Patent Description:
In recent years, head mounted displays (HMDs) are becoming widespread as a virtual image display device. The HMDs are broadly classified into transmissive and non-transmissive types. The transmissive type is used in combination with an information terminal or in combination with augmented reality (AR), and what is called "smart glass" is attracting attention. The non-transmissive type is used widely in games and virtual reality (VR), and is widely loved for the high immersion feeling.

As one genre of the virtual image display device, a virtual image display device that displays, on an image display element, an image to be displayed as a virtual image, propagates an image light from the image display element to a light guide member by a propagation optical system, and guides the propagated image light with the light guide member to emit the image light toward an observer as reflected light and thereby allow an enlarged virtual image to be observed has been known. The above smart glass belongs to such genre and is referred to as a "virtual image display device of the light guide type".

In terms of the virtual image size, the transmissive type desirably has a small size and a good portability because the transmissive type is used in combination with an information terminal or in combination with AR. On the other hand, the non-transmissive type is likely to have a wide viewing angle yielding the immersion feeling because of the use of the non-transmissive type in a game or in VR. HMDs specialized to have a reduced body size or thickness tend to have a narrow viewing angle, while HMDs with a display area of a wide viewing angle tend to have an increased body size or thickness.

Even the transmissive type is required not only to have a reduced thickness but a wide viewing angle. In a known method complying with such requirement, multiple mirrors provided with coatings of specified reflectivities are arranged in a light guide member, and each light beam is allocated to reflection or transmission depending on the angle of incidence of the relevant light beam to effectively extract an image (see Patent Literature <NUM>, for instance).

In another known method, microstructures and gap zones are provided on one side face of a light guide member, and light beams are reflected and propagated by means of such parts to effectively extract an image (see Patent Literature <NUM>, for instance).

In yet another known method, a total reflection part extending in a facing manner and a light guide plate that includes a plurality of first element faces extending in an inclined manner and a plurality of second element faces so extending as to form an obtuse angle with the first element faces, with the first element faces and the second element faces being alternately arranged, are combined together to extract an image (see Patent Literature <NUM>, for instance).

In each of the above methods, position information of an image display element is converted by a collimator optical system into angle information to introduce light into a light guide member. If the collimator optical system is an optical system that is nearly telecentric with respect to the image display element, an optical pupil position of the collimator optical system will be in the vicinity of a light beam incident part of the light guide member. Since the light as introduced into the light guide member is propagated while diverging with respect to the optical axis in the light guide member in a direction corresponding to a vertical visual field of the light guide member, light reflected on a plurality of mirrors or microstructures provided in the light guide member is emitted in a direction going away from an observer's eye, which makes the vertical visual field hardly securable.

For this reason, the collimator optical system is made non-telecentric and the optical pupil position is thus extended to cause light to converge with respect to the optical axis in the light guide member in the direction corresponding to the vertical visual field of the light guide member and emit the light reflected on a plurality of mirrors or microstructures provided in the light guide member in a direction toward the observer's eye. As indicated with an aperture A1 in <FIG>, however, light needs to pass through a narrow region in the light guide member in a direction corresponding to a horizontal visual field of the light guide member, which leads to a disadvantage of light loss due to "vignetting".

As a method for overcoming such disadvantage, it is described in Patent Literature <NUM> that light illuminating an image display element is controlled to thereby control the direction of light emitted from the image display element and enhance the light use efficiency. It, however, is difficult to control the direction of light in terms of all pixels in the whole horizontal and vertical directions. <CIT> discloses an observation optical system including an image display element, a relay optical system having a plurality of lenses and a first reflection-type volume hologram element (HOE), and an eyepiece optical system having a second reflection-type HOE. <CIT> discloses waveguide-based displays with an exit pupil expander. <CIT> discloses an image display device, image generating device, and transparent spatial light modulating device.

An object of the present invention is to provide a virtual image display device of the light guide type that is capable of further enhancing the light use efficiency.

According to one or more embodiments of the present invention, an optical member having a curved surface shape that is non-rotationally symmetric is inserted in the propagation optical system subsequent to the image display element so as to attain a virtual image display device of the light guide type that is capable of further enhancing the light use efficiency.

As described above, the virtual image display device according to an embodiment of the present invention includes an image display element, a propagation optical system, and a light guide member.

The "image display element" displays an image that is displayed as a virtual image to be observed.

The "propagation optical system" propagates light from the image display element.

The "light guide member" guides the light propagated by the propagation optical system. The light propagated by the propagation optical system includes image information of the image displayed on the image display element.

The light guide member includes a "light beam incident part" that introduces the "light including the image information" into the light guide member, an "image extractor" that extracts the "light including the image information," namely, "image light" from an inside of the light guide member, and an "image emitter" that emits the light including the image information to an outside of the light guide member.

The propagation optical system includes one or more "optical members each having a curved surface shape that is non-rotationally symmetric (or rotationally asymmetric) with respect to an optical axis". Hereinafter, an "optical member having a curved surface shape that is non-rotationally symmetric with respect to an optical axis" is also referred to as a "curved surface optical member".

As the image display element, a widely known image display element can be used.

For example, an organic EL display (OLED) having a light-emitting function or a liquid crystal display device or a digital micro color device (DMD) that is non-light-emitting and is illuminated by illumination light can be used, but the image display element is not limited to these, and a microelectromechanical system (MEMS) driven in two dimensions can also be applied as long as an image can be displayed.

The "propagation optical system" that propagates light from the image display element to the light guide member can have various configurations as exemplified below.

The propagation optical system causes nearly parallel light to enter the light beam incident part of the light guide member, for instance. If such a propagation optical system is used, when a plate-shaped member without a power is used as the light guide member, the light emitted from the image emitter forms an image on one point on the "retina of an observer's eye", and thus the observer can see a good virtual image.

The propagation optical system includes a relay optical system that forms an intermediate image of an image displayed on an image display element on the image display element side and a collimator optical system on the light guide member side of the intermediate image, and the one or more "curved surface optical members" may be included in at least one of the relay optical system and the collimator optical system. Even in such configuration, the propagation optical system can cause nearly parallel light to enter the light beam incident part of the light guide member.

In order to secure a high performance and, at the same time, reduce the lens diameter while maintaining a certain magnitude of the whole optical length, it is effective that the propagation optical system forms the intermediate image, and the diameter of the relay optical system can be made relatively small. In addition, a configuration including a relay optical system can respond to the case where the spacing between the image display element and the light guide member needs to be secured for reasons of mechanical or electrical system configuration or the like.

The relay optical system, the curved surface optical members with respect to the optical axis, and the collimator optical system are included in this order from the image display element side and the intermediate image is formed between the relay optical system and the collimator optical system, so that the surfaces of the curved surface optical members are positioned close to the intermediate image. Since the curved surface optical members are located near the intermediate image, it is possible to reduce the spherical aberration or coma aberration caused by the rotational asymmetry.

The propagation optical system having such a configuration is used to convert the light from the image display element into the intermediate image by the relay optical system, and the image display element can be thereby moved away from the vicinity of the front of the observer's head toward the ear, and the weight of the front portion of a smart glass can be thereby reduced, and therefore the wearing comfort of the smart glass can be improved. In addition, the thickness of the end piece of the smart glass can be reduced, and the obstruction of the observer's visual field can be reduced.

In an unclaimed example, the propagation optical system may also include a collimator optical system and one or more optical members each having a curved surface shape that is non-rotationally symmetric with respect to the optical axis on the image display element side of the collimator optical system. The light collimated by the collimator optical system enters the light beam incident part of the light guide member.

In an unclaimed example, the collimator optical system may be "non-telecentric on the image display element side".

When the above-mentioned "relay optical system and collimator optical system" are used, the collimator optical system may be "non-telecentric on the intermediate image side".

In this way, the image display element side of the collimator optical system or the intermediate image side of the collimator optical system can be made non-telecentric. Thus, the distance to the "pupil position of the optical system" becomes long, and light that has propagated inside the light guide member efficiently enters an eye when hitting the image extractor, and it is possible to display a wide-angle virtual image.

In addition, various cases are also possible for the "curved surface optical members" used in the propagation optical system with regard to the disposition position and number in the propagation optical system, as exemplified below.

That is, the curved surface optical members can be disposed "proximately to the intermediate image". The curved surface optical members are disposed adjacent to the image display element, thereby playing a role like a field lens, and the influence on the deterioration in aberration due to the non-rotationally symmetric curved surface shape can be reduced.

When the propagation optical system is to "form an intermediate image", the curved surface optical members can be disposed "proximately to the intermediate image". Even in this manner, the curved surface optical members can play a role like a field lens and reduce the influence on the deterioration in aberration due to the non-rotationally symmetric curved surface shape.

In addition, when the propagation optical system is to "form an intermediate image", a plurality of curved surface optical members can be included in each of the front and the back of the intermediate image. By arranging curved surface optical members in each of the front and the back of the intermediate image, an aberration generated in " respective curved surface shapes which are each rotationally asymmetric" can be reduced.

The "curved surface that is non-rotationally symmetric with respect to an optical axis" of the curved surface optical members can be, for example, a "toroidal surface" or a "cylindrical surface".

The virtual image display device uses the abovementioned curved surface optical members. Since these curved surface optical members each have the "curved surface that is non-rotationally symmetric with respect to an optical axis", the "aspect ratio of an virtual image to be observed" of the image displayed on the image display element is "different from the aspect ratio of the image displayed on the image display element" due to the rotational asymmetry of the abovementioned curved surface shape.

This "difference in the aspect ratios" is determined by the propagation optical system, and thus can be eliminated by inputting a "correction image correcting a difference in an aspect ratio" to the image display element.

According to the claimed invention, the curved surface optical members each have a "positive power in a direction corresponding to the horizontal direction of the virtual image (lateral direction as viewed from the observer)". In this way, when using a plate-shaped light guide member, "the power in the direction corresponding to the horizontal direction of the virtual image is made to be positive", and thus "more light" can be introduced into a thin portion of an incident part. Therefore, light use efficiency can be enhanced, and it is possible to achieve a virtual image display device capable of displaying a bright virtual image.

Moreover, in the virtual image display device, it is preferable that, in the "optical members (curved surface optical members) each having a curved surface shape that is non-rotationally symmetric with respect to the optical axis" of the propagation optical system, a size in a direction corresponding to a perpendicular direction (a direction orthogonal to the aforementioned horizontal direction) of the virtual image is larger than a size in a direction corresponding to the aforementioned horizontal direction. The "size in the direction corresponding to the perpendicular direction of the virtual image" of the curved surface optical members is made to be larger than the "size in the direction corresponding to the horizontal direction of the virtual image". Therefore, light use efficiency can be enhanced, and it is possible to achieve a virtual image display device capable of displaying a bright virtual image.

Furthermore, in the virtual image display device, the virtual image optical system may "include an image display element to display an image to be displayed as a virtual image, a light source to illuminate the image displayed on the image display element, a light guide member, and any of the aforementioned various propagation optical systems that causes image information of the image displayed on the image display element and illuminated by the light source to enter the light guide member".

In the following, more specific description is made on embodiments of the virtual image display device according to an embodiment of the present invention with reference to the drawings. In each embodiment, the virtual image display device according to an embodiment of the present invention is assumed to be "a smart glass using a plate-shaped light guide member". The plate-shaped light guide member is assumed to be any known light guide member "of a plate-shaped type". The light guide member of the plate-shaped type is hereinafter referred to as a "light guide plate".

<FIG> and <FIG> illustrate an example in which a propagation optical system <NUM> of a virtual image display device includes a relay optical system <NUM> and a collimator optical system <NUM>, which are essentially the same as those described above. In this example, the propagation optical system <NUM> does not include the "curved surface optical members". Therefore, the propagation optical system <NUM> is different from any of the propagation optical systems in the embodiments of the virtual image display device according to an embodiment of the present invention. The above-mentioned curved surface optical members are added to such a propagation optical system, and one of the propagation optical systems in the embodiments of the present invention is thereby configured.

<FIG> and <FIG> are conceptual diagrams illustrating a conventional virtual image display device. <FIG> is a light path diagram of an image light from an image display element <NUM> that corresponds to virtual image display in a horizontal direction, and <FIG> is a light path diagram of an image light from the image display element <NUM> that corresponds to virtual image display in a vertical direction. A light beam incident part of a light guide member <NUM> is "rectangular", and this rectangular light beam incident part is hereinafter referred to as an "aperture". In addition, a pupil of the observer with respect to the "light beam observed as a virtual image", which is emitted from an image emitter of the light guide member <NUM> and enters the pupil of the observer, is defined as an "aperture B".

In <FIG>, an aperture A1 on a light beam incident side of the light guide member <NUM> constitutes the light guide member <NUM> like an eyeglass lens and represents an aperture in the front-back direction of the eyeglass lens when viewed from the front. The aperture A1 generally has a width of about <NUM>. An aperture A2 on the light beam incident side of the light guide member <NUM> illustrated in <FIG> represents an aperture of the light guide member <NUM> that corresponds to the vertical direction of the eyeglass lens. The aperture A2 generally has a width of <NUM> or more.

Thus, the aperture A1 in <FIG> and the aperture A2 in <FIG> are significantly different from each other. If the optical systems are made non-telecentric with respect to the intermediate image and the aperture B on an image emitting side of the light guide member <NUM> is far positioned before light is caused to enter the light guide member <NUM>, the light does not converge in the vicinity of the light beam incident part of the light guide member <NUM>, so that the light suffers from considerable vignetting at the narrow apertures A1 and A2 on the light beam incident side of the light guide member <NUM>, which leads to a disadvantage of reduction in light use efficiency.

While, moreover, the light from the image display element <NUM>, which is emitted from respective pixels, namely, the image light is generally emitted in an isotropic manner, the relay optical system <NUM> and the collimator optical system <NUM> illustrated in <FIG> are subject to restrictions on size and are not capable of introducing the whole light from the image display element <NUM>. For this reason, adequate light cannot be introduced as indicated with halftone in the left part of <FIG>, leading to the reduction in light use efficiency. On the other hand, in the case of the aperture A2 illustrated in <FIG>, which has a size about ten times as large as the size illustrated in <FIG>, more light can be introduced as compared with the case illustrated in <FIG>.

<FIG> and <FIG> are conceptual diagrams illustrating one embodiment of the present invention, in which embodiment, in contrast to the example illustrated in <FIG> and <FIG>, a lens is arranged in the vicinity of the intermediate image and the lens includes an optical member having a curved surface shape that is rotationally asymmetric. The "optical member having a curved surface shape that is rotationally asymmetric" refers to an optical member that is not axially symmetric with respect to the optical axis, including a cylindrical lens, a toroidal lens, and a free-form surface lens. In the vicinity of an intermediate image <NUM> in the relay optical system <NUM>, an optical member <NUM> having a curved surface shape that is non-rotationally symmetric (hereinafter referred to as "curved surface optical member <NUM>") is inserted. By means of the curved surface optical member <NUM> thus included, the light emitted from an endmost portion of the image display element <NUM> as illustrated in <FIG> and <FIG> is changed in direction toward the intermediate image <NUM> as compared with the example illustrated in <FIG>, so that the light readily passes through the aperture A1. In addition, the amount of light from the image display element <NUM>, which is required for the pass through of the light to the periphery of the collimator optical system <NUM>, is increased as compared with the example illustrated in <FIG>, which leads to the enhancement of light use efficiency.

In <FIG>, the light emitted from the upper end part of the image display element <NUM> enters the relay optical system (hereinafter referred to as "relay lens") <NUM> of the propagation optical system <NUM> while diverging, and forms an intermediate image <NUM> by the action of the relay lens <NUM>, and then is converted into a parallel light beam by the collimator optical system (hereinafter referred to as "collimator lens") <NUM> and enters the aperture A1.

Normally, light from each pixel of the image display element <NUM> is isotropically radiated, as illustrated with dashed lines extending fanwise from the upper end part of the image display element <NUM> in <FIG>. In the example illustrated in <FIG>, however, due to the restrictions on the size of the relay lens <NUM> and the collimator lens <NUM>, it is not possible to "introduce the whole" of the light isotropically radiated from the image display element <NUM> with such lenses.

Of the luminous flux indicated by the dashed lines, that is isotropically radiated from the upper end part of the image display element <NUM> illustrated in <FIG>, only a portion indicated with halftone on the left side of the relay lens <NUM> is introduced into the propagation optical system <NUM> and passes through the apertures A1 and B, thereby causing a reduction in light use efficiency.

<FIG> corresponds to "the vertical direction of an eyeglass lens when viewed from the front" when the light guide plate is used like the eyeglass lens.

As can be seen by comparing <FIG> and <FIG>, when the range of light emitted from the image display element <NUM> is limited by the apertures A1, A2, and B, the direction of the light propagating from the image display element <NUM> to the relay optical system <NUM> and the collimator optical system <NUM> is different between the back of the image display element <NUM> and the back of the intermediate image <NUM>, as indicated with halftone. Therefore, the light in each different area of the light within the dashed lines, which is normally isotropically radiated from the upper end part of the image display element <NUM>, is used, and it is required to emit light from the image display element <NUM> at a large angle so as to include the light in each area, which leads to a disadvantage of the reduction in light use efficiency.

<FIG> and <FIG> are diagrams illustrating an operation of an embodiment of the virtual image display device according to the present invention. In order to avoid complications, components that are not likely to be confusing are denoted by the same reference signs.

In <FIG> and <FIG>, the propagation optical system <NUM> includes the curved surface optical member <NUM> in addition to the relay lens <NUM> and the collimator lens <NUM>.

As illustrated in the figures, the curved surface optical member <NUM> having a "curved surface shape that is non-rotationally symmetric with respect to an optical axis direction" is inserted near the intermediate image <NUM> of the relay lens <NUM>, and the direction of the light exiting from the uppermost end part of the image display element <NUM> toward the intermediate image <NUM> can be thereby changed independently in each cross section of <FIG> and <FIG>. Consequently, the direction of the light exiting from the upper end part of the image display element <NUM> can be made closer to the same direction in each cross section in <FIG> and <FIG>, and it is possible to decrease the reduction in light use efficiency, which has been caused by using the light in each different area of the light within the dashed lines, that is isotropically radiated from the upper end part of the image display element <NUM> in <FIG> and <FIG>.

Hereinafter, description is made on illustrative examples and embodiments of the inventive virtual image display device.

As described above, each embodiment of the virtual image display device according the present invention basically includes the image display element, propagation optical system, and light guide member. The light guide member includes the light beam incident part that introduces light including image information from the propagation optical system into the light guide member, the image extractor that extracts the light including the image information from the inside of the light guide member, and the image emitter that emits the light including the image information to the outside of the light guide member. The propagation optical system includes one or more optical members each having a curved surface shape that is non-rotationally symmetric with respect to an optical axis.

The illustrative example illustrated in <FIG> and <FIG> is an example of a mode in which the intermediate image is not formed.

In <FIG>, the narrow side (aperture A1) of the aperture of a light beam incident part <NUM> in a light guide plate <NUM> that is a plate-shaped light guide member is in the vertical direction in the drawing, and in <FIG>, the wide side (aperture A2) of the aperture of the light beam incident part <NUM> is in the vertical direction in the drawing.

As illustrated in <FIG> and <FIG>, a virtual image display device <NUM> converts the light from the image display element <NUM> into nearly parallel light by the propagation optical system <NUM>, and causes the light to enter the light guide plate <NUM> and then the pupil (aperture B) of an observer.

The propagation optical system <NUM> includes the curved surface optical member <NUM> having a curved surface shape that is non-rotationally symmetric with respect to an optical axis direction. The curved surface optical member <NUM> is disposed "proximately to the image display element <NUM>", and plays a role like a field lens and reduces the influence on the deterioration in aberration due to the curved surface shape that is rotationally asymmetric.

The light guide plate <NUM> that is a plate-shaped light guide member includes the light beam incident part <NUM> for acquiring image information from the propagation optical system <NUM>, an image extractor <NUM> including "a plurality of surfaces having an angle of Θ (theta)", and an image emitter <NUM>.

The light propagated by the propagation optical system <NUM> enters from the light beam incident part <NUM> and is guided inside the light guide plate <NUM>.

The light including image information is converted by the propagation optical system <NUM> including the "collimator optical system" in such a manner that the position information of the image display element <NUM> is converted into angle information, and the angle information enters the light guide plate <NUM>.

<FIG> and <FIG> illustrate the optical path of information at the center of the image display element <NUM>. In <FIG> and <FIG>, the light including image information enters from the light beam incident part <NUM> of the light guide plate <NUM> through the propagation optical system <NUM>, is guided inside the light guide plate <NUM>, is reflected by the image extractor <NUM> having an angle of a wedge-shaped portion of Θ (theta), and is emitted from the image emitter <NUM> as light having image information. The virtual image can be confirmed by looking through the image emitter <NUM>.

Here, the image extractor <NUM> will be described.

In <FIG>, a plurality of image extractors <NUM> are disposed on the side surface of the light guide plate <NUM>, and in <FIG>, a plurality of image extractors <NUM> are disposed inside the light guide plate <NUM>. In the case of <FIG>, the image extractors <NUM> include a slope portion <NUM>(a) and a flat portion <NUM>(b), and light hitting the slope portion <NUM>(a) is emitted from the image emitter <NUM>, and light not hitting the slope portion <NUM>(a) propagates inside the light guide plate <NUM> through the flat portion <NUM>(b) until hitting the next slope portion <NUM>(a), and is emitted from the image emitter <NUM> after hitting the slope portion <NUM>(a).

In order to enhance light use efficiency, it is preferable that the slope portion <NUM>(a) is provided with a reflective coating of aluminum or the like. In this way, light can be applied to the plurality of slope sections <NUM>(a), thereby extending an eyebox.

In the example of <FIG>, the image extractor <NUM> is provided with a coating having reflection and transmission properties. The light propagating inside the light guide plate <NUM> branches off for reflection and transmission at the image extractor <NUM>, the reflected light is emitted from the image emitter <NUM>, the transmitted light branches off for reflection and transmission at the next image extractor <NUM>, and the reflected light is emitted from the image emitter <NUM>. In this manner, the eyebox can be enlarged.

<FIG> and <FIG> illustrate an embodiment of the virtual image display device <NUM>. In this embodiment, the relay lens <NUM> is disposed in the propagation optical system <NUM>, and the light from the image display element <NUM> is once caused to form the intermediate image <NUM>. The curved surface optical member <NUM> having a curved surface shape that is non-rotationally symmetric with respect to the optical axis is disposed close to the front of the intermediate image <NUM>.

The light that has formed the intermediate image <NUM> enters the light beam incident part <NUM> of the light guide plate <NUM> through the collimator lens <NUM>, and is guided inside the light guide plate <NUM> as is the case with <FIG> and <FIG>, and is emitted from the image emitter <NUM> toward the pupil of an observer.

In the following, a specific example of the embodiment illustrated in <FIG> and <FIG> is described.

<FIG> illustrates data (a surface number, a curvature radius, a surface spacing, a material, a refractive index) reaching from the image display element <NUM> to the pupil and retina of the observer through the propagation optical system <NUM> and the light guide plate <NUM>.

The propagation optical system <NUM> includes the relay optical system <NUM> and the collimator optical system <NUM>, and the curved surface optical member <NUM> is provided in the relay optical system <NUM>.

The relay lens <NUM> includes three lenses and a curved surface optical member arranged in order from the image display element <NUM> side. The curved surface optical member <NUM> includes a toroidal surface (surface number <NUM>) on the image side. Two lenses on the image display element <NUM> side of the collimator lens <NUM> constitute a cemented lens.

The data of the light guide member (light guide plate) <NUM> is as follows.

The "eyebox" is a width of a visual field that can be confirmed as a virtual image, and the "eyerelief" is a distance from the image emitter <NUM> to an eyeball (pupil: aperture B), where the virtual image can be confirmed.

The content described with reference to <FIG> is also valid if the drawings are reversed right and left. In addition, it is possible to configure in such a manner that "one light guide member is confirmed with both eyes". It is also possible that one light guide member is divided into two and confirmed with each eye, and the light guide member can be made smaller and a monocular system is also possible.

When trying to achieve a wide-angle smart glass, the virtual image becomes a large screen, and the brightness of the virtual image tends to be dark. Light contributing to the display of the virtual image in the horizontal direction must enter in a direction toward a thin part of a light guide member, which leads to a disadvantage of the reduction in light use efficiency caused by the "vignetting" of light at the light beam incident part of the light guide member. In each embodiment of the virtual image display device according to the present invention, however, the optical member having a curved surface shape that is non-rotationally symmetric with respect to an optical axis direction is disposed in the optical system, and thus the direction of light can be controlled for directions toward thick and thin parts of the light guide member with respect to the light isotropically emitted from the image display element. Therefore, it is possible to control the direction of light that enters the thin part of the light guide member without excessively increasing the divergence angle of the light from the image display element, and thus "enhance light use efficiency".

In order to further enhance the light use efficiency and, at the same time, further reduce the diameter of the propagation optical system including the curved surface optical member <NUM>, it is desirable that the following conditional expression is satisfied.

In the expression, TLA represents the distance from a surface of a curved surface shape that is non-rotationally symmetric with respect to the optical axis to a surface of the collimator lens <NUM> that is closest to the light guide member <NUM>. TL represents the distance from a surface on the image display element <NUM> side of the relay lens <NUM> to a surface of the collimator lens <NUM> that is closest to the light guide member <NUM>. The distances are of values determined on the optical axis.

If the value of TLA / TL is <NUM> or more, the surface of a curved surface shape that is non-rotationally symmetric is too far from the light guide member <NUM>, and the diameters of the curved surface optical member <NUM> having a curved surface shape that is non-rotationally symmetric and the collimator lens <NUM> are too large. If the value of TLA / TL is <NUM> or less, the surface of a curved surface shape that is non-rotationally symmetric is too close to the light guide member <NUM> and, accordingly, achieves a less effect, so that the incident range of the light guide member <NUM> is made too wide.

In the expression, TLC represents the thickness of the collimator lens <NUM> and TLR represents the thickness of the relay lens <NUM>. The thicknesses are each of a value determined on the optical axis.

If the value of TLC / TLR is <NUM> or more, the collimator lens <NUM> is thick, and the diameters of the curved surface optical member <NUM> having a curved surface shape that is non-rotationally symmetric and the collimator lens <NUM> are too large. If the value of TLC / TLR is <NUM> or less, the collimator lens <NUM> is too thin, so that various aberrations are hard to correct in the collimator lens <NUM>.

In order to improve the performance of the propagation optical system, it is desirable that the following conditional expression is satisfied.

In the expression, Y represents the size in a diagonal direction of the image display element <NUM>. Pos1 represents the position of a surface of a curved surface shape that is non-rotationally symmetric when the position of the intermediate image <NUM> is taken as a reference. Pos1 is of a negative value if the surface of a curved surface shape that is non-rotationally symmetric is located in a position closer to the image display element <NUM> than the position of the intermediate image <NUM>. The positions are of values determined on the optical axis.

If the value of Pos1 / Y is <NUM> or more or -<NUM> or less, the distance between the surface of a curved surface shape that is non-rotationally symmetric and the intermediate image <NUM> is increased and it is difficult to prevent the generation of a non-rotationally symmetric spherical aberration or coma aberration.

In order to further reduce the size of the propagation optical system, it is desirable that the following conditional expression is satisfied.

In the expression, β_relay represents the lateral magnification of the relay lens <NUM>.

If a display part of the image display element <NUM> is made larger, electric parts including a printed circuit board (PCB) and other parts become larger correspondingly, so that the reduction in size is difficult. It, however, is necessary for an enlarged field angle being attained that the intermediate image is relatively large, so that it is desirable that the lateral magnification of the relay lens <NUM> satisfies the above conditional expression.

In the expression, f_pmax represents the focal length in a cross section with the strongest positive power of the curved surface optical member <NUM>, and f_pmin represents the focal length in a cross section with the weakest positive power of the curved surface optical member <NUM>.

If the value of f_pmax / f_pmin is <NUM> or more, the focal length is positive or negative in both the cross sections and the difference in focal length between the cross sections is little, so that the arrangement of a surface that is non-rotationally symmetric is less effective and the reduction in size of the light guide member <NUM> and the collimator lens <NUM> is difficult. If the value of f_pmax / f_pmin is -<NUM> or less, the positive power of the cross section with the strongest positive power is rather weak, so that the reduction in size of the light guide member <NUM> and the collimator lens <NUM> is difficult.

In the expression, f_y represents the focal length of the curved surface optical member <NUM> in a cross section in a long side direction of the image display element <NUM>, and f_x represents the focal length of the curved surface optical member <NUM> in a cross section in a short side direction of the image display element <NUM>.

If the value of f_y / f_x is <NUM> or more, the focal length is positive or negative in both the cross sections and the difference in focal length between the cross sections is little, so that the arrangement of a surface that is non-rotationally symmetric is less effective and the reduction in size of the light guide member <NUM> and the collimator lens <NUM> is not possible. If the value of f_y / f_x is -<NUM> or less, the positive power in the long side direction is weak, so that the reduction in size of the light guide member <NUM> and the collimator lens <NUM> is not possible.

In order to improve the performance of the propagation optical system while securing the whole length of the propagation optical system, it is desirable that the intermediate image <NUM> is arranged between the relay lens <NUM> and the collimator lens <NUM>. It is desirable, moreover, that the relay lens <NUM> includes a relay front group and a relay rear group in order from the image display element <NUM> side, and the spacing between the relay front group and the relay rear group is larger than any of the spacings between other optical members in the relay lens <NUM>.

By securing an appropriate spacing between the relay front group and the relay rear group, it is possible to correct various aberrations while securing the whole length of the propagation optical system.

In the expression, TLR represents the thickness of the relay lens <NUM> and TLRa represents the spacing between the relay front group and the relay rear group. The thickness and the spacing are of values determined on the optical axis.

If the value of TLRa / TLR is <NUM> or more, the spacing between the relay front group and the relay rear group is too large and a space formed by the relay front group or the relay rear group is too small, so that various aberrations are hard to correct. If the value of TLRa / TLR is <NUM> or less, the spacing between the relay front group and the relay rear group is too small and it is difficult to correct various aberrations in the relay lens <NUM> while securing the whole length of the propagation optical system <NUM>.

In the expression, f_r represents the focal length of a relay group and f_rf represents the focal length of the relay front group.

The relay front group chiefly has an image forming function in the relay optical system <NUM>, and it is important to achieve an appropriate power arrangement. If the value of f_r / f_rf is <NUM> or more, the focal length of the relay front group is too short and an aberration generated in the relay front group is not corrected adequately, so that it is difficult to correct various aberrations in the entire propagation optical system <NUM>. If the value of f_r / f_rf is <NUM> or less, the focal length of the relay front group is too long and the correction of aberrations in the relay lens <NUM> is difficult.

In the following, specific numerical value examples of embodiments of the virtual image display device according to the present invention are presented. In each of the following examples, the size of the image display element <NUM> is <NUM> in the vertical (X) direction, <NUM> in the horizontal (Y) direction, and <NUM> in the diagonal direction. In each of the numerical value examples, the first to thirteenth surfaces constitute the relay optical system <NUM>, and the fourteenth and fifteenth surfaces constitute the curved surface optical member <NUM> having a curved surface shape that is non-rotationally symmetric with respect to the optical axis. The sixteenth to twenty-first surfaces constitute the collimator lens <NUM>, the twenty-second and twenty-third surfaces as parallel flat surfaces constitute the light guide member <NUM>, and the distance to the twenty-third surface is the eyerelief.

Schematic optical arrangements of the respective numerical value examples are illustrated in <FIG>, <FIG>, <FIG>, and <FIG>. Aberration diagrams of the respective numerical value examples are illustrated in <FIG>, <FIG>, <FIG>, and <FIG>. <FIG> illustrates measurement points of aberrations. As illustrated in <FIG>, there are three measurement points (a), (b), and (c) in the lateral direction and three measurement points <NUM>, <NUM>, and <NUM> in the vertical direction. Each aberration diagram illustrates the result of measurement performed at the three measurement points <NUM>, <NUM>, and <NUM> for each of the three measurement points (a), (b), and (c) in the X and Y directions.

<FIG> illustrates an optical arrangement of Numerical Value Example <NUM> and <FIG> is an aberration diagram of the optical arrangement.

In each aberration diagram, calculation is made assuming that an image is formed with an ideal lens having a focal length of <NUM>. In each of the numerical value examples, aberrations are corrected on a high level. It is evident from the examples of the present invention that a very good image performance is secured with a horizontal field angle of <NUM> degrees or larger by constructing the propagation optical system as in the respective examples of the present invention.

In the above-described examples, the virtual image display device capable of obtaining a wide viewing angle of <NUM> degrees or more and enhancing light use efficiency is achieved.

While preferred embodiments of the present invention have been described above, the present invention is in no way limited to such particular embodiments. Various modifications and changes may be made within the scope of the gist of the invention as recited in the claims as long as no particular limitations are made in the description as above.

The surface of a curved surface shape that is non-rotationally symmetric may be a spherical surface in a given cross section, or may be an aspherical surface or a free-form surface in order to improve the degree of freedom for design.

The above-described embodiments are illustrative and do not limit the present invention. Thus, numerous additional modifications and variations are possible in light of the above teachings. For example, elements and/or features of different illustrative embodiments may be combined with each other and/or substituted for each other within the scope of the present invention.

Claim 1:
A virtual image display device comprising:
an image display element (<NUM>) configured to display an image to be displayed as a virtual image;
a propagation optical system (<NUM>) configured to propagate light from the image display element (<NUM>); and
a light guide member (<NUM>) configured to guide the light propagated by the propagation optical system (<NUM>),
the light guide member (<NUM>) including:
a light beam incident part (<NUM>) that introduces light including image information from the propagation optical system (<NUM>) into the light guide member;
an image extractor (<NUM>) that extracts the light including image information from an inside of the light guide member; and
an image emitter (<NUM>) that emits the light including image information to an outside of the light guide member (<NUM>),
wherein
the light beam incident part (<NUM>) includes an aperture having a width (A1) in a first direction and a width (A2) in a second direction perpendicular to the first direction, the width (A1) in the first direction being narrower than the width (A2) in the second direction,
the propagation optical system (<NUM>) includes one or more refractive lenses each having a curved surface shape that is non-rotationally symmetric with respect to an optical axis, wherein each refractive lens having a curved surface shape that is non-rotationally symmetric with respect to an optical axis has a positive power in the first direction,
wherein the propagation optical system (<NUM>) includes a relay optical system that forms an intermediate image (<NUM>) of the image displayed on the image display element (<NUM>) on a side facing the image display element (<NUM>), and a collimator optical system on a side facing the light guide member of the intermediate image (<NUM>), and
wherein the one or more refractive lenses each having a curved surface shape that is non-rotationally symmetric with respect to the optical axis are provided in at least one of the relay optical system and the collimator optical system.