JP2015102613A - Optical device and display device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an optical device capable of displaying a high-quality image with a simple configuration.SOLUTION: The optical device includes: a light guide body 20 having a light-exiting part 22; a diffraction optical element 30 for extracting at least a part of light guided by the light guide body 20, from the light-exiting part 22 of the light guide body 20 by diffracting at least a part of the light guided by the light guide body 20; and a wavelength selecting part 40 for selectively transmitting light at a predetermined wavelength. The light guided by the light guide body includes light at a first wavelength and light at a second wavelength; the diffraction optical element 30 includes a first diffraction region having diffraction characteristics corresponding to the first wavelength and a second diffraction region having diffraction characteristics corresponding to the second wavelength; and the wavelength selecting part 40 includes a first wavelength selection region which is disposed at a position corresponding to the first diffraction region and selectively transmits light at the first wavelength, and a second wavelength selection region which is disposed at a position corresponding to the second diffraction region and which selectively transmits light at the second wavelength.

Description

  The present invention relates to an optical device and a display device.

In recent years, a head-mounted display that guides and displays an image from an image display device as one of image projection devices in front of an observer's eyes using an optical device having a light guide plate has been commercialized, and further miniaturization, Development related to wide angle of view and high efficiency is underway. In such an optical device, it has been conventionally proposed to use a diffractive optical element as a configuration for causing light to enter the light guide plate or to emit light that is guided through the light guide plate.
By the way, since the diffraction characteristic of the diffractive optical element has a large wavelength dependence, the color unevenness of the observed virtual image may increase. Accordingly, a plurality of diffractive optical elements having diffraction characteristics corresponding to each of a plurality of colors (for example, red, green, and blue) included in the light guided by the light guide plate are provided corresponding to the plurality of colors. Thus, countermeasures such as reducing the efficiency difference for each color due to the wavelength dependency of the diffraction efficiency are taken (for example, Patent Document 1).

Special table 2009-186794 gazette

  However, in the prior art described in Patent Document 1, the light guiding light in the light guide plate is included in each of the structure for causing light to enter the light guide plate and the structure for emitting light from the light guide plate. Since it is necessary to provide a plurality of diffractive optical elements corresponding to a plurality of colors, the structure of the optical device becomes complicated, and as a result, the manufacturing cost of the image projection apparatus increases. In addition, when a plurality of diffractive optical elements corresponding to a plurality of colors are provided, light diffracted by the diffractive optical element corresponding to one color enters the diffractive optical element corresponding to the other color, and is thus output. In some cases, the quality of the image represented by the light is reduced.

  The present invention has been made in view of the above-described circumstances, and one of its purposes is to provide an optical device that can be used in an image projection apparatus and can display a high-quality image with a simple configuration. This is the solution issue.

  In order to solve the above problems, a first aspect of the optical device according to the present invention is to diffract at least a part of light guided by the light guide and the light guide. A diffractive optical element that extracts at least part of the light guided by the light guide from the light emitting part of the light guide, and a wavelength selection unit that selects and transmits light of a predetermined wavelength, The light guided by the light guide includes light having a first wavelength and light having a second wavelength different from the first wavelength, and the diffractive optical element has the first wavelength. A first diffraction region having a diffraction characteristic higher than that of light of the second wavelength; and a diffraction efficiency of light of the second wavelength is higher than that of light of the second wavelength. A second diffraction region having high diffraction characteristics, wherein the wavelength selection unit is perpendicular to the light emitting unit of the light guide. In a plan view as viewed from above, provided at a position overlapping the first diffraction area, provided at a position overlapping the second diffraction area, and a first wavelength selection area for selectively transmitting light of the first wavelength. And a second wavelength selection region for selecting and transmitting the light of the second wavelength.

According to the first aspect of the optical device according to the present invention described above, the light of the first wavelength guided by the light guide by the single diffractive optical element having the first diffractive region and the second diffractive region. And the second wavelength of light can be extracted. Therefore, the optical device has a diffractive optical element having a diffractive characteristic corresponding to light of the first wavelength and a diffractive optical element having a diffractive characteristic corresponding to light of the second wavelength separately. The structure of the optical device can be simplified.
In the case where a diffractive optical element having diffraction characteristics corresponding to light of the first wavelength and a diffractive optical element having diffraction characteristics corresponding to light of the second wavelength are provided separately, one diffractive optical element is provided. The light diffracted by the above may be diffracted again by the other diffractive optical element, causing light scattering and the like, which may reduce the display quality of the display device using the optical device. On the other hand, according to the first aspect of the optical device according to the present invention, since only a single diffractive optical element is provided in the light emitting portion, light is diffracted multiple times by a plurality of diffraction gratings. Deterioration of display quality can be prevented.
Further, when the diffractive optical element having the diffraction characteristic corresponding to the light of the first wavelength and the diffractive optical element having the diffraction characteristic corresponding to the light of the second wavelength are separately provided, the light of the first wavelength is changed. It may be necessary to separately provide a light guide that guides light and a light guide that guides the second light, which makes it difficult to reduce the size and weight of the optical device. On the other hand, according to the first aspect of the optical device of the present invention, it is possible to guide the light of the first wavelength and the light of the second wavelength by a single light guide. Therefore, the optical device can be reduced in size and weight.

In the first aspect of the optical device according to the present invention described above, it is preferable that the light guide includes a light incident portion that allows light to enter the light guide by geometric optical means. .
In this case, since geometrical optical means is used as means for making light incident on the light guide, the light utilization efficiency is higher than when a diffractive optical element is used as means for making light incident on the light guide. can do. The “geometric optical means” is, for example, any means that changes the traveling direction of light using at least one of light refraction and reflection, such as a prism, a lens, and a mirror. May be.

1st aspect of the optical device which concerns on this invention mentioned above WHEREIN: The said 1st light guide is provided with one said light guide, The said 1st wavelength and said 2nd wavelength are The diffractive optical element includes light having a third wavelength different from each other, and the diffraction efficiency of the light having the third wavelength is higher than the diffraction efficiency of the light having the first wavelength and the diffraction efficiency of the light having the second wavelength. A third diffraction region having high diffraction characteristics, and the wavelength selection unit is provided at a position overlapping the third diffraction region in a plan view viewed from a direction perpendicular to the light emitting unit of the light guide. It is preferable that a third wavelength selection region for selecting and transmitting the light of the third wavelength is provided.
In this case, since the light of the first wavelength, the light of the second wavelength, and the light of the third wavelength are guided by a single light guide, the optical device has a plurality of light guides. The optical device can be reduced in size and weight as compared with the case where it is provided. In this case, the first wavelength light, the second wavelength light, and the third wavelength light guided by one light guide are extracted by a single diffractive optical element. Therefore, the structure of the optical device can be simplified as compared with the case where a plurality of diffractive optical elements are provided. In this case, since the optical device is provided with only a single diffractive optical element, the occurrence of an event that causes deterioration in display quality, such as light being diffracted multiple times by a plurality of diffractive optical elements, is suppressed. can do.

In the first aspect of the optical device according to the present invention described above, it is preferable that the diffractive optical element is a light transmissive diffractive optical element.
In this case, the distance between the observer of the display device equipped with the optical device and the diffractive optical element can be shortened as compared with the case of using a reflective diffractive optical element. Therefore, it is possible to reduce the possibility that light other than the light is visually recognized by the observer, and display with high quality is possible.

In the first aspect of the optical device according to the present invention described above, it is preferable that the diffractive optical element is a surface relief type diffractive optical element in which an uneven structure is provided on one surface.
In this case, the diffractive optical element can be integrally formed on the surface of the light guide by etching or the like, which facilitates manufacture.

1st aspect of the optical device which concerns on this invention mentioned above WHEREIN: The height of the convex part of the said uneven structure is provided so that it may become equal over the said whole diffractive optical element, It is characterized by the above-mentioned. preferable.
In this case, since it is not necessary to change the height of the convex portion depending on the position of the diffractive optical element, the manufacture is facilitated. Note that “provided so that the heights of the convex portions are equal” means that the heights are provided so that they are strictly equal, and the design is the same but includes manufacturing errors. Including both.

1st aspect of the optical device which concerns on this invention mentioned above WHEREIN: The height of the convex part of the said uneven structure provided in the said 1st diffraction area is defined based on the said 1st wavelength, The said 2nd diffraction area It is preferable that the height of the convex portion of the concavo-convex structure provided in is determined based on the second wavelength.
In this case, the utilization efficiency of light having the first wavelength and the utilization efficiency of light having the second wavelength can be made uniform, and the display quality of the display device using the optical device can be improved. It becomes.

1st aspect of the optical device which concerns on this invention mentioned above WHEREIN: The direction where the convex part of the said concavo-convex structure provided in the said 1st diffraction area is extended is the convex part of the said concavo-convex structure provided in the said 2nd diffraction area It is preferable that it is provided so that it may become the same direction as the extending direction.
In this case, since the traveling direction of the light of the first wavelength and the traveling direction of the light of the second wavelength after being taken out from the light guide can be made substantially the same direction, the display quality is increased. Can do. In this case, “provided to be in the same direction” means that the directions are completely the same, and the case where the design is the same but includes manufacturing errors. This is a concept that includes

1st aspect of the optical device which concerns on this invention mentioned above WHEREIN: The said wavelength selection part is provided between the said diffractive optical element and the said light-projection part of the said light guide, It is characterized by the above-mentioned. Is preferred.
In this case, since only light having a wavelength corresponding to the diffraction characteristics of the diffractive optical element can be incident on the diffractive optical element, the occurrence of events such as light scattering can be suppressed and display quality can be improved. it can.

1st aspect of the optical device which concerns on this invention mentioned above WHEREIN: The said diffractive optical element is provided in the surface of the said light guide, The said wavelength selection part sandwiches the said diffractive optical element, and the said light guide It is preferable that it is provided on the opposite side of the light emitting portion.
In this case, since the diffractive optical element can be integrally formed on the surface of the light guide by etching or the like, manufacturing is easy. In this case, since the diffractive optical element is formed on the surface of the light guide, the flatness of the diffractive optical element is improved, so that the display quality can be improved. Furthermore, in this case, since the wavelength selection unit functions as a protective cover for the diffractive optical element, the degree of deterioration of the diffractive optical element can be reduced.

In the first aspect of the optical device according to the present invention described above, it is preferable that the wavelength selection unit is a wavelength selective absorption type or wavelength selective reflection type color filter.
In this case, since only light having a wavelength corresponding to the diffraction characteristic of the diffractive optical element can be incident on the diffractive optical element, the display quality of the display device using the optical device can be improved.

In the first aspect of the optical device according to the present invention described above, the pitch of the plurality of diffraction regions including the first diffraction region, the second diffraction region, and the third diffraction region is determined by the diffraction optical element. The pupil diameter of the exit-side optical system that controls the optical path of the light extracted from the light guide is less than or equal to the length divided by the number of types of wavelengths of light guided by the light guide. It is preferable that
In this case, it is possible to prevent the occurrence of an event that some of the lights having different wavelengths guided by the light guide are not visually recognized by the observer.

  Next, a display device according to the present invention includes the above-described optical device according to the present invention and an image forming unit that emits image light. Such an image display device may include an image forming unit such as a liquid crystal display and a collimating optical system, and can be adapted to a form mounted on the observer's head such as a head-mounted display. In the image display device according to the present invention, the “image forming unit” is, for example, an image display device such as a liquid crystal display that displays an image or a laser scanning display that allows an observer to recognize an image by scanning with laser light. And an optical system for collecting and converting image light emitted from the image display.

It is a perspective view which shows an example of the whole image of the head mounted display which concerns on 1st Embodiment of this invention. It is principal part sectional drawing which shows an example of the optical system and optical device for left eyes of the head mounted display which concern on 1st Embodiment. It is a top view which shows the wavelength selection part which concerns on 1st Embodiment. It is explanatory drawing for demonstrating the structure of the diffractive optical element which concerns on 1st Embodiment. It is principal part sectional drawing which shows an example of the optical device of the head mounted display which concerns on 2nd Embodiment of this invention. It is principal part sectional drawing which shows an example of the optical system for left eyes and an optical device of the head mounted display which concerns on 3rd Embodiment of this invention. It is a top view which shows the diffractive optical element which concerns on the modification 1 of this invention. It is principal part sectional drawing which shows an example of the optical system for left eyes and an optical device of the head mounted display which concerns on the modification 2 of this invention. It is explanatory drawing for demonstrating the structure of the diffractive optical element which concerns on the modification 3 of this invention. It is explanatory drawing for demonstrating the structure of the diffractive optical element which concerns on the modification 4 of this invention.

  Hereinafter, various embodiments according to the present invention will be described with reference to the accompanying drawings. In the drawings, the ratio of dimensions of each part is appropriately changed from the actual one. In the embodiment described below, the optical device of the present invention is described as an example applied to a head-mounted display that is an example of an image display device that is mounted on the head of an observer. The embodiment shows one embodiment of the present invention, and does not limit the present invention, and can be arbitrarily changed within the scope of the technical idea of the present invention.

<A. First Embodiment>
Hereinafter, the head mounted display 100 according to the first embodiment will be described with reference to FIGS. 1 and 4.

  FIG. 1 is an example of a perspective view showing an overall image of a head mounted display 100 according to the first embodiment. As shown in FIG. 1, the head mounted display 100 according to the present embodiment is a head mounted display having an appearance like glasses, and recognizes image light based on a virtual image for an observer wearing the head mounted display 100. It is possible to cause the observer to observe the outside world image with see-through.

  Specifically, the head mounted display 100 includes a light guide 20, a pair of left and right temples 101 and 102 that support the light guide 20, and a pair of image forming apparatuses 111 and 112 attached to the temples 101 and 102. . Here, in the drawing, the display device 100A in which the left side of the light guide 20 and the image forming device 111 are combined is a portion that forms a virtual image for the left eye, and functions alone as an image display device. In the drawing, the display device 100B that combines the right side and the image forming apparatus 112 with the light guide 20 is a portion that forms a virtual image for the right eye, and functions alone as an image display apparatus.

Next, the internal structure of the head mounted display 100 will be described.
FIG. 2 is a main part sectional view schematically showing an example of the internal structure of the display device 100 </ b> A included in the head mounted display 100. As illustrated in FIG. 2, the display device 100 </ b> A includes an image forming unit 10, a light guide 20, a diffractive optical element 30, and a wavelength selection unit 40. Hereinafter, among these components, the light guide 20, the diffractive optical element 30, and the wavelength selection unit 40 may be referred to as “optical device 1”.
Although illustration is omitted, the internal structure of the display device 100B is a configuration in which the display device 100A shown in FIG.

As shown in FIG. 2, the image forming unit 10 is a main part of the image forming apparatus 111 (and the image forming apparatus 112), and includes an image display device 11 and a projection optical system 12.
The image display device 11 includes, for example, a liquid crystal panel and a light source that emits light of three colors of red light LR, green light LG, and blue light LB and illuminates the liquid crystal panel with these three colors of light. Consists of including.

  The liquid crystal panel provided in the image display device 11 includes a plurality of liquid crystal elements that correspond one-to-one with a plurality of pixels constituting an image to be displayed by the display device 100A (100B). Each liquid crystal element is controlled so that each pixel constituting the image displayed on the display device 100A (100B) has a transmittance corresponding to the gradation to be displayed. As a result, the image forming unit 10 emits light of a light amount corresponding to the gradation of each pixel of the image displayed on the display device 100 </ b> A (100 </ b> B) toward the projection optical system 12.

However, the present invention is not limited to such an embodiment, and the image forming unit 10 may irradiate light of three colors as follows, for example.
Specifically, a screen position may be specified by an angle using a MEMS (Micro Electro Mechanical Systems) laser scan mirror, and gradations may be expressed by modulation of three colors of laser light. Even in this case, the display device 100A (100B) according to the present embodiment displays only the color to be displayed because only the wavelength corresponding to the color to be displayed is transmitted by the wavelength selection unit 40 described later. can do.

  The projection optical system 12 is a collimating lens that converts the traveling directions of the three colors of light emitted from the image display device 11 so as to be parallel and enters the light guide 20.

The wavelength of red light LR is an example of “first wavelength”, the wavelength of green light LG is an example of “second wavelength”, and the wavelength of blue light LB is “third wavelength”. Is an example. That is, in the following, red light LR is illustrated as “light of the first wavelength”, green light LG is illustrated as “light of the second wavelength”, and blue light LB is illustrated as “light of the third wavelength”. An example will be described.
However, the present invention is not limited to such an embodiment, and the first wavelength, the second wavelength, and the third wavelength are different from each other and are included in the wavelength range of visible light. Any wavelength may be used as long as it is a wavelength.

The light guide 20 is composed of a single light guide plate which is a plate-like member formed of glass or a light transmissive resin material.
As illustrated in FIG. 2, the light guide 20 includes a light incident unit 21 that causes the three colors of light (LR, LG, and LB) emitted from the image forming unit 10 to enter the light guide 20, and in front of the observer's eyes. The light emitting unit 22 is positioned, and the light guide unit 23 is a portion between the light incident unit 21 and the light emitting unit 22.
The light guide 20 is provided on the image forming unit 10 side (the + Z side in FIG. 2) of the light guide 20 and extends over the light incident unit 21, the light guide unit 23, and the light emitting unit 22. An example of an inclined surface 211 (an example of “geometric optical means”) provided on the light incident portion 21 on the opposite side (the −Z side in FIG. 2) of the panel surface 201 and the light guide 20 to the image forming portion 10. And the panel surface 202 provided on the light guide 23 and the light emitting unit 22 on the side opposite to the image forming unit 10 of the light guide 20 (the −Z side in FIG. 2).

The three colors of light emitted from the image forming unit 10 are reflected by the inclined surface 211 in a predetermined direction. Then, the three colors of light reflected by the inclined surface 211 are totally reflected by the panel surface 201 and the panel surface 202 in the light guide unit 23 and guided to the light emitting unit 22.
In the light guide 23, the panel surface 201 and the panel surface 202 may be provided with a reflective coat made of a metal film or the like. In this embodiment, the inclined surface 211 is employed as the geometric optical means. However, this is merely an example of the geometric optical means, and the light travels using the action of light refraction and reflection. What can change a method, for example, a prism, a lens, a mirror, etc., may be adopted as appropriate.

As shown in FIG. 2, the light emitting unit 22 selects light of three types of wavelengths corresponding to the three colors of light (LR, LG, LB) guided by the light guide 20 on the panel surface 201. A wavelength selection unit 40 that transmits light is provided.
The wavelength selection unit 40 is a wavelength selective absorption type or wavelength selective reflection type color filter, and includes a plurality of wavelength selection regions 40R (an example of “first wavelength selection region”) that selectively transmits the red light LR, and green. A plurality of wavelength selection regions 40G that selectively transmit light LG (an example of “second wavelength selection region”) and a plurality of wavelength selection regions 40B that selectively transmit green light LG (“third wavelength selection region”). (In FIG. 2, one each is shown for convenience of illustration).

  FIG. 3 is a plan view of the wavelength selection unit 40 provided on the panel surface 201 of the light emitting unit 22 as viewed from the + Z direction. As shown in this figure, the wavelength selection unit 40 includes a plurality of wavelength selection regions 40R, 40G, and 40B arranged in a matrix (Bayer arrangement) in a plurality of rows in the X direction and in a plurality of columns in the Y direction. Become. More specifically, in the wavelength selection unit 40 according to the present embodiment, the wavelength selection regions 40R, 40G, and 40B are repeatedly arranged in the + X direction, and the wavelength selection regions 40R, 40G, and , 40B are repeatedly arranged.

Returning to FIG. As shown in FIG. 2, the diffractive optical element 30 is provided on the + Z side of the wavelength selection unit 40. The diffractive optical element 30 is a surface relief type transmissive diffraction grating made of a light transmissive material, and is provided on the wavelength selection unit 40 by, for example, photoetching.
This diffractive optical element 30 diffracts the red light LR guided by the light guide unit 23 and then transmitted through the wavelength selection region 40R in the + Z direction and projects it to the observer's eye Ey (“the first diffraction region 30R”). 1 example) and a plurality of diffraction regions 30G (that are diffracted in the + Z direction and projected onto the observer's eye Ey after being guided by the light guide 23 and then transmitted through the wavelength selection region 40G). An example of a “second diffraction region”) and a plurality of diffraction regions that are diffracted in the + Z direction and projected onto the observer's eye Ey after being guided by the light guide 23 and transmitted through the wavelength selection region 40B 30B (an example of a “third diffraction region”).
As shown in FIG. 3, each diffraction region 30R is provided on the + Z side (front side of the paper) of each wavelength selection region 40R, and each diffraction region 30G is provided on the + Z side of each wavelength selection region 40G. The region 30B is provided on the + Z side of each wavelength selection region 40B. That is, the light transmitted through the wavelength selection unit 40 enters the diffractive optical element 30. Therefore, only the red light LR transmitted through the wavelength selection region 40R is incident on the diffraction region 30R, only the green light LG transmitted through the wavelength selection region 40G is incident on the diffraction region 30G, and the wavelength selection is performed on the diffraction region 30B. Only the blue light LB transmitted through the region 40B is incident.

  In the present embodiment, the diffraction regions 30R, 30G, and 30B (or the wavelength selection regions 40R, 40G, and 40B) are arranged at equal intervals. That is, the width dPx in the X direction of each wavelength selection region 40R, 40G, 40B and each diffraction region 30R, 30G, 30B is equal for each color, and the width dPy in the Y direction is equal for each color. In the present embodiment, the diffractive optical element 30 includes the same number of diffraction regions 30R, 30G, and 30B, and the wavelength selection unit 40 includes the same number of wavelength selection regions 40R, 40G, and 40B. For this reason, in this embodiment, the area ratio of the diffraction regions 30R, 30G, and 30B included in the red light LR diffractive optical element 30 among the diffractive optical elements 30 is 1: 1: 1.

  In general, the human pupil diameter dE varies in the range of 2 mm to 7 mm depending on the brightness of the surroundings. As in the case where the light projected from the diffractive optical element 30 is directly projected onto the observer's eye Ey, when the emission side optical system is a human eye, at least one diffractive region of one color enters the pupil. Otherwise, all colors cannot be detected. Therefore, when the light emitted from the image forming unit 10 has three colors, the head mounted display 100 is assumed to be used in an environment with a brightness such that the human pupil diameter dE is 3 mm, for example. The width dPx and the width dPy must be 1 mm or less. In this case, the thickness is preferably about 0.75 mm in order to suppress the occurrence of color unevenness. Note that if the width dPx and the width dPy are too small, diffraction or scattering occurs due to the period and the resolution is lowered. For example, if the width is smaller than 0.2 mm, the display quality deteriorates and is not preferable. The width dPy is preferably 0.2 mm or more.

FIG. 4 is an explanatory diagram for explaining the structure of the diffractive optical element 30 provided on the wavelength selector 40.
Among these, FIG. 4A shows three wavelength selection regions 40R, 40G, and 40B represented in the region Ar shown in FIG. 3, and three diffractions provided on the + Z side of these wavelength selection regions. It is the top view showing area | region 30R, 30G, and 30B. FIG. 4B is a partial cross-sectional view in which the diffractive optical element 30 and the wavelength selection unit 40 are broken along the line Ee in FIG.

As shown in FIGS. 4A and 4B, the diffraction region 30R is provided with a concavo-convex structure in which convex portions 31R extending in the Y direction are repeatedly arranged at intervals dxR, and the diffraction region 30G has , A concavo-convex structure in which convex portions 31G extending in the Y direction are repeatedly arranged at intervals dxG is provided, and a concavo-convex structure in which the convex portions 31B extending in the Y direction are repeatedly arranged at intervals dxB is provided in the diffraction region 30B. Provided.
Here, the distance dxR is the distance between the reflection angle and the red light LR when the red light LR that has been guided by the light guide unit 23 and then transmitted through the wavelength selection region 40R is reflected in the + Z direction toward the eye Ey. The wavelength is set to a length that satisfies the Bragg condition. Similarly, the interval dxG and the interval dxB are set to such lengths that the green light LG and the blue light LB are reflected in the + Z direction toward the eye Ey. That is, the diffractive optical element 30 includes a diffraction region 30R in which the diffraction efficiency of the red light LR is higher than that of the green light LG or the blue light LB, and the diffraction efficiency of the green light LG is the red light LR or the blue light. A diffraction region 30G having a diffraction characteristic higher than that of LB and a diffraction region 30B having a diffraction efficiency higher than that of red light LR or green light LG are different from each other. It has three types of diffraction regions 30R, 30G, and 30B.
Since the relationship of “the wavelength of the red light LR> the wavelength of the green light LG> the wavelength of the blue light LB” is established among the red light LR, the green light LG, and the blue light LB, “dxR> dxG > DxB ”is established. Further, the depths in the Z direction of the convex portions 31R, 31G, and 31B in the concavo-convex structure of the diffractive optical element 30 are all set to a predetermined depth dZ.

As described above, in the present embodiment, in order to extract light of a plurality of colors (red light LR, green light LG, and blue light LB) from the light guide 20, diffraction regions 30R, 30G having different diffraction characteristics, And a single diffractive optical element 30 having 30B is utilized.
Conventionally, when extracting light of a plurality of colors from a light guide, it is necessary to use a plurality of diffractive optical elements corresponding to the light of a plurality of colors. For example, when red light LR, green light LG, and blue light LB are extracted from the light guide, a diffractive optical element having diffraction characteristics corresponding to the red light LR, and diffractive optics having diffraction characteristics corresponding to the green light LG. It was necessary to use three diffractive optical elements such as an element and a diffractive optical element having a diffraction characteristic corresponding to the blue light LB.
On the other hand, in the present embodiment, the diffraction region 30R having a diffraction characteristic corresponding to the red light LR, the diffraction region 30G having a diffraction characteristic corresponding to the green light LG, and the diffraction characteristic corresponding to the blue light LB are provided. By using a single diffractive optical element 30 including the diffractive region 30B, it is possible to extract light of a plurality of colors from the light guide. For this reason, in this embodiment, the structure of the head mounted display 100 can be simplified and the manufacturing cost can be reduced as compared with the case of using a plurality of diffractive optical elements as in the prior art.

Further, when a plurality of diffractive optical elements are used for extracting light of a plurality of colors from the light guide as in the prior art, in an optical device, a plurality of diffractive optical elements are provided so as to correspond to the plurality of diffractive optical elements. Providing a light guide is necessary from the viewpoint of reducing color unevenness or luminance unevenness of an image.
On the other hand, in the present embodiment, since a plurality of colors of light guided by the light guide 20 can be extracted by the single diffractive optical element 30, in the optical device 1, the single light guide 20 is used. It is not necessary to have a plurality of light guides. For this reason, in this embodiment, compared with the case where an optical device is provided with a some light guide, size reduction and weight reduction of the optical device 1, and also size reduction and weight reduction of the head mounted display 100 are attained. .

In addition, when a plurality of diffractive optical elements are used to extract light of a plurality of colors guided by a light guide plate as in the past, light diffracted by one diffractive optical element is incident on another diffractive optical element again. Diffracted again to cause light scattering and the like, causing problems such as degradation of image quality.
On the other hand, in the present embodiment, only the single diffractive optical element 30 is used to extract light from the light guide 20, so that the light diffracted by the diffractive optical element 30 is diffracted again by the diffractive optical element 30. Is unlikely to occur, and the possibility of image quality degradation due to light scattering or the like is low. For this reason, the display device 100A (100B) according to the present embodiment can display a high-quality image.

In the optical device 1 according to this embodiment, the wavelength selection unit 40 is provided between the diffractive optical element 30 and the light guide 20. That is, in the diffractive optical element 30, only the red light LR transmitted through the wavelength selection region 40R is incident on the diffraction region 30R, and only the green light LG transmitted through the wavelength selection region 40G is incident on the diffraction region 30G. Only the blue light LB transmitted through the wavelength selection region 40B is incident on the diffraction region 30B.
For this reason, it is possible to prevent light having a wavelength different from the wavelength that should be incident on each diffraction region from entering (that is, for example, red light LR in the diffraction region corresponding to the pixel that should display red). Therefore, it is possible to prevent deterioration in image quality due to light scattering or the like.

  In the present embodiment, an inclined surface 211 that is a geometric optical means is used as a means for making light incident on the light guide 20. The amount of light that decreases when light is reflected by geometric optical means is generally about 20%, whereas the amount of light that decreases when light is diffracted by a diffractive optical element is generally 70. %. For this reason, in the present embodiment, it is possible to greatly increase the light use efficiency as compared with the case of using a diffractive optical element as the incident means.

<B. Second Embodiment>
In the optical device 1 according to the first embodiment described above, the wavelength selection unit 40 is provided between the panel surface 201 of the light guide 20 and the diffractive optical element 30.
On the other hand, the optical device according to the second embodiment relates to the first embodiment in that the diffractive optical element 30 is provided between the panel surface 201 of the light guide 20 and the wavelength selection unit 40. Different from the optical device 1.
The optical device according to the second embodiment is the same as the optical device 1 according to the first embodiment except that the arrangement positions of the diffractive optical element 30 and the wavelength selection unit 40 are different from those of the optical device 1 according to the first embodiment. It is constituted similarly. Therefore, in the second embodiment exemplified below, elements that have the same functions and functions as those of the first embodiment are diverted using the reference numerals referred to in the above description, and the detailed descriptions thereof are appropriately omitted (hereinafter referred to as the following). The same applies to the embodiments and modifications described in the above.

FIG. 5 is a main part sectional view schematically showing an example of the optical device 1A provided in the head mounted display according to the second embodiment.
As shown in this figure, the optical device 1A includes a light guide 20, a diffractive optical element 30, a wavelength selection unit 40, and a transparent substrate 401. In the present embodiment, the diffractive optical element 30 is formed directly on the panel surface 201 of the light guide 20 by, for example, photoetching. Moreover, in this embodiment, the wavelength selection part 40 is formed on the transparent substrate 401 provided between the diffractive optical element 30 and the eyes Ey of the observer. In the present embodiment, the wavelength selection unit 40 is preferably a wavelength selective absorption type color filter.

In the optical device 1A according to the second embodiment, only the red light LR out of the light diffracted in the diffraction region 30R is projected to the eye Ey, and the light diffracted or transmitted in the diffraction region 30R other than the red light LR. The light (LG, LB) is absorbed by the wavelength selection region 40R. Similarly, among the light diffracted or transmitted in the diffraction region 30G, only the green light LG is projected to the eye Ey, and among the light diffracted or transmitted in the diffraction region 30B, only the blue light LB is projected to the eye Ey. For this reason, in each diffraction region, even when light having a wavelength different from the wavelength that should be incident is incident and the light is diffracted or transmitted, the light is projected onto the eye Ey of the observer. Therefore, it is possible to prevent deterioration in image quality.
In the optical device 1A according to the second embodiment, since the transparent substrate 401 has a function as a protective cover, the degree of deterioration of the diffractive optical element 30 can be suppressed to a low level.
Furthermore, in the optical device 1A according to the second embodiment, since the diffractive optical element 30 is directly formed on the panel surface 201, the display quality can be improved by improving the flatness of the diffractive optical element 30.

<C. Third Embodiment>
In the first embodiment and the second embodiment described above, light of three colors of red light LR, blue light LB, and green light LG is emitted from the image forming unit 10, and the light guide 20 emits light of these three colors. The light was guided.
On the other hand, in the third embodiment, the image forming unit performs light including a wavelength corresponding to the red light LR, a wavelength corresponding to the green light LG, and a wavelength corresponding to the blue light LB, for example, white light LW. And the light guide 20 is different from the above-described first and second embodiments in that the light guide 20 guides the white light LW.

FIG. 6 is a cross-sectional view of an essential part schematically illustrating an example of the internal structure of the display device included in the head mounted display according to the third embodiment. As shown in this figure, the display device according to the third embodiment is the same as the display device 100A (or 100B) according to the first embodiment, except that an image forming unit 10B is provided instead of the image forming unit 10. It is configured.
The image forming unit 10B is configured in the same manner as the image forming unit 10 except that the white light LW is emitted instead of the red light LR, the green light LG, and the blue light LB.

The white light LW emitted from the image forming unit 10B is guided by the light guide 20 and enters the wavelength selection regions 40R, 40G, and 40B included in the wavelength selection unit 40.
In the white light LW incident on the wavelength selection region 40R, wavelength components other than the wavelength corresponding to the red light LR are absorbed by the wavelength selection region 40R. For this reason, only the red light LR is emitted from the wavelength selection region 40R, and the red light LR enters the diffraction region 30R. The red light LR incident on the diffraction region 30R is diffracted by the diffraction region 30R and projected onto the eye Ey. Similarly, of the white light LW, the green light LG transmitted through the wavelength selection region 40G is diffracted by the diffraction region 30G and projected onto the eye Ey, and the blue light LB transmitted through the wavelength selection region 40B is diffracted by the diffraction region 30B. Is projected onto the eye Ey.

As described above, in this embodiment, the light guided by the light guide 20 is the white light LW, but only the light of the wavelength component corresponding to each pixel is selectively transmitted by the wavelength selection unit 40. . For this reason, it is possible to prevent light having a wavelength different from the wavelength that should originally be incident from entering each diffraction region, and display with high quality image quality is possible.
In the present embodiment, the image forming unit 10B or the light incident unit 21 does not need to separate light of three colors of red light LR, green light LG, and blue light LB, and simply guides the white light LW. Since it only needs to enter the body 20, the structure of the display device and the operation of the display device can be simplified.

<C. Modification>
Each of the above forms can be variously modified. Specific modifications are exemplified below. Two or more aspects arbitrarily selected from the following examples can be appropriately combined within a range that does not contradict each other.

<Modification 1>
In the embodiment described above, the area ratio of the diffraction regions 30R, 30G, and 30B included in the diffractive optical element 30 (that is, the area ratio of the wavelength selection regions 40R, 40G, and 40B) is 1: 1: 1. Is not limited to such an embodiment, and may have different areas.
In the embodiment described above, the number of diffraction regions 30R, 30G, and 30B included in the diffractive optical element 30 (that is, the number of wavelength selection regions 40R, 40G, and 40B) is equal to each other, but may be different from each other. . For example, as shown in FIG. 7, the diffractive optical element 30 may be provided so that the number of diffraction regions 30R, 30G, and 30B is 1: 2: 1.

<Modification 2>
In the embodiment and the modification described above, the light guide 20 takes in light into the light guide 20 by geometric optical means provided in the light incident portion 21. For example, the light may be captured by a diffractive optical element.
FIG. 8 is a main part sectional view schematically showing an example of the optical device 1C according to the present modification. As shown in this figure, the optical device 1C is the same as that of the first embodiment except that the optical device 1C includes a light guide 20C instead of the light guide 20 and a diffractive optical element 50 and a wavelength selection unit 60. The optical device 1 is configured in the same manner.
20 C of light guides are comprised similarly to the light guide 20 except the point provided with 21 C of light incident parts which have the panel surface 202 instead of the light incident part 21 which has the inclined surface 211. FIG. The diffractive optical element 50 includes diffractive regions 50R, 50G, and 50B having the same configuration as the diffractive regions 30R, 30G, and 30B (that is, the diffractive optical element 50 has the same configuration as the diffractive optical element 30). The wavelength selection unit 60 includes wavelength selection regions 60R, 60G, and 60B having the same configuration as the wavelength selection regions 40R, 40G, and 40B (that is, the wavelength selection unit 60 has the same configuration as the wavelength selection unit 40). .
According to such an optical device 1C, even if the image forming unit emits white light without separating the light into the red light LR, the green light LG, and the blue light LB in the image forming unit, for example. In the light incident portion 21C, the light can be taken into the light guide body after the light is separated into the red light LR, the green light LG, and the blue light LB.

<Modification 3>
In the embodiment and the modification described above, the side surfaces of the convex portions 31R, 31G, and 31B included in the diffractive optical element 30 are all provided so as to be horizontal in the Z direction. The present invention is limited to such an aspect. For example, as shown in FIG. 9, it may be provided so as to be inclined with respect to the Z direction. In this case, the light diffraction efficiency in the diffractive optical element 30 can be increased.

<Modification 4>
In the embodiment and the modification described above, in the diffractive optical element 30, the convex portions 31R, 31G, and 31B all have the same depth dZ, but the present invention is not limited to such an embodiment. As shown in FIG. 10, the depth may be different for each corresponding color. More specifically, the depth dZR of the convex portion 31R is determined based on the wavelength of the red light LR, the depth dZG of the convex portion 31G is determined based on the wavelength of the green light LG, and the depth dZB of the convex portion 31B is determined. It may be determined based on the wavelength of the blue light LB. For example, the depth dZ may be set to be deeper as the light diffraction efficiency of each color light is lower. For example, by increasing the light use efficiency of the green light LG with high visibility, The depth dZG may be made deeper than others so as to improve the brightness.

<Modification 5>
In the embodiment and the modification described above, the optical device guides three types of light, that is, light having the first wavelength, light having the second wavelength, and light having the third wavelength. The invention is not limited to such an embodiment, and may be any one that guides two or more types of light having different wavelengths.

<Modification 6>
In the embodiment and the modification described above, the diffractive optical element is a surface relief type, but may be a hologram diffraction grating. The diffractive optical element is a transmission type, but may be a reflection type.

DESCRIPTION OF SYMBOLS 1 ... Optical device, 10 ... Image formation part, 11 ... Image display apparatus, 12 ... Projection optical system, 20 ... Light guide, 21 ... Light incident part, 22 ... Light-emission part, 23 ... ... Light guiding part 201... Panel surface 202. Panel surface 211. Inclined surface 30. Diffractive optical element 30 R. Diffractive region 30 G. Diffractive region 30 B Diffractive region 40 ... wavelength selection section, 40R ... wavelength selection area, 40G ... wavelength selection area, 40B ... wavelength selection area, 100 ... head mounted display, 100A ... display device, 100B ... display device, 111 ... image formation Device, 112... Image forming device.

Claims (13)

A light guide provided with a light emitting portion;
A diffractive optical element that diffracts at least part of the light guided by the light guide to extract at least part of the light guided by the light guide from the light emitting portion of the light guide;
A wavelength selection unit that selects and transmits light of a predetermined wavelength;
Have
The light guided by the light guide is
Light of a first wavelength;
Light of a second wavelength different from the first wavelength;
Including
The diffractive optical element is
A first diffraction region having a diffraction characteristic in which the diffraction efficiency of the light of the first wavelength is higher than the diffraction efficiency of the light of the second wavelength;
A second diffraction region having a diffraction characteristic in which the diffraction efficiency of the light of the second wavelength is higher than the diffraction efficiency of the light of the first wavelength;
With
The wavelength selector is
In a plan view seen from a direction perpendicular to the light emitting part of the light guide,
A first wavelength selection region that is provided at a position overlapping the first diffraction region and selectively transmits light of the first wavelength;
A second wavelength selection region that is provided at a position overlapping the second diffraction region and selectively transmits the light of the second wavelength;
Comprising
An optical device characterized by that. The optical device according to claim 1.
The light guide is
A light incident portion for allowing light to be incident on the light guide by geometric optical means;
An optical device characterized by that. The optical device according to claim 1 or 2,
Comprising one light guide,
The light guided by the one light guide is
Including light of a third wavelength different from the first wavelength and the second wavelength;
The diffractive optical element is
A third diffraction region having a diffraction efficiency higher than the diffraction efficiency of the light of the first wavelength and the diffraction efficiency of the light of the second wavelength;
The wavelength selector is
In a plan view seen from a direction perpendicular to the light emitting part of the light guide,
A third wavelength selection region that is provided at a position overlapping the third diffraction region and that selectively transmits light of the third wavelength;
An optical device characterized by that. The optical device according to any one of claims 1 to 3,
The diffractive optical element is
A light transmissive diffractive optical element,
An optical device characterized by that. The optical device according to any one of claims 1 to 4,
The diffractive optical element is
A surface relief type diffractive optical element provided with a concavo-convex structure on one surface,
An optical device characterized by that. The optical device according to claim 5.
The height of the convex portion of the concave-convex structure is
Provided to be equal over the entire diffractive optical element,
An optical device characterized by that. The optical device according to claim 5.
The height of the convex part of the concavo-convex structure provided in the first diffraction region is
Determined based on the first wavelength;
The height of the convex portion of the concavo-convex structure provided in the second diffraction region is
Determined based on the second wavelength;
An optical device characterized by that. The optical device according to any one of claims 5 to 7,
The direction in which the convex portion of the concavo-convex structure provided in the first diffraction region extends is as follows:
Provided in the same direction as the direction in which the convex part of the concavo-convex structure provided in the second diffraction region extends,
An optical device characterized by that. The optical device according to any one of claims 1 to 8,
The wavelength selector is
Provided between the diffractive optical element and the light emitting portion of the light guide;
An optical device characterized by that. The optical device according to any one of claims 1 to 8,
The diffractive optical element is
Provided on the surface of the light guide,
The wavelength selector is
Provided on the opposite side of the light emitting part of the light guide across the diffractive optical element,
An optical device characterized by that. The optical device according to any one of claims 1 to 10,
The wavelength selector is
It is a color filter of wavelength selective absorption type or wavelength selective reflection type,
An optical device characterized by that. The optical device according to claim 3.
The pitch of the plurality of diffraction regions including the first diffraction region, the second diffraction region, and the third diffraction region is:
The pupil diameter of the exit-side optical system that controls the optical path of the light extracted from the light guide by the diffractive optical element is less than or equal to the length divided by the number of types of wavelengths of light guided by the light guide. is there,
An optical device characterized by that. The optical device according to any one of claims 1 to 12,
An image forming unit that emits image light;
Comprising
A display device characterized by that.

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