Holographic optical element and sensor

Abstract

To provide a holographic optical element capable of increasing the resolution while reducing the size.SOLUTION: A holographic optical element in an embodiment includes: a transparent substrate 11; an incident hologram 12 placed on the transparent substrate 11 for propagating incident light 2 into the transparent substrate 11; and an emitting hologram 13 placed on the transparent substrate 11. The incident hologram 12 diffracts the incident light 2 in the direction away from the optical axis of the incident light 2 and emits the incident light 2 so that the diffracted incident light 2 achieves total reflection within the transparent substrate 11.SELECTED DRAWING: Figure 2

Description

[Technical field]

[0001] The present disclosure relates to holographic optical elements and sensors. [Background technology]

[0002] Conventionally, optical systems using holographic optical elements in light guide members have been known. For example, a light beam focusing device disclosed in Patent Document 1 includes a holographic lens for focusing a light beam, and a concentric holographic pattern is formed on the holographic lens. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Publication No. 5-066358 Summary of the Invention [Problem to be solved by the invention]

[0004] However, due to the diffraction phenomenon in which light spreads like a wave, even if a high-performance lens without aberration is used, the image cannot be focused on one point and spreads out into a disk shape. This disk-shaped pattern is called an Airy disk. The radius r of the Airy disk is expressed by the following equation (1).

[0005]

number

[0006] λ is the wavelength of light, and NA (Numerical Aperture) is the light collection limit in the absence of aberration.

[0007] The r in formula (1) is called the resolution, and in order to improve the resolution of the sensor, it is necessary to collect light with a high NA. If a glass lens is used for the sensor, multiple lenses are required, which may increase the size and weight of the sensor. In addition, the lens needs to have a large curvature, and there is a limit to the NA.

[0008] Therefore, an object of the present disclosure is to provide a holographic optical element that is compact and has improved resolution. [Means for solving the problem]

[0009] In order to achieve the above-mentioned object, a holographic optical element according to one embodiment of the present disclosure comprises a transparent substrate, an incident portion provided on the transparent substrate and propagating incident light within the transparent substrate, and an exit hologram provided on the transparent substrate, wherein the incident portion diffracts the incident light in a direction away from the optical axis direction of the incident light and emits the incident light so that the diffracted incident light is totally reflected within the transparent substrate, and the exit hologram diffracts the light propagating within the transparent substrate so as to be focused at a focusing point. Effect of the Invention

[0010] According to the present disclosure, it is possible to reduce the size of a hologram optical element while increasing the resolution. [Brief description of the drawings]

[0011] [Figure 1] FIG. 1 is a perspective view of a hologram optical element according to a first embodiment. [Diagram 2] FIG. 1 is a cross-sectional view of a hologram optical element according to a first embodiment. [Diagram 3] FIG. 2 is a plan view of an entrance hologram according to the first embodiment. [Figure 4] FIG. 2 is a plan view of an exit hologram according to the first embodiment. [Diagram 5] FIG. 11 is a cross-sectional view of a hologram optical element according to a second embodiment. [Figure 6] FIG. 11 is a cross-sectional view of a hologram optical element according to a third embodiment. [Figure 7] FIG. 13 is a cross-sectional view of a hologram optical element according to a modified example of the third embodiment. [Figure 8] FIG. 11 is a cross-sectional view of a hologram optical element according to a fourth embodiment. [Figure 9] FIG. 13 is a cross-sectional view of a hologram optical element according to a fifth embodiment. [Figure 10] FIG. 13 is a block diagram of a sensor according to a sixth embodiment. [Figure 11] FIG. 11 is a plan view of another example of an incident hologram. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0012] Hereinafter, the embodiments of the present disclosure will be described in detail with reference to the drawings. The following description of the preferred embodiments is essentially merely illustrative and is not intended to limit the present invention, its applications, or its uses. In the following description, the same parts are given the same reference numerals, and detailed descriptions will be omitted as appropriate.

[0013] The volume phase hologram used in this disclosure is different from a two-dimensional diffraction grating with fine periodic irregularities on the surface, and records a three-dimensional refractive index distribution in a sinusoidal shape within a volume. By controlling the direction and period of this sinusoidal wave and the amplitude of the refractive index difference, it is possible to control the light distribution of the volume phase hologram.

[0014] (First embodiment) Fig. 1 is a perspective view of a hologram optical element according to a first embodiment. In the following description, the traveling direction of incident light 2 (thickness direction of hologram optical element 1) is defined as the Y direction, one width direction of hologram optical element 1 is defined as the X direction, and the direction perpendicular to the X direction and Y direction (the other width direction of hologram optical element 1) is defined as the Z direction. In Fig. 1 and other figures, each light beam is appropriately illustrated by an arrow or the like.

[0015] As shown in Fig. 1, hologram optical element 1 receives incident light 2 and emits outgoing light 3. The outgoing light 3 is focused at a focusing point F. That is, hologram optical element 1 has a function of focusing incident light 2. A light control unit 5 is provided on the outer periphery of hologram optical element 1. The light control unit 5 attenuates propagated light 4 (described later) that has propagated to the outer periphery of hologram optical element 1, thereby suppressing the occurrence of stray light.

[0016] Fig. 2 is a cross-sectional view of the hologram optical element according to the first embodiment. As shown in Fig. 2, the hologram optical element 1 includes a transparent substrate 11, an entrance hologram 12 (entrance portion), an exit hologram 13, and a light control portion 5 (5a, 5b).

[0017] The transparent substrate 11 is a flat plate with high transmittance. The transparent substrate 11 is made of, for example, quartz, optical glass, etc. The transparent substrate 11 has surfaces 11a and 11b which are flat surfaces facing each other.

[0018] Incident hologram 12 is a transmission-type volume phase hologram arranged on surface 11a of transparent substrate 11. Incident hologram 12 is a hologram in which a predetermined refractive index distribution is recorded. Incident hologram 12 receives incident light 2 and emits propagating light 4 to transparent substrate 11.

[0019] Exit hologram 13 is a transmission-type volume phase hologram disposed on surface 11b of transparent substrate 11. Exit hologram 13 is a hologram in which a predetermined refractive index distribution is recorded. Exit hologram 13 receives propagating light 4 and emits exit light 3.

[0020] The light control sections 5a and 5b are formed on the outer periphery of the hologram optical element 1, and are made of a black material or the like that attenuates light and has high absorptance.

[0021] Next, the propagation of light in the hologram optical element 1 will be described.

[0022] First, incident light 2 is incident on incident hologram 12. Upon receiving incident light 2, incident hologram 12 diffracts incident light 2 and emits propagating light 4 to transparent substrate 11.

[0023] FIG. 3 is a plan view of the incident hologram according to the first embodiment. As shown in FIG. 3, when the incident hologram 12 is viewed from the Y direction, interference fringes are formed concentrically around the center. Due to these interference fringes, the incident light 2 incident on the incident hologram 12 is diffracted so as to spread outward from the center when the hologram optical element 1 is viewed in a plan view. The diffracted incident light 2 spreads outward concentrically from the center in the plan view of the hologram optical element 1 as propagating light 4. That is, the incident hologram 2 does not diffract light in only one direction, but diffracts the incident light 2 in a direction away from the optical axis direction of the incident light 2, and diffracts the incident light 2 in multiple directions.

[0024] 2, incident light 2 is diffracted by input hologram 2 and is output to transparent substrate 11 as propagating light 41, 42. In addition, input hologram 12 sets the output angles of propagating light 41, 42 so that the propagating light 41, 42 undergo total reflection when they are incident on transparent substrate 11 and output hologram 13.

[0025] When the propagating lights 41 and 42 enter the emission hologram 13, a part of them is emitted as the exit light 3, and the remaining part is totally reflected by the surface of the emission hologram 13 and propagates within the transparent substrate 11 as the propagating light 4. In Fig. 2, the propagating lights 41 and 42 are partially emitted as the exit light 31 and 32, respectively, and the remaining part propagates within the transparent substrate 11 as the propagating light 43 and 44.

[0026] Thereafter, the propagating lights 43 and 44 are totally reflected by the surface 11a of the transparent substrate 11, and then re-enter the exit hologram 13. Like the propagating lights 41 and 42, when the propagating lights 43 and 44 enter the exit hologram 13, a part of them is emitted as the exit light 3, and the remaining part is totally reflected by the exit hologram 13 and propagates within the transparent substrate 11 as the propagating light 4. In FIG. 2, the propagating lights 43 and 44 are partly emitted as the exit light 33 and 34, respectively, and the remaining part propagates within the transparent substrate 11 as the propagating lights 45 and 46.

[0027] Thereafter, the propagating lights 45 and 46 are totally reflected by the surface 11a of the transparent substrate 11 and then enter the light control units 5a and 5b, respectively. As a result, the propagating lights 45 and 46 are attenuated at the outer periphery of the hologram optical element 1, so that stray light due to reflection at the outer periphery of the hologram optical element 1 can be suppressed.

[0028] 1, the propagating light 4 is totally reflected twice by the output hologram 13, but it may be totally reflected three or more times. In this case, the propagating light 4 propagates through the holographic optical element 1 while being totally reflected within the transparent substrate 11, and a part of it is emitted as the output light 3 each time it is incident on the output hologram 13.

[0029] Fig. 4 is a plan view of the exit hologram according to the first embodiment. As shown in Fig. 4, when viewed from the Y direction, the entrance hologram 12 has interference fringes formed concentrically around the center. Due to these interference fringes, the exit hologram 13 emits the exit light beams 31 to 34 so as to focus them at a focusing point F. For example, by gradually changing the refractive index distribution of the exit hologram 13 from the center of the exit hologram 13 to the outside, the exit light beams 31 to 34 can be focused at the focusing point F.

[0030] For example, transparent substrate 11 preferably has a width of 10 mm to 150 mm in the X and Z directions and a thickness of 3 mm to 10 mm in the Y direction. Incident hologram 12 preferably has a width of 2 mm to 30 mm in the X and Z directions and a thickness of 1 μm to 100 μm in the Y direction. Exit hologram 13 preferably has a width of 30 mm to 150 mm in the X and Z directions and a thickness of 1 μm to 100 μm in the Y direction. When transparent substrate 11 has a thickness of 3 mm to 10 mm in the Y direction and exit hologram 13 has a width of 150 mm in the X and Z directions, the distance from exit hologram 13 to the focusing point F is 36 mm.

[0031] With the above configuration, the holographic optical element according to this embodiment includes a transparent substrate 11, an entrance hologram 12 (entrance portion) provided on the transparent substrate 11 and propagating the incident light 2 into the transparent substrate 11, and an exit hologram 13 provided on the transparent substrate 11. The entrance hologram 12 diffracts the incident light 2 in a direction away from the optical axis direction of the incident light 2, and emits the incident light 2 so that the diffracted incident light 2 is totally reflected within the transparent substrate 11. The exit hologram 13 diffracts the light propagating within the transparent substrate 11 so as to be focused at a focusing point F. As a result, the incident light 2 is diffused in the X direction and the Z direction by the entrance hologram 12, and the diffused propagating light 4 is focused at a focusing point F by the exit hologram 13, thereby improving the resolution. Furthermore, when using a glass lens for the sensor, improving the resolution requires using multiple lenses or increasing the thickness of the lenses. However, in this embodiment, the resolution can be improved by adjusting the refractive index distribution of the input hologram 12 and the output hologram 13, thereby making it possible to increase the resolution while miniaturizing the hologram optical element.

[0032] 2, for the sake of explanation, each light ray is illustrated as an arrow, but in reality, each light ray has a certain width in the X direction and the Z direction. Even in this case, it is possible to expand the width of the incident light 2 in the X direction and the Z direction and then focus the light to one point, thereby improving the resolution r.

[0033] Furthermore, by adjusting the diffraction direction in the manufacturing process of output hologram 13, the light focusing point F can be moved closer to hologram optical element 1. This allows the aperture NA of hologram optical element 1 to be increased.

[0034] Second embodiment Fig. 5 is a cross-sectional view of a holographic optical element according to the second embodiment. In Fig. 5, an entrance hologram 12 and exit holograms 13a and 13b are provided on a surface 11a of a transparent substrate 11. Note that the entrance hologram 12 in Fig. 5 is a transmission type volume phase hologram, and the exit holograms 13a and 13b are reflection type volume phase holograms.

[0035] In FIG. 5, incident light 2 incident on incident hologram 12 a is diffracted by incident hologram 12 a and becomes propagating light 45 and 46 that propagates within transparent substrate 11 .

[0036] Then, the propagating light 45 and 46 are totally reflected by the surface 11b of the transparent substrate 11 and enter the exit holograms 13a and 13b, respectively. When the propagating light 45 enters the exit hologram 13a, a part of it is reflected by the surface of the exit hologram 13a to become the exit light 35, and the remainder is totally reflected to become the propagating light 47 that propagates within the transparent substrate 11. Similarly, when the propagating light 46 enters the exit hologram 13b, a part of it is reflected by the surface of the exit hologram 13b to become the exit light 36, and the remainder is totally reflected to become the propagating light 48 that propagates within the transparent substrate 11.

[0037] Thereafter, the propagating lights 47 and 48 are totally reflected by the surface 11b of the transparent substrate 11, and then re-enter the exit holograms 13a and 13b, respectively. Similar to the propagating lights 45 and 46, when the propagating lights 47 and 48 enter the exit holograms 13a and 13b, a part of them is emitted as the exit lights 37 and 38, and the remaining part is totally reflected by the exit holograms 13a and 13b, and propagates within the transparent substrate 11 as the propagating light 4.

[0038] In FIG. 5, exit holograms 13a and 13b emit exit light beams 35 to 38 so as to converge the exit light beams 35 to 38 at a convergence point F.

[0039] In FIG. 5, entrance hologram 12 and exit holograms 13a and 13b are disposed only on one surface (surface 11a) of transparent substrate 11, which makes it easy to manufacture the holographic optical element.

[0040] Incidentally, the entrance hologram 12 and the exit hologram 13 may be formed on the same film.

[0041] Third embodiment Fig. 6 is a cross-sectional view of a holographic optical element according to the third embodiment. In Fig. 6, incident hologram 12b and exit holograms 13c and 13d are provided on surface 11b of transparent substrate 11. Incident hologram 12a in Fig. 6 is a reflection-type volume phase hologram, and exit holograms 13c and 13d are transmission-type volume phase holograms.

[0042] In FIG. 6, incident light 2 incident on incident hologram 12b is diffracted by incident hologram 12b, and becomes propagating lights 45a and 46a that propagate within transparent substrate 11. In FIG.

[0043] Then, the propagating light 45a, 46a is totally reflected by the surface 11a of the transparent substrate 11 and enters the exit holograms 13c, 13d. When the propagating light 45a enters the exit hologram 13c, a part of the propagating light 45a is reflected by the surface of the exit hologram 13c to become the exit light 36a, and the remaining part is totally reflected to become the propagating light 47a that propagates within the transparent substrate 11. Similarly, when the propagating light 46a enters the exit hologram 13d, a part of the propagating light 46a is reflected by the surface of the exit hologram 13d to become the exit light 37a, and the remaining part is totally reflected to become the propagating light 48a that propagates within the transparent substrate 11.

[0044] Thereafter, the propagating lights 47a and 48a are totally reflected by the surface 11a of the transparent substrate 11, and then re-enter the exit holograms 13c and 13d, respectively. Similar to the propagating lights 45a and 46a, when the propagating lights 47a and 48a enter the exit holograms 13c and 13d, a part of the propagating lights 47a and 48a is emitted as the exit lights 38a and 39a, and the remaining part is totally reflected by the exit holograms 13c and 13d, and propagates within the transparent substrate 11 as the propagating light 4.

[0045] In FIG. 6, exit holograms 13c and 13d emit exit light beams 35a to 38a so as to converge the exit light beams 35a to 38a at a convergence point F.

[0046] In FIG. 6, entrance hologram 12a and exit holograms 13c and 13d are disposed only on one surface (surface 11b) of transparent substrate 11, which makes it easy to manufacture the holographic optical element.

[0047] Incidentally, the entrance hologram 12a and the exit holograms 13c and 13d may be formed on the same film.

[0048] Fig. 7 is a cross-sectional view of a hologram optical element according to a modified example of the third embodiment. In Fig. 7, a transparent substrate 14 is provided on the side of incident hologram 12a and exit holograms 13c and 13d opposite surface 11b of transparent substrate 11. That is, incident hologram 12a and exit holograms 13c and 13d are sandwiched between transparent substrates 11 and 14. This can improve the reliability of hologram optical element 1 in terms of heat resistance, water resistance, weather resistance, and the like.

[0049] It should be noted that the transparent substrate 14 does not need to have the same thickness as the transparent substrate 11 since it does not have any optical function.

[0050] Also in the first to third embodiments, similarly to the fourth embodiment, a transparent substrate may be disposed outside the entrance hologram and exit hologram.

[0051] (Fourth embodiment) Fig. 8 is a cross-sectional view of a hologram optical element according to a fourth embodiment. In Fig. 8, compared to Fig. 6, a prism 12c (entrance portion, first prism) is provided on surface 11b of transparent substrate 11 instead of entrance hologram 12a.

[0052] Prism 12c is a recess formed on surface 11b of transparent substrate 11, and has a hollow interior. Prism 12c reflects incident light 2 and propagates propagating light 45, 46 within transparent substrate 11. In other words, prism 12c has the same function as incident hologram 12a.

[0053] In FIG. 8, prism 12c and emission holograms 13c and 13d are disposed on the same surface (surface 11b) of transparent substrate 11, so that prism 12c can be used as an alignment mark when laminating emission holograms 13c and 13d.

[0054] Fifth embodiment Fig. 9 is a cross-sectional view of a hologram optical element according to the fifth embodiment. In Fig. 9, compared to Fig. 2, a prism 14a (second prism) is formed on the outer periphery of the hologram optical element 1 instead of the light control units 5a and 5b.

[0055] 9, when the propagating light 4 propagating within the transparent substrate 11 is incident on the prism 14a on the outer periphery of the hologram optical element 1, it is reflected toward the absorbing member 15a provided on the outside of the transparent substrate 11. The absorbing member 15a is composed of a member that attenuates and absorbs the incident light. This makes it possible to suppress stray light on the outer periphery of the hologram optical element 1.

[0056] In FIG. 9, the prisms 14a are formed on the outer periphery of the transparent substrate 11, but the prisms 14a may be formed on the surfaces 11a, 11b, or the like.

[0057] Sixth embodiment Fig. 10 is a block diagram of a sensor according to the sixth embodiment. As shown in Fig. 10, the sensor according to the sixth embodiment includes a hologram optical element 1, a power supply unit 6, a light source 7, a control unit 8, and a light receiving element 9. The hologram optical element 1 is any of the hologram optical elements according to the first to fifth embodiments described above.

[0058] The power supply unit 6 supplies power to the light source 7 , the control unit 8 and the light receiving element 9 .

[0059] Based on the supplied power, the light source 7 irradiates light onto the hologram optical element 1. The light source 7 is preferably a monochromatic laser light source or an LED, but may also be a laser light source or an LED that emits light at a plurality of wavelengths.

[0060] The control unit 8 controls the power supplied to the light source 7, and thereby controls the light irradiated from the light source 7 to the hologram optical element 1.

[0061] The light receiving element 9 is an element, such as a photoelectric element or an image sensor, that converts light into a signal.

[0062] In FIG. 10, light emitted from the light source 7 via the hologram optical element 1 is irradiated onto the detected object. Then, the irradiated light is reflected off the detected object 10 and received by the light receiving element 9. This makes it possible to detect the detected object 10. That is, the present invention can be used as a sensor for detecting the detected object 10 (for example, a displacement sensor or a foreign body inspection sensor). In particular, in this embodiment, the light emitted from the light source 7 via the hologram optical element 1 can be focused onto the light receiving element 9 with a high NA, so that the detected object can be detected with high resolution.

[0063] (Other embodiments) The interference fringes recorded in the incident hologram 12 are not limited to the shape shown in Fig. 3. For example, the incident hologram 12 may have hexagonal interference fringes as shown in Fig. 11. In other words, as long as the incident light 2 can be magnified, the incident hologram 12 may have any type of interference fringes, and may have a curve, a combination of multiple straight lines, or a complex three-dimensional refractive index distribution.

[0064] In each of the above embodiments, the input hologram and the output hologram are not limited to a volume phase type hologram optical element. For example, the input hologram and the output hologram may be an embossed type hologram optical element, and any type of hologram optical element may be used as long as the hologram optical element 1 in each of the above embodiments can be realized. [Industrial Applicability]

[0065] The holographic optical element of the present disclosure can be applied to sensors, imaging devices, and the like. [Explanation of symbols]

[0066] 1 Holographic optical elements 2 Incident light 3. Emitted light 4. Propagation of light 5(5a,5b) Light control section 11,14 Transparent substrate 12, 12a, 12b Incident hologram (incident part) 12c Prism (entrance part, first prism) 13, 13a-13d Emitting hologram 14a Prism (Second Prism) 15a Absorbing member

Claims

1. A transparent substrate; an incident portion provided on the transparent substrate and configured to allow incident light to propagate within the transparent substrate; an emission hologram provided on the transparent substrate, the incidence portion diffracts the incident light in a direction away from an optical axis direction of the incident light, and emits the incident light such that the diffracted incident light is totally reflected within the transparent substrate, The exit hologram is a holographic optical element that diffracts light propagating within the transparent substrate so as to focus the light at a focusing point.

2. The holographic optical element according to claim 1 , wherein the entrance portion is an entrance hologram.

3. The holographic optical element according to claim 1 , wherein the entrance portion is a first prism provided on the transparent substrate.

4. The holographic optical element according to claim 1 , further comprising a light control unit that attenuates light propagating to an outer periphery within the transparent substrate.

5. 5. The holographic optical element according to claim 4, wherein the light control section is a black member provided on an outer periphery of the transparent substrate.

6. The light control unit is A second prism provided on the transparent substrate; The holographic optical element according to claim 4 , further comprising an absorbing member that absorbs the light reflected by the second prism to the outside of the transparent substrate.

7. A sensor comprising the hologram optical element according to any one of claims 1 to 6.

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