OPTICAL INFORMATION REPRODUCTION DEVICE AND OPTICAL INFORMATION RECORDING AND REPRODUCING DEVICE

A position control method at high speed and high accuracy for recorded hologram is obtained. An optical information recording and reproducing device records an interference fringe obtained by interfering reference beam and signal beam as a hologram on an optical information recording medium and reproduces information using the reference beam from the hologram recorded on the optical information recording medium. The optical information recording and reproducing device includes: a detection light generation unit that generates light including a part of the signal beam as detection light; a detection light incident unit that causes the detection light to be incident on the recorded hologram; and a light detection unit that detects a light amount of diffracted beam by the detection light incident on the hologram. A position of the recorded hologram is detected based on an output of the light detection unit.

TECHNICAL FIELD

The present invention relates to an optical information reproducing device, an optical information recording and reproducing device, an optical information reproducing method, and an optical information recording and reproducing method of recording information on an optical information recording medium and reproducing information from an optical information recording medium using holography.

BACKGROUND ART

At present, optical discs with a recording density of about 50 GB have been commercialized even for consumers by the Blu-ray Disc™ standard using semiconductor blue-violet lasers. In future, even for optical discs, it is desirable to increase capacities up to the same capacities as hard disk drive (HDD) capacities of about 100 GB to 1 TB.

In order to realize such very high densities by an optical disc, however, high-density technologies by new schemes different from high-density technologies by short wavelength and high NA of object lens are necessary.

While next-generation storage technologies are studied, hologram recording technologies for recording digital information using holography have been noticed.

The hologram recording technology refers to a technology for recording information in the recording medium by superposing signal beam with information regarding page data modulated 2-dimensionally by a spatial light modulator on reference beam inside a recording medium and causing refractive index modulation inside the recording medium by an interference pattern occurring at that time.

At the time of reproducing information, a hologram recorded on a recording medium operates like a diffraction grating and a diffracted beam is generated when the recording medium is exposed to reference beam used at the time of recording. The diffracted beam is reproduced as the same light, including the recorded signal beam and phase information.

The reproduced signal beam is detected 2-dimensionally at a high speed using a light detector such as a CMOS or a CCD. In this way, the hologram recording technology can serve to perform recording and reproducing information with a high capacity and at a high speed since the hologram recording technology enables 2-dimensional information to be recorded on an optical recording medium at a time by one hologram and further enables the information to be reproduced and a plurality of pieces of page data can be overwritten at a certain location of a recording medium.

A hologram recording technology is disclosed in, for example, JP-A-2004-272268 (PTL 1). This publication discloses a technology for multiplexing and recording a hologram.

CITATION LIST

Patent Literature

SUMMARY OF INVENTION

Technical Problem

Incidentally, in a recording and reproducing device using holography of an angle multiplex scheme, positioning is performed in the periphery of the hologram to gain access to the recorded target hologram, and then minute adjustment of a position is performed while confirming signal quality of the hologram. Therefore, there is a problem in that it takes access time.

Solution to Problem

The foregoing program can be achieved by causing detection light for detecting position deviation to be incident on a recording medium from an optical path of signal beam at the time of recording and detecting a diffracted beam.

Advantageous Effects of Invention

According to the invention, access to a recorded target hologram can be performed at a high speed, and thus a conveniently usable optical information recording and reproducing device can be provided.

DESCRIPTION OF EMBODIMENTS

First Embodiment

An embodiment of the invention will be descried with reference to the accompanying drawings.FIG. 2is a block diagram illustrating a recording and reproducing device of an optical information recording medium that records and/or reproduces digital information using holography.

An optical information recording and reproducing device10is connected to an external control device91via an input and output control circuit90. In the case of recording, the optical information recording and reproducing device10receives an information signal to be recorded from the external control device91by the input and output control circuit90. In the case of reproducing, the optical information recording and reproducing device10transmits a reproduced information signal to the external control device91by the input and output control circuit90.

The optical information recording and reproducing device10includes a pickup11, a reproduction reference beam optical system12, a cure optical system13, a disc rotational angle detection optical system14, a position detection optical system15, and a rotational motor50. An optical information recording medium1is configured to be able to be rotated by the rotational motor50.

The pickup11serves to emit reference beam and signal beam to the optical information recording medium1and to record digital information on a recording medium using holography. At this time, an information signal to be recorded is sent to a spatial light modulator in the pickup11via a signal generation circuit86by a controller89, so that the signal beam is modulated by the spatial light modulator.

When information recorded on the optical information recording medium1is reproduced, a light wave causing the reference beam emitted from the pickup11to be incident on an optical information recording medium in an opposite direction to a direction at the time of the recording is generated in a reproduction reference beam optical system12. Reproduced light reproduced by reproduction reference beam is detected by a light detector to be described later in the pickup11and a signal is reproduced by a signal processing circuit85.

An exposure time of the reference beam and the signal beam to which the optical information recording medium1is exposed can be adjusted by controlling opening and closing times of a shutter in the pickup11via a shutter control circuit87by the controller89.

The cure optical system13serves to generate a light beam to be used for pre-cure and post-cure of the optical information recording medium1. The pre-cure is a pre-process of exposing a predetermined light beam in advance before the reference beam and the signal beam are exposed to a desired position when information is recorded at a desired position in the optical information recording medium1. The post-cure is a post-process of recording the information at the desired position in the optical information recording medium1, and then exposing the predetermined light beam so that appending is not possible at the desired position.

The disc rotational angle detection optical system14is used to detect a rotational angle of the optical information recording medium1. When the optical information recording medium1is adjusted at a predetermined rotational angle, the disc rotational angle detection optical system14detects a signal according to the rotational angle and the controller89can control the rotational angle of the optical information recording medium1using the detected signal via a disc rotation motor control circuit88.

A predetermined light source driving current is supplied from a light source driving circuit82to light sources in the pickup11, the cure optical system13, and the disc rotational angle detection optical system14, so that a light beam with a predetermined optical amount can be emitted from each light source.

In the pickup11and the disc cure optical system13, a mechanism capable of sliding a position in a radial direction of the optical information recording medium1is provided so that position control is performed via an access control circuit81.

Incidentally, in a recording technology using an angle multiplexing principle of holography, an allowable error tends to considerably decreases with respect to deviation of a reference optical angle.

Accordingly, it is necessary to provide a mechanism detecting a deviation amount of the reference optical angle in the pickup11, generate a servo control signal in a servo signal generation circuit83, and provide a servo mechanism correcting the deviation amount via a servo control circuit84in the optical information recording and reproducing device10.

The pickup11, the cure optical system13, the disc rotational angle detection optical system14, and the position detection optical system15may be configured in several optical system structures or all of the optical system configurations may be collected in one optical system for simplicity.

FIG. 3is a diagram illustrating a recording principle in an example of a basic optical system structure of the pickup11in the optical information recording and reproducing device10. A light beam emitted from a light source301is transmitted through a collimating lens302to be incident on a shutter303. When the shutter303is opened, the light beam passes through the shutter303. Thereafter, for example, after a polarization direction of the light beam is controlled so that a light amount ratio of p-polarized light to s-polarized light becomes a desired ratio by an optical element304including a half-wavelength plate and the like, the light beam is incident on a polarization beam splitter (PBS) prism305.

The light beam transmitted through the PBS prism305works as signal beam306. After a light beam diameter is expanded by a beam expander308, the light beam is transmitted through a phase mask309, a relay lens310, and a PBS prism311to be incident on a spatial light modulator312.

The signal beam to which information is added by the spatial light modulator312is reflected from the PBS prism311to propagate through a relay lens313and a spatial filter314. Thereafter, the signal beam is condensed to the optical information recording medium1by an object lens315.

On the other hand, the light beam reflected from the PBS prism305works as reference beam307. After a predetermined polarization direction is set according to the time of recording or the time of reproducing by a polarization direction conversion element316, the reference beam is incident on a galvanometer mirror319via mirrors317and318. Since the galvanometer mirror319can adjust an angle using an actuator320, an incident angle of the reference beam pas sing through the lens321and322and then incident on the optical information recording medium1can be set to a desired angle. To set the incident angle of the reference beam, an element converting a wave front of the reference beam may be used instead of the galvanometer mirror.

In this way, by causing the signal beam and the reference beam to be incident on the optical information recording medium so that the signal beam and the reference beam are superimposed, an interference pattern is formed inside the recording medium and information is recorded by writing this pattern on the recording medium. Since the incident angle of the reference beam incident on the optical information recording medium1can be changed by the galvanometer mirror319, recording can be performed through angle multiplexing.

Thereafter, in regard to a hologram recorded by changing the reference beam angle in the same region, the hologram corresponding to each one reference beam angle is referred to as a page and a set of the pages subjected to the angle multiplexing in the same region is referred to as a book.

FIG. 4is a diagram illustrating a reproducing principle in the example of the basic optical system structure of the pickup11in the optical information recording and reproducing device10. When the recorded information is reproduced, reproduction reference beam is generated by causing the reference beam to be incident on the optical information recording medium1and reflecting the light beam transmitted through the optical information recording medium1from a galvanometer mirror324capable of adjusting an angle using an actuator323, as described above.

Reproduced light reproduced from the reproduction reference beam propagates through the object lens315, the relay lens313, and the spatial filter314. Thereafter, the reproduced light is transmitted through the PBS prism311and is incident on a light detector325so that the recorded signal can be reproduced. For example, an imaging element such as a CMOS image sensor or a CCD image sensor can be used as the light detector325. Any element may be used as long as the element can reproduce page data.

FIG. 5is a diagram illustrating another configuration of the pickup11. InFIG. 5, a light beam emitted from a light source501is transmitted through a collimating lens502to be incident on a shutter503. When the shutter503is opened, the light beam passes through the shutter503. Thereafter, for example, after a polarization direction of the light beam is controlled so that a light amount ratio of p-polarized light to s-polarized light becomes a desired ratio by an optical element504including a half-wavelength plate and the like, the light beam is incident on a polarized beam splitter505.

The light beam transmitted through the polarized beam splitter505is incident on a spatial light modulator508via a polarized beam splitter507. Signal beam506to which information is added by the spatial light modulator508is reflected from the polarized beam splitter507and propagates through an angle filter509that passes only the light beam with a predetermined incident angle. Thereafter, the signal beam is condensed to a hologram recording medium1by an object lens510.

On the other hand, the light beam reflected from the polarized beam splitter505works as reference beam512. After a predetermined polarization direction is set according to the time of recording or the time of reproducing by a polarization direction conversion element519, the light beam is incident on a lens515via mirrors513and514. The lens515serves to condense the reference beam512to the back focus surface of the object lens510. The reference beam condensed once on the back focus surface of the object lens510is returned to parallel light again by the object lens510and is incident on the hologram recording medium1.

Here, the object lens510or an optical block521can be driven, for example, in a direction indicated by reference numeral520. By shifting the position of the object lens510or the optical block521in the driving direction520, a relative positional relation between the object lens510and a condensing point on the back focus surface of the object lens510is changed. Therefore, an incident angle of the reference beam incident on the hologram recording medium1can be set to a desired angle. The incident angle of the reference beam may be set to the desired angle by driving the mirror514using an actuator instead of driving the object lens510or the optical block521.

In this way, by causing the signal beam and the reference beam to be incident on the hologram recording medium1so that the signal beam and the reference beam are superimposed, an interference pattern is formed inside the recording medium and information is recorded by writing this pattern on the recording medium. Since the incident angle of the reference beam incident on the hologram recording medium1can be changed by shifting the position of the object lens510or the optical block521along the driving direction520, recording can be performed through angle multiplexing.

When the recorded information is reproduced, as described above, the reproduction reference beam is generated by causing the reference beam to be incident on the hologram recording medium1and reflecting the light beam transmitted through the hologram recording medium1from the galvanometer mirror516. Reproduced light reproduced from the reproduction reference beam propagates through the object lens510and the angle filter509. Thereafter, the reproduced light is transmitted through the polarized beam splitter507and is incident on a light detector518so that the recorded signal can be reproduced.

Since the optical system illustrated inFIG. 5is configured such that the signal beam and the reference beam are incident on the same object lens, there is the advantageous effect of considerably miniaturizing the optical system compared to the optical system structure illustrated inFIG. 3.

FIG. 6is a diagram illustrating an operation flow of recording and reproducing in the optical information recording and reproducing device10. Here, the flow of recording and producing performed particularly using holography will be described.

FIG. 6(a) is a diagram illustrating an operation flow until the optical information recording medium1is inserted into the optical information recording and reproducing device10, and then preparation for recording and reproducing is completed.FIG. 6(b) is a diagram illustrating an operation flow until information is recorded on the optical information recording medium1from the preparation completion state.FIG. 6(c) is a diagram illustrating an operation flow until the information recorded on the optical information recording medium1is reproduced from the preparation completion state.

As illustrated inFIG. 6(a), when the medium is inserted (601), for example, the optical information recording and reproducing device10performs disc determination to determine whether the inserted medium is a medium used to record or reproduce digital information using holography (602).

When the medium is determined to be the optical information recording medium used to record or reproduce the digital information using the holography as the result of the disc determination, the optical information recording and reproducing device10reads control data installed on the optical information recording medium (603) and acquires, for example, information regarding the optical information recording medium or, for example, information regarding various setting conditions at the time of recording or the time of reproducing.

After the control data is read, a learning process related to the pickup11or various kinds of adjustment according to the control data is performed (604). Then, the optical information recording and reproducing device10completes preparation for the recording or reproducing (605).

In the operation flow until the information is recorded from the preparation completion state, as illustrated inFIG. 6(b), data to be recorded is first received (611) and information according to the data is sent to the spatial light modulator in the pickup11.

Thereafter, for example, various learning processes for the recording, such as power optimization of the light source301or exposure time optimization by the shutter303, are performed in advance (612), as necessary, so that information with high quality can be recorded on the optical information recording medium.

Thereafter, in a seek operation (613), the access control circuit81is controlled such that the positions of the pickup11and the cure optical system13are located to predetermined positions on the optical information recording medium. When the optical information recording medium1has address information, the address information is reproduced and it is confirmed whether the positions are located to target positions. When the positions are not located to the target positions, deviation amounts from predetermined positions are calculated and the locating operation is repeated again.

Thereafter, the predetermined positions are pre-cured using the light beam emitted from the cure optical system13(614) and the data is recorded using the reference beam and the signal beam emitted from the pickup11(615).

After the data is recorded, post-curing is performed using the light beam emitted from the cure optical system13(616). The data may be verified, as necessary.

In the operation flow until the recorded information is reproduced from the preparation completion state, as illustrated inFIG. 6(c), the access control circuit81is first controlled in a seek operation (621) and the positions of the pickup11and the reproduction reference beam optical system12are located to predetermined positions on the optical information recording medium. When the optical information recording medium1has address information, the address information is reproduced and it is confirmed whether the positions are located to target positions. When the positions are not located to the target positions, deviation amounts from predetermined positions are calculated and the locating operation is repeated again.

Thereafter, the reference beam is emitted from the pickup11, the information recorded on the optical information recording medium is read (622), and the reproduced data is transmitted (613).

FIG. 9is a diagram illustrating a data processing flow at the time of recording and reproducing.FIG. 9(a) is a diagram illustrating a recorded data processing flow of the signal generation circuit86until the recorded data is received in the input and output control circuit90(611) and then the recorded data is converted into 2-dimensional data on the spatial light modulator312.FIG. 9(b) is a diagram illustrating a reproduced data processing flow of the signal processing circuit85up to the transmission624of the reproduced data in the input and output control circuit90after the 2-dimensional data is detected with the light detector325.

Data processing at the time of recording will be described with reference toFIG. 9(a). When user data is received (901), each data string is subjected to CRC (Cyclic Redundancy Check) so that splitting into a plurality of data strings and error detection at the time of reproducing can be performed (902). The number of on-pixels is substantially equalized with the number of off-pixels and scrambling of adding a pseudo-random number data string to a data string is performed in order to prevent repetition of the same pattern (903). Thereafter, error correction coding such as Reed-Solomon code is performed so that error correction at the time of reproducing is performed (904). Next, 2-dimensional data corresponding to one page is configured by converting the data string into M×N 2-dimensional data and repeating this action corresponding to one page data (905). A marker serving as a criterion of image position detection at the time of reproducing or image distortion correction on the 2-dimensional data configured in this way is added (906) and the data is transmitted to the spatial light modulator312(907).

Next, a data processing flow at the time of reproducing will be described with reference toFIG. 9(b). Image data detected by the light detector325is transmitted to the signal processing circuit85(911). The image position is detected based on the marker included in the image data (912) and deformation such as inclination, magnification, distortion of an image is corrected (913). Thereafter, a binarization process is performed (914) and the marker is removed (915) so that 2-dimensional data corresponding to one page is acquired (916). After the 2-dimensional data obtained in this way is converted into a plurality of data strings, an error correction process is performed (917) to remove a parity data string. Next, a scrambling releasing process is performed (918), an error detection process is performed using the CRC (919), and the CRC parity is deleted. Thereafter, the user data is transmitted via the input and output control circuit90(920).

FIG. 7is a block diagram illustrating the signal generation circuit86of the optical information recording and reproducing device10.

When an input of the user data into the output control circuit90starts, the input and output control circuit90notifies the controller89that the input of the user data starts. The controller89receives this notification and commands the signal generation circuit86to perform a process of recording data corresponding to one page input from the input and output control circuit90. A sub-controller701in the signal generation circuit86is notified of a process command from the controller89via a control line708. The sub-controller701receiving this notification performs control of each signal processing circuit via the control line708such that each signal processing circuit operates in parallel. First, the sub-controller701performs control such that the memory control circuit703stores the user data input from the input and output control circuit90via a data line709in a memory702. When the user data stored in the memory702reaches a certain amount, the sub-controller701performs control such that a CRC arithmetic circuit704performs CRC on the user data. Next, the sub-controller701performs control such that a scrambling circuit705performs scrambling on the data subjected to the CRC to add the pseudo-random data string and an error correction coding circuit706performs error correction coding to add the parity data string. Finally, a pickup interface circuit707is caused to read the data subjected to the error correction coding from the memory702in row order of the 2-dimensional data on the spatial light modulator312, the marker serving as a criterion at the time of reproducing is added, and then the 2-dimensional data is transmitted to the spatial light modulator312in the pickup11.

FIG. 8is a block diagram illustrating the signal processing circuit85of the optical information recording and reproducing device10.

When the light detector325in the pickup11detects the image data, the controller89commands the signal processing circuit85to perform a process of reproducing data corresponding to one page input from the pickup11. A sub-controller801in the signal processing circuit85is notified of a process command from the controller89via a control line811. The sub-controller801receiving this notification performs control of each signal processing circuit via the control line811such that each signal processing circuit operates in parallel. First, the sub-controller801performs control such that the memory control circuit803stores the image data input from the pickup11via a pickup interface circuit810in a memory802via the data line812. When the data stored in the memory802reaches a certain amount, the sub-controller801performs control such that an image position detection circuit809detects the marker from the inside of the image data stored in the memory802and extracts an effective data range. Next, the sub-controller801performs control such that an image deformation correction circuit808performs deformation correction such as inclination, magnification, or distortion of an image using the detected marker and converts the size of the image data into the size of expected 2-dimensional data. The sub-controller801performs control such that a binarization circuit807binarizes each piece of bit data of a plurality of bits included in the 2-dimensional data subjected to the size conversion to determine “0” and “1” and stores the data in the rows of the output of the reproduced data on the memory802. Next, the sub-controller801performs control such that an error correction circuit806corrects an error contained in each data string, a scrambling releasing circuit805releases the scrambling of adding the pseudo-random data string, and a CRC arithmetic circuit804confirms that an error is not contained in the user data on the memory802. Thereafter, the user data is transmitted from the memory802to the input and output control circuit90.

Here, a method of performing the positioning to a recorded target hologram (book) accurately in the optical information recording and reproducing device according to the embodiment described above will be described.

First, a principle of the scheme will be described with reference toFIGS. 35 to 38.FIGS. 35 to 38are diagrams illustrating essential portions extracted in the optical system inFIG. 3. An interference fringe of the signal beam and the reference beam is recorded in the hologram recorded in the optical system inFIG. 3. Further, as illustrated inFIG. 35, signal beam3501and signal beam3502from respective pixels of the spatial light modulator312intersect in the optical information recording medium1, so that an interference fringe is formed and recorded as a hologram3503. Accordingly, as illustrated inFIG. 36, when detection light3601which is a part of the recorded signal beam is exposed to the recorded hologram3503, the recorded signal beam3502can be obtained as a diffracted beam3603. Simultaneously, transmitted light3602is also generated.

The example of two pixels has been described above, but numerous pixels are mutually interfered actually. This case will be described with reference toFIGS. 37 and 38. As illustrated inFIG. 37, signal beam3701from the spatial light modulator312is condensed in the optical information recording medium1, so that an interference fringe is formed and recorded as a hologram3702. Accordingly, as illustrated inFIG. 38, when detection light3801which is apart of the recorded signal beam is exposed to the recorded hologram3702, the recorded signal beam3701can be obtained as a diffracted beam3803. Since this diffracted beam is generated from the recorded hologram, the locating of high precision is possible by adjusting the position of the optical information recording medium1and/or the pickup11based on the diffracted beam. Simultaneously, transmitted light3802is also generated. However, the light amount of transmitted light3802is larger than that of the diffracted beam3803. Therefore, when the transmitted light3802is blocked, a signal of only the diffracted beam can be generated, and thus position detection accuracy can be improved. Further, since the recorded hologram is also subjected to angle multiplexing, characteristics are obtained in which the obtained diffracted beam is superimposed on the diffracted beam from all of the pages and the light amount of diffracted beam also increases.

Next, a case in which this principle is applied to an actual recording and reproducing device will be described.FIG. 1is a diagram illustrating an example in which a position detection optical system15is added to the recording and reproducing device inFIG. 2so that position control to a target hologram (book) is possible at the time of reproducing. After the light beam diameter of a light beam emitted from the light source301and transmitted through the PBS prism305is expanded by the beam expander308, the light beam is transmitted through the phase mask309, the relay lens310, and the PBS prism311and is incident on the spatial light modulator312. When the phase mask309is present, the phases at the time of recording and the time of detection may be deviated and a diffracted beam may not be obtained well in some cases. Therefore, at the time of position detection, the light beam may not be transmitted through the phase mask309. In the spatial light modulator312, recording data illustrated inFIG. 10is displayed at the time of recording. However, at the time of position detection, an image illustrated inFIG. 11or12is displayed in the spatial light modulator312. InFIGS. 11 and 12, white indicates that light is transmitted and black indicates that light is not transmitted. This transmission region (the region indicated by white) may include a part of a signal beam region (a region indicated by a dotted line) or may be a pattern illustrated inFIG. 13. In this case, for example, when detection light is generated from another light source, it is not necessary to put the transmission region inside the signal beam region. Therefore, there is an advantageous effect in which design is easy. The shape of the transmission region may be not only circular but also rectangular. In this case, for example, there is an advantageous effect in which design of a mask101to be described later is easy. Detection light for position detection generated by the spatial light modulator312is reflected from the PBS prism311and propagates through the relay lens313and the spatial filter314. Thereafter, the detection light is condensed to the optical information recording medium1by the object lens315. Diffracted light diffracted by the detection light propagates through relay lenses103and104and the mask101and is incident on a light detector102. As described above, since the diffracted beam includes the detection light (0th-order diffracted beam) transmitted through the optical information recording medium1, the diffracted beam is blocked by the mask101. In the case of the detection light used inFIG. 11, the mask101uses a pattern inFIG. 14. In the case of the detection light inFIG. 12, the mask101uses a pattern inFIG. 15. InFIGS. 14 and 15, white indicates that light is transmitted and black indicates that light is not transmitted. The non-transmission region can be created by disposing a material, such as metal or paint, through which light is not transmitted on a transparent plate. When the non-transmission region is disposed so that a distance between the optical information recording medium1and the relay lens103and a distance between the relay lens103and the mask101are a focal distance of the relay lens103, an image of the spatial light modulator312appears in the mask101. Therefore, masking is easy, but the invention is not limited thereto. The pattern of the mask101is preferably set to be slightly larger so that the pattern includes a pattern displayed in the spatial light modulator312in consideration of position deviation of the optical information recording medium1or the mask, aberration, and the like. The pattern of the mask can also be varied, for example, by combining a liquid crystal element and a polarization plate and changing a pattern displayed in the liquid crystal element.

Here, a pattern and a position detection sensitivity of the spatial light modulator312will be described. InFIGS. 16 and 17, graphs indicating diffraction efficiency in a movement amount of the optical information recording medium are illustrated. The horizontal axis represents a movement amount (shift at the time of recording and the time of position detection) of the optical information recording medium1. The vertical axis represents a diffracted beam intensity. The pattern of the spatial light modulator312is a result obtained by changing a radius R of the transmission region at the time ofFIG. 12. From this result, it can be understood that sensitivity is low when the transmission region is small (R=0.5 mm) and sensitivity is high when the transmission region is large (R=1.0 mm). Thus, the pattern of the spatial light modulator312can be decided in consideration of a necessary detection range and sensitivity. In the embodiment, the detection light has been generated by causing a part of the laser light from the laser light source that also generates the reference beam as the detection light to detect the position deviation to be incident from a light path of the signal beam at the time of recording, but the invention is not necessarily limited thereto. For example, the laser light source generating the detection light may be a separate light source from the laser light source generating the reference beam. That is, light may be incident to the optical information recording medium in an incident direction (which may be a partial incident direction) of the signal beam at the time of recording on the recording medium. In the embodiment, a configuration generating light serving as the function is referred to as a detection light generation unit. Further, a configuration guiding the detection light to the optical information recording medium is referred to as a detection light incident unit.

Next, a method of generating the position detection signal will be described. InFIG. 18, the details of the optical information recording medium1and the position detection optical system15are illustrated. To facilitate the description, the angle of the optical information recording medium1is changed as inFIG. 1, but the same application is possible in consideration of an inclination even when the optical information recording medium is inclined. Diffracted light1803from a recorded hologram1801is incident on the light detector102(seeFIG. 18(a)). The top view of the light detector102isFIG. 18(b). The light detector102is divided into four regions and a position detection signal is generated in accordance with the positions of light spots1804and1805of the diffracted beam. For example, a position detection signal Ex in an X direction (a rotational direction θ of the optical information recording medium1) ofFIG. 18is generated by calculating luminances of the divided regions A, B, C, and D of the light detector102with Ex=(A+C)−(B+D). InFIG. 19, a change in the position detection signal Ex with respect to the X direction is illustrated. For example, when the hologram is located at a position1801, the light spot1804is obtained, and thus Ex=0. When the hologram is located at a position1802, the light spot1805is obtained, and thus Ex>0. The optical information recording medium1and/or the pickup11may be controlled such that the position detection signal Ex becomes 0. Similarly, a position detection signal Ey in a Y direction (a radial direction r of the optical information recording medium1) ofFIG. 18is generated through calculation with Ey=(C+D)−(A+B). InFIG. 20, a change in the position detection signal Ey with respect to the Y direction is illustrated. The optical information recording medium1and/or the pickup11may be controlled such that the position detection signal Ey becomes 0. When the position detection signals Ex and Ey are small, standardization with the luminance of (A+B+C+D) is also effective. Control may be performed such that the position detection signal is set with (A+B+C+D) and the position detection signal is maximized. A control target of the pickup11may be all of the constituent elements of the pickup11or some of the constituent elements such as the spatial filter314and the object lens315. The definitions of the X, Y, θ, and r described here are not limited and can similarly be applied irrespective of the shape of the disc such as a discoid disc and a quadrate shape.

Next, a position control procedure in which the above-described configuration is used will be described. InFIG. 21, a processing flow at the time of reproducing is illustrated. When a target book is reproduced, the pattern ofFIG. 12is displayed in the spatial light modulator312(2101) and the optical element304controls the polarization direction so that the detection light is generated (2102). Next, the positioning is performed near a target book position (2103), the detection light is exposed to the optical information recording medium1and the rotational angle is controlled so that the position detection signal Ex becomes 0 (2104). Continuously, the radius position is controlled such that the position detection signal Ey becomes 0 (2105). Next, the polarization direction is controlled by the optical element304such that the reference beam for reading data is generated (2106). The generated reference beam is exposed to the optical information recording medium1to read information regarding the book (2107). The operations from2102to2107are repeated until the reproduction is completed (2108). Each book position is adjusted in the foregoing example, but a high speed can be achieved by performing steps2102,2104, and2105for every several books. The pattern displayed in the spatial light modulator312has been described with reference toFIG. 12, but the invention is not limited thereto. Any pattern may be used as long as the detection light is light including a part of the signal beam at the time of recording. The procedure of steps2104and2105may be reversed.

According to the foregoing first embodiment, the signal of the light detector of which a response speed is fast can be used generally. Further, the position control method at high speed and high accuracy is possible by controlling a position at which the detection signal is 0 to a target.

In the foregoing configuration, the spatial light modulator312is used to generate the detection light including a part of the recorded signal beam, but the invention is not limited thereto. A separate optical system for detection may be provided. For example, by decreasing the light beam diameter by the beam expander308, the light blocked by the spatial light modulator312is decreased, thereby improving efficiency. The same also applies to subsequent embodiments.

Second Embodiment

Differences between this embodiment and the first embodiment are a position control procedure and a display pattern of the spatial light modulator312. As described above, the position detection range and the sensitivity can be set arbitrarily by changing the pattern of the spatial light modulator312. However, when the position detection range is considerably taken, the sensitivity near an adjustment target may become low. From this viewpoint, in the embodiment, the position detection range and the sensitivity can be compatible with each other by performing control to switch a first position detection image in which the radius of the transmission region inFIG. 12is small so that the position detection range increases and a second position detection image in which the radius of the transmission region inFIG. 12is larger than that of the first position detection image so that the sensitivity increases near a target.

The position control procedure according to the embodiment will be described with reference to the processing flow ofFIG. 22. When a target book is reproduced, the first position detection image in which the radius inFIG. 12is small is displayed in the spatial light modulator312(2201) and the polarization direction is controlled by the optical element304so that the detection light is generated (2102). Next, the positioning is performed near a target book position (2103), the detection light is exposed to the optical information recording medium1and the rotational angle is controlled so that the position detection signal Ex becomes 0 (2104). Continuously, the radius position is controlled such that the position detection signal Ey becomes 0 (2105). Next, the second position detection image in which the radius inFIG. 12is large is displayed in the spatial light modulator312(2202) and the rotation angle is controlled such that the position detection signal Ex becomes 0 (2203). Continuously, the radius position is controlled such that the position detection signal Ey becomes 0 (2304). The subsequent operations are the same as those of the first embodiment and the operations from2201to2107are repeated until the reproduction is completed (2108). Each book position is adjusted in the foregoing example, but steps2201,2104, and2105may be performed every several books. The pattern displayed in the spatial light modulator312has been described with reference toFIG. 12, but the invention is not limited thereto. Any pattern may be used as long as the shapes of the first position detection image and the second position detection image are changed. The procedure of steps2104and2105and of steps2203and2204may be reversed.

According to the foregoing second embodiment, the position control at high speed and high accuracy in which the position detection range and the sensitivity are compatible is possible by changing the size of the detection light.

Third Embodiment

Next, another embodiment of the detection light generation unit and the detection light incident unit will be introduced. A difference between this embodiment and the first embodiment is a position control procedure. In general, it takes some time to change the polarization direction of the optical element304as in the processing flow ofFIG. 21in the first embodiment. Accordingly, this problem does not occur when the polarization direction of the optical element304is controlled so that both of the detection light and the reference beam are normally generated as inFIG. 23. Differences betweenFIG. 23andFIG. 4which is a diagram of the configuration at the time of reproducing are that the position detection optical system15and a shutter2301are disposed and light is transmitted even on the signal beam side at the time of reproducing.

The position control procedure according to the embodiment will be described with reference to the processing flow ofFIG. 24. When a target book is reproduced, the pattern ofFIG. 12is displayed in the spatial light modulator312(2101) and the polarization direction is controlled by the optical element304so that the detection light and the reference beam are generated (2401). The subsequent operations are the same as those of the first embodiment and the operations from2103to2107are repeated until the reproduction is completed (2108). A light amount ratio between the detection light and the reference beam in step2401is preferably set to “detection light:reference beam=1:9” in that the quality of a reproduced image deteriorates when the light amount of reference beam is lowered, but the invention is not limited thereto. Further, noise occurs in some cases when the reference beam is exposed at the time of position detection. In order to suppress the noise, it is effective to dispose the shutter2301in a path of the reference beam and block the reference beam at the time of position detection. This shutter may be disposed at any position as long as a path is a path along which the reference beam is exposed to the optical information recording medium1. The procedure of steps2104and2105may be reversed.

According to the foregoing third embodiment, a time taken to control the optical element304is not necessary. Therefore, the position control at high speed and high accuracy is possible.

Fourth Embodiment

Differences between this embodiment and the first embodiment are the position detection optical system15and the hologram position detection method. When it is difficult to perform the control near the target book position as in step2103ofFIG. 21in the first embodiment, there is a risk of an error occurring in an adjacent book. Accordingly, this problem does not occur when a page capable of searching a target book is recorded.

InFIG. 25, a book search page according to the embodiment is illustrated. An address pattern2501unique to the book or different from an adjacent book is disposed in the center and a reference pattern2502which is circular is disposed around the address pattern2501. Associating the address pattern2501with the address of the book is a simple method. However, to avoid error detection, it is preferable to set a pattern with low correlation with the adjacent book or a close book. The reference pattern is not limited to the reference pattern2502. To broad the detection range, the reference pattern may be a small region with respect to the region of the signal beam.

At the time of position detection, the detection light is generated by displaying the address pattern2501of a target book in the spatial light modulator312. Thus, the strong diffracted beam can be obtained only when the detection light is exposed to the hologram of the target book. The mask101at this time blocks a region including the address pattern2501as inFIG. 27.

A position detection signal Eall for book search is generated by calculating the luminances of the divided regions A, B, C, and D of the light detector102with Eall=(A+B+C+D). InFIG. 28, a change in the position detection signal Eall in the X direction is illustrated. Since Eall is maximized at the center of a target book position, the optical information recording medium1and/or the pickup11may be controlled so that the position detection signal Eall is maximized.

Next, a book search page recording procedure using the above-described configuration will be described. InFIG. 29, the processing flow is illustrated. First, the polarization direction is controlled by the optical element304so that the signal beam and the reference beam are generated (2901). Next, the positioning is performed at the target book position (2902), the book search page with the address pattern of the target book is displayed in the spatial light modulator312, and the signal beam is exposed to the optical information recording medium1to perform recording (2903). Continuously, a normal page is subjected to angle multiple recording while changing a reference beam angle (2904). The operations from2902to2904are repeated until the recording is completed (2905). The book search page is recorded for each book in the foregoing example, but high speed can be achieved by performing step2903for every several books.

Next, the position control procedure using the above-described configuration will be described. InFIG. 30, the processing flow is illustrated. When the target book is reproduced, the polarization direction is controlled by the optical element304so that the detection light is generated (3001) and the address pattern of the target book is displayed in the spatial light modulator312(3002). Next, the positioning is performed near the target book position (3003), the detection light is exposed to the optical information recording medium1, and the position detection signal Eall is detected while moving the optical information recording medium1(3004). Here, for example, when the optical information recording medium1is moved in the X direction as inFIG. 31, the position detection signal Eall increases at the target book position. The position detection signal Eall is not 0 at another book position since parts of the address pattern match, but the position detection signal Eall is smaller than the position detection signal Eall at the target book position. Accordingly, a threshold value is decided in advance. When the position detection signal is greater than the threshold value, the book position is determined to be the target book position and the movement of the optical information recording medium1is stopped (3005). Thereafter, the book is reproduced according to the method of the first embodiment or the like (3006). The operations from3002to3006are repeated until the reproduction is completed (3007). Each book is searched in the foregoing example, but a high speed can be achieved by performing steps3002to3005for only the first read book or for several books. Further, steps3004and3005have been described when the optical information recording medium1is moved, but the pickup11may be moved.

According to the foregoing fourth embodiment, the target book can be searched at a high speed, and thus the position control at high speed and high accuracy is possible without performing the control erroneously in the adjacent book.

In the foregoing description, the example in which the book search page is recorded as inFIG. 25has been described. However, when the address pattern2501is embedded in a normal page as inFIG. 32, it is not necessary to record the book search page. Since sufficient diffracted beam may not be obtained merely by recording a single book search page, it is effective to create a search book for which the book search page is recorded for a long exposure time for every several books. The position and the size of the address pattern are not limited to those of the address pattern2501, but may be disposed at any position in the page. However, when the size is small, the detection range becomes broad. Therefore, the small size is preferable for the book search. When the phase mask309is present, a phase is deviated at the time of recording and the time of detection and the diffracted beam may not be obtained well in some cases. Therefore, when the book search page is recorded and/or reproduced, the light may not be transmitted through the phase mask309.

Fifth Embodiment

A difference between this embodiment and the first embodiment is the position detection optical system15. In the first embodiment, the position control in the X and Y directions has been described. However, in the embodiment, position control in the Z direction (focus direction) is configured to be possible.

InFIG. 33, the details of the optical information recording medium1and the position detection optical system15are illustrated. A difference fromFIG. 18is a cylindrical lens3301. The cylindrical lens is a lens that has a cylindrical refraction plane. The cylindrical lens3301is disposed to be inclined at 45° from the X axis so that the inclination of a cylindrical axis matches an inclination of a diagonal line of the light detector102. Since a division direction can be configured to be common to the position detection in the X and Y directions by doing so, the efficiency is good. To facilitate the description, the angle of the optical information recording medium1is changed inFIG. 1. However, the optical information recording medium is inclined, the same applies by considering the inclination. The top view of the light detector102isFIG. 33(b). The focal distances and the positions of the cylindrical lens3301and the relay lens104are decided so that the light spot1804of the diffracted beam becomes a precise circle. When the optical information recording medium1is moved in the Z direction in this situation, the light spot3303of the diffracted beam from the recorded hologram3302becomes an elliptical shape. Accordingly, a position detection signal Ez in the Z direction (the thickness direction of the optical information recording medium1) is generated by calculating the luminances of the divided regions A, B, C, and D of the light detector102with Ez=(B+C)−(A+D). InFIG. 34, a change in the position detection signal Ez in the Z direction is illustrated. For example, when the hologram is located at a position1801, the light spot1804is obtained, and thus Ez=0. When the hologram is located at a position3302, the light spot3303is obtained, and thus Ez>0. The optical information recording medium1and/or the pickup11may be controlled such that the position detection signal Ex becomes 0.

According to the foregoing fifth embodiment, the position control at high speed and high accuracy is possible even in the Z direction (the focus direction)

In the foregoing configuration, the description has been made using the cylindrical lens. For example, when a mask in which a half region centering on the optical axis is set as a non-transmission region at the position of the cylindrical lens3301is disposed instead, cost can be reduced. Any mask may be used as long as a luminance distribution of the light spot of the light detector102is changed when the hologram is moved in the Z direction.

The invention is not limited to the foregoing embodiments, but includes various modifications. For example, the foregoing embodiments have been described in detail to facilitate the understanding of the invention. The invention is not limited to embodiments in which all of the above-described configurations are necessarily included. A part of the configuration of a certain embodiment may be substituted with the configuration of another embodiment and the configuration of another embodiment may also be added to the configuration of a certain embodiment. A part of the configuration of each embodiment can be added to, deleted from, replaced with another configuration.

Some or all of the foregoing configurations, functions, processing units, processing means, and the like may be realized with hardware, for example, by performing design with, for example, integrated circuits. Further, the foregoing configurations, functions, and the like may be realized with software by a processor analyzing and executing a program which realizes each function. Information regarding the program, tables, files, and the like realizing each function may be stored in a memory, a recording device such as a hard disk, a solid state drive (SSD), or a recording medium such as an IC card, an SD card, or a DVD.

The control lines or the information lines considered to be necessary for the description are denoted. All of the control lines or the information lines may not be denoted necessarily for products. In practice, most of all the configurations may be considered to be connected to each other.

REFERENCE SIGNS LIST