JP2008027489A - Information recording and reproducing apparatus and information reproducing method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To prevent quality degradation of a pattern image of information light reproduced from interference fringes generated by deviation of a radiation position of reference light. <P>SOLUTION: In an information recording and reproducing apparatus 10, the pattern image of information light and a pattern image of reference light are formed by a micro mirror device 27 and information light and reference light having the same axis are generated. The information light and the reference light are condensed by an objective lens 34 and recorded as interference fringes in a recording medium 11. Two parallel and flat plates 48 and 49 whose axis directions are orthogonal to each other are freely rotatably provided on an optical path of pit reading light detecting the recording position of the interference fringes. The information light is reproduced from the recording medium in which the interference fringes are previously recorded, the parallel and flat plates 48 and 49 are rotated so that density of the pattern image of the reproduced information light is made high and the position in which the best reproduced pattern image is obtained is determined. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to an information recording / reproducing apparatus and an information reproducing method for recording interference fringes obtained by causing interference between information light generated from a two-dimensional pattern image and reference light, and reproducing information light from the recorded interference fringes.

  An information recording / reproducing apparatus using a holographic data memory as a large-capacity recording medium has attracted attention (see, for example, Patent Document 1 and Patent Document 2). The holographic data memory is a recording medium that records interference fringes obtained by patterning digital information as a binary image and causing information light generated from the pattern image of the binary image to interfere with reference light. When the reference light is made to act on the interference fringes, the information light can be reproduced, the reproduced information light pattern image is detected by the image sensor, and the digital information is restored from the detected pattern image.

  A collinear holographic recording / reproducing apparatus can be significantly reduced in size of an interference optical system, and has attracted attention as a practical system. In this method, a micro-mirror device is used to form a ring-shaped reference light pattern image and an information light pattern image at the center thereof to generate reference light and information light that travel on a coaxial optical path. The reference light and the information light are collected in a spot shape by an objective lens facing the recording medium. When the reference light and the information light are collected by the objective lens, they interfere with each other, and three-dimensional interference fringes are recorded on the recording layer of the recording medium.

  On the recording medium on which the interference fringes are recorded, pits serving as a reference for determining the recording position of the interference fringes are formed. Light having a wavelength different from that of the information light and the reference light is used as the pit reading light for reading the pits, and the interference fringe recording layer is not sensitive to the pit reading light. The recording position of the interference fringes is detected by reading the pits of the recording medium, and the interference fringes can be sequentially recorded by switching the pattern image of the information light with good timing according to the recording position.

The pit information on the recording medium is also read when reproducing the information light, and the reference light is accurately irradiated to the recording position of the interference fringes. The intensity of the reproduced information light is greatly reduced by a small shift in the irradiation position of the reference light. For example, as shown in FIG. 7, the SN ratio of the reproduced information light (reproduced light) is about half when the reference light is shifted by 0.5 μm, and the SN ratio is further reduced when the shift is more than that. By utilizing this property, it is possible to reproduce information light even when multiple recording is performed such that a plurality of interference fringes partially overlap, and the recording density can be improved.
JP 2006-99880 A JP 2006-228875 A

  However, when interference fringe recording and information light reproduction are performed by separate devices, the minute positional deviation of the pit reading light existing between the two devices gives a deviation to the irradiation position of the reference light, and the information light There is a problem of greatly reducing the reproduction strength. In other words, unless the positional relationship between the reference light and the pit reading light is unified with the accuracy of 0.5 μm or more, reproduction compatibility between a plurality of devices cannot be ensured. Achieving such high accuracy by adjusting the position of the light source or the position of the micromirror device is a difficult task that requires great effort.

  The present invention has been made in view of the above problems, and provides an information recording / reproducing apparatus and information reproducing method for easily adjusting the positions of reference light and pit reading light and smoothly reproducing information light. Objective.

  In order to achieve the above object, a spatial light modulation unit that forms a two-dimensional pattern image on an image forming surface and modulates light obtained from a light source for each pixel based on the formed pattern image, and the pattern image Generating information light and reference light coaxial from each other, recording means for condensing the generated information light and reference light and interfering with each other on a recording medium, and generating reference light from the pattern image And reproducing means for reproducing information light by irradiating the interference fringes recorded on the recording medium with reference light, and recording positions of the interference fringes by irradiating pit reading light for reading pits formed in advance on the recording medium And at least one of the optical path of the information light and the reference light or the optical path of the pit reading light, and rotates between a position orthogonal to the optical path and a position inclined with respect to the optical path. Parallel plane plate Vignetting wherein the are.

  The plane parallel plate is composed of two plane parallel plates whose axes are orthogonal to each other, and the position of the light beam can be freely changed in a plane parallel to the optical axis.

  In the information reproducing method of the present invention, the light obtained from the light source is modulated for each pixel based on the two-dimensional pattern image formed on the image forming surface, and the coaxial information light and reference light generated from the pattern image are used. Are recorded on the recording medium, and the recording position of the interference fringe is detected when reproducing the information light from the interference fringe by irradiating the recording medium with the reference light. Therefore, a parallel plane plate is provided on at least one of an optical path of pit reading light for reading a pit formed in advance on the recording medium and an optical path of the reference light, and information light reproduced from the interference fringes is used as a reproduction pattern image. Detecting and rotating the plane-parallel plate between a position orthogonal to the optical path and a position inclined with respect to the optical path based on the density of the reproduction pattern image.

  According to the present invention, for example, even when the centers of the information light, the reference light, and the pit reading light do not coincide with each other and there is a shift in the positional relationship between them, the parallel flat plate provided on the optical path is rotated. Since the light beams are translated in accordance with the magnitude of the inclination angle, the positional deviation between the light beams can be eliminated. Further, even if the distance for moving the light beam in parallel is a minute amount, the angle at which the plane-parallel plate is rotated can be converted to a size that can be easily adjusted. Thereby, reproduction compatibility can be easily ensured and information light can be reproduced smoothly.

  In FIG. 1, an information recording / reproducing apparatus 10 interferes with information light that gives information on a pattern image obtained by imaging digital information as a binary image and reference light that gives information on a predetermined pattern image, so Interference fringes are recorded on the recording medium 11. Further, the interference light recorded on the recording medium 11 is irradiated with reference light that gives information of the same predetermined pattern image as that at the time of recording to reproduce the information light.

  In FIG. 2, a recording medium 11 is a disk-shaped medium, and servo information used for tracking servo control and focus servo control and positioning information for determining the recording position of interference fringes are recorded in advance as embossed pits 16 on the disk substrate 15. ing. In the recording medium 11, a reflective layer 17, a gap layer 18, a wavelength selective reflection layer 19, a recording layer 20, and a protective layer 21 are provided in order from the disk substrate 15. The reflective layer 17 increases the reflectance of the pit reading light that reads the embossed pits 16. The wavelength selective reflection layer 19 reflects the green light G1 and transmits the red light R1. The green light G1 is used as recording / reproducing light for recording interference fringes on the recording layer 20 and reproducing information light from the recorded interference fringes. The red light R1 is used as pit reading light for reading the embossed pit 16. The recording layer 20 is sensitive to green light G1 and not sensitive to red light R1. The recording layer 20 is made of a photopolymer that changes optical characteristics such as a refractive index, a dielectric constant, and a reflectance according to the intensity of light having a wavelength to be exposed.

  In FIG. 1, the information recording / reproducing apparatus 10 includes a first light source device 25, a reflection mirror 26, and a micromirror device 27 as a spatial light modulator. The first light source device 25 includes, for example, a laser light source that oscillates a green laser beam having a single wavelength of 532 nm, a polarization conversion element that converts the oscillated green laser light into P-polarized linearly polarized light, and polarization by the polarization conversion element. A collimator is provided for converting the laser light having the same surface into a parallel light beam having a predetermined diameter. The reflection mirror 26 reflects the green light emitted from the first light source device 25 and causes the light to enter the micromirror device 27 from an oblique direction.

  The micromirror device 27 includes an image forming surface 27a in which a large number of mirror elements constituting pixels for forming a two-dimensional pattern image are arranged in a matrix. The image signal input unit 28 inputs an image signal of a pattern image obtained by patterning digital information as a binary image to the micromirror device 27. In the micromirror device 27, the inclination of each mirror element is electrically controlled based on the input image signal. The inclination of each mirror element is displaced between an on position where incident light is reflected in the normal direction of the image forming surface 27a to display white, and an off position where incident light is reflected in the other direction to display black. . Thereby, the luminance information of the white pixel and the black pixel is given to the light emitted from the first light source device 25.

  In FIG. 3, a ring-shaped reference light pattern image P1 and an information light pattern image P2 located at the center of the reference light pattern image P1 are formed on the image forming surface 27a. The reference light pattern image P1 is a predetermined fixed pattern image, and the information light pattern image P2 is a pattern image representing the main body of digital information to be recorded. The micromirror device 27 modulates the light from the first light source device 25 for each pixel by the reference light pattern image P1 and the information light pattern image P2, and generates reference light and information light. The generated reference light and information light become a light beam traveling on a coaxial optical path. The image forming surface 27a of the micromirror device 27 has a rectangular shape, and the diameter of the reference light pattern image P1 is smaller than the length of the short side of the image forming surface 27a. It is a large image.

  In FIG. 1, on the optical path of the reference light and information light emitted from the micromirror device 27, a first polarizing beam splitter 30, a reflecting mirror 31, a dichroic mirror 32, a quarter-wave plate 33, An objective lens 34 is provided. The first polarization beam splitter 30 transmits P-polarized incident light and reflects S-polarized incident light. The reference light and information light emitted from the micromirror device 27 are P-polarized light and pass through the first polarization beam splitter 30. The dichroic mirror 32 transmits the green light G1 and reflects the red light R1. The reference light and information light, which are green light G1, pass through the dichroic mirror 32.

  The quarter wave plate 33 converts linearly polarized incident light into circularly polarized light. The linearly polarized light traveling from the micromirror device 27 toward the recording medium 11 is reflected by the recording medium 11 after passing through the quarter-wave plate 33 once and is incident on the quarter-wave plate 33 again. . Linearly polarized light that has passed through the quarter-wave plate 33 twice from the opposite direction on the same optical path has its polarization plane rotated 90 degrees. The objective lens 34 condenses the information light and the reference light to interfere with each other, and generates interference fringes on the recording layer 20 of the recording medium 11. The objective lens 34 is subjected to tracking servo control and focus servo control based on the servo information obtained by reading the embossed pits 16, and receives the driving force of an actuator or the like on the rotating recording medium 11 in the direction of the optical axis. Drive control is performed in a direction in a vertical plane.

  The CMOS image sensor 38 detects the reproduced information light as a two-dimensional pattern image when the reproduction reference light is irradiated to the interference fringes recorded on the recording layer 20 and the information light is reproduced from the interference fringes. . Since the reproduced information light is converted into S-polarized light by the quarter-wave plate 33, it reflects from the first polarization beam splitter 30 and enters the CMOS image sensor 38. The reproduction pattern image analysis unit 39 decodes the reproduced information light pattern image (reproduction pattern image) to restore the digital information. Further, the reproduction pattern image analysis unit 39 calculates the contrast of the reproduction pattern image based on the luminance information for each pixel of the reproduction pattern image. The contrast of the reproduction pattern image is a parameter for determining whether or not the information light is properly reproduced.

  The second light source device 41 emits red light having a wavelength different from that of the first light source device 25 as pit reading light. The second light source device 41 is provided with, for example, a laser light source that oscillates red laser light of 655 nm and a polarization conversion element that converts red laser light into S-polarized light. The pit reading light emitted from the second light source device 41 is reflected by the second polarization beam splitter 42. The pit reading light reflected by the second polarization beam splitter 42 enters the dichroic mirror 32 via the reflection mirror 43. Since the dichroic mirror 32 reflects the pit reading light which is red light, the pit reading light is combined with the information light and the reference light. The pit reading light travels on the same optical path as the information light and the reference light toward the recording medium 11.

  The pit reading light is collected by the objective lens 34 and enters the recording medium 11. When the pit reading light is reflected by the reflection layer 17 on which the embossed pits 16 are formed, the pit reading light returns along the same optical path as that when entering the recording medium 11. The pit read light passes through the quarter-wave plate 33 twice, so that the polarization plane is rotated by 90 degrees, passes through the second polarization beam splitter 42, and reaches the photodetector 44. The photodetector 44 detects pit reading light from the recording medium 11 and generates an electrical signal. This electric signal includes servo information for performing servo control of the objective lens 34 and positioning information for detecting the recording position of the interference fringes.

  A plane parallel plate 48 and a plane parallel plate 49 are provided between the reflection mirror 43 and the dichroic mirror 32. The parallel flat plate 48 and the parallel flat plate 49 have a rotation shaft 48a and a rotation shaft 49a in directions orthogonal to each other. The parallel plane plate 48 and the parallel plane plate 49 rotate around the respective rotation shafts 48a and 49a. The motor 50 and the motor 51 generate driving force for rotating the parallel flat plate 48 and the parallel flat plate 49, respectively. The motors 50 and 51 are controlled by the optical path adjustment unit 52. The optical path adjustment unit 52 determines the drive amount of the motors 50 and 51 based on the contrast of the reproduction pattern image calculated by the reproduction pattern image analysis unit 39 and adjusts the inclination angle of the parallel plane plates 48 and 49.

In FIG. 4, the plane parallel plate 48 is made of optical glass that is colorless and transparent and has no birefringence. The plane parallel plate 48 has a refractive index n ₁ and a thickness d, and a light beam incident at an incident angle θ ₁ is transmitted through the plane parallel plate 48 at a refractive angle θ ₂ . θ ₂ follows Snell's law,
θ ₂ = sin ⁻¹ [(1 / n ₁ ) · sin θ ₁ ]
It is expressed. In addition, the periphery of the plane parallel plate 48 is air. The light incident on the plane parallel plate 48 is refracted again when exiting from the plane parallel plate 48, and exits the plane parallel plate 48 at an angle parallel to the incident time. The shift amount X at the time of incidence and emission of the light beam transmitted through the plane parallel plate 48 is
X = d (sin θ ₁ −cos θ ₁ tan θ ₂ )
It is expressed. The incident angle θ ₁ is equal to the inclination angle of the plane parallel plate 48 with respect to the optical path of the pit reading light. The plane parallel plate 48 and the plane parallel plate 49 have the same configuration.

  In FIG. 5, the plane parallel plate 48 and the plane parallel plate 49 are parallel to each other in the initial state. The rotating shaft 48a of the parallel plane plate 48 is parallel to the horizontal direction. When the parallel plane plate 49 rotates and tilts, the incident pit reading light, that is, the red light R1, is shifted in the vertical direction. Further, the rotating shaft 49a of the parallel flat plate 49 is parallel to the vertical direction, and when the parallel flat plate 49 rotates, the incident pit reading light shifts in the horizontal direction. The optical path adjusting unit 52 shifts the pit reading light in a direction perpendicular to the traveling direction by controlling the inclination angle of the parallel plane plate 48 and the plane parallel plate 49. As a result, the relative positional relationship between the reference light and information light and the pit reading light changes.

  Next, the flow of position adjustment between the information light, the reference light, and the pit reading light will be described. At the time of manufacturing the information recording / reproducing apparatus 10, a reproduction test of the information recording / reproducing apparatus 10 is performed by using the recording medium 11 serving as a reference in which interference fringes are recorded in advance. The information recording / reproducing apparatus 10 is irradiated with pit reading light from the second light source device 41, and information on the recording position of the interference fringes is read from the embossed pits 16 of the recording medium 11. The image signal input unit 28 inputs an image signal of the reference light pattern image P1 to the micromirror device 27. A reference light pattern image P1 is formed on the image forming surface 27a, and the recording medium 11 is irradiated with the reference light. When the reference light is applied to the interference fringes, the information light is reproduced, and a reproduction pattern image is detected by the CMOS image sensor 38.

  The reproduction pattern image analysis unit 39 calculates the contrast of the reproduction pattern image. The optical path adjustment unit 52 determines whether or not the calculated contrast of the reproduction pattern image satisfies a specified level. At this time, if the contrast of the reproduction pattern image satisfies a prescribed level, it is determined that adjustment is unnecessary. On the other hand, when the reproduction pattern image does not satisfy the specified level, the optical path adjustment unit 52 drives the motors 50 and 51 to rotate the parallel plane plates 48 and 49.

  The optical path adjustment unit 52 first rotates the plane parallel plate 48 by a predetermined angle. Each time the parallel flat plate 48 rotates, the optical path of the pit reading light moves in a direction orthogonal to the rotation shaft 48a. The recording medium 11 is irradiated with reference light, and a reproduction pattern image is detected by the CMOS image sensor 38 while changing the positional relationship between the reference light and the pit reading light. The reproduction pattern image analysis unit 39 calculates the contrast of the detected reproduction pattern image and sends it to the optical path adjustment unit 52. The optical path adjustment unit 52 monitors the change in contrast of the reproduction pattern image. When the contrast is improved, the optical path adjustment unit 52 rotates the parallel flat plate 48 until a contrast peak is obtained. On the other hand, when the contrast is lowered, the optical path adjustment unit 52 switches the direction of rotating the parallel plane plate 48 to the opposite direction, and similarly rotates the parallel plane plate 48 until the peak of the contrast of the reproduction pattern image is obtained.

  Next, the optical path adjustment unit 52 rotates the parallel flat plate 49 by a predetermined angle, and detects the peak position while monitoring the change in contrast of the reproduction pattern image. Each time the plane-parallel plate 49 rotates, the optical path of the pit reading light moves in a direction perpendicular to the rotation shaft 49a. Since the plane parallel plate 48 and the plane parallel plate 49 rotate about axes in directions orthogonal to each other, the irradiation position of the pit reading light moves on the surface of the recording medium 11. Each time the pit reading light irradiation position changes, the position where the reference light is irradiated to the interference fringe changes, and the contrast of the reproduced pattern image of the reproduced information light changes.

  Thus, the optical path adjustment unit 52 rotates the parallel plane plate 48 and the parallel plane plate 49 to adjust the irradiation position of the pit reading light so that the clearest reproduction pattern image can be obtained. The adjustment is completed when the contrast of the reproduction pattern image satisfies the specified level. By performing the above-described adjustment on a plurality of information recording / reproducing apparatuses 10, the positional relationship between the reference light and the pit reading light can be unified. That is, reproduction compatibility is ensured among the plurality of information recording / reproducing apparatuses 10 that have been adjusted, and information light can be reproduced smoothly.

  In the above embodiment, two parallel flat plates are provided on the optical path of the pit reading light. However, two parallel flat plates are provided on the optical path of the information light and the reference light, or the information light and the reference light are provided. One plane parallel plate can be provided for each of the optical path and the optical path of the pit reading light. Although a micromirror device is used as a spatial light modulator for forming a two-dimensional pattern image, a liquid crystal display panel, a magneto-optic modulator, or the like can also be used. The information recording / reproducing apparatus of the present invention is not limited to the pit reading light combined with the reference light and the information light and irradiates the recording medium, but the pits are read from the surface opposite to the surface irradiated with the reference light and the information light. The recording medium to which the reading light is irradiated may be used. The information reproducing method of the present invention can also be applied to an information reproducing apparatus that only reproduces information light. In the above description, the reference light irradiation position is adjusted at the time of manufacturing the information recording / reproducing apparatus. However, the present invention is not limited to this, and the reference light irradiation position may be adjusted every time the information light is reproduced. .

It is a schematic block diagram of an information recording / reproducing apparatus. It is a figure which shows the pattern image which produces | generates information light and reference light. It is sectional drawing which shows the structure of a recording medium. It is sectional drawing of a parallel plane board. It is a perspective view which shows the change of the optical path according to the inclination of a parallel plane plate. It is a flowchart which shows the flow of adjustment. It is a graph which shows the change of the intensity | strength of information light according to the shift amount of the irradiation position of reference light.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Information recording / reproducing apparatus 11 Recording medium 15 Disc board | substrate 16 Emboss pit 17 Reflective layer 18 Gap layer 19 Wavelength selective reflection layer 20 Recording layer 21 Protective layer 25 1st light source device 26 Reflection mirror 27 Micromirror device 28 Image signal input part 30 1st 1 polarization beam splitter 31 reflection mirror 32 dichroic mirror 33 quarter wave plate 34 objective lens 38 CMOS image sensor 39 reproduction pattern image analysis unit 41 second light source device 42 second polarization beam splitter 43 reflection mirror 44 photodetector 48, 49 Parallel plane plates 48a, 49a Rotating shafts 50, 51 Motor 52 Optical path adjustment unit P1 Reference light pattern image P2 Information light pattern image

Claims (3)

A spatial light modulator that forms a two-dimensional pattern image, modulates light obtained from a light source for each pixel based on the formed pattern image, and generates coaxial information light and reference light from the pattern image. Recording means for recording interference fringes obtained by condensing the generated information light and reference light and interfering with each other on the recording medium, and generating reference light from the pattern image and referring to the interference fringes recorded on the recording medium Information provided with reproducing means for reproducing information light by irradiating light and recording position detecting means for detecting the recording position of the interference fringes by irradiating pit reading light for reading a pit formed in advance on the recording medium In the recording / reproducing apparatus,
At least one of the optical path of the information light and the reference light or the optical path of the pit reading light is provided with a parallel plane plate that rotates between a position orthogonal to the optical path and a position inclined with respect to the optical path. An information recording / reproducing apparatus.   2. The information recording / reproducing apparatus according to claim 1, wherein the plane-parallel plate includes two plane-parallel plates whose axes are orthogonal to each other. The light obtained from the light source based on the two-dimensional pattern image formed on the image forming surface is modulated for each pixel, and the coaxial information light and the reference light generated from the pattern image are condensed to interfere with each other. In the information reproducing method of reproducing the information light from the interference fringes by irradiating the recording medium with reference light, the interference fringes recorded on the recording medium,
In order to detect the recording position of the interference fringes, a parallel plane plate is provided in at least one of an optical path of pit reading light for reading a pit formed in advance on the recording medium and an optical path of the information light and reference light, Information light reproduced from the interference fringes is detected as a reproduction pattern image, and based on the density of the detected reproduction pattern image, the plane parallel plate is positioned between a position orthogonal to the optical path and a position inclined with respect to the optical path. An information reproducing method characterized by rotating.

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