WO2008032879A1 - Free curved-surface prism, and head-mounted display - Google Patents

Abstract

Intended is to thin a head-mounted display using a waveguide plate. The head-mounted display includes a display (133), a free curved-surface prism (134) and a waveguide plate (120). A beam having entered the free curved-surface prism (134) from the display (133) is twice reflected in the free curved-surface prism (134) so that it is enlarged at a proper magnification and goes toward the waveguide plate (120). The free curved-surface prism (134) has its emanating pupil positioned in the waveguide plate (120). The beam having entered the waveguide plate (120) advances transversely in the waveguide plate (120) so that it is emitted toward the eyes of a user. The distance from the waveguide plate (120) to the face of the free curved-surface prism (134) confronting the waveguide plate (120) is set to about 3 mm.

Description

Free-form prism, head mount display technology

 The present invention relates to a head-mounted display that is used while being worn on a user's head. Light

Background of the Invention

 Thread 1

 A head mask that is used while attached to a body such as the head and displays an image in front of the user's eyes.

The current display is used in various fields for displaying images, including virtual reality. A head-mounted display is generally formed in a gorgeous shape or a frame shape of large glasses.

 Various structures of head-mounted displays have been proposed, and some of them use waveguide plates. The waveguide plate has a structure having a large number of grooves such as a diffraction grating, and is often shaped to cover both eyes of the user. A head-mounted display that uses a waveguide plate expands the image displayed on the display from the small display force that displays the image, then guides the light into the waveguide plate. The light is displayed on the display by directing the light to the front of the user's eyes while reflecting it several times inside and then emitting the light from the waveguide plate to both eyes of the user. The image is displayed in an enlarged state.

 Although this is not limited to a head-mounted display using such a waveguide plate, a head-mounted display is generally better as it is smaller. In particular, a head-mounted display has a better design property as the thickness in the front-rear direction when it is attached to the user's head is smaller.

From such a viewpoint, research has been conducted to reduce the thickness in the front-rear direction of a head-mounted display using a waveguide plate (this may be simply referred to as “thinning” in this application). . However, the display and the display If the light path from the display to the waveguide plate is arranged in a straight line so that the lens system for enlarging the projected image and the waveguide plate have an appropriate relationship, the front of the waveguide plate The distance from the screen to the back of the display will inevitably exceed 35 mm. Attempts to bend the light path by inserting a mirror in an appropriate part of the light path from the display to the waveguide, thereby reducing the thickness of the head-mounted display. The distance can be reduced to about 25 mm and the force cannot be suppressed. Various prototypes have been made, but in fact, there is no existing head-mounted display using a waveguide plate that can be made thinner.

 However, if only the thin film is important, it is possible to develop a head-mounted display that does not use a waveguide plate. For a head-mounted display using a force waveguide plate, a waveguide plate is used. This makes it possible to enlarge the pupil on the waveguide plate when light is emitted to the user's eyes, making it easier for the user to see the image regardless of the difference in eye width due to the individuality of the user. There is an advantage that the fatigue of the user can be suppressed.

 In addition, when the waveguide plate is designed to cover both eyes of the user and the light from the display is guided to both eyes of the user, the user is more tired than when viewing the image with one eye. Can be reduced. In particular, a head-mounted display using a waveguide plate can easily be configured to guide a common image originally displayed on one display to both eyes of the user. It is relatively easy to show the same image with no difference in color and size to both eyes, and is therefore suitable for reducing fatigue caused by the user viewing the image.

 If a head-mounted display with these advantages can be thinned, the demand is very large.

 The present invention solves this problem, and an object of the present invention is to provide a technique for reducing the thickness of a head-mounted display using a waveguide plate. Disclosure of the invention

The inventor of the present application proposes the following free-form surface prism and head mount display as an invention that can solve the above-mentioned problems. The present invention solves the above-mentioned problems by using a free-form surface prism.

 The free-form surface prism has four surfaces, the first surface, the second surface, the third surface, and the fourth surface. By reflecting the light twice inside it, the direction of the incoming light is changed. In addition, the light is reflected so that the image that is the source of the incoming light is magnified by the reflection of the light twice in the interior and the two times of bending when the light enters and exits the interior. It is supposed to change. Simply put, a free-form surface prism combines the functions of a prism and a lens.

The head-mounted display of the present invention includes a display for displaying an image, a free-form curved prism, and a waveguide plate, and is used by being fixed to the user's head. The free-form curved prism in the head-mounted display has four surfaces, a first surface, a second surface, a third surface, and a fourth surface, and allows the light from the display to pass through the first surface. The light transmitted through the first surface is reflected by the second surface, the light reflected by the second surface is reflected by the third surface, and the light reflected by the third surface is reflected by the first surface. By passing through the four surfaces, the direction of the light guided to the inside is changed, and the image displayed on the display is enlarged. In addition, the first surface, the second surface, the third surface, and the fourth surface of the free-form surface prism have a planar exit pupil of the free-form surface prism that is 1 O mm away from the fourth surface. It is supposed to exist in the position within. The wave guide plate is partly located on the exit pupil and the other part is located in front of at least one eye of the user when the head mount display is used. The light is guided from the exit pupil while reflecting light from the free-form curved prism guided to the inside of the exit pupil, and is emitted to the user's eyes. Note that the definition of “the position where the exit pupil is within 1 O mm from the fourth surface” in the present invention is not uniquely determined because the fourth surface is a curved surface. Therefore, in this specification, the distance from the fourth surface to the pupil is defined as the distance between the fourth surface and the pupil at the portion where the fourth surface is farthest from the pupil. In other words, the phrase “exit pupil is a position within 10 mm from the fourth surface” in the present invention means that the plane including the exit pupil and a number of planes constituting a part of the fourth surface This means that the distance from the plane including the exit pupil to the farthest part is within 1 O mm. This head-mounted display uses a free-form surface prism as described above to change the direction of light and to enlarge an image. Since the free-form surface prism can enlarge the image by two reflections and two refractions as described above, the image can be enlarged at a large magnification for its size. In addition, since the direction of light can be changed, the light path from the display to the waveguide plate can be bent. With these functions, the head-mounted display of the present invention can be thinned.

 By the way, in the field of head-mounted displays that do not use a waveguide plate, the idea of using a free-form surface prism has existed in the past. However, in a conventional head mounted display using a free-form surface prism, it is normal to guide the light emitted from the fourth surface of the free-form surface prism directly to the user's eye without using a waveguide plate. there were. This is because if a free-form surface prism is used, it is not necessary to use a large wave guide plate to enlarge the head-mounted display in order to reduce the size and thickness of the head-mounted display. Since free-form curved prisms were used in such applications, conventional free-form prisms were designed in consideration of preventing the user from feeling pressured by placing the free-form curved prism immediately in front of the user's eyes. The distance from the eye of the exit pupil of the eye was about 2 O mm or more (in other words, in a conventional head mounted display using a free-form surface prism, the fourth surface of the free-form surface prism is It was placed at a position about 2 O mm or more away from the eye.)

 In the present invention, such conventional common sense is overturned, and the exit pupil force of the surface of the free-form surface prism is located within 1 O mm from the fourth surface, and a part of the exit pupil is located at a position overlapping the exit pupil. By arranging the waveguide plates so that they overlap, a thin head mounted display is realized. When a prototype was made with such a configuration, the distance from the front of the waveguide plate to the rear edge of the display could be reduced to about 13 mm.

The head mount display of the present invention can be mounted on a conventional head mount if the planar exit pupil of the free-form surface prism is positioned about 10 mm from the fourth surface cover. Although it can be made thinner than the display, The distance from the 4th surface of the rhythm to the exit pupil can be smaller than 1 O mm, for example, about 3 mm. Furthermore, the distance can be 1 mm or less, and can be as close to 0 as possible.

 The free-form surface prism of the present invention only needs to have the first surface, the second surface, the third surface, and the fourth surface. In many cases, conventional free-form surface prisms are a series of surfaces in which the second surface and the fourth surface are smoothly connected, and the cross-sectional shape is substantially triangular. However, in the free-form surface prism of the present invention, the second surface and the fourth surface do not have to be a series of surfaces that are smoothly connected. As long as the free-form surface prism of the present invention has the first surface, the second surface, the third surface, and the fourth surface, it may have other surfaces.

 A part of the waveguide plate is positioned on the exit pupil and the other part is positioned in front of at least one eye of the user when the head mounted display is used. Any details can be used as long as light from the free-form surface prism force guided from the exit pupil is guided while being reflected and emitted to the user's eyes. The waveguide plate may be bent as long as it is plate-shaped.

 A part of the waveguide plate is located above the exit pupil, and the other part is located in front of both eyes of the user when the head mounted display is used. The light from the free-form surface prism guided to the inside from the exit pupil may be guided while being reflected and emitted to both eyes of the user. In this case, the head-mounted display looks at the image with both eyes. In this case, since the images viewed with both eyes are the same as those displayed on the same display, the user does not feel tired even when viewing the images on the head mount display.

 The positional relationship between the display and the free-form surface prism may be any way. Since the path from the display to the wave guide plate of light can be bent by using a free-form surface prism, the display and the wave guide plate generally do not face each other (not parallel).

For example, the display can be positioned above or below the free-form surface prism. In this way, the display, free-form surface prism, and wave guide plate can be configured symmetrically with respect to the user's face. Can be.

 The present inventor proposes the following as a free-form surface prism for realizing the head-mounted display as described above.

 The free-form surface prism of the present invention has four surfaces, a first surface, a second surface, a third surface, and a fourth surface, and allows light from an external display that displays an image to pass through the first surface, The light transmitted through the first surface is reflected by the second surface, the light reflected by the second surface is reflected by the third surface, and the light reflected by the third surface is reflected by the fourth surface. By passing the light, the direction of the light guided to the inside is changed, and the image displayed on the display is enlarged.

 The first surface, the second surface, the third surface, and the fourth surface of the free curved surface prism are positioned so that the planar exit pupil of the free curved surface prism is within 1 O mm from the fourth surface. To come to exist.

 This free-form surface prism may be as follows.

 That is, the light from the display that passes through the first surface until it is reflected by the second surface is reflected by the first light flux, reflected by the second surface, and then reflected by the third surface. The second light beam is a light beam that is reflected by the third surface, and the third light beam is a light beam that is reflected by the third surface and is allowed to pass through the fourth surface. When the surfaces are a series of smoothly connected surfaces, the first surface, the second surface, the third surface, and the fourth surface are reflected to form the second light beam. The overlapping portion of the range on the second surface where the third light beam passes and the range on the fourth surface through which the third light beam passes is 30% of the range on the fourth surface through which the third light beam passes. It may be as follows. The overlapping partial force of the range on the second surface where the first light beam that is reflected and becomes the second light beam reaches the range on the second surface through which the third light beam passes passes the third light beam passes If the range is 30% or less of the range on the fourth surface, it is advantageous to bring the exit pupil closer to the fourth surface and to enlarge the exit pupil. If the exit pupil can be enlarged, it will be easier for the user to see the image, and it will be less fatigued when the user views the image.

Metal may be attached to the third surface, and the third surface may reflect light reflected by the second surface by the metal. Normal free-form surface prism Is designed to allow total reflection on the third surface. By allowing metal reflection on the third surface, the third surface is designed to have total reflection. As a result, the degree of freedom in designing the third surface of the free-form surface prism can be increased. Further, a dielectric multilayer film may be formed on the third surface, and the third surface may reflect the light reflected by the second surface by the dielectric multilayer film. In the case of reflection by metal, the reflectivity is inevitably small compared to total reflection near 100%. On the other hand, if a dielectric multilayer film is used, a reflectance close to total reflection can be obtained. Brief Description of Drawings

 FIG. 1 is a perspective view showing an appearance of a head mounted display according to an embodiment of the present invention.

 FIG. 2 is a longitudinal sectional view of the vicinity of the display unit of the head mounted display shown in FIG.

 FIG. 3 is a diagram for explaining the behavior of light from the display in the head mounted display shown in FIG.

 FIG. 4 is a diagram for explaining the behavior of light from the display in the head mount display shown in FIG.

 FIG. 5 is a plan view schematically showing the behavior of light in the waveguide plate of the head mounted display shown in FIG.

 FIG. 6 is a side view showing an example of a free-form surface prism included in Modification 3 of the head mount display shown in the embodiment. BEST MODE FOR CARRYING OUT THE INVENTION

Hereinafter, a preferred embodiment of the present invention will be described in detail with reference to the drawings. The head mounted display 100 in this embodiment has a spectacle-like appearance as shown in FIG. The head mounted display 10 0 includes a vine 1 1 0 similar to that of a normal eyepiece, a waveguide plate 1 2 0 provided at a position corresponding to a lens of a normal eyeglass, and an inside thereof. And a display unit with a built-in optical system. The

 Vine 1 1 0 fixes the head mount display 1 0 0 to the user's head. There are two vines 110 in this embodiment, which are provided on both sides of the waveguide plate 120. By hinge-connecting the vine 1 1 0 and the waveguide plate 1 2 0, the vine 1 1 0 can be folded in a direction parallel to the waveguide plate 1 2 0 like normal glasses. It ’s okay if you ’re not. The force to hold the tip of the vine 1 1 0 to the user's both ears, or the head of the user by sandwiching the user's head with two vines 1 1 0, to the head of the user 1 0 0 is fixed.

 The waveguide plate 120 has a structure like a diffraction grating. In this embodiment, the waveguide plate 120 has a rectangular flat plate shape, and before and after that (in this embodiment, for convenience, the head mounted display 100 is attached to the user's head. The front side of the user's face (the front side of the paper in Fig. 1) is the front of the head-mounted display 10 0 and the opposite side (the back side of the paper in Fig. 1) is the head-mounted display. In some cases, it is expressed as “after” in 100.) The surface is a structure in which a number of longitudinal grooves are cut. In this embodiment, the waveguide plate 120 is made of resin. The waveguide plate 120 is not necessarily rectangular. The waveguide plate 120 does not necessarily have a flat plate shape, and may be curved as long as it is a plate shape.

 The waveguide plate 120 reflects the light guided from the display unit 130 in the inside as described later, while reflecting the light very many times inside (in detail, on the front and back surfaces thereof). It is designed to lead to both ends. As such a waveguide plate 120, for example, a diffraction grating (element) disclosed in JP-T-2000-065 10 0 59 can be used.

The waveguide plate 120 is configured to cover both eyes of the user when the head mounted display 100 is fixed to the user's head, and from the user's eyes. The distance is about 20 to 3 O mm. This distance is set larger than the distance between the eye and the lens of the spectacles in the normal spectacles, so that the waveguide plate 120 does not give the user a feeling of pressure. The above-mentioned vine 1 1 0 is used for normal glasses so that when the head mount display 1 0 0 is fixed to the user's head, the waveguide plate 1 2 0 and the eye can maintain the above-mentioned relationship. Slightly longer than vine Has been long. However, the waveguide plate 120 may be configured such that the distance from the eye is maintained at a distance approximately equal to the distance between the eye and the lens of normal glasses.

 Although not shown in the figure, a nose pad-like thing in ordinary spectacles is attached to the waveguide plate 120 and placed on the nose, thereby supporting the waveguide plate 1 2 0 protruding forward. Such a configuration is also possible.

 The display unit 1 30 is configured by housing components as shown in FIG. 2 in a hollow case 1 3 1 that is open on the side facing the waveguide plate 1 2. The case 1 3 1 of this embodiment is not necessarily so, but is made of resin. Note that the case 1 3 1 does not necessarily need to be open on the entire surface facing the waveguide plate 120. The case 1 3 1 does not necessarily receive light from a free-form surface prism (to be described later) on the side facing the waveguide plate 120. It is sufficient if the range necessary for guiding to the waveguide plate 120 is open.

 In this embodiment, a control board 1 3 2, a display 1 3 3, and a free-form curved prism 1 3 4 are provided inside the case 1 3 1.

 The control board 1 3 2 controls display of an image, which will be described later, performed by the display 1 3 3. The control board 1 3 2 sends data for displaying an image to the display 1 3 3 to display an appropriate image on the display 1 3 3. The control board 1 3 2 receives image data from outside the case 1 3 1 and displays it on the display 1 3 3. In order to receive such data wirelessly, the control board 13 2 of this embodiment has a built-in antenna. However, the control board 1 3 2 may be configured to receive the data to be received by wire.

 The image data received by the control board 1 3 2 is, for example, from a predetermined device capable of transmitting image data such as a hard disk player (not shown), a DVD player, or a tuner for television broadcasting. 1 3 2 is being sent. In addition to the above, β for sending image data to the control board 1 3 2 may be a personal computer, a mobile phone, a game dedicated device for executing a computer game, an MP 3 player, or the like.

The display 1 3 3 displays an image, and in this embodiment is a liquid crystal display. When the display 1 3 3 displays an image, the light for that image is sent to the free-form surface prism 1 3 4. The free curved surface prism 1 3 4 has a substantially triangular cross section.

 The free-form surface prism 1 3 4 has a first surface S 1, a second surface S 2, a third surface S 3, and three surfaces. The first surface S1, the second surface S2, and the third surface S3 are all free-form surfaces. The second surface S 2 in this embodiment serves as both the second surface and the fourth surface in the present invention. The free-form surface prism 1 3 4 described in this embodiment corresponds to a case where, in the free-form surface prism of the present invention, the second surface and the fourth surface are a series of smoothly connected surfaces.

 The first surface S 1 faces the display 1 3 3, and passes the light from the display 1 3 3 for the image displayed on the display 1 3 3 to guide it into the free-form surface prism 1 3 4 . The light from the display 1 33 is refracted when passing through the first surface S 1 and changes so that the image displayed on the display 1 33 is enlarged.

 The second surface S 2 reflects the light that has passed through the first surface S 1 (usually total reflection). The light passing through the first surface S 1 changes its direction greatly by being reflected by the second surface S 2, and changes so that the image displayed on the display 1 33 is enlarged. Of the second surface S2, the portion that reflects the light coming from the first surface S1 is the second surface in the present invention. The second surface S 2 also allows the light reflected by the third surface S 3 to pass through. This will be described later. Of the second surface S 2, the portion that transmits light coming from the third surface S 3 force is the fourth surface in the present invention.

The third surface S 3 reflects the light reflected by the second surface S 2. The light reflected by the second surface S 2 changes its direction greatly by being reflected by the third surface S 3 and changes so that the image displayed on the display 1 3 3 is enlarged. . The reflection performed on the third surface S 3 may be total reflection or metal reflection. When the reflection performed on the third surface S3 is total reflection, the incident angle when the light reflected on the second surface S2 reaches the third surface S3 is set so that the incident angle is less than or equal to the total reflection angle. 3 surface S 3 curved surface is designed. If the reflection performed on the third surface S3 is a metal reflection, the third surface S3 does not have to be configured so that the reflection occurring there is total reflection, but the third surface S3 On the outside, metal is deposited, for example by vapor deposition. Instead of attaching metal to the outside of the third surface S3, a dielectric multilayer A film can be formed. The reflection in this case is made by a dielectric multilayer film. As described above, the light reflected by the third surface S 3 is directed again to the second surface S 2 and passes through the second surface S 2. The light passing through the second surface S 2 is refracted when passing through the second surface S 2 and changes so that the image displayed on the display 1 33 is enlarged.

 The free curved prism 13 4 configured as described above has a planar exit pupil positioned on the waveguide plate 120. In this embodiment, the exit pupil is positioned at the center of the waveguide plate 120 in the left-right direction. The second surface S 2 of the free-form surface prism 1 3 4 (more specifically, the portion of the second surface S 2 through which light from the third surface S 3 is transmitted, ie, the fourth surface in the present invention) and the waveguide The distance of the plate 120 (1 in FIG. 2) is 10 mm or less, and is approximately 3 mm in this embodiment. That is, in this embodiment, the distance from the second surface S2 to the exit pupil is 10 mm or less, more specifically about 3 mm. Note that this distance can be as close to 0 as possible.

 In this embodiment, the display 1 3 3 is arranged above the free-form surface prism 1 3 4. However, the positional relationship between the free-form surface prism 1 3 4 and the display 1 3 3 is inverted to obtain a free-form surface prism. It is also possible to place a display 1 3 3 below 1 3 4. In that case, the control board 1 3 2 may also be disposed below the free-form surface prism 1 3 4.

 Next, how to use the head mounted display 100 will be described. In order to use the head mounted display 1 0 0, first, the head mounted display 1 0 0 is fixed to the user's head. As described above, the head mounted display 1 0 0 can be fixed to the user's head by locking the heel 1 1 0 of the head mounted display 1 0 0 to the user's ear. This is done by pinching the user's head with the vine 1 1 0 of the head mount display 1 100.

 Then, the waveguide plate 120 is positioned at a distance of about 20 mm from the user's eyes.

In this state, the user operates predetermined devices such as an external hard disk player, a DVD player, and a tuner for television broadcasting, and the data about the image to be displayed on the head mount display 100 is displayed. , Those heads to β To display 1 0 0.

 As described above, the data about the image is obtained from the control board 1 in the display unit 1 3 0.

3 2 force Received by an antenna (not shown) built in it. The control board 1 3 2 sends the data to the display 1 3 3. Display 1 3 3 displays an image based on the data.

 Light for the image displayed on display 1 3 3 exits display 1 3 3 and enters the interior of free-form curved prism 1 3 4.

 Figure 3 shows the behavior of light in the free-form curved prism 1 3 4.

 The light emitted from the display 1 3 3 passes through the first surface S 1.

 The light that has passed through the first surface S 1 is reflected by the second surface S 2.

 The light reflected by the second surface S 2 is reflected by the third surface S 3.

 The light reflected by the third surface S 3 passes through the second surface S 2 and travels toward the exit pupil P. The exit pupil P has a planar shape, and as described above, is located inside the waveguide plate 120, which is omitted in FIG.

Here, the light from the first surface S 1 until it is reflected by the second surface S 2 is reflected by the first light beam L l and the second surface S 2, and then by the third surface S 3. The light until it is reflected by the second light beam L 2 and the third surface S 3 until it passes through the second surface S 2 is called the third light beam L 3. L 1 to the third light beam L 3 are not necessarily so, but in this embodiment, the relationship is as follows. That is, on the second surface S 2, the range in which the first light beam L 1 that is reflected there to become the second light beam L 2 arrives (B 1: this is the second surface in the present invention) and the third light beam. The overlapping portion with the range through which L 3 passes (B2: this is the fourth surface referred to in the present invention) is 30% or less of the range through which the third light flux L3 passes. By designing the first surface S1, the second surface S2, and the third surface S3 so that these conditions are satisfied, the distance between the exit pupil P and the second surface S2 can be made closer, It becomes easy to enlarge the exit pupil P. It should be noted that, on the second surface S 2, the range (B 1) in which the first light beam L 1, which is reflected there and becomes the second light beam L 2, and the range (B 2) in which the third light beam L 3 passes are shown Shown in 4. 4 shows only the inside of the free-form surface prism in FIG. As shown in Fig. 5, the light traveling toward the exit pupil P passes through the inside of the waveguide plate 120. While being reflected on the rear surface, the wave guide plate 120 is moved in the left-right direction and is emitted to each of the user's eyes. The light allows the user to see an image magnified to an appropriate size with both eyes.

<Modification 1>

 Modification 1 of the above-described head mounted display 100 will be described.

 The above-described head mounted display 1 0 0 includes a vine 1 1 0, a waveguide plate 1 2 0, and a display unit 1 3 0, and has a glasses-like shape as a whole. 0 can be omitted. In other words, the head mounted display 100 of this modification 1 includes the waveguide plate 120 and the display unit 130.

 Such a head-mounted display 100 is fixed to the upper edge portion of the lens of the spectacles worn by the user (or the upper frame supporting the lens). In other words, the head-mounted display 100 according to the first modification is attached to the glasses in a manner similar to the widely known clip sunglasses.

 Accordingly, the head mounted display 100 of the first modification includes a clip for fixing the head mounted display 100 to the glasses instead of the vine 110.

Modification 2>

In the above-described embodiment, the free-form surface prism 1 3 4 can use either total reflection, reflection by metal, or dielectric multilayer film on the third surface S 3. We explained only that the reflection in 2 is usually total reflection. This is because the second surface S 2 not only reflects the light that has passed through the first surface S 1 but also transmits the light that has reflected the third surface S 3. This is because, unlike S3, there is no power to deposit metal on the entire surface or to form a dielectric multilayer film. However, on the second surface S 2, the range (B 1) in which the first light beam L 1 that is reflected there and becomes the second light beam L 2 arrives, and the range in which the third light beam L 3 passes ( B 2) does not overlap at all, that is, if the second surface and the fourth surface in the present application do not overlap at all, the second surface S 2 includes the range (B 1) and includes the range (B 1). By attaching a metal to a range that does not include B 2) or forming a dielectric multilayer film, the reflection that occurs in the range (B 1) is reflected by a metal reflection or a dielectric multilayer film. It is possible to replace it with a reflection.

<Modification 3>

 The second surface S 2 of the free-form surface prism 134 in the embodiment described above was a smoothly continuous curved surface. However, 'the second surface S 2 may be divided into a plurality of continuous surfaces, for example, stepped or continuous so as to have corners instead of being smooth. As described above, the second surface S 2 has two functions: the function of reflecting the light that has passed through the first surface S 1 and the function of transmitting the light that has reflected the third surface S 3. As described above, the two functions are as follows. On the second surface S 2, the range (B 1) in which the first light beam L1 reflected by the second surface S 2 reaches the second light beam L 2 and the third light beam L It is possible to completely separate them by designing them so that they do not overlap at all with the range (B 2) through which 3 passes. In this case, the range (B 1) and the range (B 2) do not have to exist on a common surface that is smoothly connected. In other words, even if the surface including the range (B 1) and the surface including the range (B2) are the same second surface S 2, they do not continue to the sliding force. It may be on a curved surface. In that case, a metal may be attached to the outside of the curved surface including the range (B 1), or a dielectric multilayer film may be formed. Figure 6 shows a side view of an example of such a free-form surface prism. Of the second surface S 2, on the surface connecting those between the range (B 1) and the range (B 2), the reflection of the light that has passed through the first surface S 1 is also reflected on the third surface S 3. There is no transmission of reflected light.

Claims

The scope of the claims 1. It has four surfaces, the first surface, the second surface, the third surface, and the fourth surface, and displays the image. Light from an external display passes through the first surface and passes through the first surface. Reflecting the reflected light on the second surface, reflecting the light reflected on the second surface on the third surface, and allowing the light reflected on the third surface to pass through the fourth surface, A free-form surface prism that changes the direction of the light guided to the inside and enlarges the image displayed on the display;  In the first surface, the second surface, the third surface, and the fourth surface, the planar exit pupil of the free-form surface prism is positioned within 10 mm from the fourth surface. ,  Free curved prism.  2. Light from the display that passes through the first surface until it is reflected by the second surface is reflected by the first light flux, reflected by the second surface and then reflected by the third surface. The second light beam is the second light beam, and the third light beam is the light beam reflected from the third surface and allowed to pass through the fourth surface, and the second surface and the fourth surface. Is a series of smoothly connected surfaces,  The first surface, the second surface, the third surface, and the fourth surface are reflected on the second surface by the first light beam that is reflected to become the second light beam; and The overlapping portion of the range on the fourth surface through which the third light beam passes is 30% or less of the range on the fourth surface through which the third light beam passes.  The free-form surface prism according to claim 1.  3. A metal is attached to the third surface, and the third surface reflects the light reflected by the second surface by the metal.  The free-form curved prism according to claim 1 or 2.  4. A dielectric multilayer film is formed on the third surface, and the third surface reflects light reflected by the second surface by the dielectric multilayer film. The free-form surface prism according to the first or second range. 5. It has a display for displaying images, a free-form surface prism, and a waveguide plate. A free-form prism that is fixed to a user's head and has four surfaces: a first surface, a second surface, a third surface, and a fourth surface. Holding the light from the display through the first surface, reflecting the light transmitted through the first surface on the second surface, and reflecting the light reflected on the second surface on the third surface. Reflecting and allowing the light reflected by the third surface to pass through the fourth surface changes the direction of the light guided to the inside and enlarges the image displayed on the display. And  The first surface, the second surface, the third surface, and the fourth surface of the free-form surface prism are positioned so that the planar exit pupil of the free-form surface prism is within 1 O mm from the fourth surface. To be present in  A part of the waveguide plate is positioned on the exit pupil, and the other part is positioned in front of at least one eye of the user when the head mounted display is used. The light from the free-form surface prism guided from the exit pupil to the inside is guided while being reflected, and is emitted to the user's eyes.  Head mounted display. 6. A part of the waveguide plate is located above the exit pupil, and another part is located in front of both eyes of the user when the head mount display is used. The free curved prism power guided from the exit pupil to the inside is guided while reflecting, and is emitted to both eyes of the user.  The head mounted display according to claim 5.  7. The display is positioned above or below the free-form prism.  The head mount display according to claim 5 or 6.