JP7398878B2 - Optical elements and light source devices - Google Patents

Description

The present invention relates to an optical element and a light source device, and more particularly to an optical element and a light source device using a diffraction grating.

2. Description of the Related Art Conventionally, an instrument panel that displays illuminated icons has been used as a device for displaying various information in a vehicle. Additionally, as the amount of information to be displayed increases, it has also been proposed to embed an image display device in the instrument panel or to configure the entire instrument panel with an image display device.

However, since the instrument panel is located below the vehicle's windshield, in order for the driver to visually check the information displayed on the instrument panel, the driver must move his/her line of sight downwards while driving, which is not desirable for safety reasons. do not have. Therefore, a head-up display (hereinafter referred to as HUD) that projects an image onto the windshield so that the driver can read information when looking ahead of the vehicle has also been proposed (for example, Patent Document 1). Furthermore, sensor technology that measures inter-vehicle distance and detects obstacles by emitting and receiving laser light is also being developed for autonomous vehicle driving and driving assistance technology.

These head-up displays and sensors use optical elements such as lenses to irradiate a wide range with laser light. However, optical systems that use lenses require the combination of multiple lenses or a large lens diameter in order to irradiate a wide area with laser light, making it difficult to downsize the light source device. .

In order to solve these problems, a technique has been proposed in which a diffraction grating is used instead of an optical lens to expand the irradiation range of laser light. FIG. 3 is a schematic diagram showing an outline of a light source device using a conventional diffraction grating. As shown in FIG. 3, the conventional light source device includes a light guide section 1, a diffraction grating section 2, and a light source section 4. The light emitted from the light source section 4 enters the back side of the light guide section 1, passes through the inside of the light guide section 1 at an irradiation angle of Φ ₀ , and reaches the diffraction grating section 2 formed on the light guide section 1. do. In the diffraction grating section 2, the light is diffracted according to diffraction conditions and irradiated to the outside at an irradiation angle _Φ1 . By appropriately designing the wavelength of the light irradiated from the light source section 4 and the pitch of the diffraction grating section 2, it is possible to make the irradiation angle Φ ₁ of the emitted light larger than the irradiation angle Φ ₀ within the light guide section 1. can.

Japanese Patent Application Publication No. 2018-118669

However, in the conventional light source device shown in FIG. 3, since the irradiation angle Φ ₁ of the light irradiated to the outside is determined only by the pitch of the diffraction grating section 2, there is a limit to the expansion of the light irradiation range.

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned conventional problems, and it is an object of the present invention to provide an optical element and a light source device that are small, lightweight, and capable of expanding the range of light irradiation.

In order to solve the above problems, an optical element of the present invention includes a light guide section having a light entrance surface into which light enters, a light extraction surface through which the light reaches, and a light transmitting section provided on the light extraction surface. A transmission-type diffraction grating portion having a volume phase holographic grating of a type, a convex portion and a concave portion, and a side opposite to the side having the convex portion and the concave portion is provided in contact with the volume phase holographic grating. It is characterized by being prepared.

In such an optical element of the present invention, a multiple diffraction grating is configured by a combination of a volume phase holographic grating and a diffraction grating section. This allows the volume phase holographic grating to expand the light irradiation angle, and the diffraction grating section to further expand the light irradiation angle, making it possible to expand the light irradiation range with a small size and light weight.

Further, in one aspect of the present invention, the volume phase holographic grating has a periodic structure of refractive index formed inside a gelatin layer.

Further, in one aspect of the present invention, the diffraction grating section is made of a dielectric film.

Further, the image display device of the present invention includes any one of the optical elements described above and a light source section that irradiates the light onto the light incidence surface, and irradiates a part of the light from the diffraction grating section to the outside. It is characterized by

Further, in one aspect of the present invention, the light source section is an optical phased array in which a plurality of light emitting sections are two-dimensionally arranged.

According to the present invention, it is possible to provide an optical element and a light source device that are small and lightweight and can expand the range of light irradiation.

FIG. 2 is a schematic perspective view showing the structure of an optical element in the first embodiment. FIG. 1 is a schematic cross-sectional view showing the configuration and optical path of a light source device 10 using optical elements. 1 is a schematic diagram showing an outline of a light source device using a conventional diffraction grating.

(First embodiment)
Embodiments of the present invention will be described in detail below with reference to the drawings. Identical or equivalent constituent elements, members, and processes shown in each drawing are denoted by the same reference numerals, and redundant explanations will be omitted as appropriate. Note that the drawings schematically show the structures of the optical element and the light source device, and the dimensions and angles in the drawings do not indicate the actual dimensions of the optical element and the light source device 10.

FIG. 1 is a schematic perspective view showing the structure of an optical element in this embodiment. As shown in FIG. 1, the optical element includes a light guide section 11, a diffraction grating section 12, and volume phase holographic gratings (VPHG) 13.

The light guide portion 11 is a substantially plate-shaped portion made of a material that transmits light, and includes a light entrance surface 11a and a light extraction surface 11b. The size of the light guide section 11 is not limited, but may be, for example, about 10 mm wide and 3 mm thick. Although the material constituting the light guide section 11 is not limited, it is preferable to use, for example, glass containing SiO ₂ as a main component and having a refractive index of about 1.5. The light entrance surface 11a is a flat surface onto which light from a light source placed outside the optical element enters, and faces the light extraction surface 11b. The light extraction surface 11b is a flat surface on which the volume phase holographic grating 13 is formed, and faces the light incidence surface 11a.

The diffraction grating portion 12 is a substantially plate-shaped portion formed on the volume phase holographic grating 13, and a plurality of convex portions 12a and concave portions 12b are periodically formed on the surface to constitute a diffraction grating. .

Although FIG. 1 shows an example in which the convex portions 12a and concave portions 12b of the diffraction grating portion 12 are formed by extending in parallel stripes, the convex portions 12a and concave portions 12b may be arranged two-dimensionally, without being limited to stripes. You can also use it as Further, in FIG. 1, the convex portions 12a and concave portions 12b of the diffraction grating portion 12 are shown as having rectangular cross sections, but the cross-sectional shapes are not limited and may be slanted gratings or blazed gratings.

Although the material constituting the diffraction grating section 12 is not limited, it is preferable to use a dielectric material having a large refractive index difference with the volume phase holographic grating ₁₃ . Preferably, a dielectric material is used. Although the size of the diffraction grating section 12 is not particularly limited, it is preferable that it has a thickness that allows light to be guided also in the in-plane direction. The diffraction grating section 12 can be formed by a known method, for example, nanoimprint technology, EBL (Electron Beam Lithography) technology, etc. can be used.

The volume phase holographic grating 13 is a layer formed on the light extraction surface 11b of the light guide section 11, and has a three-dimensional periodic structure 13a having a refractive index therein. A diffraction grating section 12 is formed on the surface of the volume phase holographic grating 13. The material constituting the volume phase holographic grating 13 is not particularly limited, but it is preferable to use a photosensitive material, and for example, a known material such as dichromate gelatin can be used.

Although the thickness of the volume phase holographic grating 13 is not limited, it is preferably about 10 to 30 μm. This means that when the production wavelength of the volume phase holographic grating 13 is λ, the thickness is t, the angle between two light beams in the hologram is θ, and the refractive index is n, the wavelength selection range of the regenerated light is This is because Δλ=λ ² /nt (1−cosθ). For example, in order to reduce the wavelength selection range of the regenerated light to about Δλ=20 nm, t=about 24 μm is suitable under the conditions of λ=532 nm, n=1.5, and θ=90°.

An example of a method for manufacturing the optical element shown in FIG. 1 will be described. First, a plate-shaped light guide 11 is prepared in a substrate preparation process, and then a gelatin film is applied on the light guide 11 in a deposition process, and then immersed in an ammonium dichromate aqueous solution to form a dichromate gelatin film. . Next, in a lithography process, a three-dimensional refractive index periodic structure 13a is exposed inside the dichromate gelatin film using a known interference lithography technique, thereby forming a volume phase holographic grating 13.

Next, in a dielectric formation process, _{a two-} layer TiO layer is formed by vapor deposition or the like on the volume phase holographic grating 13, and then, in a diffraction grating formation process, convex portions 12a and concave portions 12b are formed on the surface of the TiO _two layer using EBL technology. Then, the diffraction grating section 12 is formed. Finally, the optical element of this embodiment can be obtained by cutting into a predetermined size in a dicing process. Although not shown in FIG. 1, if necessary, a protective film such as glass may be formed on the side surface of the optical element to seal the side surface of the volume phase holographic grating 13.

FIG. 2 is a schematic cross-sectional view showing the configuration and optical path of the light source device 10 using optical elements. As shown in FIG. 2, in the light source device 10 of this embodiment, light is irradiated from the light source section 14 onto the light incident surface 11a of the optical element shown in FIG. The light source section 14 is not limited as long as it is a light source that emits coherent light of a predetermined wavelength, but an optical phased array (OPA) in which a plurality of light emitting sections that emit laser light are two-dimensionally arranged is used. It is preferable.

As shown in FIG. 2, the laser light emitted from the light source section 14 is incident approximately perpendicularly to the light incident surface 11a of the light guide section 11, travels inside the light guide section 11 at an irradiation angle Φ ₀ , and the laser light is emitted from the light source section 14. It reaches the extraction surface 11b. The light that has reached the light extraction surface 11b is transmitted through the volume phase holographic grating 13 and the diffraction grating section 12, and is irradiated to the outside at an irradiation angle _Φ2 . At this time, the laser beam is diffracted by the periodic structure 13a of refractive index within the volume phase holographic grating 13, and then further diffracted by the diffraction grating section 12. Thereby, the irradiation angle Φ ₂ can be expanded compared to the case where the diffraction grating section 12 or the volume phase holographic grating 13 is used alone.

As shown in FIG. 2, the light that passes through the diffraction grating section 12 is the light that has been diffracted by the volume phase holographic grating 13. It is necessary to design the convex portion 12a and the concave portion 12b. Further, the angle at which the laser light emitted from the light source section 14 enters the light guide section 11 needs to be suitable for the diffraction conditions of the diffraction grating section 12 and the volume phase holographic grating 13.

In the optical element and light source device 10 of this embodiment, a multiple diffraction grating is configured by combining the diffraction grating section 12 and the volume phase holographic grating 13, so it is better to expand the irradiation angle using an optical lens or mirror. It is also possible to reduce the size and weight. Furthermore, by using the diffraction grating section 12 and the volume phase holographic grating 13, it is possible to expand the light irradiation range without setting the focal length of the optical element and the light source section 14, and the degree of freedom in design is improved. .

In the optical element according to the present invention, instead of forming the diffraction grating section 12 on the volume phase holographic grating 13, it is also possible to form an additional volume phase holographic grating layer. However, when forming an additional volume phase holographic grating layer on top of the volume phase holographic grating 13, an air gap may occur between the two layers, which may deteriorate optical properties.

On the other hand, in the optical element and light source device 10 of the present embodiment, a dielectric material is vapor-deposited on the volume phase holographic grating 13 to form the diffraction grating section 12, so that air gaps are prevented from forming at the interface. Deterioration of characteristics can be suppressed. In addition, forming the volume phase holographic grating 13 requires a large number of steps and manufacturing time, but by forming only one layer of the volume phase holographic grating 13 and combining it with the diffraction grating section 12, the manufacturing process can be reduced. It becomes possible to shorten the time.

Furthermore, since the diffraction grating section 12 made of a dielectric material is formed on the upper surface of the volume phase holographic grating 13 made of a material such as gelatin, contact between the volume phase holographic grating 13 and air is prevented. can be protected. Here, it is more preferable to form a protective film such as glass on the side surface of the optical element because the volume phase holographic grating 13 can be sealed by the diffraction grating section 12 and the protective film.

Further, as described above, the diffraction grating section 12 is not limited to the convex portions 12a and the concave portions 12b having a rectangular cross section, but it is also possible to use a slanted grating, a blazed grating, or a two-dimensional diffraction grating. This improves the degree of freedom in optical design of the diffraction grating section 12, and also makes it easy to adjust the optical characteristics of the optical element and the light source device 10.

As described above, the optical element and light source device 10 of this embodiment are smaller and lighter than using mirrors or optical lenses, and can expand the light irradiation range.

(Second embodiment)
Next, a second embodiment of the present invention will be described. Description of contents that overlap with those of the first embodiment will be omitted. Although FIG. 1 shows an example in which the light incident from the light source section 14 travels within the light guide section 11 at an irradiation angle Φ ₀ , the laser light from the light source section 14 is collimated by a lens or the like and enters the light entrance surface 11a. You may also let them do so. In this case, the irradiation angle Φ ₀ =0 degree.

By collimating the light incident on the light guide section 11, the area of the optical phased array used in the light source section 14 can be made comparable to that of the optical element, and the light intensity per unit area can be increased.

(Third embodiment)
Next, a third embodiment of the present invention will be described. Description of contents that overlap with those of the first embodiment will be omitted. In the first embodiment, an example was shown in which the back surface side of the light guide section 11 was used as the light incidence surface 11a, and the laser light was incident approximately perpendicularly to the light incidence surface 11a. The light may be irradiated onto the light incident surface 11a. In this case, the refractive index periodic structure 13a formed inside the volume phase holographic grating 13 and the convex portions 12a and concave portions 12b formed in the diffraction grating portion 12 need to be designed appropriately according to the incident angle. There is.

In addition, in FIG. 1, the back surface side of the light guide section 11 is the light entrance surface 11a, but the side surface is the light entrance surface 11a, and the laser beam is made to reach the light extraction surface 11b at an incident angle inclined at a predetermined angle. Good too.

The present invention is not limited to the embodiments described above, and various modifications can be made within the scope of the claims, and embodiments obtained by appropriately combining technical means disclosed in different embodiments. are also included within the technical scope of the present invention.

DESCRIPTION OF SYMBOLS 10... Light source device 11... Light guide part 11a... Light incidence surface 11b... Light extraction surface 12... Diffraction grating part 12a... Convex part 12b... Concave part 13... Volume phase holographic grating 13a... Periodic structure of refractive index 14... Light source part

Claims (5)

a light guiding section having a light incident surface through which light enters and a light extraction surface through which the light reaches;
a transmission type volume phase holographic grating provided on the light extraction surface;
1. An optical element comprising a transmission type diffraction grating portion having a convex portion and a concave portion, and a side opposite to the side having the convex portion and the concave portion is provided in contact with the volume phase holographic grating. The optical element according to claim 1,
An optical element characterized in that the volume phase holographic grating has a periodic structure of refractive index formed inside a gelatin layer. The optical element according to claim 1 or 2,
An optical element, wherein the diffraction grating section is made of a dielectric film. The optical element according to any one of claims 1 to 3,
comprising a light source unit that irradiates the light onto the light incidence surface,
A light source device characterized in that a part of the light is irradiated to the outside from the diffraction grating section. The light source device according to claim 4,
The light source device is characterized in that the light source section is an optical phased array in which a plurality of light emitting sections are two-dimensionally arranged.