Hologram manufacturing apparatus and hologram manufacturing method

Abstract

To provide a piece of hologram manufacturing equipment capable of improving accuracy of a copied hologram.SOLUTION: Hologram manufacturing equipment includes: a master hologram 41 formed with a diffraction grating; a copy hologram 42 placed close to the master hologram 41; a light source 1 that emits laser beam L1 for exposing the copy hologram 42; a light source 2 that emits laser beam L2 to the copy hologram 42 at an angle of incidence different from that of the laser beam L1; and a light receiving sensor 6 that measures a laser beam L3 that is the laser beam L2 reflected by the copy hologram 42. The exposure of the copy hologram 42 is terminated depending on a measurement result by the light-receiving sensor 6.SELECTED DRAWING: Figure 2

Description

Technical Field

[0001] The present disclosure relates to a hologram manufacturing apparatus and a hologram manufacturing method.

Background Art

[0002] Conventionally, an apparatus for manufacturing a replicated hologram using a master hologram has been known. In Patent Document 1, diffracted light is generated by irradiating a master hologram with laser light, and a hologram photosensitive material (photopolymer) of the replicated hologram is exposed by this diffracted light. Thereby, a replicated hologram can be manufactured.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] By the way, generally, the manufacture of a replicated hologram has been performed by controlling the exposure time of the photopolymer, that is, by controlling the amount of change in the refractive index of the photopolymer based on the light irradiation time on the photopolymer. The amount of change in the refractive index of the photopolymer is mainly determined by the integrated exposure amount, which is the product of the light intensity of the light source and the irradiation time, but is also affected by factors such as temperature and lot-to-lot variations in the sensitivity of the refractive index change of the photopolymer itself.

[0005] In addition, in order to manufacture a replicated hologram, first-order diffracted light for the replicated hologram is required. However, even if the amount of change in the refractive index of the photopolymer is as designed, if the thickness of the photopolymer is different from the designed value, an error will also occur in the first-order diffracted light. In particular, since the photopolymer is a transparent material, when the photopolymer is sandwiched between transparent substrates, it is very difficult to measure its thickness.

[0006] Based on the above, if the exposure time of the photopolymer is controlled solely by the light irradiation time of the photopolymer, the photopolymer itself of the replicated hologram and the first-order diffracted light directed at the replicated hologram may differ from the design value, potentially leading to a decrease in the accuracy of the replicated hologram.

[0007] Therefore, the purpose of this disclosure is to provide a hologram manufacturing apparatus and manufacturing method that improve the accuracy of the replicated hologram. [Means for solving the problem]

[0008] To achieve the above objective, a hologram manufacturing apparatus according to one embodiment of the present disclosure comprises a master hologram on which a diffraction grating is formed, a replica hologram arranged in close proximity to the master hologram, a first light source that emits a first laser beam for exposing the replica hologram, a second light source that emits a second laser beam to the replica hologram at a different incident angle from the first laser beam, and a sensor that measures a third laser beam reflected by the replica hologram from the second laser beam, and the exposure of the replica hologram is terminated based on the measurement result of the sensor. [Effects of the Invention]

[0009] According to this disclosure, the accuracy of the replicated hologram can be improved. [Brief explanation of the drawing]

[0010] [Figure 1] A side view of a hologram manufacturing apparatus according to the first embodiment. [Figure 2] A top view of a hologram manufacturing apparatus according to the first embodiment. [Figure 3] A diagram showing the state of a hologram recording material during exposure according to the first embodiment. [Figure 4] A perspective view showing the angle of incidence of laser light L2 onto the replicated hologram according to the first embodiment. [Figure 5] A cross-sectional view showing the state of a replicated hologram during exposure according to the first embodiment. [Figure 6] A plan view showing the state of a replicated hologram during exposure according to the first embodiment. [Figure 7] A side view of a hologram manufacturing apparatus according to the second embodiment. [Figure 8] A top view of a hologram manufacturing apparatus according to the second embodiment. [Figure 9] A perspective view of a hologram manufacturing apparatus according to the second embodiment. [Modes for carrying out the invention]

[0011] Embodiments of the present invention will now be described in detail with reference to the drawings. The following description of preferred embodiments is essentially illustrative and is not intended to limit the present invention, its applications, or its uses. In the following description, the same parts are denoted by the same reference numerals, and detailed descriptions are omitted where appropriate.

[0012] (First Embodiment) (Overall configuration of the hologram manufacturing equipment) Figures 1 and 2 are schematic diagrams of a hologram manufacturing apparatus according to the first embodiment. Specifically, Figure 1 is a side view of the hologram manufacturing apparatus according to the first embodiment, and Figure 2 is a top view of the hologram manufacturing apparatus according to the first embodiment. In Figure 1, the width direction of the hologram recording body 4 is defined as the X and Z directions, and the thickness direction (vertical direction) of the hologram recording body 4 is defined as the Y direction.

[0013] As shown in Figure 1, the hologram manufacturing apparatus according to the first embodiment comprises light sources 1 and 2, a hologram recording body 4, and a light receiving sensor 6.

[0014] The light source 1 (the first light source) is a light source that irradiates laser light, and irradiates laser light L1 for exposing a replication hologram 42 described later. The laser light L1 is laser light having a long coherence length (coherence distance), high spatial coherence, and a parallel light with a uniform intensity distribution and small wavefront aberration. The laser light L1 irradiates a region including at least the effective regions of photopolymers 412 and 422 described later. Further, it is desirable that the coherence distance of the laser light L1 is longer than the combined length of a master hologram 41 and a replication hologram 42 described later.

[0015] Specifically, the light source 1 includes a laser light source 11, an optical isolator 12, a λ / 2 wavelength plate 13, a condenser lens 14, a pinhole 15, and a collimating lens 16.

[0016] The laser light source 11 is a light source that irradiates laser light L1. The laser light source 11 emits laser light L1 that has high coherence, is parallel light, and is linearly polarized monochromatic light. Note that the laser light source 11 may be composed of an LED (Light Emitting Diode) or the like.

[0017] The optical isolator 12 suppresses the return light from the λ / 2 wavelength plate 13 side to the laser light source 11.

[0018] The λ / 2 wavelength plate 13 controls the polarization direction of the incident laser light L1. Thereby, the laser light L1 is controlled to an optimal polarization direction for exposure.

[0019] The condenser lens 14 condenses the laser light L1 incident through the λ / 2 wavelength plate 13 to the diffraction limit. <0​​​​​​​The collimating lens 16 is positioned so that its focal point is the pinhole 15, and the transmitted light (laser light L1) is made into parallel light.

[0022] Light source 2 (second light source) is a light source that emits laser light, and emits laser light L2 for controlling the exposure of the replicated hologram 42. Laser light L2, like laser light L1, is a laser light with a long coherence distance, sufficiently high spatial coherence, and a uniform intensity distribution of parallel light with small wavefront aberration. Laser light L2 illuminates approximately the center of the effective area of ​​the master hologram 41 and the replicated hologram 42.

[0023] Specifically, the light source 2 comprises a laser light source 21 and a lens 22.

[0024] The laser light source 21 is a light source that emits laser light L2. The laser light source 21 emits laser light L2, which is near-infrared light that does not have sensitivity to the photopolymer 422. The laser light source 21 may be composed of an LED or the like.

[0025] Lens 22 makes the incident laser light L2 into parallel light.

[0026] The light-receiving sensor 6 is a light-receiving sensor having a two-dimensional pixel structure. For example, the light-receiving sensor 6 is a CCD camera or a CMOS camera. As will be described in more detail later, in Figure 2, the laser light L2 is irradiated from the bottom of the drawing toward the top of the drawing. The laser light L2 is then reflected by the hologram recording body 4 (master hologram 41). This reflected laser light L2 is focused by the lens 61 and detected by the light-receiving sensor 6.

[0027] (Composition of a holographic recording) Figure 3(a) is a cross-sectional view showing the configuration of a hologram recording body according to the first embodiment.

[0028] As shown in Figures 1 and 3(a), the hologram recording body 4 is composed of a master hologram 41 and a duplicate hologram 42. In this embodiment, by irradiating the master hologram 41 with laser light L1, the same diffraction grating as that formed on the master hologram 41 is formed on the duplicate hologram 42.

[0029] As shown in Figures 1 and 3(a), the master hologram 41 comprises a transparent substrate 411, a photopolymer 412, and a protective film 413. The transparent substrate 411, the photopolymer 412, and the protective film 413 are laminated together.

[0030] The transparent substrate 411 is a flat plate with high transmittance, and materials such as quartz or optical glass are used. Furthermore, an anti-reflective coating is formed on the upper surface of the transparent substrate 411.

[0031] The photopolymer 412 is formed from an optical material whose refractive index changes when exposed to visible light. The amount of refractive index change of the photopolymer 412 is determined by the amount of energy received by the photopolymer 412, i.e., the product of light intensity and time. Furthermore, the refractive index change of the photopolymer 412 can be stopped by irradiation with ultraviolet light. The photopolymer 412 has a refractive index distribution (diffraction grating) formed in advance using visible light of varying intensity, and is then treated so that the refractive index distribution does not change when irradiated with ultraviolet light. As a result, a predetermined interference fringe is formed on the photopolymer 412. The refractive index of the photopolymer 412 is approximately 1.5 to 1.6, and the amount of refractive index change due to visible light is about 0.01 to 0.1. The thickness t of the photopolymer 412 is formed between 1 μm and 100 μm. The thicker the thickness t of the photopolymer 412, the higher the diffraction efficiency of the photopolymer 412 can be. In this case, the characteristics of the first-order diffracted light also become sensitive to the angle of incidence on the photopolymer 412, and the first-order diffracted light is greatly attenuated with even small changes in the angle of incidence.

[0032] The protective film 413 is a thin, transparent protective layer for protecting the photopolymer 412, and is formed from a scratch-resistant material such as thin, highly transparent glass. An anti-reflective coating is also formed on the upper surface of the protective film 413. The thickness of the protective film 413 is at least thinner than that of the transparent substrate 411. It is desirable that the average refractive index of the transparent substrate 411 and the photopolymer 412 be close to that of the protective film 413.

[0033] The replicated hologram 42 comprises a transparent substrate 421, a photopolymer 422, and a protective film 423. The transparent substrate 421, the photopolymer 422, and the protective film 423 are laminated together.

[0034] The transparent substrate 421, photopolymer 422, and protective film 423 have the same configuration as the transparent substrate 411, photopolymer 412, and protective film 413, respectively. However, the photopolymer 422 has the same thickness t as the photopolymer 412, and in the initial state, no refractive index distribution is formed, nor is it irradiated with ultraviolet light.

[0035] As shown in Figure 1, the duplicated hologram 42 is rotated 180° relative to the master hologram 41 and positioned close to it so that they are parallel to each other.

[0036] As described above, the photopolymer 412 has a refractive index distribution (diffraction grating) formed on it beforehand. The refractive index distribution of the photopolymer 412 is distributed within the XY cross-section and uniform in the Z-axis direction. That is, the refractive index distribution of the photopolymer 412 is the same in the XY cross-section at any Z-axis position. The refractive index distribution in the photopolymer 412 has periodically formed regions of high and low refractive index. The photopolymer 412 has a Bragg diffraction grating formed on it, which is a diffraction grating with a so-called thick refractive index distribution. This diffraction grating is formed with a pitch d and at an angle φ with respect to the Y axis in the XY plane. Therefore, in the X-axis direction, the pitch of the diffraction grating is d / cos(φ).

[0037] Figure 3(b) is a graph showing the refractive indices of cross-sections AA and BB of the photopolymer 412 shown in Figure 3(a). As shown in Figure 3(b), the refractive indices of cross-sections AA and BB change sinusoidally. The average refractive index is n, and the amount of refractive index change is Δn. The difference in refractive index change between cross-sections AA and BB is simply that the waveform is shifted laterally. When highly coherent laser light is incident on a master hologram 41 having such a periodic refractive index distribution, optical diffraction called Bragg diffraction occurs. A characteristic of Bragg diffraction is that it produces strong diffracted light in a specific direction, i.e., first-order diffracted light. Also, the emitted light from Bragg diffraction consists mostly of zero-order diffraction and first-order light, with almost no higher-order diffracted light being produced.

[0038] The Bragg diffraction condition for photopolymer 412 is 2 × n × d × sin(θ) = λ, where n is the average refractive index of photopolymer 412, d is the pitch of the diffraction grating, θ is the angle of incidence to the diffraction grating, and λ is the wavelength of the incident light. Regarding the direction of the light ray, within photopolymer 412, refraction causes an angle change based on Snell's law. That is, if α is the direction relative to the Y-axis in air, then since the refractive index of photopolymer 412 is n, the direction β within photopolymer 412 is sin(α) = n × sin(β).

[0039] When the Bragg diffraction condition is met in the photopolymer 412, the phases of the light reflected by each diffraction grating are aligned, resulting in strong diffracted light in the -θ direction relative to the diffraction grating. That is, when a laser beam L1 making an angle of φ+θ with respect to the Y axis is incident on the photopolymer 412, a ray L11 making an angle of φ-θ with respect to the Y axis is emitted as first-order diffracted light, and a ray L12 making an angle of φ+θ with respect to the Y axis is emitted (transmitted) as zero-order diffracted light (light that does not diffract). The angle between rays L11 and L12 is 2θ.

[0040] (Operation of the hologram manufacturing equipment) Next, we will explain the operation of the hologram manufacturing apparatus when creating the duplicate hologram 42.

[0041] As shown in Figure 1, the parallel laser beam L1 is reflected by the half-mirror 3 and incident on the master hologram 41. The laser beam L1 incident on the master hologram 41 is refracted by the transparent substrate 411 according to Snell's law, changing the direction of the light rays. At this time, since the transparent substrate 411, the photopolymer 412, and the protective film 413 have almost the same refractive index, the direction of the light rays within the transparent substrate 411, the photopolymer 412, and the protective film 413 are almost the same.

[0042] As shown in Figure 3(a), the diffraction grating formed by the refractive index distribution on the photopolymer 412 is formed at an angle of φ with respect to the Y axis. Therefore, the laser beam L1 is incident on the photopolymer 412 at an angle of φ+θ with respect to the Y axis. That is, the laser beam L1 is incident on the diffraction grating at an angle of θ. When the laser beam L1 is incident on the diffraction grating at an angle of θ, the Bragg diffraction condition in the photopolymer 412 is satisfied, and a first-order diffracted light (ray L11) is generated in the -θ direction relative to the diffraction grating, and a zero-order diffracted light (ray L12) is generated in the θ direction. In other words, two rays, L11 and L12, are emitted from the master hologram 41.

[0043] Light emitted from the master hologram 41 is refraction again according to Snell's law when it enters the replica hologram 42. Since the refractive index of the replica hologram 42 is the same as that of the master hologram 41, the ray direction within the replica hologram 42 is the same as the ray direction within the master hologram 41. That is, ray L11 enters the replica hologram 42 at an angle of φ+θ with respect to the Y axis, and ray L12 enters the replica hologram 42 at an angle of φ-θ with respect to the Y axis. The angle between ray L11 and ray L12 is 2θ, and the midpoint direction between ray L11 and ray L12 is at an angle of φ with respect to the Y axis. Rays L11 and L12 are highly coherent and are parallel rays with an angle of 2θ between them, so interference fringes, which represent the strength of the light, are produced. The condition for constructive interference between interference fringes is 2 × n × d × sinθ = λ, so the fringe pitch is pitch d in the XY plane at an angle of φ + 90 degrees to the Y axis. In the direction of φ to the Y axis, the optical path lengths of rays L11 and L12 are the same, so the light intensity distribution is uniform. Similarly, the light intensity distribution does not change in the Z axis direction. Therefore, the interference fringes (diffraction grating) in the photopolymer 422 of the replicated hologram 42, i.e., the distribution of light intensity, is the same as the shape of the diffraction grating g1 due to the refractive index distribution of the photopolymer 412 of the master hologram 41. In the photopolymer 422, the refractive index changes with light intensity, so by stopping the irradiation of light to the replicated hologram 42 when the ratio of 0th-order diffracted light to 1st-order diffracted light emitted from the replicated hologram 42 becomes the same ratio as that of the master hologram 41, a diffraction grating g1 with the same refractive index distribution as the master hologram 41 can be formed in the replicated hologram 42. In this case, if there is an error in the exposure time, the direction of the first-order diffracted light relative to the zero-order diffracted light in the replicated hologram 42 does not change, but an error occurs in the ratio of the zero-order diffracted light to the first-order diffracted light. Here, in the replication of the replicated hologram 42, the orientations of the zero-order diffracted light and the first-order diffracted light from the master hologram 41 do not change, that is, the pitch of the diffraction grating formed in the replicated hologram 42 does not change, so in the replicated hologram 42, the orientation of the first-order diffracted light does not change even if there is an error in the exposure time. What is affected by the error in exposure time is the magnitude of the refractive index difference of the diffraction grating formed in the photopolymer 422 of the replicated hologram 42.As the difference in refractive index increases, the first-order diffracted light becomes larger relative to the zero-order diffracted light, and conversely, as the difference in refractive index decreases, the first-order diffracted light becomes smaller.

[0044] Incidentally, the amount of change in refractive index of the photopolymer 422 due to exposure time is determined by temperature and the photosensitivity of each manufacturing lot. Also, the ratio of first-order diffracted light to zero-order diffracted light changes depending on the thickness of the photopolymer 422. That is, the thicker the photopolymer 422, the more light passes through the lattice of the refractive index distribution, resulting in more first-order diffracted light. For this reason, if the exposure time is determined simply by time, the ratio of zero-order diffracted light to first-order diffracted light from the photopolymer 422 will differ from the design value. Therefore, it is conceivable to measure the first-order diffracted light of the replicated hologram 42, but since the master hologram 41 and the replicated hologram 42 are placed on top of each other, it is difficult to measure the first-order diffracted light of the replicated hologram 42 during exposure.

[0045] Figure 4 is a perspective view showing the incident angle of laser light L2 onto the replica hologram according to the first embodiment. Although not shown in the illustration, the laser light L1 and L2 are incident on the master hologram 41 and the replica hologram 42 at different angles in a plan view (when viewing the master hologram 41 and the replica hologram from above).

[0046] Figure 5 is a cross-sectional view showing the state of the replica hologram during exposure according to the first embodiment. As shown in Figure 5, when the laser beam L2 is irradiated onto the refractive index distribution (diffraction grating) of the replica hologram 42 in such a way that the Bragg diffraction conditions are met, a portion of the laser beam L2, which is laser beam L3, is generated towards the upper left side of the drawing. The laser beam L3 is generated symmetrically with respect to the direction normal to the refractive index distribution of the replica hologram 42 (Y' direction).

[0047] Figure 6 is a plan view showing the state of the replica hologram during exposure according to the first embodiment. As shown in Figure 6, when the incident angle of the laser beam L2 with respect to the refractive index distribution is θ', the laser beam L2 is highly coherent, so when 2 × n × d × sinθ' = λ holds, the light reflected from the refractive index distribution interferes with each other and reinforces each other. By incidenting the replica hologram 42 with the laser beam L2 under the conditions that this equation holds, laser beam L3 is generated. A light receiving sensor 6 is positioned to detect this laser beam L3.

[0048] A portion of the laser beam L2 is reflected by the master hologram 41 and the replica hologram 42. Specifically, the laser beam L2 includes laser beam L4 (not shown) reflected by the refractive index distribution of the master hologram 41 and laser beam L3 reflected by the refractive index distribution of the replica hologram 42. Of these, the refractive index distribution of the master hologram 41 does not change, so the laser beam L4 remains constant. The light intensity of the laser beam L3 increases as the exposure of the replica hologram 42 progresses. Therefore, by ending the irradiation of the laser beam L2 when the laser beam L3 reaches a predetermined light intensity, a replica hologram 42 that matches the design value can be obtained. The light intensity of the laser beam L3 at which exposure ends can be determined experimentally in advance.

[0049] After the exposure of the duplicate hologram 42 is complete, the master hologram 41 is removed from the hologram recording medium 4, and the duplicate hologram 42 is irradiated with ultraviolet light to prevent further exposure of the photopolymer 422 with visible light.

[0050] With the above configuration, the hologram manufacturing apparatus according to the first embodiment comprises a master hologram 41 on which a diffraction grating is formed, a replica hologram 42 positioned in close proximity to the master hologram 41, a light source 1 (first light source) that emits laser light L1 (first laser light) to expose the replica hologram 42, a light source 2 (second light source) that emits laser light L2 (second laser light) to the replica hologram 42 at a different incident angle than laser light L1, and a light receiving sensor 6 that measures the laser light L3 (third laser light) reflected by the replica hologram 42 from the laser light L2, and the exposure of the replica hologram 42 is terminated based on the measurement result of the light receiving sensor 6.

[0051] In this configuration, since the laser beams L1 and L2 are emitted from the replicated hologram 42 at different incident angles, only the laser beam L2 can be reflected by the diffraction grating (refractive index distribution) of the replicated hologram 42, and the light receiving sensor 6 can measure only the laser beam L2 (laser beam L3). As a result, by measuring the laser beam L3, the exposure progress of the replicated hologram 42 can be measured, thereby improving the accuracy of the replicated hologram.

[0052] The wavelengths of laser beams L1 and L2 may be the same or they may be different.

[0053] Furthermore, although light source 2 is a laser light source that emits laser light L2 as parallel light, the laser light L2 may also be irradiated by aligning the light emitted from a laser light source 21, which is composed of LEDs, with a lens 22.

[0054] Furthermore, light source 2 irradiates laser beam L2 so that it is directed near the center of laser beam L1 (near the center of master hologram 41), but the irradiation position of laser beam L2 is not limited to this.

[0055] Furthermore, although this embodiment describes an example where there is one set of measurement optical systems including the light source 2 and the light receiving sensor 6, multiple measurement optical systems may be arranged to measure the replicated hologram 42 at multiple locations.

[0056] (Second Embodiment) Figures 7 to 9 are schematic diagrams of a hologram manufacturing apparatus according to the second embodiment. Specifically, Figure 7 is a side view of the hologram manufacturing apparatus according to the second embodiment, Figure 8 is a top view of the hologram manufacturing apparatus according to the second embodiment, and Figure 9 is a perspective view of the hologram manufacturing apparatus according to the second embodiment. In the first embodiment, the replicated hologram 42 was exposed by being placed in air, but in the second embodiment, the replicated hologram 42 is exposed by being immersed in liquid.

[0057] As shown in Figures 7 to 9, the hologram recording body 4 (master hologram 41 and duplicate hologram 42) is placed in a water tank 7 filled with water. The inner wall of the water tank 7 is made of a material with low light reflectivity to reduce light reflection from the inner wall.

[0058] Furthermore, a coupling prism 8 is positioned above the hologram recording body 4. The coupling prism 8 is made of a material whose refractive index is approximately the same as that of water. The bottom surface of the coupling prism 8 is placed in water, and its sides 81-83 are placed in air. The sides 82 and 83 of the coupling prism 8 are positioned opposite each other.

[0059] Here, the laser beam L1 passes through the side surface 81 of the coupling prism 8 and irradiates the hologram recording medium 4. As a result, even when the laser beam L1 passes through the water from the coupling prism 8, no refraction of light according to Snell's law occurs. Therefore, the laser beam L1 can irradiate the hologram recording medium 4 without refraction.

[0060] Furthermore, the laser beam L2 passes through the side surface 82 of the coupling prism 8, irradiates the hologram recording medium 4, and is emitted through the side surface 83. Like the laser beam L1, the laser beam L2 can irradiate the hologram recording medium 4 without refraction. The laser beam L3, which is the reflected light of the laser beam L2, can also be detected by the light receiving sensor 6 without being affected by refraction or total internal reflection.

[0061] As shown in Figure 9, the coupling prism 8 has a prism 8a with side surface 81 positioned in the center, and prisms 8b with side surface 82 and 8c with side surface 83 formed at both ends in the X direction. By making the coupling prism 8 in this shape, a prism that can handle both exposure light and measurement light can be created as a single unit. This improves operability within the equipment and improves the light utilization efficiency of exposure light and measurement light by improving the precision of the parts.

[0062] In the second embodiment, similar to the first embodiment, laser light L2 is emitted onto the replicated hologram 42 in such a way that it satisfies the Bragg diffraction conditions. The amount of light from the reflected light (laser light L3) of the laser light L2 at this time is measured by the light receiving sensor 6. When the laser light L3 reaches a predetermined amount, the irradiation of laser light L2 is terminated, thereby obtaining a replicated hologram 42 that matches the design specifications. The amount of laser light L3 at which exposure ends can be determined in advance through experiments. This makes it possible to improve the accuracy of the replicated hologram.

[0063] Furthermore, the master hologram 41 and the duplicate hologram 42 are immersed in water by being placed in a water tank 7 filled with water. This suppresses refraction by the Snell side when the laser beam L1 is incident on the transparent substrates 411 and 421. As a result, the incident angle of the laser beam L1 on the master hologram 41 and the duplicate hologram 42 can be increased.

[0064] Furthermore, since the light receiving sensor 6 is located on the outside of the water tank 7, the equipment can be simplified.

[0065] Although it has been stated that the tank 7 is filled with water, it may also be filled with a liquid such as oil having the same refractive index as the transparent substrates 411 and 421 of the master hologram 41 and the duplicate hologram 42. This eliminates the refractive index difference between the liquid filled in the tank 7 and the transparent substrates 411 and 421, thereby eliminating interfacial reflection. [Industrial applicability]

[0066] The hologram manufacturing apparatus of this disclosure can be applied to holographic optical element systems such as projectors, bed-mounted displays, and head-up displays. [Explanation of Symbols]

[0067] 1,2 Light source (1st light source, 2nd light source) 4. Holographic recordings 41 Master Hologram 42 Replica Holograms 412,422 Photopolymers 6. Light receiving sensor 7 Aquariums 8 Coupling Prisms L1~L3 Laser beams (1st to 3rd laser beams)

Claims

1. A master hologram on which a diffraction grating has been formed, A replica hologram is placed in close proximity to the master hologram, A first light source emits a first laser beam to expose the replica hologram to the master hologram and the replica hologram, A second light source emits a second laser beam at a different incident angle from the first laser beam to the master hologram and the replica hologram, The system includes a sensor that measures the third laser beam reflected by the replicated hologram, the second laser beam being measured. A hologram manufacturing apparatus that terminates the exposure of the replica hologram when the third laser light measured by the sensor reaches a predetermined light intensity.

2. The hologram manufacturing apparatus according to claim 1, wherein the first laser beam and the second laser beam have different wavelengths of light.

3. The hologram manufacturing apparatus according to claim 1, wherein the second laser beam is irradiated onto the replica hologram in such a manner that the Bragg diffraction conditions of the diffraction grating formed on the master hologram are satisfied.

4. The hologram manufacturing apparatus according to claim 1, further comprising a water tank for immersing the master hologram and the replica hologram.

5. The hologram manufacturing apparatus according to claim 4, further comprising a coupling prism positioned above the master hologram and the duplicate hologram.

6. The hologram manufacturing apparatus according to claim 4, wherein the sensor is located outside the water tank.

7. The hologram manufacturing apparatus according to claim 1, wherein the third laser light is the laser light obtained by the second laser light being reflected by a diffraction grating formed on the replicated hologram.

8. The steps include: placing a master hologram and a replica hologram, on which a diffraction grating has been formed, in close proximity; The steps include: emitting a first laser beam to expose the replica hologram to the master hologram and the replica hologram, and emitting a second laser beam to the master hologram and the replica hologram at a different incident angle from the first laser beam; A method for manufacturing a hologram, comprising the steps of: measuring a third laser beam reflected by the replicated hologram from the second laser beam; and ending the exposure of the replicated hologram when the third laser beam reaches a predetermined light intensity as a result of the measurement.

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