Grism and aerial image display device

Abstract

[Problem] To miniaturize an optical device. In particular, provided is a miniaturized grism which is a high-performance grism that achieves higher angular dispersion (wavelength resolution) under the condition of retaining the same size and refractive index, or having a smaller refractive index. [Solution] A grism is provided with: a prism and a prism array, or two prism arrays; and a transmission-type grating arranged between the prism and the prism array or between the two prism arrays.

Description

Grisms and aerial image displays

[0001] The present invention relates to a grism and an aerial image display device.

[0002] A grism is a transmissive, direct-view dispersive element that combines a grating and a prism to direct light of any order and wavelength. The light of the desired wavelength can be directed straight by using a prism to return the light deflected by the grating. Therefore, by inserting a grism into the collimated beam of light in an astronomical observation device and placing a slit on the focal plane of the telescope, it is possible to quickly switch from imaging observations to spectroscopic observations.

[0003] In order to increase the angular dispersion (wavelength resolution) of a grism, it is necessary to increase the apex angle of the prism, increase the refractive index, or both.

[0004] Increasing the apex angle of the prism increases the angular dispersion, but this increases the size of the prism. The parallel beam part of the observation device also requires the placement of filters and pupil diaphragms, which limits the size of the grism that can be placed, so there is a need to make the grism more compact.

[0005] Zinc selenide (ZnSe) has a refractive index of approximately 2.5, making it a promising material for obtaining grisms with large angular dispersion in the wavelengths from visible light longer than 600 nm to infrared light up to 15 μm. However, ZnSe is difficult to obtain and expensive, and its toxicity makes it difficult to process. Therefore, obtaining a ZnSe prism requires a higher cost and longer delivery time than optical glass prisms.

[0006] Aerial image display devices form real images in the air using optical elements (mirror arrays) with multiple mirrors arranged in parallel, optical elements (dihedral corner reflector arrays) with multiple square through-holes and mirror films formed on the inner walls of the through-holes, lenses, concave mirrors, etc. Patent Document 3 proposes displaying an aerial image by bonding two mirror arrays together so that the parallel directions of the mirrors are orthogonal. Patent Document 4 also proposes displaying an aerial image using a dihedral corner reflector array.

[0007] In the aerial image display devices shown in Patent Documents 3 and 4, a light beam from an object such as a monitor is obliquely incident on the device and the light beam is then obliquely emitted at an angle opposite to the incident angle to form an image, so the device must be placed obliquely with respect to the line of sight, which requires a large space for placement of the device.

[0008] JP 2004-13080 A JP 2002-14209 A JP 2011-81300 A JP 2008-158114 A

[0009] The present disclosure aims to reduce the size of optical devices.

[0010] Miniaturization of a grism means achieving a desired angular dispersion (wavelength resolution) at a smaller size if the material has the same refractive index, or at the same or smaller size if the material has a smaller refractive index. A first aspect of the present invention aims to provide such a miniaturized grism, i.e., a high-performance grism with a smaller refractive index and increased angular dispersion (wavelength resolution) at the same size. A second aspect of the present invention aims to provide a high-performance grism with the same or a smaller refractive index but with the same or increased angular dispersion at a smaller size. However, the second aspect requires consideration of a slight decrease in efficiency and ghosting.

[0011] If an aerial image display device could be placed directly opposite an object such as a monitor and perpendicular to the line of sight, the installation space could be reduced, and the overall device could be made smaller. Therefore, an object of a third aspect of the present invention is to provide an aerial image display device that can be placed directly opposite an object such as a monitor and perpendicular to the line of sight or at an angle close to that.

[0012] A first aspect of the present invention is a grism comprising: a prism; a prism array; and a transmission diffraction grating disposed between the prism and the prism array.

[0013] A second aspect of the present invention is a grism comprising: a first prism array; a second prism array; and a transmission diffraction grating disposed between the first prism array and the second prism array.

[0014] A third aspect of the present invention is an aerial image display device comprising: a first prism array; a second prism array; and an aerial image display element disposed between the first prism array and the second prism array.

[0015] According to the present invention, it is possible to reduce the size of the optical device.

[0016] More specifically, according to the first and second aspects of the present invention, by using a prism array for the grism, it is possible to achieve the desired angular dispersion (wavelength resolution) with a smaller size if the material has the same refractive index, or with the same or a smaller size if the material has a smaller refractive index. According to the third aspect of the present invention, by sandwiching the aerial image display element between prism arrays, it becomes possible to arrange the aerial image display device vertically, thereby reducing the arrangement space.

[0017] FIG. 1 is a diagram showing the configuration of a grism according to embodiment 1. FIG. 2 is a diagram showing the configuration of a VB diffraction grating included in the grism according to embodiment 1. FIG. 3 is a partially enlarged view of an exit-side prism array included in the grism according to embodiment 1. FIG. 4 is a diagram showing the configuration of a grism according to embodiment 2. FIG. 5 is a partially enlarged view of an entrance-side prism array included in the grism according to embodiment 2. FIG. 6 is a diagram showing the configuration of a grism according to a reference example. FIG. 7 is a diagram showing the configuration of an aerial image display device according to embodiment 3. FIG. 8 is a diagram showing the configuration of an aerial image display element included in the aerial image display device according to embodiment 3.

[0018] Hereinafter, embodiments of the present invention will be described with reference to the drawings, but the present invention is not limited thereto. The components of the embodiments described below can be combined as appropriate.

[0019] [1. Grism] The following describes a compact grism, i.e., a grism that can achieve a desired angular dispersion (wavelength resolution) with a smaller size if the material has the same refractive index, or with the same or a smaller size if the material has a smaller refractive index. The following describes an example of a grism that targets light in the near ultraviolet to near infrared wavelength range, for example, 600 to 2500 nm, but the grism according to the present invention may also target light of other wavelengths.

[0020] <Prior Art> A grism 300 according to the prior art will be described with reference to Figure 6. The grism 300 has a configuration in which a volume binary (VB) diffraction grating 130 is disposed between two prisms 110 and 120. The wavelength resolution of the grism is a value corresponding to the angular dispersion of the VB diffraction grating 130 (dθdiff / dλ = Nm / cosθdiff, where θdiff is the diffraction angle, λ is the wavelength, N is the number of grooves per mm, and m is the diffraction order). In order to increase the angular dispersion, it is necessary to increase the apex angles of the prisms 110 and 120 or use materials with a high refractive index, as described above.

[0021] If the grism is required to have a size of 110 mm × 110 mm × 65 mm, the maximum apex angle of the prisms 110 and 120 will be 15°. If zinc selenide (ZnSe), which has a high refractive index of 2.47, is used as the material for the prisms 110 and 120, the resulting diffraction angle will be 22.6°.

[0022] 1 is a diagram showing the configuration of a grism 100 according to embodiment 1. The grism 100 includes a prism 10, a prism array 20, and a VB diffraction grating 30. The VB diffraction grating 30 is provided between the prism 10 and the prism array 20.

[0023] As shown in FIG. 2 , the VB diffraction grating 30 is a thick rectangular diffraction grating having grooves with a high aspect ratio (e.g., S:t = 1:3 or more). By adjusting the L&S (Line and Space, the ratio of the ridge width to the groove width) and the groove depth t, high diffraction efficiency and a wide wavelength bandwidth (FWMH: Full Width at Half Maximum) can be achieved. Note that thick diffraction gratings are also called "thick gratings" or "volume gratings." Gratings with the following index Q > 10 are sometimes classified as thick gratings, and those with Q < 1 as thin gratings. However, diffraction gratings with Q > 2 or so are sometimes also called thick gratings. In the present disclosure, diffraction gratings with Q > 2 are called thick diffraction gratings. The index Q is expressed as Q = 2πλt / (nΛ 2 ), λ: wavelength, t: grating thickness, n: grating refractive index, and Λ: grating period. The VB diffraction grating 30 can be obtained by anisotropically etching quartz glass to form grooves, or by replica processing using a silicon grating as a mold. Note that while FIG. 2 shows an example in which the refractive indexes of the base and ridge portions are different, they may also be the same.

[0024] Prism 10 is disposed on the incident side, and refracts light incident from a direction perpendicular to the surface of VB diffraction grating 30 at a predetermined angle (30.9° in this case) and causes it to enter VB diffraction grating 30. In this example, prism 10 is made of ZnSe (refractive index 2.47) and has an apex angle of 20°.

[0025] Prism array 20 is configured with multiple prisms aligned. While Fig. 1 shows an example in which five prisms are aligned, the number is not particularly limited as long as the pitch is not so small that it affects diffraction broadening, for example, the pitch is 20 times the wavelength or more. Prism array 20 is arranged so that the apex of each prism faces away from VB diffraction grating 30, and light enters the flat surface and exits the slope.

[0026] The material of the prism array 20 is acrylic resin (PMMA, refractive index 1.48 @ 589 nm), but other resin materials, optical glass, and crystalline materials may be used. Resin materials other than acrylic resin include polycarbonate resin (PC, refractive index 1.585) and amorphous fluorocarbon resin (e.g., CYTOP (registered trademark) manufactured by AGC, refractive index 1.34). Examples of optical glass include S-FSL5 (refractive index 1.487) and S-BSL7 (refractive index 1.516) manufactured by Ohara Corporation, and J-LASFH16HS (refractive index 2.001) manufactured by Hikari Glass Co., Ltd. Crystal materials include zinc selenide (ZnSe, refractive index 2.44 @ 2000 nm), silicon (Si, refractive index 3.45), and germanium (Ge, refractive index 4.10). The prism array 20 can be manufactured by cutting a block of transparent resin, injection molding using a metal mold, hot pressing using a metal mold of optical glass, grinding and cutting a block of material, or the like.

[0027] 3 is a partially enlarged view of the prism array 20. One surface of the prism array 20 is a flat surface 21, and the other surface has prisms, each of which is made up of an inclined surface 22 and an inclined surface 23, arranged repeatedly. The prism array 20 is inclined at a predetermined angle θ ０ The angle α of the inclined surface 22 is determined so that the light incident at the angle α is emitted parallel to the normal to the plane 21 .

[0028] Specifically, the angle α is calculated using Snell's law and θ ２ = α-θ １ and θ ３ Based on the condition α, it can be calculated using the following formula.

[0029] In this embodiment, θ ０ = 30.9°, n ０ = 1, n １ = 1.48, and in this case, α = 41.9°.

[0030] The angle β is not particularly limited as long as it is an angle that does not cause vignetting. ２ In this example, the angle θ ２ = 20.3°, the angle β may be any value between 69.7° and 90°. Taking into consideration the influence of diffraction, it is also preferable to set the angle β to a value intermediate between these two values.

[0031] In this embodiment, the refraction angle at the prism interface is 41.9°, and the reflectance is low at 4.5% (s-polarized light: 7.8%, p-polarized light: 1.1%), so sufficient efficiency is obtained. To suppress reflection, an anti-reflection film may be provided on the sloped surface of the prism array 20.

[0032] Furthermore, since the hatched areas in the figure are areas where light beams do not pass, if light is incident from the right side of the figure, not only will the light beam in that area be lost, but it will also become stray light and may cause ghosts. Therefore, it is preferable to have light incident on the prism array 20 from the left side of the figure.

[0033] In this embodiment, five prism arrays 20 are arranged at a 22 mm pitch, resulting in a prism height of 17.4 mm. Combined with the 6.6 mm thickness of the flat plate, the total height (horizontal length in the drawing) of the prism array 20 is 24 mm. Using a prism array makes it possible to direct light beams at a predetermined angle in a smaller size than using a single prism. While maintaining the same width and height of 65 mm and 110 mm as the conventional example ( FIG. 6 ), this embodiment increases the diffraction angle from 22.6° to 30.9°, resulting in an angular dispersion approximately 1.44 times larger (= tan 30.9° / tan 22.6°). Furthermore, the amount of zinc selenide used can be reduced.

[0034] 4 is a diagram showing the configuration of a grism 200 according to embodiment 2. The grism 200 has a prism 10, prism arrays 20 and 40, and a VB diffraction grating 30. The VB diffraction grating 30 is provided between the prism arrays 20 and 40.

[0035] The configurations of the prism array 20 and the VB diffraction grating 30 are the same as those in the first embodiment, and therefore a description thereof will be omitted.

[0036] Prism array 40 is configured with multiple prisms aligned. While the figure shows an example in which five prisms are aligned, the number is not particularly limited as long as the pitch is not so small that it affects diffraction broadening, for example, the pitch is 20 times the wavelength or more. Prism array 40 is arranged so that the apex of each prism faces VB diffraction grating 30, and light enters the flat surface and exits from the sloped surface.

[0037] The material of the prism array 40 is acrylic resin (refractive index 1.48), but it may be other resin materials, optical glass, crystalline materials, or other materials, as with the prism array 20. In this embodiment, the material of the prism array 40 is the same as the material of the prism array 20, but the materials of the prism arrays 20 and 40 may be different.

[0038] 5 is a partially enlarged view of the prism array 40. One surface of the prism array 40 is a flat surface 41, and the other surface has a repeated arrangement of prisms each consisting of an inclined surface 42 and an inclined surface 43. The prism array 40 converts light that is perpendicular to the flat surface 41 into a prism that is angled at an angle θ ４ The angle α of the inclined surface 42 is determined so that the light is emitted at a wavelength of 1000 nm.

[0039] Specifically, the angle α is calculated using Snell's law and θ ２ = α and θ ３ = θ ４ From the condition +α, it can be calculated using the following formula.

[0040] In one embodiment, θ ４ = 30.9°, n ０ = 1, n １= 1.48, and in this case, α = 41.9°.

[0041] The angle β of the inclined surface 43 is not particularly limited as long as it is an angle that does not cause vignetting. In this example, β=90°, but it can be set to any angle from 90° to 90°+θ ４ It is sufficient if it is in the range.

[0042] In this embodiment, the refraction angle at the prism interface is 70.5°, so the reflectance at the interface on the exit side is approximately 17.4% (s-polarized light: 30.0%, p-polarized light: 4.8%). To suppress reflection, an anti-reflection film may be provided on the sloped surface of the prism array 40.

[0043] Furthermore, since the hatched areas in the figure are areas where light beams do not pass, if light is incident from the right side of the figure, not only will the light beam in those areas be lost, but it will also become stray light and may cause ghosts. Therefore, it is preferable to have light incident on the prism array 40 from the left side of the figure.

[0044] In this embodiment, five prisms are arranged in the prism array 40 at a 22 mm pitch, resulting in a prism height of 18 mm. Combined with the 7 mm thickness of the flat plate portion, the height (horizontal length in the drawing) of the prism array 40 is 24 mm. By using two prism arrays, a diffraction angle of 30.9° can be achieved with a thickness of 51 mm, which is smaller than the conventional example ( FIG. 6 ) and embodiment 1. Furthermore, zinc selenide need not be used.

[0045] <Modifications> The above-described embodiments are merely examples for explaining the invention, and are not intended to limit the scope of the present invention to the above-described embodiments.

[0046] For example, the target wavelength and diffraction angle can be set as required, and the prism slope angle can be set accordingly. Also, the number of stages in the prism array is not limited to the above example (5), and can be any number.

[0047] Furthermore, the material of the prism or prism array may be selected appropriately. A material with a lower refractive index than zinc selenide, such as acrylic resin or optical glass, may be used for the prism 10, and zinc selenide may be used for the prism arrays 20 and 40. Transparent resin or optical glass with a refractive index of 1.3 to 2.0 is an easily available material with a relatively low refractive index. The angular dispersion (wavelength resolution) of a grism improves depending on the refractive index and size of the material, and the present invention can improve the angular dispersion (wavelength resolution) compared to a conventional grism of the same size that uses a material with the same refractive index.

[0048] Although a VB diffraction grating is used as the diffraction grating, any transmission type diffraction grating that can obtain the required diffraction angle may be used, such as a VPH (Volume Phase Holographic) diffraction grating or a transmission grating from LightSmyth Technologies (Finisar) or other thick diffraction gratings.

[0049] 2. Aerial Image Display Device Hereinafter, an aerial image display device that can be placed perpendicular or at an angle close to perpendicular to the line of sight and therefore requires a reduced installation space will be described.

[0050] 7 is a diagram showing the configuration of an aerial image display device 400 according to embodiment 3. The aerial image display device 400 has a structure in which an aerial image display element 50 is sandwiched between a prism array 60 and a prism array 70. In this structure, the ridges and valleys of the prism arrays 60 and 70 are inclined at 45° or 135° with respect to the arrangement of the mirrors of the mirror arrays 51 and 52 of the aerial image display element 50.

[0051] FIG. 8 is a diagram showing an example of the configuration of an aerial image display element 50. The aerial image display element 50 has a structure in which mirror arrays 51 and 52, each of which has a plurality of mirrors arranged in parallel, are stacked so that the mirror arrangement directions are orthogonal to each other. The mirror arrays 51 and 52 have a structure in which a plurality of transparent rectangular parallelepiped materials 53 are arranged. The rectangular parallelepiped materials 53 are plastic or glass rods with a quadrangular (e.g., square or rectangular) cross section, and the length of one side of the cross section is approximately several tens of μm to several cm. The longitudinal length of the rectangular parallelepiped materials 53 is approximately several mm to several m. As shown at the bottom of FIG. 8 , a light-reflecting film 54 is formed on one side of the rectangular parallelepiped material 53, and the opposite side 55 is an optically polished surface or has a light-absorbing film formed thereon.

[0052] When the light of an object image is obliquely incident on the mirror array 51 of the aerial image display device 50, it is reflected by the mirror arrays 51 and 52, and is output obliquely from the mirror array 52, forming a real image.

[0053] The prism array 60 has a configuration similar to that of the prism array 40 of the second embodiment, and is configured to emit light incident perpendicularly at a predetermined angle. The prism array 70 has a configuration similar to that of the prism array 20 of the first and second embodiments, and is configured to emit light incident at the predetermined angle perpendicularly.

[0054] In this way, the aerial image display device 400 as a whole forms a real image by emitting the light of an object image that is perpendicularly incident on the device perpendicularly to the opposite side, which makes it possible to place the aerial image display device 400 perpendicular to the user's line of sight or at an angle close to that, thereby reducing the installation space.

[0055] The above embodiment is merely an example, and the aerial image display element 50 may be configured with an element other than a mirror array. For example, the aerial image display element 50 may be an element in which a substrate is provided with a plurality of rectangular holes and mirror surfaces are formed on two orthogonal inner walls of each hole (see Patent Document 4). Alternatively, the aerial image display element 50 may be an element in which two prism arrays (e.g., a triangular lattice with a more acute angle than the prism array 20, in which a light beam incident on one side of the lattice is reflected by the other side and exits from the back surface, or in which a light beam travels back along the opposite optical path; see Patent Application No. 2024-123459) are stacked such that the arrangement directions of the prism arrays are orthogonal to each other.

[0056] 7 shows the incident light and the outgoing light to the aerial image display device 400 as being parallel, but they do not have to be perfectly parallel. If the incident light and the outgoing light are nearly parallel, the aerial image display device 400 can be placed at an angle nearly perpendicular to the user's line of sight, which can contribute to reducing the placement space. Also, one or both of the two prism arrays may be replaced with a single prism.

[0057] The grism according to the present invention can be suitably used in various observation devices in astronomy, earth and planetary science, meteorology, environmental measurement, environmental hygiene, etc., various spectroscopic analyzers in physics and chemistry, mineralogy, biology, pathology, etc., manufacturing and quality control devices for food, biotechnology, pharmaceuticals, and chemical products, communication and information fields such as optical communications, and fields of inorganic and organic materials, etc. In particular, it can contribute to the miniaturization of hyperspectral cameras.

[0058] The aerial image display device of the present invention is expected to be applicable in a variety of fields as a technology for forming three-dimensional aerial images, and can be used, for example, in digital signage, in-vehicle head-up displays, medical image display devices, entertainment facilities, product displays in commercial facilities, security systems, etc. Furthermore, this space-saving technology is expected to contribute to the development of new information presentation methods by combining it with next-generation user interfaces and AR (augmented reality) technology.

[0059] 100, 200 Grism 400 Aerial image display device 10: Prism 20: Prism array 30: VB diffraction grating 40: Prism array 50: Aerial image display element 51, 52: Mirror array

Claims

1. A grism comprising: a prism; a prism array; and a transmission diffraction grating disposed between the prism and the prism array.

2. The grism according to claim 1, wherein the prism array is provided on the output side of the transmission diffraction grating.

3. The grism according to claim 1, characterized in that the prism array is arranged such that the apexes of the prisms constituting the prism array are directed away from the transmission diffraction grating.

4. The grism according to claim 1, wherein the refractive index of the prism array is 1.3 to 4.

1.

5. The grism according to claim 1, wherein the material constituting the prism array is a resin material, optical glass, or a crystalline material.

6. A grism comprising: a first prism array; a second prism array; and a transmission diffraction grating disposed between the first prism array and the second prism array.

7. The grism according to claim 6, wherein the first prism array is arranged such that the apexes of the prisms constituting the prism array face the transmission diffraction grating, and the second prism array is arranged such that the apexes of the prisms constituting the prism array face away from the transmission diffraction grating.

8. The grism according to claim 6, wherein the refractive index of the prism array is 1.3 to 4.

1.

9. The grism according to claim 6, wherein the material constituting the prism array is a resin material, optical glass or a crystalline material.

10. An aerial image display device comprising: a first prism array; a second prism array; and an aerial image display element disposed between the first prism array and the second prism array.

11. The aerial image display device according to claim 10, characterized in that the first prism array is arranged such that the apexes of the prisms constituting the prism array face the aerial image display element, and the second prism array is arranged such that the apexes of the prisms constituting the prism array face away from the aerial image display element.

12. The aerial image display device according to claim 10, wherein the refractive index of the prism array is 1.3 to 4.

1.

13. The aerial image display device according to claim 10, wherein the material constituting the prism array is a resin material, optical glass, or crystalline material.

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