JP5298267B2 - Optical information reproducing apparatus and reproducing method - Google Patents

Description

  The present invention relates to an optical information reproducing apparatus and reproducing method for reproducing information from an optical information recording medium including an information recording layer in which information is recorded by an interference pattern between information light and a recording reference light, and more particularly to a space. The present invention relates to an optical information reproducing apparatus and a reproducing method that use spatially modulated reproduction reference light in order to reproduce information from an interference pattern recorded by a locally modulated reference light for recording.

  Conventionally, holographic recording in which information is recorded on a recording medium using holography is generally performed by superimposing information light carrying image information constituting recording light and recording reference light inside the recording medium. This is done by writing the interference pattern generated at that time on the recording medium. At the time of reproducing the recorded information, the image information is reproduced by diffraction by the interference pattern by irradiating the recording medium with the reference light for reproduction.

  In recent years, volume holography, particularly digital volume holography, has been developed and attracted attention for practical use for ultra-high density optical recording. Volume holography is a method of writing interference patterns in three dimensions by actively utilizing the thickness direction of the recording medium. Increasing the thickness increases the diffraction efficiency and increases the recording capacity using multiple recording. There is a feature that can be planned. Digital volume holography is a computer-oriented holographic recording method that uses a recording medium and a recording method similar to those of volume holography, but restricts image information to be recorded to a binarized digital pattern. In this digital volume holography, for example, image information such as an analog picture is once digitized and recorded as image information. At the time of reproduction, the digital pattern information is read and decoded so that the original image information is restored and displayed. As a result, even if the S / N ratio (signal to noise ratio) is somewhat poor at the time of reproduction, the original information is reproduced very faithfully by performing differential detection or encoding binary data and performing error correction. It becomes possible.

  Among them, a method (collinear method) in which the optical axis of the information light and the optical axis of the recording reference light are coaxially arranged and the interference pattern is recorded by one objective lens is attracting attention as a next-generation recording method ( Patent Document 1 and Non-Patent Document 1). A schematic configuration of an optical system for explaining the principle of an optical information recording apparatus in conventional collinear holographic recording is shown in FIG. 8A, and a schematic configuration of an optical system for explaining the principle of an optical information reproducing apparatus is shown in FIG. Shown in B).

  As shown in FIG. 8A, the optical system of the recording apparatus records information on a recording medium 120 having a protective layer 121, an information recording layer 122, and a reflective layer 123, and includes a light source 101, a collimator lens 102, A spatial light modulator 103 and an objective lens 104 are provided. The recording operation is briefly described as follows. First, the divergent light beam emitted from the light source 101 is incident on the spatial light modulator 103 as a substantially parallel light beam by the collimator lens 102. A spatial modulation pattern 111 is displayed on the spatial light modulator 103, and the incident parallel light is spatially modulated to generate information light 112 and recording reference light 113. In the spatial modulation pattern 111, digital pattern information in which information to be recorded is developed is arranged in the central portion, and a radial pattern displayed in an annular area is arranged around the information. The light 112 is generated, and the recording reference light 113 is generated by the surrounding radial pattern (Patent Document 2). The information beam 112 and the recording reference beam 113 are irradiated onto the recording medium 120 as a bundle of rays converged as a whole by the objective lens 104, and an interference pattern between the spatial frequency components of the information beam 112 and the recording reference beam 113 subjected to Fourier transform. Is recorded in the information recording layer 122.

  The optical system of the reproducing apparatus for reproducing information from the optical information recording medium 120 on which the interference pattern is recorded in this way is a light source 101, a collimator lens 102, and a spatial light modulator 103 as shown in FIG. 8B. In addition to the objective lens 104, a beam splitter 105 and a photodetector 106 are provided. In the reproduction apparatus, a spatial modulation pattern 114 is displayed on the spatial light modulator 103, and the parallel light beams from the light source 101 and the collimator lens 102 are spatially modulated to generate reproduction reference light 115. In the spatial modulation pattern 114, only the radial pattern that generated the recording reference light at the time of recording is arranged in the same manner as at the time of recording, and the reproduction reference light 115 similar to the recording reference light is generated by the radial pattern. The The reproduction reference beam 115 is applied to the interference pattern of the recording medium 120 as a bundle of rays converged by the objective lens 104 as a whole, and is diffracted by the interference pattern to generate the reproduction beam 116. The reproduction reference light 115 and the reproduction light 116 reflected by the reflective layer 123 of the recording medium 120 are partially reflected by the beam splitter 105, and the digital pattern information of the reproduction light 116 is detected by the photodetector 106.

Japanese Patent No. 36552339 International Publication No. 2004/102542 Pamphlet Hideyoshi Horime and four others "Realizing 200GB in the near-takeoff holographic medium 2006", Nikkei Electronics, January 17, 2005, p. Pages 105-114

  In the reproducing apparatus in the conventional holographic recording as described above, the diffraction efficiency due to the interference pattern is low at present, and the intensity of the reproducing light 116 is several tenths of several tens of minutes compared to the irradiated reproducing reference light 115. It is only 1 of. For this reason, in order to reproduce the reproduction light 116 having a sufficient intensity for detection from the interference pattern, it is necessary to further increase the intensity of the reproduction reference light 115 by several tens to several hundreds.

  In addition, when the reproduction reference beam 115 is generated by the spatial modulation pattern 114 displayed on the spatial light modulator 103, most of the light from the light source 101 is not used and the light use efficiency is low. . In addition, since the pixel pitch of the spatial light modulator 103 is fine, the reproduction reference beam 115 is diffracted and scattered, resulting in a further decrease in light utilization efficiency.

  As a result, the light source 101 of the reproducing apparatus requires a high-power laser, so that there is a problem that the optical system becomes expensive and large. In addition, since a high-output light source is used, power consumption during use increases and running costs also increase. In addition, since a high-output light source generates a large amount of heat, it has also been a problem in that the SN ratio and reliability are lowered due to the influence of temperature rise, for example, expansion of the recording medium. Furthermore, since the optical system is enlarged, the access speed to the reproduction position cannot be increased in terms of inertia and driving force, leading to a restriction on the transfer speed.

  Further, in the collinear method, the spatial modulation pattern 114 of the reproduction reference beam 115 needs to be accurately displayed on the entrance pupil plane of the objective lens 104. However, an optical system (beam splitter 105) that separates reproduction light needs to be disposed between the spatial light modulator 103 and the objective lens 104, and the spatial light modulator 103 is disposed on the entrance pupil plane of the objective lens 104. It was physically difficult to do. For this reason, an optical system for transmitting an image such as a relay lens is further arranged to transmit the spatial modulation pattern 114 displayed on the spatial light modulator 103 to the entrance pupil plane of the objective lens 104. As described above, the conventional reproducing apparatus has a problem that the optical system becomes complicated. FIG. 8 is a schematic diagram for explaining the principle of the recording / reproducing operation, and an optical system for transmitting an image such as a relay lens is omitted.

  In view of the above problems, an object of the present invention is to provide an optical information reproducing apparatus and a reproducing method with improved light use efficiency. It is another object of the present invention to provide an optical information reproducing apparatus and reproducing method that can be easily configured and / or easily reduced in size. In addition, it is an object of the present invention to provide an optical information reproducing apparatus and a reproducing method that are inexpensive and can reduce power consumption.

  An optical information reproducing apparatus of the present invention is an optical information reproducing apparatus that reproduces information from an optical information recording medium including an information recording layer in which an interference pattern between information light and recording reference light is recorded. Holographic optical element on which a reference light generating pattern for reproducing spatially modulated reference light for reproduction is formed, and reproduction light generated by irradiating the interference pattern of the optical information recording medium with the reference light for reproduction And a photodetector for detecting.

  Furthermore, in the optical information reproducing apparatus, it is preferable that the holographic optical element is detachably provided at a predetermined position.

  Furthermore, in the optical information reproducing apparatus, it is preferable that a plurality of reference light generation patterns are recorded on the holographic optical element.

  Further, in the optical information reproducing apparatus, the holographic optical element has an interference pattern formed by intersecting the light beam of the reproduction reference light and the light beam of the auxiliary reference light as a reference light generation pattern. Another recorded optical information recording medium may be used. The holographic optical element may have a structure in which light from a light source is incident from a side end surface.

  Furthermore, in the optical information reproducing apparatus, the holographic optical element and the photodetector may be disposed adjacent to each other.

  Further, in the optical information reproducing apparatus, the relative position of the holographic optical element in the optical system with respect to the optical information recording medium may be provided so as to be movable.

  The optical information reproducing method of the present invention is an optical information reproducing method for reproducing information from an optical information recording medium provided with an information recording layer on which an interference pattern between information light and recording reference light is recorded. The reference light generation pattern formed on the holographic optical element is irradiated with the light from the reference light generation pattern to reproduce the spatially modulated reproduction reference light, and the reproduced reproduction reference light is used as the reproduction reference light. Irradiating an interference pattern of the optical information recording medium to reproduce reproduction light from the interference pattern, and detecting the reproduced reproduction light by a photodetector.

  Further, in the optical information reproducing method, the holographic optical element is spatially modulated into a different pattern by changing an irradiation angle of light from the light source irradiated on the reference light generation pattern. The reference light may be regenerated.

  Further, in the optical information reproducing method, the reproduction reference light is irradiated on the optical information recording medium by moving a relative position of the holographic optical element in the optical system with respect to the optical information recording medium. The position or the irradiation angle may be corrected.

  In the optical information reproducing apparatus and reproducing method of the present invention, since the reference light generating pattern of the holographic optical element has a high reproduction efficiency, the light use efficiency can be remarkably improved. For this reason, it is possible to adopt a light source having a smaller output than the conventional one, and it is possible to reduce the size, weight and cost of the optical information reproducing apparatus, and to improve the reliability and reduce the power consumption. It is possible to reduce and increase the transfer speed. Further, the holographic optical element itself is lighter and cheaper than the conventional spatial light modulator, and from this point, the weight and cost can be reduced.

  In addition, the reproduction reference light reproduced from the holographic optical element is adjusted when the reference light generation pattern is formed, so that the spatial modulation pattern of the reproduction reference light is imaged (virtual display surface) Therefore, the allowable range of arrangement is greatly expanded in relation to the entrance pupil plane of the objective lens, and the downsizing of the optical information reproducing apparatus can be realized. For example, a holographic optical element that generates reproduction reference light and a photodetector can be adjacent to each other in the optical axis direction.

  Other effects and details of the effects will be clarified in the description of the embodiments described below.

  Embodiments of the present invention will be described below. FIG. 1 is an explanatory diagram showing the principle of information reproduction in the optical information reproducing apparatus of the present invention.

  In FIG. 1, an optical information reproducing apparatus 10 includes a light source 11, a collimator lens 12, a holographic optical element 13, an objective lens 14, a beam splitter 15, and a photodetector 16. In the operation of the reproducing apparatus 10, first, light from the light source 11 is made into a substantially parallel light beam 17 by the collimator lens 12 and irradiated to the holographic optical element 13. In the holographic optical element 13, a reference light generation pattern 13a for reproducing the spatially modulated reproduction reference light is formed, and the parallel light beam 17 from the light source is diffracted by the reference light generation pattern 13a. The spatially modulated reproduction reference beam 18 is reproduced. Here, the spatial modulation pattern of the reproduction reference beam 18 is the same as the spatial modulation pattern of the recording reference beam during recording. Then, the reproduction reference beam 18 that has passed through the beam splitter 15 is irradiated onto the interference pattern recorded on the information recording layer 22 of the optical information recording medium 20 as a light beam converged by the objective lens 14 as a whole, and is diffracted by the interference pattern. Thus, the reproducing light 19 is reproduced. The reproduced reproduction light 19 is reflected by the reflection layer 23 of the recording medium 20 together with the reproduction reference light 18, passes through the objective lens 14, is reflected by the beam splitter 15, and is digital pattern information of the reproduction light 19 by the photodetector 16. Is detected.

  Thus, in the optical information reproducing apparatus 10 and the reproducing method of the present invention, a holographic optical element 13 (HOE: Holographic Optical Element) is used to generate the reproduction reference beam 18. As the holographic optical element 13, interference between the reproduction reference light spatially modulated in the same pattern as the spatial modulation pattern of the recording reference light during recording and other light (hereinafter referred to as “auxiliary reference light”). It may be an optical information recording medium in which the reference light generation pattern 13a is recorded by a pattern, or the reference light generation pattern is written by writing a pattern calculated using a computer so that the reproduction reference light is reproduced by a drawing device. 13a may be formed. Moreover, it can also be set as the structure which injects light from the side end surface of the holographic optical element 13. FIG. Diffraction by the reference light generation pattern 13a of the holographic optical element 13 can increase the reproduction efficiency (diffraction efficiency).

  The reproduction reference light may be diffracted light that is spatially modulated by a spatial modulation pattern, or may be a Fourier image that is Fourier transformed by an objective lens. When recording a Fourier image, the reference light for reproduction having a spatial modulation pattern displayed on the entrance pupil plane of the objective lens is irradiated by the objective lens so as to converge at a position intersecting the auxiliary reference light, and the auxiliary reference light is emitted. What is necessary is just to make it interfere.

  As the auxiliary reference light, a plane wave is used for easy design. However, the auxiliary reference light is not particularly limited, and may be a convergent light beam or a divergent light beam. The auxiliary reference light used when recording the reference light generation pattern 13a is reproduced. It may be used also when the reference light for reproduction is reproduced. However, the auxiliary reference light that has passed through the holographic optical element 13 must be separated from the reproduced reproduction reference light. For example, as shown in FIG. 1, the optical path of the parallel light beam 17 that is the auxiliary reference light and the reproduction reference light If the two-beam interference type configuration is used so that the optical path of the light 18 is different, the parallel light beam 17 that has passed through (not shown, but travels diagonally down to the left in the drawing) of the reproduction reference light 18 is reproduced. It can be excluded from the optical system.

  In addition, by recording a plurality of reference light generation patterns 13a on the holographic optical element 13, it is possible to generate a plurality of reference light for reproduction with different spatial modulation patterns. The plurality of reference light generation patterns 13a can use, for example, shift multiple recording recorded at different positions, angle multiplexing recorded by changing the irradiation angle of the auxiliary reference light, and the like.

  Since the reference light generating pattern 13a of the holographic optical element 13 has a high reproduction efficiency, the light use efficiency can be remarkably increased. For this reason, it is possible to adopt a light source having a smaller output than the conventional one, and it is possible to reduce the size, weight and cost of the optical information reproducing apparatus, and to improve the reliability and reduce the power consumption. It is possible to reduce and increase the transfer speed. Further, the holographic optical element 13 itself is lighter and cheaper than the conventional spatial light modulator, and from this point, the weight and cost can be reduced.

  In addition, the reproduction reference light reproduced from the holographic optical element 13 is adjusted when the reference light generation pattern 13a is formed, whereby the position (virtual display) where the spatial modulation pattern of the reproduction reference light is imaged. Surface) can be designed as appropriate, so that the allowable range of arrangement is greatly expanded in relation to the entrance pupil plane of the objective lens, and the optical information reproducing apparatus can be downsized. For example, the holographic optical element 13 that generates the reproduction reference light and the photodetector 16 can be adjacent to each other in the optical axis direction.

  Further, if the holographic optical element 13 is detachable, information reproduction can be selected using the holographic optical element 13 as a key. That is, a reference light generation pattern 13a is formed on each holographic optical element 13 so that reproduction reference light having a different spatial modulation pattern is generated, and a certain holographic optical element 13 is attached to the apparatus. The information reproduced from the optical information recording medium can be different depending on whether the holographic optical element 13 is attached to the apparatus or not. Typically, information can be reproduced only by the holographic optical element 13 capable of generating reference light for reproduction having a specific spatial modulation pattern.

  Hereinafter, a more specific optical information reproducing apparatus will be described with reference to FIGS. FIG. 2 is a schematic diagram showing the overall structure of the apparatus 30, in which an interference pattern between the apparatus for producing the holographic optical element 43 on which the reference light generating pattern 43 a is formed, the information light, and the recording reference light is recorded. An optical information reproducing apparatus for reproducing information from the optical information recording medium 70 is combined. FIG. 3 is an enlarged view of an optical system in the vicinity of the holographic optical element 43 in FIG. 2 (portion surrounded by a dotted square in FIG. 2). In FIG. 2, the holographic optical element manufacturing apparatus and the optical information reproducing apparatus share some members. However, it is easy to separate them into independent apparatuses.

  In FIG. 2, the composite apparatus 30 includes a light source 31, a beam expander 32, a first half-wave plate 33 (hereinafter, the half-wave plate is abbreviated as “HWP”), and a first polarization beam splitter 34 (hereinafter, referred to as “HWP”). , Polarization beam splitter is abbreviated as “PBS”), second HWP 35, mirror 36, second PBS 37, mirror 38, spatial light modulator 39, third HWP 40, mirrors 41 and 42, optical information recording medium (holo) Graphic optical element) 43, first relay lens systems 44 and 45, third PBS 46, second relay lens systems 47 and 48, aperture 49, quarter-wave plate 50, objective lens 51, and third relay Lens systems 52 and 53, a magnification adjusting lens 54, a mirror 55, and a photodetector 56 are included.

  The light source 31 generates a coherent linearly polarized light bundle, and for example, a semiconductor laser can be used. The light generated from the light source 31 preferably has the same wavelength as the recording reference light during recording, and generates auxiliary reference light and reproduction reference light.

  The beam expander 32 is composed of two lenses in FIG. 2, but the aperture of the light from the light source 31 is formed to be large and almost parallel.

  The first HWP 33 and the first PBS 34 function as a light amount adjusting means. The first HWP 33 changes the ratio of P-polarized light and S-polarized light, and the first PBS 34 separates one polarized light. It can be adjusted to any light quantity. 2 is a composite apparatus, it is necessary to record a reference light generation pattern on the optical information recording medium 43 to manufacture a holographic optical element, and to reproduce reproduction reference light from the holographic optical element. It is necessary to refer to the reproduction light from the optical information recording medium 70, and the first HWP 33 and the first PBS 34 are arranged to adjust the light amount according to two different purposes. In the case of a simple optical information reproducing apparatus, the light amount adjusting means may not be provided.

  The second HWP 35 and the second PBS 37 adjust the light quantity balance of the two light beams separated in the second PBS 37. One of the two light fluxes separated in the second PBS 37 (61 in FIG. 3) is the reproduction reference light, and the other one (62 in FIG. 3) is the auxiliary reference light. The second HWP 35 and the second PBS 37 are also arranged because it is necessary to manufacture a holographic optical element, and may not be provided in the case of a simple optical information reproducing apparatus.

  The mirror 36 is arranged to change the light path in order to reduce the area occupied by the optical system. The mirror 38 reflects one of the lights separated by the second PBS 37 toward the spatial light modulator 39.

  The spatial light modulator 39 generates reproduction reference light for forming the reference light generation pattern 43a on the holographic optical element 43, and has a large number of pixels arranged in a lattice pattern. A transmissive or reflective spatial light modulator that can modulate the phase or / and intensity of the emitted light every time can be used. As the spatial light modulator 39, a DMD (digital micromirror device) or a matrix type liquid crystal element can be used. The DMD can modulate the intensity by changing the reflection direction of incident light for each pixel, and spatially modulate the phase by changing the reflection position of the incident light for each pixel. The liquid crystal element can spatially modulate the intensity and phase of incident light by controlling the alignment state of the liquid crystal for each pixel. For example, the phase of the light can be spatially modulated by setting the phase of the emitted light for each pixel to one of two values that differ from each other by π radians. In FIG. 2, a DMD is employed as the spatial light modulator 39, and the same spatial modulation pattern as the recording reference light at the time of recording is displayed to spatially modulate the light incident from the mirror 38 at a constant angle. Reproduction reference light (63 in FIG. 3) is generated.

  The third HWP 40 is arranged to rotate the polarization direction of the auxiliary reference light (62 in FIG. 3) by 90 degrees to match the polarization direction of the reproduction reference light 63.

  The mirrors 41 and 42 are arranged so that the optical path lengths from the second PBS to the optical information recording medium 43 are the same. As in the case where the reproduction reference beam 63 is reflected by the mirror 38 and the DMD 39, the auxiliary reference is made. The light 62 is reflected by the mirrors 41 and 42 and is incident on the optical information recording medium 43.

  The optical information recording medium (holographic optical element) 43 is formed with a reference light generation pattern (43a in FIG. 3), and is used in the optical information reproducing apparatus after the reference light generation pattern 43a is formed. In this case, it becomes a holographic optical element. In FIGS. 2 and 3, a transmission type optical information recording medium is shown, but a reflection type optical information recording medium may be used. The transmissive optical information recording medium 43 shown in FIGS. 2 and 3 has a structure in which a photosensitive material is sealed between a pair of translucent substrates.

  The apparatus for producing the holographic optical element 43 in which the reference light generating pattern 43a is formed functions by the structure from the light source 31 to the optical information recording medium 43 described so far.

  Further, the first relay lens systems 44 and 45 and the second relay lens systems 47 and 48 apply the spatial modulation pattern of the reproduction reference light 63 displayed on the spatial light modulator 39 to the entrance pupil plane of the objective lens 51. Arranged to communicate. That is, the distance from the display surface of the spatial light modulator 39 to the lens 44 is the focal length of the lens 44, and the distance from the lens 44 to the lens 45 is the sum of the focal length of the lens 44 and the focal length of the lens 45, The distance from the lens 45 to the lens 47 is the sum of the focal length of the lens 45 and the focal length of the lens 47, and the distance from the lens 47 to the lens 48 is the sum of the focal length of the lens 47 and the focal length of the lens 48. The lens 48 is arranged such that the distance from the entrance pupil plane of the objective lens 51 is the focal length of the lens 48.

  Incidentally, in the optical information reproducing apparatus, the spatial light modulator 39 itself does not generate reproduction reference light, and reproduction reference light (64 in FIG. 3) is reproduced from the holographic optical element 43. The positional relationship between the holographic optical element 43 and the lens 44 is not direct, and the position (virtual display surface) where the reproduced spatial modulation pattern of the reproduced reference light 64 is displayed becomes the focal length of the lens 44. Arrange as follows. According to the configuration of FIG. 2, the position of the spatial light modulator 39 becomes the virtual display surface.

  The third PBS 46 and the quarter-wave plate 50 separate the reproduction light reproduced from the optical information recording medium 70, and the polarization directions of the reproduction reference light 64 irradiated to the optical information recording medium 70 are divided into four directions. By passing the quarter-wave plate 50 twice at the time of irradiation and at the time of reflection, the polarization direction of the reflected reference light for reproduction can be rotated by 90 degrees and separated by the third PBS 46. Similarly, when recording as information light, the reproduction light reproduced from the optical information recording medium 70 passes through the quarter-wave plate 50 once again by passing through the quarter-wave plate 50. , The polarization direction is rotated 90 degrees and separated by the third PBS 46.

  The aperture 49 is disposed at a focal position between the second relay lens systems 47 and 48, and can remove high-order diffracted light.

  The objective lens 51 irradiates the optical information recording medium 70 with reproduction reference light imaged on the entrance pupil plane, and enters the reproduction light generated from the optical information recording medium 21 to form an image on the exit pupil plane. .

  The third relay lens systems 52 and 53, together with the second relay lens systems 47 and 48, transmit the reproduction light imaged on the exit pupil plane of the objective lens 51 to the photodetector 56. In FIG. 2, a magnification adjustment lens 54 is disposed thereafter, and the magnification of the spatial modulation pattern of the reproduction light imaged on the photodetector 56 is changed. The mirror 55 is disposed at the focal position between the third relay lens systems 52 and 53, and is disposed in order to change the light path in order to reduce the area occupied by the optical system.

  The photodetector 56 has a large number of pixels arranged in a lattice pattern, and can detect the intensity of received light for each pixel, and is formed by spatially modulating the intensity of light. Spatial modulation patterns can be detected. As the photodetector 56, a CCD solid-state image sensor or a MOS solid-state image sensor can be used. Further, as the photodetector 56, a smart optical sensor in which a MOS solid-state imaging device and a signal processing circuit are integrated on one chip (for example, a document “O plus E, September 1996, No. 202, Nos. 93 to 93). (See page 99). Since this smart optical sensor has a high transfer rate and a high-speed calculation function, it is possible to perform high-speed reproduction by using this smart optical sensor, for example, reproduction at a transfer rate on the order of G (giga) bits / second. Can be performed.

  Next, the operation of forming the reference light generation pattern 43a on the optical information recording medium 43 in the composite apparatus 30 of FIG. 2 will be described. The light 60 from the light source appropriately adjusted by the optical systems 32 to 36 is separated into two light beams 61 and 62 whose polarization directions are different by 90 degrees by the second PBS 37 (FIG. 3). The light beam 61 is reflected by the mirror 38 and enters the spatial light modulator 39. The spatial light modulator 39 displays the spatial modulation pattern of the reference light shown in FIG. 4 (A). The reference light 63 for reproduction is generated by spatially modulating the light beam 61, and the optical information recording medium 43. Is irradiated. Further, since the polarization direction of the light beam 62 is rotated by 90 degrees by the third HWP 40, the polarization direction of the reproduction reference light 63 coincides with the polarization direction. Thereafter, the light is reflected by the mirrors 41 and 42, and a plane wave is applied to the optical information recording medium 43 as auxiliary reference light 62. 2 and 3, the optical information recording medium 43 is tilted so that the incident angles of the reproduction reference light 63 and the auxiliary reference light 62 are 45 degrees, and the reproduction reference light 63 and the auxiliary reference light 62 are included. Are arranged so as to intersect at an intersection angle of 90 degrees in the optical information recording medium 43. As a result, an interference pattern between the reproduction reference light 63 and the auxiliary reference light 62 is recorded on the photosensitive material of the optical information recording medium 43, and a holographic optical element in which the reference light generation pattern 43a is formed can be manufactured.

  Further, by providing a part of the optical system so as to be movable, the crossing angle between the reproduction reference light 63 and the auxiliary reference light 62 can be changed, and a plurality of reference light generation patterns 43a at the same position or different positions. Can be angle-multiplexed. For example, the mirror 41 or the mirror 42 may be configured to rotate, and the irradiation angle of the auxiliary reference light 62 with respect to the optical information recording medium 43 may be changed. Although it is possible to change the irradiation angle of the reproduction reference light, in this case, when the holographic optical element is used in the optical information reproduction apparatus, the reproduction reference light reproduced from the holographic optical element is emitted. Since the angle also differs depending on each reference light generation pattern 43a, the structure of the optical information reproducing apparatus becomes complicated. As described above, when angle multiplexing recording is performed, it is possible to generate reference light for reproduction having a different spatial modulation pattern depending on the irradiation angle of the auxiliary reference light.

  Further, the operation of the optical information reproducing apparatus for reproducing information from the optical information recording medium 70 using the holographic optical element 43 will be described. FIG. 5 is a diagram showing an optical path during reproduction. As shown in FIG. 5, only the auxiliary reference light 62 is generated by the second HWP 35 and the second PBS 37, and the reference light generation pattern 43 a of the holographic optical element 43 is irradiated with the plane-wave auxiliary reference light 62. Then, the reproduction reference light 64 in which the auxiliary reference light 62 is diffracted by the reference light generation pattern 43a is reproduced. The diffraction efficiency at this time is very high, and the light utilization efficiency can be increased. FIG. 4B shows a spatial modulation pattern of the reproduced reference light 64 for reproduction. The spatial modulation pattern of the reproduction reference beam 64 is transmitted to the entrance pupil plane of the objective lens 51 by the first relay lens systems 44 and 45 and the second relay lens systems 47 and 48 and is Fourier transformed by the objective lens 51. An image is irradiated onto the optical information recording medium 70. Then, reproduction light is generated by diffracting with the interference pattern recorded on the information recording layer of the optical information recording medium 70, and the generated reproduction light is separated by the third PBS 46, and the second relay lens system 47 and 48, the third relay lens systems 52 and 53 and the magnification adjustment lens 54 form an image of the spatial modulation pattern of the photodetector 56. Although not shown, it is preferable to provide means for removing the reproduction reference light reflected by the optical information recording medium 70.

  Further, in FIG. 5, the mirror 41 or the mirror 42 is configured to be rotatable so that the irradiation angle of the auxiliary reference light 62 to the optical information recording medium 43 can be changed, and a plurality of reference light generation patterns are angle-multiplexed. Different reproduction reference beams may be reproduced as appropriate from the recorded holographic optical elements.

  Furthermore, in FIG. 5, the irradiation position or irradiation of the reproduction reference light 64 irradiated to the optical information recording medium 70 by moving the relative position of the holographic optical element 43 in the optical system with respect to the optical information recording medium. The angle can be corrected. For example, in FIG. 5, if the holographic optical element 43 is translated in a direction perpendicular to the optical axis of the reproduction reference light 64, the reproduction reference light irradiated on the optical information recording medium 70 by the objective lens 51 is reproduced. The irradiation angle can be changed. When the interference pattern between the Fourier image of the reproduction reference light and the auxiliary reference light is recorded as the reference light generation pattern of the holographic optical element 43, the objective lens 51 is moved by moving the holographic optical element 43. Thus, the irradiation position irradiated on the optical information recording medium 70 can be corrected. In addition, as the correction of the irradiation position, the position of the focal point irradiated to the optical information recording medium 70 by the objective lens 51, the magnification of the Fourier image, and the like can be corrected.

  Actually, the error bit of the information reproduced by the apparatus of FIG. 5 was 3, and the SN ratio was 3.78. Further, the ratio of the intensity of the 0th-order and 1st-order diffracted light (the intensity actually used) of the reproduced reproduction reference light 64 to the intensity of the light incident on the holographic optical element 43 was 13.9%. It was.

  On the other hand, as a comparative example, information was reproduced on the optical path shown in FIG. 6 as a conventional optical information reproducing method. In FIG. 6, only the light 61 that becomes the reproduction reference light 63 is generated by the second HWP 35 and the second PBS 37, and spatially modulated by the spatial modulation pattern displayed on the spatial light modulator 39, the reproduction reference. Light 63 was generated. In FIG. 6, the experiment was performed with the holographic optical element 43 removed and a dummy glass placed. The error bit of the information reproduced by the apparatus shown in FIG. 6 is 0 and the SN ratio is 4.04. However, the generated reproduction reference light 64 has an intensity of light incident on the spatial light modulator 39. The ratio of the 0th-order and 1st-order diffracted light intensities (intensities actually used) was only 1.41%.

  As described above, in the optical information reproducing apparatus of the present invention, the light utilization efficiency of about 10 times can be realized. For this reason, the light source 31 having an output of 1/10 can be used, and the spatial light modulator 39 is not necessary, so that an optical information reproducing apparatus can be manufactured at a very low cost.

  FIG. 7 shows another embodiment, which has a structure in which the optical system of the optical information reproducing apparatus 80 is integrated as a very small pickup apparatus. In FIG. 7, the optical information reproducing apparatus 80 includes a light source 81, a holographic optical element 82, a partial polarizing plate 83, a quarter-wave plate 84, an objective lens 85, and a photodetector 86.

  In FIG. 7, a holographic optical element 82 is an end face incident type HOE in which light enters from a side end face. In the holographic optical element 82, a reference light generating pattern 82a is formed in the waveguide layer. For example, the reference light generation pattern 82a may be manufactured by drawing a pattern calculated using a computer so that the reproduction reference light is reproduced in advance. When light is incident from the end face, the light is scattered by the reference light generation pattern in the waveguide layer, and the reproduction reference light is reproduced. Here, the virtual display surface of the spatial modulation pattern of the reproduction reference light reproduced from the holographic optical element 82 is arranged on the entrance pupil plane of the objective lens 85 (the same position as the exit pupil plane for the reproduction light). Has been calculated.

  The partial polarizing plate 83 is provided with a polarizing plate only at a portion through which the reproduction reference light passes. By combining with the quarter-wave plate 84, the partial reference light 83 reflected by the optical information recording medium 70 is obtained. Can be removed. That is, the reproduction reference light 91 reproduced from the holographic optical element 82 is made to coincide with the polarization direction of the partial polarizing plate 83, and therefore can pass through the partial polarizing plate 83. After that, the reproduction reference light 91 passes through the quarter-wave plate 84 before the reproduction reference light 91 is applied to the optical information recording medium 70, and the reproduction reference light 93 reflected from the optical information recording medium 70 again becomes the quarter wave. By passing through the single wavelength plate 84, the polarization direction of 90 degrees is rotated. As a result, the reflected reproduction reference light 93 cannot pass through the partial polarizing plate 83 and is blocked.

  The photodetector 86 is arranged so that the incident surface is located on the exit pupil plane of the objective lens 85, and the reproduction light 92 reproduced from the optical information recording medium 70 forms an image on the incident surface, and spatial modulation of the reproduction light is performed. This is a configuration for detecting a pattern. Since the photodetector 86 is disposed adjacent to the holographic optical element 82 in the optical axis direction, a virtual modulation pattern of the reference light for reproduction reproduced from the incident surface of the photodetector 86 and the holographic optical element 82 is assumed. The display surface completely matches. By adopting such a configuration, the pickup of the optical information reproducing apparatus can be greatly reduced in size.

  Furthermore, since the holographic optical element 82 can enhance wavelength selectivity by using a thick hologram medium, the holographic optical element 82 is not only a laser light source that has been converted into a single mode as the light source 81 that is incident from the side end face and has increased coherency, An inexpensive light source such as a multimode-oscillated semiconductor laser or a light-emitting diode with low coherency can also be used.

Explanatory drawing which shows the principle of the reproduction | regeneration of information in the optical information reproducing | regenerating apparatus of this invention Schematic which shows one Embodiment of the optical information reproducing | regenerating apparatus of this invention. Partial enlarged view of FIG. (A) is a spatial modulation pattern of the reference light displayed on the spatial light modulator, and (B) is a diagram showing a spatial modulation pattern of the reference light reproduced from the holographic optical element. The figure explaining the operation | movement at the time of reproduction | regeneration of the optical information reproducing | regenerating apparatus of this invention The figure explaining the operation | movement at the time of reproduction | regeneration of the conventional optical information reproduction | regeneration apparatus Schematic which shows other one Embodiment of the optical information reproducing | regenerating apparatus of this invention. (A) is a schematic diagram of an optical system for explaining the principle of a conventional optical information recording apparatus, and (B) is a schematic diagram of an optical system for explaining the principle of a conventional optical information reproducing apparatus.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Optical information reproduction | regeneration apparatus 11 Light source 12 Collimator lens 13 Holographic optical element 13a Reference light generation pattern 14 Objective lens 15 Beam splitter 16 Photo detector 18 Reproduction reference light 19 Reproduction light 20 Optical information recording medium

Claims (10)

An optical information reproducing device for reproducing information from an optical information recording medium comprising an information recording layer and an reflecting layer on which an interference pattern between information light and recording reference light is recorded,
A light source;
A holographic optical element having a reference light generation pattern for reproducing a spatially modulated reference light for reproduction; and
By irradiating the light from the light source onto the reference light generation pattern of the holographic optical element, the optical information recording is performed as a light bundle that converges the reproduction reference light reproduced from the reference light generation pattern as a whole. An objective lens for illuminating the medium;
By irradiating the reproducing reference beam to the interference pattern of the optical information recording medium, generated from the optical information recording medium, the light for detecting the reproduction light focused on the exit pupil plane of the objective lens by the objective lens have a detector,
The optical information reproducing apparatus, wherein the holographic optical element is disposed so that a position where a reproduced spatial modulation pattern of the reproduced reference light is displayed is an entrance pupil plane of the objective lens . The optical information reproducing apparatus according to claim 1, wherein the holographic optical element is detachably provided at a predetermined position. 3. The optical information reproducing apparatus according to claim 1, wherein a plurality of reference light generation patterns are recorded on the holographic optical element. The holographic optical element is another optical information recording medium in which an interference pattern formed by intersecting a light beam of reproduction reference light and a light beam of auxiliary reference light at a certain angle is recorded as a reference light generation pattern. The optical information reproducing apparatus according to claim 1, wherein the optical information reproducing apparatus is an optical information reproducing apparatus. 4. The optical information reproducing apparatus according to claim 1, wherein the holographic optical element has a structure in which light from a light source is incident from a side end surface. The optical information reproducing apparatus according to claim 1, wherein the holographic optical element and the photodetector are disposed adjacent to each other. The optical information reproducing apparatus according to claim 1, wherein a relative position of the holographic optical element in the optical system with respect to the optical information recording medium is movably provided. In an optical information reproducing method for reproducing information from an optical information recording medium comprising an information recording layer and an reflecting layer on which an interference pattern between information light and recording reference light is recorded ,
Reproducing the reference light for reproduction, which is spatially modulated from the reference light generation pattern by irradiating the reference light generation pattern formed on the holographic optical element with light from the light source,
Reproducing the reproduction light from the interference pattern by irradiating the reproduced reproduction reference light on the interference pattern of the optical information recording medium as a bundle of rays converged as a whole by the objective lens ,
The pre Symbol playback light is imaged on the exit pupil plane of the objective lens by the objective lens to an optical information reproducing method for detecting by a photodetector,
Further, the optical information is characterized in that the holographic optical element is arranged such that a position where the spatial modulation pattern of the reproduced reference light for reproduction is displayed is an entrance pupil plane of the objective lens. Playback method. The reproduction reference light spatially modulated in a different pattern is reproduced from the holographic optical element by changing an irradiation angle of light from the light source irradiated on the reference light generation pattern. The optical information reproducing method according to claim 8. Correcting the irradiation position or irradiation angle of the reproduction reference light irradiated to the optical information recording medium by moving the relative position of the holographic optical element in the optical system with respect to the optical information recording medium. 10. The optical information reproducing method according to claim 8 or 9, characterized in that: