JP2008097723A - Optical disk device, tracking control method, and optical disk - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To perform recording of information with high density to an optical disk and to perform stable tracking control. <P>SOLUTION: A guide track Tg having a track interval twice as wide as a track interval Pr of a recording track Tr is provided on a reflection layer transmitting an information light beam Lb1 and reflecting a position controlling light beam Lr1 having a wavelength longer than that of the information light beam Lb1. Thereby, tracking control can be reliably performed by using the position controlling light beam Lr1 having the wavelength longer than that of the information light beam Lb1 while the recording track Tr is set in an interval according to a spot diameter of the information light beam Lb1 to enhance recording density. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

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

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

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

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

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

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

  On the other hand, as an information recording method for an optical disc, an optical disc apparatus using a recording mark based on a minute hologram has been proposed (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 made 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, Non-Patent Document 4).

  For example, as shown in FIG. 3, the optical disc apparatus 15 irradiates the optical disc 18 with a position control light beam L1 via a beam splitter 16 and an objective lens 17.

  In this case, the optical disk 18 has a reflective / transmissive film 18A for controlling the irradiation position of the recording / reproducing light beam L2, and the reflective / transmissive film 18A has a guide track Tg composed of lands and grooves for tracking servo. Is provided.

  The optical disc apparatus 15 irradiates the land or groove of the guide track Tg on the reflection / transmission film 18A of the optical disc 18 with a spot of the position control light beam L1 in the same manner as a conventional CD or DVD, and responds to the detection result of the return light. Then, position control such as focus control and tracking control of the objective lens 17 is performed, and the position control light beam L1 is focused on a desired guide track Tg on the reflection surface.

  In this state, the optical disc apparatus 15 reflects the recording / reproducing light beam L2 different from the position control light beam L1 by the beam splitter, and focuses the information on the recording layer 18B of the optical disc 18 through the position-controlled objective lens 17 to obtain information. (Record mark RM etc.) is recorded or reproduced.

In this way, the optical disc device 15 records the recording mark RM along the virtual recording track Tr in the recording layer 18B by positioning control based on the guide track Tg formed on the reflection / transmission film 18A.
Y. Kasami, Y. Kuroda, K. Seo, O. Kawakubo, S. Takagawa, M. Ono, and M. Yamada, Jpn. J. Appl. Phys., 39, 756 (2000) I. Ichimura et al, Technical Digest of ISOM'04, pp52, Oct. 11-15, 2005, Jeju Korea RRMcleod er al., “Microholographicmultilayer optical disk data storage,” Appl. Opt., Vol.44, 2005, pp3197 S-KPark, TDMilster, TMMiller, J. Buts and W. Bletscher, Jpn. J. Apply. Phys., Vol 44 (2005) pp.3442-3444

  In the optical disk apparatus that condenses the position control light beam L1 and the recording / reproducing light beam L2 using the single objective lens 17 having the above-described configuration, the shorter the wavelength of the recording / reproducing light beam L2, the smaller the spot diameter, The recording density of the optical disc 100 can be increased by forming a small recording mark RM. For this reason, it is considered appropriate to make the wavelength of the recording / reproducing light beam L2 shorter than the wavelength of the position control light beam L1.

  However, in the optical disc 100 configured as described above, the interval between the recording tracks Tr (recording track pitch Pr) and the interval between the guide tracks Tg (guide track pitch Pg) are the same, and the minimum value of the guide track pitch Pg is the position control light beam. It depends on the spot diameter of L1.

  Therefore, even if the recording / reproducing light beam L2 having a shorter wavelength than the position control light beam L1 is used to reduce the spot diameter, the recording track pitch Pr corresponds to the position control light beam L1 having a long wavelength and a large spot diameter. As a result, the recording density of the optical disc 100 cannot be increased even though the recording mark RM is downsized using the recording / reproducing light beam L2 having a short wavelength.

  On the other hand, when recording density is prioritized and the recording track pitch Pr is narrowed according to the spot diameter of the recording / reproducing light beam L2, the guide track pitch Pg becomes narrower than the spot diameter of the position control light beam L1, There was a problem that stable tracking control could not be performed.

  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 tracking control method, and an optical disc capable of recording information at high density and performing stable tracking control.

  In order to solve this problem, in the optical disc apparatus of the present invention, an information light beam and an information light beam are applied to an optical disc provided with a guide track having a track interval twice the track interval of a recording track for recording information. In addition, the objective lens for condensing and irradiating the position control light beam having a long wavelength, the detection means for detecting the reflected light reflected by the guide track, and the detection result by the detection means Position control means for controlling the position of the objective lens so that the control light beam is focused on the land or groove constituting the guide track, and focusing the information light beam on the target recording track corresponding to the land or groove; Provided.

  For the guide track having a track interval twice as large as the recording track, the position control light beam is focused on the land or the groove according to the position of the target recording track, and tracking control is performed, so that the recording track becomes the information light beam. Tracking control can be reliably performed using a position control light beam having a wavelength longer than that of the information light beam, while improving the recording density by setting the interval according to the spot diameter.

  Further, in the tracking control method of the present invention, in the tracking control method for controlling the irradiation position of the information light beam on the optical disc provided with the guide track having the track interval twice the track interval of the recording track for recording information, A first control step of irradiating a position control light beam having a wavelength longer than that of the light beam so as to focus on the guide track, and detecting the reflected light reflected by the guide track; Based on the detection result of the control step, the position of the objective lens is controlled so that the position control light beam is focused on the land or groove constituting the guide track, and the information light is applied to the target recording track corresponding to the land or groove. And a second control step for focusing the beam.

  For the guide track having a track interval twice as large as the recording track, the position control light beam is focused on the land or the groove according to the position of the target recording track, and tracking control is performed, so that the recording track becomes the information light beam. Tracking control can be reliably performed using a position control light beam having a wavelength longer than that of the information light beam, while improving the recording density by setting the interval according to the spot diameter.

  In the optical disk of the present invention, the recording layer for recording the standing wave formed by the first and second information light beams irradiated from both sides via the first and second objective lenses, and the standing wave A guide track having a track interval twice as long as the recorded track interval is formed, transmits the information light beam, and has a wavelength longer than that of the information light beam. The position control is used for tracking control. A reflective layer for reflecting the light beam was provided on the optical disc.

  A guide track having a track interval twice the track interval of a recording track for recording information is provided in a reflective layer that transmits the information light beam and reflects a position control light beam having a longer wavelength than the information light beam. Thus, it is possible to reliably perform tracking control using a position control light beam having a wavelength longer than that of the information light beam while setting the recording track at an interval corresponding to the spot diameter of the information light beam to improve the recording density. it can.

  According to the present invention, the information light beam is transmitted through the guide track having a track interval twice the track interval of the recording track for recording information, and the position control light beam having a longer wavelength than the information light beam is reflected. By providing the reflective layer, the recording track is set at an interval according to the spot diameter of the information light beam to improve the recording density, and reliably using the position control light beam having a longer wavelength than the information light beam. Tracking control can be performed, and thus an optical disc apparatus, a tracking control method, and an optical disc that can record information at high density and perform stable tracking control can be realized.

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

(1) Configuration of Optical Disc First, the optical disc 100 used as an information recording medium in the present invention will be described. As shown in the external view of FIG. 4A, the optical disc 100 is generally formed in a disc shape having a diameter of about 120 [mm], similar to the conventional CD, DVD and BD, and has a hole 100H at the center. Is formed.

  Further, as shown in the cross-sectional view of FIG. 4B, the optical disc 100 has a recording layer 101 for recording information in the center, and the recording layer 101 is sandwiched from both sides by the substrates 102 and 103. It is configured.

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

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

  Similar to the optical disc 8 (FIG. 1), the recording layer 101 is made of a photopolymer whose refractive index changes depending on the intensity of irradiated light, and responds to a blue light beam having a wavelength of 405 [nm]. As shown in FIG. 4B, when two blue light beams Lb1 and Lb2 having relatively strong intensities interfere in the recording layer 101, a standing wave is generated in the recording layer 101. Thus, an interference pattern having properties as a hologram as shown in FIG. 2A is formed.

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

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

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

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

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

  In practice, when information is recorded on the optical disc 100, the red light beam Lr1 is condensed by the position-controlled objective lens OL1 as shown in FIG. Focus on the guide track.

  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 guide track in the recording layer 101. In other words, it is focused on a position corresponding to the substrate 102 side. At this time, the focal point Fb1 of the blue light beam Lb1 is located farther than the focal point Fr on the common optical axis Lx with reference to the objective lens OL1.

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

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

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

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

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

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

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

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

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

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

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

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

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

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

(2) Configuration of Optical Disc Device Next, the optical disc device 20 corresponding to the optical disc 100 described above will be described. As shown in FIG. 5, the optical disc apparatus 20 is configured to control the whole by a control unit 21.

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

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

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

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

  As shown in FIG. 6, the optical pickup 26 has a substantially U-shaped side surface. As shown in FIG. 4B, the optical pickup 26 irradiates the optical disk 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. 5), so that the recording track indicated by the recording address information in the recording layer 101 of the optical disc 100 (hereinafter referred to as target recording). A recording mark RM corresponding to the recording signal from the signal processing unit 23 is recorded by aligning the irradiation position of the light beam with the track).

  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. 5), thereby irradiating the target recording track indicated by the reproduction address information on the recording layer 101 of the optical disc 100 with the light beam irradiation position. And irradiating a predetermined amount of light beam. At this time, the optical pickup 26 detects a reproduction light beam generated from the recording mark RM of the recording layer 101 in the optical disc 100, and supplies a detection signal corresponding to the amount of light to the signal processing unit 23 (details will be described later).

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

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

(3) Configuration of Optical Pickup Next, the configuration of the optical pickup 26 will be described. As schematically shown in FIG. 7, the optical pickup 26 is provided with a large number of optical components, and is roughly divided into a guide surface position control optical system 30, a guide surface information optical system 50, and a recording light irradiation surface optical system 70. It is comprised by.

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

  In FIG. 8, the laser diode 31 of the guide surface position control optical system 30 can emit a red laser beam having a wavelength of about 660 [nm]. Actually, the laser diode 31 emits a predetermined amount of red light beam Lr1 made of divergent light based on the control of the control unit 21 (FIG. 5) and makes it incident on the collimator lens 32. The collimator lens 32 converts the red light beam Lr1 from diverging light to parallel light and makes it incident on the non-polarizing beam splitter 34 via the slit 33.

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

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

  The objective lens 38 condenses the red light beam Lr1 and irradiates it toward the guide surface 100A of the optical disc 100. At this time, as shown in FIG. 4B, the red light beam Lr1 is transmitted through the substrate 102 and reflected by the reflective / transmissive film 104, and becomes a red reflected light beam Lr2 that goes in the opposite direction to the red light beam Lr1.

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

  Thereafter, the red reflected light beam Lr2 (FIG. 8) is sequentially transmitted through the objective lens 38, the dichroic prism 37, and the correction lenses 36 and 35 to be converted into parallel light, and then enters the non-polarizing beam splitter 34.

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

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

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

  Therefore, in order to make the focal point Fr (FIG. 4B) of the red light beam Lr1 follow the target guide track in the guide surface position control optical system 30, the focal point Fr is in the proximity direction or the separation direction with respect to the optical disc 100. It is necessary to move in the focusing direction and the tracking direction which is the inner or outer peripheral side direction of the optical disc 100.

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

  In the guide surface position control optical system 30 (FIG. 8), the focusing state when the red light beam Lr1 is condensed by the objective lens 38 and applied to the reflection / transmission film 104 of the optical disc 100 is red by the condensing lens 41. The optical positions of the various optical components are adjusted so that the reflected light beam Lr2 is collected and reflected in the focused state when the photodetector 43 is irradiated.

  As shown in FIG. 9, the photodetector 43 has four detection areas 43A, 43B, 43C, and 43D that are divided in a lattice pattern on the surface irradiated with the red reflected light beam Lr2. Incidentally, the direction (vertical direction in the figure) indicated by the arrow a1 corresponds to the traveling direction of the track when the red light beam Lr1 is applied to the reflective / transmissive film 104 (FIG. 4B).

  The photodetector 43 detects a part of the red reflected light beam Lr2 by the detection regions 43A, 43B, 43C, and 43D, respectively, and generates detection signals SDAr, SDBr, SDCr, and SDDr according to the detected light amount, respectively. These are sent to the signal processing unit 23 (FIG. 5).

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

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

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

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

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

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

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

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

(3-2-1) Irradiation with Blue Light Beam In FIG. 10, the laser diode 51 of the guide surface information optical system 50 is configured to emit blue laser light having a wavelength of about 405 [nm]. In practice, the laser diode 51 emits a blue light beam Lb0 made of divergent light based on the control of the control unit 21 (FIG. 5) 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 guide surface information optical system 50 extends the optical path length of the blue light beam Lb1 by the polarizing beam splitter 55, the quarter wavelength plate 56, and the movable mirror 57.

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

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

  Here, the movable lens 61 is moved in the optical axis direction of the blue light beam Lb1 by the actuator 61A. In practice, the relay lens 60 can change the convergence state of the blue light beam Lb1 emitted from the fixed lens 62 by moving the movable lens 61 by the actuator 61A based on the control of the control unit 21 (FIG. 5). Has been made.

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

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

  At this time, as shown in FIG. 4B, the blue light beam Lb1 is transmitted through the substrate 102 and the reflection / transmission film 104, and is focused in the recording layer 101. Here, the position of the focal point Fb1 of the blue light beam Lb1 is determined by a convergence state when the blue light beam Lb1 is emitted from the fixed lens 62 of the relay lens 60. That is, the focal point Fb1 moves to the guide surface 100A side or the recording light irradiation surface 100B side in the recording layer 101 according to the position of the movable lens 61.

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

  In practice, the guide surface information optical system 50 is controlled by the control unit 21 (FIG. 5) to control the position of the movable lens 61, so that the focal point Fb1 of the blue light beam Lb1 in the recording layer 101 of the optical disc 100 (FIG. 4 (FIG. 4)). The depth d1 of B)) (that is, the distance from the reflective / transmissive film 104) is adjusted.

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

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

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

  At this time, in the guide surface information optical system 50, as shown in FIG. 11, after the blue light beam Lb2 is converged to some extent by the objective lens 38, it is reflected by the dichroic prism 37 and enters the relay lens 60. Incidentally, when the blue light beam Lb2 is reflected by the reflection / transmission surface 37S, the polarization direction of the circularly polarized light is inverted, and is converted from, for example, right circularly polarized light to left circularly polarized light.

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

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

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

  The photodetector 64 detects the 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. 5).

  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 is finally irradiated on the photodetector 64 by passing through the same optical path as the blue light beam Lb2 in the guide surface information optical system 50.

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

  The photodetector 64 detects the light amount of the blue light beam Lb3, generates a reproduction detection signal SDp according to the light amount detected at this time, and supplies this to the signal processing unit 23 (FIG. 5).

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

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

(3-3) Configuration of Recording Light Irradiation Surface Optical System The recording light irradiation surface optical system 70 (FIG. 7) irradiates the recording light irradiation surface 100B of the optical disc 100 with the blue light beam Lb2. Further, the blue light beam Lb1 irradiated from the guide surface information optical system 50 and transmitted through the optical disc 100 is received.

(3-3-1) Irradiation of Blue Light Beam In FIG. 11, as described above, the polarization beam splitter 55 of the guide surface information optical system 50 applies approximately 50% of the blue light beam Lb0 that is p-polarized light on the reflection / transmission surface 55S. And is incident on the shutter 71 as a blue light beam Lb2 from the surface 55D.

  The shutter 71 is configured to block or transmit the blue light beam Lb2 based on the control of the control unit 21 (FIG. 5). When the blue light beam Lb2 is transmitted, the shutter 71 enters the polarization beam splitter 72.

  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 voltage applied to the liquid crystal panel is changed. A liquid crystal shutter or the like that blocks or transmits the blue light beam Lb2 can be used.

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

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

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

  Similarly to the relay lens 60, the relay lens 75 moves the movable lens 76 by the actuator 76 </ b> A based on the control of the control unit 21 (FIG. 5), thereby changing the convergence state of the blue light beam Lb <b> 2 emitted from the fixed lens 77. It can be changed.

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

  The galvanometer mirror 78 can change the angle of the reflecting surface 78A. The traveling direction of the blue light beam Lb2 is adjusted by adjusting the angle of the reflecting surface 78A according to the control of the control unit 21 (FIG. 5). It can be adjusted.

  The objective lens 79 is configured integrally with the biaxial actuator 79A. Like the objective lens 38, the objective lens 79 is integrated with the focus direction which is the approaching or separating direction of the optical disc 100 and the inner circumference of the optical disc 100. It can be driven in a biaxial direction with a tracking direction which is a side direction or an outer peripheral side direction.

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

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

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

  In practice, the recording light irradiation surface optical system 70 controls the recording of the optical disk 100 by controlling the position of the movable lens 61 in the relay lens 75 together with the position of the movable lens 61 in the relay lens 60 by the control unit 21 (FIG. 5). The depth d2 of the focal point Fb2 (FIG. 4B) of the blue light beam Lb2 in the layer 101 is adjusted.

  At this time, in the optical disc apparatus 20, the objective lens 38 in the recording layer 101 when it is assumed by the control unit 21 (FIG. 5) that surface blurring or the like has not occurred in the optical disc 100 (that is, in an ideal state). The focal point Fb2 of the blue light beam Lb2 when the objective lens 79 is at the reference position is aligned with the focal point Fb1 of the blue light beam Lb1 when it is at the reference position.

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

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

(3-3-2) Reception of Blue Light Beam By the way, as described above, the blue light beam Lb1 irradiated from the objective lens 38 of the guide surface information optical system 50 (FIG. 10) is contained in the recording layer 101 of the optical disc 100. , Once converged, becomes divergent light and enters the objective lens 79.

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

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

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

  However, the optical disc 100 may actually cause a surface blur or the like. For this reason, as described above, the objective lens 38 is subjected to focus control and tracking control by the guide surface position control optical system 30 and the drive control unit 22 (FIG. 5).

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

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

  As shown in FIG. 12, the photodetector 82 has four detection regions 82A, 82B, 82C, and 82D that are divided in a lattice pattern on the surface irradiated with the blue light beam Lb1, as with the photodetector 43. . Incidentally, the direction indicated by the arrow a2 (the horizontal direction in the figure) corresponds to the track traveling direction in the reflective / transmissive film 104 (FIG. 4B) when the blue light beam Lb1 is irradiated.

  The photodetector 82 detects a part of the blue light beam Lb1 by the detection areas 82A, 82B, 82C, and 82D, respectively, generates detection signals SDAb, SDBb, SDCb, and SDDb according to the detected light amount, respectively. Is sent to the signal processing unit 23 (FIG. 5).

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

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

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

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

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

  Specifically, the signal processing unit 23 performs tangential control using a push-pull signal. The signal processing unit 23 calculates a lateral error signal SNEb according to the following equation (7), and uses this to calculate the drive error of the drive control unit 22. To supply.

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

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

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

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

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

(3-4) Adjustment of Optical Path Length By the way, as described above, the optical pickup 26 of the optical disc apparatus 20 records the blue light beam Lb0 to the blue light beam Lb1 by the polarization beam splitter 55 (FIG. 10) as described above. By separating Lb2 and causing the blue light beams Lb1 and Lb2 to interfere with each other in the recording layer 101 of the optical disc 100, the recording mark RM is recorded at the target mark position in the recording layer 101.

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

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

  On the other hand, in the optical pickup 26, the blue light beam Lb1 passes through the optical path in the guide surface information optical system 50 (FIG. 10) and is irradiated from the guide surface 100A side of the optical disc 100, and the blue light beam Lb2 is irradiated with the recording light irradiation surface. The light is irradiated from the recording light irradiation surface 100B side of the optical disc 100 through the optical path in the optical system 70 (FIG. 11). 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.

  Accordingly, the control unit 21 (FIG. 5) adjusts the optical path length of the blue light beam Lb1 by controlling the position of the movable mirror 57. In this case, the control unit 21 uses the relationship between the position of the movable lens 61 in the relay lens 60 and the depth of the target mark position, and moves the movable mirror 57 in accordance with the position of the movable lens 61, thereby the blue color. The optical path length of the light beam Lb1 is changed.

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

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

(4) Recording and Reproducing Information (4-1) Recording Information on Optical Disc When recording information on the optical disc 100, the control unit 21 (FIG. 5) of the optical disc apparatus 20 is an external device (not shown) as described above. When the information recording command, the recording information, and the recording address information are received, the driving command and the recording address information are supplied to the drive control unit 22 and the recording information is supplied to the signal processing unit 23.

  At this time, the drive control unit 22 irradiates the red light beam Lr1 from the guide surface 100A side of the optical disc 100 by the guide surface position control optical system 30 (FIG. 8) of the optical pickup 26, and the red reflected light beam Lr2 that is the reflected light. Based on this detection result, focus control and tracking control (that is, position control) of the objective lens 38 are performed, so that the focus Fr of the red light beam Lr1 follows the target guide track corresponding to the recording address information.

  Further, the control unit 21 causes the guide surface information optical system 50 (FIG. 10) to irradiate the blue light beam Lb1 from the guide surface 100A side of the optical disc 100. At this time, the focal point Fb1 of the blue light beam Lb1 is focused by the position-controlled objective lens 38, thereby being positioned behind the target guide track.

  Furthermore, the control unit 21 adjusts the depth d1 of the focal point Fb1 (FIG. 4B) to the target depth by adjusting the position of the movable lens 61 in the relay lens 60. As a result, the focal point Fb1 of the blue light beam Lb1 is adjusted to the target mark position.

  On the other hand, the control unit 21 controls the shutter 71 of the recording light irradiation surface optical system 70 (FIG. 11) to transmit the blue light beam Lb2, and irradiates the blue light beam Lb2 from the recording light irradiation surface 100B side of the optical disc 100. Let

  The control unit 21 adjusts the depth d2 of the blue light beam Lb2 (FIG. 4B) by adjusting the position of the movable lens 76 in the relay lens 75 according to the position of the movable lens 61 in the relay lens 60. To do. As a result, the depth d2 of the focal point Fb2 of the blue light beam Lb2 is adjusted to the depth d1 of the focal point Fb1 in the blue light beam Lb1 when it is assumed that no surface blur has occurred in the optical disc 100.

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

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

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

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

  By the way, the signal processing unit 23 (FIG. 5) generates a recording signal representing binary data having a value “0” or “1” based on recording information supplied from an external device (not shown) or the like. In response to this, the laser diode 51 emits the blue light beam Lb0 when the recording signal has the value “1”, for example, and does not emit the blue light beam Lb0 when the recording signal has the value “0”. .

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

(4-2) Reproduction of Information from Optical Disc When reproducing information from the optical disc 100, the control unit 21 (FIG. 5) of the optical disc apparatus 20 is red by the guide surface position control optical system 30 (FIG. 8) of the optical pickup 26. A light beam Lr1 is irradiated from the guide surface 100A side of the optical disc 100, and based on the detection result of the reflected red light beam Lr2, the drive control unit 22 performs focus control and tracking control (that is, position control) of the objective lens 38. ).

  Further, the control unit 21 causes the guide surface information optical system 50 (FIG. 10) to irradiate the blue light beam Lb1 from the guide surface 100A side of the optical disc 100. At this time, the focal point Fb1 of the blue light beam Lb1 is focused by the position-controlled objective lens 38, thereby being positioned behind the target track.

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

  Furthermore, the control unit 21 adjusts the depth d1 of the focal point Fb1 (FIG. 4B) to the target depth by adjusting the position of the movable lens 61 in the relay lens 60. As a result, the focal point Fb1 of the blue light beam Lb1 is adjusted to the target mark position.

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

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

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

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

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

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

(5) Track pitch of the optical disc according to the present invention As described above, in the optical disc apparatus 20 of the present invention, the guide track of the optical disc 100 is focused and irradiated with the red light beam Lr1 having a wavelength of 660 [nm], and the guide track. The blue light beam Lb1 having a wavelength of 405 [nm] (and the blue light beam Lb2 at the time of recording) is condensed on the recording layer 101 while performing tracking control using the red reflected light beam Lr2 reflected on the recording track 101, and is used as a guide track. The recording mark RM is recorded and reproduced along the corresponding virtual recording track.

  Here, the minimum spot diameter when the light beam is condensed is substantially proportional to the wavelength and substantially inversely proportional to the NA of the objective lens. In a conventional DVD using a red light beam having a wavelength of 660 [nm] and an objective lens having an NA of 0.6, the track pitch is selected to be 0.74 [μm], so that the wavelength 405 [nm] of the present invention is used. In the optical disc 100 using the blue light beam and NA 0.5 objective lens, the recording track pitch Pr is selected to be 0.54 [μm] based on the proportional calculation of wavelength and NA according to the following equation (8). It is considered that the recording mark RM can be reliably recorded and reproduced while preventing the interference between tracks.

  As shown in FIG. 3, when the recording track pitch Pr and the guide track pitch Pg are the same, the guide track pitch Pg is 0.54 [μm]. However, an appropriate guide track pitch Pd for a spot when the red light beam Lr1 having a wavelength of 660 [nm] is condensed by an objective lens of NA 0.41 is shown below from a DVD track pitch of 0.74 [μm]. Based on the proportional calculation of NA by equation (9), it is considered to be 1.08 [μm]. That is, when the guide track pitch Pg is made to coincide with the recording track pitch Pr, the guide track pitch Pg is too narrow, which causes a problem that stable tracking control cannot be performed.

  Therefore, in the optical disc 100 of the present invention, the guide track pitch Pg is selected to be 1.08 [μm], which is twice the recording track pitch Pr (that is, Pg = 2Pr).

  The guide track pitch Pg selected in this way matches the track pitch Pd determined as described above and suitable for the spot condensed on the guide track, whereby reliable tracking control can be performed. .

  Here, in the optical disc 100 of the present invention, since the guide track pitch Pg is selected to be twice the recording track pitch Pr, each recording track Tr is a land (concave portion) or groove (convex portion) of the guide track Tg. It is in a position corresponding to either one.

  Therefore, in the optical disc apparatus 20 of the present invention, in the tracking control for the optical disc 100 in which the guide track pitch Pg is twice the recording track pitch Pr, the target recording track Tr is the guide track Tg as shown in FIG. If it is at a position corresponding to the land, the spot of the red light beam Lr1 is positioned on the land of the guide track Tg (FIG. 13A), and the target recording track Tr is at a position corresponding to the groove of the guide track Tg. In this case, the spot of the red light beam Lr1 is positioned on the groove of the guide track Tg (FIG. 13B) and tracking control is performed.

  As described above, the optical disc apparatus 20 performs tracking control on both the land and the groove constituting the guide track Tg (so-called land / groove method), so that the guide track pitch Pg becomes twice the recording track pitch Pr. With respect to the optical disc 100 having two recording tracks Tr with respect to one guide track Tg, it is possible to reliably track all the recording tracks Tr.

(6) Operation and effect In the above configuration, in the optical disc 100, the recording track pitch Pr of the recording mark RM to be recorded and reproduced using a blue light beam with a wavelength of 405 [nm] is reliably prevented by preventing interference between tracks. The guide track Tg is selected to be 0.54 [μm] and tracking control is performed using a red light beam with a wavelength of 660 [nm] so that recording and reproduction can be performed and a high recording density can be achieved. By selecting the pitch Pg as 1.08 [μm] which is twice the recording track pitch Pr, it is possible to perform reliable tracking control with a red light beam having a spot diameter larger than that of the blue light beam.

  In the optical disc 100 having such a configuration, since two recording tracks Tr correspond to one guide track Tg, the optical disc apparatus 20 can be used for both lands and grooves constituting the guide track Tg. On the other hand, by performing tracking control by the land groove method, the objective lens can be positioned at a half pitch of the guide track pitch Pg, and thus a narrow recording track pitch Pr corresponding to a blue light beam that can form a small spot. The recording track Tr (recording mark RM) can be tracked using a red light beam that forms a spot larger than the blue light beam.

  According to the above configuration, the guide track pitch Pg is set to twice the recording track pitch Pr, and tracking control is performed on the guide track Tg by the land-groove method, so that a blue light beam having a short wavelength is transmitted as information light. The recording mark RM is recorded and reproduced by irradiation as a beam, and tracking control is performed using a red light beam having a wavelength longer than that of the blue light beam as a position control light beam, thus recording information at a high density. An optical disc and an optical disc apparatus capable of performing stable tracking control can be realized.

(7) Other Embodiments In the above-described embodiments, the present invention is applied to the optical disc apparatus 20 using a double-sided irradiation type hologram that irradiates light beams from both sides of the optical disc 100 to form a standing wave. Although the present invention is not limited to this, the present invention is not limited to this, and the present invention is applied to an optical disk apparatus using a single-sided irradiation type hologram in which the irradiated light beam is reflected by a reflective film provided on the optical disk to form a standing wave. Can also be applied.

  Furthermore, in the above-described embodiment, a blue light beam having a wavelength of about 405 [nm] is used as the recording light for forming the recording mark RM, and the wavelength control light for controlling the position of the objective lens 38 is about a wavelength. Although a red light beam of 660 [nm] is used, the present invention is not limited to this, and the position control light and the recording light may each have an arbitrary wavelength. Further, the recording track pitch Pr is set to 0.54 [μm] and the guide track pitch Pg is set to 1.08 [μm] which is twice the recording track pitch Pr. However, the present invention is not limited to this, and the guide is not limited thereto. If the track pitch Pg is twice the recording track pitch Pr, the guide track pitch Pg and the recording track pitch Pr may be set to arbitrary values.

  Furthermore, in the above-described embodiment, the case where the present invention is applied to an optical disc having a guide track composed of grooves and lands has been described. However, the present invention is not limited to this, and for example, pits are used instead of grooves. The present invention can also be applied to optical disks having various configurations such as an optical disk having a guide track or an optical disk having a guide track formed by a signal recorded on a recording film.

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

It is a basic diagram which shows the structure of the conventional standing wave recording-type optical disk apparatus. It is a basic diagram which shows the mode of formation of a hologram. It is a basic diagram which shows the structure of the optical disk apparatus which uses two types of light beams. It is a basic diagram which shows the structure of the optical disk by one Embodiment of this invention. 1 is a schematic diagram illustrating a configuration of an optical disc device according to an embodiment of the present invention. It is a basic diagram which shows the external appearance structure of an optical pick-up. It is a basic diagram which shows the structure of an optical pick-up. It is a basic diagram which shows the optical path of a red light beam. It is a basic diagram which shows the structure of the detection area | region in a photodetector. It is a basic diagram which shows the optical path (1) of a blue light beam. It is a basic diagram which shows the optical path (2) of a blue light beam. It is a basic diagram which shows the structure of the detection area | region in a photodetector. It is an approximate line for explanation of tracking control by a land groove system.

Explanation of symbols

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

Claims (5)

An information light beam and a position control light beam having a wavelength longer than that of the information light beam are respectively collected on an optical disc provided with a guide track having a track interval twice the track interval of a recording track for recording information. An irradiating objective lens;
Detecting means for detecting reflected light reflected by the guide track by the position control light beam;
Based on the detection result of the detection means, the position of the objective lens is controlled so that the position control light beam is focused on the land or groove constituting the guide track, and the target corresponding to the land or groove is controlled. An optical disc apparatus comprising: position control means for focusing the information light beam on a recording track. The optical disc apparatus condenses a second information light beam obtained by separating the information light beam with a second objective lens, and irradiates the recording track from the opposite side of the information light beam to focus on the recording track. The optical disc apparatus according to claim 1, wherein a standing wave formed by the information light beam and the second information light beam is recorded on the optical disc. The optical disc apparatus according to claim 1, wherein the guide track is formed in a reflective layer that reflects the position control light beam and transmits the information light beam. In a tracking control method for controlling an irradiation position of an information light beam on an optical disc provided with a guide track having a track interval that is twice the track interval of a recording track for recording information,
A first control step of irradiating a position control light beam having a wavelength longer than that of the information light beam so as to focus on the guide track, and detecting the reflected light reflected by the guide track;
Based on the detection result of the first control step, the position of the objective lens is controlled so that the position control light beam is focused on the land or groove constituting the guide track, so that the land or groove corresponds. A tracking control method comprising: a second control step of focusing the information light beam on the target recording track. A recording layer for recording standing waves formed by the first and second information light beams irradiated from both sides via the first and second objective lenses;
A guide track having a track interval twice as long as the track interval at which the standing wave is recorded is formed, transmits the information light beam, and has a longer wavelength than the information light beam. An optical disc comprising a reflective layer that reflects a position control light beam used for control.

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