JP6070441B2 - Hologram recording apparatus and optical module for hologram recording - Google Patents

Description

  The present invention relates to a hologram recording technique for recording information on a recording medium using holography.

  In recent years, development of storage devices using holography has been promoted. A storage device using holography is a promising candidate for a next-generation storage device because it has a higher recording density than a conventional magnetic recording device.

  As a recording / reproducing apparatus capable of recording / reproducing optical information to / from a storage device using holography, Patent Document 1 discloses that a recording medium is irradiated with signal light and reference light by separate optical systems, and the signal light and reference are recorded on the recording medium. An apparatus for recording optical information by causing interference with light is disclosed. In this apparatus, in order to avoid mechanical interference with the reference light, the optical axis of the signal light lens is set to be inclined rather than perpendicular to the recording medium. This apparatus records a plurality of page data on the same part of the recording medium by changing the relative angle between the signal light and the reference light by changing the incident angle of the reference light to the recording medium, so-called angle multiplexing. The recording density is increased by recording.

JP 2008-96783 A

  However, the apparatus of Patent Document 1 has a problem that it is difficult to increase the recording density because the volume occupied by each page data recorded corresponding to each angle of the reference light in the recording medium is not reduced. There is.

The present invention has been made to solve these problems, and the signal light optical axes tilted optical system irradiating the record medium in the art of recording a hologram on a recording medium, the page data one An object of the present invention is to provide a technique capable of reducing the volume of a recording medium required for recording per sheet.

  In order to solve the above-described problem, a hologram recording apparatus according to a first aspect includes a holding unit that holds a recording medium including a recording layer capable of recording a hologram, a light source that emits coherent light, and the recording medium A condensing lens system whose optical axis is inclined with respect to the surface of the light source, and generating signal light from the coherent light as a spatially modulated parallel light beam, and the parallel light beam is recorded by the condensing lens system. A signal light optical system that condenses the recording layer of the medium, and a reference light optical system that generates reference light from the coherent light and irradiates a portion of the recording layer on which the signal light is condensed. The condenser lens system and the holding portion are relatively relative to each other so that the amount of the focal point of the condenser lens system entering the recording medium along the optical axis of the condenser lens system falls within a target range. Positioning A side view is defined by a direction view perpendicular to both the optical axis of the condenser lens system and the normal of the surface at the intersection of the optical axis and the surface of the recording medium, and the normal direction Is defined as the vertical direction, the recording medium side is down, and the condenser lens system side is up, and the principal plane of the condenser lens system is the lowest in the side view among the light bundles included in the parallel light bundle. When the lower most off-axis light beam is defined by the transverse light beam, the target range of the penetration amount is that each light beam included in each light beam in the parallel light beam passes through the condensing lens system and passes through the recording layer. Each distribution range along the extending direction of the recording medium in a side view of each optical path traversing indicates that the extension of the reference region in which the lowermost off-axis light beam crosses the recording layer through the condenser lens system The input when included in the reference distribution range along the direction. It is in the range of the write amount.

  The hologram recording apparatus according to the second aspect is the hologram recording apparatus according to the first aspect, wherein the main plane of the condenser lens system is the uppermost side in a side view among the light bundles included in the parallel light bundle. When the uppermost off-axis light bundle is defined by the transverse light bundle, the absolute value of the absolute value of the intrusion amount in the target range is the most in the side view among the light rays included in the lower most off-axis light bundle. The first light beam crossing the main plane on the lower side passes through the condensing lens system and intersects the upper surface of the recording layer of the recording medium, and each light beam included in the uppermost off-axis light beam bundle When the second light rays crossing the main plane at the lowest side in a side view coincide with each other in the extending direction with the second intersection that intersects the lower surface of the recording layer through the condenser lens system. Excessive amount of penetration Is the value.

The hologram recording apparatus according to the third aspect is the hologram recording apparatus according to the first or second aspect, wherein the maximum value of the absolute value of the amount of penetration in the target range is the light beam included in the parallel light bundle. and each angle uppermost in the optical path to the Symbol recording medium each of the upper beam across the main plane of the focusing lens system, which makes with the optical axis of the condenser lens system in a side view in each bundle, the A coma aberration curve showing the relationship between each upper ray passing through the condensing lens system and each position in the extending direction at each intersection where the lower ray intersects the lower surface of the recording layer is the lowermost of the upper rays. It is the absolute value of the amount of penetration when taking an extreme value with respect to the third light beam included in the off-axis light beam.

  A hologram recording apparatus according to a fourth aspect is the hologram recording apparatus according to the third aspect, wherein the maximum value of the absolute value of the amount of penetration in the target range is determined by the coma aberration curve being determined by the upper side rays. Of these, the value is half of the absolute value of the amount of penetration when the extreme value is taken for the third light beam included in the lower most off-axis light beam.

  A hologram recording apparatus according to a fifth aspect is the hologram recording apparatus according to the first aspect, wherein the recording medium further includes a protective layer for protecting the recording layer on an upper surface of the recording layer, and the amount of intrusion The target range is a range of the penetration amount that satisfies the inequality (1).

  A hologram recording apparatus according to a sixth aspect is the hologram recording apparatus according to the fifth aspect, wherein the target range of the penetration amount is from the center of the range of the penetration amount that satisfies the inequality (1). The absolute value of the penetration amount is a range on the smaller side.

  An optical module for hologram recording according to a seventh aspect includes a holding unit for holding a recording medium having a recording layer capable of recording a hologram, and a condensing lens system in which an optical axis is inclined with respect to the surface of the recording medium The condensing lens system is configured to condense the signal light, which is generated from the coherent light in advance and is incident as a spatially modulated parallel light beam, onto the recording layer of the recording medium, and the condensing lens system And the holding portion are positioned relative to each other so that the amount of penetration of the focal point of the condenser lens system into the recording medium along the optical axis of the condenser lens system falls within a target range. A side view is defined by a direction view perpendicular to both the optical axis of the condenser lens system and the normal of the surface at the intersection of the optical axis and the surface of the recording medium, and the normal direction is defined as the vertical direction. The recording medium side down, the collection The lens system side is defined as upper, and the lower most off-axis light beam is defined by the light beam that traverses the principal plane of the condensing lens system at the bottom in the side view among the light beams included in the parallel light beam. Then, the target range of the penetration amount is the extending direction of the recording medium in a side view of each optical path in which each light beam included in each light beam in the parallel light beam crosses the recording layer through the condenser lens system Each of the distribution ranges along the lowermost off-axis ray bundle is included in the reference distribution range along the extending direction of the reference region that crosses the recording layer through the condenser lens system. A range of quantities.

By the invention according to the first to 7 any aspect of, the holding portion of the condenser lens system and record medium for condensing the signal beam incident as a parallel light beam, the optical axis direction of the focal point of the condenser lens system Are positioned relative to each other so that the amount of penetration into the recording medium is within the target range. Target range, the distribution range of the light beam along the extending direction of the optical path of the record medium when crossing the recording layer comprising parallel light beam is a reference to the most off-axis light flux of the lower crosses the recording layer This is the range of the amount of entry when included in the reference distribution range along the extending direction of the region. The most off-axis light flux and the lower is because the largest angle formed between the normal line of the recording medium, the distribution width along the extending direction of the record medium in each ray bundle contained in the parallel light beam widest bundle of rays, i.e., the volume required to record the optical information is most significant ray bundle. The reference distribution range is a length along the extending direction of the recording medium in at least an area necessary for recording one page data on the recording medium. Therefore, if the condensing lens system and the holding unit are positioned relative to each other so that the amount of entering the recording medium along the optical axis direction of the focal point of the condensing lens system is within the target range, the signal light can be obtained. The distribution range of the optical path in the recording layer of all the contained light rays can be kept within the reference distribution range. Thereby, the volume of the recording medium required for recording one page data can be reduced.

It is a side block diagram which shows an example of schematic structure of the hologram recording device which concerns on embodiment. FIG. 2 is a schematic side view illustrating a state in which signal light of page data is incident on a recording medium in the signal light optical system of the hologram recording apparatus of FIG. 1. FIG. 3 is an enlarged view of a recording medium portion in FIG. 2. FIG. 3 is a schematic side view illustrating the incidence of signal light generated from three points of the center, right end, and left end of the SLM in the schematic diagram of FIG. 2 on a recording medium. It is an enlarged view of the recording medium part of FIG. It is a figure which shows the reference | standard distribution range in FIG. It is a side surface schematic diagram which shows an example of the amount of penetration | invasion into the recording medium of the focus (pupil) of a signal light lens. It is a side surface schematic diagram which illustrates a shallow state compared with the state of FIG. It is a side surface schematic diagram which illustrates a deep state compared with the state of FIG. FIG. 4 is a schematic side view showing a state in which a light beam incident on a recording medium is refracted at a protective layer surface and an interface between the protective layer and the recording layer. It is a figure which illustrates the coma aberration curve computed using the aberration lens (ideal lens). It is a figure which shows the form of Example 1 of a signal light lens. It is a figure which shows the form of Example 2 of a signal light lens. It is a figure which shows the form of Example 3 of a signal light lens. It is a figure which shows the form of Example 4 of a signal light lens. It is a figure which shows the form of Example 5 of a signal light lens. It is a figure which shows the form of Example 6 of a signal light lens. It is a figure which shows the form of Example 7 of a signal light lens. It is a figure which shows the form of Example 8 of a signal light lens. It is a figure which shows the form of Example 9 of a signal light lens. It is a figure which shows the form of Example 10 of a signal light lens. It is a figure which shows the form of Example 11 of a signal light lens. It is a figure which shows the form of Example 12 of a signal light lens. It is a figure which shows the result of having calculated the upper limit of the index value of the amount of penetration about the signal light lens of Examples 1-12 by the approximate expression and ray tracing. It is a figure which shows the result of having calculated the lower limit of the index value of the amount of penetration about the signal light lens of Examples 1-12 by the approximate expression and ray tracing. FIG. 10 is a diagram illustrating the relationship between the signal light angle with respect to the optical axis when the amount of penetration is changed and the x coordinate of the intersection point of the light ray toward the left end of the recording layer with respect to the signal light lens of Example 3. 6 is a diagram illustrating spherical aberration of the signal light lens of Example 3. FIG. In the signal light lens of Example 12, it is a figure which shows the relationship between the signal light angle with respect to the optical axis when the amount of penetration is changed, and the x coordinate of the intersection of the light ray toward the pupil left end and the lower surface of the recording layer. FIG. 10 is a diagram showing spherical aberration of the signal light lens of Example 12. It is a figure which shows the curvature radius, surface spacing, etc. of the signal light lens of Example 1 in a tabular format. It is a figure which shows the aspherical coefficient of the signal light lens of Example 1 in a tabular form. It is a figure which shows the curvature radius of the signal light lens of Example 2, a surface interval, etc. in a table | surface form. It is a figure which shows the aspherical coefficient of the signal light lens of Example 2 in a tabular form. It is a figure which shows the curvature radius, surface interval, etc. of the signal light lens of Example 3 in a table format. It is a figure which shows the aspherical coefficient of the signal light lens of Example 3 in a tabular form. It is a figure which shows the curvature radius of the signal light lens of Example 4, a surface interval, etc. in a table | surface form. It is a figure which shows the aspherical coefficient of the signal light lens of Example 4 in a tabular form. It is a figure which shows the curvature radius, surface interval, etc. of the signal light lens of Example 5 in a tabular format. It is a figure which shows the aspherical coefficient of the signal light lens of Example 5 in a tabular form. It is a figure which shows the curvature radius of a signal light lens of Example 6, surface spacing, etc. in a table | surface form. It is a figure which shows the aspherical coefficient of the signal light lens of Example 6 in a table format. It is a figure which shows the curvature radius of the signal light lens of Example 7, surface spacing, etc. in a table | surface form. It is a figure which shows the aspherical coefficient of the signal light lens of Example 7 in a tabular form. It is a figure which shows the curvature radius, surface interval, etc. of the signal light lens of Example 8 in a table format. It is a figure which shows the aspherical coefficient of the signal light lens of Example 8 in a tabular form. It is a figure which shows the curvature radius, surface interval, etc. of the signal light lens of Example 9 in a table format. It is a figure which shows the aspherical coefficient of the signal light lens of Example 9 in a table format. It is a figure which shows the curvature radius of the signal light lens of Example 10, a surface space | interval, etc. in a table | surface form. It is a figure which shows the aspherical coefficient of the signal light lens of Example 10 in a tabular form. It is a figure which shows the curvature radius of the signal light lens of Example 11, a surface space | interval, etc. in a table | surface form. It is a figure which shows the aspherical coefficient of the signal light lens of Example 11 in a tabular form. It is a figure which shows the curvature radius of a signal light lens of Example 12, a surface interval, etc. in a table | surface form. It is a figure which shows the aspherical coefficient of the signal light lens of Example 12 in a tabular form. It is a figure which shows the focal distance etc. of the signal light lens of Examples 1-12 in tabular form.

  Hereinafter, an embodiment of the present invention will be described with reference to the drawings. In the drawings, parts having the same configuration and function are denoted by the same reference numerals, and redundant description is omitted in the following description. In some of the drawings, an XZ orthogonal coordinate system is described as appropriate for explanation of directions. The Z axis is parallel to the normal direction of the surface of the recording medium 40 described later, and the X axis is parallel to the extending direction of the recording medium 40 in a side view described later.

<Embodiment>
<Configuration of hologram recording device>
FIG. 1 is a side block diagram illustrating an example of a schematic configuration of a hologram recording apparatus 100 according to the embodiment. FIG. 2 is a schematic side view illustrating a state in which the signal light 12 of page data generated by a spatial light modulator (SLM) 21 is incident on the recording medium 40 in the signal light optical system 20 of the hologram recording apparatus 100. It is.

  The hologram recording apparatus 100 mainly includes a light source 10 that emits coherent light 1, a signal light optical system 20, a reference light optical system 30, and a holding unit 50 that holds a recording medium 40. The hologram recording apparatus 100 records the hologram by irradiating the recording medium 40 with the reference light 14 while condensing the signal light 12, and receiving the reproduction light by irradiating the recording medium 40 with the reference light 14 during reproduction. And reproduce the hologram. The recording medium 40 further includes a recording layer 41 capable of recording a hologram, and a protective layer 42 such as a cover glass provided on the upper surface of the recording layer 41 to protect the recording layer 41, and is held by the holding unit 50. Has been. The signal light lens 23 and the holding unit 50 are a hologram recording optical module 300. Further, the signal light lens 23 and the holding unit 50 are relatively relative to each other so that the amount of entering the recording medium 40 along the optical axis 91 (FIG. 4) of the focus of the signal light lens 23 falls within a target range described later. Is positioned. In this positioning, the orientation of the signal light optical system 20 including the signal light lens 23 with respect to the recording medium 40 and the optical characteristics of the signal light lens 23 are maintained, and the signal light lens 23 and the recording medium 40 are maintained. The relative positional relationship is changed.

  Here, in the description of the present embodiment, the side view refers to the optical axis 91 of the signal light lens 23 and the normal (main normal) 92 of the surface at the intersection of the optical axis 91 and the surface of the recording medium 40 ( FIG. 4) is a direction view orthogonal to both. The vertical direction is the direction of the normal line 92, and the signal light lens 23 side is up, and the recording medium 40 side is down.

  The coherent light 1 emitted from the light source 10 is converted into a parallel light beam by an optical system (not shown) and is incident on a polarization beam splitter (not shown) included in the reference light optical system 30. At the time of recording, the coherent light 1 is divided into two parallel light bundles by the polarizing beam splitter. One parallel light beam is guided to the signal light optical system 20. The other parallel light beam is guided to the reference light optical system 30, and is guided to a lens system (not shown) through a scanning unit (not shown) such as a galvano mirror, and corresponds to each data page on the lens surface of the lens system. Scanned to position. The scanned light bundle is deflected at an angle corresponding to the incident position on the lens system and emitted as reference light 14 from the reference light optical system 30 to the recording medium 40, and the signal light 12 of the recording medium 40 is collected. Irradiates the lighted part. Note that even if the reference light optical system 30 does not include a scanning unit and the reference light 14 is not scanned, the usefulness of the present invention is not impaired. The light flux is also referred to as a light flux as appropriate.

  The SLM 21 included in the signal light optical system 20 generates the signal light 12 by spatially modulating the parallel beam bundle of the coherent light 1 guided to the signal light optical system 20 according to the page data to be recorded. The signal light 12 is incident on a signal light lens (“condensing lens optical system”) 23 as a spatially modulated parallel light bundle. The optical axis 91 of the signal light lens 23 is inclined with respect to the surface (upper surface) of the recording medium 40. The signal light lens 23 condenses the signal light 12 incident as a parallel light flux on the recording layer 41 of the recording medium 40. The reference light optical system 30 generates the other parallel light bundle of the coherent light 1 divided into two by the polarization beam splitter as the reference light 14 and irradiates the portion of the recording layer 41 where the signal light 12 is collected. To do. The signal light 12 and the reference light 14 interfere with each other in the recording layer 41 of the recording medium 40 and are recorded as a hologram corresponding to the page data.

  At the time of reproduction, the polarization state of the polarization beam splitter is changed, and the coherent light 1 is not guided to the signal light optical system 20 side. Thereby, the signal light optical system 20 does not irradiate the signal light 12, and only the reference light optical system 30 irradiates the recording medium 40 with the reference light 14. By irradiating the reference light 14, the signal light 12 at the time of recording is reproduced as reproduction light from the recording medium 40, guided to an imaging element (not shown) provided in the signal light optical system 20, and recorded on the recording medium 40. Information is read out.

<About signal light>
In the schematic side view of FIG. 2, some light bundles S <b> 1 to S <b> 11 of the parallel light bundles of the signal light 12 modulated in each part of the SLM 21 are shown. Each of the light bundles S1 to S11 is refracted by the signal light lens 23, deflected toward the focal point (exit pupil 95 (FIG. 5)) of the signal light lens 23, and condensed, and crosses the recording layer 41. That is, each of the light beams S1 to S11 crosses the recording layer 41 through the signal light lens 23. The signal light lens 23 forms a telecentric optical system on the SLM 21 side, and the focal point of the signal light lens 23 (the focal point on the recording medium 40 side) and the exit pupil 95 coincide. The exit pupil is also simply referred to as the pupil.

Each light beam emitted from the SLM 21 enters the signal light lens 23 while spreading according to the numerical aperture NA _img (FIG. 2) on the SLM side of the signal light lens 23. The ray bundle S6 is an on-axis ray bundle, and the ray bundles S1 and S11 are the most off-axis ray bundles. The light bundle S1 is a light bundle that crosses the main plane 93 of the signal light lens 23 at the lowest side in a side view among the light bundles included in the signal light 12 incident on the signal light lens 23 as a parallel light bundle. The light beam S1 is also referred to as a lower most off-axis light beam. The light bundle S11 is a light bundle that crosses the main plane 93 of the signal light lens 23 on the uppermost side in a side view among the light bundles included in the signal light 12. The light bundle S11 is also referred to as the uppermost off-axis light bundle.

  In each of the light bundles incident on the signal light lens 23, among the light beams included in the light bundle, the light beam passing through the uppermost side of the main plane 93 (FIG. 4) of the signal light lens 23 in the side view is It is also referred to as a light beam, and the light beam that passes through the lowermost side is also referred to as a lower light beam. The upper light beam and the lower light beam form an outer edge (maximum angle of view) in a side view of each light beam incident on the signal light lens 23. In each of the light bundles S1 to S11, the light beams Q1 to Q11 are upper light beams, and the light beams V1 to V11 are lower light beams. Moreover, the chief rays of the respective light bundles S1 to S11 are the light rays T1 to T11.

  FIG. 3 is an enlarged view of the recording medium 40 portion of FIG. In FIG. 3, light rays Q <b> 1 to Q <b> 11 are collected on the upper end side (left side) of the exit pupil 95 (FIG. 5) inclined with respect to the normal line 92 of the recording medium 40. The light rays V <b> 1 to V <b> 11 are condensed on the lower end side (right side) of the exit pupil 95. Further, as shown in FIG. 3, coma aberration is generated in the light flux in the recording medium 40, which is caused by the signal light lens 23 being inclined with respect to the surface of the recording medium 40. ing.

  FIG. 4 shows the incidence of light bundles generated on the recording medium 40 from the three points of the center, right end, and left end of the SLM 21 in the schematic diagram of FIG. 2 among the signal light 12 incident on the signal light lens 23 from the SLM 21. It is a side surface schematic diagram. FIG. 5 is an enlarged view of the recording medium 40 portion of FIG. FIG. 6 is a diagram showing a reference distribution range 81 along the extending direction of the recording medium 40 in the reference area 89 in which the light beam S1, which is the lowermost off-axis light beam, passes through the recording medium 40 in FIG. is there. FIG. 7 is a schematic side view illustrating an example of the amount of penetration L of the focal point (exit pupil 95) of the signal light lens 23 into the recording medium 40. FIG. FIG. 8 is a schematic side view illustrating a state where the intrusion amount L is shallower than that in FIG. FIG. 9 is a schematic side view illustrating a state where the intrusion amount L is deeper than the state of FIG.

  In FIGS. 4 and 5, a light beam traveling toward the recording medium 40 and a light beam incident on the recording medium 40 and refracted are indicated by solid lines, and an extension line of the light beam toward the recording medium 40 is illustrated by dotted lines. This display is similarly adopted in other drawings showing the optical path of the light beam.

As shown in FIGS. 4 and 5, the points A _P , B _P , B _P ′, B _P ″, B _P ″ ″, C _P , C _P ′, C _P ″, C _P ″ '' take. That is, the point A _P is a position on the main plane 93 of the signal light lens 23 of the light ray T6 that is emitted from the center of the SLM 21 and goes toward the center of the exit pupil 95 (“pupil center”). 5-7, the intersection of the optical axis 91 of the signal light lens 23 and the surface (incident surface) of the recording medium 40 is taken as the coordinate origin, and the x axis and the z axis perpendicular to each other are obtained. Is set. Therefore, the light beam emitted from the SLM center and heading toward the pupil center always passes through the origin.

Point _BP is the position on the main plane 93 of the light ray T1 that is emitted from the right end of the SLM 21 and goes toward the center of the pupil. A point B _P ′ is an intersection of the light beam T1 and the surface (incident surface) of the recording medium 40, that is, the surface of the protective layer 42. A point B _P ″ is an intersection of the light beam T1 and the upper surface of the recording layer 41. A point B _P ″ ″ is an intersection between the light beam T 1 and the lower surface of the recording layer 41.

Point C _P is emitted from the left end of SLM21, a position on the main plane 93 of the light rays T11 towards the center of the pupil. A point C _P ′ is an intersection of the light beam T11 and the surface of the protective layer 42. A point C _P ″ is an intersection of the light beam T11 and the upper surface of the recording layer 41. A point C _P ″ ″ is an intersection between the light beam T11 and the lower surface of the recording layer 41.

As described above, in each figure showing the optical path of the light ray, the light ray (light rays T1, T6, and T11 in FIGS. 5 and 6) toward the center (pupil center) of the exit pupil 95 is displayed with a suffix _P. Has been. Also, as shown in FIG. 6, in each figure, the light rays (light rays Q1, Q6, and Q11 in FIG. 6) heading to the right end (right pupil end) of the exit pupil 95 (the right side is the + x side) are A suffix ₊ is added instead of the suffix _P , and rays (in FIG. 6, rays V1, V6, V11 in FIG. 6) toward the left end of the exit pupil 95 (the left side is the −x side) are suffixed instead of the suffix _{P. -} is displayed in tufts.

<Reduction of volume occupied by signal light in recording layer>
<Target range for the amount of signal light lens focus entering the recording medium>
Hereinafter, the reduction of the volume occupied by the signal light 12 in the recording layer 41 of the recording medium 40, that is, the reduction of the volume of the recording medium required for recording one page data will be described.

  In the hologram recording apparatus 100, the target range of the intrusion amount L1 into the recording medium 40 along the optical axis 91 of the signal light lens 23 at the focal point of the signal light lens 23 is the reference distribution range 81 as shown in FIG. Set based on. More specifically, the target range includes the recording medium 40 in a side view of each optical path in which each light beam included in the signal light 12 incident on the signal light lens 23 as a parallel light beam passes through the signal light lens 23 and crosses the recording layer 41. Each distribution range along the extending direction is a range of the intrusion amount L <b> 1 when included in the reference distribution range 81.

  The reference distribution range 81 is a range (length) along the extending direction in a side view of the reference region 89 where the lowermost off-axis light beam S1 passes through the signal light lens 23 and crosses the recording layer 41. More specifically, the reference region 89 is in the recording layer 41 when the upper light beam Q1 and the lower light beam V1 of the lower most off-axis light beam S1 pass through the signal light lens 23 and cross the recording layer 41. This is an area of the recording layer 41 sandwiched between the optical paths.

The reference area 89 is surrounded by intersection points B ₊ ″, B ₊ ″ ″, B ₋ ″, and B ₋ ″ ''. The reference distribution range 81 is a range along the extending direction of the recording medium 40 between the intersection B ₊ ″ and the intersection B ₋ ″ ″.

  The lower most off-axis light beam S <b> 1 has the largest angle with the normal line 92 of the recording medium 40 among the light beams included in the signal light 12 incident on the signal light lens 23. For this reason, the lowermost off-axis light beam S1 is the light beam having the widest distribution width along the extending direction of the recording medium 40, that is, the light beam having the largest volume required for storing optical information. The reference distribution range 81 is a length along the extending direction of the recording medium 40 in at least an area necessary for recording one page data on the recording medium 40.

  Therefore, if the signal light lens 23 and the holding unit 50 are positioned relative to each other so that the focus penetration amount L of the signal light lens 23 falls within the target range, all of the light rays included in the signal light 12 can be obtained. The distribution range of the optical path in the recording layer 41 can be kept within the reference distribution range 81. Thereby, the volume required for recording one page data in the recording medium 40 can be reduced. That is, the volume occupied by the signal light 12 in the recording layer 41 can be reduced.

<Minimum absolute value of intrusion amount>
The relationship between the point B ₊ ″ (“first intersection”) and the point C ₊ ″ ″ (“second intersection”) in FIG. 6 will be examined below. Point B ₊ ″ (“first intersection point”) is a lower ray V1 (which crosses the principal plane 93 at the lowest side in a side view among the rays included in the lower most off-axis light beam S1 (FIG. 2). The “first light beam” is a point that intersects the upper surface of the recording layer 41 through the signal light lens 23. Further, the point C ₊ ″ ″ indicates a lower ray V11 (“second ray”) that crosses the main plane 93 at the lowest side in the side view among the rays included in the uppermost off-axis light beam S11 (FIG. 2). ) Crosses the lower surface of the recording layer 41 through the signal light lens 23.

In FIG. 6, the point C ₊ ′ ″ is in the reference distribution range 81. Here, when the absolute value of the intrusion amount L is smaller than the state of FIG. 6, that is, when the signal light lens 23 is separated from the recording medium 40, the point C ₊ ′ ″ gradually becomes the reference distribution range. The point B ₊ ″, which is the right end of FIG. As shown in FIG. 8, when the point C ₊ ″ ″ protrudes from the reference distribution range 81 and is located on the right side (+ x side) of the point B ₊ ″, the signal light 12 is recorded on the recording layer 41. As a width of the area occupied by the recording medium 40 along the extending direction of the recording medium 40, at least a distribution range in which the range 82 is added to the reference distribution range 81 is necessary, so that the recording density of the signal light 12 is lowered. Therefore, in the hologram recording apparatus 100, the minimum value of the absolute value of the penetration amount L is the point B ₊ ″ (“first intersection point”) and the point C ₊ ″ ″ (“second intersection point”). Is set to the absolute value of the penetration amount L when the positions in the extending direction in the side view of the recording medium 40 coincide with each other. Since the sign of the penetration amount L becomes negative depending on how the coordinate system is taken, a minimum value is set for its absolute value.

<Maximum absolute value of intrusion amount>
Next, the maximum value of the penetration amount L (maximum absolute value) will be examined. In the state of FIG. 6, the point C ₋ ″ where the upper ray Q11 of the upper most off-axis light beam S11 intersects the front surface of the recording layer 41 is included in the reference distribution range 81 in the extending direction of the recording medium 40. It is. However, as the absolute value of the intrusion amount L increases, that is, as the signal light lens 23 approaches the recording medium 40, the point C ₋ ″ eventually protrudes from the reference distribution range 81 and recording is performed. The recording density of the signal light 12 in the medium 40 is reduced.

However, actually, the distribution range in the X direction of the passing region of the signal light 12 in the recording medium 40 exceeds the reference distribution range 81 before the point C ₋ ″ protrudes from the reference distribution range 81 due to the influence of coma aberration. As a result, a phenomenon that the recording density is reduced occurs.

For example, in FIG. 9, the upper beam Q1 of the lower most off-axis light bundle S1 is point B _- intersects the lower surface of the recording layer 41 in the '''. On the other hand, in FIG. 2, the upper beam Q2 off-axis light beam S2 of adjacent outermost off-axis light bundle S1 and the lower point D _- intersects the lower surface of the recording layer 41 in the '''. Then, the point D _- '''is the point B _-' left of the '', i.e. in the position protruding from the reference distribution range 81. This phenomenon is caused by coma aberration generated due to the optical axis 91 of the signal light lens 23 being inclined with respect to the normal line 92 of the recording medium 40. Even if the signal light lens 23 is an ideal lens, coma aberration occurs if the optical axis 91 is inclined with respect to the surface of the recording medium 40. As a result, a distribution range obtained by adding at least the reference distribution range 81 to the range 83 as the width along the extending direction of the recording medium 40 in the area occupied by the signal light 12 in the recording layer 41 is required. 12 recording density decreases.

That in the main plane 93 than the most off-axis light bundle S1 of the lower side the upper beam comprising the off-axis light beam of the upper crossing the lower surface of the recording layer 41, point B _- '''shown than the left (-x If it is not located on the side), the above-described decrease in recording density due to coma does not occur. The limit at which the recording density does not decrease is given when a coma aberration curve described below takes an extreme value with respect to the upper ray Q1 (“third ray”) of the lower most off-axis ray bundle S1. .

  Therefore, in the hologram recording apparatus 100, the maximum value of the absolute value of the penetration amount L in the target range of the penetration amount L is determined by the coma aberration curve described below by the upper ray Q1 (“the first beam” of the lower most off-axis light beam S1. It is set to the absolute value of the intrusion amount L in the case of taking an extreme value for “three rays”). The upper light beam Q1 is also a light beam included in the lower most off-axis light beam S1 among the upper light beams of each light beam of the signal light 12.

  This coma aberration curve indicates that each optical path from the signal light lens 23 to the recording medium 40 with each upper light beam of the signal light 12 forms an optical axis 91 of the signal light lens 23 and each upper light beam has the signal light lens 23. 4 is a curve (intersection position curve) showing the relationship between each intersection point intersecting the lower surface of the recording layer 41 and each position in the extending direction.

<Examination of formulas that give the minimum and maximum absolute values of the amount of penetration>
Consider the equations that give the minimum and maximum absolute values of the penetration amount L described above. In the drawing, as a method of describing the x coordinate value at each point (coordinate value in the extending direction of the recording medium 40 in a side view), a method of adding a suffix x to a symbol indicating each point is appropriately employed. For example, the x coordinate value of the point C _P '''is represented as C _P ''' _x .

<Formula that gives the minimum absolute value of the amount of penetration>
As shown in FIGS. 2 to 4, the numerical aperture on the SLM 21 side of the signal light lens 23 is NA _img , the numerical aperture on the recording medium 40 side is NA _obj , and the signal light with respect to the normal 92 (incident surface normal) of the recording medium 40. The inclination of the optical axis 91 of the lens 23 is φ. When an arbitrary light beam enters the recording medium 40, the angle formed with the optical axis 91 on the surface of the recording medium 40 is θ, the thickness of the protective layer (cover glass layer) 42 of the recording medium 40 is d _C , and the refractive index is N _C , the thickness of the recording layer 41 is d _R , and the refractive index is N _R. Further, when the focal length of the signal light lens 23 is f and the diameter (light flux width) of the pupil (exit pupil 95) is D, equations (2-1) and (2-2) are established.

θ _max is an angle formed by the light axis T1 emitted from the right end of the SLM 21 and directed toward the center of the pupil. In addition, an angle θ _min formed by the light beam T11 emitted from the left end of the SLM 21 and directed toward the center of the pupil with the optical axis 91 is given by Expression (3).

Since the incident angle of the light beam having the angle θ described above to the recording medium 40 is φ + θ, the angle formed by the light beam and the normal line 92 of the incident surface of the recording medium 40 in the protective layer 42 is ω _C. If the angle formed with the normal line 92 in the layer 41 is ω _R , Equation (4) is established from the law of refraction.

  If the system is not immersed, the medium will be air and N = 1. Therefore, Expression (5) is established.

Here, the sign of the amount of entry L of the exit pupil 95 (the focal point of the signal light lens 23) measured along the optical axis 91 into the recording medium 40 is negative when the pupil center enters the recording medium 40. To do. For example, the position at which the light beam V1 that exits from the right end of the SLM 21 toward the right end of the pupil passes through the boundary between the protective layer 42 and the recording layer 41 is B ₊ ″. Further, since the coordinate origin is taken as described above, the point A _P 'always matches the origin. As can be seen from FIG. 6, in consideration of the necessary exposure region in the x-axis direction, the region from the x-coordinate value of the point B ₊ ″ to the x-coordinate value of the point B ₋ ″ is always necessary.

That is, the x coordinate of the intersection of the arbitrary light beam emitted from other than the right end of the SLM 21 with the upper surface and the lower surface of the recording layer 41 is changed from the x coordinate value of the point B ₊ ″ to the x coordinate value of the point B ₋ ″. If it falls within the corresponding range, it is useful to increase the recording density.

Consider a case where only the amount of penetration L is changed without changing the above f, NA _img , NA _obj , φ, d _C , N _C , d _R , N _{R and the} like.

  FIG. 8 shows a state where the amount L of the pupil of the signal light lens 23 enters the recording medium 40 is shallower than that in FIG. As described above, since the sign of the intrusion amount L in the state where the pupil enters the recording medium 40 is negative, in this state, the intrusion amount L is a numerical value larger than that in the state of FIG.

At this time, the position at which the light beam emitted from the right end of the SLM 21 enters the recording medium 40 moves closer to the optical axis 91 than in the state of FIG. In other words, 'the x-coordinate value of smaller, i.e., the point B _+' point B ₊ is moved to the left in FIG.

As described above, since f, NA _img , NA _obj , φ, d _C , N _C , d _R , N _{R and the} like are not changed, the incident angle of the light beam on the recording medium 40 does not change, and the angle after refraction Will not change. Thus point B ₊ '', B ₊ '' position relative to the point B ₊ 'of' does not change, similarly, x-coordinate value of each point is changed more negative.

On the other hand, the position where the light beam emitted from the left end of the SLM 21 enters the recording medium 40 moves so as to approach the optical axis 91 as compared with FIG. That is, the x-coordinate value of the point C ₊ 'becomes more positive and becomes the right direction in the figure.

Since f, NA _img , NA _obj , φ, d _C , N _C , d _R , N _{R and the} like are not changed, the incident angle of the light beam on the recording medium 40 does not change, and the angle after refraction does not change. Thus the point C ₊ '', C ₊ 'relative position is not changed with respect to''point C _+', x coordinate value changes more positive.

As a result, there exists a state in which the x coordinate value of the point C ₊ '''is larger than the x coordinate value of the point B ₊ ''. Therefore, the necessary exposure area becomes larger and the recording density is lowered.

Here, a condition is considered in which the x coordinate values of the points B ₊ ″ and C ₊ ′ ″ coincide with each other. First, the coordinates are calculated for general light rays. FIG. 7 shows the state of a light beam emitted from an arbitrary point on the SLM 21. The suffix to the symbol X at each intersection is the same as the symbols A, B, and C at the intersection.

In FIG. 4, the intersection A _P (A _x , A _z ) between the main plane 93 and the optical axis 91 satisfies the expressions (6-1) and (6-2).

The position X _P where the principal ray of the light beam which has exited from the arbitrary point of SLM21 crosses the main plane 93, the equation (7-1), is established (7-2).

Point X _P from the pupil center P (Fig. 4) the point light towards the incident on the recording medium 40 X _P 'is given in equation (8).

  An expression representing this light ray is Expression (9).

Here, since X _P ′ _z = 0, Expressions (10) and (11) hold.

Next, the width measured along the x-axis on the recording medium 40 of the light beam that is inclined by θ from the optical axis 91 of the signal light lens 23 and is incident on both ends of the exit pupil 95 is obtained. The pupil center P (P _x , P _z ) satisfies the expressions (12-1) and (12-2).

If the right end (+ side end) of the pupil is P ₊ (P _{+ x} , P _{+ z} ), equations (13-1) and (13-2) hold.

  An expression representing the incident light beam is Expression (14).

Since X ₊ ' _z = 0 at the incident position X ₊ ' (X ₊ ' _x , X ₊ ' _z ) on the recording medium 40, equations (15) and (16) hold.

  That is, the width (one side) measured along the x-axis on the surface of the recording medium 40 is given by Expression (17).

  FIG. 10 is a schematic side view illustrating how light rays incident on the recording medium 40 are refracted at the surface of the protective layer (cover glass) 42 and at the boundary surface between the protective layer 42 and the recording layer 41. The above-mentioned refraction law is established, and the light beam of the protective layer 42 is given by the equation (18).

At the incident point X _P ″ on the recording layer 41, the equation (19) is established, and thus the equations (20) and (21) are established.

  Similarly, the light beam in the recording layer 41 is given by equation (22).

At the incident point X _P ″ ″ on the lower surface of the recording layer 41, Expression (23) is established, and thereby Expressions (24) and (25) are established.

The x-coordinate value of the point B ₊ ″ is obtained by adding θ to θ _max and the coordinate value X _P ″ x to the beam width (one side) measured along the x-axis on the surface of the recording medium 40. (26).

Point C ₊ '''x-coordinate value of, theta = .theta.min and then the coordinate values X _P' becomes plus the beam width measured along the x-axis on the surface of the recording medium 40 in the '' _x (one side), Is given by equation (27).

  Further, since Expression (28) is satisfied, Expressions (29) to (32) are satisfied, and Expression (33) is satisfied.

  On the other hand, since Expression (3) holds, Expression (34) is obtained from Expression (33).

The expression (34) gives the first condition “the x coordinate values of the point B ₊ ″ and the point C ₊ ″” match each other, that is, the minimum absolute value of the penetration amount L. It is a formula.

<Expression that gives the maximum absolute value of the amount of penetration>
Next, another factor that causes a decrease in recording density is considered. FIG. 9 shows a state in which the pupil of the signal light lens 23 is deeply inserted into the recording medium 40. At this time, when attention is focused on the light converging state after the light rays emitted from each point of the SLM 21 and proceeding toward the left end of the pupil are incident on the recording medium 40, it can be seen that so-called coma is strongly generated.

As a result, as shown in FIG. 9, a minimum necessary exposure area is provided, and a light beam Q1 (light beam giving θ = θ _max ) emitted from the right end of the SLM 21 and traveling toward the right end of the pupil is the lower surface of the recording layer 41. It passes the position B _- than _'' ', so that the light such as light ray Q2 passing through more left side (minus side) at the lower surface of the recording layer 41 is present. In this case, the exposure area is expanded by the range 83, and the recording density is lowered.

FIG. 11 is a coma aberration curve calculated using a non-aberration lens (ideal lens). Three types of curves are drawn by changing the amount L of the pupil entering the recording medium. The horizontal axis is the angle θ from the lens optical axis and is normalized with θ _max being 1.

In FIG. 9, the coma aberration curve G1 is a case where the penetration amount L is made large (shallow), and takes a minimum value when θ = 1, that is, θ _max . This intersection of the light rays passing through the leftmost and the lower surface of the recording layer 41 is the point B _- is meant to be _'' 'represents that there is no reduction in recording density due to coma. The coma aberration curve G3 has a minimum value when θ is approximately 0.65 when the penetration amount L is small (deeper).

This means that the intersection of the lower surface of the recording layer 41 and the light beam that passes through the leftmost side is not B ₋ ″ ″, which means that the recording density is reduced due to coma aberration. Of course, when the penetration amount L takes another value, or when the focal length f or the inclination φ of the optical axis 91 of the signal light lens 23 is changed, the value of θ that takes the minimum value changes variously.

  The coma aberration curve G2 is when the amount of penetration L is medium (between the coma aberration curves G1 and G3), and the slope of the curve is almost 0 at θ = 1, that is, a minimum value (in this case, the minimum value). It turns out that it becomes the last place.

Here, the pupil penetration amount L giving the state of the coma aberration curve G2 is obtained. For this purpose, a condition may be obtained in which the position X ₋ ″ ″ _x where the light beam exiting from the right end point on the SLM 21 and traveling toward the left end of the pupil passes through the lower surface of the recording layer has an inclination of 0 with respect to θ. That is, a condition that the inclination becomes 0 at θ = θ _max may be obtained.

That is, when X ₋ ′ ″ _x is a function of θ, the expression (35) may be satisfied. On the other hand, the differentiated X ₋ ′ ″ _x is given by Expression (36).

The derivative of θ of the first term (−d _C · tan ω _C ) is expressed by Expression (37).

  Here, since Expression (38) holds, Expression (37) is converted to Expression (39).

Similarly, the derivative of θ of the second term (−d _R · tan ω _R ) is given by the equation (40).

  Further, the differentiation of the third term is given by the equation (41).

An expression obtained by differentiating X ₋ ′ ″ _x by θ by Expressions (39) to (41) is given by Expression (42).

Equation (43) may be satisfied when θ = θ _max . Thereby, Formula (44) is calculated | required and Formula (45) is calculated | required from Formula (44).

The expression (45) indicates that the second condition “the position X ₋ ″ ″ _x where the light ray that has exited from the right end point on the SLM 21 and travels toward the left end of the pupil passes the lower surface of the recording layer 41 has an inclination of 0 with respect to θ. Is an expression that gives the maximum absolute value of the penetration amount L.

<Example of Signal Light Lens 23>
FIGS. 12-23 is a figure which shows the form of Example 1-Example 12 of the signal light lens 23, respectively.

  30, 32, 34, 36, 38, 40, 42, 44, 46, 48, 50, 52 are tabular representations of the radius of curvature, surface spacing, and refractive index of the signal light lenses of Examples 1 to 12. FIG.

  31, 33, 35, 37, 39, 41, 43, 45, 47, 49, 51, and 53 are diagrams showing the aspheric coefficients of the signal light lenses of Examples 1 to 12 in a tabular form, respectively. . 30 to 53, the wavelength of 405 nm, which is currently widely used for optical devices, is adopted as the wavelength.

  In the first embodiment, the surface to which the aspheric coefficient is given is an aspheric surface in which the sag amount z from the vertex of the surface is expressed by Expression (46). The same applies to other embodiments.

  In Examples 4 to 6, the achromatic structure is used at a wavelength of 650 nm in addition to a wavelength of 405 nm. For this reason, in FIGS. 36, 38, and 40, the refractive index for a wavelength of 650 nm is also shown.

FIG. 54 is a table showing the focal length f of the signal light lenses, the numerical aperture NA _obj on the recording medium 40 side, and the numerical aperture NA _img on the SLM side in the table format in Examples 1 to 12 of FIGS. The numerical aperture shown in FIG. 54 is the maximum value, the numerical aperture NA _obj on the recording medium side is changed at 0.05 pitch, and the numerical aperture NA _img on the SLM side is changed at 0.01 pitch.

<Approximate expression that gives the minimum and maximum absolute values of the amount of penetration>
FIG. 24 shows the upper limit value (minimum value of the absolute value) of the penetration amount L, that is, the points B + ″ and C + ′ ″, which are the first condition described above, in Examples 1 to 12 of the signal light lens 23. It is the figure which calculated and displayed the conditions where x coordinate value corresponds.

FIG. 25 is a graph showing a lower limit value (maximum absolute value) of the penetration amount L for Examples 1 to 12, that is, exiting from the rightmost point on the SLM 21 which is the second condition described above, to the left end of the pupil. FIG. 6 is a diagram showing a calculation and display of a condition that a position X ₋ ′ ″ _x where a traveling light beam passes through the lower surface of the recording layer 41 has an inclination of 0 with respect to θ.

More specifically, in FIG. 24, for the first to twelfth embodiments, NA _obj , NA _img , φ, d _C , N _C , d _R , N _R is an index of the amount L of penetration of the upper limit value. The horizontal axis and the vertical axis are respectively displayed so that the value L / f obtained by ray tracing can be compared with the result obtained by the approximate expression (47). Similarly, in FIG. 25, the index value L of the lower limit entry amount L when NA _obj , NA _img , φ, d _C , N _C , d _R , and N _R are changed in Examples 1 to 12. The horizontal axis and the vertical axis are displayed so that the result of / f obtained by ray tracing can be compared with the result of the approximate expression (48).

  Approximation formulas (47) and (48) show the calculation results of the index value L / f by ray tracing shown in FIGS. 24 and 25, and the parameters shown in approximation formulas (47) and (48). Are approximated as linear functions for.

  In FIG. 24, that is, the first condition, the correlation coefficient between the calculation result by ray tracing and the calculation result by the approximate expression (47) is 0.860. 25, that is, the second condition, the correlation coefficient between the calculation result by ray tracing and the calculation result by the approximate expression (48) is 0.524. The second condition is a condition determined by coma aberration that is more easily affected by the correction state of the spherical aberration of the signal light lens 23. For this reason, the correlation of the calculation result by ray tracing and the calculation result by the approximate expression is higher under the first condition.

FIG. 26 is a diagram illustrating a coma aberration curve obtained for the signal light lens 23 of Example 3. FIG. The horizontal axis, the signal light angle, which is normalized with respect to the optical axis 91 is shown on the vertical axis, the coordinate value C _- ''_'x, i.e., the lower surface of the recording layer 41 of the light beam towards the pupil left The x coordinate of the intersection is shown. As the conditions of the signal light lens 23 of Example 3, NA _obj : 0.65, NA _img : 0.05, φ: 30 degrees, N _C : 1.5, N _R : 1.5, d _C : 0.5 mm, d _R : 1.5 mm are adopted. Has been. The coma aberration curves G4 to G7 shown in FIG. 26 are calculated for four types of penetration amounts L of +0.2, 0, −0.2, and −0.4, respectively.

  Here, when the value of the above condition is applied, Expression (49) and Expression (50) are obtained. Therefore, the penetration amount L according to the theoretical formula (45) is obtained as the formula (51).

When the smallest penetration amount L allowed to minimize the exposure area is obtained for an actual lens, the result is -0.090 mm. According to FIG. 26, it can be seen that θ _max is minimum at L: 0.0, but in reality, there is still room for the amount of penetration L, that is, there is room for the pupil to further enter the recording medium 40. Further, at L: −0.2, the minimum value is taken in the vicinity of θ = 0.9θ _max , and the minimum exposure area is determined other than θ _max .

FIG. 28 is a diagram illustrating a result of obtaining the same coma aberration curve as that of FIG. 26 for the signal light lens 23 of Example 12. The horizontal and vertical axes are set in the same manner as in FIG. As the conditions of the signal light lens 23 of Example 12, NA _obj : 0.65, NA _img : 0.05, φ: 30 degrees, N _C : 1.5, N _R : 1.5, d _C : 0.5 mm, d _R : 1.5 mm are adopted. Has been. The coma aberration curves G8 to G11 are respectively calculated for four types of penetration amounts L of -0.1, -0.3, -0.5, and -0.7. Since the numerical values of the conditions are the same as the conditions of the lens of Example 3, the same result is obtained as Expression (52) when applied to the theoretical Expression (45).

As in the case of FIG. 26, when the smallest penetration amount L allowed to minimize the exposure area is obtained for an actual lens, the result is −0.624 mm. According to FIG. 28, θ _max is minimum at L: −0.5, but there is still room for more pupils to enter the recording medium. L: At -0.7, the minimum value is taken around θ = 0.8θ _max , and it can be seen that the minimum exposure area is determined by other than θ _max .

  FIG. 27 is a diagram illustrating the spherical aberration of the signal light lens 23 according to the third embodiment, and FIG. 29 is a diagram illustrating the spherical aberration of the signal light lens 23 according to the twelfth embodiment. As shown in FIGS. 27 and 29, the spherical aberration of the signal light lens 23 of Example 3 is sharply over in marginal, and the spherical aberration of the signal light lens 23 of Example 12 is marginal. It suddenly becomes under. As described above, when the spherical aberration fluctuates rapidly, the correction state of the spherical aberration also affects the coma aberration, and the influence appears as shapes at both ends of each curve in FIGS. . Due to the influence, the first condition with respect to the pupil penetration amount L has a higher correlation between the calculation results of the ray tracing and the approximate expression than the second condition (due to coma aberration). It is thought that it has become.

  As described above, when the approximate expressions (47) and (48) are used, the hologram recording apparatus 100 enters the recording medium 40 along the optical axis 91 of the focal point (exit pupil 95) of the signal light lens 23. The target range of the amount L is set to a range of the intrusion amount L that satisfies the inequality (53).

  If the inequality (53) is used, the range of the intrusion amount L that can reduce the volume occupied by the signal light 12 in the recording layer 41 can be easily specified. Therefore, the relative positioning of the signal light lens 23 and the holding unit 50 can be further improved. It becomes easy.

  Further, when the first condition having a high correlation between the calculation results of the penetration amount L based on the ray tracing and the approximate expression is used, the maximum value of the absolute value of the penetration amount L in the target range is, for example, lower side A half value of the absolute value of the intrusion amount L when the coma aberration curve takes an extreme value with respect to the upper side light beam Q1 included in the most off-axis light beam S1 may be adopted. For example, when using the inequality (53), the target range of the penetration amount L is set to a range on the side where the absolute value of the penetration amount L is smaller than the center in the range of the penetration amount L that satisfies the inequality (53). That's fine. As a result, the required exposure area can be reduced more reliably and the recording density can be increased.

  In any of the hologram recording apparatus 100 and the optical module 300 according to the present embodiment as described above, the intrusion amount L1 of the focal point of the signal light lens 23 into the recording medium 40 along the optical axis 91 of the signal light lens 23 is obtained. The target range is set based on the reference distribution range 81. The target range is along the extending direction of the recording medium 40 in a side view of each optical path where each light beam included in the signal light 12 incident on the signal light lens 23 as a parallel light beam passes through the signal light lens 23 and crosses the recording layer 41. Each distribution range is a range of the intrusion amount L1 when included in the reference distribution range 81. The reference distribution range 81 is a range (length) along the extending direction of the recording medium 40 in a side view of the reference region 89 in which the lowermost off-axis light beam S1 passes through the signal light lens 23 and crosses the recording layer 41. ).

  The lower most off-axis light beam S <b> 1 has the largest angle with the normal line 92 of the recording medium 40 among the light beams included in the signal light 12 incident on the signal light lens 23. For this reason, the lowermost off-axis light beam S1 is the light beam having the widest distribution width along the extending direction of the recording medium 40, that is, the light beam having the largest volume required for storing optical information. The reference distribution range 81 is a length along the extending direction in a side view of the recording medium 40 in an area necessary for recording at least one page data on the recording medium 40. Therefore, if the signal light lens 23 and the holding portion 50 are positioned relative to each other so that the focal amount L of the signal light lens 23 falls within the target range, all of the light rays included in the signal light 12 can be obtained. The distribution range of the optical path in the recording layer 41 can be kept within the reference distribution range 81. Thereby, the volume required for recording one page data in the recording medium 40 can be reduced. That is, the volume occupied by the signal light 12 in the recording layer 41 can be reduced.

  Although the invention has been shown and described in detail, the above description is illustrative in all aspects and not restrictive. Therefore, embodiments of the present invention can be modified or omitted as appropriate within the scope of the invention.

1 Coherent Light 10 Light Source 100 Hologram Recording Device 12 Signal Light 20 Signal Light Optical System 21 SLM
23 Signal light lens (Condenser lens system)
DESCRIPTION OF SYMBOLS 300 Optical module 40 Recording medium 41 Recording layer 42 Protective layer 50 Holding | maintenance part 81 Reference | standard distribution range 89 Reference | standard area 91 Optical axis 92 Normal 93 Main plane 95 Exit pupil S1 Ray bundle (lower most off-axis ray bundle)
S11 ray bundle (uppermost off-axis ray bundle)
B ₊ '' point (first intersection)
C ₊ '''point (second intersection point)
V1 ray (first ray)
V11 ray (second ray)

Claims (7)

A holding unit for holding a recording medium including a recording layer capable of recording a hologram;
A light source that emits coherent light;
A condensing lens system having an optical axis inclined with respect to the surface of the recording medium, generating signal light from the coherent light as a spatially modulated parallel light beam, and generating the parallel light beam as the condensing lens system; And a signal light optical system for condensing on the recording layer of the recording medium,
A reference light optical system that generates reference light from the coherent light and irradiates a portion of the recording layer on which the signal light is collected; and
With
The condenser lens system and the holding unit are
The focal points of the condenser lens system are positioned relative to each other so that the amount of penetration into the recording medium along the optical axis of the condenser lens system falls within a target range;
A side view is defined by a direction view orthogonal to both the optical axis of the condenser lens system and the normal of the surface at the intersection of the optical axis and the surface of the recording medium;
The normal direction is defined as the vertical direction, the recording medium side is defined as the bottom, and the condenser lens system side is defined as the top.
When defining the lowermost off-axis light beam by the light beam crossing the principal plane of the condenser lens system at the lowermost side in a side view among the light beams included in the parallel light beam,
The target range of the intrusion amount is
Each light beam included in each light beam in the parallel light beam passes through the condenser lens system and crosses the recording layer. The hologram recording apparatus, which is the range of the penetration amount when the most off-axis light beam is included in a reference distribution range along the extending direction of a reference region that passes through the condenser lens system and crosses the recording layer. The hologram recording apparatus according to claim 1,
When the uppermost off-axis ray bundle is defined by the ray bundle that crosses the principal plane of the condenser lens system at the uppermost side in a side view among the ray bundles included in the parallel ray bundle,
The minimum absolute value of the penetration amount in the target range is:
The first light ray that crosses the main plane at the lowest side in a side view among the light rays included in the lowermost off-axis light beam intersects the upper surface of the recording layer of the recording medium through the condenser lens system. Of the light beams included in the uppermost off-axis light beam, the second light beam crossing the main plane at the lowest side in a side view intersects the lower surface of the recording layer through the condenser lens system. A hologram recording device, which is the absolute value of the amount of penetration when the positions in the extending direction of the second intersection coincide with each other. The hologram recording apparatus according to claim 1 or 2, wherein
The maximum absolute value of the penetration amount in the target range is
Each optical path each of the upper beam across the main plane uppermost in a side view in each of the light beams the parallel light beam comprises reaches the Symbol recording medium from the condenser lens system, the light of the condenser lens system The coma aberration curve showing the relationship between each angle formed by the axis and each position in the extending direction of each intersection where each upper light beam intersects the lower surface of the recording layer through the condenser lens system, A hologram recording apparatus, which is an absolute value of the amount of penetration when taking an extreme value with respect to a third light ray included in the lowermost off-axis light beam among light rays. The hologram recording apparatus according to claim 3, wherein
The maximum absolute value of the penetration amount in the target range is when the coma curve has an extreme value with respect to the third light ray included in the lower most off-axis light bundle among the upper light rays. Hologram recording apparatus which is a half value of the absolute value of the penetration amount. The hologram recording apparatus according to claim 1,
The recording medium further comprises a protective layer for protecting the recording layer on the upper surface of the recording layer,
The target range of the intrusion amount is
A hologram recording apparatus that is in the range of the penetration amount that satisfies the inequality (I).

The hologram recording device according to claim 5,
The target range of the intrusion amount is
A hologram recording apparatus, wherein the absolute value of the intrusion amount is smaller than the center in the intrusion amount range satisfying the inequality (I). A holding unit for holding a recording medium including a recording layer capable of recording a hologram;
A condensing lens system whose optical axis is inclined with respect to the surface of the recording medium;
With
The condensing lens system condenses signal light, which is generated in advance from coherent light, and incident as a spatially modulated parallel light bundle, on the recording layer of the recording medium,
The condenser lens system and the holding unit are
The focal points of the condenser lens system are positioned relative to each other so that the amount of penetration into the recording medium along the optical axis of the condenser lens system falls within a target range;
A side view is defined by a direction view orthogonal to both the optical axis of the condenser lens system and the normal of the surface at the intersection of the optical axis and the surface of the recording medium;
The normal direction is defined as the vertical direction, the recording medium side is defined as the bottom, and the condenser lens system side is defined as the top.
When defining the lowermost off-axis light beam by the light beam crossing the principal plane of the condenser lens system at the lowermost side in a side view among the light beams included in the parallel light beam,
The target range of the intrusion amount is
Each light beam included in each light beam in the parallel light beam passes through the condenser lens system and crosses the recording layer. Optical module for hologram recording, which is the range of the amount of penetration when the most off-axis light bundle is included in the reference distribution range along the extending direction of the reference region that crosses the recording layer through the condenser lens system .

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