WO2016208046A1

WO2016208046A1 - Optical information recording and reproducing apparatus, optical information recording apparatus, and optical information recording and reproducing method

Info

Publication number: WO2016208046A1
Application number: PCT/JP2015/068440
Authority: WO
Inventors: 誠保坂; 利樹石井
Original assignee: 日立コンシューマエレクトロニクス株式会社
Priority date: 2015-06-26
Filing date: 2015-06-26
Publication date: 2016-12-29

Abstract

Provided are: an optical information recording and reproducing apparatus that utilizes holography and that can perform reproduction with fine quality even when recording is performed at high recording density; and a method therefor. This optical information recording and reproducing apparatus for recording and reproducing, as a hologram, a pattern of interference between reference light and signal light on/from optical information recording medium by utilizing holography is characterized by being provided with: a light source that emits laser light; an optical element that separates the laser light into reference light and signal light; a phase control unit that controls the phase of the signal light or the reference light during recording; and a photodetector that detects signal light reproduced through irradiation of the optical information recording medium with the reference light, wherein when reproduction light reproduced from a first hologram when irradiation with the reference light is performed is defined as first reproduction light and reproduction light reproduced from a second hologram recorded on a page adjacent to a page on which the first hologram is recorded is defined as second reproduction light, the phase control unit controls the phase of the reference light or the signal light during recording such that the phase difference between the first reproduction light and the second reproduction light is at a predetermined value.

Description

Optical information recording / reproducing apparatus, optical information recording apparatus, and optical information recording / reproducing method

The present invention relates to an apparatus and method for recording and / or reproducing information using holography.

Currently, the Blu-ray Disc (TM) standard using a blue-violet semiconductor laser makes it possible to commercialize an optical disc having a recording density of about 100 GB even for consumer use. In the future, it is desired to increase the capacity of optical disks exceeding 500 GB. However, in order to realize such a high density with an optical disc, a high density technology by a new method different from the conventional high density technology by shortening the wavelength and increasing the NA of the objective lens is necessary.

While research on next-generation storage technology is underway, hologram recording technology that records digital information using holography is drawing attention. As a hologram recording technique, for example, there is JP-A-2004-272268 (Patent Document 1). This publication discloses a multiplexing method and apparatus in which holograms are spatially multiplexed by partial spatial overlap between adjacent stacks of holograms. Each stack is for example an angle, a wavelength, a phase. The full advantage of another multiplexing technique such as sign, peritropy, or fractal multiplexing can be further taken in. An amount equal to the beam waist of the signal light writing the hologram separates the individual stacks of holograms. A hologram and a hologram adjacent to the hologram are all read out simultaneously, and the adjacent hologram read out is not transmitted to the camera surface by arranging a filter at the beam waist of the reproduced data, or These undesired reproductions can be found in optical systems with limited angular passbands. Information, it is described that may be filtered. "By the intermediate plane of the angular filter.

Further, as a technique for controlling the phase of signal light during recording and performing multiplex recording, there is, for example, JP-A-2013-114716 (Patent Document 2). This publication includes “recording light sources 105 and 106 such as at least two semiconductor lasers, and objective lenses 119 and 121 that condense light beams from the respective recording light sources into the optical information recording medium 120, and Each of the light sources for output outputs a light beam whose intensity is modulated, and each light beam of the recording light source has reflected light having a phase difference of approximately 90 degrees from each other when the reproducing light beam is condensed on the optical information recording medium. In other words, the recording is performed on the optical information recording medium in such a manner as to generate an arbitrary amplitude of light without using a phase modulator.

JP 2004-272268 A JP 2013-114716 A

By the way, in the optical information recording / reproducing apparatus using holography, when the recording density is increased by narrowing the angle or the spatial distance which is a parameter to be controlled at the time of multiplexing, the information is reproduced from the vicinity in terms of angle or space. There is a problem that the crosstalk component with the signal increases and the quality of the reproduced signal is significantly deteriorated.
The present invention has been made in view of the above problems, and an object of the present invention is to provide an optical information recording / reproducing apparatus and method capable of obtaining high recording density and good reproduction quality.

The above problem is solved by, for example, the invention described in the scope of claims.

According to the present invention, it is possible to provide an optical information recording / reproducing apparatus and method capable of reproducing with good quality even when recording with a high recording density is performed in a holographic memory.

Schematic diagram showing an embodiment of an optical information recording / reproducing apparatus Schematic showing an embodiment of a pickup in an optical information recording / reproducing apparatus Schematic showing an embodiment of a pickup in an optical information recording / reproducing apparatus (A) Schematic diagram showing an example of inter-page crosstalk, (b) Simulation result showing an example of the relationship between inter-page phase difference and noise amount The figure showing the Example of the operation | movement flow of an optical information recording / reproducing apparatus Schematic showing an embodiment of a pickup in an optical information recording / reproducing apparatus Schematic showing an embodiment of inter-page phase difference control by a retarder Schematic showing an embodiment of phase difference control between pages by phase mask movement Schematic showing an embodiment of a pickup in an optical information recording / reproducing apparatus The figure showing the Example of the operation | movement flow of an optical information recording / reproducing apparatus The figure showing the definition of the angle of the signal beam and the reference beam in the medium Schematic representation of reproduction light intensity and phase relative to the reference beam angle during reproduction Diagram showing the relationship between signal light angle and crosstalk Diagram showing the relationship between signal light angle and crosstalk Schematic showing an embodiment of phase difference control between pages

Hereinafter, embodiments of the present invention will be described with reference to the drawings.

A first embodiment of the present invention will be described with reference to FIGS.
FIG. 1 is a block diagram showing a recording / reproducing apparatus of an optical information recording medium for recording and / or reproducing digital information using holography.
The optical information recording / reproducing device 10 is connected to an external control device 91 via an input / output control circuit 90. In the case of recording, the optical information recording / reproducing apparatus 10 receives the information signal to be recorded from the external control device 91 by the input / output control circuit 90. When reproducing, the optical information recording / reproducing apparatus 10 transmits the reproduced information signal to the external control apparatus 91 by the input / output control circuit 90.

The optical information recording / reproducing apparatus 10 includes a pickup 11, a reproduction reference light optical system 12, a cure optical system 13, a disk rotation angle detection optical system 14, and a rotation motor 50. The optical information recording medium 1 is a rotation motor. 50 can be rotated.
The pickup 11 plays a role of emitting reference light and signal light to the optical information recording medium 1 and recording digital information on the recording medium using holography. At this time, the signal to be recorded is sent to the spatial light modulator in the pickup 11 by the controller 89 via the signal generation circuit 86, and the signal light is modulated by the spatial light modulator.

When reproducing the information recorded on the optical information recording medium 1, the reproduction reference light optical system 12 generates a light wave that causes the reference light emitted from the pickup 11 to enter the optical information recording medium in a direction opposite to that during recording. Generate. The reproduction light reproduced by the reproduction reference light is detected by the photodetector in the pickup 11, and the signal is reproduced by the signal processing circuit 85.

The irradiation time of the reference light and the signal light applied to the optical information recording medium 1 can be adjusted by controlling the opening / closing time of the shutter in the pickup 11 via the shutter control circuit 87 by the controller 89.
The cure optical system 13 plays a role of generating a light beam used for pre-cure and post-cure of the optical information recording medium 1. Precure is a pre-process for irradiating a predetermined light beam in advance before irradiating the desired position with reference light and signal light when recording information at a desired position in the optical information recording medium 1. Post-cure is a post-process for irradiating a predetermined light beam after recording information at a desired position in the optical information recording medium 1 so that additional recording cannot be performed at the desired position.

The disk rotation angle detection optical system 14 is used to detect the rotation angle of the optical information recording medium 1. When adjusting the optical information recording medium 1 to a predetermined rotation angle, a signal corresponding to the rotation angle is detected by the disk rotation angle detection optical system 14, and a disk rotation motor control circuit is detected by the controller 89 using the detected signal. The rotation angle of the optical information recording medium 1 can be controlled via 88.
A predetermined light source driving current is supplied from the light source driving circuit 82 to the light sources in the pickup 11, the cure optical system 13, and the disk rotation angle detection optical system 14, and each light source emits a light beam with a predetermined light amount. Can do.
Further, the pickup 11 and the disc cure optical system 13 are provided with a mechanism capable of sliding the position in the radial direction of the optical information recording medium 1, and position control is performed via the access control circuit 81.

By the way, the recording technology using the principle of angle multiplexing of holography tends to have a very small tolerance for the deviation of the reference beam angle.

Therefore, a mechanism for detecting the deviation amount of the reference beam angle is provided in the pickup 11, a servo control signal is generated by the servo signal generation circuit 83, and the deviation amount is corrected via the servo control circuit 84. It is necessary to provide a servo mechanism for this purpose in the optical information recording / reproducing apparatus 10.

Further, the pickup 11, the cure optical system 13, and the disk rotation angle detection optical system 14 may be simplified by combining several optical system configurations or all optical system configurations into one.

The phase difference control circuit 100 is a circuit for controlling the relative phase difference between the signal light and the reference light during recording so that the phase difference between adjacent or adjacent signals during reproduction is approximately π / 2. The retarder in the pickup 11 is controlled in response to the command from. A retarder is an element that changes the phase of light. For example, the retarder may be formed of a medium having a refractive index different from that of air, such as glass. The phase difference may be generated by shifting the phase difference, or a phase modulation element using a liquid crystal represented by LCOS may be used. Alternatively, an element that does not have a plurality of pixels and gives a single phase difference that is uniform in the plane may be used. As described above, the retarder aims to set the phase difference between signals during reproduction to approximately π / 2, and is an element having a different purpose from the phase mask described later. However, an element in which both the retarder and the phase mask are rationalized and both effects are provided by one component may be used.

FIG. 2 shows a recording principle in an example of a basic optical system configuration of the pickup 11 in the optical information recording / reproducing apparatus 10. The light beam emitted from the light source 301 passes through the collimator lens 302 and enters the shutter 303. When the shutter 303 is open, after the light beam passes through the shutter 303, the optical ratio of the p-polarized light and the s-polarized light becomes a desired ratio by the optical element 304 composed of, for example, a half-wave plate. After the polarization direction is controlled, the light is incident on a PBS (Polarization Beam Splitter) prism 305.

The light beam that has passed through the PBS prism 305 functions as signal light 306, and after the light beam diameter is expanded by the beam expander 308, the light beam passes through the phase mask 309, the relay lens 310, and the PBS prism 311 and passes through the spatial light modulator 312. Is incident on. The phase mask intentionally disturbs the wavefront of the signal light, and when the signal light is collected by the objective lens, the concentration of the amount of light is alleviated to locally consume the hologram precursor in the optical information recording medium. It is an element that can be reduced. As described above, the required functions of the phase mask and the retarder are different, but it is natural that the effects of the phase mask and the retarder can be realized simultaneously by one element.

The signal light to which information is added by the spatial light modulator 312 reflects the PBS prism 311 and propagates through the relay lens 313 and the spatial filter 314. Thereafter, the phase distribution at the time of recording is controlled by the retarder 400 so that the phase difference between adjacent signals at the time of reproduction becomes approximately π / 2, and the signal light is condensed on the optical information recording medium 1 by the objective lens 315. . The retarder 400 may be an element that can be given a fixed phase uniformly in the plane, but it is preferably an element that is composed of a plurality of pixels and that can electrically modulate the additional phase of each pixel. This is because it is possible to cope with the case where the required value of the additional phase for making it approximately π / 2 differs depending on the position in the plane due to the influence of the phase mask, wavefront aberration, and the like. When the retarder 400 is positioned at the position where the spatial light modulator 312 forms the 4F image with the relay lens 313, a phase distribution equivalent to the phase distribution added by the retarder and inverted is imaged on the camera during reproduction. This is desirable because it can reduce the effects of disturbance. However, the position where the retarder 400 is disposed is not limited to the example of FIG. 2, and any position may be used as long as a desired phase difference can be added in the optical path of the signal light.

On the other hand, the light beam reflected from the PBS prism 305 functions as reference light 307 and is set to a predetermined polarization direction according to recording or reproduction by the polarization direction conversion element 316 and then galvano- lated via the mirror 317 and the mirror 318. Incident on the mirror 319. Since the angle of the galvanometer mirror 319 can be adjusted by the actuator 320, the incident angle of the reference light incident on the optical information recording medium 1 after passing through the lens 321 and the lens 322 can be set to a desired angle. In order to set the incident angle of the reference light, an element that converts the wavefront of the reference light may be used instead of the galvanometer mirror. In this specification, for example, the reference light angle is defined as a positive direction for a counterclockwise direction and a negative direction for a clockwise direction, with the direction perpendicular to the optical information recording medium being 0 degrees as shown in the figure.

In this way, the signal light and the reference light are incident on the optical information recording medium 1 so as to overlap each other, whereby an interference fringe pattern is formed in the recording medium, and information is recorded by writing this pattern on the recording medium. To do. In addition, since the incident angle of the reference light incident on the optical information recording medium 1 can be changed by the galvanometer mirror 319, recording by angle multiplexing is possible.
Hereinafter, in holograms recorded in the same area with different reference beam angles, holograms corresponding to each reference beam angle are called pages, and a set of pages angle-multiplexed in the same area is called a book. .

FIG. 3 shows a reproduction principle in an example of a basic optical system configuration of the pickup 11 in the optical information recording / reproducing apparatus 10. When reproducing the recorded information, the reference light is incident on the optical information recording medium 1 as described above, and the light beam transmitted through the optical information recording medium 1 is reflected by the galvanometer mirror 324 whose angle can be adjusted by the actuator 323. By doing so, the reproduction reference light is generated.

The reproduction light reproduced by the reproduction reference light propagates through the objective lens 315, the retarder 400, the relay lens 313, and the spatial filter 314. Thereafter, the reproduction light passes through the PBS prism 311 and enters the photodetector 325, and the recorded signal can be reproduced. At the time of reproduction, there is no need to intentionally add a phase to the reproduction light, so that the retarder 400 displays a uniform pattern, for example, so that no phase is added or only DC phase addition occurs. Keep it. As the photodetector 325, for example, an image sensor such as a CMOS image sensor or a CCD image sensor can be used. However, any element may be used as long as page data can be reproduced.

FIG. 4A shows a schematic diagram illustrating an example of crosstalk between pages. Inter-page crosstalk is an unnecessary component that leaks from a different page with respect to page data to be reproduced. The horizontal axis represents the reference light angle, and the vertical axis represents the reproduction light intensity. For example, when data is reproduced at an optimal reference light angle θ _n for reproducing data of page n, data of page n + 1 that is an adjacent page is also reproduced. In the example in which two page data of n page and n + 1 page shown in the figure are reproduced, the total reproduction light intensity is | E _n | ² + | E _{n + 1} | ² +2 | E _n || E _{n + 1} | cosΦ. Here, E _n is the amplitude of the reproduction light on page _n , E _{n + 1} is the amplitude of the reproduction light on page n + 1, and Φ is the phase difference between the recording on page n and page n + 1. . Here, assuming that the data of the nth page is reproduced, the first term | E _n | ² is a desired reproduction signal, the second term | E _{n + 1} | ² and the third term 2 | E _n || E _{n + 1} | cosΦ is an unnecessary crosstalk component. In this example, since reproduction is performed at the reference light angle θ _n , there is a relationship of | E _n | >> | E _{n + 1} |, and the second term is relatively smaller than the first term. However, the third term may include a factor of | E _n |, and may have a relatively large crosstalk compared to the second term. Here, when Φ = ± π / 2, cos (± π / 2) = 0, so that the third term becomes zero, and what is assumed to have a large internal influence of the crosstalk component is removed, and the signal quality Will improve. In general, when the phase of signal light or reference light at the time of recording is changed, the position of interference fringes is shifted, and phase information can be recorded on an optical information recording medium. During reproduction, the diffracted light based on the recorded phase information is reproduced, so that the phase difference between adjacent pages can be set to π / 2 by controlling and recording the phase using the aforementioned retarder.

FIG. 4B shows a simulation result showing an example of the relationship between the inter-page phase difference and the noise amount during reproduction. This simulation shows an example in which the center page is reproduced when three-time recording is performed at a wavelength of 405 nm and an angular interval of about 60 mdeg. The horizontal axis represents the inter-page phase difference Φ during reproduction, and the vertical axis represents reproduction signal noise. From this graph, it can be seen that the noise is reduced when the inter-page phase difference Φ is π / 2 or −π / 2. Here, the noise is equivalent to the reciprocal of the SNR generally used for evaluating the quality of the reproduction signal in the holographic memory, and is defined by the following equation.

Here, σ ₁ is the standard deviation of the luminance of the reproduced signal group of data '1' when binary signals of data '1' and data '0' are recorded and reproduced, and σ ₀ is the reproduced signal group of data '0' the standard deviation of the brightness, mu ₁ is an average value of the luminance of the reproduced signal group of data '1', mu ₀ is the mean value of the luminance of the reproduced signal group of data '0'.

As is apparent from this figure, the phase difference ± π / 2 has the highest noise reduction effect. However, the present invention is limited to the phase difference ± π / 2 because it has a sufficient noise reduction effect other than the phase difference 0. Of course, the phase difference between signals may be controlled to a value other than 0 by a retarder. For example, when the phase difference is ± π, the noise reduction effect is inferior to π / 2, but there is an advantage that the tolerance when the additional phase deviates from the intended phase π is stronger than π / 2. The retarder may be controlled so as to be π.

FIG. 5 is a diagram showing an example of an operation flow of the optical information recording / reproducing apparatus. First, in S501, the optical information recording medium is positioned at the recording position. In S502, the retarder adds a phase to the signal light or the reference light so that the phase difference between the adjacent reproduction lights becomes approximately π / 2. In S503, the book is recorded on the optical information recording medium. In step S504, it is determined whether the recorded book is the last book to be recorded. If the book is the last book, the process ends. If not, the process returns to step S501.
In the method of this embodiment, since recording is performed by directly changing the phase of the signal light, there is an advantage that an intended phase difference can be added with high accuracy. The second embodiment of the present invention will be described below. Note that a description of parts that are the same as those in the first embodiment is omitted.

A second embodiment of the present invention will be described with reference to FIG. The apparatus configuration and the like can be realized with the same configuration as that of the first embodiment, and thus the description thereof is omitted.

FIG. 6 is a schematic diagram showing an embodiment of a pickup in the optical information recording / reproducing apparatus. The difference from FIG. 2 is that the retarder 400 in the signal light optical path is eliminated and the retarder 401 is added in the reference light optical path. In general, when the phase of signal light or reference light at the time of recording is changed, the position of interference fringes is shifted, and phase information can be recorded on an optical information recording medium. During reproduction, diffracted light based on the recorded phase information is reproduced. Therefore, by controlling the phase with a retarder and recording, Φ, that is, the phase difference between adjacent pages can be π / 2. As in the first embodiment, the retarder 401 controls the phase of the reference light during recording so that the phase difference between adjacent pages is approximately π / 2. The retarder 401 may be an element to which a fixed-value phase pattern is provided, but may be an element that is configured by a plurality of pixels capable of phase modulation and that can control the in-plane phase distribution. Note that the position where the retarder 401 is disposed is not limited to the example of FIG. 6, and may be any place as long as a desired phase difference can be added in the optical path of the reference light. Further, for example, if the retarder 401 is disposed after the mirror 319 with the actuator 320, the phase distribution intended by the retarder 401 may be changed to other aberration components when the angle of light is changed by the mirror with the actuator. Is desirable.
In the method of the present embodiment, since the phase of the reference light that is relatively smaller than the signal light is controlled, there is an advantage that a small retarder can be used and the cost can be reduced.

A third embodiment of the present invention will be described with reference to FIG. The apparatus configuration and the like can be realized with the same configuration as that of the first embodiment, and thus the description thereof is omitted.

FIG. 7 is a schematic diagram showing an embodiment of inter-page phase difference control by the retarder 400. In the drawing, for the sake of simplicity, only parts necessary for explanation are shown as parts in the optical path. When recording a hologram, for example, the phase mask 309 may be driven to suppress local consumption of the hologram precursor in the recording medium. At this time, by driving the phase mask 309, the phase distribution changes between pages during recording and a phase difference between pages occurs during reproduction. Therefore, when the retarder 400 gives a phase difference of π / 2 in a DC manner, The phase difference during reproduction is slightly different from π / 2. In this embodiment, the in-plane phase distribution of the retarder 400 is set so that the sum of the phase difference between pages caused by the movement of the phase mask 309 and the phase difference between pages added by the retarder 400 is approximately π / 2. It aims to improve quality by controlling. In this embodiment, a retarder 400 composed of a plurality of pixels is necessary. Further, depending on the phase mask pattern to be used, it is necessary to change the pattern of the retarder 400 for each page. For example, the pattern of the retarder 400 is learned in advance so that the SNR becomes substantially maximum using the SNR as an index. It may be used at the time of recording, or an optimum pattern theoretically derived from the phase mask pattern 309 may be calculated and stored in an apparatus or a device that controls the apparatus.

When the phase of the P _n by the phase mask 309 to be superimposed on the n-th page of the signal light, a phase due to the retarder 400, which is superimposed on the n-th page of the signal light and the R _n, the phase Psig of n pages during recording of the signal light _n is P _n + R _n , and the phase Psig _{n + 1} of the signal light at the time of n + 1 page recording is P _{n + 1} + R _{n + 1} . When the phase difference between adjacent reproduction lights is π / 2, | Psig _{n + 1} -Psing _n | = π / 2 holds. That is, the pattern R _{n + 1} of the retarder 400 at the time of recording n + 1 pages may be P _n −P _{n + 1} + R _n ± π / 2.
In the method of this embodiment, since the phase is controlled by the retarder 400 provided in the optical path of the signal light, for example, by changing the in-plane phase distribution by the retarder 400 having a plurality of pixels, different phase modulation is performed depending on the position in the page. There is an advantage that the phase difference between pages at the time of reproduction can be controlled to approximately π / 2 in the entire area of the signal light.

A fourth embodiment of the present invention will be described with reference to FIG. The apparatus configuration and the like can be realized with the same configuration as that of the first embodiment, and thus the description thereof is omitted.

FIG. 8 is a schematic diagram showing an example of phase difference control between pages by moving the phase mask 309. In the drawing, for the sake of simplicity, only parts necessary for explanation are shown as parts in the optical path. When recording a hologram, for example, the phase mask 309 may be driven to suppress local consumption of the hologram precursor in the recording medium. At this time, by driving the phase mask 309, a phase difference occurs between recording pages. In this embodiment, a pattern designed so that the phase difference between pages at the time of reproduction generated by moving the pattern of the phase mask 309 by one page is approximately π / 2 is used. By appropriately controlling the movement speed of the phase mask 309 to the speed assumed at the time of design, inter-page crosstalk is reduced. As the pattern of the phase mask, for example, as shown in the figure, a pattern in which the additional phase is alternately different depending on the width of the phase mask movement amount corresponding to one page and the phase difference in the adjacent portion is π / 2 may be used. .
In the method of this embodiment, the inter-page phase difference during reproduction is set to approximately π / 2 only by moving the phase mask 309, so that it can be realized with a smaller number of parts than the methods of other embodiments, and the cost is low. There is an advantage that it can be realized.

A fifth embodiment of the present invention will be described with reference to FIGS. The apparatus configuration and the like can be realized with the same configuration as that of the first embodiment, and thus the description thereof is omitted.

FIG. 9 is a schematic diagram showing an embodiment of a pickup in the optical information recording / reproducing apparatus. The difference from FIG. 6 is that the actuator 402 is attached to the retarder 401. In the method of this embodiment, for example, the pages to be recorded are divided into even pages and odd pages, and the retarder is inserted in the optical path when the even pages are recorded, and the retarder is recorded when the odd pages are recorded. Are not arranged in the optical path. By doing so, an optical path length difference, that is, a phase difference due to the presence or absence of a retarder is produced when recording even-numbered pages and odd-numbered pages. Can be reduced. Note that the above is only an example, a retarder may be inserted when recording an odd page, and a retarder may not be disposed when recording an even page, and the retarder can be electrically controlled in phase. The phase difference between signals at the time of reproduction may be set to approximately π / 2 by changing the retarder pattern at the switching timing of even-numbered pages and odd-numbered pages while being always arranged in the optical path. In the drawing, an example is shown in which a retarder is inserted in the optical path of the reference light. However, a retarder may be inserted in the optical path of the signal light, or a retarder may be inserted in the optical paths of both the reference light and the signal light. It doesn't matter.

FIG. 10 is a diagram showing an example of an operation flow of the optical information recording / reproducing apparatus. First, in S1001, the optical information recording medium is positioned at the recording position. In S1002, only odd pages are first recorded on the optical information recording medium. In S1003, a retarder for adding a desired phase difference is inserted into the path of the signal light or reference light. In S1004, the remaining even pages are recorded on the optical information recording medium. In step S1005, it is determined whether the recorded book is the last book to be recorded. If the book is the last book, the process ends. If the book is not the last book, the retarder is saved from the signal light or reference light path in step S1006. The process returns to S1001.
In the method of this embodiment, even-numbered pages and odd-numbered pages are recorded separately, so that the number of retarder phase switching can be reduced, and even if a retarder operating at a low speed is used, the influence on the decrease in transfer speed is minimized. There is an advantage that a retarder that can be kept to a minimum or that can be used at a lower speed and lower cost can be used.

A sixth embodiment of the present invention will be described with reference to FIGS. 11, 12, and 13. FIG. The apparatus configuration and the like can be realized with the same configuration as that of the first embodiment, and thus the description thereof is omitted.
Consider the phase of crosstalk between pages. When angle multiplexing is used, the reproduction light intensity, that is, the amount of diffracted light can be expressed by Equation 2.

Here, n is the refractive index of the optical information recording medium, L is the thickness of the recording layer of the optical information recording medium, λ is the wavelength of the signal light and the reference light, θ _MRS is the angle formed by the signal light and the reference light, and θ _MS is The angle Δθ _MR of the signal light with respect to the normal line of the optical information recording medium is an angular deviation during reproduction with respect to recording. The angle in Equation 2 is an angle in the optical information recording medium, and is affected by the refractive index of the optical information recording medium. As the angle of the reference light theta _MR relative to the normal of the optical information recording medium, shown theta _MRS with respect to the optical information recording medium, theta _MS, the relationship between theta _MR in Figure 11. The angles in the air corresponding to θ _MRS , θ _MS , θ _MR , and Δθ _MR are θ _ARS , θ _AS , θ _AR , and Δθ _AR , respectively.

FIG. 12 shows the reproduction light intensity with respect to the reference light angle during reproduction and the phase difference with respect to the phase during recording. The reproduction light intensity decreases while oscillating according to Equation 2 according to the reference light angle deviation from the time of recording. The angle at which the reproduction light intensity becomes 0 is called null, and is called 1st null, 2nd null, 3rd null from the side near the reference light angle at the time of recording. The phase difference with respect to the phase at the time of recording is 0 within 1st null, π between 1st null and 2nd null, and 0 between 2nd null and 3rd null. That is, there is a phase difference of 0 between even null and odd null, and π between odd null and even null.

When considering crosstalk between pages, Δθ _MR may be set as an angular interval between adjacent pages in Equation 2, and the amount of crosstalk is shown in FIG. 13 and the horizontal axis is expressed as an angle θ _AS in the air of signal light. Show things. Here, as an example, n = 1.5, L = 1.5 [mm], λ = 405 [nm], θ _AR = 45 [deg], and Δθ _AR = 50 [mdeg]. When the angle range used as the signal light is between 1st null and 2nd null, and between -8 deg and 29 deg, it can be seen that the phase at the time of crosstalk recording is π. Here, the angle to be null can be obtained as a variable of the sinc function as an integer multiple of π in Equation 2, and can be expressed by Equation 3 where m is an integer.

In FIG. 4, the total reproduction light intensity becomes | E _n | ² + | E _{n + 1} | ² +2 | E _n || E _{n + 1} | cosΦ, and 2 | E _n || E in the third term _{As described above, n + 1} | cosΦ is an unnecessary crosstalk component, and when Φ = ± π / 2, the third term becomes zero and the signal quality is improved. When the angle range used as signal light is between 1st null and 2nd null of the crosstalk component, the phase difference between the nth page and the (n + 1) th page is originally π, and the third term is negative. Since this becomes zero, the reproduction light intensity increases. On the other hand, when the angle range used as signal light is inside the 1st null of the crosstalk component or outside the 3rd null, the phase difference between the nth page and the (n + 1) th page is originally 0. Since the third term is positive, the reproduction light intensity decreases. If the effect of increasing the reproduction light intensity is won as a whole, the signal quality as a whole can be improved.

When the angle range used as signal light is between 1st null and 2nd null of the crosstalk component, the phase difference between the nth page and the (n + 1) th page is originally π, and the third term is It is negative. Here, if the phase difference between adjacent pages during recording is Φ = π, the third term becomes positive, and the reproduction light intensity increases compared to when Φ = ± π / 2, which further improves the signal quality. be able to. On the other hand, if the angle range used as signal light is inside the 1st null of the crosstalk component or outside the 3rd null, the phase difference between the nth page and the (n + 1) th page is originally 0. The third term is positive. Here, if the phase difference between adjacent pages during recording is Φ = π, the third term becomes negative, and the reproduction light intensity decreases compared to when Φ = ± π / 2. End up.

Therefore, when the angle range used as signal light is mainly between 1st null and 2nd null of the crosstalk component, Φ = ± π is obtained by setting the phase difference with the adjacent page to Φ = π during recording. The signal quality can be further improved compared to the case of / 2.
The configuration of the recording / reproducing apparatus, the configuration of the pickup, and the operation flow are the same as those in the first embodiment, and the phase difference between adjacent or neighboring signals during recording is controlled to be approximately π / 2. Can be realized.
The method of this embodiment has an advantage that the signal quality can be further improved as compared with the case of the phase difference π / 2 depending on the angle range used as the signal light.

A seventh embodiment of the present invention will be described with reference to FIG. The apparatus configuration and the like can be realized with the same configuration as that of the first embodiment, and thus the description thereof is omitted.

FIG. 14 is the same as the optical conditions of FIG. 13 except for the angle of the signal light. The angle between the crosstalk phase and the adjacent page added to the signal light when the angle range used as the signal light is −20 deg to 60 deg. Shows the phase difference.
When the angle range used as signal light is between 1st null and 2nd null of the crosstalk component, the phase difference between the nth page and the (n + 1) th page is originally π, and the third term is negative. Therefore, the third term is made positive by setting the phase difference Φ = π between adjacent pages. On the other hand, when the angle range used as signal light is inside the 1st null of the crosstalk component or outside the 3rd null, the phase difference between the nth page and the (n + 1) th page is originally 0. Since the third term is positive, no phase difference is added during recording, and the third term is kept positive with Φ = 0. More generally expressed, the angle at the time of recording is defined as 0th null, the phase difference from the adjacent page at the time of recording between the even-order null and the odd-order null is 0, and between the odd-order null and the even-order null Let π be the phase difference between adjacent pages during recording. Since the reproduction light intensity increases at all signal light angles, the signal quality can be improved even when the angle range of the signal light is large.

FIG. 15 shows an example in which the retarder 400 is given a different phase difference for each signal light region. As described above, a phase is given during recording so that the phase difference between adjacent pages is equal to π between odd and even nulls, and no phase difference is given otherwise. Since the null position changes according to the angle of the reference light and the angle between adjacent pages, the boundary of the phase difference may be configured to be variable. Further, in the vicinity of the angle where the crosstalk becomes null, the amplitude of the crosstalk is small, and therefore it is not necessary to strictly define a boundary for switching the phase difference.
The method of the present embodiment has an advantage that even when the angle range of the signal light is large, the reproduction light intensity increases in the entire signal light, and the signal quality can be improved.

The present invention is described on the assumption that signal light information is given in amplitude. In the case where signal light information is given by phase, it is difficult to control the phase difference between pages in the data portion in the page. However, even when signal light information is given in phase, for known patterns at fixed positions in the page, the phase difference is controlled to reduce the amount of crosstalk and improve the signal quality of the known patterns. Can do.

In addition, this invention is not limited to said Example, Various modifications are included. For example, the above-described embodiments have been described in detail for easy understanding of the present invention, and are not necessarily limited to those having all the configurations described. Further, a part of the configuration of one embodiment can be replaced with the configuration of another embodiment, and the configuration of another embodiment can be added to the configuration of one embodiment. Further, it is possible to add, delete, and replace other configurations for a part of the configuration of each embodiment.

In addition, each of the above-described configurations, functions, processing units, processing means, and the like may be realized by hardware by designing a part or all of them with, for example, an integrated circuit. Each of the above-described configurations, functions, and the like may be realized by software by interpreting and executing a program that realizes each function by the processor. Information such as programs, tables, and files that realize each function can be stored in a memory, a hard disk, a recording device such as an SSD (Solid State Drive), or a recording medium such as an IC card, an SD card, or a DVD.

Further, the control lines and information lines indicate what is considered necessary for the explanation, and not all the control lines and information lines on the product are necessarily shown. Actually, it may be considered that almost all the components are connected to each other.
Further, in this specification, an example of reducing crosstalk between adjacent reproduction lights has been described. However, the present invention is not limited to adjacent pages, and crosstalk between neighboring pages that are not adjacent to each other is not limited. It may be used for the purpose of reducing, or may be used for the purpose of reducing crosstalk between adjacent or neighboring books.
In this specification, an example of an angle multiplexing type hologram is shown, but it may be used for other hologram multiplexing methods such as a shift multiplexing type.
Moreover, although the example in which the phase of the optical path of either the signal light or the reference light is changed is shown, it may be realized by changing the phases of both the signal light and the reference light.
Further, since the phase difference between adjacent signals is not substantially π / 2 in all pixels of the signal light, even if it is used in some pixels of the signal light, there is an effect of reducing crosstalk. The phase difference may be set to approximately π / 2 only with the pixels of the portion, and as is clear from FIG. 4, there is an effect of reducing noise by changing the phase difference from 0, so that it is not approximately π / 2. The phase difference may be controlled to other than zero.

DESCRIPTION OF SYMBOLS 1 ... Optical information recording medium, 10 ... Optical information recording / reproducing apparatus, 11 ... Pickup, 12 ... Reference optical system for reproduction | regeneration, 13 ... Disc Cure optical system, 14 ... Disc Rotation angle detection optical system, 81 ... access control circuit, 82 ... light source drive circuit, 83 ... servo signal generation circuit, 84 ... servo control circuit, 85 ... signal processing circuit, 86 ..Signal generation circuit, 87... Shutter control circuit, 88.
89 ... Controller, 90 ... Input / output control circuit, 91 ... External control device, 100 ... Phase difference control device,
301 ... Light source, 302 ... Collimating lens, 303 ... Shutter, 304 ... Half-wave plate, 305 ... PBS prism, 306 ... Signal light, 307 ... Reference light, 308 ... Beam expander, 309 ... Phase mask, 310 ... Relay lens, 311 ... PBS prism, 312 ... Spatial light modulator, 313 ... Relay lens, 314 ..Spatial filter, 315... Objective lens 316... Polarization direction conversion element, 317... Mirror, 318. 322 ... Lens, 323 ... Actuator, 324 ... Mirror, 325 ... Photodetector, 400 ... Retarder, 401 ... Retarder, 402 Actuator,

Claims

In an optical information recording / reproducing apparatus for recording and reproducing an interference pattern of signal light and reference light as a hologram on an optical information recording medium using holography,
A light source that emits laser light;
An optical element for separating the laser light into reference light and signal light;
A phase control unit for controlling the phase of the signal light or reference light during recording;
A photodetector for detecting signal light reproduced by irradiating the reference light onto the optical information recording medium;
With
The reproduction light reproduced from the first hologram when irradiated with the reference light is used as the first reproduction light, and reproduction is performed from the second hologram recorded on the page adjacent to the page on which the first hologram is recorded. The reproduced light to be used as the second reproduced light,
The phase control unit controls the phase of signal light or reference light during recording so that a phase difference between the first reproduction light and the second reproduction light becomes a predetermined value. Information recording / reproducing apparatus.
The optical information recording / reproducing apparatus according to claim 1.
The phase control unit controls the phase of signal light or reference light during recording so that a phase difference between the first reproduction light and the second reproduction light is other than zero. Information recording / reproducing apparatus.
The optical information recording / reproducing apparatus according to claim 1.
The phase control unit controls the phase of signal light or reference light during recording so that a phase difference between the first reproduction light and the second reproduction light is approximately π / 2. Optical information recording / reproducing apparatus.
The optical information recording / reproducing apparatus according to claim 1.
A phase mask for modulating the phase distribution of the signal light;
A drive unit for driving the phase mask,
The phase control unit takes into account a phase difference generated by driving the phase mask by the driving unit, and a phase difference between the first reproduction light and the second reproduction light is approximately π / 2. An optical information recording / reproducing apparatus characterized by controlling the phase of signal light or reference light during recording.
The optical information recording / reproducing apparatus according to claim 1.
The phase control unit controls the phase of signal light or reference light during recording so that a phase difference between the first reproduction light and the second reproduction light is approximately π. Information recording / reproducing apparatus.
The optical information recording / reproducing apparatus according to claim 1.
The hologram is recorded in multiple in a predetermined area of the optical information recording medium while changing the reference light angle,
A hologram corresponding to the reference beam angle is set as a page,
A set of the pages as a book,
The book is composed of a first set of pages and a second set of pages;
The phase control unit performs recording so that a phase difference between the set of first pages reproduced by irradiation of the reference light and the set of reproduced second pages is approximately π / 2. An optical information recording / reproducing apparatus for controlling the phase of signal light or reference light at the time.
In an optical information recording / reproducing apparatus that records or reproduces an interference pattern of signal light and reference light as a hologram on an optical information recording medium using holography,
A light source that emits laser light;
An optical element for separating the laser light into reference light and signal light;
A phase mask having a predetermined phase pattern capable of modulating the phase distribution of the signal light;
A drive unit for driving the phase mask;
A photodetector for detecting signal light reproduced by irradiating the reference light onto the optical information recording medium;
With
The reproduction light reproduced from the first hologram when irradiated with the reference light is used as the first reproduction light, and reproduction is performed from the second hologram recorded on the page adjacent to the page on which the first hologram is recorded. The reproduced light to be used as the second reproduced light,
The optical information recording characterized in that the drive unit controls driving of a phase mask during recording so that a phase difference between the first reproduction light and the second reproduction light is approximately π / 2. Playback device.
In an optical information recording / reproducing method for recording and reproducing an interference pattern of signal light and reference light as a hologram on an optical information recording medium using holography,
Laser light is emitted from the light source,
Separating the laser light into reference light and signal light;
The reproduction light reproduced from the first hologram when irradiated with the reference light is used as the first reproduction light, and reproduction is performed from the second hologram recorded on the page adjacent to the page on which the first hologram is recorded. When the reproduced light to be used is the second reproduced light,
Controlling the phase of the signal light or reference light at the time of recording so that the phase difference between the first reproduction light and the second reproduction light becomes a predetermined value;
An optical information recording / reproducing method, comprising: detecting signal light reproduced by irradiating the optical information recording medium with the reference light.
The optical information recording / reproducing method according to claim 8,
An optical information recording / reproducing method, wherein the phase of signal light or reference light at the time of recording is controlled so that a phase difference between the first reproducing light and the second reproducing light is other than zero.
The optical information recording / reproducing method according to claim 8,
An optical information recording / reproducing method comprising controlling a phase of signal light or reference light during recording so that a phase difference between the first reproducing light and the second reproducing light is approximately π / 2 .
The optical information recording / reproducing method according to claim 8,
In consideration of the phase difference generated by driving the phase mask, the signal light or the reference signal at the time of recording is set so that the phase difference between the first reproduction light and the second reproduction light is approximately π / 2. An optical information recording / reproducing method comprising controlling the phase of light.
The optical information recording / reproducing method according to claim 8,
The hologram is recorded in a multiplex manner by changing the reference light angle in a predetermined area of the optical information recording medium,
The hologram corresponding to the reference beam angle is a page,
A set of the pages as a book,
The book is composed of a first set of pages and a second set of pages;
Signal light or reference during recording so that the phase difference between the set of first pages reproduced by irradiation of the reference light and the set of reproduced second pages is approximately π / 2. An optical information recording / reproducing method comprising controlling the phase of light.
In an optical information recording / reproducing method for recording and reproducing an interference pattern of signal light and reference light as a hologram on an optical information recording medium using holography,
Emitting laser light;
A separation step of separating the laser light into reference light and signal light;
A modulation step for modulating the phase distribution of the signal light;
A driving step for driving a phase mask for modulating the phase distribution;
A detection step of detecting signal light reproduced by irradiating the reference light to the optical information recording medium;
Have
The reproduction light reproduced from the first hologram when irradiated with the reference light is used as the first reproduction light, and reproduction is performed from the second hologram recorded on the page adjacent to the page on which the first hologram is recorded. When the reproduced light to be used is the second reproduced light,
In the driving step, the phase mask at the time of recording is driven so that a phase difference between the first reproduction light and the second reproduction light is approximately π / 2. Method.
In an optical information recording apparatus that multiplex-records an interference pattern of signal light and reference light as a hologram on an optical information recording medium using holography,
A light source that emits laser light;
An optical element for separating the laser light into reference light and signal light;
A phase control unit for controlling the phase of the signal light or reference light at the time of recording;
With
The phase control unit is configured to record the first signal light when recording the first signal light and when recording the second signal light on a page adjacent to the page on which the first signal light is recorded. An optical information recording apparatus, wherein a phase added to the signal light or the reference light is controlled so that a phase difference between the recorded page and the page on which the second signal light is recorded becomes a predetermined value.
The optical information recording apparatus according to claim 14,
The phase control unit is added to the signal light or the reference light so that a phase difference between a page on which the first signal light is recorded and a page on which the second signal light is recorded is approximately π / 2. An optical information recording apparatus characterized by controlling a phase to be transmitted.
The optical information recording apparatus according to claim 14,
The phase controller adds a phase to the signal light or the reference light so that a phase difference between the page on which the first signal light is recorded and the page on which the second signal light is recorded is approximately π. An optical information recording apparatus characterized by controlling the above.
The optical information recording apparatus according to claim 14,
When the crosstalk is between 1 st null and 2 nd null in the region of the signal light and the angle of the reference light is between odd number null and even number null, the phase control unit An optical information recording apparatus, wherein a phase added to the signal light is controlled so that a phase difference between a page on which light is recorded and a page on which the second signal light is recorded is approximately π.
The optical information recording apparatus according to claim 14,
In the signal light region, the phase control unit may detect the first signal when crosstalk is between 1 st null and 2 nd null and the angle of the reference light is between even null and odd null. An optical information recording apparatus, wherein a phase added to the signal light is controlled so that a phase difference between a page on which light is recorded and a page on which the second signal light is recorded is substantially zero.