LIGHT GUIDE AND VIRTUAL-IMAGE DISPLAY DEVICE

A light guide includes light guiding members including first and second light guiding members, an optical entrance having a plane on which the light is incident, a light guiding unit to guide the light incident on the optical entrance with repeated reflection, a light beam ejection unit to eject the light to an outside of the light guide, and an extraction unit to reflect the light guided by the light guiding unit toward the light beam ejection unit. The light guiding members guide and eject a light, and the second light guiding member is bonded to, at least, the light guiding unit of the first light guiding member.

TECHNICAL FIELD

Embodiments of the present disclosure relate to a light guide and a virtual-image display device.

BACKGROUND ART

As a virtual-image display device, for example, a head-mounted display (HMD) is commonly used. Such a head-mounted display (HMD) is classified into a transparent type and a nontransparent type, and for example, Google glass (registered trademark) is well known in the art as a see-through HMD of transparent type through which an image can be seen. Various kinds of HMD of nontransparent type that achieves deep immersive simulation are also released by several companies. Regarding the size of a virtual image that is visually recognized by human through a virtual-image display device, a HMD of transparent type is used in combination with an external information terminal, or is used in combination with the augmented reality (AR) technologies. For this reason, a small and portable HMD is desired. By contrast, a HMD of nontransparent type is used for, for example, games or virtual-reality (VR) technologies. For this reason, a HMD that realizes immersive feeling and a wide viewing angle is desired. Some common characteristics of a virtual-image display device are given below. The viewing angle of a virtual-image display device that is dedicated to its downsizing and reduction in thickness of the main body tends to be narrow. By contrast, when the viewing angle of the display area is widened, the size of the main body of the virtual-image display device tends to be increased and its thickness tends to be increased. Currently, a HMD of transparent type whose thickness is reduced is demanded, and a wide viewing angle is also required for such a HMD of transparent type whose thickness is reduced is demanded.

The technologies are known in the art that satisfies such demands as described above (see, for example, PTLs 1 to 3). However, in such technologies known in the art, the light is guided to the eyes of a user as the light is ejected to the outside of a light guide by the reflection by a plurality of mirrors or a plurality of micro parts. In such technologies or configurations, some of the light beams that are guided through a light guide at varying angles that correspond to the multiple pixels of an image formed by an image display element does not hit any of a plurality of mirrors or a plurality of micro parts. Given these circumstances, a dropout error of brightness may occur on a virtual image that is observed.

In order to deal with the above technical problems, a method of preventing dropout error of brightness has been suggested as follows (see, for example, PTL 4). In such a method of preventing dropout error of brightness, a layer that splits the light is disposed inside the light guide, and the timing at which light beams with varying angles that are guided through a light guide plate are reflected is adjusted. Due to such a configuration, there is a high probability that light beams with angles that tend to cause a dropout error of brightness hit a plurality of mirrors or a plurality of micro parts.

A virtual-image display device with a light guide is known in the art as a device that magnifies a two-dimensional (2D) image by a virtual image optical system and display a magnified virtual image such that an observer or user can observe the displayed magnified virtual image. As an example configuration of such a virtual-image display device with a light guide, head-mounted displays (HMDs) are known in the art. Such head-mounted displays (HMDs) are classified into HMDs of a transparent type and HMDs of a nontransparent type. For example, Google glass (registered trademark of Google limited liability company (LLC) in the US) is well known in the art as a see-through HMD of transparent type through which an image can be seen.

Such a see-through HMD of transparent type is used in combination with an external information terminal, or is used in combination with, for example, the augmented reality (AR) technologies. For this reason, a small and portable HMD is desired. HMDs of nontransparent type are used when, for example, movies are watched, games are played, or when virtual-reality (VR) technologies are provided. For this reason, HMDs that realize immersive feeling and a wide viewing angle are desired.

In HMDs of transparent type, reduction in thickness, reduction in size, and a wide viewing angle are desired. Moreover, it is desired that reduction in transmittance of extraneous light or reduction in reflectivity of light is prevented from occurring, and that a ghost image is prevented from being formed. As a feature that meets such demands, a light guide plate as disclosed in, for example, PTL 3 and a virtual-image display device with the light guide are known in the art.

The light guide plate disclosed in PTL 3 includes a first total reflection plane and a second total reflection plane that face each other and extend in the same direction. The light guide plate disclosed in PTL 3 turns the optical path between such a pair of reflection planes, and guides the light toward the light beam ejection unit that has an image extraction unit. The image extraction unit includes a plurality of first planes that extend with inclination toward the inside of a light guiding unit on the far side of the image extraction unit in the light-guiding direction, and a plurality of second planes that form an obtuse angle with the multiple first planes. The multiple first planes and the multiple second planes are alternately arranged. A virtual-image display device may be implemented using the light guide plate as configured above.

When a wide viewing angle is to be achieved using the light guide plate disclosed in PTL 3, a problem is known in the art that an unevenness in brightness or dropout error of brightness occurs on a virtual image. The reasons why such an unevenness in brightness or dropout error of brightness occurs on a virtual image are described with reference to a control sample where the light guide plate according to the disclosure of PTL 3 is used as illustrated inFIG.39.

As illustrated inFIG.39, a light guide plate is a horizontally-oriented plate-like member made of a transparent material. For example, such a light guide plate is placed in front of the eyes of human like glasses. With the use of such a light guide plate, an image can be observed through the light that is ejected through a light beam ejection unit, and the sight ahead of the light guide plate can be observed through the light that passes through the light guide plate. InFIG.39, the directions perpendicular to the sheet of paper indicate the up-and-down directions of the light guide plate under normal operating conditions, and these directions are referred to as the X-directions. The up-and-down directions inFIG.39that are perpendicular to the X-directions are referred to as the Y-directions. In other words, the forward and backward directions under in-use conditions are referred to as the Y-direction. The directions that are orthogonal to both the X-direction and the Y-direction, which correspond to the right and left directions inFIG.39, are referred to as the Z-direction.

In the light guide plate as illustrated inFIG.39, an optical entrance108is illustrated on a bottom-left side, and a light beam ejection unit140is illustrated on a bottom-right side. Moreover, a light guiding unit130is illustrated between the optical entrance108and the light beam ejection unit140. The optical entrance108includes a prism111on which the light is incident, and includes a mirror101that reflects the incident light, which has passed through the prism111, toward the light guiding unit130.

The light guiding unit130according to the present control sample includes a first reflection plane102and a second reflection plane103that are parallel with each other and totally reflect the light reflected by the mirror101in alternating sequence in a zigzag manner to guide the light toward the light beam ejection unit140. The second reflection plane103functions as a plurality of image extraction units105and a plurality of sub-reflection planes133at the portions that face and correspond to the light beam ejection unit140. These image extraction units105and the multiple sub-reflection planes133are alternately arranged in the Z-direction.

Each one of the multiple image extraction units105is an inclined plane at a certain angle that steps down toward the light beam ejection unit140, and the multiple sub-reflection planes133are parallel to the first reflection plane102. For this reason, the thickness of light guide plate in the forward and backward directions gradually gets thinner in stages toward the light beam ejection unit140.

The light that is emitted from, for example, a prescribed image forming element is collimated and is incident on the light guide plate through the optical entrance108. Then, the light is obliquely reflected by the mirror101toward the first reflection plane102, and is obliquely reflected by the first reflection plane102toward the second reflection plane103. As a result, the light travels toward the light beam ejection unit140with reflection at a certain incident angle and reflection angle in a zigzag manner between the first reflection plane102and the second reflection plane103.

Once the light reaches each one of the multiple image extraction units105, each one of the multiple image extraction units105reflects some of the incident light toward the light beam ejection unit140. The light that is reflected by each one of the multiple image extraction units105passes through the light beam ejection unit140, and is incident on the eyes of human that are located to face the light beam ejection unit140. An image that is formed by the image forming element or the like can be observed by the eyes of a human through the light that is reflected by each one of the multiple image extraction units105. The light ahead of the light guide plate is introduced through the light beam ejection unit140, and the introduced light is observed by the eyes of human. Due to this configuration, the sight ahead of the light guide plate can be observed together with the above image.

According to the flat light guide plate as illustrated inFIG.39, the light with a relatively wide total-reflection angle with reference to a normal line to the principal plane of the light guide plate and the light with a relatively narrow total-reflection angle with reference to a normal line to the principal plane of the light guide plate are guided depending on the field angle of the image. Due to this configuration, as the light with a relatively wide total-reflection angle on the first reflection plane102and the second reflection plane103is guided, the field angle of a virtual image to be observed can be increased and the angle of visibility can be widened.

FIG.39is a diagram illustrating the optical path of the light that is transmitted within a known light guide plate from the optical entrance108that is disposed at left end of the light guide plate to the first reflection plane102and the second reflection plane103with a relatively wide total-reflection angle.

CITATION LIST

Patent Literature

Japanese Patent Application Publication No. 2013-210633

Japanese Patent Application Publication No. 2011-509417

Japanese Patent Application Publication No. 2011-198260

US Patent Application Publication No. 2017/0285346

SUMMARY OF INVENTION

Technical Problem

However, when a layer that splits the light is disposed inside the light guide, at least one split face needs to be provided for the light guide. More specifically, the light guide needs to be divided into a plurality of parts, and then these parts of the light guide need to be coupled to each other through the above at least one split face. Due to such a complicated configuration, the degree of difficulty tends to increase in production or manufacturing.

As described above, when the light that is transmitted within the light guide plate with a relatively wide total-reflection angle and the total-reflection intervals by the first reflection plane and the second reflection plane are wide, the irradiance levels of the light beams that reach the multiple image extraction units105tend to vary easily, and some of the multiple image extraction units105may partially be irradiated with no light. As a result, unevenness in brightness may occur on a virtual image that is observed through the light beam ejection unit140. Alternatively, a dropout error of brightness may occur on a virtual image that can be observed through the light beam ejection unit140. In other words, some of the light does not reach the light beam ejection unit140, which is undesirable. In other words, when a virtual-image . display device is configured using such a light guide plate as described above and when the viewing angle of the image is increased, unevenness in brightness or a dropout error of brightness occurs on a virtual image depending on the field angle or the position at which the virtual image is to be visually recognized, which is undesirable.

Solution to Problem

A light guide includes two or more light guiding members including a first light guiding member and a second light guiding member, an optical entrance having a plane on which the light is incident, a light guiding unit to guide the light incident on the optical entrance with repeated reflection, a light beam ejection unit to eject the light to an outside of the light guide, and a extraction unit to reflect the light guided by the light guiding unit toward the light beam ejection unit. The two or more light guiding members guide and eject a light, and the second light guiding member is bonded to, at least, the light guiding unit of the first light guiding member.

Advantageous Effects of Invention

According to one aspect of the present disclosure, a dropout error of brightness can be controlled, and a light guide with easy production can be achieved.

With the light guide and the virtual-image display device according to the embodiments of the present disclosure, an optical-path separator is arranged apart from the optical entrance and is disposed between the first reflection plane and the second reflection plane. As a result, an unevenness in brightness or dropout error of brightness that may occur on a virtual image to be observed can be reduced.

DESCRIPTION OF EMBODIMENTS

FIG.1is a schematic diagram illustrating a virtual-image display device1000provided with a light guide300, according to a first embodiment of the present disclosure.

The virtual-image display device1000according to the first embodiment of the present disclosure is provided with an image display element100, an optical system200, and the light guide300according to the first embodiment of the present disclosure.

The image display element100is a device that emits the image light of an image that forms a virtual image that is projected and displayed through the light guide300. The image display element100is a plate-like element that extends in the depth direction of the drawing. Various kinds of display element such as an organic light emitting diode (OLED) or a liquid crystal display (LCD) may be applied to the image display element100. As long as it can display information such as an image, for example, a digital micromirror device (DMD) that is a micro-electromechanical systems (MEMS) in which a large number of minute specular surfaces (micromirrors) are arrayed on a plane, or a liquid crystal on silicon (LCoS) may be used for the image display element100. In such a configuration, for example, a light-emitting diode (LED), a laser diode (LD), or a discharge lamp may be used for the light source that irradiates the image display element100with light.

The optical system200according to the present embodiment is configured by, for example, a plurality of optical lenses and a stop, and collimates the light beam that is emitted from the image display element100and includes the image data and changes the angle of the light beam that is emitted from the image display element100and includes the image data to a direction that is consistent with the varying positions of the image display element100. Note that the light beam that includes the image data may be referred to simply as image light in the following description.

The light guide300that is used for the virtual-image display device1000guides the image light that is emitted from the image display element100and then is collimated by the optical system200, which includes the image data, and ejects the image light to the eyes of human. As a result, a virtual image is displayed. The light guide300is a plate-like member that extends in the depth direction of the drawing. The light guide300according to the present embodiment includes an optical entrance301, a light guiding unit302, an extraction unit303, and a light beam ejection unit304. Moreover, the light guide300according to the present embodiment includes a reflector305. The optical entrance301, the light guiding unit302, the extraction unit303, the light beam ejection unit304, and the reflector305extend in the depth direction of the drawing. In the longer-side directions of the light guide300that are the right and left directions ofFIG.1, a side at which the optical entrance301is arranged may be referred to as a base-end side, and a side apart from the optical entrance301may be referred to as a tip side view in the following description.

The optical entrance301is a site arranged at a site that faces the optical system200on which the image light that is emitted from the image display element100and then is collimated by the optical system200is incident. The reflector305is a site that reflects the light beam of the image light that has entered the light guide300through the optical entrance301.

The light guiding unit302has a pair of principal planes that are approximately parallel to each other, and is a site that guides the light beam that is reflected by the reflector305with repeated total internal reflection between the pair of principal planes.

The extraction unit303according to the present embodiment is a site that reflects the light beam guided by the light guiding unit302toward the light beam ejection unit304so as to be extracted to the outside of the light guide300. The light beam ejection unit304is a site through which the light beam, which is reflected by the extraction unit303so as to be extracted to the outside of the light guide300, is ejected to the outside of the light guide300. Due to this configuration, a user of the virtual-image display device1000can visually recognize a virtual image by looking at the light guide300from the light beam ejection unit304side.

FIG.2is a magnified view of a part of the light guide300that includes some of the extraction unit303, according to the present embodiment.

The extraction unit303includes a plurality of planes303athat are approximately parallel to the light beam ejection unit304and a plurality of planes303bthat are inclined with reference to the light beam ejection unit304. The multiple planes303aand the multiple planes303bare arranged in alternating sequence in the right and left directions of the drawing (i.e., the direction heading for the tip of the light guide300from the base end).

Once the light that is guided through the light guiding unit302with repeated total internal reflection hits each one of the multiple planes303b,for example, the light is reflected toward the light beam ejection unit304as indicated as a light beam R1. As each one of the multiple plane303ais arranged between each pair of the multiple planes303b,the light can move toward the tip side of the light guide300until the light hits one of the multiple planes303b. Accordingly, the light can be guided by a site of the light beam ejection unit304arranged on the tip side of the light guide300. Due to such a configuration, the virtual-image display device1000that enables wide-angle display can be implemented using the light guide300that has a relatively thin shape.

In the present embodiment, the light guide300is configured by a pair of light guiding members including a first light guiding member310and a second light guiding member320. As illustrated inFIG.1, in the light guide300according to the present embodiment, the optical entrance301, the light guiding unit302, the extraction unit303, the light beam ejection unit304, and the reflector305are provided for the first light guiding member310. Moreover, in the light guide300according to the present embodiment, the first light guiding member310and the second light guiding member320are configured by a material with an approximately equivalent refractive index, and are configured by, for example, the same material.

FIG.3is a magnified view of a part of the light guide300that includes some of the second light guiding member320, according to the present embodiment.

As illustrated inFIG.3, the second light guiding member320has a pair of edge faces321on the base-end side and tip side, respectively, and is shaped like a parallel plate. Moreover, the second light guiding member320is bonded to the light guiding unit302of the first light guiding member310having a middle layer400therebetween.

The middle layer400, which is disposed at the bonding portion between the first light guiding member310and the second light guiding member320, includes a reflective or transmissive film401and an adhesive layer402.

The reflective or transmissive film401is formed on the second light guiding member320by means of, for example, vapor deposition. The reflective or transmissive film401may be, for example, a dielectric film and a metal film made of a silver (Ag) material or the like. The reflective or transmissive film401is a coating film that has half-mirror characteristics. The reflective or transmissive film401transmits some of the light that is guided through the first light guiding member310to the second light guiding member320side, and reflects the rest of the light that is guided through the first light guiding member310to the first light guiding member310side. The half-mirror characteristics of the reflective or transmissive film401may be characteristics close to 50% for the reflectivity and 50% for the transparency. However, no limitation is intended thereby, and the half-mirror characteristics of the reflective or transmissive film401may be, for example, 30% for the reflectivity and 70% for the transparency.

The adhesive layer402is a layer that bonds the first light guiding member310and the second light guiding member320together, and is configured by, for example, adhesive material.

Moreover, the adhesive layer402has a refractive index that is, for example, almost equal to that of the first light guiding member310and the second light guiding member320.

In the light guide300according to the present embodiment as configured above, the second light guiding member320is shaped like a parallel plate, and is bonded at least to the light guiding unit302of the first light guiding member310. Due to such a configuration, a dropout error of brightness can be controlled on a virtual image to be observed in the virtual-image display device1000provided with the light guide300, and a light guide with easy production can be achieved.

Some advantageous effects of the light guide300according to the present embodiment are described below in comparison to a light guide330according to a control sample of the above embodiment of the present disclosure.

FIG.4is a schematic diagram illustrating a virtual-image display device1100provided with a light guide330, according to a control sample of the above embodiment of the present disclosure.

In the virtual-image display device1100according to the present control sample of the above embodiment of the present disclosure, the light guide300of the virtual-image display device1000is replaced with the light guide330. The light guide330according to the present control sample of the above embodiment is provided with the optical entrance301, the light guiding unit302, the extraction unit303, the light beam ejection unit304, and the reflector305. The light guide330according to the present control sample of the above embodiment has a shape similar to that of the first light guiding member310and is configured by a material similar to that of the first light guiding member310, but is not provided with the second light guiding member320.

FIG.5is a diagram illustrating a light beam guided by the light guide330according to the present control sample of the above embodiment of the present disclosure.

A light beam R2is a part of the image light that is emitted from a part of the image display element100as illustrated inFIG.4, and is incident on a plane of the optical entrance301at a certain angle. As illustrated inFIG.5, a light beam R2is guided through the light guiding unit302with repeated total internal reflection. However, the light beam R2ends up reaching the tip end of the light guide330without hitting any one of the multiple inclined planes303b(seeFIG.2) inside the extraction unit303. Such a light beam R2does not reach an eye E of a user. As a result, a loss in the picture exists on a virtual image that the user visually recognize. In other words, a dropout error of brightness occurs on a virtual image that the user visually recognize. As a result, the image quality of a virtual image deteriorates.

Compared with the control sample as illustrated inFIG.5,FIG.6is a diagram illustrating a light beam guided by the light guide300according to the first embodiment of the present disclosure.

A light beam R3is a part of the image light that is emitted from a part of the image display element100as illustrated inFIG.1, and is incident on a plane of the optical entrance301at the same angle as that of the light beam R2as illustrated inFIG.5. In this configuration, as illustrated inFIG.6, the light beam R3is divided into a light beam R4, a light beam R5, a light beam R6, and a light beam R7as multiple reflection occurs due to the existence of the second light guiding member320. As a result, the external appearance of the light flux of the light beam R3or even the entire image light inside the light guide300can be expanded. Due to this configuration, for example, the light beam R6ends up reaching the tip end of the light guide330without hitting any one of the multiple inclined planes303b(seeFIG.2) inside the extraction unit303. However, the light beam R4and the light beam R5are reflected by the extraction unit303so as to be ejected to the outside of the light guide300through the light beam ejection unit304, and reach the eye E of a user. In other words, there is a high probability that the light beam R3or even the entire image light will hit the multiple inclined planes303b(seeFIG.2) inside the extraction unit303. For this reason, compared with the configuration or structure according to the above control sample of the first embodiment of the present disclosure as illustrated inFIG.5, a dropout error of brightness on a virtual image that the user visually recognize can be prevented from occurring. Accordingly, the image quality of a virtual image can be prevented from deteriorating.

In the configuration and structure as illustrated inFIG.6, there is a light beam such as a light beam R7that reaches an edge face321of the second light guiding member320. In order to handle such a situation, the edge face321may be coated with a material for absorbing the light with wavelengths that correspond to an image light, or the edge face321may be shaped so as to eject the incident light such as the light beam R7to the outside of the second light guiding member320. Due to such a configuration, the reflection light that is the light beam R7reflected by the edge face321is prevented from being guided through the second light guiding member320or the first light guiding member310again. As a result, unnecessary light can be prevented from being stray light and contaminating a virtual image, and deterioration in image quality can be prevented from occurring. For example, a material for absorbing a visible light may be used for the coating that absorbs the light with wavelengths that correspond to an image light. The shape that eject the incident light such as the light beam R7to the outside of the second light guiding member320is achieved by, for example, the roughening and coarsening of the edge face321.

As described above, in the light guide300according to the present embodiment, the second light guiding member320is shaped like a parallel plate, and is bonded at least to the light guiding unit302of the first light guiding member310. Due to such a configuration, a dropout error of brightness can be controlled on a virtual image to be observed in the virtual-image display device1000provided with the light guide300. Moreover, the second light guiding member320that is shaped like a parallel plate as described above can easily be produced or prepared independently from the first light guiding member310, and the second light guiding member320that is shaped like a parallel plate as described above can easily be coupled to the first light guiding member310. For this reason, the light guide300according to the present embodiment can easily be produced or manufactured.

As the light guide300according to the present of embodiment includes the reflective or transmissive film401, the introduction or multiple reflection of an image light to the second light guiding member320can easily be controlled, and the external appearance of the light flux can further be expanded.

Moreover, in the light guide300according to the present embodiment, it is desired that the first light guiding member310and the second light guiding member320be configured by a material with an approximately equivalent refractive index. If the first light guiding member310and the second light guiding member320are configured by a material with an approximately equivalent refractive index, the displacements in angle can efficiently be controlled between the light beam that is guided through the first light guiding member310and the light beam that returns to the first light guiding member310by reflection after being guided and introduced from the first light guiding member310to the second light guiding member320. As a result, a desirable virtual image can be displayed. Note also that the refractive indexes are not necessarily completely matched, and there may be some displacements in angle between the light beam that is guided through the first light guiding member310and the light beam that returns to the first light guiding member310by reflection after being guided and introduced from the first light guiding member310to the second light guiding member320as long as such displacements do not significantly affect a virtual image to be displayed.

Moreover, in the light guide300according to the present embodiment, the first light guiding member310and the second light guiding member320are bonded together by an adhesive layer402that has a refractive index that is almost equal to that of the first light guiding member310and the second light guiding member320. Due to such a configuration, changes in angle can be controlled when the light beam passes through the adhesive layer402, and a desirable virtual image can be displayed.

Moreover, in the light guide300according to the present embodiment, the image light that is approximately collimated is incident on the optical entrance301, and thus there is a high probability that the image light that is emitted from the light beam ejection unit304will be formed at a single point on the retina of the eyes of a user. Due to such a configuration, even if the optical power of the image light is relatively weak, a desirable virtual image can be displayed.

Second Embodiment

FIG.7is a schematic diagram illustrating a light guide300A according to a second embodiment of the present disclosure.

The light guide300in the virtual-image display device1000as illustrated inFIG.1may be replaced with the light guide300A according to the second embodiment of the present disclosure. In the light guide300A according to the second embodiment of the present disclosure, the second light guiding member320and the middle layer400in the light guide300are replaced with a second light guiding member320A and a middle layer400A, respectively.

FIG.8is a magnified view of a part of the light guide300A that includes some of the second light guiding member320A, according to the present embodiment.

As illustrated inFIG.7andFIG.8, the second light guiding member320A is shaped like a parallel plate, and extends to a tip side of the first light guiding member310. The reflective or transmissive film401of the middle layer400A exists at a position of the light guiding unit302of the first light guiding member310. However, the reflective or transmissive film401of the middle layer400A

does not extend to a position of the extraction unit303or the light beam ejection unit304. By contrast, an adhesive layer402A as illustrated inFIG.8extends to a tip side of the first light guiding member310and the second light guiding member320A, and the first light guiding member310and the second light guiding member320A are bonded together till the tip end.

In a similar manner to the light guide300according to the above embodiment of the present disclosure as described above, easy production can be achieved and a dropout error of brightness can be controlled on a virtual image to be observed also in the light guide300A according to the present embodiment as configured above. In the light guide300A according to the second embodiment of the present disclosure, when the curve of the second light guiding member320A fits the curve of the light beam ejection unit304of the first light guiding member310, the second light guiding member320A and the light beam ejection unit304are bonded together. Due to this configuration, the curve can be reduced, and thus a desirable virtual image with little distortion can be displayed.

In the light guide300A according to the second embodiment of the present disclosure, the reflective or transmissive film401does not extend to the light beam ejection unit304. Due to such a configuration, the light that is reflected by the reflective or transmissive film401can be prevent from hitting the extraction unit303and causing undesired light such as stray light. Due to this configuration, reduction in image quality of a virtual image can be controlled.

FIG.9is a magnified view of a part of a light guide according to a modification of the second embodiment of the present disclosure.

In the light guide according to the present modification of the second embodiment of the present disclosure, the adhesive layer402of the middle layer400does not extend to a tip side of the first light guiding member310and the second light guiding member320A, and airspace403exists between the first light guiding member310and the second light guiding member320A at a position of the extraction unit303and the light beam ejection unit304and at a position closer to the tip side than the extraction unit303and the light beam ejection unit304.

FIG.10is a diagram illustrating another configuration or structure of the first light guiding member310, according to the present embodiment.

Such a first light guiding member310B, which has a configuration or structure different from the first light guiding member310, has a plane310Ba bonded together with the second light guiding member320, and the plane310B a has low flatness due to, for example, a manufacturing error or production error. However, a middle layer400B includes the reflective or transmissive film401and an adhesive layer402B in the present embodiment, and the adhesive layer402B has a refractive index that is, for example, almost equal to that of the first light guiding member310B. Due to such a configuration, the compatibility or integrity in refractive index between the first light guiding member310B and the second light guiding member320is maintained in spite of the low flatness of the plane310Ba, and a virtual image with desirable image quality can be obtained.

FIG.11AandFIG.11Bare diagrams each illustrating another configuration or structure of the extraction unit303, according to the present embodiment.

More specifically,FIG.11AandFIG.11Bare diagrams each illustrating another configuration or structure of the extraction unit303that includes the plane303aand the plane303bas illustrated inFIG.2.FIG.11Bis a diagram illustrating a configuration or structure of an extraction unit303A that has a configuration or structure different from that of the extraction unit303, according to the present embodiment. The extraction unit303A has the multiple planes303athat are approximately parallel to the light beam ejection unit304, the multiple planes303bthat are inclined with reference to the light beam ejection unit304, and a plurality of planes303cthat are inclined with reference to the light beam ejection unit304. The multiple planes303band the multiple planes303care orthogonal to the multiple planes303a, and are inclined with reference to a plane that extends in the depth direction of the drawing, in directions that differ from one another. The multiple planes303a,the multiple planes303c, and the multiple planes303bare arranged in alternating sequence in the right and left directions of the drawing.

When the extraction unit303is adopted as in the present embodiment, a light beam R9may exist that is reflected by the plane303aand then is further reflected by the plane303band travels toward the light beam ejection unit304, in addition to a light beam R8that is reflected by the plane303band travels toward the light beam ejection unit304. Such a light beam R9may serve as a stray light for the virtual image to be observed.

By contrast, when the extraction unit303A as illustrated inFIG.11Bis adopted, the light beam R9does not hit the plane303bafter reflected by the plane303a.This is because, due to the existence of the plane303c,the next plane303ais arranged at a position where none of the light beam R9reach. Accordingly, it is unlikely that the light beam R9serve as a stray light for the virtual image to be observed, and the image quality of a virtual image can be prevented from deteriorating.

Third Embodiment

FIG.12is a schematic diagram illustrating a light guide300B according to a third embodiment of the present disclosure.

The light guide300in the virtual-image display device1000as illustrated inFIG.1may be replaced with the light guide300B according to the third embodiment of the present disclosure. In the light guide300B according to the second embodiment of the present disclosure, the extraction unit303of the light guide300is replaced with an extraction unit303B.

The extraction unit303B is configured by a large number of mirrors that area arranged inside the first light guiding member310and coated with a material of a specific reflectance ratio. In a similar manner to the light guide300according to the above embodiment of the present disclosure as described above, easy production can be achieved and a dropout error of brightness can be controlled on a virtual image to be observed also in the light guide300B according to the present embodiment as configured above.

Fourth Embodiment

FIG.13is a schematic diagram illustrating a light guide300C according to a fourth embodiment of the present disclosure.

The light guide300in the virtual-image display device1000as illustrated inFIG.1may be replaced with the light guide300C according to the fourth embodiment of the present disclosure.

In the light guide300C according to the fourth embodiment of the present disclosure, the extraction unit303of the light guide300is replaced with an extraction unit303C.

The extraction unit303C is provided with micro parts and gap zones on the plane on the other side of the light beam ejection unit304of the first light guiding member310. In a similar manner to the light guide300according to the above embodiment of the present disclosure as described above, easy production can be achieved and a dropout error of brightness can be controlled on a virtual image to be observed also in the light guide300C according to the present embodiment as configured above.

Example and Control Sample

As an example of the present disclosure, a result of simulating the brightness distribution of a virtual image under the following conditions in the virtual-image display device according to the first embodiment of the present disclosure as illustrated inFIG.1is given below. As a control sample of the above embodiment of the present disclosure, a result of simulating the brightness distribution of a virtual image under the following conditions in the virtual-image display device as illustrated inFIG.4is given below. Note that the second light guiding member320does not exist in the above control sample and that condition is not taken into consideration.

Conditions

Image display element100

Second light guiding member320

First light guiding member310

Thickness: 0.5 mm at the thinnest portion; and 2.0 mm at the thickest portion

Width of Plane303b: 0.2 mm

Angle with reference to Light beam ejection unit304: 27 degrees

Width of Plane303a:0.76 mm

Eye box: Equal to or wider than 5 mm

Eye relief: Equal to or wider than 15 mm

FIG.14is a diagram illustrating a result of simulating the brightness distribution of a virtual image in a virtual-image display device according to a control sample of the above embodiments of the present disclosure.

FIG.15is a diagram illustrating a result of simulating the brightness distribution of a virtual image in the virtual-image display device1000according to the above embodiment of the present disclosure.

InFIG.14andFIG.15, the X-direction indicates the longer-side directions of the light guide (the right and left directions inFIG.1andFIG.4), and the Y-direction indicates the width directions of the light guide (the depth directions inFIG.1andFIG.4). The values in the X-direction and Y-direction indicate a relative position, and zero indicates the center.

In the control sample as illustrated inFIG.14, significant dropouts where the brightness is close to zero exist at positions P1, P2, and P3that are separated from each other in the X-direction. However, no such significant dropout where the brightness is close to zero exists in the result of simulation as illustrated inFIG.15according to the above embodiment of the present disclosure.

For example, the optical system200may be configured to generate an approximately collimated beam after an intermediate image of an image light that is emitted from the image display element100is formed. In such a configuration, the approximately collimated beam is incident on the light guide300. As the optical system200is configured to form an intermediate image beforehand, the image display element100whose weight percentage is relatively high in the virtual-image display device1000can be arranged on the rear side in a direction apart from the light guide300. Due to this configuration, when the virtual-image display device1000is configured like glasses, the weight on the front side can be reduced, and a comfortable virtual-image display device shaped like glasses, which is also referred to as a smart glass, can be achieved.

In the above embodiments of the present disclosure, a light guide is configured by two light guiding members such as the first light guiding member310and the second light guiding member320. However, no limitation is indicated thereby, and a light guide may be configured by two or more light guiding members in some embodiments.

The second light guiding member320is bonded to the principal plane of the light guiding unit302that is arranged on the same side of the light beam ejection unit304in the first light guiding member310. However, no limitation is indicated thereby, and the second light guiding member320may be bonded to the principal plane of the light guiding unit302that is arranged on the same side of the extraction unit303.

The reflective or transmissive film401is not limited to the reflective or transmissive film that is formed on the second light guiding member320, but may be formed on the first light guiding member310by means of, for example, vapor deposition.

Note also that the configuration or structure of the light guide or the virtual-image display device as described above is applicable even if the right and left in the drawing is reversed. The virtual-image display device according to the above embodiments of the present disclosure may be configured such that a single light guide is observed by both eyes of a user, or may be configured such that a pair of light guides are observed by a pair of eyes, respectively. Alternatively, the virtual-image display device according to the above embodiments of the present disclosure may be configured to be small such that a single light guide is observed by a single eye. Due to the configurations and structure as described above, a light smart glass that is free from a dropout error of brightness even when a virtual image with a wide angle equal to or wider than, for example, 30 degrees is to be displayed can be achieved. The virtual-image display device according to the above embodiments of the present disclosure may be configured as a heads-up display (HUD).

A light guide embodiments of the present disclosure and a virtual-image display device provided with the light guide are described below with reference to the drawings.

The light guide according to an embodiment of the present disclosure includes an optical entrance through which the light is taken into the inside of the light guide, a light guiding unit that guides the light by internal reflection, and a light beam ejection unit through which the light guided by the light guiding unit ejects. The light guiding unit includes a first reflection plane and a second reflection plane that face each other and are approximately parallel to each other. The light that is taken into the inside of the light guiding unit is guided within the light guiding unit from an optical entrance side toward a light beam ejection unit with alternate total internal reflection between the first reflection plane and the second reflection plane.

The second reflection plane is configured by a plurality of image extraction units and a plurality of sub-reflection planes that are arranged in alternating sequence on the rear side in the light-guiding direction. The multiple image extraction units are inclined in a downward direction toward the light beam ejection unit, so as to extract the light to the outside of the light guide through the light beam ejection unit. Each one of the multiple sub-reflection planes is formed subsequent to one of the multiple image extraction units so as to be approximately parallel to the first reflection plane. A plurality of image extraction units and a plurality of sub-reflection planes (33,133) are alternately arranged.

There is at least one optical-path separator between the first reflection plane and the second reflection plane. The optical-path separator is approximately parallel to the first reflection plane and the second reflection plane. The optical-path separator exists at some area between the first reflection plane and the second reflection plane, and the optical-path separator does not exist at the other area between the first reflection plane and the second reflection plane. The optical-path separator serves as a boundary surface that totally reflects the light depending on the angle of incidence of the light, and that transmits the light when the angle of incidence of the light falls within a predetermined range.

Light beams with a wide reflection angle and light beams with a narrow reflection angle with reference to a normal line to the second reflection plane are included in the light that is taken into the light guide through the optical entrance. Assuming that the wavelength of the light is constant, the optical-path separator with the boundary surface as described above totally reflects the light when the reflection angle by the second reflection plane is wide and the angle of incidence is wider than a critical angle of the optical-path separator. On the other hand, the optical-path separator with the boundary surface as described above transmits the light when the reflection angle by the second reflection plane is narrow and the angle of incidence is narrower than a critical angle of the optical-path separator.

The optical-path separator may be a single unit, or may consist of a plurality of units that are arranged at prescribed intervals in the light-guiding direction. In both cases, the optical-path separator is detached from the optical entrance, and transmits or totally reflects the light reflected by the second reflection plane, depending on whether the incident angle is less than or equal to or greater than the critical angle that serves as a boundary.

The light that is reflected by the second reflection plane and passes through the boundary surface of at least one optical-path separator and travels to the first reflection plane is referred to as the first light. The light that is reflected by the second reflection plane and then reflected by the boundary surface of at least one optical-path separator and travels to the second reflection plane is referred to as the second light. In other words, the first light is a light where at least one incident angle with reference to a normal line to the above boundary surface has an incident angle narrower than the critical angle for the above boundary surface, and the second light is a light where at least one incident angle with reference to a normal line to the above boundary surface has an incident angle equal to or wider than the critical angle.

There is an area with no boundary surface between the optical entrance and the area that includes at least one boundary surface, and in such an area with no boundary surface, the second light travels within the light guide with total internal reflection between the second reflection plane and the boundary surface. Due to the provision of the above boundary surface, the intervals at which the second light of incident lights with varying angles of view that have approximately been collimated is totally reflected by the second reflection plane can be shortened, and the second reflection plane can be irradiated with light beams with varying angles of view with even light intensity.

Among light beams with varying angles of view that are approximately collimated and incident on the optical entrance, the intervals at which the first light is totally reflected by the second reflection plane are narrower than the intervals at which the second light is totally reflected when there is no boundary surface in the first place. Due to this configuration, the second reflection plane can be irradiated with light beams that have varying angles of view with even light intensity.

As described above, in the planar light guide where the multiple image extraction units are arranged on the plane on the other side of the plane through which a virtual image is to be observed, the optical-path separator is disposed between the first reflection plane and the second reflection plane. Due to such a configuration, light beams with reduced unevenness in brightness and a reduced dropout error of brightness can be taken out and obtained.

Fifth Embodiment

FIG.16is a schematic diagram illustrating a light guide3000according to a fifth embodiment of the present disclosure.

As illustrated inFIG.16, the light guide3000according to the fifth embodiment of the present disclosure is a plate-like component made of a transparent material such as a glass or plastic. The light guide3000may be referred to as a planer light guide plate. The light guide3000according to the present embodiment is provided with an optical entrance8, a light guiding unit30, and a light beam ejection unit40.

The optical entrance8is provided with a wedge-shaped prism11on the plane on which the light that is incident, and a mirror1is arranged on the other side of the plane on which the prism11is disposed. The light is incident on the bottom face of the prism11at right angles. The prism11is a polyhedron made of a transparent material such as a glass or crystal. The mirror1totally reflects the light that has passed through the prism11so as to guide the light to the light guiding unit30.

The light guiding unit30according to the present embodiment guides the incident light that enters through the optical entrance8to the light beam ejection unit40. Moreover, the light guiding unit30according to the present embodiment includes a first reflection plane2, a second reflection plane3, and an optical-path separator4. The first reflection plane2reflects the light that is reflected by the mirror1toward the second reflection plane3. The second reflection plane3reflects the light that is reflected by the first reflection plane2toward the first reflection plane2. The optical-path separator4is a thin film made of a material with a low refractive index such as aluminum fluoride (AlF3) and sodium fluoride (NaF), and the light guide3000is formed by a material with a high refractive index such as a plastic material. The optical-path separator4is a member that transmits the light of the first reflection angle θ1that is reflected by the second reflection plane3, and that reflects the light of the second reflection angle θ2that is reflected by the second reflection plane3.

The second reflection plane3includes a plurality of image extraction units5and a plurality of sub-reflection planes33. The second reflection plane3has a part subsequent to a specific position, where a plurality of oblique faces and a plurality of flat faces are alternately arranged, and such a plurality of oblique faces of the second reflection plane3are referred to as the image extraction units5. The multiple flat faces of the second reflection plane3after the first oblique face of the multiple image extraction units5are referred to as the sub-reflection planes33.

A first light wave6belongs to a group of light beams with varying angles of view that are incident on the optical-path separator4with an angle of incidence smaller than a critical angle of optical-path separator4. A second light wave7belongs to a group of light beams with varying angles of view that are incident on the optical-path separator4with an angle of incidence equal to or greater than a critical angle of optical-path separator4.

The optical-path separator4may include a plurality of planes. When the optical-path separator4has a plurality of planes, the first light wave6and the second light wave7are defined with reference to a plurality of light beams that are approximately collimated and are incident on the multiple planes of optical-path separator4with several angles of view.

The first reflection angle θ1is the angle at which the first light wave6is reflected with reference to a normal line to the second reflection plane3. The second reflection angle θ2is the angle at which the second light wave7is reflected with reference to a normal line to the second reflection plane3.

In the present embodiment, the triaxial directions that includes the X-direction, the Y-direction, and the Z-direction are defined in a similar manner to the control sample of the above embodiment of the present disclosure as described above with reference toFIG.40.

Regarding the Y-axis direction, the direction toward the light beam ejection unit40when viewed from the position of an eye is referred to as the normal (positive) direction, and the direction from the front side toward the position of the eye is referred to as the negative direction. Regarding the Z-axis direction, the light-guiding direction, i.e., the direction of travel from the left side of the right side as illustrated inFIG.16, is referred to as the normal (positive) direction.

The light that is reflected by the multiple image extraction units5exits from the light beam ejection unit40of the first reflection plane2in the negative direction of the Y-axis as illustrated inFIG.16. The light beam ejection unit40includes the multiple image extraction units5and a plurality of sub-reflection planes33. Each one of the multiple image extraction units5undergoes, for example, aluminum vapor deposition and dielectric multilayer vapor deposition, and serves as a mirror. The multiple image extraction units5are arranged at a plurality of positions, and divide the second reflection plane3into a plurality of segments or areas. Each one of the multiple image extraction units5couples the second reflection plane3to one of the sub-reflection planes33, and couples each pair of the sub-reflection planes33. Each one of the multiple image extraction units5is inclined with reference to the second reflection plane3at an obtuse angle.

The multiple image extraction units5that are inclined at an obtuse angle and the second reflection plane3configure a part of the multiple sub-reflection planes33. The multiple image extraction units5and the multiple sub-reflection planes33are alternately linked to each other, and the size of the space between the multiple sub-reflection planes33and the first reflection plane2gets narrower toward the light-guiding direction (i.e., the positive Z-direction inFIG.16).

In the present embodiment, the light that has approximately been collimated is emitted toward the light guide3000. The light beam that corresponds to the pixel of the center of an image is incident on the bottom face of the prism11at right angles, and enters the light guide3000that is a planer light guide plate. The incident light is reflected by the mirror1that is integrated with the light guide3000, and travels toward the first reflection plane2. The first reflection plane2totally reflects the light at the same angle as the incident angle.

The light beams with varying wavelengths that are totally reflected by the first reflection plane2is emitted toward the second reflection plane3. After that, the light beams with varying wavelengths that are approximately collimated travel toward the light beam ejection unit40through the light guide3000with repeated incidence and reflection between the first reflection plane2and the second reflection plane3. The first reflection plane2and the second reflection plane3are approximately parallel to each other, and the amount of misalignment with reference to being parallel with each other need to be equal to or less than ±1°.

In the present embodiment, the optical-path separator4is disposed between the first reflection plane2and the second reflection plane3. The optical-path separator4totally reflects or transmits the light depending on whether the incident angle is greater or narrower than a predetermined critical angle. In other words, optical-path separator4totally reflects the light whose incident angle is wider than a critical angle, and transmits the light whose incident angle is narrower than the critical angle.

In the present embodiment, the first light wave6and the second light wave7are respectively defined as follows. The light wave that travels toward the first reflection plane2from the position at which the light is totally reflected first by the second reflection plane3and then is totally reflected by optical-path separator4and travels toward the second reflection plane3is referred to as a second light wave7in the following description. The light wave that is totally reflected first by the second reflection plane3and then passes through the optical-path separator4and travels toward the first reflection plane2is referred to as a first light wave6in the following description. The second light wave7is guided between the second reflection plane3and the optical-path separators4with repeated total internal reflection, and the first light wave6is guided through the space between the first reflection plane2and the second reflection plane3with repeated total internal reflection.

As described above, the first light wave6does not meet the conditions for total reflection and thus passes through the optical-path separator4. By contrast, the second light wave7meets the conditions for total reflection and thus is totally reflected by optical-path separator4. The multiple image extraction units5are irradiated with the first light wave6and the second light wave7that are guided through the light guide3000. Then, the first light wave6and the second light wave7are reflected at an angle different from the total-reflection angle by the first reflection plane2and the second reflection plane3, and are ejected to the outside of the light guide3000through the light beam ejection unit40. By observing the ejected light with eyes, the image that is formed by the image forming element can be observed.

In the light guide3000according to the above embodiment of the present disclosure as described above, the optical-path separator4that separates the incident light into the light to be totally reflected and the light to be transmitted depending on the reflection angle of the light by the second reflection plane3is provided between the first reflection plane2and the second reflection plane3. With the light guide with such a configuration as described above according to the above embodiment of the present disclosure, light beams with reduced unevenness in brightness and a reduced dropout error of brightness can be taken out and obtained.

FIG.17is a diagram illustrating the light guide3000ofFIG.16that is divided into several functional areas, according the present embodiment.

As illustrated inFIG.17, the optical entrance8is a functional area that converts the light that is approximately collimated and is incident on the planer light guide plate into light beams with angles suitable for being guided through the light guide3000. An optical-path not-separating region9is a functional area where at least one optical-path separator4does not exist between the first reflection plane2and the second reflection plane3. In the present embodiment as illustrated inFIG.16, one optical-path separator4exists, and a pair of optical-path not-separating regions9exist on both right and left sides of optical-path separator4.

The optical-path not-separating region9that exists between the optical entrance8and the optical-path separation region10is a functional area to irradiate an area of the second reflection plane3that totally reflects the light for the first time with the light that is totally reflected first by the first reflection plane2. In the absence of the pair of optical-path not-separating regions9, the second light wave7is totally reflected first by the first reflection plane2, and then is totally reflected by optical-path separator4and is guided and travels forward between the first reflection plane2and the optical-path separators4with repeated total internal reflection. However, there is a problem that the multiple image extraction units5to be irradiated with light are not irradiated with the second light wave7and the light cannot be taken out at a desired position.

For example, the above problem may be solved by dividing the first reflection plane2into several sections and arranging a diffraction grating between each pair of the divided sections of the first reflection plane2as one of the image extraction units5. However, the diffraction angle of each diffraction grating differs depending on the wavelength. For this reason, there is a problem that, for example, the wavelength of the transmission light may disperse or color irregularities or mottling may occur on a virtual image. In the above embodiment of the present disclosure, a problem that, for example, the wavelength of the transmission light may disperse or color irregularities or mottling may occur on a virtual image is solved by dividing the second reflection plane3into several sections and arranging a mirror between each pair of the divided sections of the second reflection plane3as one of the image extraction units5such that the light will be extracted.

The optical-path separation region10includes at least one boundary surface between the first reflection plane2and the second reflection plane3. The optical-path separation region10guides the light with a relatively wide total-reflection angle such as the second light wave7between the second reflection plane3and the optical-path separator4with repeated total internal reflection. Due to such a configuration, the intervals at which total internal reflection is performed is shortened, and the area of the second reflection plane3that is not irradiated with any light wave is reduced. As a result, desired lights can be taken out and obtained from the multiple image extraction units5.

In the optical-path not-separating region9that is adjacent to the optical-path separation region10in the positive axial direction of the Z-axis, light beams with a relatively narrow total-reflection angle such as the first light wave6is taken out from the multiple image extraction units5. For this reason, no boundary surface is necessary by optical-path separator4.

FIG.38is a diagram illustrating how the first light wave6and the second light wave7reach the eye box15in the light guide3000, according to the present embodiment.

The description or the like of each element or member of the light guide3000is omitted as the configuration or structure of these drawings is equivalent to that ofFIG.16according to the fifth embodiment of the present disclosure. As illustrated inFIG.38, both the first light wave6and the second light wave7reach the eye box15in the present embodiment.

FIG.18is a diagram illustrating how a light is guided through the light guide3000when such a light is incident on the light guide3000under the condition same as the condition in the control sample as illustrated inFIG.39, according to the fifth embodiment of the present disclosure.

The description or the like of each element or member of the light guide3000is omitted as the configuration or structure of these drawings is equivalent to that ofFIG.16according to the fifth embodiment of the present disclosure. As illustrated inFIG.18, almost even light beams can be taken out and obtained from the multiple image extraction units5that are disposed within an area where the optical-path separator4exists between the first reflection plane2and the second reflection plane3.

FIG.19is a schematic diagram illustrating how a light like the first light wave6is incident on the light guide3000with a relatively small reflection angle and then is transmitted and guided through the light guide3000at a relatively small total-reflection angle.

The description or the like of each element or member of the light guide3000is omitted as the configuration or structure of these drawings is equivalent to that ofFIG.16according to the fifth embodiment of the present disclosure.

The first light wave6as illustrated inFIG.19does not meet conditions for total reflection when hitting the optical-path separator4. Accordingly, the first light wave6as illustrated inFIG.19passes through the boundary surface of the optical-path separator4, and is guided through the first reflection plane2and the second reflection plane3with repeated total internal reflection. The first light wave6has a small total-reflection angle and thus is totally reflected by the second reflection plane3with relatively narrow intervals. Due to this configuration, almost all area of the second reflection plane3is irradiated with the light beams with varying angles of view that have approximately been collimated, and some light beams are taken out to the outside of the light guide3000through all of the multiple image extraction units5.

Modification

FIG.20is a diagram illustrating a light guide4000according to a modification of the above embodiment of the present disclosure.

In such a modification of the above embodiment of the present disclosure, the size of each space between the second reflection plane3and the first reflection plane2that are divided into a plurality of segments or areas remain unchanged. In other words, the size of the space between the second reflection plane3and the first reflection plane2does not get narrow as the position shifts in the Z-direction that is the light-guiding direction.

Moreover,FIG.20illustrates how a light wave like a second light wave7is guided through the light guide4000with a relatively wide total-reflection angle.

Also in the configuration or structure according to the modification of the fifth embodiment of the present disclosure as illustrated inFIG.20, at least one optical-path separator4is provided between the first reflection plane2and the second reflection plane3, and is detached from the optical entrance. The description or the like of each element or member of the light guide3000except for the multiple image extraction units5and a plurality of sub-reflection planes provided for those image extraction units5is omitted as the configuration or structure of these drawings is equivalent to that ofFIG.16according to the fifth embodiment of the present disclosure.

As illustrated inFIG.20, the light wave that is emitted to one of the multiple image extraction units5is reflected by the multiple image extraction units5, and passes through the optical-path separator4and is ejected and taken out to the outside of the light guide3000. However, the light intensity of the light that reaches the image extraction units5may decrease as the light travels to the tail end of the multiple image extraction units5that are arranged in the direction of travel of the light, and no light may be taken out through some of the multiple image extraction units5.

In view of that point, if the size of the space between the second reflection plane3and the first reflection plane2that are divided into a plurality of segments or areas is gradually reduced in the light-guiding direction (i.e., in the Z-direction) as in the configuration or structure according to the fifth embodiment of the present disclosure, the gap between a pair of light beams to be taken out can be eliminated, or the gap between a pair of light beams to be taken out can at least be reduced. However, if the optical-path separator4is arranged between the first reflection plane2and the second reflection plane3in the modification of the fifth embodiment of the present disclosure as illustrated inFIG.20where the size of the space between the second reflection plane3and the first reflection plane2does not change, the gap between a pair of light beams to be taken out can at least be reduced.

FIG.21,FIG.22, andFIG.23are diagrams each illustrating how the light reaches a retina14through a crystalline lens12of an eye of a user and an image is formed in the light guide3000when the second light wave7is transmitted with the second reflection angle th θ2that is relatively wide and is taken out to the outside of the light guide3000through the multiple image extraction units5, according to the fifth embodiment of the present disclosure.

FIG.21is a diagram illustrating a situation in which an eye is at the center of the eye box15, according to the present embodiment.

FIG.22is a diagram illustrating a situation in which an eye is at the left edge of the eye box15, according to the present embodiment.

FIG.23is a diagram illustrating a situation in which an eye is at the right edge of the eye box15, according to the present embodiment.

The description or the like of each element or member of the light guide3000is omitted as the configuration or structure of these drawings is equivalent to that ofFIG.16according to the fifth embodiment of the present disclosure. In the present embodiment as illustrated in FIG.21,FIG.22, andFIG.23, even light beams can be taken out from the multiple image extraction units5and an image is formed on the retina14based on the even light beams, regardless of the position of an eye within the eye box15.

FIG.24,FIG.25, andFIG.26are diagrams each illustrating how the light reaches the retina14through the crystalline lens12of an eye of a user and an image is formed in the light guide3000when the first light wave6is transmitted with the first reflection angle θ1that is relatively narrow and is taken out to the outside of the light guide3000through the multiple image extraction units5, according to the fifth embodiment of the present disclosure.

FIG.24is a diagram illustrating a situation in which an eye is at the center of the eye box15, according to the present embodiment.

FIG.25is a diagram illustrating a situation in which an eye is at the left edge of the eye box15, according to the present embodiment.

FIG.26is a diagram illustrating a situation in which an eye is at the right edge of the eye box15, according to the present embodiment.

The description or the like of each element or member of the light guide3000is omitted as the configuration or structure of these drawings is equivalent to that ofFIG.16according to the fifth embodiment of the present disclosure. In the present embodiment as illustrated inFIG.24FIG.25, andFIG.26, even light beams can be taken out from the multiple image extraction units5and an image is formed on the retina14based on the even light beams, regardless of the position of an eye within the eye box15.

As understood from the above description with reference toFIG.21toFIG.26, at least one optical-path separator4is provided between the first reflection plane2and equal to or more than half of the multiple image extraction units5. Due to such a configuration, the width of eye box15can be increased to have a sufficient size.

The light that is guided within the light guide3000with a relatively wide total-reflection angle is emitted to the eye box15as the light that is taken out and emitted from one of the multiple image extraction units5on the optical entrance8side. By contrast, the light that is guided within the light guide3000at a first reflection angle θ1is emitted to the eye box15as the light that is taken out and emitted from one of the multiple image extraction units5on the opposite side of the optical entrance8. In an augmented reality (AR) display, the retina14has to be irradiated with light beams with all the angles of view regardless of the position of an eye within the eye box15as a result of eye motion. For this reason, it is beneficial to increase the width of the eye box15.

As understood fromFIG.24, the light that is guided within the light guide3000with a relatively narrow total-reflection angle is guided through the space between the first reflection plane2and the second reflection plane3with repeated total internal reflection. Due to such a configuration, no dropout error occurs. In order to achieve such functions, at least one optical-path separator4is disposed between the first reflection plane2and equal to or more than half of the multiple image extraction units5. Due to this configuration, even if an eye is located at a position further than the center of the area in which the multiple image extraction units5exist with respect to the optical entrance8, the light that is guided within the light guide3000with a relatively wide total-reflection angle can be observed, and the area from which the light can be observed increases.

FIG.27is a diagram illustrating conditions for achieving a state in which almost all area of the second reflection plane3is irradiated with the second light wave7when the second light wave7is guided between the second reflection plane3and the optical-path separators4with repeated total internal reflection at the second reflection angle θ2, according to the fifth embodiment of the present disclosure.

The description or the like of each element or member of the light guide3000is omitted as the configuration or structure of these drawings is equivalent to that ofFIG.16according to the fifth embodiment of the present disclosure. An area or site that is not irradiated with the light wave7is referred to as a dropout error in the following description.

A dropout error16disappears when the relationships in the following two equations hold true.

In the above equations, W2denotes the first light-flux width of the second light wave7(see, for example,FIG.21) that is emitted toward an area28of the second reflection plane3that totally reflects the incident light for the first time, which is on a rear side in the light-guiding direction than a boundary21between the optical-path separation region10and the optical-path not-separating region9that is closest to the optical entrance8, and d denotes the distance between the second reflection plane3and the optical-path separator4. Moreover, W2′ denotes the second light-flux width of the second light wave7that is emitted toward the second reflection plane3for the first time.

As illustrated inFIG.28, even if the optical-path separator4is located closer to the second reflection plane3than in the example configuration as illustrated inFIG.27, no dropout error occurs as long as the above conditions are met. The description or the like of each element or member of the light guide3000is omitted as the configuration or structure of these drawings is equivalent to that ofFIG.16according to the fifth embodiment of the present disclosure.

FIG.29,FIG.30, andFIG.31are diagrams each illustrating conditions for a dropout error as described above to take place, according to the present embodiment.

The dropout error16occurs as the relationships in the following two equations do not hold true.

In the above equations, W2denotes the first light-flux width of the second light wave7(see, for example,FIG.21) that is emitted toward an area28of the second reflection plane3that totally reflects the incident light for the first time, which is on a rear side in the light-guiding direction than the boundary21between the optical-path separation region10and the optical-path not-separating region9that is closest to the optical entrance8, and W2′ denotes the second light-flux width of the second light wave7that is emitted toward the second reflection plane3for the first time. Moreover, d denotes the distance between the second reflection plane3and the optical-path separator4.

The description or the like of each element or member of the light guide3000is omitted as the configuration or structure of these drawings is equivalent to that ofFIG.16according to the fifth embodiment of the present disclosure.

In the condition as illustrated inFIG.29, the conditions in regard to W2, W2′, and θ2are equivalent to the conditions in the example configuration as illustrated inFIG.27. However, the distance d between the second reflection plane3and the optical-path separator4in the condition as illustrated inFIG.29is longer than the conditions as illustrated inFIG.27. Accordingly, the relation in the following equation is met in a similar manner to the example configuration as illustrated inFIG.27.

However, the following equation holds true and one of the above equations does not hold true.

Accordingly, the dropout error16occurs where the second reflection plane3is not irradiated with the light wave7.

In the condition as illustrated inFIG.30, the conditions in regard to W2, θ2, and d are equivalent to the conditions in the example configuration as illustrated inFIG.27. However, the boundary21in the condition as illustrated inFIG.30is at a position closer to the optical entrance than in the conditions as illustrated inFIG.27. Accordingly, some of the light flux that is totally reflected first by the first reflection plane2and then and travels toward the second reflection plane3in light-guiding direction is totally reflected by optical-path separator4, and the second light-flux width W2′ is narrower than the condition as described above with reference toFIG.27. Accordingly, the relationship in the following equation is satisfied.

However, the following equation holds true and one of the above equations does not hold true.

Accordingly, the dropout error16occurs on the second reflection plane3.

In the condition as illustrated inFIG.31, the conditions in regard to W2′, θ2, and d are equivalent to the conditions in the example configuration as illustrated inFIG.27. However, the boundary21in the condition as illustrated inFIG.31is at a position further from the optical entrance than in the conditions as illustrated inFIG.27. For this reason, the first light-flux width W2is narrower than the condition as described above with reference toFIG.27.

Accordingly, the relationship in the following equation is satisfied.

However, the following equation holds true and one of the above equations does not hold true.

Accordingly, the dropout error16occurs on the second reflection plane3.

As in the example configurations as illustrated inFIG.29,FIG.30,FIG.31, when the dropout error16occurs and one of the image extraction units5is located at the position of the dropout error16,

the light cannot be taken out through that image extraction unit5, and unevenness in brightness or a dropout error of brightness occurs on a virtual image to be observed. The conditions need to be designed to prevent the dropout error16.

FIG.32andFIG.33are diagrams each illustrating the conditions for the first light wave6, which is guided between the first reflection plane2and the second reflection plane3with repeated total internal reflection at the first reflection angle θ1, not to cause any dropout error on the second reflection plane3in the light guide3000, according to the present embodiment.

The description or the like of each element or member of the light guide3000is omitted as the configuration or structure of these drawings is equivalent to that ofFIG.16according to the fifth embodiment of the present disclosure.

FIG.32andFIG.33are diagrams each illustrating the first light wave6whose entirety of light that does not meet the conditions for total reflection by the optical-path separator4and thus passes through the optical-path separator4, according to the present embodiment.

When the condition in the equation given below is satisfied, the dropout error16due to the first light wave6disappears.

In the above equation, W1denotes the third light-flux width of the first light wave6that is emitted to an area of the second reflection plane3that totally reflects the incident light for the first time. Moreover, D denotes the distance between the first reflection plane2and the second reflection plane3at an area of the second reflection plane3that totally reflects the incident light for the first time.

The above condition needs to be satisfied in order to eliminate the chances of a dropout error of brightness or unevenness in brightness due to the first light wave6under the above condition.

FIG.34is a diagram illustrating a state in which the dropout error16occurs as the light does not meet conditions for total reflection, according to a control sample of the above embodiment of the present disclosure.

The light guide3000may be configured so as to satisfy the above-described conditions for a reflection plane not to cause any dropout error. By so doing, the chances of a dropout error of brightness or unevenness in brightness on an image to be visually recognized can be reduced in both cases of the reflection angle θ1that is relatively narrow and the reflection angle θ2that is relatively wide. As the first reflection plane102and the second reflection plane103can guide both the light with a relatively wide reflection angle and the light with a relatively narrow reflection angle, the field angle of the image can be increased, and the angle of visibility of a virtual image to be observed can be widened.

Sixth Embodiment

FIG.35andFIG.36are diagrams each illustrating a part of the light guide3000in which the optical-path separator4has two layers, according to a sixth embodiment of the present disclosure.

The members of the light guide3000other than optical-path separator4are equivalent to the members in the configuration or structure according to the fifth embodiment of the present disclosure as illustrated inFIG.16, and thus its detailed description is omitted. As illustrated inFIG.35andFIG.36, the optical-path separator is divided into two layers including the optical-path separator4that is close to the first reflection plane2and the optical-path separator4that is close to the second reflection plane3, and these two layers are arranged on top of one another so as to be parallel with each other, having a certain space therebetween.

As illustrated inFIG.35, the second light wave7is totally reflected by one of the optical-path separators4that is closer to the second reflection plane3than the other optical-path separator at the second reflection angle02. As illustrated inFIG.36, a light wave whose total-reflection angle is narrower than that of the second light wave7and is wider than that of the first light wave6passes through one of the optical-path separators4that is close to the second reflection plane3, and is totally reflected by one of the optical-path separators4that is close to the first reflection plane2as the conditions for total reflection are met.

As described above, the optical-path separator4is provided in a plurality of layers in the present embodiment. Due to such a configuration, the dropout error16can be eliminated while maintaining a wide light-flux width for each angle of view. In order to provide and enable a plurality of layers of optical-path separators4, the critical angle of one of the optical-path separators4that is closer to the first reflection plane2than the other optical-path separator is reduced to have a smaller value than the other optical-path separator. The critical angle is determined based on the relation between the refractive index of the optical-path separator4and the refractive index of the light guiding unit30. For this reason, the refractive index of the optical-path separator may be reduced depending on the relative positions of the first reflection plane2and each layer of the multiple optical-path separators4so as to arrange a plurality of optical-path separators4. The conditions for such a plurality of optical-path separators are described below in detail.

It is assumed that the optical-path separator4consists of i thin films. The relation in the following formula needs to be satisfied.

In the above formula, d(m) denotes the distance between the second reflection plane3and the m-th optical-path separator4counted from the first reflection plane2, and D denotes the distance between the first reflection plane2and the second reflection plane3. Moreover, p denotes any desired natural number that is equal to or greater than one and less than i.

Moreover, the relation in the following formula needs to be satisfied.

In the above formula, n(m) denotes the refractive index of the m-th optical-path separator4. Moreover, N denotes the refractive index of the light guiding unit30.

Note also that i denotes a natural number equal to or greater than two, and m denotes a natural number equal to or greater than two but equal to or less than i. Moreover, p denotes a natural number equal to or greater than one but less than m.

FIG.37is a diagram illustrating a case in which light beams with varying angles of view are transmitted with repeated dispersion in order to display a virtual image at a short distance, according to the sixth embodiment of the present disclosure.

As illustrated inFIG.37, when both the light wave that is reflected by the second reflection plane3at the second reflection angle θ2and the light wave that is reflected by the second reflection plane3at the total-reflection angle θ2+Δθ exist in a mixed manner, some areas of the second reflection plane3may be irradiated with two or more light waves in an overlapping manner, and the intensity of irradiation increases at such areas of the second reflection plane3. When the image is formed by the parallel light that is completely collimated and the intensity of such collimated parallel light is even, the intensity of the light with which the second reflection plane3is irradiated is even. InFIG.37, reference sign25indicates an area at which light flux overlap with different light flux, and reference sign26indicates a light beam whose reflection angle on the second reflection plane3is θ2. Moreover, reference sign27indicates a light beam whose reflection angle on the second reflection plane3is θ2+Δθ. The configuration or structure of the light guide according to the present embodiment is equivalent to the configuration or structure according to the fifth embodiment of the present disclosure as illustrated inFIG.16, and thus its detailed description is omitted.

A virtual-image display device may be configured using the light guide3000according to the above embodiments of the present disclosure as described above.

As illustrated inFIG.40, such a virtual-image display device includes an image display apparatus50that outputs the image light of a displayed image, a collimator optical system51that collimates the light emitted from the image display apparatus50and emits the collimated light, and the light guide3000according to the above embodiment of the present disclosure as a virtual-image displaying optical system.

The image display apparatus50is a device that outputs the image light of a display image that forms a virtual image that is projected and displayed through the light guide3000. An organic light emitting diode (OLED) or a liquid crystal display (LCD) is preferably used for the image display apparatus50. However, no limitation is indicated thereby, and other various kinds of display element may be used for the image display apparatus50. For example, a digital micromirror device (DMD) may be used as the image display apparatus50. Alternatively, a thin film transistor (TFT) or a liquid crystal on silicon (LCoS) may be used as the image display apparatus50. Further, a micro-electromechanical system (MEMS) may be used as the image display apparatus50.

In the embodiment as illustrated inFIG.40, cases in which, for example, a liquid crystal on silicon (LCoS) and a digital micromirror device (DMD) that require a light source are used for the image display apparatus50are described, and the light source52that emits illumination light to irradiates the image display surface of the image display apparatus50with light is added. Various kinds of elements or devices may be used for the light source52, and for example, a light-emitting diode (LED), a semiconductor laser, a laser diode (LD), or a discharge lamp may be used as the light source52.

The collimator optical system51is configured by, for example, a plurality of optical lenses or stops, and magnifies the light that is output from the image display apparatus50and ejects collimated light.

According to such a virtual-image display device, the light that is formed by the image display apparatus50as emitted from the light source52is magnified by the collimator optical system51, and is incident on the light guide3000. In other words, the light that is magnified by the collimator optical system51is incident on the optical entrance8of the light guide3000, and is guided to the inside of the light guide3000as reflected by the mirror1. As described above as the configuration according to the fifth embodiment of the present application, the light is further guided to the light beam ejection unit40. Then, the guided light is ejected from the light beam ejection unit40toward the eyes of a user as image data. Due to this configuration, a user of the virtual-image display device can visually recognize a virtual image by looking at the sight ahead of the light guide3000through the light beam ejection unit40of the light guide3000.

In the embodiments of the present disclosure as described above with reference toFIG.16toFIG.40, cases in which the optical entrance8of the light guide3000is arranged on the left side of an observer who observes a virtual image and the light is incident on the light guide3000from the left side of the observer who observes a virtual image are described. Even if the arrangement or structure as described above is reversed in the right and left directions, i.e., even if the optical entrance8of the light guide3000is arranged on the right side of an observer who observes a virtual image and the light is incident on the light guide3000from the right side of the observer who observes a virtual image, advantageous effects similar to those of the above embodiments of the present disclosure can be achieved.

FIG.41A,FIG.41B, andFIG.41Care diagrams each illustrating a cases in which the light guide3000according to the fifth embodiment of the present disclosure is used for a virtual-image display device configured like glasses, i.e., a head-mounted display (HMD), according to an embodiment of the present disclosure.

More specifically,FIG.41Ais a diagram illustrating a case in which a single light guide3000is used for a head-mounted display (HMD) for both eyes, and the optical entrance8of the light guide3000is arranged on the right side of a user that is an observer who observes a virtual image. The light guide3000according to the present embodiment is fixed to a pair of frames410that serves as a sidepiece of the glasses hung on the ears of the user. InFIG.41A,FIG.41B, andFIG.41C, the pair of frames410are illustrated in a simplified manner. However, no limitation is indicated thereby, and it is not always necessary for the pair of frames410to be arranged on both sides of the light guide3000. The pair of frames400may be shaped as a single unit to cover the edge on the topside or bottom side of the light guide3000.

By contrast,FIG.41BandFIG.41Care diagrams each illustrating an embodiment in which a single light guide3000is downsized and is used for a head-mounted display (HMD) for a single eye. More specifically,FIG.41Bis a diagram illustrating a case in which a pair of light guides3000are arranged so as to be suited for both right and left eyes of the user, and the optical entrance8of each one of the light guides3000is arranged at an extraneous portion on both right and left sides.

InFIG.41A,FIG.41B, andFIG.41C, the illustration of a virtual image optical system or a light source is omitted. However, such elements may be attached to the pair of frames400. In other words, in the embodiments as illustrated inFIG.41AandFIG.41C, the light source52, the image display apparatus50, and the collimator optical system51may be attached to one of the pair of frames410on the right eye side. In the embodiment as illustrated inFIG.41B, the light source52, the image display apparatus50, and the collimator optical system51may be attached to the pair of frames400on both right and left sides.

In the embodiments as illustrated inFIG.41A,FIG.41B,FIG.41C, cases in which the light guide3000according to the fifth embodiment of the present disclosure is used for a HMD configured like glasses are described as above. Note that the light guide4000according to the above modification of the fifth embodiment of the present disclosure may also be used for a HMD configured like glasses. The light guide3000according to the above embodiments of the present disclosure may be used for other kinds of HMDs, and may further be used for a heads-up display (HUD). In particular, the light guide3000according to the above embodiments of the present disclosure is suited to display a virtual image of the original image that is formed by the light flux that are optically modulated by a minute devices.

As described above, the light guide3000according to the embodiments of the present disclosure may be fitted to a human face like glasses. If the light that is emitted from, for example, an image display element is collimated and is made incident on the optical entrance8, as described above, the image that is formed by, for example, the image display element can be observed as a virtual image. As the light guide3000according to the above embodiments of the present disclosure has a transparent body, the scene around the image can be observed together with the image.

This patent application is based on and claims priority to Japanese Patent Application Nos. 2020-007085 and 2020-050321, filed on Jan. 20, 2020, and Mar. 19, 2020, respectively, in the Japan Patent Office, the entire disclosures of which are hereby incorporated by reference herein.

REFERENCE SIGNS LIST