JP2009104717A - Recording and reproducing device, and recording and reproducing method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a recording and reproducing device for stably recording or reproduction data from a recording medium having a multilayer structure. <P>SOLUTION: The recording and reproducing device for a three-dimensional recording medium including a plurality of recording layers and a servo layer layered in a film thickness direction includes: a movable holding device of the recording medium; an optical device including a light source of laser light for servo having a first wavelength, a light source of laser light for recording having a second wavelength different from the first wavelength, and an objective lens common to a laser light optical system for servo and laser light optical system for recording; a means for detecting light returned from the servo layer and the recording layers via the objective lens and having the first and the second wavelengths; and a focus adjusting device setting the numerical aperture of the laser light optical system for servo so that the spot size of the laser light for servo on the servo layer is made nearly equal to the spot size of the laser light for recording on a prescribed recording layer and setting focus positions of the laser light for servo and the laser light for recording by the objective lens so as to be separated from each other in the film thickness direction of the plurality of recording layers. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a recording / reproducing apparatus and a recording / reproducing method for a recording medium on which information is recorded or reproduced optically, such as an optical disk or an optical card having a recording layer capable of recording or reproducing information by irradiation of a light beam.

  In recent years, an optical disk as a recording medium has been widely used as means for recording and reproducing data such as video data, audio data, and computer data. For example, in the DVD (Digital Versatile Disc) and Blu-ray Disc (Blu-ray Disc) standards, a dual-layer disc that can be read from one side of the disc and has two recording layers on one side is used as a playback and recording disc. It has been put into practical use.

  In a dual-layer disc, the electrical signals of both the shallow recording layer and the deep recording layer can be read from one side of the disc simply by moving the focus of the reproducing light beam to each layer. The shallow recording layer is made a semi-transparent film so that the light beam can be transmitted through the shallow recording layer and the electrical signal of the deep recording layer can be read, and the film thickness and material are selected. A reflective film is used for the deep recording layer. In order to separate these between the shallow recording layer and the deep recording layer with a certain thickness, a light-transmitting spacer layer having a high transmittance at the wavelength of light is provided.

  On the other hand, next-generation optical discs are required to have higher density than Blu-ray discs. For this reason, the recording layers are further increased to be multilayered. There has been proposed a system in which a recording layer is provided separately and recording is performed on each recording layer with a recording laser beam while obtaining a signal from the servo layer with the servo laser beam (see Patent Documents 1 to 5).

  In the technique of Patent Document 1, servo laser light and recording laser light have different frequencies for the servo layer and the recording layer, respectively, in order to achieve tracking control and focus control of the multilayer optical disk without using a pinhole. By irradiating with modulation or turning on in a time-division manner, a single photodetector can detect a tracking error signal and a focus shift signal, and information from each layer can be separated.

  In the technique of Patent Document 2, the servo layer is irradiated with a servo laser beam to perform servo, and the recording layer is irradiated with a recording laser beam to record on a recording medium. The pitch of the recording track in the radial direction is formed by performing the interlayer movement only in the recording layer and forming the recording mark by shifting the recording track adjacent to the recording layer in the radial direction by a half of the layer in the depth direction. It is possible to increase the density by narrowing.

  In the technique of Patent Document 3, a three-dimensional recording medium is used as a recording medium in which a control layer in which a tracking control signal is formed in advance and a photosensitive material capable of changing optical properties are overlapped in the volume of the photosensitive material. An area where discrete optical properties corresponding to the data to be recorded are distributed is layered (each layer is referred to as a “recording layer”), and the light beam guided by the tracking control signal of the control layer is It is formed so as to overlap the route (control track) that passes.

  The technique of Patent Document 4 performs a focus and tracking servo on a three-dimensional optical disk in a bulk state (recording layer) in which a servo layer has been formed in advance by a signal returned from the servo layer by a servo laser beam, and a recording laser beam When recording data on the recording layer in the back of the servo layer and irradiating another recording layer with the recording laser beam, move the objective lens with the actuator of the optical system so that the deeper layer is focused By operating, data is recorded in the recording layer thickness direction.

The technique of Patent Document 5 uses a recording laser beam that performs recording or reproduction with respect to a recording layer and a servo laser beam that reads a servo layer in a multilayer information medium in which a plurality of data layers such as a recording layer are stacked. Used in a recording or reproducing method in which the servo layer is read out by a servo layer arranged behind the layer, and the absorption rate for the data laser is higher than the absorption rate for the servo laser beam between the data layer and the servo layer. A filter layer is provided.
JP 2007-4897 JP 2006-107668 Gazette JP 2003-36537 A JP 2002-3129581 A JP 2002-63738 A

  As shown in FIG. 1, in the optical disk system having a multilayer structure that has been studied in the past, the servo laser beam SB and the recording laser beam RB are condensed by an objective lens having the same numerical aperture. The effective spots SB7 and RB7 on the target layer (servo layer 11 and recording layer 5) have different sizes. For example, when the effective spot size SB7 on the servo layer 11 and the effective spot size RB7 on the recording layer 5 are different, the recording capacity is limited to the larger spot size.

  Thus, the problem to be solved by the present invention is to provide a recording / reproducing apparatus and method that enable efficient recording or reproduction as an example.

The recording / reproducing apparatus of the present invention irradiates condensed light onto a recording medium including a plurality of recording layers stacked in the film thickness direction and a servo layer carrying focus servo and tracking servo information. A recording / reproducing apparatus for recording / reproducing data at a three-dimensional recording position on the recording medium,
A movable holding device for detachably holding the recording medium;
A light source of servo laser light of the first wavelength;
A light source for recording laser light having a second wavelength different from the first wavelength;
An optical device including a servo laser beam optical system for condensing the servo laser beam and the recording laser beam on the servo layer and the recording layer, respectively, and an objective lens common to the recording laser beam optical system;
Means for detecting light of the first and second wavelengths returning from the servo layer and the recording layer via the objective lens,
The numerical aperture of the servo laser light optical system is set so that the spot size of the servo laser light on the servo layer is substantially equal to the spot size of the recording laser light on the predetermined recording layer, and And a focus adjusting device for setting the focus positions of the servo laser beam and the recording laser beam by the objective lens so as to be separated from each other in the film thickness direction of the plurality of recording layers. In this case, the optical spot size of the servo laser and the recording laser is substantially equal when the optical system has a wavefront aberration of 30 mλ (where λ indicates the wavelength of the servo laser or recording laser light). It means to match within the error range of the spot size spreading to. The reason why the wavefront aberration value of 30 mλ, that is, 3λ / 100 is used as a reference is that it is less than half of the so-called Marechal limit λ / 14 = 0.071λ [rms]. Needless to say, it is most desirable that the light spot sizes of the servo laser and the recording laser are completely the same.

The recording / reproducing method of the present invention irradiates a condensed light onto a recording medium including a plurality of recording layers laminated in the film thickness direction and a servo layer carrying focus servo and tracking servo information. A recording / reproducing method for recording / reproducing data at a three-dimensional recording position on the recording medium,
Holding the recording medium detachably;
Via the objective lens common to the servo laser light optical system and the recording laser light optical system, the servo laser light of the first wavelength and the recording laser light of the second wavelength different from the first wavelength are supplied to the servo layer and Condensing each of the recording layers;
Detecting light of the first and second wavelengths returning from the servo layer and the recording layer via the objective lens,
The numerical aperture of the servo laser light optical system is set so that the spot size of the servo laser light on the servo layer is substantially equal to the spot size of the recording laser light on the predetermined recording layer, and A focusing setting step of setting the focus positions of the servo laser beam and the recording laser beam by the objective lens apart from each other in the film thickness direction of the plurality of recording layers.

  In the above prior art, the mutual spot sizes of the servo laser beam and the recording laser beam in the servo layer and the recording layer are not controlled. However, according to the configuration of the present invention, the servo laser beam and the recording laser beam are not controlled. The mutual spot sizes are controlled so that the effective spot sizes of the light are substantially equal, and the wavelengths of the servo laser beam and the recording laser beam and the numerical aperture of the lens system are set. Playback can be performed. Therefore, by making the effective spot size of the servo laser beam and the spot size of the recording laser beam the same and making the track pitch of the servo layer and the recording layer the same, it is possible to efficiently perform recording and reproduction from the recording medium. .

BEST MODE FOR CARRYING OUT THE INVENTION

  Embodiments of the present invention will be described below with reference to the drawings.

(Recording and playback device)
FIG. 2 shows a schematic configuration of the recording medium of the present embodiment and a recording / reproducing system for recording or reproducing the recording medium.

  As shown in FIG. 2, the recording / reproducing apparatus irradiates the recording motor 2 with a spindle motor 8 having a turntable (movable holding device) that rotatably holds the disk-shaped recording medium 2 and a recording / reproducing light beam. A pickup 23 including an objective lens and a control device 101 for controlling these are provided. The control device 101 controls the spindle motor 8 and the pickup 23 based on output data output from various sensors provided on the spindle motor 8 and the pickup 23, and processes the data. In response to a signal from the control device 101, the pickup 23 irradiates the recording medium 2 whose rotation is controlled while controlling the position of the recording light beam using the servo-control light beam, and the recording mark is applied to the recording medium 2. Record. The control device 101 obtains a signal generated from the return light of the reproduction light beam from the pickup 23, decodes it, and outputs it.

(recoding media)
FIG. 3 shows an example of a cross-sectional structure of a multilayer optical disc as a multilayer recording medium that uses a refractive index change type multiphoton absorption material as a recording layer, which is the recording medium 2 of the first embodiment. The recording medium 2 includes a cover layer 13, a servo layer 11, a wavelength selective reflection film 9 for reflecting the servo laser beam SB, a recording layer group 50, and a holding layer from the incident side of the recording laser beam RB and the servo laser beam SB. It consists of a substrate 3.

  The cover layer 13 is made of a light transmissive material, and functions to flatten the laminated structure and protect the recording layer group 50 and the like.

  The servo layer 11 is a layer for detecting a focus and tracking servo signal in which a servo groove or the like is recorded.

  The recording layer group 50 is a stack of a plurality of recording layers 5 each recording information.

  The wavelength selective reflection film 9 between the servo layer 11 and the recording layer group 50 reflects the servo laser beam SB having a wavelength different from the recording laser beam RB (first wavelength, for example, a wavelength longer than the recording laser beam). In addition, it is set so as to transmit the recording laser beam RB (second wavelength). That is, in this example, the servo layer 11 is arranged on the light incident side of the recording layer group 50.

  Three-dimensionally at the condensing point of each recording layer 5 of the recording laser beam RB of the recording layer group 50 by the recording laser beam RB having a specific positional relationship with the servo laser beam SB condensed by the objective lens OB. Data (record mark RM) is recorded in the. The objective lens OB having a predetermined numerical aperture irradiates a condensed beam and collects reflected light from the recording layer group 50. The condensed beam is irradiated from the cover layer 13 side in order to write or read a signal from any recording layer of the recording layer group 50, and information is recorded and reproduced.

  The holding substrate 3 is made of, for example, glass, plastic such as polycarbonate, amorphous polyolefin, polyimide, PET, PEN, or PES, or an ultraviolet curable acrylic resin. The outer shape of the recording medium 2 may be a card shape in addition to the above disk shape.

  FIG. 4 shows a schematic configuration of the recording medium 2 of the second embodiment.

  In the recording medium 2 shown in FIG. 4, the servo layer 11 is not covered on the light incident side of the recording layer group 50 of the first embodiment, but on the innermost side through the recording layer group 50 when viewed from the light incident side. Except for having a structure arranged via the layer 131, it is almost the same as that of the first embodiment. Each layer of the recording layer group 50 is set so as to at least partially reflect the recording laser beam RB during operation and always transmit the wavelength of the servo laser beam SB. With this configuration, the servo laser beam SB is incident on the innermost servo layer 11 from the light incident side without being affected by the recording layer group 50.

  The second cover layer 131 is made of a light transmissive material, and functions to flatten the servo layer 11 and protect the recording layer group 50 and the like.

  In both embodiments, the recording medium 2 basically includes a first recording layer 5a, a first separation layer 7a, a second recording layer 5b, a second separation layer 7b,. The recording layer 5n includes a light-transmitting multilayer portion (recording layer group 50) of the n-th separation layer 7n, and a light-transmitting holding substrate 3 that supports these multilayer portions. Each separation layer (refractive index = ns) has a constant film thickness in order to maintain a predetermined interlayer distance between adjacent recording layers (refractive index of unrecorded portions = nb), and the recording layers and separation layers are alternately laminated. Yes. If the refractive index difference between the recording layer and the separation layer is increased, reflection at the interface increases and light does not reach the back layer. Therefore, it is desirable that the refractive index difference between the recording layer and the separation layer is as small as possible.

  In each recording layer, a plurality of recording marks RM having a refractive index different from the surroundings are formed. A recording mark (refractive index = na ≠ nb) is formed on an arbitrary recording layer by, for example, causing multiphoton absorption only in a region having a high photon density near the focal point when a short pulse laser beam or the like is condensed by an objective lens. Can be formed. A known method is applied as a method for forming the recording mark. In the recording layer, the recording marks are distributed like the conventional optical disc as a difference in refractive index. A known method is applied to the modulation method of the recorded information. As described above, in the multilayer recording medium, the separation layer and the recording layer having a predetermined film thickness formed on the substrate are alternately stacked, and a plurality of recording marks RM having different refractive indexes from the surroundings are formed on the recording layer. The information to be recorded is carried on the.

  Here, a recording mechanism called photon recording using multiphoton absorption will be described.

Conventional optical discs are heat mode recording using light energy as heat. In the heat mode recording method, there is a limit to increasing the density of the material. An alternative multiphoton absorption process recording method using photons is proposed. The multiphoton absorption process is a process in which one atom or molecule simultaneously interacts with a plurality of photons, unlike a normal one-photon reaction (linear optical process). In general, when the photon density is low as in ordinary laser light irradiation, the photon having an energy of E = hC / λ (where λ = wavelength, h = Planck constant, C = light velocity). Only one substance (atom or molecule) absorbs (one-photon absorption). However, for example, when ultrashort pulse laser light is focused and irradiated with a high numerical aperture objective lens, the photon density becomes very high near the focal point, and the substance absorbs two or three photons at a time (n-photon absorption). In this way, a lot of energy such as 2 or 3 times E can be received at once. For example, in the femtosecond laser, since the electric field strength is very strong, only the vicinity of the portion where the beam is condensed causes a non-linear reaction of multiphoton absorption in a spatially selective manner. When data is recorded using the two-photon absorption process, it becomes possible to record data in multiple points at many points in the three-dimensional space. If this is utilized, a super multi-layer optical disk having, for example, 10 layers or more can be realized. In other words, by irradiating light having a wavelength longer than the absorption wavelength region of the recording layer, the recording layer in front of which the light is not sufficiently narrowed does not cause absorption but is sufficiently condensed and is to be reproduced. Absorption can occur only in the recording layer.

  When a substance absorbs light by multiphoton absorption, the absorption intensity is proportional to the nth power of the intensity of irradiation light when n photon absorption is performed. As a result, the substance is absorbed in a sharp distribution within the substance, and a strong chemical reaction occurs locally to allow formation of a heterogeneous phase. For example, since the pulse width is very short, from several femtoseconds to several hundred femtoseconds, a very large energy density is generated at the focal position, and a multiphoton reaction occurs and is absorbed by the adjacent layer. Further, since the pulse width is very short compared with the reciprocal of the lattice vibration of the material, it is hardly affected by heat in the laser light absorption process.

  Therefore, the recording / reproducing method of the present invention enables reproduction by changing the optical characteristics in the target layer of the plurality of recording layers in the nonlinear optical process of n-photon absorption and detecting the change in the optical characteristics. Therefore, the servo laser beam SB (first wavelength) is set so as not to overlap with the periphery of the wavelength of the recording laser beam RB (second wavelength) that is 1 / n wavelength.

  For example, as a two-photon absorption material, a fluorescent type that uses a fluorescent substance that changes the fluorescence intensity in a region where two-photon absorption occurs, and a refractive index change type that uses a photorefractive substance whose refractive index changes due to localization of electrons. There is. Use of a photochromic compound, a bis (aralkylidene) cycloalkanone compound, or the like is promising as a refractive index change type two-photon absorption material.

  As an optical disc structure using a two-photon absorption material, a bulk type in which the entire optical disc is made of a two-photon absorption material, a recording layer of the two-photon absorption material, and a layer structure type in which separate layers of another transparent material are alternately laminated. is there. The layer structure type has the advantage that focus servo control can be performed using light reflected at the interface between the recording layer and the separation layer, but the multilayer type has more multilayer film forming steps and the production cost is likely to increase.

  The other material of the recording layer 5 is sensitive to, for example, the recording laser light RB according to at least one of the wavelength and intensity thereof, and the refractive index, the transmittance, the absorptivity, the reflectance, and the like change. Any material can be used as long as it is stable. For example, a photopolymer that causes a photopolymerization reaction, a light anisotropic material, a photorefractive material, a hole burning material, a translucent light sensitive material such as a photochromic material that absorbs light and changes its absorption spectrum, and the like are used. .

  In the system for performing recording / reproduction with respect to the recording medium 2 produced by separating the servo layer 11 and the recording layer group 50 of the recording layer 5 from the recording medium of both embodiments, The numerical aperture NA of the objective lens is set by a focus adjustment liquid crystal panel (to be described later) in accordance with the wavelength of the laser beam so that the spot size of the servo laser beam SB becomes substantially equal to the spot size of the recording laser beam RB ( 3 and 4).

For example, in a multi-layer recording system using two-photon absorption,
Φservo is the spot size (diameter) of servo laser beam SB,
Φrec is the spot size (diameter) of the recording laser beam RB for two-photon absorption,
λservo is the wavelength of the servo laser beam SB (first wavelength),
λrec is the wavelength (second wavelength) of the recording laser beam RB for two-photon absorption,
NAservo is the numerical aperture (first wavelength) of the servo optical system,
If NArec is the numerical aperture (second wavelength) of a two-photon absorption recording optical system, and k is a coefficient (k = 1.22),
Φservo = k · λservo / NAservo,
Φrec = k · λrec / NArec.

  However, since the photon recording uses two-photon absorption, the recording threshold (absorption intensity) is proportional to the square of the irradiation light intensity.

Therefore, the effective spot size Φrec ′ is
Φrec ′ = 0.71 · k · λrec / NArec,
The conditions for the effective spot size of the servo laser beam SB and the recording laser beam RB to be the same are as follows:
Φservo = k · λservo / NAservo≈Φrec ′ = 0.71k · λrec
/ NArec.

  Further, since the wavelength of the servo laser beam SB should not overlap with the wavelength of one-photon absorption of the recording material, λserver ≠ λrec / 2 is set.

(pick up)
FIG. 5 shows a schematic configuration of the recording medium 2 and a pickup for recording or reproduction thereof in the recording / reproducing apparatus.

  As Example 1, in the two-photon recording, the pickup of this system uses a long wavelength (first wavelength) servo laser light source SBLD and a short wavelength (first wavelength) recording laser light source RBLD. When the second wavelength λrec of the servo laser light source is set to 660 nm, the second numerical aperture NArec is set to 0.55, and the first wavelength λservo of the recording laser light source is set to 780 nm, the first numerical aperture NAservo is 0. It becomes about 92. In this case, it is desirable that the spot size of the servo laser and the recording laser be the same within the error range of the spot size that expands when there is an aberration of 30 mλ, and it is more preferable that the spot sizes coincide completely. . In this case, the second numerical aperture NArec <the first numerical aperture NAservo, and the recording laser beam RB has a longer working distance than the servo laser beam SB. In addition, it is desirable that the recording layer 5 of the recording medium 2 is disposed behind the servo layer 11.

  In this recording system, the servo laser beam and the recording laser beam are condensed on the servo layer and the recording layer, respectively, via an objective lens OB common to the servo laser beam optical system and the recording laser beam optical system. The recording laser beam optical system includes a collimator lens CL, a polarizing beam splitter PBS, a dichroic prism DP, a quarter-wave plate 1 / 4λ, a reading detection lens CL3, and an objective lens OB. The servo laser optical system includes a collimator lens CL2, a polarization beam splitter PBS2, a dichroic prism DP, a focus adjustment liquid crystal panel LCP, a quarter-wave plate 1 / 4λ, a servo detection lens SCL, and an objective lens OB. The recording system includes a servo device that controls the relative positions of the recording medium 2 and the objective lens based on an electrical signal photoelectrically converted from the light returning from the servo layer 11.

  In such a pickup configuration of the recording system, a mechanism (lens actuator 36) that moves the objective lens OB with respect to the recording medium 2 in the optical axis AX direction (focus direction) and in the direction orthogonal to the optical axis (for example, the tracking direction). By adjusting the relative position of the condensing spot of the recording laser beam RB with respect to the recording medium 2, the recording laser beam is applied to the recording layer 5 (any position on the optical axis) of the recording medium 2. RB is condensed and irradiated to record information, and the intensity of the recording laser beam is reduced (reading light) to irradiate the recording part RM of the recording layer 5, and the reflected return light is detected as reading light. The recorded data can be read by detecting with the device PD.

  That is, the position of the recording / reproducing laser beam RB focused by the objective lens OB is controlled so that the light is focused on a predetermined layer position in the recording layer group 50 of the recording medium 2.

  Although FIG. 5 mainly shows the optical pickup optical system and the control device 101, although not shown, the pickup includes a position control mechanism other than the focusing and tracking lens actuator 36 for the focusing spot, and recording / reproduction. The apparatus includes a slider movement control mechanism that moves the entire optical pickup along the recording surface of the recording medium 2, a servo mechanism for controlling the rotation of the disk-shaped recording medium, and the like. Further, the control device 101 processes information detected by the control circuit for controlling the light source of the recording laser light source RBLD and the servo laser light source SBLD, and the reading light detector PD (second wavelength detecting means), and outputs information and an output signal. A control circuit for controlling the entire device such as a CPU including a circuit and a microcomputer, a storage circuit for storing each data such as a ROM and a RAM, and an interface for inputting / outputting data to / from an external device are provided. .

  In the recording step, as shown in FIG. 5, the recording laser beam RB is converted into parallel light by the collimator lens CL, passes through the polarization beam splitter PBS and the dichroic prism DP, passes through the quarter-wave plate 1 / 4λ, and becomes objective. The light is condensed on the recording layer group 50 of the recording medium 2 by the lens OB.

  Since the wavelength selective reflection film 9 is on the laser light incident surface side of the recording medium 2, the recording laser light RB is transmitted without being reflected. The recording laser beam RB is incident on the recording layer group 50. The recording laser beam RB can form the focal point FP of the recording laser beam RB in any recording layer 5 of the recording layer group 50.

  The servo laser light SB from the servo laser light source SBLD is converted into parallel light by the collimator lens CL2, reflected by the polarization beam splitter PBS2 and the dichroic prism DP, and merged with the recording laser light RB. The servo laser beam SB that has passed through the focus adjustment liquid crystal panel LCP and the quarter-wave plate ¼λ and passed through the objective lens OB is condensed on the servo layer 11 of the recording medium 2.

  The focus adjustment liquid crystal panel LCP that diffracts only the servo laser beam SB is set so as to focus the servo laser beam SB on the servo layer 11 near the surface of the recording medium. The focus adjustment liquid crystal panel LCP functions to keep the spot of the servo laser beam SB at a predetermined different focal length (for each predetermined interlayer distance of the recording layer) on the optical axis with respect to the spot of the recording laser beam RB. To do. Since the servo layer 11 has servo control grooves, address marks, and the like, the servo laser beam SB reflected by the servo layer 11 passes through the servo detection lens SCL in the same manner as a normal optical disk, and is used as a servo photodetector SPD. Incident on (first wavelength detecting means). The servo photodetector SPD can control the focus and tracking of the objective lens OB by a normal astigmatism method or push-pull tracking error detection.

  That is, the lens actuator 36 that drives the objective lens OB in the focus and tracking directions is driven by an error signal obtained by calculation based on the output of the servo photodetector SPD by positioning servo control of the control device 101.

  The control device 101 controls the distance between the objective lens OB and the recording medium 2 to be constant, and at the same time, sets the focus position of the servo laser light via the objective lens by the focus adjustment liquid crystal panel LCP, thereby recording the recording laser. The focal point FP can be moved in the optical axis direction (film thickness direction) so that the target recording layer 5 is switched in the recording layer group 50 for the spot of the light RB. In this recording system, the recording layer 5 is alternatively selected as the recording laser beam RB to be condensed by the servo laser beam dependent on the focus adjustment liquid crystal panel LCP. That is, the focus adjustment liquid crystal panel LCP condenses the focus positions of the servo laser beam RB and the recording laser beam RB by the objective lens OB at different positions in the film thickness direction.

  In the reproduction step, while the position is controlled by the servo laser beam in the same manner as described above, the read laser beam with the intensity of the recording laser beam lowered from the recording laser light source RBLD is irradiated to the recording unit RM, and the reflected return light is reflected. The recorded data can be read by detecting the light by the reading photodetector PD. At this time, as shown in FIG. 5, the light is focused by the reading detection lens CL3, condensed on the pinhole filter 15, and irradiated onto the reading photodetector PD. Here, the pinhole filter 15 blocks unnecessary return light reflected by the recording layer group 50. Thereby, the return light under the same reflection condition as that during recording can be obtained on the reading photodetector PD. At the same time, the pinhole filter 15 can also suppress the reflected light from the recording units in other layers above and below a certain recording unit RM in the recording medium 2. For this reason, it is possible to prevent the influence from the recording unit of the other layer that is crosstalked by the optical signal incident on the reading photodetector PD.

<Focus adjustment LCD panel>
The transmissive focus adjustment liquid crystal panel LCP in FIG. 6 includes a central region CR disposed on the optical axis AX and an annular peripheral region PR disposed so as to surround the central region CR. This is a transmissive liquid crystal device including a plurality of transparent electrodes that partially change the phase of the wavefront. In the focus adjusting liquid crystal panel LCP, the orientation of the liquid crystal changes according to the potential difference generated in the liquid crystal, and the refractive index changes according to the voltage, thereby changing the phase of the wavefront passing through the liquid crystal, thereby The focus adjustment liquid crystal panel LCP itself, in particular, the function of the convex lens or concave lens, that is, the variable focus, is made to function in the central region CR.

  FIG. 6 shows a focus adjustment liquid crystal panel LCP composed of a transmissive liquid crystal device. The focus adjustment liquid crystal panel LCP is connected to the drive circuit LCPD and includes an annular peripheral region PR and a central region CR therein. FIG. 7 is a partial cross-sectional view of a transmission-type focus adjusting liquid crystal panel in a recording / reproducing apparatus, a portion obtained by cutting off a line XX in FIG.

  As shown in FIGS. 6 and 7, in the focus adjustment liquid crystal panel LCP, a fluid transparent liquid crystal composition 211 is sandwiched between two glass substrates 212a and 212b, and the periphery of the substrate is sealed. Have. On the inner surfaces of both glass substrates 212a and 212b, transparent electrode layers (213ai, 213a) and (213b) for applying a voltage to the liquid crystal, and alignment films 214a and 214b for defining the direction (alignment) of the axis of the adjacent liquid crystal molecules, Are stacked in order. For the transparent electrode layer, ITO (indium tin oxide), IZO (indium zinc oxide), or the like can be used.

  The central region CR through which only servo laser light is transmitted has an electrode division shape. For example, when at least one of the opposing electrode layers of the central region CR is divided into a plurality of transparent electrodes as a phase adjusting unit, and servo laser light reaches each of the plurality of transparent electrodes via the objective lens to the servo layer By applying a voltage in accordance with a predetermined numerical aperture, the divergence or convergence of servo laser light transmitted through the focus adjustment liquid crystal panel LCP can be adjusted, and the focus adjustment liquid crystal panel LCP functions as a convex lens or a concave lens. . In FIG. 7, the transparent electrode 213b is a common electrode, but the transparent electrode 213a in the annular peripheral region PR, and a plurality of transparent electrodes 213ai (i = 1, 2, 3,...) In the central region C inside. The voltage is applied independently by the drive circuit LCPD. The control device including the drive circuit LCPD sets the position of the combined focus FP of the focus adjustment liquid crystal panel LCP and the objective lens OB every integral multiple of the distance between two adjacent layers of the recording layer 5 in the film thickness direction of the recording layer group 50 of the medium. Are set apart from each other.

  FIG. 8 is a plan view of an electrode pattern schematically showing an example of the structure of the central region CR of the focus adjustment liquid crystal panel LCP. The central region CR has a plurality of concentric (annular) transparent electrodes 213a1, 213a2, 213a3, which are partitioned by a gap around the optical axis and electrically separated within the effective diameter of the incident servo laser light beam. 213a4, 213a5, 213a6, 213a7. The width of each of the transparent electrodes 213a1-213a7 can be varied so that the width gradually decreases in the radial direction from the center in the figure, but may be configured equally. FIG. 8 shows a case where the central region CR has seven transparent electrodes, but the number of electrodes may be two or more. When a voltage is applied to the transparent electrodes 213a1-213a7 via the lead line 214, the refractive index alignment of the liquid crystal molecules in each part in the liquid crystal layer 11 changes according to the electric field generated by the voltage. As a result, the wavefront of the light passing through the liquid crystal layer 11 changes in phase due to the birefringence of the liquid crystal layer 11. That is, the wavefront of the servo laser light passing therethrough can be controlled by the voltage applied to the liquid crystal layer 11.

  In the first embodiment, as shown in FIG. 5, the servo laser beam SB and the recording laser beam RB are respectively applied to the recording medium 2 by the focus adjustment liquid crystal panel LCP and the objective lens OB so as to have different numerical apertures NA depending on the wavelength. While focusing and detecting the servo signal of the recording medium 2 with the servo laser beam SB, recording is performed with the recording laser beam RB focused on an arbitrary recording layer 5 of the recording medium 2 based on the signal. .

  In the first embodiment, the pitch of the track 6 of the servo layer 11 and the recording layer 5 are adjusted by adjusting the wavelengths and the numerical aperture NA of the servo laser beam SB and the recording laser beam RB so that the respective spot sizes are the same. The pitches of the tracks 6 can be matched, and recording can be performed efficiently on the recording medium 2 (see FIG. 9).

  In n-photon absorption, large one-photon absorption is exhibited at a wavelength 1 / n of the second wavelength (λrec / n), and therefore the first wavelength λserver is not set for the wavelength. As a result, it is possible to prevent deterioration of data recorded by the servo laser beam SB. Since the two-photon absorption attenuates in proportion to the square of the light intensity, the standardized effective spot size is 0.71 times larger than the normal one-photon absorption. In consideration of this, the spot sizes of both laser beams are adjusted to be the same.

(Example 2)
FIG. 9 shows a schematic configuration of the recording medium 2 of Embodiment 2 and a pickup for recording or reproduction thereof. In contrast to the first embodiment, the recording medium 2 is configured by sequentially laminating the recording layer 5 and the servo layer 11 from the light irradiation side.

  In the two-photon recording, when the second wavelength λrec is set to 660 nm, the second numerical aperture NArec is set to 0.8, and the first wavelength λservo is set to 405 nm, the first numerical aperture NAservo is about 0.71 from the above relational expression. . In this case, since the second numerical aperture NArec> the first numerical aperture NAservo, the recording laser beam RB has a shorter working distance than the servo laser beam SB, so that the recording layer 5 of the recording medium 2 is used as the servo layer. It is desirable to arrange it in front of 11. Description of the optical path for the recording laser light source RBLD, except that the center area of the focus adjustment liquid crystal panel LCP has an unpolarized light passing function and a transparent electrode in the surrounding annular peripheral area to function as a convex lens or a concave lens, that is, to change the focus. Is omitted because it is the same as that of the first embodiment.

  As shown in FIG. 9, the servo laser light SB from the servo laser light source SBLD is converted into parallel light by the collimator lens CL2, reflected by the polarization beam splitter PBS2 and the dichroic prism DP, and merged with the recording laser light RB. Both lights pass through the dichroic prism DP, pass through the quarter-wave plate 1 / 4λ, pass through the recording layer group 50 by the objective lens OB, and are focused on the recording medium 2 toward the servo focus SFP. The recording laser beam RB is reflected by the recording layer group 50, but the servo laser beam SB is set to focus on the servo layer 11. The servo layer 11 has servo control grooves, address marks, and the like as used in ordinary optical disks. The servo laser beam SB reflected by the servo layer 11 passes through the servo detection lens SCL and enters the servo photodetector SPD as in the case of a normal optical disk. The servo photodetector SPD can control the focus and tracking of the objective lens OB by a normal astigmatism method or push-pull tracking error detection.

It is a typical perspective exploded view of the conventional multilayered optical disk. 1 is a diagram illustrating a schematic configuration of a recording medium according to an embodiment of the present invention and a recording / reproducing system for recording or reproducing the same. It is a fragmentary sectional view of the recording medium of the embodiment by the present invention. It is a fragmentary sectional view explaining schematic structure of the recording medium in the recording / reproducing apparatus of embodiment by this invention, and the pickup for the recording or reproduction | regeneration. It is a fragmentary sectional view explaining schematic structure of the recording medium in the recording / reproducing apparatus of the Example by this invention, and the pick-up for the recording or reproduction | regeneration. It is a fragmentary perspective view of the transmissive | pervious focus adjustment liquid crystal panel in the recording / reproducing apparatus of the Example by this invention. It is a fragmentary sectional view of the transmission type focus adjustment liquid crystal panel in the recording and reproducing apparatus of the Example by this invention. FIG. 3 is a plan view of an electrode pattern schematically showing a structure of a central region of a transmission type focus adjustment liquid crystal panel in a recording / reproducing apparatus of an embodiment according to the present invention. 1 is a schematic perspective exploded view of an optical disk having a multilayer structure according to an embodiment of the present invention. It is a fragmentary sectional view explaining schematic structure of the recording medium in the recording / reproducing apparatus of the other Example by this invention, and the pick-up for the recording or reproduction | regeneration.

Explanation of symbols

1 / 4λ quarter-wave plate 2 recording medium 3 holding substrate 5 recording layer 5a first recording layer 5b second recording layer 5n nth recording layer 6 track 7a first separation layer 7b second separation layer 7n nth separation layer DESCRIPTION OF SYMBOLS 9 Wavelength selective reflecting film 11 Servo layer 13 Cover layer 15 Pinhole filter 23 Pickup 36 Lens actuator 50 Recording layer group 101 Control apparatus 131 2nd cover layer 211 Transparent liquid crystal composition 212a, 212b Glass substrate 213ai, 213a, 213b Transparent electrode Layer 214a, 214b Alignment film 213a1-213a7 Transparent electrode 214 Lead line SB7, RB7 Effective spot SBLD Servo laser light source RBLD Recording laser light source RB Recording laser light SB Servo laser light OB Objective lens CL Collimator lens PBS Polarizing beam splitter DP dichroic prism CL3 readout detection lens CL2 collimator lens PBS2 polarizing beam splitter LCP focus adjustment liquid crystal panel LCPD drive circuit SCL servo detection lens SPD servo photodetector PD readout photodetector

Claims (12)

Three-dimensional recording on the recording medium is performed by irradiating a recording medium including a plurality of recording layers stacked in the film thickness direction and a servo layer carrying focus servo and tracking servo information. A recording / reproducing apparatus for recording / reproducing data at a position,
A movable holding device for detachably holding the recording medium;
A light source of servo laser light of the first wavelength;
A light source for recording laser light having a second wavelength different from the first wavelength;
An optical device including a servo laser beam optical system for condensing the servo laser beam and the recording laser beam on the servo layer and the recording layer, respectively, and an objective lens common to the recording laser beam optical system;
Means for detecting light of the first and second wavelengths returning from the servo layer and the recording layer via the objective lens,
The numerical aperture of the servo laser light optical system is set so that the spot size of the servo laser light on the servo layer is substantially equal to the spot size of the recording laser light on the predetermined recording layer, and A recording / reproducing apparatus, comprising: a focus adjusting device that sets the focus positions of the servo laser beam and the recording laser beam by the objective lens so as to be separated from each other in the film thickness direction of the plurality of recording layers.   The focus adjustment device may be configured such that the servo laser beam by the objective lens is set so that the spot size of the servo laser beam on the servo layer is the same as the spot size of the recording laser beam on a predetermined recording layer. The recording / reproducing apparatus according to claim 1, wherein focus positions of the recording laser light are set apart from each other in a film thickness direction of the plurality of recording layers.   When the numerical aperture of the recording laser beam optical system is larger than the numerical aperture of the servo laser beam optical system, the plurality of recording layers are positioned before the servo layer when viewed from the light irradiation side, The recording / reproducing apparatus according to claim 1, wherein the recording medium is arranged.   When the numerical aperture of the recording laser beam optical system is smaller than the numerical aperture of the servo laser beam optical system, so that the plurality of recording layers are located at the back of the servo layer as viewed from the light irradiation side, The recording / reproducing apparatus according to claim 1, wherein the recording medium is arranged.   The recording / reproducing apparatus according to claim 1, wherein the plurality of recording layers are made of a multiphoton absorbing material.   When the multi-photon absorption material of the plurality of recording layers changes the optical characteristics of the plurality of recording layers by a non-linear optical process of n-photon absorption, and the change in the optical characteristics is detected, the first wavelength is determined by the n-photon absorption process. 6. The recording / reproducing apparatus according to claim 5, wherein the recording / reproducing apparatus is set so as not to overlap with a periphery of the wavelength of 1 / n of the second wavelength. Three-dimensional recording on the recording medium is performed by irradiating a recording medium including a plurality of recording layers stacked in the film thickness direction and a servo layer carrying focus servo and tracking servo information. A recording / reproducing method for recording / reproducing data at a position,
Holding the recording medium detachably;
Via the objective lens common to the servo laser light optical system and the recording laser light optical system, the servo laser light of the first wavelength and the recording laser light of the second wavelength different from the first wavelength are supplied to the servo layer and Condensing each of the recording layers;
Detecting light of the first and second wavelengths returning from the servo layer and the recording layer via the objective lens,
The numerical aperture of the servo laser light optical system is set so that the spot size of the servo laser light on the servo layer is substantially equal to the spot size of the recording laser light on the predetermined recording layer, and A recording / reproducing method comprising: a condensing setting step of setting focus positions of the servo laser beam and the recording laser beam by an objective lens so as to be separated from each other in the film thickness direction of the plurality of recording layers.   In the condensing setting step, the servo laser by the objective lens is set so that the spot size of the servo laser light on the servo layer is the same as the spot size of the recording laser light on the predetermined recording layer. 8. The recording / reproducing method according to claim 7, wherein the focus positions of the light and the recording laser beam are set apart from each other in the film thickness direction of the plurality of recording layers.   When the numerical aperture of the recording laser beam optical system is larger than the numerical aperture of the servo laser beam optical system, the plurality of recording layers are positioned before the servo layer when viewed from the light irradiation side, 9. The recording / reproducing method according to claim 7, wherein the recording medium is arranged.   When the numerical aperture of the recording laser beam optical system is larger than the numerical aperture of the servo laser beam optical system, so that the plurality of recording layers are located at the back of the servo layer when viewed from the light irradiation side, 9. The recording / reproducing method according to claim 7, wherein the recording medium is arranged.   The recording / reproducing method according to claim 7, wherein the plurality of recording layers are made of a multiphoton absorbing material.   When the multi-photon absorption material of the plurality of recording layers changes the optical characteristics of the plurality of recording layers by a non-linear optical process of n-photon absorption, and the change in the optical characteristics is detected, the first wavelength is determined by the n-photon absorption process. 12. The recording / reproducing method according to claim 11, wherein the recording / reproducing method is set so as not to overlap with a wavelength of 1 / n of the second wavelength.

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