JP5459148B2 - Light guide plate for virtual image display device and virtual image display device - Google Patents

Description

  The present invention relates to a light guide plate used for a head mounted display or the like used by being mounted on a head, and a virtual image display device incorporating the same.

  2. Description of the Related Art In recent years, various types of virtual image display devices that enable formation and observation of virtual images, such as a head-mounted display, have been proposed that guide video light from a display element to an observer's pupil using a light guide plate. As a light guide plate for such a virtual image display device, a plurality of partial reflection surfaces arranged to be parallel to each other at a predetermined angle with respect to the main surface of the light guide plate while guiding image light using total reflection. There is known a technique in which image light is reflected and taken out from the light guide plate to cause the image light to reach the retina of the observer (see Patent Document 1). As a method of forming a plurality of partial reflection surfaces of such a light guide plate, two transparent substrates having a comb-like cross section are prepared, and after coating one slope of the transparent substrates, A method of overlapping the slopes is considered (see FIG. 33, etc.). As a similar technique, there is also known a technique in which a reflective layer is formed on a sawtooth section in order to extract image light (see Patent Document 2).

Special table 2003-536102 gazette JP 2004-157520 A

  In the light guide plate having a plurality of partial reflection surfaces as described above, keeping the partial reflection surfaces flat is indispensable for extracting high-quality image light. Since the flat part for forming the partial reflection surface is produced by injection molding using a metal mold, it is important to increase the flatness on the surface of the metal mold or its original mold. Depending on the shape, it is not easy to increase the flatness in processing, and if it is intended to increase the flatness, the production cost may be very high. In particular, when multiple partial reflective surfaces are arranged in a sawtooth shape or the like in cross section, unstable vibration is generated in the cutting tool during mold production, and the mold surface tends to deteriorate, and mold release during transfer The deterioration of the properties may reduce the mold life or the manufacturing throughput.

  Therefore, the present invention has an object to provide a light guide plate for a virtual image display device and a virtual image display device incorporating the same, which can improve the precision and life of the mold, improve the manufacturing throughput, and reduce the production cost. To do.

  In order to solve the above-described problems, a light guide plate according to the present invention includes (a) a light incident portion that takes in image light therein, and (b) first and second total reflection surfaces that extend opposite to each other. A light guide unit that guides image light taken from the incident unit by total reflection on the first and second total reflection surfaces; and (c) forms a predetermined angle with respect to the first reflection surface and the first reflection surface. A plurality of reflection units each having a second reflection surface and arranged in a predetermined arrangement direction, and entering each of the reflection units constituting the plurality of reflection units through the light guide portion by the first reflection surface. (D) an image extraction unit that allows image light to be extracted to the outside by bending an optical path that reflects the image light and further reflects the image light reflected by the first reflection surface by the second reflection surface; A light emitting part for emitting image light that has passed through the extraction part to the outside; (E) In each reflection unit, the first reflection surface and the second reflection surface are opposed to each other in an inclined state toward the light emitting portion side, and are arranged at an acute angle. A tapered groove extending toward the injection part is formed. Here, the fact that the first reflecting surface and the second reflecting surface are inclined to the light emitting portion side means that the surface perpendicular to the light emitting portion is a reference surface and is inclined from the reference surface. say. Moreover, about the 1st reflective surface and the 2nd reflective surface, the taper-shaped groove | channel which spreads toward a light emission part is formed, and the 1st reflective surface and the 2nd reflective surface are light emission surfaces. When it inclines so that it may each oppose to, it says that it inclines so that the space | interval of both surfaces may become large as it approaches a light emission part. Total reflection is not only when all the light is reflected and transmitted by the inner surface, but also by applying a mirror coat or a half mirror film with a semi-transmissive aluminum film on the surface that satisfies the total reflection condition. The case of reflection is also included.

  In the light guide plate, flat portions corresponding to the first and second reflecting surfaces constituting the image extraction portion are inclined to the light emitting portion side at a predetermined inclination angle. Accordingly, the back side of the first reflection surface and the second reflection surface exposed to the opposite side of the light emitting portion at the time of molding, that is, the first total reflection surface side, is inclined to face the exposure side. In other words, the surface on the back side of the first reflecting surface or the second reflecting surface is equivalent to the surface of the tapered portion extending in the depth direction, that is, the light emitting side. For this reason, it is relatively easy to keep the flatness high in the production of the mold part corresponding to the flat part, and the flat part molded from the mold by, for example, injection molding or the like can be easily separated. Can be typed. By making the flat part easy to release, not only can the deformation of the light guide plate be suppressed during the release, but also the mold load can be suppressed to extend the life of the mold and improve the manufacturing throughput of the light guide plate. it can. As described above, the manufacturing cost of the light guide plate can be reduced.

  In a specific aspect of the present invention, the first reflection surface of the image extraction unit has a direction perpendicular to both the normal direction of the first total reflection surface of the light guide unit and the arrangement direction of the plurality of reflection units. It is inclined toward the light emitting part side at a predetermined inclination angle with respect to a surface perpendicular to the first total reflection surface as an axial direction of rotation. Here, the first reflecting surface is inclined toward the light emitting portion side means that the surface on the reflecting side is inclined toward the light emitting portion side, that is, the front surface and the light emitting portion are configured. This means that the angle formed with the surface to be cut is smaller than 90 degrees. In this case, it is possible to keep the flatness high and easily release the corresponding flat portion in the production of the first reflecting surface which is relatively likely to cause a problem in manufacturing throughput.

  In a specific aspect of the present invention, the inclination of the second reflecting surface of the image extraction unit toward the light emitting unit is larger than that of the first reflecting surface. In this case, the flat part can be more easily released.

  In still another aspect of the present invention, the predetermined inclination angle of the first reflecting surface changes according to the position in the arrangement direction of the plurality of reflecting units. In this case, by appropriately determining the inclination angle according to the position, for example, it is possible to improve the releasability of a portion corresponding to the image extraction unit.

  In still another aspect of the invention, the predetermined inclination angle of the first reflecting surface is not less than 0.5 ° and not more than 5 °. In this case, the ease of release can be ensured, and the characteristics of the image light emitted from the image extraction unit can be kept good.

を満たす。この場合、各反射ユニットにおいて第１の反射面で反射された光を確実に第２の反射面で反射させることができ、光の利用効率の低下を抑制できる。 In still another aspect of the present invention, the predetermined angle of inclination of the first reflecting surface is α, the predetermined angle formed by the second reflecting surface with respect to the first reflecting surface is β, and the light emitting unit extracts the predetermined angle. If the horizontal angle of view of the image light is θ,

Meet. In this case, the light reflected by the first reflecting surface in each reflecting unit can be reliably reflected by the second reflecting surface, and a decrease in light utilization efficiency can be suppressed.

  In still another aspect of the present invention, the image light incident on each reflection unit is emitted from the light emitting unit as virtual image light by passing the image extraction unit only once and bending the optical path. In this case, the image extraction unit can extract the virtual image light, which is an effective component for the observer, from the image light without being lost due to the transmission of the other reflection units.

  In still another aspect of the present invention, the second reflection surface forms an angle of 30 ° to 40 ° with respect to the first total reflection surface of the light guide section. In this case, it is possible to suppress an extreme decrease in luminance of the image light extracted through the second reflecting surface.

  In still another aspect of the present invention, the first and second reflecting surfaces are partially reflecting surfaces capable of transmitting some light. In this case, the present invention can be applied to a virtual image display device that allows an observer to observe an external world image with see-through.

  In order to solve the above problems, a virtual image display device according to the present invention includes (a) the light guide plate according to any one of the above, and (b) an image forming device that forms image light guided to the light guide plate. In this case, by using any of the light guide plates described above, the virtual image display device can improve the manufacturing throughput of the light guide plate constituting the light guide plate, extend the life of the mold, and reduce the manufacturing cost.

(A) is sectional drawing which shows the virtual image display apparatus which concerns on embodiment, (B) and (C) are the front views and top views of the light-guide plate which concern on embodiment. (A) is a schematic diagram for explaining the structure of the image extraction unit and the optical path of the image light in the image extraction unit, and (B) is a diagram showing a state of reflection on the back side of the image extraction unit. (C) is a diagram showing a state of reflection on the entrance side of the image extraction unit. It is the figure which expanded a part of image extraction part. (A) is a conceptual diagram explaining the process of injection molding among an example of the manufacturing process of a light-guide plate, (B) is a conceptual diagram explaining the process of protective layer formation among manufacturing processes. (A) is a perspective view for demonstrating the mode of the cutting process of original mold preparation, (B) is a top view, (C) is a figure of a comparative example. It is a figure which shows the specific state of the original sawtooth-shaped flat surface cut out by cutting. It is a schematic diagram for demonstrating the light-guide plate which concerns on 2nd Embodiment.

[First Embodiment]
A light guide plate for a virtual image display device and a virtual image display device incorporating the light guide plate according to the first embodiment of the present invention will be described below.

[A. Structure of light guide plate and virtual image display device]
A virtual image display device 100 according to this embodiment shown in FIG. 1A is applied to a head-mounted display, and includes an image forming device 10 and a light guide plate 20 as a set. 1A corresponds to the AA cross section of the light guide plate 20 shown in FIG.

  The virtual image display device 100 allows an observer to recognize image light based on a virtual image, and allows the observer to observe an external image in a see-through manner. The image forming apparatus 10 and the light guide plate 20 are usually provided one by one corresponding to the right eye and the left eye of the observer. However, since the right eye and the left eye are symmetrical, the left eye is used here. For the right eye, illustration is omitted. The virtual image display device 100 as a whole has, for example, an appearance (not shown) like general glasses.

  The image forming apparatus 10 includes a liquid crystal device 11 that is an image display element, and a collimating lens 12 for forming a light beam. The liquid crystal device 11 spatially modulates illumination light from a light source (not shown) to form image light to be a display target such as a moving image. The collimating lens 12 converts the image light emitted from each point on the liquid crystal device 11 into a light beam in a parallel state. The lens material of the collimating lens 12 can be either glass or plastic.

  As shown in FIGS. 1A to 1C, the light guide plate 20 according to this embodiment includes a light guide plate main body 20 a, an incident light bending portion 21, and an image extraction portion 23. The light guide plate 20 emits the image light formed by the image forming apparatus 10 as virtual image light toward the observer's eye EY and recognizes it as an image.

  The overall appearance of the light guide plate 20 is formed by a light guide plate body 20a which is a flat plate extending parallel to the YZ plane in the drawing. In addition, the light guide plate 20 has an image extraction portion 23 composed of a number of micromirrors embedded in the light guide plate main body portion 20a at one end in the longitudinal direction, and extends the light guide plate main body portion 20a at the other end in the longitudinal direction. The prism portion PS formed as described above and the incident light bending portion 21 associated therewith are configured.

  The light guide plate main body 20a is a light incident portion that is formed of a light-transmitting resin material or the like and takes in image light from the image forming apparatus 10 on a front side plane that is parallel to the YZ plane and faces the image forming apparatus 10. It has a certain light incident surface IS and a light emitting surface OS which is a light emitting portion for emitting image light toward the observer's eye EY. The light guide plate main body 20a has a rectangular inclined surface RS in addition to the light incident surface IS as a side surface of the prism portion PS, and a mirror layer 21a is formed on the inclined surface RS so as to cover it. . Here, the mirror layer 21a functions as the incident light bending portion 21 inclined with respect to the light incident surface IS by cooperating with the inclined surface RS. Further, in the light guide plate main body 20a, an image extraction portion 23 having a fine structure is formed along a plane on the back side of the light exit surface OS.

  The incident light bending portion 21 as the mirror layer 21a disposed to be inclined and opposed to the light incident surface IS of the light guide plate main body portion 20a is formed by depositing aluminum vapor deposition or the like on the slope RS of the light guide plate main body portion 20a. It is formed by applying, and functions as a reflection surface for reflecting incident light and bending the optical path in a predetermined direction close to a substantially orthogonal direction. That is, the incident light bending portion 21 guides the image light by bending the image light incident from the light incident surface IS and traveling in the + X direction as a whole so as to be directed in the + Z direction biased in the −X direction as a whole. It couple | bonds reliably in the optical plate main-body part 20a.

  Further, the light guide plate main body 20 a receives the image light incident on the inside through the incident light bending portion 21 from the entrance-side incident light bending portion 21 to the back-side image extraction portion 23 to the image extraction portion 23. It has a light guide 22 for guiding.

  The light guide 22 is a main surface of the flat light guide plate main body 20a and is two planes facing each other and extending in parallel to the YZ plane, and totally reflects the image light bent by the incident light bending portion 21, respectively. The first total reflection surface 22a and the second total reflection surface 22b are provided. Here, it is assumed that the first total reflection surface 22 a is on the back side far from the image forming apparatus 10 and the second total reflection surface 22 b is on the front side close to the image forming apparatus 10. In this case, the second total reflection surface 22b is a common surface portion with the light incident surface IS and the light exit surface OS. The image light reflected by the incident light bending portion 21 first enters the second total reflection surface 22b and is totally reflected. Next, the image light enters the first total reflection surface 22a and is totally reflected. Hereinafter, by repeating this operation, the image light is guided to the back side of the light guide plate 20, that is, the + Z side where the image extraction unit 23 is provided.

  The image extraction unit 23 disposed to face the light exit surface OS of the light guide plate main body 20a is arranged along the extended plane of the first total reflection surface 22a on the back side (+ Z side) of the light guide unit 22. It is formed close to the extension plane. The image extraction unit 23 reflects the image light incident through the first and second total reflection surfaces 22a and 22b of the light guide unit 22 at a predetermined angle and bends it toward the light exit surface OS. Here, it is assumed that the image light first incident on the image extraction unit 23 is an extraction target as virtual image light. The detailed structure of the image extraction unit 23 will be described later with reference to FIG.

  The light guide plate body 20a has a termination surface ES as a side surface that defines the + Z side end surface of the outer shape of the light guide plate 20. The light guide plate body 20a has an upper end surface TP and a lower end surface BP as an upper surface and a bottom surface that define an end surface on the ± Y side.

  In addition, the refractive index n of the transparent resin material used for the light guide plate body 20a is a high refractive index material of 1.5 or more. By using a transparent resin material having a relatively high refractive index for the light guide plate 20, it becomes easier to guide the image light inside the light guide plate 20, and the angle of view of the image light inside the light guide plate 20 is made relatively small. be able to.

  The light guide plate 20 has the above structure. As a result, the image light emitted from the image forming apparatus 10 and incident on the light guide plate 20 from the light incident surface IS is uniformly reflected and bent by the incident light bending portion 21, and the first and first light guide portions 22. The two total reflection surfaces 22a and 22b are repeatedly totally reflected, proceed in a state of having a certain spread substantially along the optical axis OA, and further bendable at an appropriate angle at the image extraction unit 23 so that the image can be extracted. Finally, the light exits from the light exit surface OS. The image light emitted from the light exit surface OS enters the observer's eye EY as virtual image light. By forming the virtual image light on the retina of the observer, the observer can recognize image light such as video light by the virtual image.

[B. (Optical path of image light)
Hereinafter, the optical path of the image light will be described in detail. As shown in FIG. 1A, a component emitted from the central portion of the emission surface 11a indicated by a dotted line in the image light emitted from the emission surface 11a of the liquid crystal device 11 is referred to as image light GL1. The component emitted from the left side (-Z side) of the drawing surface 11a in the vicinity of the emission surface 11a indicated by the middle one-dot chain line is the image light GL2, and the right side (+ Z side) of the periphery of the emission surface 11a indicated by the two-dot chain line in the drawing. Let the component emitted from the image light GL3.

The main components of the image lights GL1, GL2, and GL3 that have passed through the collimating lens 12 are all incident at different angles on the first and second total reflection surfaces 22a and 22b after entering from the light incident surface IS of the light guide plate 20, respectively. Repeat reflection. Specifically, among the image lights GL1, GL2, and GL3, the image light GL1 emitted from the central portion of the emission surface 11a of the liquid crystal device 11 is reflected by the incident light bending portion 21 as a parallel light flux, and then is standardized. The light enters the second total reflection surface 22b of the light guide unit 22 at the reflection angle γ ₀ and is totally reflected. Thereafter, the image light GL1 is, while maintaining the standard reflection angle gamma _0, first and second total reflection surface 22a, repeating total reflection at 22b. The image light GL1 is totally reflected N times (N is a natural number) at the first and second total reflection surfaces 22a and 22b, and enters the central portion 23k of the image extraction unit 23. The image light GL1 is reflected at a predetermined angle at the central portion 23k, and is emitted from the light exit surface OS as a parallel light flux in the optical axis AX direction perpendicular to the YZ plane including the light exit surface OS. The image light GL2 emitted from one end side (−Z side) of the emission surface 11a of the liquid crystal device 11 is reflected by the incident light bending portion 21 as a parallel light beam, and is then reflected by the light guide portion 22 at the maximum reflection angle γ ₊ . The light enters the second total reflection surface 22b and is totally reflected. The image light GL2 is totally reflected NM times (M is a natural number) at the first and second total reflection surfaces 22a and 22b, and is predetermined at a peripheral portion 23m on the innermost side (+ Z side) of the image extraction portion 23. And is emitted from the light exit surface OS as a parallel light beam in a predetermined angle direction. The exit angle at this time is such that it is returned to the incident light bending portion 21 side, and becomes an obtuse angle with respect to the + Z axis. The image light GL3 emitted from the other end side (+ Z side) of the emission surface 11a of the liquid crystal device 11 is reflected by the incident light bending portion 21 as a parallel light beam, and then the minimum reflection angle γ ₋ of the light guide portion 22. The light enters the second total reflection surface 22b and is totally reflected. The image light GL3 is totally reflected N + M times at the first and second total reflection surfaces 22a and 22b, and is reflected at a predetermined angle by the peripheral portion 23h on the most entrance side (−Z side) of the image extraction portion 23, The light exits from the light exit surface OS in a predetermined angular direction as a parallel light flux. The exit angle at this time is such that it is away from the incident light bending portion 21 side, and is an acute angle with respect to the + Z axis. In addition, since the reflection efficiency of light by the total reflection at the first and second total reflection surfaces 22a and 22b is very high, the number of reflections differs between the image lights GL1, GL2, and GL3 as described above. However, this hardly causes luminance unevenness, and does not feel the influence of image unevenness or the like on visual recognition. Further, the image light GL1, GL2, and GL3 are described on behalf of a part of the entire light beam of the image light. However, light beam components constituting other image light are guided in the same manner as the image light GL1 and the like. Since these are emitted from the light exit surface OS, illustration and description thereof are omitted. Note that the image lights GL2 and GL3 are slightly refracted when passing through the light exit surface OS.

Here, as an example of the value of the refractive index n of the transparent resin material used for the incident light bending part 21 and the light guide part 22, when n = 1.5, the value of the critical angle γ _c is γ _c ≈41. .8 ° and n = 1.6, the critical angle γ _c is γ _c ≈38.7 °. Each image light GL1, GL2, reflection angle gamma ₀ of _GL3, γ _+, γ _- reflection angle is the smallest among the gamma _- a by a value larger than the critical angle gamma _c, the light guide portion for the required image light 22 to satisfy the total reflection condition.

[C. The structure of the image extraction part and the bending of the optical path by the image extraction part)
Hereinafter, the structure of the image extraction unit 23 and the bending of the optical path of the image light by the image extraction unit 23 will be described in detail with reference to FIG.

  First, the structure of the image extraction unit 23 will be described. The image extraction unit 23 includes a large number of linear reflection units 23c arranged in a stripe shape. That is, as shown in FIGS. 2A to 2C, the image extraction unit 23 includes a large number of elongated reflection units 23c extending in the Y direction in the direction in which the light guide unit 22 extends, that is, in the Z direction at a predetermined pitch PT. It is composed by arranging. Each reflection unit 23c has a first reflection surface 23a disposed on the back side, that is, on the downstream side of the optical path, and a second reflection surface 23b disposed on the entrance side, that is, on the upstream side of the optical path. At least the second reflecting surface 23b is a partially reflecting surface capable of transmitting a part of light, and allows an observer to observe an outside world image with see-through. Each reflection unit 23c is formed in a V shape or a wedge shape in the XZ sectional view by the adjacent first and second reflection surfaces 23a and 23b. More specifically, the first and second reflection surfaces 23a and 23b are parallel to the first total reflection surface 22a shown in FIG. 1A and the like and are arranged in the Z direction in which the reflection units 23c are arranged. A direction extending perpendicularly to the longitudinal direction, that is, the Y direction, is linearly extended. Further, for example, as shown in a partially enlarged view in FIG. 3, the first and second reflecting surfaces 23a and 23b are arranged so that the longitudinal direction, that is, the Y direction, is the first total reflecting surface 22a or perpendicular thereto. The reflecting surfaces 23a and 23b are inclined at different angles (that is, different angles with respect to the YZ plane) with respect to the reference plane CS which is a reference for determining the angle. As a result, the multiple first reflective surfaces 23a are periodically arranged repeatedly and extend in parallel with each other, and the multiple second reflective surfaces 23b are also periodically arranged repeatedly and extend in parallel with each other.

  Hereinafter, the inclination of the first reflecting surface 23a and the second reflecting surface 23b will be described in detail. First, the first reflection surface 23a is a Y direction that is a direction perpendicular to both the direction of the normal line NL (X direction) of the first total reflection surface 22a and the arrangement direction of each reflection unit 23c (Z direction). Is inclined to the light exit surface OS side by an inclination angle α (α> 0) from a state parallel to the reference surface CS perpendicular to the first total reflection surface 22a. In other words, the first reflecting surface 23a has the direction (Y direction) in which the V-shaped groove formed by the reflecting unit 23c extends as the axis direction of rotation, and the counterclockwise direction with respect to the Z direction as a positive direction. In this state, it is inclined by an inclination angle α from a state perpendicular to the first total reflection surface 22a. Here, the value of the inclination angle α is set to 0.5 ° or more and 5 ° or less. The second reflecting surface 23b extends in a direction that forms a predetermined angle (relative angle) β (β> 0) with respect to the corresponding first reflecting surface 23a. From another viewpoint, the second reflecting surface 23b is inclined toward the light exit surface OS by an angle β-α in a negative direction from a state parallel to the reference surface CS, with the Y direction as the axial direction of rotation. As described above, in each reflection unit 23c, the first reflection surface 23a and the second reflection surface 23b are inclined to the light emission surface OS side, are arranged to face each other and form an acute angle, and emit light. A taper-shaped groove that extends in the direction toward the surface OS, that is, the −X direction is formed. In this case, the second reflection surface 23b is arranged in a range of a relative angle β = 50 ° to 60 ° with respect to the first reflection surface 23a. Here, as a specific example, it is assumed that β = 54.7 °, for example. Further, regarding the inclination of the first and second reflection surfaces 23a and 23b with respect to the reference surface CS, the second reflection surface 23b is larger than the first reflection surface 23a.

  Hereinafter, the bending of the optical path of the image light by the image extraction unit 23 will be described in detail. Here, among the image light, the image light GL2 and the image light GL3 that enter the both ends of the image extraction unit 23 are shown, and the other optical paths are the same as those described above, and thus the illustration and the like are omitted.

First, as shown in FIGS. 2A and 2B, the image light GL2 guided at the reflection angle γ ₊ having the largest total reflection angle among the image light is the light incident surface IS of the image extraction unit 23. The light is incident on one reflection unit 23c disposed in the peripheral portion 23m on the + Z side farthest from (see FIG. 1A). In the reflection unit 23c, the image light GL2 is first reflected by the first reflection surface 23a on the back side, that is, the + Z side, and then reflected by the second reflection surface 23b on the entrance side, that is, the −Z side. The image light GL2 that has passed through the reflection unit 23c is emitted from the light exit surface OS shown in FIG. 1A or the like without passing through the other reflection unit 23c. That is, the image light GL <b> 2 is bent at a desired angle and extracted to the observer side by only one pass through the image extraction unit 23.

Further, as shown in FIGS. 2A and 2C, the image light GL3 guided at the reflection angle γ ₋ having the smallest total reflection angle is incident on the light incident surface IS (see FIG. The light is incident on one reflection unit 23c arranged in the peripheral portion 23h on the -Z side closest to (A). In the reflection unit 23c, as in the case of the image light GL2, the image light GL3 is first reflected by the first reflection surface 23a on the back side, that is, the + Z side, and then the second light on the entrance side, that is, the −Z side. Is reflected by the reflecting surface 23b. The image light GL3 that has passed through the reflection unit 23c is bent to a desired angle and taken out to the viewer side by passing through the image extraction unit 23 only once without passing through the other reflection unit 23c.

Here, in the case of the two-stage reflection on the first and second reflecting surfaces 23a and 23b as described above, as shown in FIG. 2, the direction when each image light is incident and the direction when it is emitted The bending angle ψ which is an angle formed is ψ = 2 (R−β) (R: right angle). That is, the bending angle ψ is constant regardless of the values of the incident angles with respect to the image extraction unit 23, that is, the reflection angles γ ₀ , γ ₊ , γ _{− and the} like that are the total reflection angles of the respective image lights. Accordingly, as described above, a component having a relatively large total reflection angle in the image light is incident on the peripheral portion 23m side on the + Z side of the image extracting unit 23, and a component having a relatively small total reflection angle is input to the image extracting unit. Even when the light is incident on the −Z side peripheral portion 23 h side of the image 23, it is possible to efficiently extract the image light in an angle state that collects the image light as a whole on the eyes EY of the observer. Since the image light is extracted in such an angular relationship, the light guide plate 20 can pass the image light only once without passing the image light a plurality of times in the image extraction unit 23, and the virtual image can be obtained with little loss. It can be extracted as light.

と表される。よって、以上の条件式（２），（３）を用いて（１）'は、

と表される。この条件を画像取出部２３に入射する全ての光に対して満たすように傾斜角度αを設定することで、画像取出部２３における光利用効率の低下を回避できる。ここでは、一例として、β＝５４．７°、θ＝１５°、ｎ＝１．６であるとすると、式（１）"の右辺の値は、約５．０５°となり、傾斜角度αの値を５°以下とすることで、条件を満たすものとなる。 Hereinafter, with reference to FIG. 3, there is reflection angle _{γ (γ - ≦ γ ≦ γ} +) by the first reflecting surface incident light PL1 is a light incident on the reflecting surface 23a is the image extraction unit 23 of the image extraction unit 23 The conditions for taking out from the light exit surface OS will be described. In any reflection unit 23c, in order for the reflection surface incident light PL1 to be reflected by the first reflection surface 23a and to be folded back by the corresponding second reflection surface 23b, the value of the inclination angle α must not exceed a certain upper limit. is necessary. That is, if the value of the inclination angle α is too large, the reflection surface reflected light PL2 that is the reflection light on the first reflection surface 23a of the reflection surface incident light PL1 does not go to the second reflection surface 23b, but the light guide section 22. Since it is returned to the side, it is lost without being emitted from the light exit surface OS. As an example for preventing this, the optical path of the reflection surface reflected light PL2 and the normal line NL of the first total reflection surface 22a have an angle of less than 90 ° (R) on the first total reflection surface 22a side. Just do it. Specifically, as shown in the drawing, in the reflection surface incident light PL1 directed toward the first reflection surface 23a at a certain reflection angle γ, the incident angle λ at the first reflection surface 23a is the first reflection surface 23a. Λ = R−γ−α. Further, the value of the reflection angle λ ′ is equal to λ, and λ ′ = λ = R−γ−α. From the above, when the angle between the optical path of the reflection surface reflected light PL2 and the normal line NL of the first total reflection surface 22a is an angle φ,
φ = 2R−γ−λ−λ ′
= 2R-γ-2 (R-γ-α) <R (1)
That means
α <(R−γ) / 2 (1) ′
It is understood that it is sufficient if On the other hand, for the reflection angle γ, using the above-mentioned ψ = 2 (R−β), the refraction angle θ ′ in the light guide plate, etc.,
γ = ψ + θ ′ = 2 (R−β) + θ ′ (2)
It is expressed. Further, the refraction angle θ ′ in the light guide plate and the horizontal angle of view θ of the image light are determined by using the refractive index n of the light guide plate,

It is expressed. Therefore, using the above conditional expressions (2) and (3), (1) ′ is

It is expressed. By setting the inclination angle α so as to satisfy this condition for all the light incident on the image extraction unit 23, it is possible to avoid a decrease in light utilization efficiency in the image extraction unit 23. Here, as an example, assuming that β = 54.7 °, θ = 15 °, and n = 1.6, the value on the right side of Equation (1) ″ is about 5.05 °, and the inclination angle α By satisfying the value of 5 ° or less, the condition is satisfied.

In addition, in the optical design such as the shape and refractive index of the light guide 22 and the shape of the reflection unit 23c constituting the image extraction unit 23, by appropriately adjusting the angle etc. through which the image light GL2, GL3, etc. are guided, As shown in FIG. 2A, the image light emitted from the light exit surface OS is observed as virtual image light in a state in which symmetry is maintained as a whole around the basic image light GL1, that is, the optical axis AX. Can be incident on the eye EY. That is, the angle [delta] ₂ with respect to the X direction or the optical axis AX of the image light GL2 at one end, and the angle [delta] ₃ relative to the X direction or the optical axis AX of the image light GL3 the other end, in a substantially equal opposite magnitude Yes. Note that the angles δ ₂ and δ ₃ of the image light GL2 and GL3 are relatively close to the light exit surface OS or the second total reflection surface 22b, and are sufficiently transmitted through the light exit surface OS. Pass at a rate.

  Further, as already described, the pitch PT and the relative angle β are constant in the first reflecting surface 23a or the second reflecting surface 23b constituting the group of reflecting units 23c. Thereby, the image light which is the virtual image light incident on the eye EY of the observer can be made uniform, and the deterioration of the quality of the observed image can be suppressed.

  The specific numerical range of the pitch PT, which is the interval between the reflecting units 23c constituting the image extraction unit 23, is 0.5 mm or more, more preferably 0.5 mm to 1.3 mm. By being in this range, it is possible to prevent the image light to be extracted from being affected by diffraction in the image extraction unit 23 and to prevent the lattice fringes due to the reflection unit 23c from being noticeable to the observer.

[D. Method for manufacturing light guide plate]
Hereinafter, with reference to FIG. 4 (A) etc., an example of the manufacturing method of the light-guide plate concerning this embodiment is demonstrated first. Note that some parts are omitted in FIG. 4A and the like for simplicity.

  As shown in FIG. 4A, in the light guide plate manufacturing method according to the present embodiment, first, for example, the sawtooth portion DT of the image extraction portion 23 or the light guide portion 22 of the light guide plate body portion 20a (FIG. 1A). The base material portion to be formed is integrally formed as a translucent resin member Pa. For this reason, first and second metal molds MP1 and MP2, which are a set of metal molds for integrally forming the translucent resin member Pa by injection molding, are prepared (mold preparation step).

  Here, of the set of metal molds MP1 and MP2, the metal mold MP1 has a sawtooth shape for forming the first and second reflection surfaces 23a and 23b of the image extraction portion 23 as a part of the transfer surface. It has a mold surface SS. Accordingly, the mold surface SS has a sawtooth shape corresponding to the shapes of the first and second reflecting surfaces 23a and 23b.

  The metal molds MP1 and MP2, which are a pair of injection molds, are heated moderately and matched and clamped (mold space forming step). Thereafter, the resin material to be the translucent resin member Pa is injected into the mold space formed between the pair of metal molds MP1 and MP2 in a softened state at a predetermined temperature, and the injected translucent resin is The entire surface including the mold surface SS is transferred by being pressurized (injection process). The cured translucent resin member Pa is taken out between the pair of metal molds MP1 and MP2 by subsequent cooling and mold release (mold release process). At this time, since the both side surfaces of the V groove formed by the mold surface SS spread outward, the transferred portion is easily released. Through the above steps, a large number of first portions which are flat portions respectively corresponding to the first and second reflecting surfaces 23a and 23b by the mold surface SS of the metal mold MP1 are formed on the molded translucent resin member Pa. A sawtooth portion DT composed of the first and second flat surfaces FSa and FSb is formed (groove forming step). That is, each flat surface FSa, FSb is a flat surface that constitutes a part of the image extraction portion 23 so as to form the first and second reflection surfaces 23a, 23b. Each flat surface FSa, FSb needs to have a flatness that does not diffuse in reflection by the corresponding reflection surfaces 23a, 23b.

  Next, as shown in FIG. 4B, a reflective film MB, which is a reflective part for forming the first and second reflective surfaces 23a and 23b, is formed on the serrated part DT by aluminum vapor deposition. (Film forming step), and further, an ultraviolet curable resin Qa, which is a translucent resin curable by ultraviolet rays, is applied from above the reflective film MB (resin application step), and the applied ultraviolet curable resin Qa is applied to a predetermined amount. After pressing the surface of the reflective film MB with pressure so that there is no gap, it is cured by irradiation with ultraviolet rays (resin curing step). Thereby, the protective layer of the reflective film MB is formed (protective layer forming step), and the light guide plate 20 is manufactured. In the film formation step, for example, oblique vapor deposition can be used as the vapor deposition method. Further, the ultraviolet curable resin Qa is a resin having substantially the same refractive index as that of the translucent resin member Pa.

  In the present embodiment, as described above, of the flat surfaces FSa and FSb constituting the serrated portion DT, the flat surface FSa does not become vertical corresponding to the first reflecting surface 23a, but is on the light emitting surface OS side. The flat surface FSb is also inclined to the light exit surface OS side by an angle β-α corresponding to the second reflecting surface 23b (see FIG. 2B, etc.). Therefore, when the mold surface is removed from the mold surface SS, the flat surfaces FSa and FSb corresponding to the back sides of the first and second reflecting surfaces 23a and 23b are tapered surfaces extending in the depth direction, that is, the light emission side. It is equivalent to. In other words, as a result of the first and second reflecting surfaces 23a and 23b being inclined toward the second total reflecting surface 23b side, that is, the light emitting surface OS side, the grooves formed are the same as the first reflecting surface 23a and the first reflecting surface 23a. The shape is open in the −X direction from the apex where the second reflecting surface 23b intersects. As a result, in the mold release process among the processes for producing the light guide plate 20, the friction at the time of die reduction is reduced, the mold release property is improved, and the portion of the sawtooth portion DT is easily detached. The member Pa as a whole is easily released from the metal mold MP1. Therefore, in the production of the image extraction portion 23, the manufacturing throughput is improved, and the burden at the time of releasing the metal mold MP1 is reduced, thereby extending the life. In this case, the value of the inclination angle α (see FIG. 2B and the like) is set to 0.5 ° or more, thereby satisfying the condition for having a function as a draft taper.

  In addition, as long as the translucent resin member Pa to be injection-molded includes the serrated portion DT, the translucent resin member Pa does not include the entire light guide plate main body 20a of FIG. It may be. For example, the prism portion PS for forming the incident light bending portion 21 in the light guide plate main body portion 20a may be attached to the translucent resin member Pa by bonding or the like after a separate triangular prism is produced.

  In the film forming step, aluminum vapor deposition may be performed by a method other than oblique vapor deposition. For example, the flat surface FSa and the flat surface FSb may be vapor-deposited one by one.

  In the above description, it is assumed that the translucent resin member Pa is a thermoplastic resin, but the translucent resin member Pa can be formed of a thermosetting resin or a photocuring resin.

[E. (Manufacturing method of original mold)
Hereinafter, with reference to FIG. 5A and the like, an example of a method for manufacturing a master mold for manufacturing the light guide plate according to the present embodiment will be described. Here, the production of the mold surface SSa corresponding to the sawtooth mold surface SS for forming the reflective surfaces 23a and 23b having the characteristic shape in the metal mold MP1 of FIG. 4 will be described.

  The mold surface SSa shown in FIG. 5A is a rectangular parallelepiped shape which is parallel to the xy plane of an installation table (not shown) and is fixed on a reference plane CC serving as a reference for determining the position where the mold surface SSa is formed. It is formed by cutting the surface FF of the base material BB with a diamond cutting tool DB. Of the mold surface SSa, the first flat surface S1 corresponding to the first reflecting surface 23a of FIG. 4B, that is, the first flat surface FSa of FIG. It is cut out by one cutting surface D1. Further, of the mold surface SSa, the second flat surface S2 corresponding to the second reflective surface 23b of FIG. 4B, that is, the second flat surface FSb of FIG. Is cut out by the second cutting surface D2. That is, each flat surface S1, S2 is a flat surface constituting the mold surface SSa in order to form the first and second flat surfaces FSa, FSb by transfer. The first cutting surface D1 and the second cutting surface D2 of the diamond cutting tool DB correspond to an angle β (see FIG. 2A, etc.) formed by the first reflecting surface 23a and the second reflecting surface 23b. For example, the angle β is 54.7 °. On the base material BB fixed on the installation table, the sawtooth portion DTa is formed by scanning the diamond tool DB a plurality of times in a certain direction (y direction in the figure) indicated by the arrow AW as shown in the figure. . Here, as shown in FIG. 5B, the first cutting surface D1 corresponding to the first reflecting surface 23a is not parallel to the normal direction (z direction in the drawing) of the reference surface CC, and is inclined. It is tilted by the angle α. Thus, the first cutting surface D1 forms the first flat surface S1 while applying a stress component in the oblique direction indicated by the arrow A1. Similarly, the second cutting surface D2 is maintained in a state where a pressure component is appropriately applied in an oblique direction indicated by an arrow A2. By applying an appropriate pressure to the work material during cutting, it is possible to suppress the occurrence of the occurrence of the occurrence of the occurrence of the occurrence of the trapping during the machining of the diamond bite DB with respect to the base material BB due to the stress in the material. Further, it is possible to suppress the diamond bite DB from being caught due to the stress generated at the fixing portion between the base material BB and the installation base (not shown).

  On the other hand, as shown in FIG. 5C as a comparative example, when the first cutting surface D1 is perpendicular to the reference surface CC, the second cutting surface is cut when cutting with the diamond cutting tool DB. Even if the pressure applied to the second flat surface S2 in the direction of the arrow A2 by D2 is sufficient, the pressure applied to the first flat surface S1 in the direction of the arrow A1 by the first cutting surface D1 is small and insufficient. there is a possibility. In this case, the pressure applied to the first flat surface S1 loses the stress generated in the base material BB or the stress generated in the fixing portion between the base material BB and the installation base (not shown), thereby being caught or unstable during processing. There is a possibility that vibration or the like is generated, and irregularities due to streaks or chattering are formed on the first flat surface S1 to make the mold surface inferior in flatness.

  As described above, in the manufacture of the original mold, it is possible to suppress the occurrence of unevenness on the mold surface SSa to avoid deterioration of the mold surface, and to cut out the flat surfaces S1 and S2 having high flatness relatively easily. . The metal mold MP1 produced from such an original mold has high flatness on the mold surface SS. In addition, the surface as shown in FIG. 6 is cut out by the cutting process as described above.

  As described above, in the light guide plate 20 of the present embodiment, since the first reflection surface 23a of the image extraction unit 23 has the inclination angle α, first, a portion corresponding to the first reflection surface 23a is formed. A flat surface with high flatness can be cut out relatively easily during the manufacture of the original mold to be formed. For this reason, in the production of the light guide plate 20, the image extraction portion 23 can have high reflection characteristics. Further, in the manufacturing process of the light guide plate 20, the releasability can be enhanced for the image extraction portion 23, so that the manufacturing throughput of the light guide plate 20 is improved. Moreover, since the mold release property can be improved, the deformation of the light guide plate 20 can be suppressed and the load on the mold can be reduced. Therefore, the life of the mold can be extended. In addition, as a result of the above, it is possible to reduce the manufacturing cost of the light guide plate 20. Note that, as described above, the value of the inclination angle α is, for example, not less than 0.5 ° and not more than 5 °, so that the improvement of the throughput is maintained and the function of the image extraction unit 23 is not impaired. Can do.

[F. Second Embodiment]
Hereinafter, a second embodiment obtained by modifying the first embodiment will be described with reference to FIG. Since the light guide plate according to the present embodiment has the same structure as the light guide plate 20 in FIG. 2 and the like except for the structure of the image extraction unit, only the image extraction unit and its periphery are illustrated in FIG. The illustration and description of the structure of the entire light guide plate and virtual image display device are omitted. In addition, in 2nd Embodiment shown to FIG. 7 (A) -7 (C), about the thing of the same sign as the light-guide plate 20 of FIG. The equivalent is shown.

The light guide plate 120 of the second embodiment shown in FIG. 7A is composed of a large number of linear reflection units 123c arranged in a stripe shape. That is, the image extraction unit 123 includes a long and narrow reflection unit 123c extending in the Y direction. The reflection unit 123c includes a first reflection surface 123a and a second reflection surface 123b arranged in a large number in the Z direction at a predetermined pitch PT. And have. Here, in the image extraction unit 123, the inclination angle of each first reflection surface 123a changes according to the arrangement direction of the plurality of reflection units 123c, that is, the position in the Z direction. Specifically, as shown in FIGS. 7B and 7C, the inclination angle α1 of the _first reflecting surface 123a located on the downstream side of the optical path, that is, on the + Z side, is on the upstream side of the optical path, that is, on the −Z side. It is smaller than the inclination angle alpha ₂ of the first reflection surface 123a is located. This inclination angle α reflection angle γ of the light incident on the reflecting surface 123a of the optical path upstream i.e. -Z side corresponding to _{2 -} the angle, the inclination angle α reflecting surface of the corresponding optical path downstream ie + Z side ₁ This is because the angle of reflection of light incident on 123a is smaller than the angle γ ₊ . More specifically, using mathematical expressions, generally, the conditions for the light reflected by the first reflecting surface 123a with respect to the inclination angle α to be reflected by the second reflecting surface 123b are as described above.
α <(R−γ) / 2 (1) ′
It is. Therefore, the condition for the inclination angle α ₂ is
α ₂ <(R−γ ₋ ) / 2 (4)
In this case, the reflection angle γ ₋ is a relatively small value. Therefore, the condition of (4) is satisfied even if the value of the angle α ₂ is set to be somewhat larger than the value of the angle α ₁ . By changing the tilt angle, an optimum tilt angle can be determined according to various designs. For example, when the mold corresponding to the first reflecting surface 123a on the + Z side is reduced in friction at the time of punching, the releasability as the entire image extraction unit 123 can be further improved during the production.

  As described above, in the second embodiment, by changing the inclination angle according to the + Z side position, for example, the manufacturing throughput of the light guide plate can be improved, the life of the mold can be increased, and the manufacturing cost can be reduced.

[Others]
Although the present invention has been described based on the above embodiments, the present invention is not limited to the above embodiments, and can be implemented in various modes without departing from the gist thereof. Such modifications are also possible.

  First, the pitch PT of the arrangement of the reflection units 23c constituting the image extraction unit 23 is not limited to the case where all the first reflection surfaces 23a are the same, and there is a certain difference between the pitches PT. Shall also be included.

  In the above description, the transmissive liquid crystal device 11 is used as the image display element. However, the image display element is not limited to the transmissive liquid crystal device, and various devices can be used. For example, a configuration using a reflective liquid crystal panel is possible, and a digital micromirror device or the like can be used instead of the liquid crystal device 11. Moreover, the structure using the self-light-emitting element represented by LED array, OLED (organic EL), etc. is also possible. Further, a configuration using a laser scanner in which a laser light source and a polygon mirror or other scanner are combined is possible.

  In the above description, the virtual image display device 100 is configured to be provided in the image forming device 10 and the light guide plate 20 one by one corresponding to both the right eye and the left eye, but either the right eye or the left eye. For this, only the image forming apparatus 10 and the light guide plate 20 may be provided so that the image is viewed with one eye.

  In the above description, a see-through type virtual image display device is described, but the image extraction unit 23 can also be applied to a virtual image display device other than the see-through type. When it is not necessary to observe an external image, the light reflectance of both the first and second reflecting surfaces 23a and 23b can be set to approximately 100%.

  In the above description, the light incident surface IS and the light exit surface OS are arranged on the same plane. However, the present invention is not limited to this. For example, the light incident surface IS is the same plane as the first total reflection surface 22a. The light emission surface OS may be disposed on the same plane as the second total reflection surface 22b.

  In the above description, the angle of the mirror layer 21a and the inclined surface RS constituting the incident light bending portion 21 is not particularly mentioned, but the present invention makes the mirror layer 21a and the like other specifications for the optical axis OA. Depending on the value, various values can be used.

  In the above description, the V-shaped groove formed by the reflection unit 23c is illustrated with the tip sharpened, but the V-shaped tip is cut flat or the tip is rounded. Those which are substantially V-shaped grooves are also included. Further, even when the cut portion is larger and trapezoidal, the reflection unit 23c is configured as long as the first reflection surface 23a and the second reflection surface 23b are tapered. It becomes.

  In the above description, the virtual image display device 100 of the embodiment has been specifically described as a head-mounted display. However, the virtual image display device 100 of the embodiment can be modified to a head-up display.

  In the above description, the first and second total reflection surfaces 22a and 22b totally reflect the image light by the interface with the air without applying a mirror or a half mirror film made of a semi-transmissive aluminum film on the surface. The total reflection in the present invention includes the reflection formed by forming a mirror coat or a half mirror film on the whole or a part of the first and second total reflection surfaces 22a and 22b. . For example, the case where the incident angle of the image light satisfies the total reflection condition and the whole or a part of the total reflection surfaces 22a and 22b is subjected to mirror coating or the like to reflect substantially all the image light is included. . Moreover, as long as image light with sufficient brightness can be obtained, the whole or a part of the total reflection surfaces 22a and 22b may be coated with a somewhat transmissive mirror.

  DESCRIPTION OF SYMBOLS 10 ... Image forming apparatus 11 ... Liquid crystal device 20, 120 ... Light guide plate, 20a ... Light guide plate main-body part, 21 ... Incident light bending part, 22 ... Light guide part, 22a, 22b ... Total reflection surface, 23 ... Image Extraction part, 23a, 23b ... reflective surface, 23c ... reflective unit, 100 ... virtual image display device, IS ... light incident surface (light incident part), OS ... light exit surface (light exit part), EY ... eye, PT ... pitch GL1, GL2, GL3 ... image light (incident light to the light guide plate, emitted light from the light guide plate), PL1, PL2 ... reflective surface incident light, reflective surface reflected light (incident light to the reflective surface of the image extraction unit, Reflected light at the reflection surface of the image extraction portion) α, β, γ, δ, θ ... angle, S1, S2 ... flat surface (flat surface of the image extraction portion), FSa, FSb ... flat surface (metal type flat surface) ), CS ... reference plane (reference plane with respect to angle of reflection plane), C C: Reference plane (reference plane for determining the position of the mold surface)

Claims (10)

A light incident part for taking image light inside;
A light guide unit having first and second total reflection surfaces extending opposite to each other, and guiding the image light captured from the light incident unit by total reflection on the first and second total reflection surfaces;
A plurality of reflection units each having a first reflection surface and a second reflection surface having a predetermined angle with respect to the first reflection surface and arranged in a predetermined arrangement direction; In each of the reflection units to be configured, the image light incident through the light guide unit is reflected by the first reflection surface and the image light reflected by the first reflection surface is reflected by the second reflection surface. Further, an image extraction unit that enables the image light to be extracted to the outside by bending the reflecting optical path;
A light emitting unit that emits the image light that has passed through the image extraction unit;
A light guide plate comprising:
In each of the reflection units, the first reflection surface and the second reflection surface are arranged to form an acute angle so as to face each other while being inclined toward the light emission portion side, and toward the light emission portion. A light guide plate that forms a tapered groove that widens.   The first reflecting surface of the image extraction unit rotates in a direction perpendicular to both the normal direction of the first total reflecting surface of the light guide unit and the arrangement direction of the plurality of reflecting units. 2. The light guide plate according to claim 1, wherein the light guide plate is inclined toward the light emitting part side at a predetermined inclination angle from a state perpendicular to the first total reflection surface as a direction.   The light guide plate according to any one of claims 1 and 2, wherein an inclination of the second reflection surface of the image extraction unit toward the light emitting unit is larger than that of the first reflection surface.   The said predetermined inclination angle of a said 1st reflective surface is changing according to the position about the said arrangement | positioning direction of these reflective units, It is any one of Claim 1- Claim 3 characterized by the above-mentioned. Light guide plate.   The light guide plate according to any one of claims 1 to 4, wherein the predetermined inclination angle of the first reflecting surface is not less than 0.5 ° and not more than 5 °. The predetermined angle of inclination of the first reflecting surface is α, the predetermined angle formed by the second reflecting surface with respect to the first reflecting surface is β, and the horizontal direction of the image light taken out from the light emitting unit Assuming that the angle of view is θ, the following relationship

The light guide plate according to claim 1, wherein the light guide plate satisfies the following conditions.   The image light incident on each of the reflection units is emitted from the light emitting unit as virtual image light by passing through the image extraction unit only once and bending the optical path. The light guide plate according to any one of the above.   The second reflection surface according to any one of claims 1 to 7, wherein the second reflection surface forms an angle of 30 ° to 40 ° with respect to the first total reflection surface of the light guide unit. Light guide plate.   The light guide plate according to any one of claims 1 to 8, wherein the first and second reflection surfaces are partial reflection surfaces capable of transmitting a part of light. The light guide plate according to any one of claims 1 to 9,
An image forming apparatus that forms the image light guided to the light guide plate;
A virtual image display device.

Images