JP7363031B2 - Exit pupil expansion element, waveguide member - Google Patents

Description

The present invention relates to an exit pupil expansion element and a waveguide member.

In a proximity display such as a head-mounted display, one of the mechanisms for displaying images is to expand the exit pupil. The exit pupil expansion element used to expand the exit pupil is configured with a waveguide section and two or three types of diffraction gratings, and the diffraction grating in the entrance section diffracts light such as an image to produce a first-order diffracted light. is incident on the waveguide. In the waveguide, the light propagates by total reflection, and at the diffraction grating in the output part, the light undergoes first-order diffraction and exits, and also undergoes zero-order diffraction and reflection propagation. The exit pupil is expanded by repeating folding and reflecting propagation.

In addition, in order to expand the exit pupil two-dimensionally, a diffraction grating (hereinafter referred to as a second expansion grating) has the function of first-order diffraction and reflection of the light propagated from the entrance part at a specific angle and propagation through zero-order diffraction and reflection propagation. In some cases, a diffraction grating (also referred to as a part) is provided between the diffraction grating of the input part and the diffraction grating of the output part.
In this case, in the diffraction grating of the second extension part, the propagating light is separated into the first-order diffraction reflected light and the zero-order diffraction reflection propagation light, the first-order diffraction reflection light goes to the diffraction grating of the output part, and the zero-order diffraction reflection propagation light , is totally reflected on the back surface, and is separated into a first-order diffracted reflected light and a zero-order diffracted reflected propagated light again at the second extended portion diffraction grating, which is repeated in the second extended portion diffraction grating (for example, see Patent Document 1) .

In such an exit pupil expansion element, light travels through the waveguide through repeated total reflection and exits from the output section (extension section), but the light reaches the end of the waveguide without exiting from the output section. There is also stray light. If such light is reflected at the end and reaches the output section and is emitted, light that has traveled an optical path different from the original image light will be observed along with the original image light. There was a risk that the observed image would deteriorate.
Moreover, there are cases where it is desired to reduce unnecessary stray light that reaches the end of a waveguide member that is equipped with a waveguide section and guides light, not only the exit pupil expansion element.

Special Publication No. 2006-510059

An object of the present invention is to provide an exit pupil expansion element and a waveguide member that can reduce stray light reaching the end of a waveguide.

The present invention solves the above problems by the following solving means. Note that, in order to facilitate understanding, the description will be given with reference numerals corresponding to the embodiments of the present invention, but the present invention is not limited thereto.

A first invention provides a waveguide section (10a) configured in a planar shape having a first plane (10b) and a second plane (10c) parallel to each other and guides light; an extension part (22, 22B, 23) disposed in the waveguide part (10a) or configured integrally with the waveguide part (10a), which divides the exit pupil into a plurality of parts, expands it, and emits the light; A stray light reducing section () that is provided at at least a part of the end of the waveguide ( 25, 225), and an exit pupil expansion element (1, 1B).

A second invention is the exit pupil expansion element (1, 1B) according to the first invention, in which the stray light reducing section (25, 225) is arranged on the first plane (10b) of the waveguide section (10a). and an exit pupil expansion element (1, 1B) characterized in that it has a slope portion (25a, 25b) that is inclined with respect to at least one of the second plane (10c).

In a third invention, in the exit pupil expansion element (1, 1B) according to the second invention, the slope portion provided on the same side as the first plane (10b) is a first slope portion (25a). , the slope part provided on the same side as the second plane (10c) and facing the first slope part (25a) is a second slope part (25b), and the first plane (10b) The angle formed by the second plane (10c) and the second slope part (25b) is δ1, and the angle formed by the second plane (10c) and the second slope part (25b) is δ2. When the angle that the waving light makes with the normal to the first plane (10b) is θ, and the refractive index of the waveguide (10a) is n1, 0°≦δ1<90°, and 0° ≦δ2<90°, and when δ1=0°, the first slope portion (25a) is on the same plane as the first plane (10b), and when δ2=0°, , the second slope part (25b) is on the same plane as the second plane (10c), and includes at least one of the first slope part (25a) and the second slope part (25b), This is an exit pupil expansion element (1, 1B) characterized by satisfying both δ1<θ-asin(1/n1) and δ2<θ-asin(1/n1).

A fourth invention is the exit pupil expanding element (1, 1B) according to any one of the second invention to the third invention, wherein the sloped portion (25a, 25b) has a light absorption function. This is an exit pupil expansion element (1, 1B) characterized by being provided with an absorption layer.

A fifth invention is the exit pupil expansion element (1, 1B) according to any one of the first invention to the fourth invention, in which the direction in which incident light travels is deflected to the expansion part (22B). The exit pupil expansion element (1, 1B) further comprises a second expansion part (23) that expands the exit pupil in a direction that intersects the direction in which the expansion part (22B) extends light. be.

A sixth invention provides a waveguide section (10a) configured in a planar shape having a first plane (10b) and a second plane (10c) parallel to each other and guides light; a stray light reduction section (25, 225).

According to the present invention, it is possible to provide an exit pupil expansion element and a waveguide member that can reduce stray light that reaches the end of the waveguide.

1 is a diagram showing a first embodiment of an exit pupil expansion element 1 according to the invention; FIG. 2 is a cross-sectional view of the exit pupil expansion element 1 taken along arrow AA in FIG. 1. FIG. FIG. 2 is an enlarged cross-sectional view of a stray light reduction section 25. FIG. It is a figure which shows the shape of the comparative example and Example which performed simulation. FIG. 3 is a diagram showing the conditions and results of simulation. It is a figure which shows the 2nd embodiment of the exit pupil expansion element 1B by this invention. 17 is a cross-sectional view of the exit pupil expansion element 1B taken along the arrow BB in FIG. 16. FIG. 17 is a cross-sectional view of the exit pupil expansion element 1B taken along the arrow CC in FIG. 16. FIG. It is a figure explaining simulation conditions. 7 is a diagram arranging and comparing images obtained by simulation with and without a stray light reduction unit 225. FIG. 11 is a diagram showing a graph of the luminance distribution on the line indicated by the arrow in FIG. 10. FIG. FIG. 3 is a diagram illustrating brightness numerically.

Hereinafter, the best mode for carrying out the present invention will be described with reference to the drawings and the like.

(First embodiment)
FIG. 1 shows a first embodiment of an exit pupil expansion element 1 according to the invention.
FIG. 2 is a cross-sectional view of the exit pupil expansion element 1 taken along the arrow AA in FIG.
Note that each figure shown below, including FIG. 1, is a schematic diagram, and the size and shape of each part are appropriately exaggerated for easy understanding.
Further, in the following description, specific numerical values, shapes, materials, etc. are shown, but these can be changed as appropriate.
In this specification, terms that specify shapes or geometrical conditions, such as terms such as parallel and orthogonal, do not have strict meanings, but also mean that they have similar optical functions and can be considered parallel or orthogonal. This also includes states with errors.
In this specification, words such as plate, sheet, film, etc. are used, but these are generally used in the order of thickness, such as plate, sheet, film, etc. This is also used in the book. However, since there is no technical meaning in these different uses, these words can be replaced as appropriate.
In this specification, the sheet surface refers to the surface of each sheet that is in the planar direction of the sheet when the sheet is viewed as a whole.
Furthermore, in the present invention, transparent refers to something that transmits at least light of the wavelength to be used. For example, even if a material does not transmit visible light, if it transmits infrared rays, it will be treated as transparent when used for infrared purposes.
Note that the specific numerical values specified in this specification and claims should be treated as including general error ranges. In other words, a difference of approximately ±10% is essentially no difference, and a value set in a range slightly exceeding the numerical range of the present invention is, in fact, not a difference of the present invention. It should be interpreted as within the range.

The exit pupil expansion element 1 of this embodiment is a sheet-like element used in a head-mounted display and has an optical function of dividing the exit pupil into a plurality of parts and expanding it. It has a structure in which these are stacked in layers. Note that the exit pupil expansion element 1 may be configured in a film shape or a plate shape.
The base material layer 10 is used as a base when manufacturing the exit pupil expansion element 1, and is a layer that constitutes the main part of the waveguide section through which light is guided.
The shaping layer 20 is laminated on the surface side of the base material layer 10. The shaping layer 20 includes an entrance section 21 and an exit section 22 on its surface.

The base material layer 10 and the molding layer 20 constitute a waveguide section (core) 10a for guiding light such as image light incident from the input section 21 toward the output section 22 side. Therefore, the base layer 10 and the molding layer 20 are made of materials that have substantially the same refractive index for the guided light or that have very similar refractive indexes. Furthermore, the region where light is guided (propagated), including the portion where the input section 21 and the output section 22 are configured, will be referred to as a waveguide section 10a. The waveguide section 10a has two planes parallel to each other (a first plane 10b and a second plane 10c), is configured in a flat plate shape, and guides light by repeating reflection inside.
Examples of the material constituting the base layer 10 include optical glass, PET, polycarbonate, and acrylic resin. Furthermore, examples of the material constituting the molding layer 20 include ultraviolet curable resin materials such as acrylic ultraviolet curable resins. Both the material constituting the base material layer 10 and the material constituting the molding layer 20 are transparent to the guided light.

In this embodiment, the base material layer 10 and the shaping layer 20 constitute the core (waveguide section 10a), and the air (atmosphere) located around the core constitutes the cladding, so that the base material layer 10 and the shaping layer 20 constitute the core (waveguide section 10a), and the air (atmosphere) located around it constitutes the cladding. Light can be guided using the layer 20 as the waveguide section 10a. Therefore, as the material constituting the base material layer 10 and the molding layer 20, a material having a higher refractive index than the air (atmosphere) constituting the cladding is used. Thereby, light can be efficiently guided while being reflected at the interface between the core made up of the base material layer 10 and the shaping layer 20 and the cladding made up of air (atmosphere).

In this embodiment, the incidence section 21 is configured by a three-level diffraction grating. The diffraction gratings of the entrance part 21 are arranged repeatedly at a constant pitch P, and are arranged in one direction (the vertical direction in FIG. 1, the vertical direction in FIGS. 2 and 3) orthogonal to the direction of the arrangement (the horizontal direction in FIGS. A high refractive index portion 211 is provided that extends in the depth direction of the plane of the paper in FIG.
Furthermore, the diffraction grating of the entrance section 21 has a low refractive index section 212 that is formed between the high refractive index sections 211 and has a lower refractive index than the high refractive index section 211 . In this embodiment, as described above, the low refractive index section 212 is made of air, but this region may be filled with a material whose refractive index is sufficiently lower than that of the high refractive index section 211.

The light that travels perpendicularly to the sheet surface of the exit pupil expansion element 1 and enters the entrance section 21 is diffracted by the diffraction grating of the entrance section 21, and the diffracted light travels into the base material layer 10 (waveguide section 10a). The pitch P of the diffraction grating is set so that the diffraction angle θ of this diffracted light satisfies the total reflection condition of the waveguide 10a. Specifically, the pitch P of the diffraction grating in the incident section 21 is configured to be shorter than the wavelength λ of the guided light.

The conditions for light to propagate in the waveguide 10a must satisfy the total reflection condition, so the core: the refractive index of the waveguide 10a (base material layer 10 and imprinting layer 20) is n1, and the cladding (air portion) When the refractive index of is n2 and the critical angle of total reflection is θ, sin(θ)=n2/n1, and the conditions for total reflection must satisfy the following equation.
θ>asin(n2/n1)
sin(θ)>n2/n1...Formula (1)
On the other hand, if the diffraction angle of the light incident on the incident part 21 is θ, then the relationship between the wavelength λ, the pitch P, and the diffraction angle θ can be expressed by the following formula from the formula of the diffraction grating.
n1×sin(θ)=λ/P
sin(θ)=λ/(P×n1)...Formula (2)
By substituting this equation (2) into the total reflection condition of the above equation (1), the following relational expression is obtained.
λ/(P×n1)>n2/n1
λ>P×n2
Here, since n2=1 (the refractive index of air), P<λ, and by making the pitch P of the diffraction grating in the input section 21 shorter than the wavelength λ of the guided light, the input section 21 is The vertically incident light can be guided while undergoing total reflection inside the waveguide section 10a.

The light guided within the waveguide section 10a reaches the output section 22. Here, as shown in FIG. 2, a diffraction grating is also configured in the output section 22, and the light guided within the waveguide section 10a is emitted from the output section 22 by the diffraction grating of the output section 22. .
The diffraction grating of the output section 22 is constituted by a three-level diffraction grating similar to the diffraction grating of the input section 21. Further, the diffraction gratings of the output section 22 are repeatedly arranged at a constant pitch P, and extend in one direction perpendicular to the direction of the arrangement (the same direction as the direction in which the diffraction gratings of the input section 21 extend). It has a high refractive index section 221. Further, the diffraction grating of the output section 22 is arranged such that the direction of the multi-stage uneven shape is opposite to that of the diffraction grating of the input section 21 in order to output the light guided in the waveguide section 10a. There is.

Since the diffraction efficiency of the diffraction grating of the output section 22 is not 100%, only a part of the light that first reaches the diffraction grating of the output section 22 is output, and the remaining light continues to be reflected and guided. It further advances toward the downstream side of the direction (the direction away from the incident section 21, the right side in FIG. 2), and reaches the diffraction grating of the output section 22 again. Only a portion of this light that reaches the diffraction grating of the emission section 22 again is emitted, and the remaining light continues to be reflected. By repeating this, a plurality of exit pupils are formed, and an effect of expanding the exit pupils can be obtained. In this way, in this embodiment, the exit section 22 also functions as an expansion section that expands the exit pupil. By expanding the exit pupil (dividing it into multiple parts), even if the observation position (eye position) moves, any exit pupil can be observed, making it easier to use without being limited to a specific eye position. can be improved. Note that in FIG. 2, the exit pupils are simplified so as to be divided into three exit pupils, but in reality, they are expanded (divided) into more exit pupils.

Here, the amount of diffracted light emitted from the diffraction grating of the emitting section 22 is determined by the diffraction efficiency of the diffraction grating at the position where the light reaches, and the light that cannot be emitted is further guided. Therefore, the amount of light that reaches the diffraction grating decreases as it moves downstream in the light waveguide direction, but there is light (stray light) that cannot be emitted from the output section 22 and reaches the end of the waveguide section 10a. do. If this stray light is reflected at the end and returns to the emission section 22, the stray light will be emitted along with the original image light, and there is a risk that the contrast of the observed image will decrease, resulting in deterioration of the image.

In order to reduce this stray light, the exit pupil expansion element 1 of this embodiment includes a stray light reduction section 25.
FIG. 3 is an enlarged cross-sectional view of the stray light reduction section 25. As shown in FIG.
The stray light reducing section 25 of this embodiment is provided at all ends of the waveguide section 10a. The stray light reduction section 25 has a wedge-shaped cross-sectional shape, and has two slope sections, a first slope section 25a and a second slope section 25b, which are inclined with respect to the first plane 10b and the second plane 10c of the waveguide section 10a. It is composed of As shown in FIG. 25, the stray light reduction section 25 prevents the stray light from returning to the emission section 22 by completely reflecting the stray light once on the slope section and then emitting the stray light to the outside from the opposing slope section. By doing so, stray light emitted from the emitting section 22 is reduced. In order to effectively exhibit this effect, it is desirable that the stray light reduction section 25 satisfy the following conditions.

A slope portion provided on the same side as the first plane 10b is a first slope portion 25a, and a slope portion provided on the same side as the second plane 10c and opposite to the first slope portion 25a is a second slope portion. Section 25b. Further, the angle formed between the first plane 10b and the first slope portion 25a is δ1, the angle between the second plane 10c and the second slope portion 25b is δ2, and the light guided through the waveguide portion 10a is Let θ be the angle made with the normal line of one plane (that is, the reflection angle of the guided light), and let n1 be the refractive index of the waveguide portion 10a.
Here, assuming that 0°≦δ1<90° and 0°≦δ2<90°, when δ1=0°, the first slope portion 25a is on the same plane as the first plane 10b. If δ2=0°, the second slope portion 25b is on the same plane as the second plane 10c. It is assumed that the stray light reduction section 25 includes at least one of a first slope section 25a and a second slope section 25b. Under this condition, the stray light reduction unit 25
δ1<θ-asin(1/n1)...Formula (3)
and δ2<θ-asin(1/n1)...Equation (4)
If both of these conditions are satisfied, stray light can be appropriately emitted to the outside as illustrated in FIG.

The above formulas (3) and (4) are based on the total reflection conditions at the first slope portion 25a and the second slope portion 25b,
θ−δ1>asin(1/n1)
and θ−δ2>asin(1/n1)
It is derived from

Note that even if a film (layer) with a refractive index of n2 is provided on the surfaces of the first slope portion 25a and the second slope portion 25b, the same effect can be obtained as long as the above formulas (3) and (4) are satisfied. be able to.
Therefore, a light absorption layer may be provided on the surfaces of the first slope portion 25a and the second slope portion 25b. By providing this light absorption layer, it is possible to absorb the light emitted from the first slope portion 25a and the second slope portion 25b, and it is possible to prevent the end portions from appearing shiny when observed from the outside.

Here, a simulation was performed to verify the effect of the stray light reduction unit 25. This simulation was performed using the beam propagation method (``Numerical analysis of diffractive optical elements and its applications'', Maruzen Publishing, supervised by Kashiko Kodate).
FIG. 4 is a diagram showing the shapes of a comparative example and an example in which simulation was performed.
FIG. 5 is a diagram showing the conditions and results of the simulation.
In FIG. 5, the return rate (%) indicates the rate at which light that has traveled toward the end of the waveguide section 10a returns in the opposite direction.
In Comparative Example 1, since the stray light reduction section 25 was not included, the return rate was as high as 3.79%.
Comparative Example 2 has the shape of the stray light reducing section 25, but the dimensions of the stray light reducing section 25 do not satisfy equations (3) and (4), so the return rate is 1.32%. there were. Although this result shows a better result than the comparative example, it is desirable that the return rate be less than 1.0% in order to prevent deterioration of the image light.
In Example 1 and Example 2, formulas (3) and (4) are satisfied, and the return rates are 0.46% and 0.47%, respectively, which are very good results. . Furthermore, since there is virtually no difference between the results of Example 1 and Example 2, it is confirmed that stray light is effectively emitted to the outside as long as formulas (3) and (4) are satisfied. can. Therefore, there is no need to make the shape of the stray light reduction section 25 longer than necessary.

As described above, according to the first embodiment, the exit pupil expansion element 1 is able to effectively reduce stray light returning to the emission section 22 by including the stray light reduction section 25.

(Second embodiment)
FIG. 6 is a diagram showing a second embodiment of the exit pupil expansion element 1B according to the present invention.
FIG. 7 is a cross-sectional view of the exit pupil expansion element 1B taken along the arrow BB in FIG. 16.
FIG. 8 is a cross-sectional view of the exit pupil expansion element 1B taken along the arrow CC in FIG. 16.
Note that parts that perform the same functions as those in the first embodiment described above are denoted by the same reference numerals, and redundant explanations will be omitted as appropriate.
Further, in FIGS. 6 to 8, orthogonal coordinate axes of X, Y, and Z are shown so that the directions are clear.

The exit pupil expansion element 1 of the first embodiment described above is an element that expands the exit pupil only in one direction (one-dimensional direction: left and right direction in FIG. 1). In contrast, the exit pupil expansion element 1B of the second embodiment is configured to expand the exit pupil in two orthogonal directions (two-dimensional directions).
The exit pupil expansion element 1B of the second embodiment has three exit pupil expansion elements 1B-1, exit pupil expansion element 1B-2, and exit pupil expansion element 1B-3, which have the same basic configuration, with an air layer between them. It is composed of a combination of . The configuration for holding the three exit pupil expansion elements 1B-1, 1B-2, and 1B-3 may be supported by a frame, or may be partially glued, In addition to these, a protective plate or the like may be further laminated.

The exit pupil expansion element 1B-1, the exit pupil expansion element 1B-2, and the exit pupil expansion element 1B-3 each have different wavelengths of light to be diffracted, guided, and expanded. , the pitch of the diffraction grating is different. The diffraction grating has high wavelength selectivity and does not diffract light other than the target wavelength. Therefore, by configuring each exit pupil expansion element 1B-1, exit pupil expansion element 1B-2, and exit pupil expansion element 1B-3 to diffract the wavelengths of the three primary colors of red, blue, and green, , it is possible to perform exit pupil expansion of color images.
In addition, regarding points other than the pitch, the exit pupil expansion element 1B-1, the exit pupil expansion element 1B-2, and the exit pupil expansion element 1B-3 all have the same configuration, so in the following description, These three elements will be described as an exit pupil expansion element 1B without making any particular distinction between them.

The exit pupil expansion element 1B of the second embodiment includes a base material layer 10 and a forming layer 20, similarly to the exit pupil expansion element 1 of the first embodiment.
The shaping layer 20 of the second embodiment includes an entrance section 21, a second extension section 23, and an output section 22B on its surface.

The incidence section 21 is similar to the incidence section 21 of the first embodiment.
The second extension part 23 is composed of a two-level diffraction grating, and has a high refractive index part 231 extending in a direction inclined at 45 degrees with respect to the direction in which the light guided from the input part 21 travels. It is located. The second expansion part 23 deflects the direction in which the light incident from the input part 21 travels by 90 degrees and advances it to the output part 22B, and the direction intersects by 90 degrees with the direction in which the light is expanded by the output part 22 (first expansion part). That is, the exit pupil is expanded in the X-axis direction in the figure (see FIG. 6). In addition, in FIG. 6, the exit pupil is depicted as being expanded into three, but in reality, the exit pupil is divided and expanded into a number corresponding to the number of repeated reflections in the second expanding section 23. In addition, in FIG. 6, the light incident from the entrance part 21 is deflected by 90 degrees by the second extension part 23 inclined by 45 degrees, and the light travels to the output part 22B, but the angle and arrangement are not limited to this. isn't it.

The emission part 22B differs from the emission part 22 of the first embodiment in that the arrangement position is different and the arrangement direction of the high refractive index parts 221B is different. The light deflected and expanded by the second expansion unit 23 reaches the output unit 22B, and similarly to the output unit 22 of the first embodiment, the exit pupil is divided and expanded while sequentially outputting the light (see FIG. 8). The direction in which the exit section 22B expands the exit pupil is perpendicular to the direction in which the second expansion section 23 expands the exit pupil, specifically, the exit pupil is expanded in the Y-axis direction in the figure.

Furthermore, the exit pupil expansion element 1B of the second embodiment includes a stray light reduction section 225 at the end of the waveguide section 10a, similar to the first embodiment. The configuration of the stray light reduction section 225 is similar to the stray light reduction section 25 of the first embodiment.

Regarding the configuration of the exit pupil expansion element 1B of the second embodiment, the appearance of the image was simulated and the effect was confirmed, which will be described below. This simulation was performed using the ray tracing method (``Numerical Analysis of Diffractive Optical Elements and Its Applications'', Maruzen Publishing, supervised by Kashiko Kodate).
FIG. 9 is a diagram illustrating simulation conditions.
The simulation was performed on a configuration in which a light source LS, a pattern PT, a lens L1, a lens L2, and a screen S are arranged in addition to the exit pupil expansion element 1B.
The exit pupil expansion element 1B has an entrance section 21 of 0.5 mm x 0.5 mm, a second extension section 23 of 1 mm x 2 mm, and an exit section 22B of 2 mm x 2 mm. 23 is 5 mm, and the center distance between the second extension part 23 and the emission part 22B is 4 mm. Further, the exit pupil expansion element 1B had a base material layer 10 with a thickness of 0.3 mm and a size of 10 mm x 10 mm.
The exit pupil expansion element 1B was prepared in this embodiment, which includes a stray light reducing section 225, and in a comparative example, which does not include the stray light reducing section 225 and has a flat end surface. In the embodiment including the stray light reducing section 225, its shape is similar to that of the first embodiment shown in FIG. 4(c).

As the incident optical system, the light source LS is assumed to be an LED light source, and a single wavelength light having a wavelength of 530 nm is transmitted through a transparent black and white checkered pattern PT. The distance between the light source LS and the pattern PT is 0.1 mm. A lens L1 was placed on the downstream side of this optical path. The lens L1 has a focal length of 4 mm, and the distance between the pattern PT and the lens L1 is 4 mm. Further, the distance between the lens L1 and the entrance section 21 is 1 mm.
As the output optical system, the lens L2 has a focal length of 8 mm, and the distance between the output section 22B and the lens L2 is 2 mm. The light transmitted through the lens L2 is projected onto the screen S. The screen S was placed at a position 8 mm from the lens L2.

FIG. 10 is a diagram comparing images obtained by simulation with and without the stray light reduction unit 225.
The image shown in FIG. 10(b) with the stray light reduction unit 225 was observed to have clearly improved contrast than the image shown in FIG. 10(a) without the stray light reduction unit 225. However, in the printed image of FIG. 10, it is difficult to understand the difference, so data at the positions indicated by arrows in FIG. 10 will be extracted and explained numerically in more detail.

FIG. 11 is a graph showing the luminance distribution on the line indicated by the arrow in FIG.
FIG. 12 is a diagram showing the brightness numerically.
In FIG. 12, the integrated value of brightness in range a indicated by an arrow in FIG. 11 is designated as A, the integrated value of brightness in range b is designated as B, and the integrated value of brightness in range c is designated as C. Further, FIG. 12 also shows the result of calculating ((A+C)/2)/B.
In FIG. 10, it can be said that the larger the luminance difference between the white area and the black area, the higher the contrast of the image. The calculated value of ((A+C)/2)/B represents the size of the white range with respect to the black range, and it can be determined that the larger this value is, the higher the contrast is. Looking at the results in FIG. 12, it is clear that the contrast is higher when the stray light reducing section is provided than when the stray light reducing section is not provided, confirming the effect of reducing stray light.

As explained above, the exit pupil expansion element 1B of the second embodiment is equipped with the stray light reducing section 225, so that the stray light reaching the end of the waveguide section can be reduced similarly to the first embodiment. I can do it.
Further, the exit pupil expansion element 1B of the second embodiment includes the exit section (first expansion section) 22 and the second expansion section 23, so that the exit pupil can be expanded in two orthogonal directions. , it is possible to provide an environment where it is easier to view videos, etc.

(Deformed form)
Various modifications and changes are possible without being limited to the embodiments described above, and these are also within the scope of the present invention.

(1) In each embodiment, a three-level diffraction grating and a two-level diffraction grating are illustrated and explained. The present invention is not limited to this, and the present invention may be applied to, for example, a diffraction grating having a multi-level uneven shape of four or more levels.

(2) In each of the embodiments, the exit pupil expansion element has been explained using an example of being used in a head-mounted display, but the application of the exit pupil expansion element is not limited to a head-mounted display. Good too.

(3) In each of the embodiments, the example in which the stray light reducing section is provided in the exit pupil expanding element has been described, but the present invention is not limited to this. may be provided.

(4) In each of the embodiments, an example has been described in which the stray light reducing section is provided at all ends. However, the present invention is not limited to this, and, for example, the stray light reducing section may be provided at some of the ends.

(5) In each embodiment, the stray light reduction section has two opposing slopes of equal length, a first slope section and a second slope section, and has an isosceles triangular cross-sectional shape. I listed and explained. However, the present invention is not limited to this, and, for example, the first slope portion and the second slope portion may have different lengths, or the slope portion may be provided only on one side. Furthermore, the slope portion is not limited to a straight cross-sectional shape, and may be a slope having a curved cross-sectional shape, that is, a curved surface. Furthermore, the shape of the stray light reduction section may include three or more sloped sections. Further, the tip of the stray light reducing portion does not need to be sharp, and may be rounded or curved.

In addition, although each embodiment and modification can also be used in combination suitably, detailed description is abbreviate|omitted. Furthermore, the present invention is not limited to the embodiments described above.

1, 1B Exit pupil expansion element 10 Base material layer 10a Waveguide section 10b First plane 10c Second plane 20 Imprinting layer 21 Entrance section 22, 22B Output section 23 Second expansion section 25 Stray light reduction section 25a First slope section 25b Second-person surface portion 211, 221, 221B, 231 High refractive index portion 212, 222, 222B, 232 Low refractive index portion 225 Stray light reduction portion

Claims (4)

a waveguide section that is configured in a flat plate shape and has a first plane and a second plane that are parallel to each other and guides light;
an extension part disposed on the waveguide part or configured integrally with the waveguide part, which divides the exit pupil into a plurality of parts, expands the exit pupil, and outputs the light;
a second expansion section that deflects the direction in which the incident light travels to the expansion section and expands the exit pupil in a direction that intersects the direction in which the expansion section expands the light;
Equipped with
a stray light reduction unit that is provided at all ends of the waveguide and has at least one of the functions of emitting or absorbing light that reaches the end of the waveguide;
Equipped with
An exit pupil expansion element in which three elements, each of which has a different wavelength of light to be diffracted, guided, and expanded, are stacked with an air layer in between. The exit pupil expansion element according to claim 1,
The stray light reduction section has a slope section that is inclined with respect to at least one of the first plane and the second plane of the waveguide section;
An exit pupil expansion element featuring: The exit pupil expansion element according to claim 2,
The slope portion provided on the same side as the first plane is a first slope portion,
The slope portion provided on the same side as the second plane and facing the first slope portion is a second slope portion,
Let δ1 be the angle formed by the first plane and the first slope,
Let the angle between the second plane and the second slope be δ2,
Let θ be the angle that the light guided through the waveguide makes with the normal to the first plane,
When the refractive index of the waveguide is n1,
0°≦δ1<90°, 0°≦δ2<90°,
When δ1=0°, the first slope portion is on the same plane as the first plane,
When δ2=0°, the second slope portion is on the same plane as the second plane,
comprising at least one of the first slope portion and the second slope portion,
δ1<θ−asin(1/n1)
and δ2<θ−asin(1/n1)
satisfying both of the following;
An exit pupil expansion element featuring: In the exit pupil expansion element according to any one of claims 2 to 3,
The slope portion is provided with a light absorption layer having a light absorption function;
An exit pupil expansion element featuring:

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