JP5024557B2 - Optical pickup device and recording medium - Google Patents

Description

  The present invention relates to an optical pickup device, and more particularly to an optical pickup device that records information on a recording medium on which information is recorded using holography and reproduces information from the recording medium on which information is recorded.

  In recent years, optical pickup devices capable of recording and reproducing high-density information have been proposed using the principle of holography as disclosed in Patent Documents 1 and 2. In such an optical pickup device, the recording operation is performed as follows. Information light modulated according to recording data by a spatial light modulator (SLM: Spatial Light Modulator) and predetermined reference light are generated by laser light from the same light source, and these are irradiated onto a hologram recording medium, In the hologram recording medium, signal light and information light are caused to interfere with each other to form a hologram (diffraction fringe). In this way, the recording data is recorded as a hologram on the hologram recording medium. One hologram recorded here contains extremely large amount of information. This one hologram is called one page, and the recording data is specified and managed for each page (see Non-Patent Document 1). .

  In such an optical pickup device, the reproduction operation from the recorded hologram recording medium is performed as follows. Reproduction light (diffracted light) is generated by irradiating the hologram formed according to the above-described recording data with predetermined reference light. Since this reproduction light includes recording data for one page, the reproduction light can be received by a two-dimensionally arranged light receiving element and subjected to signal processing to reproduce the recording data.

The generation of the information light and the reference light and the reception of the reproduction light described above are performed by an optical unit configured by combining optical elements. One optical path design method in the optical unit is a so-called coaxial optical pickup device in which signal light and reference light are arranged coaxially and have a common optical path through which these light beams pass. Yes.
JP 2008-65932 A JP 2003-178484 A Standard ECMA-377

  By the way, in the coaxial type optical pickup apparatus shown in Patent Document 1, for example, a so-called two-wavelength type optical recording apparatus that records / reproduces information using light beams of different wavelengths such as blue laser light and red laser light. There is. In such a system, blue laser light is used for recording and reproduction, and red laser light is used for tracking adjustment. Tracking adjustment is performed by irradiating pits or grooves formed along the track in the guide layer superimposed on the recording layer of the recording medium with red laser light and detecting the reflected light with a photodetector. Yes.

  Here, in all the optical pickup devices, if the amount of deviation of the focusing position between the tracking red laser light and the information recording blue laser light is constant (preferably zero), any optical pickup device With respect to the recorded recording medium, it is possible to read the information on the recording medium with another optical pickup device. However, since there is always variation between devices in an optical pickup device, if the amount of misalignment between the tracking red laser light and the information recording blue laser light is different, recording is performed by any of the optical pickup devices. When the recording medium is reproduced by another optical pickup device, even if tracking control is performed, the blue laser beam is not irradiated to the information recording position, which may cause a reading error. On the other hand, there is an idea that reading errors can be suppressed by narrowing the track interval. However, since the red laser beam having a long wavelength has a relatively large condensing spot diameter, if the track interval is narrowed, it may straddle between adjacent tracks, which may make tracking control impossible. Also, a laser position adjusting device can be provided to adjust the irradiation position of the blue laser light, but the configuration becomes complicated and there is a risk of increasing the cost.

  The present invention has been made in view of the problems of the prior art, and an object thereof is to provide an optical pickup device and a recording medium capable of appropriately recording / reproducing information with respect to the recording medium using holography. To do.

The optical pickup device according to claim 1, wherein a first light source that emits a first light flux having a wavelength λ1, a second light source that emits a second light flux having a wavelength λ2 (λ1 ≠ λ2), and the first light source A spatial light modulation element that converts a part of the first light flux from the light source into information light; and the remainder of the first light flux is condensed as a reference light on the recording layer of the recording medium together with the information light, and the second light flux An objective lens that focuses the light on the guide layer of the recording medium, an actuator that drives the objective lens at least in the tracking direction, a control circuit for the actuator, and the first light flux from the recording layer of the recording medium is received. An image light receiving element; and a photodetector that receives the second light flux from the guide layer of the recording medium, and records information on the recording layer of the recording medium by causing the reference light and the information light to interfere with each other. And the reference light Irradiating the recording layer of the serial recording medium, reproducing information leading to the image receiving element of the first light flux emitted from the recording medium, the optical pickup device using the coaxial method,
The guide layer overlaid on the recording layer in the recording medium forms a plurality of pits or grooves by shifting in the width direction at intervals smaller than the track width interval along tracks provided concentrically or spirally. And
The control circuit detects a reflected light of the second light beam condensed on the guide layer from the second light source through the objective lens, and thereby detects a plurality of pits in the guide layer. Alternatively, one of the grooves is selected and the objective lens is positioned and fixed in the tracking direction by driving the actuator based on the selected pit or groove.
Recording the information by condensing the information light and the reference light emitted from the first light source on the recording layer through the objective lens while the objective lens is positioned and fixed in the tracking direction. There line,
In the guide layer, one track includes a plurality of sector groups each including two or more same numbers of sectors, and in each sector group, the same first sector extends in the width direction at the same interval with respect to the reference track line. After having shifted pits or grooves and controlling the positioning of the objective lens in the tracking direction based on the pits or grooves in the mth sector in the sector group, recording information for one track, The objective lens is positioned and controlled in the tracking direction based on the pits or grooves in the (m + 1) th sector, and information for one track is recorded .

  According to the present invention, while the objective lens is positioned and fixed in the tracking direction, the information light and the reference light emitted from the first light source are focused on the recording layer via the objective lens. Since information is recorded by forming, the light is condensed on the recording layer along the track at intervals of the pits or grooves separated in the width direction of the track, that is, at an interval narrower than the track interval of the guide layer. Spots can be formed side by side with high accuracy, so that information can be reproduced even when variations occur between devices.

An optical pickup device according to a second aspect is the optical pickup device according to the first aspect , wherein the information light and the reference light are focused on the recording layer via the objective lens in the track direction. It is characterized in that the preceding condensing position and the condensing position following it are not aligned in the radial direction.

According to a third aspect of the present invention, there is provided a recording medium for use in the optical pickup device according to the first or second aspect , wherein the recording layer overlaps with the recording layer and is provided along a concentric or spiral track. And a guide layer in which a plurality of pits or grooves are formed by shifting in the width direction at intervals smaller than the track width .

  ADVANTAGE OF THE INVENTION According to this invention, the optical pick-up apparatus and recording medium which can record / reproduce information appropriately with respect to a recording medium using holography can be provided.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. The optical pickup device PU1 according to the present embodiment can be incorporated in an optical disk drive device. FIG. 1 is a diagram showing a schematic configuration of the optical pickup device PU1. The rotating hologram recording medium HLD is formed by stacking a protective layer PL, a recording layer RL capable of recording information, and a single guide layer GL in this order in the thickness direction.

  FIG. 2 is a diagram schematically showing the relationship between tracks formed on the deepest guide layer GL and servo sectors. In order to facilitate understanding, track lines are drawn in a straight line. In the tracks N to N + 4 extending in parallel, the first servo sector to the fourth servo sector are periodically provided. As shown in FIG. 3, one servo sector has three sample pits, a monotone for clock extraction, a header for synchronization, and address data. As shown in FIG. 6, the sample pits are the most first first pit PT1, the second pit PT2 followed by the interval Δ1, and the last delta PT (Δ1> Δ2) in the rotation direction of the recording medium. The second pit PT2 is shifted to the right in the direction of travel with respect to the first pit PT1 by a quarter of the track interval TP, and the third pit PT3 is the first pit. It is shifted to the left in the traveling direction with respect to PT1 by an interval of 1/4 of the track interval TP. The monotone, header, and address data are located on a line that passes through the first pit PT1. The above is an example of a servo sector, and the present invention is not limited to this.

  FIG. 4 is a diagram illustrating one servo sector group including four servo sectors, and FIG. 5 is a diagram illustrating a track format including servo sector groups. The first pit PT1 of the second to fourth servo sectors is sequentially shifted with respect to the first pit PT1 of the preceding servo sector at a quarter interval of the track interval TP (1.6 μm). One pit PT1 is shifted to the third side opposite to the track interval TP with respect to the first pit PT1 of the preceding fourth servo sector. Each servo sector is spirally arranged while maintaining the track interval TP with respect to the servo sectors adjacent in the track width direction. In the present embodiment, the line connecting all the first pits PT1 of the first servo sector (referred to as the reference track line) is a complete spiral (or concentric circle), and the second to fourth servo sectors are It is assumed that they are shifted in parallel with the above-mentioned interval in the track width direction (that is, the direction orthogonal to the reference track line).

  Here, a method of detecting sample pits by the sample hold circuit will be described. When the condensing spot SP is scanned in the rotation direction of the recording medium, a pulse signal is output from the photodetector when passing through a pit having a high reflectance. For example, when the condensing spot SP passes on the line including the first pit SP1, the amount of reflected light when passing through the first pit SP1 increases, but the reflected light when passing through the second pit SP2 and the third pit SP3 deviated from the line. The amount is small. Therefore, as shown in FIG. 6A, first, a large pulse PL1 (corresponding to the first pit PT1) is generated, and thereafter, the small pulses PL2 and PL3 (corresponding to the second pit PT2 and the third pit PT3) are spaced apart. ) Will follow.

  On the other hand, when the focused spot SP passes on the line including the second pit PT2, as shown in FIG. 6B, first, a medium pulse PL1 (corresponding to the first pit PT1) is generated, and thereafter A large pulse PL2 (corresponding to the second pit PT2) is generated at an interval, and a small pulse PL3 (corresponding to the third pit PT3) is subsequently generated.

  Further, when the focused spot SP passes on the line including the third pit PT3, as shown in FIG. 6C, first, an intermediate pulse PL1 (corresponding to the first pit PT1) is generated, and thereafter the interval is increased. Then, a small pulse PL2 (corresponding to the second pit PT2) is generated, and then a large pulse PL3 (corresponding to the third pit PT3) is generated. Therefore, the tracking spot shift between the focused spot SP and the first pit PT1 is adjusted by tracking the objective lens so that the pulses PL2 and PL3 have the same height, thereby adjusting the position of the focused spot SP. Can be eliminated. As is apparent from the above, in order to perform the tracking servo, not only the first pit PT1 but also the second pit PT2 and the third pit PT3 are necessary. By applying servo so that the maximum values of the output signals (PL2, PL3) when passing through the second pit PT2 and the third pit PT3 are the same, the tracking direction along the line including the first pit PT1 Can be positioned.

  More specifically, the tracking adjustment of the objective lens will be described. In the optical pickup device PU1 shown in FIG. 1, when the control circuit CONT controls the laser drive circuit LDR2 to emit the second semiconductor laser LD2, the divergent light beam (λ2 = 780 nm) emitted from the second semiconductor laser LD2 is After passing through the second polarizing beam splitter PBS2 and the second collimator CL2, reflected by the dichroic prism DP, further reflected by the rising mirror M, passed through the λ / 4 wavelength plate QWP, and incident on the objective lens OBJ, The spots SP are formed on the guide layer GL through the protective substrate (including the recording layer RL) of the recording medium HLD (see FIG. 6).

  The reflected light beam modulated by the pits in the guide layer GL again passes through the objective lens OBJ and the λ / 4 wave plate QWP, is reflected by the rising mirror M, is further reflected by the dichroic prism DP, and passes through the second collimator CL2. Then, it is reflected by the second polarization beam splitter PBS2 and enters the second photodetector PD2 via the second sensor lens SL2.

  Here, a focus error signal and a tracking error signal are generated using the reflected light of wavelength λ2 from the pit. The signal from the second photodetector PD2 is input to the focus error detection circuit FD, and a focus error signal is generated using a known astigmatism method or the like. Based on this, the servo unit SVR and the focus drive circuit FDR are connected. Thus, the biaxial actuator AC2 is driven and controlled, and the focusing control of the objective lens OBJ with respect to the light flux having the wavelength λ2 is performed. On the other hand, the signal from the photodetector PD2 is input to the sample hold circuit SH (holds the maximum value of the output signal based on the sample pit), and the tracking error signal is generated based on the signal from the sample pit as described above. And input to the servo section SVR via the tracking error detection circuit TED. The servo unit SVR controls the tracking drive circuit TED based on the generated tracking error signal, and controls the objective lens OBJ in the tracking direction using the biaxial actuator AC2.

  Here, assuming that the first servo sector of the Nth track has come to the position of the focused spot SP of wavelength λ2, the control circuit CONT reads the sample pit of the first servo sector and selects it, thereby selecting 2 Using the axis actuator AC2, the objective lens OBJ is positioned and fixed in the tracking direction based on the sample pits of the first servo sector. Such fixing is performed by continuously supplying the same current to the tracking coil of the biaxial actuator AC2. In such a case, the control circuit CONT can detect the address data via the address processing unit ADP, but the address data of the first servo sector can be read out without any problem because it is on the Nth track as in the first pit PT1. it can.

  Next, when information is recorded on the recording layer RL, information to be recorded is input from the data signal processing unit SPR1 to the SLM drive circuit SDR based on the control of the control circuit CONT, and the spatial light modulation element SLM. Is controlled.

  The spatial light modulator SLM is a transmissive liquid crystal, and the SLM drive circuit SDR controls whether each of the two-dimensionally arranged liquid crystal elements constituting the transmissive liquid crystal transmits or does not transmit the light beam. Is done. Further, the spatial light modulation element SLM has two regions, a donut-shaped reference light region and a circular information light region inside thereof, although not shown. Each of the liquid crystal elements belonging to the reference light region is a predetermined reference expressed by a combination of “1” and “0” stored in a storage region of the SLM drive circuit SDR, for example, a RAM (Random Access Memory). Depending on the light pattern, “1” is maintained in the transmissive state, and “0” is maintained in the non-transmissive state.

  Similarly, each of the liquid crystal elements belonging to the information light region has “1” in accordance with recording data in units of pages expressed by a combination of “1” and “0” output from the SLM drive circuit SDR. In the case of, the transmission state is maintained, and in the case of “0”, the non-transmission state is maintained. Here, the recording data is encoded as modulation recording data which is a block code. For example, one block of the modulation recording data is associated with the area of 16 liquid crystal elements in 4 rows and 4 columns, A 16: 3 code is used in which three of the sixteen are in a transparent state. In the control area in the recording data, the track number used as a reference (overlapping with the first servo sector) used during recording, the servo sector number (1-4) used during recording, and the continuation of the servo sector on the same track line. Number information (1, 2, 3,...) Is included. For example, TOC information or the like may be recorded in other areas.

  During recording, the control circuit CONT controls the laser drive circuit LDR1 to emit light from the first semiconductor laser LD1 while performing the tracking control described above. The divergent light beam (λ1 = 405 nm) emitted from the first semiconductor laser LD1 is converted into a parallel light beam by the first collimator CL1, passes through the expander EXP and the beam shaper BPS, and passes through the spatial light modulator SLM. Two-dimensional modulation corresponding to the information to be recorded is applied to become a coaxial reference beam and information beam, which further passes through the first polarizing beam splitter PBS1, the lens L1, the pinhole P1, the lens L2, and the dichroic prism DP, and is raised. The light is reflected by M, passes through the λ / 4 wavelength plate QWP, enters the objective lens OBJ, and is then collected on the recording layer RL via the protective layer PL of the recording medium HLD, where reference light, signal light, Interfere to generate interference fringes (hologram HP shown in FIGS. 7 and 8). Thereby, information can be recorded.

  Here, when the “holo pitch” is the minimum distance at which adjacent holograms can be normally recorded and reproduced, the minimum holo pitch in the radial direction is HPR and the minimum holo pitch in the circumferential direction is HPT. In addition, the shift margin (maximum shift amount at which information can be read when shifted from the center) in a spot including two-dimensional information is ± 0.25 μm.

  Note that the positioning of the objective lens OBJ in the tracking direction remains fixed as described above. As described above, information can be accurately recorded on the Nth track TR until the first servo sector in the next servo sector group is reached. When the next first servo sector comes to the position of the focused spot SP of wavelength λ2, tracking control (fine adjustment) is similarly applied to the sample pit. By repeating the above, the servo can be continuously applied so that information can be continuously recorded on the Nth track TR. When the information recording on the Nth track TR is completed, the information is recorded at a position shifted by + TP / 4 with respect to the Nth track TR by using the second servo sector.

  A case where the servo is applied using the second servo sector will be described. After the recording of information using the first servo sector, when the second servo sector comes to the position of the focused spot SP having the wavelength λ2, the control circuit CONT uses the second servo sector based on the signal from the second photodetector PD2. By selecting this sample pit, the objective lens OBJ is positioned and fixed in the tracking direction so as to shift by + TP / 4 according to the position of the sample pit of the second servo sector. As a result, the objective lens OBJ is fixed in the tracking direction until the second servo sector in the next servo sector group is reached, and information can be accurately recorded at a position shifted by + TP / 4 from the Nth track TR. . Further, when the next second servo sector comes to the position of the focused spot SP having the wavelength λ2, tracking control (fine adjustment) is similarly applied to the sample pit. By repeating the above, the servo can be continuously applied so that information can be continuously recorded at a position shifted by + TP / 4 from the Nth track TR. When the recording of information at a position deviated by + TP / 4 from the Nth track TR is completed, recording of information is performed at a position deviated by + TP / 2 with respect to the Nth track TR by using the third servo sector. I do.

  A case where the servo is applied using the third servo sector will be described. After the recording of information using the second servo sector, when the third servo sector comes to the position of the focused spot SP of wavelength λ2, the control circuit CONT uses the third servo sector based on the signal from the second photodetector PD2. By selecting this sample pit, the objective lens OBJ is positioned and fixed in the tracking direction so as to further shift by + TP / 4 according to the position of the sample pit of the third servo sector. As a result, the objective lens OBJ is fixed in the tracking direction until the third servo sector in the next servo sector group arrives, and information can be accurately recorded at a position shifted by + TP / 2 from the Nth track TR. . Further, when the next third servo sector comes to the position of the focused spot SP having the wavelength λ2, tracking control (fine adjustment) is similarly applied to the sample pit. By repeating the above, the servo can be continuously applied so that information can be continuously recorded at a position shifted by + TP / 2 from the Nth track TR. When the recording of information at a position deviated by + TP / 2 from the Nth track TR is completed, recording of information is performed at a position deviated by + 3TP / 4 from the Nth track TR by using the fourth servo sector. I do.

  A case where servo is applied using the fourth servo sector will be described. After the recording of information using the third servo sector, when the fourth servo sector comes to the position of the focused spot SP having the wavelength λ2, the control circuit CONT uses the fourth servo sector based on the signal from the second photodetector PD2. By selecting this sample pit, the objective lens OBJ is positioned and fixed in the tracking direction so as to further shift by + TP / 4 according to the position of the sample pit of the fourth servo sector. As a result, the objective lens OBJ is fixed in the tracking direction until the fourth servo sector in the next servo sector group arrives, and information can be accurately recorded at a position shifted by + 3TP / 4 from the Nth track TR. . Further, when the next fourth servo sector comes to the position of the focused spot SP having the wavelength λ2, tracking control (fine adjustment) is similarly applied to the sample pit. By repeating the above, the servo can be continuously applied so that information can be continuously recorded at a position shifted by + 3TP / 4 from the Nth track TR. When the recording of information at a position shifted by + 3TP / 4 from the Nth track TR is completed, the next movement is made to the N + 1th track, and information can be recorded in the same manner as described above. The servo may be continuously applied to the same servo sector, and after recording on the entire disk surface, it may be switched to another servo sector. Further, when the information light and the reference light are collected on the recording layer RL via the objective lens OBJ, the preceding hologram HP and the succeeding hologram HP are not aligned in the radial direction in the track direction. (See FIG. 7). Thereby, the required minimum holo pitch can be secured.

  At the time of reproduction, all the liquid crystal elements in the information light region are made non-transmissive. Further, while performing the tracking control described above, the control circuit CONT controls the laser driving circuit LDR1 to cause the first semiconductor laser LD1 to emit light. The divergent light beam emitted from the first semiconductor laser LD1 is converted into a parallel light beam by the first collimator CL1, passes through the expander EXP and the beam shaper BPS, and passes through the spatial light modulation element SLM, so that only the reference light is emitted. Further, the light passes through the first polarizing beam splitter PBS1, the lens L1, the pinhole P1, the lens L2, and the dichroic prism DP, is reflected by the rising mirror M, passes through the λ / 4 wavelength plate QWP, and enters the objective lens OBJ. After that, the information is condensed on the recording layer RL on which the information is recorded via the protective layer PL of the recording medium HLD.

  At this time, the reflected light beam modulated in accordance with the information recorded in the hologram passes through the objective lens OBJ and the λ / 4 wavelength plate QWP again, is reflected by the rising mirror M, and is reflected by the dichroic prism DP, lens L2, and so on. The first photodetector PD1 that passes through the pinhole P1 and the lens L1, is further reflected by the first polarization beam splitter PBS1, and passes through the first sensor lens SL1 (here, CMOS, but may be a CCD). Is incident on. The image received by the first photodetector PD1 is formed in the same form as that displayed on the spatial light modulator PLM during recording. That is, an image corresponding to the reference light component included in the reproduction light is reproduced on the outer peripheral portion, and an image corresponding to the signal light component included in the reproduction light is reproduced on the inner peripheral portion. An output signal of the first photodetector PD1 obtained by converting such an image into an electric signal is transmitted to the CMOS drive circuit CDR and further transmitted to the data signal processing unit SPR1.

  The error signal generated by the control circuit CONT is transmitted to the servo unit SVR based on the signal from the second photodetector PD2, and the servo unit SVR controls the focus drive circuit FDR in response to this, The biaxial actuator AC2 is driven to focus the objective lens OBJ.

  FIG. 7 is a schematic view showing a state in which information is recorded while shifting in the width direction by TP / 4 with respect to the track as described above, according to this embodiment. It is a comparative example, and is a schematic diagram showing a state where information is recorded in a line on a track. In any of the figures, the track is drawn straight as shown by a thick line, and the thin line between them is a tracking line shifted by ± TP / 4 in the track width direction with reference to the track. Further, a hologram HP in which information is recorded by collecting the reference light and the information light is indicated by a circle.

  Here, there is a device-to-device variation between the optical pickup device that records information on the recording medium and the optical pickup device that tries to reproduce information from the recording medium, and the light flux emitted from the first semiconductor laser LD1 is condensed. There may be a difference in the amount of deviation in the track width direction between the position and the condensing position of the emitted light beam of the second semiconductor laser LD2. If the amount of deviation is large, when tracking control is performed using a light beam emitted from the second semiconductor laser LD2 along a certain track, the reference light is, for example, between adjacent tracks as indicated by an arrow X. It may be scanned along. Here, since the shift margin (± 0.25 μm) is limited, the reference light passes through in the comparative example shown in FIG. 8, and any hologram HP cannot be recognized, which may cause a reading error. is there.

  On the other hand, according to the present embodiment shown in FIG. 7, since the hologram HP is formed with a shift of TP / 4 with respect to the track width direction, even when the same amount of deviation as described above occurs, for example, When the reference light is scanned between adjacent tracks as indicated by the arrow X, it can be recognized by passing over any hologram HP (here, ●) (that is, an image generated from the hologram HP). Therefore, even if the shift margin (± 0.25 μm) is limited, the occurrence of reading errors can be suppressed. Also, in any hologram HP, the track number used as a reference (overlapping with the first servo sector) used at the time of recording, the information of the servo sector number (1 to 4) used at the time of recording, and the information of the consecutive number in the same servo sector ( 1, 2, 3,...) Is recorded, the information can be acquired by scanning any hologram HP with reference light. Based on this acquired information and the address information of the servo sector obtained by detecting the light beam of wavelength λ2 simultaneously emitted for tracking servo by the photodetector PD2, the current is detected by scanning the reference light. It is possible to determine which servo sector corresponds to the hologram HP. That is, the relative deviation in the track width direction between the condensing position of the emitted light beam of the first semiconductor laser LD1 and the condensing position of the emitted light beam of the second semiconductor laser LD2 is determined based on the information on the hologram HP and the reference used at the time of recording. Track number and servo sector number, and the relative displacement in the track direction can be determined from information on the hologram HP and information on successive numbers in servo sectors on the same track line. By correcting the tracking servo based on the relative shift amount, the target hologram HP can be quickly and appropriately scanned on the target track or on the tracking line shifted by TP / 4 with respect to the target track. .

  According to the present embodiment, the allowable shift margin of the hologram HP is TP / 4. It is desirable that the recorded pit length in the circumferential direction is TP / 4. However, if the clock cycle generated from the pit is set to at least TP / 4, this clock is used to reduce the reading accuracy below the shift margin. Can be suppressed. Actually, since the clock generated from the recording medium has jitter, it is desirable to use a more multiplied clock. Note that the order of recording is not particularly important, and it can be said that the arrangement of the finally recorded patterns is important. According to the present embodiment, a holographic optical pickup device that does not require a laser position adjustment mechanism can be configured.

  In the above embodiment, a light beam of λ2 = 780 nm is used as the servo light. However, a light beam of λ2 = 650 nm may be used. In this case, for example, the track pitch TP is 0.74 μm. As three, it is preferable to shift each first servo pit by TP / 4 = 0.4 μm. Furthermore, tracking servo control may be performed in the same manner for information reproduction. A groove may be provided instead of the pit.

It is a figure which shows schematically the structure of optical pick-up apparatus PU1. It is a figure which shows roughly the relationship between the track formed in the guide layer GL, and a servo sector. It is a figure which shows one servo data. It is a figure which shows one servo sector group which consists of four servo sectors. It is a figure which shows the track format which consists of a servo sector group. It is a figure which shows the relationship between a sample pit and the signal of a photodetector. FIG. 10 is a schematic diagram showing a state in which information is recorded while shifting in the width direction by TP / 4 with respect to a track according to the embodiment. It is a comparative example, and is a schematic diagram showing a state where information is recorded in a line on a track.

Explanation of symbols

AC1 1-axis actuator AC2 2-axis actuator ADP Address processing unit CL1 First collimator CL2 Second collimator CONT Control circuit DP Dichroic prism FD Focus error detection circuit FDR Focus drive circuit GL Guide layer LD1 First semiconductor laser LD2 Second semiconductor laser LDR1 Laser Drive circuit LDR2 Laser drive circuit M Mirror OBJ Objective lens PBS1 First polarization beam splitter PBS2 Second polarization beam splitter PD1 First photodetector PD2 Second photodetector PU1 Optical pickup device QWP λ / 4 wavelength plate RL Recording layer RP1 Surface RP2 Light receiving surface RP3 Light receiving surface SH Sample hold circuit SL1 Sensor lens SL2 Sensor lens SP Data signal processing unit SP Spot SPR1 Data signal processing unit SVR Servo unit DR tracking drive circuit TED tracking error detecting circuit TP track spacing

Claims (3)

Information on a first light source that emits a first light flux having a wavelength λ1, a second light source that emits a second light flux having a wavelength λ2 (λ1 ≠ λ2), and a part of the first light flux from the first light source. A spatial light modulation element that converts light, and the remaining light of the first light beam is condensed as a reference light on the recording layer of the recording medium together with the information light, and the second light beam is condensed on the guide layer of the recording medium. An objective lens, an actuator that drives the objective lens in at least a tracking direction, a control circuit for the actuator, an image light receiving element that receives the first light flux from the recording layer of the recording medium, and a guide layer of the recording medium A light detector for receiving the second light flux from the recording medium, the reference light and the information light are interfered to record information on a recording layer of the recording medium, and the reference light is recorded on the recording medium. Irradiating the layer, the recording medium The first light flux emitted from reproducing the guidance information to said image receiving element, the optical pickup device using the coaxial method,
The guide layer overlaid on the recording layer in the recording medium forms a plurality of pits or grooves by shifting in the width direction at intervals smaller than the track width interval along tracks provided concentrically or spirally. And
The control circuit detects a reflected light of the second light beam condensed on the guide layer from the second light source through the objective lens, and thereby detects a plurality of pits in the guide layer. Alternatively, one of the grooves is selected and the objective lens is positioned and fixed in the tracking direction by driving the actuator based on the selected pit or groove.
Recording the information by condensing the information light and the reference light emitted from the first light source on the recording layer through the objective lens while the objective lens is positioned and fixed in the tracking direction. There line,
In the guide layer, one track includes a plurality of sector groups each including two or more same numbers of sectors, and in each sector group, the same first sector extends in the width direction at the same interval with respect to the reference track line. After having shifted pits or grooves and controlling the positioning of the objective lens in the tracking direction based on the pits or grooves in the mth sector in the sector group, recording information for one track, An optical pickup device, wherein the objective lens is positioned and controlled in the tracking direction based on a pit or groove in the (m + 1) th sector, and information for one track is further recorded . When the information light and the reference light are condensed on the recording layer via the objective lens, the preceding condensing position and the condensing position following it are aligned in the radial direction in the track direction. The optical pickup device according to claim 1 , wherein the optical pickup device is not provided. The recording medium used for the optical pickup device according to claim 1 or 2 , wherein the recording layer and a track overlapped with the recording layer and provided concentrically or spirally in the width direction are smaller than the track width. And a guide layer formed with a plurality of pits or grooves shifted at intervals .