JPWO2017077978A1 - Light guiding element, bonding optical element, image display device, and head mounted display - Google Patents

Abstract

The light guide element has a plurality of optical surfaces necessary for guiding light inside. The plurality of optical surfaces include two optical surfaces that intersect at an acute angle. The intersection line serving as the boundary between the two optical surfaces has a shape different from the straight line connecting both ends of the intersection line. When the two optical surfaces are cut by a plane including the straight line or a plane parallel to the straight line, at least one of the cross sections of the two optical surfaces includes a curve (C). Curve (C) has an inflection point (M).

Description

  The present invention relates to a light guide element having a plurality of optical surfaces necessary for guiding light therein, a bonded optical element including the light guide element, and an image display device including the light guide element or the bonded optical element. And a head mounted display (hereinafter also referred to as HMD (Head Mounted Display)) provided with the image display device.

  2. Description of the Related Art Conventionally, there has been proposed an image display device that allows an observer to observe an image by guiding image light from a display element inside a light guide element (for example, a light guide prism) and guiding it to an observation pupil. For example, in the image display devices disclosed in Patent Documents 1 to 3, after the image light from the display element is totally reflected by the two optical surfaces facing the light guide element and then guided, The light is reflected by an optical surface obliquely intersecting the optical surface and guided to the observation pupil. For convenience of explanation, the two optical surfaces are also referred to as a total reflection surface, and an optical surface that obliquely intersects the total reflection surface is also referred to as an inclined surface. One of the two total reflection surfaces also serves as a transmission surface (exit surface) that transmits the image light reflected by the inclined surface to the observation pupil side.

JP 2014-153643 A (refer to claim 1, FIG. 3 etc.) Japanese Patent Laying-Open No. 2015-106012 (refer to claim 1, FIG. 2, etc.) JP 2014-174519 A (refer to claim 1, FIG. 11 etc.)

  However, as in Patent Documents 1 to 3, in the configuration in which the light guide element has two total reflection surfaces and an inclined surface, and the inclined surface obliquely intersects with the two total reflection surfaces, one total reflection surface Intersects the inclined surface at an acute angle. And the part pinched | interposed by said one total reflection surface and an inclined surface becomes a taper shape which becomes thin toward an acute-angled front-end | tip. In the tapered portion, the strength is weaker than the constant thickness portion (for example, the portion where the two total reflection surfaces face each other). For example, external force due to simple pressing when the light guide element is incorporated into the product, If it works in a direction that penetrates the total reflection surface and the inclined surface that intersect at an acute angle, deformation tends to occur due to the force in that direction.When the tapered part deforms, the optical surface that forms the tapered shape (total reflection surface The light transmission direction or reflection direction on the inclined surface is changed from the direction defined by the original optical design, and the light guided inside the light guide element can be guided to an appropriate external direction. Disappear.

  The present invention has been made to solve the above-described problems, and its purpose is a configuration having a tapered shape in which two optical surfaces necessary for guiding light inside intersect at an acute angle. However, it is possible to suppress the deformation at the tapered portion with respect to the external force, thereby using the light guide element that can guide the light guided inside in an appropriate direction outside, and the light guide element. It is to provide a bonding optical element, an image display device using the light guide element or the bonding optical element, and an HMD using the image display device.

  A light guide element according to one aspect of the present invention is a light guide element having a plurality of optical surfaces necessary for guiding light inside, wherein the plurality of optical surfaces include two optical surfaces intersecting at an acute angle. And an intersection line that is a boundary between the two optical surfaces has a shape different from a straight line connecting both ends of the intersection line, and is a plane including the straight line or a plane parallel to the straight line. When the surface is cut, at least one of the cross sections of the two optical surfaces includes a curve, and the curve has an inflection point.

  A bonded optical element according to another aspect of the present invention includes an optical surface and a surface different from the optical surface that guides light by total reflection, of the light guide element described above and the two optical surfaces of the light guide element. And a joining optical member joined to the light guide element so that the opposing optical surfaces have substantially the same shape, and the different optical surfaces and the opposing surfaces face each other.

  An image display device according to still another aspect of the present invention includes: a display element that displays an image; and an eyepiece optical system that guides image light from the display element and guides the image light to an observation pupil. The system includes the light guide element described above.

  An image display device according to still another aspect of the present invention includes: a display element that displays an image; and an eyepiece optical system that guides image light from the display element and guides the image light to an observation pupil. The system includes the bonding optical element described above.

  A head mounted display according to still another aspect of the present invention includes the above-described image display device and a support member that supports the image display device in front of an observer's eyes.

  The light guide element includes two optical surfaces that intersect at an acute angle as a plurality of optical surfaces necessary for guiding light inside, and a portion sandwiched between the two optical surfaces has a tapered shape. Yes. In such a configuration, when the two optical surfaces are cut at a plane including a straight line connecting both ends of the intersection of the two optical surfaces or a plane parallel to the straight line, at least a cross section of the two optical surfaces is cut. One contains a curve. The curve has an inflection point. That is, at least one of the cross sections of the two optical surfaces includes both a shape with a positive curvature and a shape with a negative curvature. For this reason, compared to a configuration in which the optical surface does not have an inflection point (for example, a configuration in which the cross-sectional shape consists of only a straight line), the optical surface is less likely to be deformed, and deformation of the tapered portion due to external force can be suppressed. It becomes. As a result, the light guided inside the light guide element can be guided to an appropriate external direction through the two optical surfaces constituting the tapered portion.

It is sectional drawing which shows the schematic structure of the light guide element which concerns on one Embodiment of this invention. It is a perspective view of the said light guide element. It is a front view of the said light guide element. In the above light guide element, an explanation schematically showing a cross-sectional shape of one optical surface (inclined surface) when two optical surfaces (total reflection surface, inclined surface) intersecting at an acute angle are simultaneously cut by the second surface. FIG. It is explanatory drawing which shows typically the other example of the cross-sectional shape of said one optical surface. It is explanatory drawing which shows typically the other example of the cross-sectional shape of said one optical surface. It is a perspective view which shows the other structure of the said light guide element. In the light guide element of FIG. 7, when two optical surfaces (total reflection surface, inclined surface) that intersect at an acute angle are cut simultaneously by the second surface, the cross-sectional shape of the other optical surface (total reflection surface) is schematically illustrated. It is explanatory drawing shown in. It is a horizontal sectional view showing other composition of the above-mentioned light guide element. It is sectional drawing which shows the structure of the outline of the joining optical element which concerns on other embodiment of this invention. It is a perspective view of the said joining optical element. It is a front view of the said joining optical element. It is sectional drawing which shows the structure of the outline of the image display apparatus which concerns on other embodiment of this invention. It is a perspective view of the image display device. It is a front view of the image display device. It is a top view of the head mounted display which concerns on other embodiment of this invention. It is a front view of the head mounted display. It is a bottom view of the head mounted display. It is a perspective view from the front side of the head mounted display.

[Embodiment 1]
An embodiment of the present invention will be described below with reference to the drawings. The present invention is not limited to the following contents.

(About light guide element)
FIG. 1 is a cross-sectional view illustrating a schematic configuration of a light guide element 10 according to the present embodiment, FIG. 2 is a perspective view of the light guide element 10, and FIG. 3 is a front view of the light guide element 10. is there. In addition, the arrow of the broken line in the figure has shown the optical path of arbitrary rays. The light guide element 10 is an optical element that guides light incident from outside and emits the guided light in a predetermined direction outside. The light guide prism 1 and the optical member 2 are connected to each other. Contains.

  The light guide prism 1 is made of, for example, a transparent acrylic resin. The light guide prism 1 has a plurality of optical surfaces necessary for guiding light inside, that is, a surface having an optically effective region that transmits or reflects incident light (optically effective surface). Specifically, the light guide prism 1 has a first optical surface 1a, a second optical surface 1b, a third optical surface 1c, and a fourth optical surface 1d as the optical surfaces. In the first optical surface 1a, the second optical surface 1b, and the third optical surface 1c, the entire optical surface is an optical effective region, but a part of the optical surface (only necessary portions) is the optical effective region. It may be. In the fourth optical surface 1d, as shown in FIG. 3, a part of the optical surface is an optical effective region R, and the optical member 2 is disposed in the optical effective region R. That is, the optical effective area R of the fourth optical surface 1d and the arrangement area of the optical member 2 are the same.

  The first optical surface 1a is a surface that transmits light incident from the outside and guides it to the inside of the light guide prism 1, and is formed of, for example, a flat surface. The 2nd optical surface 1b and the 3rd optical surface 1c are comprised by the plane, for example, and are arrange | positioned so that it may become mutually perpendicular | vertical and parallel to the 1st optical surface 1a. The second optical surface 1b and the third optical surface 1c cause the light incident on the inside through the first optical surface 1a to be totally reflected at least once and led to the fourth optical surface 1d. The third optical surface 1c functions not only as a total reflection surface that totally reflects incident light, but also as a transmission surface that transmits the light reflected by the fourth optical surface 4d (or the optical member 2) to the outside. Function. The third optical surface 1c may include a curved surface (see FIGS. 7 and 9), which will be described later.

  The fourth optical surface 1d is an inclined surface that is configured to include, for example, a curved surface and is arranged so as to obliquely intersect the second optical surface 1b and the third optical surface 1c. In particular, the fourth optical surface 1d is disposed so as to intersect the third optical surface 1c at an acute angle. As a result, the shape of the portion sandwiched between the third optical surface 1c and the fourth optical surface 1d is a tapered shape that becomes narrower toward the tip of the acute angle. On the other hand, the fourth optical surface 1d is arranged to intersect the second optical surface 1b at an obtuse angle. The details of the surface shape and the inclined arrangement of the fourth optical surface 1d will be described later.

  The optical member 2 is composed of, for example, a volume phase type reflection type hologram optical element that transmits only light in a predetermined wavelength range and diffracts and reflects light in other wavelength ranges. It is disposed on the fourth optical surface 1 d of the optical prism 1. For example, when the light incident on the inside of the light guide prism 1 through the first optical surface 1a is light in a wavelength region that is diffracted and reflected by the optical member 2, the light is inside the light guide prism 1, After being totally reflected by the second optical surface 1b and the third optical surface 1c, it is incident on the optical member 2, where it is diffracted and reflected, guided again to the third optical surface 1c, and transmitted through the third optical surface 1c. The light is emitted in a desired external direction.

  In addition to the hologram optical element, the optical member 2 may be configured by a reflecting member (including a half mirror) made of an aluminum film or a multilayer film formed by vapor deposition or the like. In this case, at least a part of the light incident on the inside of the light guide prism 1 through the first optical surface 1a is reflected by the optical member 2 and guided to the outside through the third optical surface 1c. Alternatively, the optical member 2 may not be disposed on the fourth optical surface 1d, and the light may be simply reflected by the fourth optical surface 1d due to the refractive index difference between the prism and air and guided to the third optical surface 1c.

(Details of surface shape and inclined arrangement of the fourth optical surface)
Next, details of the surface shape and the inclined arrangement of the fourth optical surface 1d will be described.

  For convenience of explanation below, each direction in the light guide element 10 is defined as follows. First, as shown in FIG. 2, a line formed by the intersection of the third optical surface 1c and the fourth optical surface 1d, that is, a ridge line that becomes a boundary between the third optical surface 1c and the fourth optical surface 1d is intersected. Let it be line L. Here, as shown in FIG. 2, since the fourth optical surface 1d has a wavy shape, the intersecting line L has a shape different from a straight line (for example, a shape including a curve that bends two-dimensionally or three-dimensionally). ing.

Then, a straight line connecting both ends of the intersection line L, that, the direction along the line a connecting the end portion L ₂ one end L ₁ and the other lines of intersection L, and the X direction, perpendicular to the X direction Two directions perpendicular to each other in the plane are defined as a Y direction and a Z direction, respectively. Among these, the Z direction is assumed to be equal to the direction in which the second optical surface 1b and the third optical surface 1c face each other. A plane perpendicular to the X direction, that is, a YZ plane perpendicular to the straight line a is also referred to as a _first plane P1, and a plane including the straight line a or a plane parallel to the straight line a is referred to as a second plane. also referred to as the plane _{P 2} of.

Using the above definition, “the fourth optical surface 1d intersects the third optical surface 1c at an acute angle” can be rephrased as follows. That is, the third when the optical surface 1c and a fourth optical surface 1d cut in the first surface P _1, the third any two points on the cross section of the optical surface 1c (for example in the cross-section of a third optical surface 1c a straight line 1c ₁ passing through two points E ₁ · E ₂₎ at both ends in the two points at both ends of the fourth any two points on the cross section of the optical surface 1d (e.g. in the cross-section of a fourth optical surface 1d E ₁ · E ₃ ) and the straight line 1d ₁ intersect at an acute angle α (0 ° <α <90 °). In addition, “the fourth optical surface 1d intersects the second optical surface 1b at an obtuse angle” can also be described in the same manner as described above. That is, when the cut and the second optical surface 1b and a fourth optical surface 1d in a first plane P _1, any two points on the cross section of the second optical surface 1b (for example, in the cross section of the second optical surface 1b a straight line 1b ₁ passing through two points E ₃ · E ₄₎ at both ends in the two points at both ends of the fourth any two points on the cross section of the optical surface 1d (e.g. in the cross-section of a fourth optical surface 1d E ₁ · E ₃ ) and the straight line 1d ₁ intersect at an obtuse angle β (90 ° <β <180 °).

4, when the cut third optical surface 1c and a fourth optical surface 1d at the same time the second plane P _2, and the cross-sectional shape of the fourth optical surface 1d show schematically. The cross-sectional shape shown in FIG. 4 corresponds to the cross-sectional shape along the line AA ′ in FIG. As shown in FIG. 4, the curve C is included in the cross section when the fourth optical surface 1 d is cut by the second surface P ₂ . This curve C has two inflection points M ₁ and M ₂ .

Here, the inflection point refers to a point where the direction of bending is changed by a curved line on the plane, that is, a point where the sign of curvature changes from positive to negative or from negative to positive on the curved line (a point where unevenness changes). . This inflection point is also a point where the sign of the second derivative f ″ (x) changes when the curve is expressed as a function y = f (x). Line segments V ₁ -V ₂ and line segments W ₁ -W ₂ in FIG. 3 indicate that the cutting position by the second surface P _{2 on} the fourth optical surface 1 d is the second optical surface from the third optical surface 1 c side. in the case of changing the 1b side, it shows a set of the inflection point _M 1 · _{M 2} (movement locus of the inflection point _M 1 · _{M 2),} respectively. In addition, when it is not necessary to distinguish the inflection points M ₁ and M ₂ , these are collectively referred to as the inflection points M.

Thus, the fourth optical surface 1d is a cross section when taken along a second plane P _2, as contained curve C with inflection point M, is composed of a surface shape of undulating. That is, the cross-sectional shape of the fourth optical surface 1d includes a shape with a positive curvature (for example, a curved shape on one side with respect to the inflection point M) and a shape with a negative curvature (for example, with respect to the inflection point M) And a curved shape on the opposite side to one side). Thereby, compared with the case where the cross-sectional shape is a shape having no inflection point M, the strength of the fourth optical surface 1d is stronger than the external force in the direction penetrating the fourth optical surface 1d. On the other hand, the fourth optical surface 1d itself is difficult to bend. In addition, as the shape in which the cross-sectional shape does not have the inflection point M, for example, when the cross-sectional shape is configured by only a straight line (when the entire fourth optical surface 1d is configured by a plane), It can be assumed that is a shape having only one of positive and negative curvatures.

  For this reason, for example, when the light guide element 10 is incorporated into a product (for example, an image display device described later), an external force due to simple pressing or tightening acts in a direction penetrating the third optical surface 1c and the fourth optical surface 1d. Even so, it is possible to prevent the tapered portion sandwiched between the third optical surface 1c and the fourth optical surface 1d from being deformed by the external force. Further, for example, even if stress (thermal stress) is generated due to expansion and contraction of the prism itself due to heat, the fourth optical surface 1d has high strength, so that deformation of the tapered portion due to thermal stress can be suppressed. As a result, the light guided inside the light guide element 10 is defined by an appropriate external direction (original optical design) via the fourth optical surface 1d (or the optical member 2) and the third optical surface 1c. Direction).

  Further, since the plurality of optical surfaces (the first optical surface 1a to the fourth optical surface 1d) of the light guide prism 1 are surfaces having an optically effective region that transmits or reflects incident light, the optically effective optical surfaces of these optical surfaces are used. In the region, incident light can be reliably transmitted or reflected, guided inside the prism, and emitted outside.

  The fourth optical surface 1d (especially in the optical effective region R) reflects light incident on the inside of the light guide element 10 (light guide prism 1) and guides it to the third optical surface 1c. An optical member 2 is arranged. By using the optical member 2, the light guided inside the light guide element 10 is reliably reflected by the optical member 2 in the direction of the third optical surface 1 c, and externally via the third optical surface 1 c. It can be taken out.

  In particular, the optical member 2 is composed of a hologram optical element. In this case, the light guided inside the light guide element 10 is reflected by the hologram optical element in a desired direction by setting the optical power, diffraction angle, and the like of the hologram optical element, and passes through the third optical surface 1c. Can be taken out. That is, the light guide element 10 that extracts light in a desired direction can be easily realized by the optical design of the hologram optical element.

  Further, since the optical member 2 is composed of a hologram optical element, for example, it is diffracted by the optical member 2 included in light (external light) incident on the optical member 2 from the side opposite to the light guide prism 1. Light outside the reflected wavelength range can be transmitted and guided to the third optical surface 1c. Accordingly, light guided through the light guide prism 1 (light diffracted and reflected by the hologram optical element) and external light (light transmitted through the hologram optical element) are simultaneously passed through the third optical surface 1c. And can be taken out to the outside. Such a configuration is very effective in an application in which an image displayed on a display element and an external image are simultaneously observed, like an image display device according to a third embodiment described later.

Incidentally, in the present embodiment, as shown in FIG. 4, a fourth optical surface 1d, i.e., the cross section when taken along a second plane P _2, optical as contained curve C with inflection point M In the plane, the inflection point M is outside the optical effective region R. In this case, in the fourth optical surface 1d, the surface shape of the region where the optical design is necessary, that is, the region where the optical member 2 is arranged is a simple shape without the inflection point M, so the optical design of the optical member 2 Is preferable in that it is simple. In addition, since the optical design of the optical member 2 is possible even if the inflection point M is inside the optical effective region M on the fourth optical surface 1d, such a configuration may of course be used.

5 and 6 show variations of the cross-sectional shape when cut a fourth optical surface 1d in the second plane P _2. The cross-sectional shape of the fourth optical surface 1d may be a shape including a straight line other than a curved line. For example, as shown in FIG. 5, the cross-sectional shape of the fourth optical surface 1d may be a shape in which two straight lines F and one curve C having an inflection point M are alternately connected. As shown in FIG. 6, the shape may be such that three straight lines F and two curves C each having an inflection point M are alternately connected. Further, the number of inflection points M in the cross-sectional shape of the fourth optical surface 1d may be one as shown in FIG. 5, or may be two as shown in FIGS. Although not shown, there may be three or more (the cross-sectional shape may be a shape having three or more curves C having inflection points M).

FIG. 7 is a perspective view showing another configuration of the light guide element 10. As shown in the figure, in the light guide prism 1, in addition to the fourth optical surface 1d, the third optical surface 1c may have a wavy shape. 8, when taken along a third optical surface 1c and a fourth optical surface 1d simultaneously second surface P ₂ of the light guide element 10 in FIG. 7, the cross-sectional shape of the third optical surface 1c schematically show ing. The surface shape of the fourth optical surface 1d is the same as the shape shown in FIG.

As shown in FIG. 8, the cross section when taken along a third optical surface 1c in the second plane P _2, which contains the curve D. This curve D has two inflection points N (N ₁ · N ₂ ). In the cross-sectional shape of the third optical surface 1c, the number of inflection points N may be one or may be three or more, like the fourth optical surface 1d. Further, in the cross-sectional shape of the third optical surface 1c, the number of the curves D having the inflection points N may be at least one.

Thus, in addition to the fourth optical surface 1d, the even third optical surface 1c, a cross section when taken along a second plane P _2, as contained curve D with inflection points N, undulating By adopting the shape, the third optical surface 1c itself is less likely to bend with respect to the external force as compared with the case where the entire third optical surface 1c is configured as a flat surface. For this reason, even if an external force is exerted in a direction penetrating the third optical surface 1c and the fourth optical surface 1d, the tapered portion of the light guide prism 1 can be further suppressed from being deformed by the external force. Therefore, the light guided inside the light guide element 10 can be reliably guided to an appropriate external direction via the fourth optical surface 1d (or the optical member 2) and the third optical surface 1c. .

  Note that even if only the third optical surface 1c has a wavy shape as shown in FIG. 8 and the fourth optical surface 1d is formed as a flat surface, the third optical surface 1c is difficult to bend with respect to an external force. The tapered portion of the prism 1 can be prevented from being deformed by an external force.

From the above, when the light guide element 10 of this embodiment, taken along the same time a third optical surface 1c and a fourth optical surface 1d of the light guide prism 1 in the second plane P _2, the third optical surface 1c As long as at least one of the cross sections of the fourth optical surface 1d includes a curve (curve C, curve D), the curve has an inflection point (inflection point M, inflection point N). It can be said.

FIG. 9 is a horizontal sectional view (a sectional view in the ZX plane) showing still another configuration of the light guide element 10. As shown in the figure, the third optical surface 1c of the light guide element 10 may have a shape recessed toward the second optical surface 1b. In such a light guide element 10, when a plane including a straight line a (a straight line connecting _one end L ₁ of the intersection line L and the other end L ₂ ) is considered as the second surface P ₂ , Since the third optical surface 1c is recessed toward the second optical surface 1b, the third optical surface 1c and the fourth optical surface 1d cannot be cut simultaneously on the plane. In this case, the second surface P _2, by considering a plane parallel to the straight line a, and a third optical surface 1c and a fourth optical surface 1d can be cut simultaneously in the plane.

Conversely, as shown in FIG. 7, when the third optical surface 1c is the second optical surface 1b is a shape protruding to the opposite side, a second side P _2, consider a plane containing a straight line a also be considered a plane parallel to the straight line a, it can be cut at the same time a third optical surface 1c and a fourth optical surface 1d in the second plane P _2. Therefore, whether the plane including the straight line a or the plane parallel to the straight line a is considered as the second plane P ₂ is such that the third optical surface 1c and the fourth optical surface 1d can be cut simultaneously. What is necessary is just to determine suitably according to the surface shape of each optical surface of the light guide element 10. FIG.

In the above, when the cut third optical surface 1c and a fourth optical surface 1d in a first plane P _1, with the cross-sectional shape of the third optical surface 1c and a fourth optical surface 1d both linear (see Figure 1) However, the cross-sectional shape is not limited to a straight line. For example, when the cut third optical surface 1c and a fourth optical surface 1d in a first plane P _1, at least one of the cross-sectional shape of the third optical surface 1c and a fourth optical surface 1d is include curves Also good. Even in this case, the fact that the third optical surface 1c and the fourth optical surface 1d intersect at an acute angle can be expressed using the definition described in the present embodiment. That is, when the cut and the third optical surface 1c and a fourth optical surface 1d in a first plane P _1, and the straight line passing through any two points on the section of the third optical surface 1c, a fourth optical surface 1d A straight line passing through two arbitrary points on the cross section intersects at an acute angle α (0 ° <α <90 °). The “arbitrary two points” in the cross-sectional shapes of the third optical surface 1c and the fourth optical surface 1d are selected as long as they are two points that can satisfy 0 ° <α <90 °. May be.

From the above, the light guide element 10 of the present embodiment can also be expressed as follows. That is, the light guide element 10 of the present embodiment has a plurality of optical surfaces necessary for guiding light inside. The plurality of optical surfaces include two optical surfaces that intersect each other (for example, the third optical surface 1c and the fourth optical surface 1d). The intersecting line L serving as the boundary between the two optical surfaces has a shape different from the straight line a connecting both ends of the intersecting line L. The plane perpendicular to the straight line a, the first and the plane P _1, a plane parallel to the plane or line a comprises a linear a, the second surface P _2. When off the two optical surfaces at the first surface P _1, straight lines and the other through any two points on the cross-section of one of the optical surfaces (e.g., the third optical surface 1c) (e.g. across two points) A straight line passing through two arbitrary points (for example, two points at both ends) on the cross section of the optical surface (for example, the fourth optical surface 1d) intersects at an acute angle. When off the two optical surfaces at the second side P _2, the least one of the cross-section of the two optical surfaces, contains curve C. The curve C has an inflection point.

[Embodiment 2]
The following will describe another embodiment of the present invention with reference to the drawings. In this embodiment, a bonded optical element configured using the light guide element described in Embodiment 1 will be described.

  FIG. 10 is a cross-sectional view illustrating a schematic configuration of the cemented optical element 11 of the present embodiment, FIG. 11 is a perspective view of the cemented optical element 11, and FIG. 12 is a front view of the cemented optical element 11. . The bonding optical element 11 is configured by bonding the bonding optical member 3 to the light guide element 10 of the first embodiment. In addition, although the example which comprised the joining optical element 11 using the light guide element 10 shown in FIG. 1 etc. is demonstrated here, a joining optical element using the other light guide element 10 shown in Embodiment 1 is demonstrated. 11 may be configured.

  The joining optical member 3 is formed of, for example, a transparent acrylic resin, and is formed in a shape that becomes a substantially parallel flat plate when joined to the light guide element 10. The bonding optical member 3 includes a first optical surface 3a, a second optical surface 3b, and a third optical surface 3c. The first optical surface 3a is a facing surface that has substantially the same surface shape as the fourth optical surface 1d of the light guide element 10 and is positioned facing the fourth optical surface 1d. The fourth optical surface 1d is an optical surface (third optical surface 1c) that guides light by total reflection among the third optical surface 1c and the fourth optical surface 1d that form a tapered shape in the light guide element 10. ) Is a different optical surface. The second optical surface 3 b of the bonding optical member 3 is a surface located on the same plane as the third optical surface 1 c of the light guide element 10, and the third optical surface 3 c is the second optical surface of the light guide element 10. It is a surface located on the same surface as 1b. The second optical surface 3b and the third optical surface 3c are arranged in parallel, for example.

  The optical member 3 for bonding having such a configuration has the light guide element 10 and the adhesive 4 so that the fourth optical surface 1d of the light guide element 10 faces the first optical surface 3a of the optical member 3 for bonding. It is joined via. As the adhesive 4, for example, an adhesive (photocurable adhesive) that is cured by irradiation with ultraviolet rays can be used, but other adhesives may be used.

  The fourth optical surface 1d of the light guide element 10 and the first optical surface 3a of the bonding optical member 3 have substantially the same surface shape, so that a large gap is not formed between these optical surfaces. The optical element 10 and the bonding optical member 3 can be bonded.

  Further, in the light guide element 10, the third optical surface 1c and the fourth optical surface 1d intersect each other at an acute angle, and the tip is tapered, but the surface shape is substantially the same as that of the fourth optical surface 1d. By joining the joining optical member 3 having the first optical surface 3a to the light guide element 10, the thickness of the joining optical member 3 is added to the tapered shape thickness of the light guide element 10, so that the tapered shape is obtained. It can be virtually eliminated. Thereby, even when an external force is applied to the portion that has formed the tapered shape, the change in the shape of the portion due to the external force is further compared to the configuration of the first embodiment in which the bonding optical member 3 is not bonded. Can be suppressed.

  Further, when the light guide element 10 and the bonding optical member 3 are bonded using the adhesive 4, stress due to curing shrinkage of the adhesive 4 is applied to the tapered portion of the light guide element 10. However, by setting the surface shape of the third optical surface 1c or the fourth optical surface 1d as described in the first embodiment, the light guide element 10 can suppress deformation due to stress at the tapered portion. it can. Therefore, even when the bonding optical member 3 is bonded to the light guide element 10 via the adhesive 4, the tapered portion of the light guide element 10 is deformed due to the curing shrinkage of the adhesive 4. Can be suppressed.

[Embodiment 3]
The following will describe still another embodiment of the present invention with reference to the drawings. In the present embodiment, an example in which the bonding optical element 11 according to the second embodiment is applied to an image display device will be described.

  In this embodiment, the XYZ directions shown in the first and second embodiments correspond to the left-right direction (eye width direction), the up-down direction, and the front-rear direction (the direction of each direction is not particularly limited). ). Here, the left, right, up, down, and front / rear directions refer to the left, right, up, down, and front / rear directions based on the position (line-of-sight direction) when the observer observes the image. In the drawings shown below, only representative optical paths are indicated by broken lines in order to avoid complicated optical paths.

  13 is a cross-sectional view illustrating a schematic configuration of the image display device 20 according to the present embodiment, FIG. 14 is a perspective view of the image display device 20, and FIG. 15 illustrates the image display device 20 from the observer side. It is a front view when seen. The image display device 20 includes a light source 21, an illumination mirror 22, a diffusion plate 23, a polarization beam splitter (PBS) 24, a display element 25, and an eyepiece optical system 26. The light source 21 and the illumination mirror 22 constitute an illumination optical system 30 that illuminates the display element 25.

  The light source 21 includes RGB integrated LEDs that emit light corresponding to each color of R (red), G (green), and B (blue). A plurality of light emitting points (each light emitting point of RGB) are arranged in a substantially straight line in the horizontal direction. The wavelength of light emitted from the light source 21 is, for example, a peak wavelength of light intensity and a wavelength width of half value of light intensity, 462 ± 12 nm (B light), 525 ± 17 nm (G light), 635 ± 11 nm (R light). It is. The light source 21 may be a laser light source.

  In the present embodiment, the light source 21 includes two pairs of RGB integrated LEDs. For each of R, G, and B, the light emission points are arranged substantially linearly (for example, in the X direction) so that the light emission points are positioned symmetrically with respect to the optical axis incident surface of the hologram optical element constituting the optical member 2. , The light emitting points are arranged in the order of BGRRGB). Thereby, the distribution of RGB light intensity can be made symmetric in the X direction. The optical axis incident surface of the hologram optical element is the optical axis of the incident light with respect to the hologram optical element, where the optical axis is the axis that optically connects the center of the display surface of the display element 25 and the center of the observation pupil OP. And the surface including the optical axis of the outgoing light (reflected light). This optical axis incident surface is parallel to the YZ plane.

  The illumination mirror 22 reflects light (illumination light) emitted from the light source 21 toward the diffusion plate 23, and the observation pupil OP, which is an optical pupil (exit pupil), and the light source 21 are substantially conjugate in the YZ plane. It is an optical element that bends the illumination light so that

  The diffusion plate 23 is a diffusion plate that diffuses incident light in all directions. Although it is possible to omit the arrangement of the diffusing plate 23, it is desirable to dispose the diffusing plate 23 from the viewpoint of widening the light distribution angle of incident light and making the light intensity of the light source 21 more uniform. The diffuser plate 23 may be a diffuser plate (unidirectional diffuser plate) that diffuses incident light only in one direction (for example, the X direction).

  The PBS 24 reflects only S-polarized light of the incident light in the direction of the display element 25, while out of the light reflected by the display element 25, transmits light corresponding to the image signal ON, that is, a flat plate that transmits P-polarized light. And is attached to the light incident surface (first optical surface 1 a) of the light guide prism 1 of the eyepiece optical system 26.

  The display element 25 is a display element that displays an image by modulating light from the light source 21, and is configured by a reflective liquid crystal display element in the present embodiment. The display element 25 may have a configuration including a color filter, and is driven in a time division manner so that an RGB image corresponding to the emission color is displayed in synchronization with the time division emission for each RGB of the light source 21. It may be a configuration.

  The display element 25 is arranged so that light that enters from the PBS 24 substantially vertically is reflected substantially vertically and travels toward the PBS 24. This facilitates optical design that increases the resolution as compared with a configuration in which light is incident on the reflective display element at a large incident angle. The display surface of the display element 25 is rectangular, and is arranged so that the longitudinal direction of the display surface is the X direction and the short side direction is perpendicular to the X direction.

  The eyepiece optical system 26 is an optical system for guiding the image light from the display element 25 to the observation pupil OP, and has positive optical power that is non-axisymmetric (non-rotationally symmetric). The eyepiece optical system 26 includes the cemented optical element 11. The bonding optical element 11 includes the light guide prism 1, the optical member 2, and the bonding optical member 3 as described in the second embodiment. A light guide element 10 is constituted by the light guide prism 1 and the optical member 2. Therefore, it can be said that the eyepiece optical system 26 includes the light guide element 10.

  The light guide prism 1 is an optical element that guides image light incident from the display element 25 through the PBS 24 and transmits light of the external image (external light), and is also called an eyepiece prism. The light guide prism 1 has a shape in which the upper end portion of the parallel plate is thickened toward the upper end and the lower end portion is thinned toward the lower end.

  As described in the first embodiment, the light guide prism 1 has the first optical surface 1a to the fourth optical surface 1d. The plurality of optical surfaces will be described below with a focus on the function of the image display device 20. The first optical surface 1 a is a light incident surface on which image light is incident from the display element 25 via the PBS 24. The second optical surface 1b and the third optical surface 1c are two parallel planes positioned substantially parallel to the observation pupil OP and facing each other, and serve as total reflection surfaces that totally reflect and guide the image light. Yes. Among them, the third optical surface 1 c on the observation pupil OP side also serves as an emission surface (transmission surface) for image light that is diffracted and reflected by the optical member 2. The 4th optical surface 1d connects the 2nd optical surface 1b and the 3rd optical surface 1c, and is an affixing surface to which the optical member 2 is affixed, and inclines with respect to the 2nd optical surface 1b and the 3rd optical surface 1c. Yes. The surface shape of the fourth optical surface 1d is as described in the first embodiment.

  The light guide prism 1 is bonded to the bonding optical member 3 with an adhesive 4 so as to sandwich the optical member 2 disposed at the lower end thereof. The joining optical member 3 is also called a deflection prism, and is bonded together via the light guide prism 1 and the optical member 2 to form a substantially parallel plate. By bonding the bonding optical member 3 to the light guide prism 1, the bonding optical member 3 cancels refraction when external light is transmitted through the wedge-shaped lower end portion (tapered portion) of the light guide prism 1. It is possible to prevent distortion in the observed external image.

  The optical member 2 is an optical element that is provided in contact with the light guide prism 1 and diffracts the image light guided inside the light guide prism 1 to guide it to the observation pupil OP. A reflection type hologram optical element is used. The volume phase type hologram optical element is formed by irradiating a hologram photosensitive material with laser light with two light beams to form fringes (interference fringes) due to interference of the two light beams. When, for example, a photopolymer is used as the hologram photosensitive material, the above interference fringes can be easily formed by photopolymerization of the photopolymer. Since the interference fringes are formed by alternately laminating a plurality of resin layers having different refractive indexes, the volume phase type optical member 2 has a plurality of resin layers having different refractive indexes and positioned alternately. It can be said that the structure includes.

  The hologram optical element constituting the optical member 2 has, for example, 465 ± 5 nm (B light), 521 ± 5 nm (G light), and 634 ± 5 nm (R light) at the peak wavelength of diffraction efficiency and the half width of the diffraction efficiency. Diffracts (reflects) light in three wavelength ranges. That is, the RGB diffraction wavelengths in the hologram optical element substantially correspond to the wavelengths of the RGB image light (the emission wavelength of the light source 21).

  In the above configuration, the light emitted from the light source 21 is reflected by the illumination mirror 22, diffused by the diffusion plate 23, and then enters the PBS 24, where only S-polarized light is reflected in the direction of the display element 25. . In the display element 25, incident light is modulated in accordance with an image signal. At this time, the image light corresponding to the image signal ON is converted by the display element 25 into light (P-polarized light) whose polarization direction is orthogonal to the incident light and is emitted, and thus passes through the PBS 24 and passes through the light guide prism 1. From the first optical surface 1a. On the other hand, the image light corresponding to the image signal OFF is output as S-polarized light without being converted in the polarization direction by the display element 25, so that it is blocked by the PBS 24 and does not enter the light guide prism 1.

  In the light guide prism 1, the incident image light is totally reflected at least once by the two optical surfaces (second optical surface 1 b and third optical surface 1 c) facing the light guide prism 1, and then is reflected on the optical member 2. Then, the light is selectively diffracted and reflected for each of the RGB colors, and is emitted from the third optical surface 1c to reach the observation pupil OP. Therefore, the observer can observe the image displayed on the display element 25 as a virtual image at the position of the observation pupil OP.

  On the other hand, since the light guide prism 1, the joining optical member 3 and the optical member 2 transmit almost all of the outside light, the observer can observe the outside image (outside scenery) with see-through. Therefore, the virtual image of the image displayed on the display element 25 is observed while overlapping a part of the external image.

  In the light guide element 10 included in the eyepiece optical system 26, the surface shape of the optical surfaces (the third optical surface 1c and the fourth optical surface 1d) described above is set, so that deformation of the tapered portion due to external force is suppressed. The light guided inside the light guide element 10 can be guided in an appropriate external direction via the fourth optical surface 1d and the third optical surface 1c. Therefore, in the image display device 20 using the light guide element 10, the image light from the display element 25 can be appropriately guided toward the observation pupil OP by the light guide element 10. As a result, it is possible to reduce the occurrence of deterioration (image deterioration) such as distortion and blurring in the image obtained by the observation pupil OP, and the quality of the observed image can be improved.

  In addition, as described above, of the illumination light from the illumination optical system 30 (the light source 21 and the illumination mirror 22), light having a predetermined polarization direction (for example, S-polarized light) is reflected by the PBS 24 and guided to the display element 25. In the configuration in which light reflected by the display element 25 and having a polarization direction orthogonal to the incident light to the display element 25 (for example, P-polarized light) is transmitted to the light guide prism 1, the light is directed to the light guide prism 1. Since the light path on the incident side is bent, the optical members disposed on the light incident side with respect to the light guide prism 1 are arranged in a compact manner while ensuring a desired optical path length from the light source 21 to the light guide prism 1. Can do. Thereby, the size reduction of the image display apparatus 20 becomes easy.

  In addition, by using a volume phase type hologram optical element having a plurality of resin layers having different refractive indexes and alternately arranged as the optical member 2, desired diffraction characteristics can be obtained by two-beam interference of laser light. The optical member 2 having can be easily realized. The optical member 2 is not limited to a volume phase hologram optical element, and may be, for example, a blazed (cross-sectional sawtooth) optical element.

  In this embodiment, the bonding optical member 3 is arranged to realize a good see-through property that enables observation of an external image without distortion. However, if it is not necessary to obtain a good see-through property, the bonding optical member is used. The arrangement of the member 3 may be omitted. That is, the eyepiece optical system 26 may be configured by only the light guide element 10 shown in the first embodiment.

  In the present embodiment, a reflective liquid crystal display element is used as the display element 25, but a transmissive liquid crystal display element may be used. In this case, the liquid crystal display element is arranged so that light having a desired polarization direction (for example, light whose polarization direction is parallel to the optical axis incident surface of the hologram optical element) is emitted from the transmissive liquid crystal display element. Thereby (by setting the direction of the transmission axis of the polarizing plate (polarizer) on the light exit side with respect to the liquid crystal cell), the arrangement of the PBS 24 can be made unnecessary.

  It is also possible to apply the light guide element 10 as shown in FIGS. 7 and 9, that is, the light guide element 10 having a waved third optical surface 1 c to the image display device 20. In this case, the image light from the display element 25 is transmitted through the third optical surface 1c and guided to the observation pupil OP, so that the observation image may be distorted. However, in this case, the observer can observe an image with reduced distortion by performing an optical design that can cancel the distortion of the observation image or by correcting the display image of the display element 25.

[Embodiment 4]
The following will describe still another embodiment of the present invention with reference to the drawings. In the present embodiment, an HMD that is an application example of the image display apparatus according to the third embodiment will be described. 16A, 16B, and 16C are a top view, a front view, and a bottom view of the HMD 40 of the present embodiment, and FIG. 17 is a perspective view from the front side of the HMD 40.

  The HMD 40 includes the image display device 20 described above, a frame 42, a lens 43, a nose pad 44, and a position adjustment mechanism 45.

  The image display apparatus 20 includes the above-described illumination optical system 30 (light source 21, illumination mirror 22), diffusion plate 23, PBS 24, and display element 25 in a housing 20a. It is located in the housing 20a. The eyepiece optical system 26 is located in front of the right-eye lens 43R (on the outside side opposite to the observer). The light source 21 and the display element 25 in the housing 20a are connected to a circuit board (not shown) via a cable (not shown) provided through the housing 20a, and drive power and image signals are output from the circuit board. Etc. are supplied.

  The image display device 20 further includes an imaging device that captures still images and moving images, a microphone, a speaker, an earphone, and the like, and information on the captured image and the display image via an external server or terminal and a communication line such as the Internet. Or a configuration for exchanging (transmitting / receiving) audio information.

  The frame 42 corresponds to a frame of eyeglasses, and is a support member that is mounted on the observer's head and supports the image display device 20. The frame 42 includes temples that come into contact with the left and right temporal regions of the observer.

  The lens 43 includes a right-eye lens 43 </ b> R and a left-eye lens 43 </ b> L disposed in front of the right and left eyes of the observer. The right-eye lens 43R and the left-eye lens 43L are connected to the position adjustment mechanism 45 via the right connection portion 46R and the left connection portion 46L. The right-eye lens 43R and the left-eye lens 43L may be lenses for correcting vision, or may be simple dummy lenses that do not correct vision.

  The nose pad 44 includes a right nose pad 44R and a left nose pad 44L that come into contact with the nose of the observer. The right nose pad 44R and the left nose pad 44L are connected to the position adjusting mechanism 45 via the right connecting part 47R and the left connecting part 47L.

  The position adjustment mechanism 45 moves the nose pad 44 relative to the frame 42 in the vertical direction perpendicular to the eye width direction of the observer, thereby moving the vertical position of the image display device 20 supported by the frame 42. It is a mechanism that adjusts. Note that the lens 43 and the nose pad 44 may be directly fixed to the frame 42 without providing the position adjusting mechanism 45.

  When the HMD 40 is mounted on the observer's head and an image is displayed on the display element 25, the image light is guided to the observation pupil OP (see FIG. 10) via the eyepiece optical system. Therefore, by aligning the observer's pupil with the position of the observation pupil OP, the observer can observe an enlarged virtual image of the display image of the image display device 20. At the same time, the observer can observe the external image through the eyepiece optical system 26 in a see-through manner.

  As described above, the image display device 20 is supported by the frame 42 as the support member, so that the observer can observe the image provided by the image display device 20 stably in a hands-free manner for a long time.

  In FIG. 16A and the like, the eyepiece optical system 26 and the lens 43 of the image display device 20 are configured separately, but the eyepiece optical system 26 may be integrated with the lens 43. . Further, two image display devices 20 may be used so that an image can be observed with both eyes.

(Other)
The light guide element, the bonding optical element, the image display device, and the head mounted display described above may be expressed as follows.

  The light guide element described above is a light guide element having a plurality of optical surfaces necessary for guiding light inside, and the plurality of optical surfaces include two optical surfaces that intersect at an acute angle. The intersecting line serving as the boundary between the two optical surfaces has a shape different from the straight line connecting both ends of the intersecting line, and the two optical surfaces are cut by a plane including the straight line or a plane parallel to the straight line. Then, at least one of the cross sections of the two optical surfaces includes a curve, and the curve has an inflection point.

  The plurality of optical surfaces may be surfaces having an optically effective region that transmits or reflects incident light.

  In an optical surface in which the curve is included in a cross section when cut by any one of the planes, it is preferable that the inflection point of the curve is outside the optical effective region.

  Of the two optical surfaces, an optical member may be disposed on one of the optical surfaces so as to reflect light that is guided and incident on the inside of the light guide element and guides the light to the other optical surface.

  Among the two optical surfaces, an optical member is disposed in the optical effective region of one optical surface to reflect the light that is guided inside the light guide element and enters the other optical surface. It may be.

  The optical member may be a hologram optical element.

  The above-described bonded optical element has substantially the same surface shape as the above-described light guide element and an optical surface that is different from the optical surface that guides light by total reflection among the two optical surfaces of the light guide element. And a joining optical member that is joined to the light guide element so that the different optical surface and the facing surface are opposed to each other.

  The bonding optical member may be bonded to the light guide element via an adhesive.

  The image display device described above includes a display element that displays an image, and an eyepiece optical system that guides image light from the display element and guides it to the observation pupil. A light guide element is included.

  The image display device described above includes a display element that displays an image, and an eyepiece optical system that guides image light from the display element and guides it to the observation pupil. It includes a bonding optical element.

  The head-mounted display described above includes the above-described image display device and a support member that supports the image display device in front of the observer's eyes.

  The light guide element of the present invention can be used for, for example, a bonding optical element, an image display device, and an HMD.

1c Third optical surface (optical surface)
1c ₁ straight line 1d 4th optical surface (optical surface)
DESCRIPTION OF SYMBOLS 1d ₁ straight line 2 Optical member 3 Bonding optical member 3a Opposite surface 4 Adhesive 10 Light guide element 11 Bonding optical element 20 Image display apparatus 40 HMD (head mounted display)
42 Frame (support member)
a straight line C curve D curve L intersection line M, M ₁ , M ₂ inflection point N, N ₁ , N ₂ inflection point OP observation pupil P ₁ first surface P ₂ second surface R optical effective area

Claims (11)

A light guide element having a plurality of optical surfaces necessary for guiding light inside,
The plurality of optical surfaces include two optical surfaces that intersect at an acute angle;
The line of intersection serving as the boundary between the two optical surfaces has a shape different from the straight line connecting both ends of the line of intersection,
When the two optical surfaces are cut by a plane including the straight line or a plane parallel to the straight line, at least one of the cross sections of the two optical surfaces includes a curve,
The light guide element, wherein the curve has an inflection point.   The light guide element according to claim 1, wherein the plurality of optical surfaces are surfaces having an optically effective area that transmits or reflects incident light.   3. The light guide element according to claim 2, wherein an inflection point of the curved line is outside the optical effective area on an optical surface in which the curved line is included in a cross section when cut by any one of the planes.   2. An optical member is disposed on one optical surface of the two optical surfaces so as to reflect the light guided and incident on the inside of the light guide element to the other optical surface. 4. The light guide element according to any one of items 1 to 3.   Among the two optical surfaces, an optical member is disposed in the optical effective region of one optical surface to reflect the light that is guided inside the light guide element and enters the other optical surface. The light guide element according to claim 2 or 3.   The light guide element according to claim 4, wherein the optical member is a hologram optical element. A light guide element according to any one of claims 1 to 6,
Of the two optical surfaces of the light guide element, an optical surface different from the optical surface that guides light by total reflection and an opposing surface having substantially the same surface shape, the different optical surface and the opposing surface are A bonding optical element including a bonding optical member bonded to the light guide element so as to face each other.   The bonded optical element according to claim 7, wherein the bonding optical member is bonded to the light guide element via an adhesive. A display element for displaying an image;
An eyepiece optical system that guides image light from the display element and guides it to the observation pupil,
The said eyepiece optical system is an image display apparatus containing the light guide element in any one of Claim 1 to 6. A display element for displaying an image;
An eyepiece optical system that guides image light from the display element and guides it to the observation pupil,
The said eyepiece optical system is an image display apparatus containing the joining optical element of Claim 7 or 8. An image display device according to claim 9 or 10,
A head-mounted display having a support member that supports the image display device in front of an observer's eyes.

Images