Exit pupil expansion element, and display device using exit pupil expansion element

Abstract

To provide an exit pupil expanding optical element with a large output part and high diffraction efficiency at the input part, and a display device using the same.SOLUTION: The exit pupil expansion element includes: a waveguide part 50 that is configured as a flat plate and guides light L2; an incident part 31 for directing light into the waveguide; an emission part 32 that is located on the waveguide part, in which exit apertures 3221 and 3222 are divided into multiple sections through which the light entered from the incident part and guided within the waveguide part is emitted. The incident part includes a relief-type diffraction grating 311 that is arranged to bend the light entering the incident part into the waveguide part. The emission part includes a volume holographic diffraction grating 321 that is arranged to emit a portion of the light guided within the waveguide from each of the multiple exit apertures.SELECTED DRAWING: Figure 3

Description

[Technical Field]

[0001] The present invention relates to an exit pupil widening element and a display device using the exit pupil widening element. [Background technology]

[0002] In proximity displays such as head-mounted displays, one of the mechanisms for displaying images is to expand the exit pupil (see, for example, Patent Document 1). The exit pupil expansion element used for this expansion of the exit pupil is configured with a waveguide and two or three types of diffractive optical elements. Light such as an image is diffracted by the diffractive optical element at the entrance, and the first-order diffracted light is incident on the waveguide. Within the waveguide, light propagates by total reflection at the interface between the substrate and air. At the diffractive optical element at the exit, the light undergoes first-order diffraction and exits, and is reflected and propagated. The diffractive optical element at the exit expands the exit pupil by repeating first-order diffraction emission and zero-order diffraction reflection and propagation.

[0003] As described in Patent Document 1, such exit pupil expansion elements use relief-type diffractive optical elements. Considering applications other than head-mounted (for example, head-up displays), it is essential to increase the size of the diffraction grating at the exit section. Relief-type manufacturing methods involve forming a mask with submicron spacing by electron beam exposure, and then creating the pattern shape by reactive ion etching or the like. In other words, semiconductor processes are used, and the size of the exit pupil expansion element that can be fabricated is limited to 30 mm square in order to ensure seamless exposure, making it difficult to increase the size of the diffraction grating at the exit section to, for example, 400 mm square for head-up displays.

[0004] On the other hand, to increase the size of the diffraction grating at the exit section, there is also a method of using a volume hologram diffraction grating, as described in Patent Document 2. This method uses a method in which optical interference fringes generated by irradiating reference light and object light onto a photoresist sheet of a diffraction grating as the entrance section, so it is possible to increase the size of the exit pupil expansion element by increasing the size of the optical system. However, as the area increases, the number of exit pupils increases significantly from 729 in the case of a 30 mm square exit section to 132,496 in the case of a 400 mm square exit section. However, due to the small difference in refractive index of the photoresist sheet before and after exposure, the diffraction efficiency at the entrance section decreases, resulting in a problem of dim exit light.

[0005] For these reasons, it can be said that it is difficult to realize an exit pupil expansion element with a large exit section, such as a 400 mm square, and with high diffraction efficiency at the entrance section. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Special Publication No. 2006-510059 [Patent Document 2] International Publication No. 2005 / 093493 Summary of the Invention [Problem to be solved by the invention]

[0007] An object of the present invention is to provide an exit pupil expansion element having a large exit portion and high diffraction efficiency at an entrance portion, and a display device using the exit pupil expansion element. [Means for solving the problem]

[0008] In order to achieve the above object, an exit pupil expansion element according to one aspect of the present invention comprises: a waveguide portion configured in a flat plate shape to guide light; an input section for inputting the light into the waveguide section; an exit portion that is disposed on the waveguide portion and divides the light that is incident from the incident portion and guided within the waveguide portion into a plurality of exit pupils; a relief-type diffraction grating is disposed in the incident portion to bend the light incident on the incident portion into the waveguide portion; The exit section is provided with a volume hologram diffraction grating that causes a portion of the light that has been guided through the waveguide section to exit from each of the plurality of exit pupils. [Effects of the Invention]

[0009] According to the above aspect of the present invention, by disposing a relief-type diffraction grating at the entrance portion, it is possible to increase the diffraction efficiency even if the size is not large, while by disposing a volume hologram-type diffraction grating at the exit portion, it is possible to easily increase the number of exit pupils by taking advantage of the low diffraction efficiency, making it easier to increase the size. Thus, it is possible to provide an exit pupil expansion element and a display device using an exit pupil expansion element that improves light utilization efficiency, has a large exit portion, and has high diffraction efficiency at the entrance portion. [Brief explanation of the drawings]

[0010] [Figure 1] 1 is a schematic diagram of a display device using a diffraction grating according to an embodiment of the present invention; [Figure 2] FIG. 1 is a plan view of an exit pupil expanding element according to an embodiment of the present invention; [Figure 3] 1 is a cross-sectional view of an exit pupil expanding element according to an embodiment of the present invention; [Figure 4] Graph showing the effect of connection step (flatness) on MTF resolution [Figure 5] 1 is a plan view of a two-dimensional expansion type exit pupil expansion element according to an embodiment of the present invention; DETAILED DESCRIPTION OF THE INVENTION

[0011] Hereinafter, embodiments of the present invention will be described with reference to the drawings.

[0012] (Embodiment) 1 is a diagram showing an overview of a display device 1 using an exit pupil expansion element according to an embodiment of the present invention. The display device 1 includes an image source 20 and an exit pupil expansion element 30, which expands the image light from the image source 20 by dividing the exit pupil 35 into multiple parts and outputs the expanded image light to the eyes of an observer 100. The display device 1 can be, for example, a fixed type, or can be attached to the head in a glasses-type or head-mounted type, but details thereof will be omitted.

[0013] The exit pupil expanding element 30 includes a waveguide section 50, an entrance section 31, and an exit section 32. The waveguide section 50, the entrance section 31, and the exit section 32 are transparent.

[0014] The waveguide section 50 is formed in a flat plate shape and guides the light L2.

[0015] The incident portion 31 inputs the light L1 into the waveguide portion 50 at one end of the waveguide portion 50.

[0016] The exit portion 32 is disposed on the other end of the waveguide portion 50, and divides the exit pupil 35 (3221, 3222, 3223) from which the light beams L1 and L2 incident from the entrance portion 31 and guided within the waveguide portion 50 exit.

[0017] In the incident portion 31, a relief type diffraction grating 311 that bends the light L1 incident on the incident portion 31 into the waveguide portion 50 is arranged.

[0018] In the exit section 32, a volume hologram type diffraction grating 321 is arranged, which outputs a part of the light L2 guided in the waveguide section 50 from each of a plurality of exit pupils 35 (3221, 3222, 3223).

[0019] Image source 20 irradiates image light L1 onto incident portion 31 of exit pupil expansion element 30, where relief-type diffraction grating 311 is formed. Image light L1 propagates through waveguide 50 of exit pupil expansion element 30, which is composed of first base material layer 40 and patternable layer 42, and is emitted from volume hologram-type diffraction grating 321, which is output portion 32. Note that image source 20 can be, for example, a microdisplay, and may be a narrow-band light source such as a laser light source, or a wide-band light source such as an OLED or LED.

[0020] Fig. 2 is a plan view of exit pupil expansion element 30, and Fig. 3 is a cross-sectional view of exit pupil expansion element 30 taken along the position of arrow AA in Fig. 2. Exit pupil expansion element 30 of this embodiment is a plate-like element with the optical function of dividing exit pupil 35 into multiple parts and expanding it, and has a configuration in which a first base material layer 40 and a pattern-imparting layer 42, which serve as an example of a waveguide 50, are stacked in layers.

[0021] The first base layer 40 is used as, for example, a rectangular plate-shaped base when manufacturing the exit pupil expansion element 30, and is a layer that constitutes the main part of the waveguide section 50 through which light is guided.

[0022] The shape-imparting layer 42 is laminated on the surface side of the first base layer 40. The shape-imparting layer 42 has an incident portion 31 at one end in the longitudinal direction of its surface, and a rectangular parallelepiped recess 51, which penetrates the shape-imparting layer 42 in the thickness direction to reach the middle of the first base layer 40 and is provided at the other end in the longitudinal direction of the shape-imparting layer 42, as an example for accommodating and arranging the emission portion 32. A second base layer 41, which is, for example, in the form of a thin rectangular plate, is fixed to the bottom surface of the recess 51 via a transparent adhesive 43, which will be described later.

[0023] The first substrate layer 40 and the shape-imparting layer 42 constitute the waveguide 50 for guiding light L1, such as image light, incident from the incident portion 31 toward the exit portion 32. Therefore, the first substrate layer 40 and the shape-imparting layer 42 are made of materials with refractive indices very similar to those of the guided light L2. The region between the incident portion 31 and the exit portion 32 of the first substrate layer 40 and the shape-imparting layer 42 also serves as a region for guiding (propagating) the light L2, where the light L2 is guided by repeated reflections within the first substrate layer 40 and the shape-imparting layer 42. Examples of materials for the first substrate layer 40 and the second substrate layer 41 include PET, polycarbonate, acrylic resin, and glass. Examples of materials for the shape-imparting layer 42 include ultraviolet-curable resin materials such as acrylic ultraviolet-curable resins. The materials constituting the first base material layer 40 and the second base material layer 41 and the material constituting the pattern-imparting layer 42 are all transparent to the guided light L2.

[0024] The incident section 31 is configured with a relief-type diffraction grating 311, which has higher diffraction efficiency than a volume hologram-type diffraction grating and has, for example, a circular planar shape, and is configured as a slanted grating with grooves inclined in the thickness direction. The incident section 31 having such a configuration can be formed, for example, by creating a mold using a method that applies semiconductor processing and creating a pattern on the first base layer 40 by UV-curing imprinting. This makes it possible to bend the image light incident on the incident section 31 in any direction with high diffraction efficiency and minimal loss. The diffracted light travels into the first base layer 40. The relief-type diffraction grating 311 is configured so that the diffracted light satisfies the total reflection condition of the first base layer 40.

[0025] The exit section 32 has a volume hologram diffraction grating 321, the planar shape of which is larger than that of the entrance section 31 and is, for example, rectangular, formed on the second base layer 41 within the recess 51. The volume hologram diffraction grating 321 is arranged to be housed within the recess 51, so that the surface of the pattern-imparting layer 42 and the surface of the volume hologram diffraction grating 321 are flush with each other. For example, the volume hologram diffraction grating 321 can be manufactured by causing two parallel beams of light to interfere with a photoresist formed on the second base layer 41, generating interference fringes, thereby forming a large-area fine pattern (refractive index distribution). It is desirable that the outermost surface of the volume hologram diffraction grating 321 manufactured by such a method be located in the same plane as the outermost surface of the pattern-imparting layer 42 of the exit pupil expansion element 30. Specifically, the shape-imparting layer 42 and the first base layer 40 of the exit pupil expansion element 30 are carved by etching or the like to the thickness of the second base layer 41 and the volume hologram diffraction grating 321 to form a recess 51, and then a transparent adhesive 43 (e.g., a UV-curable adhesive) is placed on the bottom and four side surfaces of the recess 51 as a connecting portion and fixed with the transparent adhesive 43.

[0026] With this configuration, distortion does not occur in the image light propagating when the diffracted light passes through the transparent adhesive 43 and travels through the first base layer 40 and the second base layer 41. In other words, by configuring the surface of the waveguide 50, the surface of the volume hologram diffraction grating 321, and the surface of the connection portion 44 connecting the waveguide 50 and the emission portion 32 to be flush with each other, distortion does not occur in the image light propagating when traveling through the waveguide 50, the connection portion 44, and the emission portion 32. Specifically, as shown in FIG. 4, the influence of the difference in level (flatness) of the connection portion formed by the transparent adhesive 43 on the MTF (Modulation Transfer Function) resolution can be ensured by setting the flatness of the connection portion 44 on the surface of the first base layer 40 and the surface of the second base layer 41 to be between 0 micrometers and 0.1 micrometers. That is, if a large amount of diffused reflection occurs at the boundary between the first base material layer 40 and the connecting portion 44 and / or the boundary between the second base material layer 41 and the connecting portion 44, this will have an adverse effect on the MTF resolution. Therefore, in practice, when the spatial frequency required for the exit pupil expansion optical element is, for example, 18 LP / deg. or higher as the MTF resolution Lp / deg. (35% contrast), the flatness should be between 0 micrometers and 0.1 micrometers.

[0027] The light that has been guided within the first base material layer 40 reaches the exit portion 32. Here, the exit portion 32 is configured with the volume hologram diffraction grating 321 as described above, and the light that has been guided by the volume hologram diffraction grating 321 of the exit portion 32 is emitted from the exit portion 32. Because the diffraction efficiency of the diffraction grating of the exit portion 32 is not 100%, only a portion of the light that initially reaches the volume hologram diffraction grating 321 of the exit portion 32 is emitted (i.e., emitted as the first exit pupil 3221), and the remaining light continues to be totally reflected and travels further downstream in the waveguiding direction (the direction away from the entrance portion 31, that is, to the right in FIG. 3 ) before reaching the volume hologram diffraction grating 321 of the exit portion 32 again. Of this light that reaches the volume hologram diffraction grating 321 of the exit unit 32 again, only a portion of it is emitted (i.e., emitted as the second exit pupil 3222), and the remaining light continues to be totally reflected. By repeating this process, multiple exit pupils 35 are formed in the extension direction of the exit unit 32, thereby achieving the effect of expanding the exit pupil 35. The exit unit 32 also functions as an exit unit 32 that expands the exit pupil 35. By expanding the exit pupil 35 (in other words, dividing it into multiple parts), any of the exit pupils 35 can be observed even if the observation position (i.e., the eye position of the observer 100) moves, thereby improving usability by not limiting the eye position to a specific position. Note that while FIG. 3 simply shows three exit pupils 35—the first exit pupil 3221, the second exit pupil 3222, and the third exit pupil 3223—in reality, the exit pupil 35 is expanded (divided) into more exit pupils 35.

[0028] According to the embodiment, the relief-type diffraction grating 311 is disposed at the entrance portion 31, thereby enabling high diffraction efficiency without requiring a large size, while the volume hologram-type diffraction grating 321 is disposed at the exit portion 32, thereby utilizing the low diffraction efficiency to easily increase the number of exit pupils 35 and facilitate size increase. Thus, it is possible to provide an exit pupil extension element 30 that is bright, has a large exit portion, and has high diffraction efficiency at the entrance portion, and a display device 1 that uses the exit pupil extension element 30.

[0029] As an example of enlarging the diffraction grating of the exit section 32, in the case of a 400 mm square for a head-up display, the exit pupils 35 of the exit section 32 must have at least 132,496 (364 × 364) pieces, and it is practically preferable that they be spaced apart. As another example, in the case of a 250 mm × 80 mm square for an electronic mirror, it is practically preferable that the exit pupils 35 of the exit section 32 have at least 16,644 (228 × 73) pieces, and it is practically preferable that they be spaced apart.

[0030] In other words, as a specific practical design example, when the size of the image incident on the entrance portion 31 is about 5 mm, adjacent exit pupils 35 in the extension direction of the exit portion 32 are formed at intervals of 1.1 to 1.4 mm. In other words, the total exit light L3 from three to four exit pupils 35 is visible. Assuming that this is viewed by the eyes of the observer 100, it is advisable to adjust the number of overlapping exit pupils 35 by adjusting the thickness of the substrate so that the light flux (brightness) is uniform at each angle between them.

[0031] (Other embodiments) FIG. 5 is a diagram showing an exit pupil expansion element 30B configured to expand the exit pupil 35 in two-dimensional directions on the outermost surface of the waveguide 50. The exit pupil expansion element 30 described above is an element configured to expand the exit pupil only in one direction on the outermost surface of the waveguide 50 (one-dimensional direction: the longitudinal direction of the exit pupil expansion element 30 in FIG. 2). Alternatively, an exit pupil expansion element 30B may be used that expands the exit pupil 35 in two orthogonal directions (two-dimensional directions) by adding a new expansion section 33 (which may be either a relief diffraction grating or a volume hologram diffraction grating) that bends the traveling direction of light by 90 degrees. That is, the expansion section 33 is disposed on the waveguide 50 at the other end of the waveguide 50, and bends the traveling direction of light that has entered from the entrance section 31 and been guided within the waveguide 50 by 90 degrees so that the light enters the exit section 32. The exit section 32 is disposed on the other end of the waveguide 50, and is disposed adjacent to the extension section 33 with a gap therebetween. The method of arranging the diffraction grating in the extension section 33 is similar to the method of arranging the diffraction grating in the exit section 32, which uses the recess 51, the transparent adhesive 43, and the second base layer 41.

[0032] According to this other embodiment, by adding an extension portion 33 to the exit pupil expansion element 30 described above, the exit pupil 35 can be expanded in two orthogonal directions (two-dimensional directions).

[0033] It should be noted that any of the various embodiments or modifications described above can be appropriately combined to achieve the effects of each. In addition, combinations of embodiments, combinations of examples, or combinations of embodiments and examples are possible, and combinations of features from different embodiments or examples are also possible.

[0034] (Addendum) The above description of the embodiments discloses the following techniques.

[0035] (Technology 1) A waveguide section formed in a flat plate shape to guide light; an input section for inputting the light into the waveguide section; an exit portion that is disposed on the waveguide portion and divides the light that is incident from the incident portion and guided within the waveguide portion into a plurality of exit pupils; a relief-type diffraction grating is disposed in the incident portion to bend the light incident on the incident portion into the waveguide portion; The exit pupil expansion element includes a volume hologram diffraction grating disposed in the exit section, which causes a portion of the light guided through the waveguide section to exit from each of the plurality of exit pupils.

[0036] (Technology 2) An exit pupil expansion element according to Technology 1, in which the exit portion of the waveguide has a recess, the volume hologram diffraction grating is disposed within the recess of the waveguide, and the surface of the waveguide, the surface of the volume hologram diffraction grating, and the surface of the connection portion connecting the waveguide and the exit portion are flush with each other.

[0037] With this configuration, the difference in level with the volume hologram diffraction grating formed in the waveguide section is eliminated, thereby making it possible to suppress distortion of the expanded and emitted image.

[0038] (Technology 3) The exit pupil expansion element according to Technology 2, wherein the flatness of the connection portion where the waveguide portion and the exit portion are connected is 0 micrometers or more and 0.1 micrometers or less.

[0039] With this configuration, distortion of the expanded and emitted image can be suppressed by eliminating the step between the volume hologram diffraction grating formed in the wave guide portion.

[0040] (Technology 4) An exit pupil expansion element according to Technology 2 or 3, in which the waveguide section, the incident section, and the exit section are transparent, and the volume hologram diffraction grating of the exit section is connected to the waveguide section via a transparent adhesive as the connecting section.

[0041] With this configuration, by connecting via a transparent adhesive material, it becomes possible to emit image light without loss of light quantity.

[0042] (Technology 5) The exit pupil expansion element according to any one of Technology 1 to Technology 4; a video source that causes the light to be incident on the incident portion.

[0043] This configuration makes it possible to provide a display device that allows a display to be viewed superimposed on a see-through field of view.

[0044] With each of these configurations, the incident portion is provided with a relief-type diffraction grating, thereby enabling high diffraction efficiency without a large size, while the exit portion is provided with a volume hologram-type diffraction grating, which allows the number of exit pupils to be easily increased by taking advantage of the low diffraction efficiency, making it easier to increase the size. Thus, it is possible to provide an exit pupil expansion element or a display device using an exit pupil expansion element that improves light utilization efficiency, has a large exit portion, and has high diffraction efficiency at the incident portion. [Industrial Applicability]

[0045] The exit pupil expansion element and the display device using the exit pupil expansion element according to the above aspect of the present invention have a technique for separating light by a plurality of exit pupils, and can also be applied to optical signal processing and the like. [Explanation of symbols]

[0046] 1 Display device 20 Video Source 30 Exit pupil expander 30B Exit pupil expander 31 Input part 311 Relief type diffraction grating 32 Exit section 321 Volume Hologram Diffraction Grating 3221 First exit pupil 3222 Second exit pupil 3223 Third Exit Pupil 33 Extension 35 Exit pupil 40 First base material layer 41 Second base layer 42 Imposition layer 43 Transparent adhesive 44 Connection 50 Waveguide 51 Recess 100 Observer L1, L2, L3 light

Claims

1. a waveguide portion configured in a flat plate shape to guide light; an input section for inputting the light into the waveguide section; an exit portion that is disposed on the waveguide portion and divides the light that is incident from the incident portion and guided within the waveguide portion into a plurality of exit pupils; a relief-type diffraction grating is disposed in the incident portion to bend the light incident on the incident portion into the waveguide portion; The exit pupil expansion element includes a volume hologram diffraction grating disposed in the exit section, which causes a portion of the light guided through the waveguide section to exit from each of the plurality of exit pupils.

2. 2. The exit pupil expansion element of claim 1, wherein the exit portion of the waveguide has a recess, the volume hologram diffraction grating is disposed within the recess, and the surface of the waveguide, the surface of the volume hologram diffraction grating, and the surface of the connection portion connecting the waveguide and the exit portion are flush with each other.

3. 3. The exit pupil expansion element according to claim 2, wherein the flatness of the connection portion where the waveguide portion and the exit portion are connected is 0 micrometers or more and 0.1 micrometers or less.

4. The exit pupil expansion element according to claim 2 or 3, wherein the waveguide portion, the incident portion, and the exit portion are transparent, and the volume hologram diffraction grating of the exit portion is connected to the waveguide portion via a transparent adhesive as the connecting portion.

5. The exit pupil expanding element according to any one of claims 1 to 3; a video source that causes the light to be incident on the incident portion.

6. The exit pupil expanding element of claim 4; a video source that causes the light to be incident on the incident portion.

Images