detection light is applied to the second reflection layer on the second reflection layer based on the reflected light. Second position control means for focusing on a second target position corresponding to the target position;
Based on the position control result by the first position control means and the position control result by the second position control means, the virtual line connecting the first and second target positions in the volume type recording medium is used as a reference. An optical disc apparatus comprising: focus position setting means for setting the focus positions of the first and second lights. The focal position setting means includes
Based on the position control result by the first position control means and the position control result by the second position control means, the distance between the first target position and the second target position is calculated as a reflection layer interval. 2. The optical disc apparatus according to claim 1, wherein an internal dividing point that internally divides the interval between the reflective layers at a ratio corresponding to the position of the recording mark is set as a focal position of the first and second lights. . The focal position setting means includes
By setting three or more different internal dividing points within the reflective layer interval, three or more standing wave recording layers are formed between the first reflective layer and the second reflective layer. Or the standing wave is reproduced from each of the three or more standing wave recording layers. The focal position setting means includes
In the vicinity of the first and second reflective layers, the distance between the standing wave recording layers becomes relatively small, and the distance between the standing wave recording layers as the distance from the first and second reflective layers increases. The optical disc apparatus according to claim 2, wherein the inner dividing point is set so that is relatively large. The first position control means includes:
By controlling the position of the first objective lens that collects the first light and the first position detection light, the first position detection light is aligned with the target position in the first reflective layer. Burn
The second position control means includes
By controlling the position of the second objective lens that collects the second light and the second position detection light, the second position detection light is aligned with the corresponding position in the second reflective layer. Burn
The focal position setting means includes
The distance between the focal point of the first light and the focal point of the first position detection light is set based on the interval between the reflection layers and the predetermined ratio, and the focal point of the second light and the second position are set. The optical disk apparatus according to claim 2, wherein a distance from the focus of the detection light is set. The first position control means and the second position control means are:
Of the plurality of reflective layers, two reflective layers sandwiching a position where the standing wave in the volume type recording medium is to be recorded are the first reflective layer and the second reflective layer, respectively. The optical disc apparatus according to claim 1. The optical disk apparatus according to claim 1, wherein the first position detection light and the second position detection light have different wavelengths from the first and second lights. The first and second reflective layers are
8. The optical disc device according to claim 7, wherein the optical disc apparatus has wavelength selectivity for transmitting the first and second lights and reflecting the first and second position detection lights. The optical disc apparatus according to claim 7, wherein the first position detection light and the second position detection light have different wavelengths. The second position control means includes
Irradiating the volume type recording medium with the second position detection light from the same surface as the first position detection light;
The first reflective layer is
Having wavelength selectivity for transmitting the first and second lights and the second position detection light and reflecting the first position detection light;
The second reflective layer is
The optical disc apparatus according to claim 9, wherein the optical disc apparatus has wavelength selectivity for transmitting the first and second lights and reflecting the second position detection light. The standing wave is recorded as a recording mark by irradiating the first and second light emitted from the same light source so as to have the same focal position from both sides of the disk-shaped volume recording medium, or the volume In the focal position control method when reproducing the recording mark by irradiating the first light from one surface of the mold recording medium to the focal position,
Of the plurality of reflective layers provided on the volume type recording medium and formed with the position detection pattern, the first reflective layer is irradiated with the first position detection light, and the first position detection light is applied based on the reflected light. A first position control step for focusing position detection light on a first target position in the first reflective layer;
The second position detection light is irradiated to the second reflection layer among the plurality of reflection layers, and the second position detection light is applied to the second reflection layer on the second reflection layer based on the reflected light. A second position control step for focusing on a second target position corresponding to the target position;
Based on the position control result by the first position control step and the position control result by the second position control step, the virtual line connecting the first and second target positions in the volume type recording medium is used as a reference. A focal position control method comprising: a focal position setting step for setting a focal position of the first and second lights. In the volume type recording medium provided with the recording layer for recording the standing wave generated by the first and second light irradiated from both sides,
A first reflective layer for forming a position detection pattern, and focusing the first position detection light on the first target position on the position detection pattern;
A position detection pattern corresponding to the first reflective layer is formed, and the second position detection light is focused on the second target position corresponding to the first target position on the position detection pattern. And a second reflective layer of
The recording layer is
A recording position of the standing wave is determined with reference to an imaginary line connecting the first and second target positions in the volume recording medium. The first and second reflective layers are
The wavelength selectivity which reflects the said 1st and 2nd position detection light which transmits the said 1st and 2nd light and differs in the wavelength of the said 1st and 2nd light is characterized by the above-mentioned. 12. The volume type recording medium according to 12. The volume type recording medium according to claim 12, wherein the first and second reflective layers are formed so as to sandwich the recording layer from both sides. The recording layer is
A position detection pattern corresponding to the first reflection layer is formed between the first recording layer and the second reflection layer, and the first or second position detection light is used as the position detection pattern. 15. The volume type recording medium according to claim 14, wherein one or more other reflective layers for focusing on other target positions corresponding to the first and second target positions are provided. . The first and second reflective layers and the other reflective layer are:
The reflectance with respect to the first or second position detection light is adjusted so that the reflected light reflecting the first or second position detection light reaches the outside of the recording layer, respectively. The volume type recording medium according to claim 15. The first reflective layer is
The first and second lights have different wavelengths and transmit both the second position detection light and the first and second lights irradiated from the same direction as the first position detection light, The first and second light and the second position detection light have a wavelength selectivity for reflecting the first position detection light having a wavelength different from that of the second position detection light,
The second reflective layer is
13. The volume type recording medium according to claim 12, wherein the volume type recording medium has a wavelength selectivity for transmitting both the first and second lights and reflecting the second position detection light.

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