The present invention relates to a lightguide and a head-mounted display. A lightguide according to the present invention is suitably used for a head-mounted display.
Patent Document 1 discloses a light beam expander which is suitable for a head-mounted display. The light beam expander which is shown in FIG. 16 of Patent Document 1 includes a light guiding plate (i.e., a substrate through which light is transmitted) which receives a collimated displaying light beam. On the light guiding plate, a reflecting surface and a plurality of first partially reflecting surfaces and a plurality of second partially reflecting surfaces are provided.
A light beam which is incident on a light guiding plate is reflected in a first direction by the reflecting surface, and propagates within the light guiding plate along the first direction. The plurality of first partially reflecting surfaces adjoin one another, in parallel, along the first direction. Portions of the light beam propagating along the first direction are reflected by the plurality of first partially reflecting surfaces in a second direction which is orthogonal to the first direction. Over the course of this, the light beam is expanded in the first direction. The plurality of second partially reflecting surfaces adjoin one another, in parallel, along the second direction. Portions of the light beam propagating along the second direction are reflected by the plurality of second partially reflecting surfaces in a third direction which is orthogonal to the first and second directions. Over the course of this, the light beam is expanded in the second direction. The light beam which is reflected off the plurality of second partially reflecting surfaces exits the light guiding plate. The light beam exiting the light guiding plate has been expanded in the first and second directions, thus allowing the eye to be situated in a broad range of positions to view a virtual image.
[Patent Document 1] Japanese National Phase PCT Laid-Open Publication No. 2003-536102 (USP No. 6829095)
However, a study by the inventors has found that the light beam expander described in Patent Document 1 has a problem in that the brightness of the virtual image to be viewed is lower in peripheral portions than in the central portion.
The size (viewing angle) of a virtual image to be viewed by using the light beam expander described in Patent Document 1 is determined by the angle range in which a collimated displaying light beam enters the eye of a viewer through the light beam expander. For example, a displaying light beam having exited the display panel is collimated in a different direction depending on the position (i.e., the pixel position) at which the light beam made the exit. In other words, the direction in which a light beam that exits a peripheral pixel of the display panel is collimated constitutes a predetermined angle with the direction in which a light beam that exits a pixel in the center of the display panel is collimated. This angle difference determines the viewing angle (i.e., the angle of view of the virtual image).
A light beam exiting a pixel in the center of the display panel strikes the plurality of first partially reflecting surfaces and the plurality of second partially reflecting surfaces in the center. On the other hand, a light beam exiting a peripheral pixel of the display panel strikes the plurality of first partially reflecting surfaces and the plurality of second partially reflecting surfaces in the center; however, while some of the light beam exiting a peripheral pixel of the display panel strikes the plurality of first partially reflecting surfaces and the plurality of second partially reflecting surfaces in a peripheral portion thereof, the rest fails to be incident on the plurality of first partially reflecting surfaces or the plurality of second partially reflecting surfaces. This is the cause of the problem where the brightness of the virtual image to be viewed is lower in peripheral portions than in the central portion.
As a method for suppressing this, it might be possible to reduce the diameter of the collimated displaying light beam, or conversely, enlarge the first and second partially reflecting surfaces. However, reducing the diameter of the displaying light beam has a disadvantage in that the efficiency of light utility will be lowered; on the other hand, enlarging first and second partially reflecting surfaces has a disadvantage in that the light beam expander will increase in size. Although it might be possible to reduce the angle difference between directions of collimated displaying light beams, this will create a disadvantage in that the viewing angle (i.e., the angle of view of the virtual image) is decreased.
A main objective of the present invention is to provide a lightguide which is able to reduce unevenness in the brightness of a virtual image to be viewed, while restraining the aforementioned disadvantages. Another objective of the present invention is to provide a head-mounted display including such a lightguide.
A lightguide according to an embodiment of the present invention comprises: a first light guiding member having a first light-receiving surface to receive a collimated light beam, a first lightguide section to allow the light beam entering at the first light-receiving surface to propagate in a first direction, and a first outgoing face through which the light beam propagating in the first lightguide section is allowed to exit in a second direction intersecting the first direction; and a second light guiding member having a second light-receiving surface to receive the light beam exiting from the first outgoing face, a second lightguide section to allow the light beam entering at the second light-receiving surface to propagate in the second direction, and a second outgoing face through which the light beam propagating in the second lightguide section is allowed to exit in a third direction intersecting the first and second directions.
In one embodiment, the first light guiding member includes a coupling section having the first light-receiving surface; and the first light-receiving surface is inclined at predetermined angles with respect to the first, second and third directions.
In one embodiment, the first light guiding member has a plurality of first slopes inclined in the first direction; and the plurality of first slopes allow the light beam propagating in the first lightguide section to be reflected in the second direction, and expands the light beam in the first direction.
In one embodiment, the second light guiding member has a plurality of second slopes inclined in the second direction; and the plurality of second slopes allow the light beam propagating in the second lightguide section to be reflected in the third direction, and expands the light beam in the second direction.
In one embodiment, the plurality of first slopes constitute an angle α1 with a plane P13 containing the first and third directions, and the plurality of second slopes constitute an angle α2 with a plane P12 containing the first and second directions, the angle α1 and the angle α2 each independently being 45° or less.
In one embodiment, the first light-receiving surface constitutes, in the plane P12, an angle of 2·α1 with the plane P23, and in a plane P′23 resulting from rotating the plane P23 by (90−2·α1) degrees around the third direction, an angle of 2·α2 with the plane P12. It is preferable that α1 is not less than 1 and not more than 30, for example.
In one embodiment, the first light-receiving surface has a side whose length is equal to or greater than twice the length along the second direction of a cross section of the first lightguide section which is parallel to the plane P23, and a side whose length is equal to or greater than twice the length along the third direction of a cross section of the first lightguide section which is parallel to the plane P13.
In one embodiment, the first lightguide section includes a rod portion which is elongated in the first direction, and the second lightguide section includes a planar portion which is parallel to a plane containing the first and second directions.
One embodiment comprises one said first light guiding member and two said second light guiding members arrayed in parallel along the first direction.
A head-mounted display according to an embodiment of the present invention comprises: a display panel; a collimating optical system to collimate displaying light exiting the display panel and emit a collimated light beam; and any of the above lightguides, the lightguide being disposed so that the first light-receiving surface receives the light beam having been collimated through the collimating optical system.
According to an embodiment of the present invention, there is provided a lightguide which is able to reduce unevenness in the brightness of a virtual image to be viewed. According to an embodiment of the present invention, there is provided a head-mounted display including such a lightguide.
Hereinafter, with reference to the drawings, lightguides and head-mounted displays (hereinafter referred to as “HMDs”) according to embodiments of the present invention will be described. Although lightguides for HMDs will be described herein, lightguides according to embodiments of the present invention are not limited thereto, but may be head-up displays (which may also be referred to as “HUDs”) or other virtual image display or the like.
With reference to
As shown in
The lightguide 100a includes: a first light guiding member 1A having a first light-receiving surface 12A to receive a collimated light beam, a first lightguide section 20A to allow a light beam entering at the first light-receiving surface 12A to propagate in a first direction (the Y direction), and a first outgoing face 29A through which a light beam propagating in the first lightguide section 20A is allowed to exit in a second direction (the X direction) intersecting the first direction; and a second light guiding member 30A having a second light-receiving surface 31A to receive a light beam exiting from the first outgoing face 29A, a second lightguide section 30A to allow a light beam entering at the second light-receiving surface 31A to propagate in the second direction (the X direction), and a second outgoing face 39A through which a light beam propagating in the second lightguide section 30A is allowed to exit in a third direction (the Z direction) intersecting the first and second directions. Note that the second lightguide section and the second light guiding member are denoted by the same reference numeral 30A. For the first outgoing face 29A and the second light-receiving surface 31A, see
The lightguide 100a, which includes the first light guiding member 1A and the second light guiding member 30A, is able to reduce unevenness in the brightness of a virtual image to be viewed. A light beam which enters the first lightguide section 20A and the second lightguide section 30A strikes each outgoing face at an angle which is equal to or greater than the critical angle, and through repetitive total reflection, propagates in the first lightguide section 20A and the second lightguide section 30A. Therefore, the diameter of a light beam propagating in the first lightguide section 20A and the second lightguide section 30A does not depend on the cross-sectional area of the first lightguide section 20A and the second lightguide section 30A. In other words, the brightness of a virtual image which is obtained by using the lightguide 100a does not depend on the position in a cross section of the first lightguide section 20A and the second lightguide section 30A, whereby the aforementioned unevenness in the brightness of a virtual image can be reduced.
The first lightguide section 20A includes a rod portion which is elongated in the first direction (the Y direction), whereas the second lightguide section 30A includes a planar portion which is parallel to the plane P12 (the XY plane) that contains the first and second directions.
The first light guiding member 1A includes a coupling section 10A having the first light-receiving surface 12A, such that the first light-receiving surface 12A is inclined at predetermined angles with respect to the first, second and third directions. In other words, the normal of the first light-receiving surface 12A is not parallel to any of the first, second and third directions. The coupling section 10A and the first lightguide section 20A may be formed as an integral piece; or, after the coupling section 10A and the first lightguide section 20A are separately produced, the coupling section 10A and the first lightguide section 20A may be allowed to be adhesively bonded to each other. As will be described in detail later, providing the coupling section 10A enhances the efficiency of light utility. Note that the coupling section 10A may be omitted.
Although an example is illustrated herein where the first direction is the Y direction, the second direction is the X direction, and the third direction is the Z direction, it does not matter if the second direction is the −X direction. In other words, the coupling section 10A may be provided on the left-hand side in
An operation of the HMD 100A will be described.
Displaying light which has exited the display panel 50 is collimated by the collimating optical system 60, and the collimated light beam strikes the first light-receiving surface 12A of the first light guiding member 1A. The collimating optical system 60 collimates displaying light from each pixel of the display panel 50, and emits a light beam having a predetermined diameter in a direction corresponding to the position of the respective pixel. Let the central direction be defined as the direction in which the displaying light exiting a pixel in the center of the displaying region of the display panel 50 is collimated; then, the direction in which displaying light exiting a pixel at an edge (the upper edge, the lower edge, the left edge, or the right edge) of the displaying region is collimated constitutes a predetermined angle with the central direction. The diameter of a light beam which exits the collimating optical system 60 is adjusted by the collimating optical system 60. As will be described later, the diameter of the light beam can be increased through size adjustment of the coupling section 10A.
As the display panel 50 and the collimating optical system 60, those which are known can be broadly used. For example, a transmission type liquid crystal display panel or an organic EL display panel may be used as the display panel 50, while a lens system which is described in e.g. Japanese Laid-Open Patent Publication No. 2004-157520 may be used as the collimating optical system 60. Alternatively, a reflection type liquid crystal display panel (LCOS) may be used as the display panel 50, while concave mirrors or lenses described in e.g. Japanese Laid-Open Patent Publication No. 2010-282231 may be used as the collimating optical system 60. The entire disclosure of Japanese Laid-Open Patent Publication No. 2004-157520 and Japanese Laid-Open Patent Publication No. 2010-282231 is incorporated herein by reference. The display panel 50 is sized so that it diagonally measures about 0.2 inches to about 0.5 inches, for example.
The first lightguide section 20A of the first light guiding member 1A has, for example, a prism region 22A having formed therein a plurality of first slopes that are inclined in the first direction (the Y direction). The prism region 22A is a region defining a so-called prism surface. Note that a direction in which a slope is inclined means the direction in which the normal of the slope is inclined. Each first slope reflects a light beam propagating through the first lightguide section 20A in the second direction (the X direction), and also expands the light beam in the first direction (the Y direction). Note that arrows heading toward the second lightguide section 30A from the prism region 22A in
The second light guiding member (second lightguide section) 30A has, for example, a prism region 32A having formed therein a plurality of second slopes that are inclined in the second direction (the X direction). The prism region 32A of the second lightguide section 30A may include, as shown in
Each second slope reflects a light beam propagating through the second lightguide section 30A in the third direction (the Z direction), and also expands the light beam in the second direction (the X direction). The viewer (eye) is in the Z direction of the second light guiding member 30A, thus being able to see a virtual image of an image as displayed on the display panel 50 which is created by a light beam that exits the second light guiding member 30A. Herein, the diameter of the light beam entering the eye of the viewer has been expanded in the first direction (the Y direction) and in the second direction (the X direction) by the first lightguide section 20A and the second lightguide section 30A, thus resulting in a broad range in which the virtual image is viewable.
Next, the structure and action of each individual constituent element of the lightguide 100a will be described in detail.
As shown in
Light beams entering the first lightguide section 20A, in the course of their propagation inside the first lightguide section 20A, are reflected in the X direction from the plurality of first slopes 24 arrayed along the Y direction in the prism region 22A, thus exiting the first lightguide section 20A through the first outgoing face 29A, which opposes the plane carrying the first slopes 24 (prism surface). At this time, the light beams are expanded in the Y direction. Note that the angle difference between the light beam from each pixel and any light beam from a central pixel (the aforementioned ±θy) is conserved. Note that an optional reflective layer 26 is formed on the prism surface. The reflective layer 26 is made of a metal such as aluminum, for example. Providing the reflective layer 26 allows even a light beam which is incident on the prism surface at an angle smaller than the critical angle to be reflected, thereby enhancing the efficiency of light utility.
Note that air (or a low-refractive index medium: a medium whose refractive index is lower than that of the first lightguide section 20A) exists between the first outgoing face 29A of the first lightguide section 20A and the second light-receiving surface 31A of the second lightguide section 30A, so that a light beam propagating in the first lightguide section 20A undergoes total reflection when incident on the internal plane of the first outgoing face 29A at a critical angle or greater. As a result, the angle difference in a displayed image between light beams along the top-bottom direction (the Y direction) (i.e., the angle of view of the virtual image) is constrained only by the critical angle of the first lightguide section 20A.
Moreover, the first lightguide section 20A can be arranged so that light beams exiting the respective pixels uniformly reach the first slopes 24. For example, as schematically shown in
That is, by using the first light guiding member 1A of the aforementioned structure, the following advantages are additionally obtained.
(1) Without enlarging the first light guiding member 1A, the diameter of any light beam to be collimated by the collimating optical system 60 can be increased, whereby the efficiency of light utility can be improved.
(2) Since the diameter of a light beam to exit the first lightguide section 20A does not depend on the cross-sectional area of the first lightguide section 20A, a first lightguide section 20A with a smaller cross-sectional area can be used than in the case of adopting the construction of
Patent Document 1. In other words, the first light guiding member 1A can be downsized.
(3) Since the angle of view (screen size) of a virtual image is determined by the angle difference between light beams, the angle difference between light beams being determined based on the critical angle of the first lightguide section 20A, the angle of view (screen size) of the virtual image can be increased in the Y direction without having to increase the cross-sectional area of the first lightguide section 20A.
Given an angle difference ±θ0(Y) between light beams along the Y direction (i.e., the angle of view of the virtual image), the following relational expression is derived from the refractive index n and the critical angle θ c of the first lightguide section 20A.
θ0(Y)<sin−1(n·sin((90−θc)/2)),θc=sin−1(1/n)
Next, see
As shown in
Light beams entering the first lightguide section 20A, in the course of their propagation inside the first lightguide section 20A, are reflected in the X direction from the plurality of first slopes 24 arrayed along the Y direction in the prism region 22A, thus exiting the first lightguide section 20A through the first outgoing face 29A, which opposes the plane carrying the first slopes 24 (prism surface). At this time, the light beams are expanded in diameter in the Y direction. Note that the angle difference (the aforementioned ±θ x) between the light beam from each pixel and any light beam from a central pixel is conserved.
Light beams exiting the first outgoing face 29A of the first lightguide section 20A strike the second light-receiving surface 31A of the second light guiding member (second lightguide section) 30A. Light beams entering the second lightguide section 30A, in the course of their propagation inside the second lightguide section 30A, are reflected in the Z direction by the plurality of second slopes 34a arrayed along the X direction in the prism region 32A, thus exiting the second lightguide section 30A through the second outgoing face 39A, which opposes the plane carrying the second slopes 34a (prism surface). At this time, the light beams are expanded in the X direction. Note that the angle difference (the aforementioned ±θy and ±θx) between the light beam from each pixel and any light beam from a central pixel is conserved. Note that an optional reflective layer 36a is formed on the prism surface. The reflective layer 36a is made of a metal such as aluminum, for example. Providing the reflective layer 36a allows even a light beam which is incident on the prism surface at an angle smaller than the critical angle to be reflected, thereby enhancing the efficiency of light utility. Furthermore, an optional transparent resin layer 38 is formed on the reflective layer 36a. In the case where the reflective layer 36a has openings, by providing a transparent resin layer 38 having the same or a sufficiently close refractive index to that of the second conductive section 30A, double imaging to be created by the light transmitted through the openings can be suppressed.
The second outgoing face 39A of the second lightguide section 30A is in contact with air (or a low-refractive index medium: a medium whose refractive index is lower than that of the second lightguide section 30A), so that a light beam propagating in the second lightguide section 30A undergoes total reflection when incident on the internal plane of the second outgoing face 39A at a critical angle or greater. As a result, the angle difference in a displayed image between light beams along the right-left direction (the X direction) (i.e., the angle of view of the virtual image) is constrained only by the critical angle of the second lightguide section 30A.
Moreover, the second lightguide section 30A can be arranged so that light beams exiting the respective pixels uniformly reach the second slopes 34a. For example, as schematically shown in
That is, by using the second light guiding member 30A of the aforementioned structure, advantages similar to advantages (1) to (3) above being obtained by using first the light guiding member 1A are attained. However the angle of view of the virtual image in (3) above will be expanded in the X direction.
Given an angle difference ±θ0(X) between light beams along the X direction (i.e., the angle of view of the virtual image), the following relational expression is derived from the refractive index n and the critical angle θ c of the second lightguide section 30A.
θ0(X)<sin−1(n·sin((90−θc)/2)),θc=sin−1(1/n)
Next, with reference to
First, see
Each prism has a counterparting slope for the first slope 24 (i.e., a slope constituting an angle β1 with the YZ plane). However, any light beam striking this slope will cause stray light; therefore, in order to prevent any light beam from striking this slope, β1 is set so as to satisfy the relationship β1>2·α1−θy.
The arraying pitch p1 of the prisms (first slopes 24) is made smaller away from the first light-receiving surface 12A, so that light beams from the respective pixels will reach the first slopes 24 with a uniform intensity. In addition, or in the alternative, the thickness of the first lightguide section 20A may be made smaller away from the first light-receiving surface 12A. Various light guiding member constructions are known, and any known construction is broadly applicable; however, from the display quality standpoint, it is preferable to use a first lightguide section 20A which includes the first slopes 24 as described above.
As shown in
The first light guiding member 1A is produced by through injection molding using a transparent resin, for example. An example of a specific construction is given below.
The angle difference between light beams along the screen top-bottom direction (the Y direction) (i.e., the angle of view of a virtual image):±θ0(Y)=±9 degrees
material: cycloolefin resin, e.g., Zeonor resin manufactured by ZEON CORPORATION (refractive index n≈1.53)
cross-sectional shape of the first lightguide section 20A: a1(the X direction)×b1 (the Z direction)=2.0 mm×1.0 mm
prism width: c1=0.1 mm
prism pitch: p1=0.8 mm to 0.15 mm
As necessary, a reflective layer 26 may be formed on the prism surface of the first lightguide section 20A. The reflective layer 26 may be formed through vapor deposition of aluminum, for example. The reflective layer 26 may have a thickness of e.g. several dozen to several hundred nm.
Note that the first lightguide section 20A of the first light guiding member 1A and the coupling section 10A may be formed as an integral piece, or they may be separately produced and attached to each other with an adhesive. At this time, the refractive indices of the first lightguide section 20A, the coupling section 10A, and the adhesive are preferably equal, as much as possible.
Next, see
Each prism has a counterparting slope for the second slope 34a (i.e., a slope constituting an angle β2 with the XY plane). However, any light beam striking this slope will cause stray light; therefore, in order to prevent any light beam from striking this slope, β2 is set so as to satisfy the relationship β2>2·α2−θx. If any stray light occurs, it will unfavorably affect the virtual image that is perceived by the viewer (eye).
The arraying pitch p2 of the prisms (second slopes 34a) is made smaller away from the second light-receiving surface 31A, so that light beams from the respective pixels will reach the second slopes 34a with a uniform intensity. In addition, or in the alternative, the thickness of the second lightguide section 30A may be made smaller away from the second light-receiving surface 31A. Various light guiding member constructions are known, and any known construction is broadly applicable; however, from the display quality standpoint, it is preferable to use a second lightguide section 30A which includes the second slope 34a as described above.
As shown in
Next, with reference to
As shown in
Next, as shown in
An example of a specific construction of the second light guiding member 30A is given below.
The angle difference between light beams along the screen right-left direction (the X direction)(i.e., the angle of view of a virtual image):±θ0x=±16 degrees
material: cycloolefin resin, e.g., Zeonor resin manufactured by ZEON CORPORATION (refractive index n≈1.53)
cross-sectional shape of the second lightguide section 30A: a2(the Z direction)×b2 (the Y direction)=1.0 mm×40 mm
prism width: c2=0.1 mm
prism pitch: p2=0.8 mm to 0.3 mm
reflective layer 36a: an Al (aluminum) layer with a thickness of several dozen to several hundred nm
transparent resin layer 38: a UV-curing resin with a thickness of several dozen to several hundred μm
Next, with reference to
Preferably, the first light-receiving surface 12A not only has a predetermined gradient but also has an adequate size. The reason is that, if the size of the first light-receiving surface 12A is inadequate, then during propagation of light beams inside the first lightguide section 20A and/or the second light guiding member 30A, there will be regions in which light beams cannot exist, consequently creating regions in which outgoing light cannot exist (i.e., the virtual image will become partially lost). In
By taking into account the difference ±θy along the screen top-bottom direction and the difference ±θx along the screen right-left direction between collimated light beams incident on the first light-receiving surface 12A, the first light-receiving surface 12A may be sized so that these light beams uniformly exist in the first lightguide section 20A and the second lightguide section 30A. The size of the first light-receiving surface 12A can be determined through geometric construction.
In the case of the above-sized first lightguide section 20A and second lightguide section 30A, as shown in
With reference to
As shown in
The lightguide 100b includes: a first light guiding member 1B having a first light-receiving surface 12B to receive a collimated light beam, a first lightguide section 20B to allow a light beam entering at the first light-receiving surface 12B to propagate in a first direction (the X direction), and a first outgoing face 29B through which a light beam propagating in the first lightguide section 20B is allowed to exit in a second direction (the Y direction) intersecting the first direction; and a second light guiding member 30B having a second light-receiving surface 31B to receive a light beam exiting from the first outgoing face 29B, a second lightguide section 30B to allow a light beam entering at the second light-receiving surface 31B to propagate in the second direction (the Y direction), and a second outgoing face 39B through which a light beam propagating in the second lightguide section 30B is allowed to exit in a third direction (the Z direction) intersecting the first and second directions. Note that the second lightguide section and the second light guiding member are denoted by the same reference numeral 30B. For the first outgoing face 29B and the second light-receiving surface 31B, see
The lightguide 100b, which includes the first light guiding member 1B and the second light guiding member 30B, is able to reduce unevenness in the brightness of a virtual image to be viewed. A light beam which enters the first lightguide section 20B and the second lightguide section 30B strikes each outgoing face at an angle which is equal to or greater than the critical angle, and through repetitive total reflection, propagates in the first lightguide section 20B and the second lightguide section 30B. Therefore, the diameter of a light beam propagating in the first lightguide section 20B and the second lightguide section 30B does not depend on the cross-sectional area of the first lightguide section 20B and the second lightguide section 30B. In other words, the brightness of a virtual image which is obtained by using the lightguide 100b does not depend on the position in a cross section of the first lightguide section 20B and the second lightguide section 30B, whereby the aforementioned unevenness in the brightness of a virtual image can be reduced.
The first lightguide section 20B includes a rod portion which is elongated in the first direction (the X direction), whereas the second lightguide section 30B includes a planar portion which is parallel to the plane P12 (the XY plane) that contains the first and second directions.
The first light guiding member 1B includes a coupling section 10B having the first light-receiving surface 12B, such that the first light-receiving surface 12B is inclined at predetermined angles with respect to the first, second and third directions. In other words, the normal of the first light-receiving surface 12B is not parallel to any of the first, second and third directions. The coupling section 10B and the first lightguide section 20B may be formed as an integral piece; or, after the coupling section 10B and the first lightguide section 20B are separately produced, the coupling section 10B and the first lightguide section 20B may be allowed to be adhesively bonded to each other. As described earlier, providing the coupling section 10B enhances the efficiency of light utility. Note that the coupling section 10B may be omitted.
Although an example is illustrated herein where the first direction is the X direction, the second direction is the Y direction, and the third direction is the Z direction, it does not matter if the first direction is the −X direction. In other words, the coupling section 10B may be provided on the left-hand side in
The HMD 100B is arranged so that the first light guiding member 1B propagates light beams in the X direction (or the −X direction) and that the second light guiding member 30B propagates light beams in the Y direction (or the −Y direction), thus being distinct from the earlier-described HMD 100A, which is arranged so that the first light guiding member 1A propagates light beams in the Y direction (or the −Y direction) and that the second light guiding member 30A propagates light beams in the X direction (or the −X direction).
An operation of the HMD 100B will be described.
Displaying light which has exited the display panel 50 is collimated by the collimating optical system 60, and the collimated light beam strikes the first light-receiving surface 12B of the first light guiding member 1B. The collimating optical system 60 collimates displaying light from each pixel of the display panel 50, and emits a light beam having a predetermined diameter in a direction corresponding to the position of the respective pixel. Let the central direction be defined as the direction in which the displaying light exiting a pixel in the center of the displaying region of the display panel 50 is collimated; then, the direction in which displaying light exiting a pixel at an edge (the upper edge, the lower edge, the left edge, or the right edge) of the displaying region is collimated constitutes a predetermined angle with the central direction. The diameter of a light beam which exits the collimating optical system 60 is adjusted by the collimating optical system 60. The diameter of the light beam can be increased through size adjustment of the coupling section 10A.
As the display panel 50 and the collimating optical system 60, those which are known can be broadly used, as has been mentioned above with respect to the HMD 100A.
The first lightguide section 20B of the first light guiding member 1B has, for example, a prism region 22B having formed therein a plurality of first slopes that are inclined in the first direction (the X direction). The prism region 22B is a region defining a so-called prism surface. Note that a direction in which a slope is inclined means the direction in which the normal of the slope is inclined. Each first slope reflects a light beam propagating through the first lightguide section 20B in the second direction (the Y direction), and also expands the light beam in the first direction (the X direction). Note that arrows heading toward the second lightguide section 30B from the prism region 32A in
The second light guiding member (second lightguide section) 30B has, for example, a prism region 32B having formed therein a plurality of second slopes that are inclined in the second direction (the Y direction). The prism region 32A of the second lightguide section 30B may include, as shown in
Each second slope reflects a light beam propagating in the second lightguide section 30B in the third direction (the Z direction), and also expands the light beam in the second direction (the Y direction). The viewer (eye) is in the Z direction of the second light guiding member 30B, thus being able to see a virtual image of an image as displayed on the display panel 50 which is created by a light beam that exits the second light guiding member 30B. Herein, the diameter of the light beam entering the eye of the viewer has been expanded in the first direction (the X direction) and in the second direction (the Y direction) by the first lightguide section 20B and the second lightguide section 30B, thus resulting in a broad range in which the virtual image is viewable.
Next, the structure and action of each individual constituent element of the lightguide 100b will be described in detail.
As shown in
Light beams entering the first lightguide section 20B, in the course of their propagation inside the first lightguide section 20B, are reflected in the X direction from the plurality of first slopes 24 arrayed along the X direction in the prism region 22B, thus exiting the first lightguide section 20B through the first outgoing face 29B, which opposes the plane carrying the first slopes 24 (prism surface). At this time, the light beams are expanded in the X direction. Note that the angle difference (the aforementioned ±6 x) between the light beam from each pixel and any light beam from a central pixel is conserved. Note that an optional reflective layer 26 is formed on the prism surface. The reflective layer 26 is made of a metal such as aluminum, for example. Providing the reflective layer 26 allows even a light beam which is incident on the prism surface at an angle smaller than the critical angle to be reflected, thereby enhancing the efficiency of light utility.
Note that air (or a low-refractive index medium: a medium whose refractive index is lower than that of the first lightguide section 20B) exists between the first outgoing face 29B of the first lightguide section 20B and the second light-receiving surface 31A of the second lightguide section 30B, so that a light beam propagating in the first lightguide section 20B undergoes total reflection when incident on the internal plane of the first outgoing face 29B at a critical angle or greater. As a result, the angle difference in a displayed image between light beams along the right-left direction (the X direction) (i.e., the angle of view of the virtual image) is constrained only by the critical angle of the first lightguide section 20B.
Moreover, the first lightguide section 20B can be arranged so that light beams exiting the respective pixels uniformly reach the first slopes 24. For example, as shown in schematically shown in
That is, by using the first light guiding member 1B of the aforementioned structure, the following advantages are additionally obtained.
(1) Without enlarging the first light guiding member 1B, the diameter of any light beam to be collimated by the collimating optical system 60 can be increased, whereby the efficiency of light utility can be improved.
(2) Since the diameter of a light beam to exit the first lightguide section 20B does not depend on the cross-sectional area of the first lightguide section 20B, a first lightguide section 20B with a smaller cross-sectional area can be used than in the case of adopting the construction of Patent Document 1. In other words, the first light guiding member 1B can be downsized.
(3) Since the angle of view (screen size) of a virtual image is determined by the angle difference between light beams, the angle difference between light beams being determined based on the critical angle of the first lightguide section 20B, the angle of view (screen size) of the virtual image can be increased in the X direction without having to increase the cross-sectional area of the first lightguide section 20B.
Given an angle difference ±θ0(X) between light beams along the X direction (i.e., the angle of view of the virtual image), the following relational expression is derived from the refractive index n and the critical angle θ c of the first lightguide section 20B.
θ0(X)<sin−1 (n·sin((90−θc)/2)), θc=sin−1(1/n)
Next, see
As shown in
Light beams entering the first lightguide section 20B, in the course of their propagation inside the first lightguide section 20B, are reflected in the Y direction by the plurality of first slopes 24 arrayed along the X direction in the prism region 22B, thus exiting the first lightguide section 20B through the first outgoing face 29B, which opposes the plane carrying the first slopes 24 (prism surface). At this time, the light beams are expanded in diameter in the X direction. Note that the angle difference between the light beam from each pixel and any light beam from a central pixel (the aforementioned ±θy) is conserved.
Light beams exiting the first outgoing face 29B of the first lightguide section 20B strike the second light-receiving surface 31B of the second light guiding member (second lightguide section) 30B. Light beams entering the second lightguide section 30B, in the course of their propagation inside the second lightguide section 30B, are reflected in the Z direction by the plurality of second slopes 34a arrayed along the Y direction in the prism region 32B, thus exiting the second lightguide section 30B through the second outgoing face 39B, which opposes the plane carrying the second slopes 34a (prism surface). At this time, the light beams are expanded in the Y direction. Note that the angle difference (the aforementioned ±θx and ±θy) between the light beam from each pixel and any light beam from a central pixel is conserved. Note that an optional reflective layer 36a is formed on the prism surface. The reflective layer 36a is made of a metal such as aluminum, for example. Providing the reflective layer 36a allows even a light beam which is incident on the prism surface at an angle smaller than the critical angle to be reflected, thereby enhancing the efficiency of light utility. Furthermore, an optional transparent resin layer 38 is formed on the reflective layer 36a. In the case where the reflective layer 36a has openings, by providing a transparent resin layer 38 having the same or a sufficiently close refractive index to that of the second conductive section 30A, double imaging to be created by the light transmitted through the openings can be suppressed.
The second outgoing face 39B of the second lightguide section 30B is in contact with air (or a low-refractive index medium: a medium whose refractive index is lower than that of the second lightguide section 30B), so that a light beam propagating in the second lightguide section 30B undergoes total reflection when incident on the internal plane of the second outgoing face 39B at a critical angle or greater. As a result, the angle difference in a displayed image between light beams along the top-bottom direction (the Y direction) (i.e., the angle of view of the virtual image) is constrained only by the critical angle of the second lightguide section 30B.
Moreover, the second lightguide section 30B can be arranged so that light beams exiting the respective pixels uniformly reach the second slopes 34a. For example, as schematically shown in
That is, by using the second light guiding member 30B of the above structure, advantages similar to advantages (1) to (3) above being obtained by using the first light guiding member 1B are attained. However, the angle of view of the virtual image in (3) above will be expanded in the Y direction.
Given an angle difference ±θ0(Y) between light beams along the Y direction (i.e., the angle of view of the virtual image), the following relational expression is derived from the refractive index n and the critical angle θ c of the second lightguide section 30B.
θ0(Y)<sin−1(n·sin((90−θc)/2)),θc=sin−1(1/n)
Next, with reference to
First, see
Each prism has a counterparting slope for the first slope 24 (i.e., a slope constituting an angle 1321 with the XZ plane). However, any light beam striking this slope will cause stray light; therefore, in order to prevent any light beam from striking this slope, β21 is set so as to satisfy the relationship β21>2·α21−θx.
The arraying pitch p21 of the prisms (first slopes 24) is made smaller away from the first light-receiving surface 12B, so that light beams from the respective pixels will reach the first slopes 24 with a uniform intensity. In addition, or in the alternative, the thickness of the first lightguide section 20B may be made smaller away from the first light-receiving surface 12B. Various light guiding member constructions are known, and any known construction is broadly applicable; however, from the display quality standpoint, it is preferable to use a first lightguide section 20B which includes the first slopes 24 as described above.
As shown in
The first light guiding member 1B is produced by through injection molding using a transparent resin, for example. An example of a specific construction is given below.
The angle difference between light beams along the screen right-left direction (the X direction) (i.e., the angle of view of a virtual image):±00(x)=±16 degrees
material: cycloolefin resin, e.g., Zeonor resin manufactured by ZEON CORPORATION (refractive index n≈1.53)
cross-sectional shape of the first lightguide section 20B: a21 (the Y direction)×b21(the Z direction)=2.0 mm×1.0 mm
prism width: c21=0.1 mm
prism pitch: p21=0.8 mm to 0.15 mm
As necessary, a reflective layer 26 may be formed on the prism surface of the first lightguide section 20B.
The reflective layer 26 may be formed through vapor deposition of aluminum, for example. The reflective layer 26 may have a thickness of e.g. several dozen to several hundred nm.
Note that the first lightguide section 20B of the first light guiding member 1B and the coupling section 10B may be formed as an integral piece, or they may be separately produced and attached to each other with an adhesive. At this time, the refractive indices of the first lightguide section 20B, the coupling section 10B, and the adhesive are preferably equal, as much as possible.
Next, see
The second light guiding member 30A is shaped so as to have a rectangular (a2×b2) cross section extending along the x axis direction, with prisms being arrayed along the X direction on a plane (prism surface) which is parallel to the XY plane, these prisms having a length c2 along the X direction. Each prism has a second slope 34a to reflect a light beam in the Z direction. The second slope 34a is inclined in the X direction, constituting an angle α22 (greater than 0° but 45° or less) with the XY plane. It also has a counterparting second slope constituting an angle β22.
Each prism has a counterparting slope for the second slope 34a (i.e., a slope constituting an angle β22 with the XY plane). However, any light beam striking this slope will cause stray light; therefore, in order to prevent any light beam from striking this slope, β22 is set so as to satisfy the relationship β22>2·α22−θx. If any stray light occurs, it will unfavorably affect the virtual image that is perceived by the viewer (eye).
The arraying pitch p2 of the prisms (second slopes 34a) is made smaller away from the second light-receiving surface 31B, so that light beams from the respective pixels will reach the second slopes 34a with a uniform intensity. In addition, or in the alternative, the thickness of the second lightguide section 30A may be made smaller away from the second light-receiving surface 31B. Various light guiding member constructions are known, and any known construction is broadly applicable; however, from the display quality standpoint, it is preferable to use a second lightguide section 30A which includes the second slopes 34a as described above.
As shown in
An example of a specific construction of the second light guiding member 30B is given below.
The angle difference between light beams along the screen top-bottom direction (the Y direction)(i.e., the angle of view of a virtual image):±θ0(y)=±9 degrees
material: cycloolefin resin, e.g., Zeonor resin manufactured by ZEON CORPORATION (refractive index n≈1.53)
cross-sectional shape of the second lightguide section 30A: a2s(the Z direction)×b22 (the X direction)=1.0 mm×50 mm
prism width: c22=0.1 mm
prism pitch: p22=0.8 mm to 0.3 mm
reflective layer 36a: an Al (aluminum) layer with a thickness of several dozen to several hundred nm
transparent resin layer 38: a UV-curing resin with a thickness of several dozen to several hundred μm
Next, with reference to
Preferably, the first light-receiving surface 12B not only has a predetermined gradient but also has an adequate size. As has been described with reference to
By taking into account the difference ±θy along the screen top-bottom direction and the difference ±θx along the screen right-left direction between collimated light beams incident on the first light-receiving surface 12B, the first light-receiving surface 12B may be sized so that these light beams uniformly exist in the first lightguide section 20B and the second lightguide section 30B. The size of the first light-receiving surface 12B can be determined through geometric construction.
In the case of the above-sized first lightguide section 20B and second lightguide section 30B, as shown in
Next, see
Generally speaking, the collimating optical system 60 has aberration, such that displaying light exiting the screen center of the display panel 50, which is disposed on the optical axis of the collimating optical system 60, becomes a light beam with a relatively good precision (i.e., having a high degree of parallelism) through collimation, but the degree of parallelism of the light beam will become lower away from the screen center. Stated otherwise, displaying light exiting pixels adjoining the predetermined pixel will stray into the collimated light beam. Therefore, the lowered degree of parallelism of the light beam exhibits itself as a blur of the virtual image that is finally viewed (as indicated by the blur in a virtual image 50′ in
Moreover, the display panel 50 is often longer from side to side than from top to bottom (having an aspect ratio of 4:3 or 16:9, etc.), and thus the degree of parallelism tends to be low at the upper and lower edges of the center of the displaying region and even lower at the right and left edges of the center, with the lowest degree of parallelism existing in the four corners of the displaying region.
Therefore, when the collimating optical system 60 has such aberration, light exiting the upper and lower regions of the collimating optical system 60 causes substantial blurs at the screen corners and right and left edges of the virtual image. Conversely, blurs in the virtual image can be reduced by preventing the light exiting the upper and lower regions of the collimating optical system 60 from entering the first lightguide section 20A.
With reference to
In the HMD 100A, as shown in
On the other hand, in the HMD 100B, as shown in
Thus, in the case of a collimating optical system having aberration as illustrated in
Since the aberration of the collimating optical system 60 may be of various characteristics, either construction of the HMD 100A or the HMD 100B may be appropriately selected in accordance with such characteristics.
The HMD 100C includes, for a single first light guiding member 1C, two second light guiding members 30B that are arrayed in parallel along the first direction (the X direction). The first light guiding member 1C has a similar construction to that of the first light guiding member 1B, but differs from the first light guiding member 1B in that it includes a connecting lightguide section 20c, which connects the two first lightguide sections 20B. The distance between the two first lightguide sections 20B (i.e., the length of the connecting lightguide section 20c) may be adjusted in accordance with the interval between both eyes. Such a construction allows the number of parts to be decreased over the case where either an HMD 100A or an HMD 100B is provided for each eye. It will be appreciated that, as the first light guiding member 1C, an integral piece may be used into which the two first lightguide sections 20B and the connecting lightguide section 20c are made.
The present specification discloses lightguides and head-mounted displays as described in the following Items.
A lightguide comprising:
a first light guiding member having a first light-receiving surface to receive a collimated light beam, a first lightguide section to allow the light beam entering at the first light-receiving surface to propagate in a first direction, and a first outgoing face through which the light beam propagating in the first lightguide section is allowed to exit in a second direction intersecting the first direction; and
a second light guiding member having a second light-receiving surface to receive the light beam exiting from the first outgoing face, a second lightguide section to allow the light beam entering at the second light-receiving surface to propagate in the second direction, and a second outgoing face through which the light beam propagating in the second lightguide section is allowed to exit in a third direction intersecting the first and second directions.
The lightguide of Item 1 is able to reduce unevenness in the brightness of a virtual image to be viewed.
The lightguide of Item 1, wherein,
the first light guiding member includes a coupling section having the first light-receiving surface; and
the first light-receiving surface is inclined at predetermined angles with respect to the first, second and third directions.
The lightguide of Item 2 is able to effectively enhance the efficiency of light utility.
The lightguide of Item 1 or 2, wherein,
the first light guiding member has a plurality of first slopes inclined in the first direction; and
the plurality of first slopes allow the light beam propagating in the first lightguide section to be reflected in the second direction, and expands the light beam in the first direction.
With the lightguide of Item 3, the range in which a virtual image is viewable (viewing angle) is expanded in the first direction.
The lightguide of Item 3, wherein,
the second light guiding member has a plurality of second slopes inclined in the second direction; and
the plurality of second slopes allow the light beam propagating in the second lightguide section to be reflected in the third direction, and expands the light beam in the second direction.
With the lightguide of Item 4, the range in which a virtual image is viewable (viewing angle) is expanded also in the second direction.
The lightguide of Item 4, wherein the plurality of first slopes constitute an angle α1 with a plane P13 containing the first and third directions, and the plurality of second slopes constitute an angle α2 with a plane P12 containing the first and second directions, the angle α1 and the angle α2 each independently being 45° or less.
With the lightguide of Item 5, a virtual image with a high display quality can be obtained.
The lightguide of Item 5, wherein the first light-receiving surface constitutes, in the plane P12, an angle of 2·α1 with the plane P23, and in a plane P′23 resulting from rotating the plane P23 by (90−2·α1) degrees around the third direction, an angle of 2·α2 with the plane P12.
With the lightguide of Item 6, a light beam can be efficiently led to the first lightguide section.
The lightguide of Item 5 or 6, wherein the first light-receiving surface has a side whose length is equal to or greater than twice the length along the second direction of a cross section of the first lightguide section which is parallel to the plane P23, and a side whose length is equal to or greater than twice the length along the third direction of a cross section of the first lightguide section which is parallel to the plane P13.
With the lightguide of Item 7, a virtual image without partial losses can be formed.
The lightguide of any of Items 1 to 7, wherein the first lightguide section includes a rod portion which is elongated in the first direction, and the second lightguide section includes a planar portion which is parallel to a plane containing the first and second directions.
The lightguide of Item 8 has a shape which is suitably used for an HMD.
The lightguide of any of Items 1 to 8 comprising one said first light guiding member and two said second light guiding members arrayed in parallel along the first direction.
The lightguide of Item 9 is to be used in an HMD which allows a virtual image to be viewed with both eyes.
A head-mounted display comprising: a display panel;
a collimating optical system to collimate displaying light exiting the display panel and emit a collimated light beam; and
the lightguide of any of Items 1 to 9,
the lightguide being disposed so that the first light-receiving surface receives the light beam having been collimated through the collimating optical system.
The HMD of Item 10 allows a virtual image with reduced unevenness in brightness to be viewed.
A lightguide according to the present invention is applicable to an HMD, an HUD or any other virtual image display or the like.
Number | Date | Country | Kind |
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2013-243108 | Nov 2013 | JP | national |
Filing Document | Filing Date | Country | Kind |
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PCT/JP2014/080770 | 11/20/2014 | WO | 00 |