WO2023044660A1

WO2023044660A1 - Image projection device and retinal projection method

Info

Publication number: WO2023044660A1
Application number: PCT/CN2021/119868
Authority: WO
Inventors: Tatsuya Nakatsuji
Original assignee: Guangdong Oppo Mobile Telecommunications Corp., Ltd.
Priority date: 2021-09-23
Filing date: 2021-09-23
Publication date: 2023-03-30
Also published as: CN117693788A

Abstract

There is provided an image projection device that may easily enlarge an eye-box. The image projection device according to one aspect of the present invention includes a light source and an optical system. The light source is configured to be able to project light. The optical system may transmit outside light from an outside world. The optical system may reflect the light from the light source. The optical system concentrates the light in a vicinity of a pupil of an eyeball of a user to project an image created according to the light from the light source on a retina of the eyeball.

Description

IMAGE PROJECTION DEVICE AND RETINAL PROJECTION METHOD

TECHNICAL FIELD

The present invention relates to an image projection device and a retinal projection method.

BACKGROUND

An image projection device using a retinal projection method has been known as an image projection device for realizing AR (augmented reality) (e.g., see Patent literature 1) . In the image projection device using a retinal projection method, an optical system may transmit light from the outside world. Along with that, the optical system may reflect light from a light source and concentrate the light in a vicinity of a pupil of an eyeball of a user to project an image created according to the light from the light source on a retina of the eyeball. As a result, the user may easily visually recognize a clear AR image.

SUMMARY

[Problem to be Solved by the Invention]

However, because the image projection device using a retinal projection method concentrates the light from the light source in the vicinity of the pupil of the eyeball of the user, there is a possibility that the user cannot see the AR image when the user moves the eyeball. In other words, a range (eye-box) in which an AR image may be visually recognized within the eyeball of the user may be narrow.

The present invention has been made in view of the above problem, and an object of the invention is to provide an image projection device that may easily enlarge an eye-box.

[Means for Solving Problem]

To solve the problem described above and achieve the object, an image projection device according to one aspect of the present invention includes a light source and an optical system. The light source is configured to be able to project light. The optical system is configured to be able to transmit outside light from an outside world. The optical system is configured to be able to reflect the light from the light source. The optical system concentrates the light in a vicinity of a pupil of an eyeball of a user to project an image created according to the light from the light source on a retina of the eyeball.

[Effect of the Invention]

According to one aspect of the present invention, it is possible to easily enlarge an eye-box.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram illustrating a schematic configuration of an image projection device according to an embodiment;

FIG. 2 is a diagram illustrating a configuration of an optical element group according to the embodiment;

FIG. 3 is a diagram illustrating a characteristic of an optical element according to the embodiment;

FIG. 4 is a diagram illustrating an arrangement of a plurality of optical elements according to the embodiment;

FIG. 5 is a diagram illustrating an operation of the plurality of optical elements according to the embodiment;

FIG. 6 is a diagram illustrating an operation of the plurality of optical elements according to the embodiment;

FIG. 7 is a diagram illustrating an operation of the plurality of optical elements according to the embodiment;

FIG. 8 is a diagram illustrating a configuration of an optical element group according to a first modification example of the embodiment;

FIG. 9 is a diagram illustrating a configuration of an optical element group according to a second modification example of the embodiment;

FIG. 10 is a diagram illustrating a configuration of an optical element group according to a third modification example of the embodiment; and

FIG. 11 is a diagram illustrating a configuration of an optical element group according to a fourth modification example of the embodiment.

DETAILED DESCRIPTION

Hereinafter, an embodiment of an image projection device will be described in detail with reference to the accompanying drawings.

Embodiment

An image projection device according to the embodiment is an image projection device such as AR glasses for realizing AR (augmented reality) . The image projection device causes a user wearing the image projection device to visually recognize an image obtained by superimposing an AR image on a real image of the outside world. An image projection device using the retinal projection method has been known as an image projection device for realizing AR. In the image projection device, an optical system may transmit light from the outside world. Along with that, the optical system may reflect light from a light source and concentrate the light in a vicinity of a pupil of an eyeball of the user to project an image created according to the light from the light source on a retina of the eyeball. As a result, the user may easily visually recognize a clear AR image. Moreover, because the image projection device using a retinal projection method may project the image created according to the light from the light source on the retina of the eyeball, it is possible to suppress the number of reflections in the optical system and to easily secure the brightness of the image. As a result, the user may easily visually recognize a clear AR image out of doors.

However, because the image projection device using a retinal projection method concentrates the light from the light source in the vicinity of the pupil of the eyeball of the user, there is a possibility that the user cannot see the AR image when the user moves the eyeball. In other words, a range (eye-box) in which an AR image may be visually recognized on the eyeball of the user may be narrow.

In contrast, in the image projection device using a retinal projection method, a technology (first technology) of detecting a movement of the pupil position in the eyeball of the user and changing an incident angle of light incident on the eyeball of the user in accordance with the detected movement to aim at enlarging an eye-box may be considered. The first technology is a technology of irradiating detection light at a position to be a white portion of the eyeball of the user and measuring the intensity of the reflected light to detect a movement of the pupil position in the eyeball and then moving the light source for AR image by using an actuator in an opposite direction to the movement of the pupil position to change an incident angle of light incident on the eyeball of the user. Because a light source for detection light, an optical system for detection light, a detection light measuring instrument, an actuator for the light source, and the like are provided in addition to a light source for AR image and an optical system for AR image, the first technology easily results in complicating a hardware configuration. Moreover, because a movement of the eyeball position is calculated and the optical system is controlled to cancel the influence of the calculated movement, the first technology easily results in complicating a software configuration. In other words, the first technology easily increases costs due to the complexity of hardware and software configurations.

Moreover, because the first technology changes an incident angle of light incident on the eyeball of the user in accordance with the movement of the pupil position, an AR image moves around on a real image in accordance with the movement of the eyeball when being observed by the user. For this reason, a predetermined observation target in the real image may be overlapped by the AR image and be hard to be visually recognized by the user. In other words, the first technology is easy to deteriorate convenience when realizing AR.

Therefore, in the present embodiment, the image projection device using a retinal projection method includes multiplexed optical elements for reflecting light from a light source, which may make it possible to enlarge an eye-box while suppressing the complexity of hardware and software configurations.

Specifically, the optical system of the image projection device includes a plurality of optical elements. The plurality of optical elements are located separately from each other in a first direction. The first direction is a direction along an optical axis of transmitted light. The plurality of optical elements are located at positions shifted each other in the first direction so as to intersect with the optical axis of the transmitted light. The plurality of optical elements concentrate the light from the light source at a plurality of concentrating points. The plurality of concentrating points are located at positions shifted each other in a second direction. The second direction is a direction intersecting with the optical axis of the transmitted light. One of the plurality of concentrating points may be located in a vicinity of the optical axis of the transmitted light. The optical characteristics of the plurality of optical elements may be adjusted so that the plurality of concentrating points are located in a vicinity of a first plane. The first plane is a plane that passes through the pupil and is perpendicular to the optical axis of the transmitted light. For example, when the user is wearing the image projection device, the image projection device may have a configuration that one concentrating point is located in a vicinity of the pupil when the pupil of the eyeball of the user is located at a front position and another concentrating point is located in the vicinity of the pupil when the pupil of the eyeball of the user is moved from the front position to a predetermined side. In other words, by employing the multiplexed optical elements for reflecting the light from the light source, the light from the light source may be concentrated in the vicinity of the pupil even when the pupil of the eyeball of the user is moved. As a result, an eye-box may be enlarged while suppressing the complexity of hardware and software configurations of the image projection device. Moreover, by appropriately designing the optical characteristics of the optical elements to concentrate light in the vicinity of the first plane passing through the pupil, incident angles of light incident on the eyeball of the user may be substantially equalized even when the pupil position is moved. As a result, even when the eyeball is moved when being observed by the user, the movement of the AR image on the real image may be suppressed and thus convenience when realizing AR may be improved.

More specifically, an image projection device 1 may be configured as illustrated in FIG. 1. FIG. 1 is a diagram illustrating a schematic configuration of the image projection device 1.

The image projection device 1 includes a controller 10, a light source 20, and an optical system 30. The optical system 30 may transmit light from the outside world. In FIG. 1, an optical axis PA of transmitted light is illustrated with a dashed-dotted line. In FIG. 1, a direction along the optical axis PA is set to an X direction, and two directions orthogonal to each other in a plane perpendicular to the X direction are set to Y and Z directions. The optical system 30 includes a lens 31, a mirror 32, a mirror 33, a scanning drive unit 34, and an optical element group 35.

The controller 10 is connected to the light source 20 and the scanning drive unit 34 to be able to communicate with them, and may control the light source 20 and the scanning drive unit 34.

The light source 20 generates light to be projected on a retina 101 of an eyeball 100 of a user via the optical system 30. The light source 20 generates light having directivity. The light source 20 includes a laser oscillator such as a laser diode to generate a monochromatic laser beam. For example, the light source 20 may generate a red laser beam, may generate a green laser beam, or may generate a blue laser beam. The light source 20 emits the generated laser beam.

The optical system 30 may transmit light from the outside world, and also may reflect light from the light source 20 and concentrate the light in a vicinity of a pupil 103 (see FIG. 2) of the eyeball 100 of the user to project an image created according to the light from the light source 20 on the retina 101 of the eyeball 100. As a result, the user may visually recognize an image obtained by superimposing an AR image on a real image of the outside world.

In the optical system 30, the lens 31, the mirror 32, the mirror 33, and the optical element group 35 are sequentially arranged along and on the optical axis of the light from the light source 20. The lens 31 is, for example, a collimator lens. The light from the light source 20 is adjusted to collimated light by the lens 31, is reflected by the mirror 32, and is guided to the mirror 33. The mirror 33 may be rotatably driven by the scanning drive unit 34 in rotation directions around the Z-axis and the Y-axis. The mirror 33 is, for example, a micro-electromechanical system (MEMS) mirror. The controller 10 controls an angle of the mirror 33 via the scanning drive unit 34 to scan light, which is reflected by the mirror 33 and guided to the optical element group 35, in the Y and Z directions as illustrated by dashed-dotted line arrows in FIG. 1. When the description is made for the Y direction, the optical element group 35 includes an optical element (first optical element) HOE_A, an optical element (second optical element) HOE_B, and an optical element (third optical element) HOE_C. The controller 10 controls the mirror 33 at an angle illustrated by a solid line in FIG. 1 to irradiate the light on the plus Y-side ends of the dashed-dotted line arrows in the optical elements HOE_A, HOE_B, and HOE_C. The controller 10 also controls the mirror 33 at an angle illustrated by a dotted line in FIG. 1 to irradiate the light on the minus Y-side ends of the dashed-dotted line arrows in the optical elements HOE_A, HOE_B, and HOE_C. As a result, the light from the light source 20 may be reflected by the optical element group 35 while being scanned in the optical element group 35 and the reflected light may be concentrated in the vicinity of the pupil 103 of the eyeball 100 of the user to project an AR image on the retina 101.

The optical element group 35 may be configured as illustrated in FIG. 2. FIG. 2 is a diagram illustrating a configuration of the optical element group 35.

In the optical element group 35, the optical elements HOE_A, HOE_B, and HOE_C respectively extend in a flat plate shape in the Y and Z directions. The optical elements HOE_A, HOE_B, and HOE_C are located separately from each other in the X direction. The optical element HOE_C is located on the opposite side of the optical element HOE_A while placing the optical element HOE_B therebetween in the X direction. The optical element HOE_A intersects with the optical axis PA of the transmitted light. The optical element HOE_B intersects with the optical axis PA of the transmitted light at a position shifted to the minus X side from the optical element HOE_A. The optical element HOE_C intersects with the optical axis PA of the transmitted light at a position shifted to the minus X side from the optical element HOE_B.

The optical element HOE_A concentrates the light from the light source 20 at a concentrating point (first concentrating point) FP_A, the optical element HOE_B concentrates the light from the light source 20 at a concentrating point (second concentrating point) FP_B, and the optical element HOE_C concentrates the light from the light source 20 at a concentrating point (third concentrating point) FP_C. The concentrating point FP_C is located on the opposite side of the concentrating point FP_A while placing the concentrating point FP_B therebetween in the Y direction. The concentrating point FP_B may be located in the vicinity of the optical axis PA of the transmitted light.

The optical characteristics of the optical elements HOE_A, HOE_B, and HOE_C may be substantially equal to each other. The phrases “optical characteristics of the optical elements are substantially equal” may include that differences of focal lengths of optical elements fall within range smaller than the X-width of a pupillary portion 102. The optical elements HOE_A, HOE_B, and HOE_C are, for example, a holographic optical element (HOE) , respectively. Each of the optical elements HOE_A, HOE_B, and HOE_C is configured to have an optical characteristic illustrated in (a) of FIG. 3 with respect to light of a wavelength range Δλ ₁ having a spectral peak at wavelengths near λ ₁. Herein, (a) of FIG. 3 illustrates the optical characteristics of the optical elements HOE_A, HOE_B, and HOE_C. In the optical elements HOE_A, HOE_B, and HOE_C, incident surfaces of the light from the light source 20 extend in the Y and Z directions, and their normal directions are the X direction. It is assumed that, with respect to the plus X direction, an angle in a clockwise rotation direction around the Z-axis in the XY plane is a plus angle.

As illustrated in (a) of FIG. 3, each of the optical elements HOE_A, HOE_B, and HOE_C is configured to have a peak of a reflection (diffraction) spectrum near a wavelength of λ ₁ with respect to the light of the wavelength range Δλ ₁. For example, with respect to light having a spectral peak near the wavelength of λ ₁, a first-order diffraction angle is θ _r1 when an incident angle is θ _i1, a first-order diffraction angle is θ _r2 when an incident angle is θ _i2, and a first-order diffraction angle is θ _r3 when an incident angle is θ _i3. When the three incident angles θ _i1, θ _i2, and θ _i3 satisfy Formula (1) , Formula (2) is established if the first-order diffraction angle θ _r2 substantially corresponds to a normal direction. Moreover, if an angle difference between the two incident angles θ _i1 and θ _i2 and an angle difference between the two incident angles θ _i2 and θ _i3 are substantially equal to each other, Formula (3) is established.

θ _i1 > θ _i2 > θ _i3 (1)

θ _r2 ≈ 0 (2)

θ _r3 ≈ -θ _r1 (3)

For example, in the case of λ ₁ = 532 nm, Δλ ₁ = 450-650 nm, θ _i1 = 49.7 degrees, θ _i2 = 52.5 degrees, and θ _i3 = 55 degrees, the diffraction angles are θ _r1 = 12.9 degrees, θ _r2 = 0 degrees, and θ _r3 = -12.9 degrees. Moreover, each of the optical elements HOE_A, HOE_B, and HOE_C may have an intensity ratio 1: 1 between the zero-order transmitted light and the first-order diffracted light.

At this time, when a scanning range of light in the optical element HOE_B has the width of 2W in the Y direction, the optical element HOE_B is arranged to be located separately by a distance L indicated by Formula (4) to the minus X side from the pupillary portion 102 of the eyeball 100 as illustrated in (b) of FIG. 3. As a result, the light reflected by the optical element HOE_B may be concentrated so that the concentrating point FP_B is located near the pupil 103 when the pupil 103 of the eyeball 100 of the user is located at a front position.

L = W / (tan θ _r1) (4)

Herein, the pupillary portion 102 of the eyeball 100 of the user includes the pupil 103 and an iris 104. It should be noted that the size of the pupil 103 may be changed depending on an opening degree of the iris 104 in the pupillary portion 102 of the eyeball 100 of the user as illustrated in FIG. 2. If the brightness of the transmitted light from the outside world is high, the opening degree of the iris 104 becomes small and the diameter of the pupil 103 becomes small. If the brightness of the transmitted light from the outside world is low, the opening degree of the iris 104 becomes large and the diameter of the pupil 103 becomes large.

Assuming that an interval between the optical element HOE_A and the optical element HOE_B in the X direction is "d" and an interval between the optical element HOE_B and the optical element HOE_C in the X direction is "d'" , Formula (5) is established.

L >> d, L >> d' (5)

If the optical characteristics of the optical elements HOE_A, HOE_B, and HOE_C are the characteristics as illustrated in (b) of FIG. 3, the concentrating point FP_B is located with shifted at the minus Y side from the concentrating point FP_A as illustrated in FIG. 2. The concentrating point FP_C is located with shifted at the minus Y side from the concentrating point FP_B. If Formula (6) is established, a distance between the concentrating point FP_A and the concentrating point FP_B in the Y direction and a distance between the concentrating point FP_B and the concentrating point FP_C in the Y direction may be substantially equalized. Phrases “distances of concentrating points are substantially equalized” may include that differences of Y-locations of concentrating points fall within the range with smaller Y-width than the radius of the pupillary portion 102.

d ≈ d' (6)

Formula (6) indicates the interval d and the interval d’ may be substantially equalized. Phrases “intervals of optical elements are substantially equalized” may include that difference of intervals of optical elements fall within the range of machining tolerance. For example, the interval d between the optical element HOE_A and the optical element HOE_B in the X direction may be defined as illustrated in FIG. 4. FIG. 4 is a diagram illustrating an arrangement of the plurality of optical elements HOE_A, HOE_B, and HOE_C. FIG. 4 is a diagram schematically illustrating a case where the eyeball 100 of the user brings the line of sight on the edge of an image with a viewing angle 2δ.

It is assumed that the diameter of the eyeball 100 of the user is

Because the diameter of an eyeball of an adult is generally said to be 24 mm, φ is 24 mm, for example. An incident angle of the light from the light source 20 onto the optical element HOE_A is defined as θ _i, a first-order diffraction angle is defined as θ _r, and an angle incident on the pupil 103 corresponding to a half angle of view of an image is defined as δ. Assuming that a movement amount of the eyeball 100 to the edge of the angle of view is "D _i" , the movement amount D _i is calculated by Formula (7) and the interval d is calculated by Formula (8) .

Herein, if the optical axis PA of the transmitted light corresponds to the front position of the eyeball and an incident surface of the light from the light source 20 in the optical element

HOE_A is perpendicular to the optical axis PA, Formula (9) is established.

δ = θ _r (9)

The diameter of the pupil 103 (see FIG. 2) is generally said to be 2 mm to 8 mm. Even when the diameter of the pupil 103 becomes small in a situation where the brightness of the outside world is dazzling, a condition that the light from the light source 20 enters the pupil 103 when the eyeball is moved is provided by Formula (10) with using Formula (7) .

When substituting

in Formula (10) , Formula (11) is derived.

δ > 4.78 [°] (11)

By means of a formula obtained by assigning

and θ _i = 49.7 [°] in Formula (8) , Formula (11) is converted to Formula (12) as follows.

d > 0.8 [mm] (12)

In other words, if the interval d between the optical element HOE_A and the optical element HOE_B in the X direction is secured to satisfy Formula (12) , the light from the light source 20 may enter the pupil 103 when the eyeball is moved even when the diameter of the pupil 103 becomes small in a situation where the brightness of the outside world is dazzling.

Similarly, Formula (13) is derived by Formulae (6) and (12) .

d'> 0.8 [mm] (13)

In other words, if the interval d' between the optical element HOE_B and the optical element HOE_C in the X direction is secured to satisfy Formula (13) , the light from the light source 20 may enter the pupil 103 when the eyeball is moved even when the diameter of the pupil 103 becomes small in a situation where the brightness of the outside world is dazzling.

For example, when the user is wearing the image projection device 1, the concentrating point FP_B of the optical element HOE_B is mainly located in the vicinity of the pupil 103 as illustrated in FIG. 5 when the pupil 103 of the eyeball 100 of the user is located at the front position. The user visually recognizes a real image IM2 of the outside world through the optical elements HOE_A to HOE_C. Along with that, the light from the light source 20 is reflected by the optical element HOE_B and is concentrated at the concentrating point FP_B to be projected on the retina 101 as an AR image. As a result, the user visually recognizes an AR image IM1 on a minus-X-side extended line with respect to an optical path between the concentrating point FP_B and the optical element HOE_B, as depicted in FIG. 5. In other words, the image projection device 1 causes the user to visually recognize an image obtained by superimposing the AR image IM1 on the real image IM2 of the outside world.

It is assumed that the pupil 103 of the eyeball 100 of the user is moved to the plus Y side from the front position in the state of FIG. 5. At this time, as illustrated in FIG. 6, the concentrating point FP_A of the optical element HOE_A is mainly located in the vicinity of the pupil 103. The user visually recognizes the real image IM2 of the outside world through the optical elements HOE_A to HOE_C. Along with that, the light from the light source 20 is reflected by the optical element HOE_A and is concentrated at the concentrating point FP_A to be projected on the retina 101 as the AR image. As a result, the user visually recognizes the AR image IM1 on a minus-X-side extended line with respect to an optical path between the concentrating point FP_A and the optical element HOE_A. In other words, the image projection device 1 causes the user to visually recognize an image obtained by superimposing the AR image IM1 on the real image IM2 of the outside world.

It is assumed that the pupil 103 of the eyeball 100 of the user is moved to the minus Y side from the front position in the state of FIG. 5. At this time, as illustrated in FIG. 7, the concentrating point FP_C of the optical element HOE_C is mainly located in the vicinity of the pupil 103. The user visually recognizes the real image IM2 of the outside world through the optical elements HOE_A to HOE_C. Along with that, the light from the light source 20 is reflected by the optical element HOE_C and is concentrated at the concentrating point FP_C to be projected on the retina 101 as the AR image. As a result, the user visually recognizes the AR image IM1 on a minus-X-side extended line with respect to an optical path between the concentrating point FP_C and the optical element HOE_C. In other words, the image projection device 1 causes the user to visually recognize an image obtained by superimposing the AR image IM1 on the real image IM2 of the outside world.

As illustrated in FIGS. 5 to 7, by multiplexing the optical elements HOE_A to HOE_C to reflect the light from the light source 20, the light from the light source 20 may be concentrated in the vicinity of the pupil 103 even when the pupil 103 of the eyeball 100 of the user is moved. In other words, an eye-box may be enlarged while suppressing the complexity of hardware and software configurations of the image projection device 1.

Moreover, as illustrated in FIGS. 5 to 7, if the optical characteristics of the multiplexed optical elements HOE_A to HOE_C are designed so that the light is concentrated on the same plane perpendicular to the optical axis PA at the position in the vicinity of the pupil, incident angles of light incident on the eyeball of the user may be substantially equalized even when the position of the pupil 103 is moved. As a result, when the observation by the user is conducted, a relative position between the AR image IM1 and the real image IM2 may be almost unchanged as illustrated in FIGS. 5 to 7 even when the eyeball 100 is moved. In other words, the movement of the AR image IM1 on the real image IM2 may be suppressed and thus convenience when realizing AR may be improved.

As described above, in the present embodiment, the image projection device 1 using a retinal projection method includes the multiplexed optical elements HOE_A to HOE_C for reflecting the light from the light source 20. As a result, an eye-box may be enlarged while suppressing the complexity of hardware and software configurations.

It should be noted that, when Formula (5) is established, the plurality of concentrating points FP_A to FP_C may be located in the vicinity of the pupil and the light may be concentrated in the vicinity of the same plane perpendicular to the optical axis PA by arranging the plurality of optical elements HOE_A to HOE_C having substantially equal optical characteristics along the optical axis PA, but the optical characteristics of the plurality of optical elements HOE_A to HOE_C may be adjusted so as to be concentrated in the vicinity of the same plane. For example, when the optical characteristic of the optical element HOE_B has the characteristic illustrated in FIG. 3, the optical characteristic of the optical element HOE_A is adjusted to satisfy Formula (14) .

L -d = W _A / (tan θ _r1') (14)

In Formula (14) , “L -d” is an X-direction distance from the X position of the optical element HOE_A to the X position of the pupil. Moreover, W _A indicates a scanning range 2W _A of light in the Y direction in the optical element HOE_A, and Formula (15) is established.

2W _A = 2W + d (tan θ _i1 -tan θ _r3) (15)

A first-order diffraction angle θ _r1' is an angle slightly larger than the first-order diffraction angle θ _r1. Similarly, the optical characteristic of the optical element HOE_C is adjusted to satisfy Formula (16) .

L + d'= W _C / (tan θ _r1" ) (16)

In Formula (16) , “L + d'” is an X-direction distance from the X position of the optical element HOE_C to the X position of the pupil. Moreover, W _C indicates a scanning range 2W _C of light in the Y direction in the optical element HOE_C, and Formula (17) is established.

2W _C = 2W -d (tan θ _i1 + tan θ _r3) (17)

A first-order diffraction angle θ _r1" is an angle slightly smaller than the first-order diffraction angle θ _r1. As a result, regardless of whether Formula (5) is established, the plurality of optical elements HOE_A to HOE_C may be arranged so as to be concentrated in the vicinity of the same plane.

Moreover, each of the optical elements HOE_A to HOE_C in the optical element group 35 may be a stacked-type holographic optical element in which holograms having the recorded interference fringe patterns are stacked. Each interference fringe pattern to be recorded corresponds to the wavelength of light to be reflected. Alternatively, each of the optical elements HOE_A to HOE_C in the optical element group 35 may be a multiply-exposed-type holographic optical element in which a plurality of interference fringe patterns are multiply-exposed and recorded on a single photosensitive material. Each interference fringe pattern to be multiply-exposed corresponds to the wavelength of light to be reflected.

Alternatively, the optical element group 35 may include a plurality of optical elements DOE_A to DOE_C instead of the plurality of optical elements HOE_A to HOE_C. Each of the optical element (first optical element) DOE_A, the optical element (second optical element) DOE_B, and the optical element (third optical element) DOE_C is a diffractive optical element (DOE) in which a diffraction grating structure such as periodic unevenness is formed on the surface of a light-transmissive member (e.g., quartz plate, glass plate) . A spatial period such as unevenness in the diffraction grating structure corresponds to the wavelength of light to be reflected. Also in this case, the light from the light source 20 may be reflected by the optical element group 35 while being scanned in the optical element group 35 and the reflected light may be concentrated in the vicinity of the pupil 103 of the eyeball 100 of the user to project an AR image on the retina 101.

Alternatively, the optical element group 35 may include a plurality of optical elements ROE_A to ROE_C instead of the plurality of optical elements HOE_A to HOE_C. Each of the optical element (first optical element) ROE_A, the optical element (second optical element) ROE_B, and the optical element (third optical element) ROE_C is a semi-transmissive-type reflective optical element (ROE) having a concave reflecting surface on the eyeball 100 side. The semi-transmissive-type reflective optical element is also referred to as a half mirror. Also in this case, the light from the light source 20 may be reflected by the optical element group 35 while being scanned in the optical element group 35 and the reflected light may be concentrated in the vicinity of the pupil 103 of the eyeball 100 of the user to project an AR image on the retina 101.

Moreover, the image projection device 1 may be configured to correspond to multi-colored (e.g., full color) AR image. The light source 20 may generate multi-colored light. For example, the light source 20 includes a first laser oscillator, a second laser oscillator, a third laser oscillator, and an optical multiplexer. The first laser oscillator generates a first-color (e.g., red) laser beam. The first-color laser beam is light having a spectral peak at wavelengths near 630 nm, for example. The second laser oscillator generates a second-color (e.g., green) laser beam. The second-color laser beam is light having a spectral peak at wavelengths near 530 nm, for example. The third laser oscillator generates a third-color (e.g., blue) laser beam. The third-color laser beam is light having a spectral peak at wavelengths near 440 nm, for example. The optical multiplexer multiplexes the first-color laser beam, the second-color laser beam, and the third-color laser beam to generate a synthetic-color (e.g., white) laser beam. The light source 20 emits the synthetic-color laser beam.

At this time, the optical element group 35 may be configured to correspond to multi-colored light. When each optical element included in the optical element group 35 is a diffractive optical element (DOE) , for example, it is difficult to create an optical element DOE corresponding to a plurality of wavelengths, due to wavelength selectivity. For this reason, an optical element group is made by stacking multiple optical elements DOE each corresponding to a single wavelength with the number of elements corresponding to multiple colors. The optical element group 35 may be configured as illustrated in FIG. 8. FIG. 8 is a diagram illustrating a configuration of the optical element group 35 according to a first modification example of the embodiment.

The optical element group 35 includes a plurality of

optical element groups

35A, 35B, and 35C, instead of the plurality of optical elements HOE_A, HOE_B, and HOE_C (see FIG. 2) . The optical element group 35A is arranged at a position corresponding to the optical element HOE_A. The optical element group 35A includes an optical element (first optical element) DOE_A_B, an optical element (first optical element) DOE_A_R, and an optical element (first optical element) DOE_A_G, which are stacked in order from the plus X side to the minus X side. In FIG. 8, the optical element DOE_A_B is illustrated with a two-dot chain line, the optical element DOE_A_R is illustrated with a solid line, and the optical element DOE_A_G is illustrated with a dashed-dotted line. The optical elements DOE_A_B, DOE_A_R, and DOE_A_G respectively extend in a flat plate shape in the Y and Z directions. The optical element DOE_A_B is a diffractive optical element (DOE) for a B (blue) wavelength, and has a diffraction grating structure such as unevenness on its surface with a period corresponding to the B (blue) wavelength. The optical element DOE_A_R is a diffractive optical element (DOE) for an R (red) wavelength, and has a diffraction grating structure such as unevenness on its surface with a period corresponding to the R (red) wavelength. The optical element DOE_A_G is a diffractive optical element (DOE) for a G (green) wavelength, and has a diffraction grating structure such as unevenness on its surface with a period corresponding to the G (green) wavelength.

Each of the optical elements DOE_A_B, DOE_A_R, and DOE_A_G corresponds to a single wavelength. The optical element DOE_A_B concentrates a B (blue) wavelength component of synthetic-color light from the light source 20 at the concentrating point FP_A. The optical element DOE_A_R concentrates an R (red) wavelength component of the synthetic-color light from the light source 20 at the concentrating point FP_A. The optical element DOE_A_G concentrates a G (green) wavelength component of the synthetic-color light from the light source 20 at the concentrating point FP_A.

Similarly, the optical element group 35B is arranged at a position corresponding to the optical element HOE_B. The optical element group 35B includes an optical element (second optical element) DOE_B_B, an optical element (second optical element) DOE_B_R, and an optical element (second optical element) DOE_B_G, which are stacked in order from the plus X side to the minus X side. The optical elements DOE_B_B, DOE_B_R, and DOE_B_G extend in a flat plate shape in the Y and Z directions. Each of the optical elements DOE_B_B, DOE_B_R, and DOE_B_G corresponds to a single wavelength. The optical element DOE_B_B concentrates the B (blue) wavelength component of the synthetic-color light from the light source 20 at the concentrating point FP_B. The optical element DOE_B_R concentrates the R (red) wavelength component of the synthetic-color light from the light source 20 at the concentrating point FP_B. The optical element DOE_B_G concentrates the G (green) wavelength component of the synthetic-color light from the light source 20 at the concentrating point FP_B.

The optical element group 35C is arranged at a position corresponding to the optical element HOE_C. The optical element group 35C includes an optical element (third optical element) DOE_C_B, an optical element (third optical element) DOE_C_R, and an optical element (third optical element) DOE_C_G, which are stacked in order from the plus X side to the minus X side. The optical elements DOE_C_B, DOE_C_R, and DOE_C_G respectively extend in a flat plate shape in the Y and Z directions. Each of the optical elements DOE_C_B, DOE_C_R, and DOE_C_G corresponds to a single wavelength. The optical element DOE_C_B concentrates the B (blue) wavelength component of the synthetic-color light from the light source 20 at the concentrating point FP_C. The optical element DOE_C_R concentrates the R (red) wavelength component of the synthetic-color light from the light source 20 at the concentrating point FP_C. The optical element DOE_C_G concentrates the G (green) wavelength component of the synthetic-color light from the light source 20 at the concentrating point FP_C.

As a result, the light from the light source 20 may be reflected by the optical element group 35 while being scanned in the optical element group 35 and the reflected light may be concentrated near the pupil 103 of the eyeball 100 of the user to project a multi-colored (e.g., full color) AR image on the retina 101.

In this way, the optical elements DOE_A_B, DOE_A_R, DOE_A_G to DOE_C_B, DOE_C_R, DOE_C_G for reflecting multi-colored light from the light source 20 are multiplexed in the image projection device 1 using a retinal projection method. As a result, an eye-box may be enlarged with respect to multi-colored (e.g., full color) light while suppressing the complexity of hardware and software configurations.

Alternatively, when each optical element included in the optical element group 35 is a holographic optical element (HOE) , for example, it is possible to create the optical element HOE corresponding to the plurality of wavelengths. For this reason, one optical element HOE is configured to correspond to the plurality of colors. The optical element group 35 may be configured as illustrated in FIG. 9. FIG. 9 is a diagram illustrating a configuration of the optical element group 35 according to a second modification example of the embodiment.

The optical element group 35 includes a plurality of optical elements HOE_A', HOE_B', and HOE_C' instead of the plurality of optical elements HOE_A, HOE_B, and HOE_C (see FIG. 2) . The optical element (first optical element) HOE_A' is arranged at a position corresponding to the optical element HOE_A, and extends in a flat plate shape in the Y and Z directions. The optical element HOE_A' is a stacked-type or multiply-exposed-type holographic optical element, and includes an interference fringe pattern for a B (blue) wavelength, an interference fringe pattern for an R (red) wavelength, and an interference fringe pattern for a G (green) wavelength.

The optical element HOE_A' corresponds to a plurality (e.g., three) of wavelengths. The optical element HOE_A' concentrates a B (blue) wavelength component of synthetic-color light from the light source 20 at the concentrating point FP_A. The optical element HOE_A' concentrates an R (red) wavelength component of the synthetic-color light from the light source 20 at the concentrating point FP_A. The optical element HOE_A' concentrates a G (green) wavelength component of the synthetic-color light from the light source 20 at the concentrating point FP_A.

Similarly, the optical element (second optical element) HOE_B' is arranged at a position corresponding to the optical element HOE_B, and extends in a flat plate shape in the Y and Z directions. The optical element HOE_B' is a stacked-type or multiply-exposed-type holographic optical element, and includes an interference fringe pattern for the B (blue) wavelength, an interference fringe pattern for the R (red) wavelength, and an interference fringe pattern for the G (green) wavelength.

The optical element HOE_B' corresponds to a plurality (e.g., three) of wavelengths. The optical element HOE_B' concentrates the B (blue) wavelength component of the synthetic-color light from the light source 20 at the concentrating point FP_B. The optical element HOE_B' concentrates the R (red) wavelength component of the synthetic-color light from the light source 20 at the concentrating point FP_B. The optical element HOE_B' concentrates the G (green) wavelength component of the synthetic-color light from the light source 20 at the concentrating point FP_B.

The optical element (third optical element) HOE_C' is arranged at a position corresponding to the optical element HOE_C, and extends in a flat plate shape in the Y and Z directions. The optical element HOE_C' is a stacked-type or multiply-exposed-type holographic optical element, and includes an interference fringe pattern for the B (blue) wavelength, an interference fringe pattern for the R (red) wavelength, and an interference fringe pattern for the G (green) wavelength.

The optical element HOE_C’ corresponds to a plurality (e.g., three) of wavelengths. The optical element HOE_C’ concentrates the B (blue) wavelength component of the synthetic-color light from the light source 20 at the concentrating point FP_C. The optical element HOE_C' concentrates the R (red) wavelength component of the synthetic-color light from the light source 20 at the concentrating point FP_C. The optical element HOE_C' concentrates the G (green) wavelength component of the synthetic-color light from the light source 20 at the concentrating point FP_C.

As a result, the light from the light source 20 may be reflected by the optical element group 35 while being scanned in the optical element group 35 and the reflected light may be concentrated in the vicinity of the pupil 103 of the eyeball 100 of the user to project a multi-colored (e.g., full color) AR image on the retina 101.

In this way, the optical elements HOE_A' to HOE_C' for reflecting the multi-colored light from the light source 20 are multiplexed in the image projection device 1 using a retinal projection method. As a result, an eye-box may be enlarged with respect to multi-colored (e.g., full color) light while suppressing the complexity of hardware and software configurations.

Alternatively, when each optical element included in the optical element group 35 is a holographic optical element (HOE) , for example, it is possible to mix an optical element HOE corresponding to a plurality of wavelengths and an optical element HOE corresponding to a single wavelength. The optical element group 35 may be configured as illustrated in FIG. 10. FIG. 10 is a diagram illustrating a configuration of the optical element group 35 according to a third modification example of the embodiment.

The optical element group 35 includes a plurality of

optical element groups

35A, 35B, and 35C, instead of the plurality of optical elements HOE_A, HOE_B, and HOE_C (see FIG. 2) . The optical element group 35A is arranged at a position corresponding to the optical element HOE_A. The optical element group 35A includes an optical element (first optical element) HOE_A_BG and an optical element (first optical element) HOE_A_R, which are stacked in order from the plus X side to the minus X side. In FIG. 10, the optical element HOE_A_BG is illustrated with a dashed-dotted line, and the optical element HOE_A_R is illustrated with a solid line. The optical elements HOE_A_BG and HOE_A_R respectively extend in a flat plate shape in the Y and Z directions. The optical element HOE_A_BG is a stacked-type or multiply-exposed-type holographic optical element, and includes an interference fringe pattern for a B (blue) wavelength and an interference fringe pattern for a G (green) wavelength. The optical element HOE_A_R is a stacked-type or multiply-exposed-type holographic optical element, and includes an interference fringe pattern for an R (red) wavelength.

The optical element HOE_A_BG corresponds to a plurality of wavelengths, and the optical element HOE_A_R corresponds to a single wavelength. The optical element HOE_A_BG concentrates a B (blue) wavelength component of synthetic-color light from the light source 20 at the concentrating point FP_A. The optical element HOE_A_BG concentrates a G (green) wavelength component of the synthetic-color light from the light source 20 at the concentrating point FP_A. The optical element HOE_A_R concentrates an R (red) wavelength component of the synthetic-color light from the light source 20 at the concentrating point FP_A.

Similarly, the optical element group 35B is arranged at a position corresponding to the optical element HOE_B. The optical element group 35B includes an optical element (second optical element) HOE_B_BG and an optical element (second optical element) HOE_B_R, which are stacked in order from the plus X side to the minus X side. The optical elements HOE_B_BG and HOE_B_R respectively extend in a flat plate shape in the Y and Z directions. The optical element HOE_B_BG corresponds to a plurality of wavelengths, and the optical element HOE_B_R corresponds to a single wavelength. The optical element HOE_B_BG concentrates the B (blue) wavelength component of the synthetic-color light from the light source 20 at the concentrating point FP_B. The optical element HOE_B_BG concentrates the G (green) wavelength component of the synthetic-color light from the light source 20 at the concentrating point FP_B. The optical element HOE_B_R concentrates the R (red) wavelength component of the synthetic-color light from the light source 20 at the concentrating point FP_B.

The optical element group 35C is arranged at a position corresponding to the optical element HOE_C. The optical element group 35C includes an optical element (third optical element) HOE_C_BG and an optical element (third optical element) HOE_C_R, which are stacked in order from the plus X side to the minus X side. The optical elements HOE_C_BG and HOE_C_R extend in a flat plate shape in the Y and Z directions. The optical element HOE_C_BG corresponds to a plurality of wavelengths, and the optical element HOE_C_R corresponds to a single wavelength. The optical element HOE_C_BG concentrates the B (blue) wavelength component of the synthetic-color light from the light source 20 at the concentrating point FP_C. The optical element HOE_C_BG concentrates the G (green) wavelength component of the synthetic-color light from the light source 20 at the concentrating point FP_C. The optical element HOE_C_R concentrates the R (red) wavelength component of the synthetic-color light from the light source 20 at the concentrating point FP_C.

In this way, the optical elements HOE_A_BG and HOE_A_R to HOE_C_BG and HOE_C_R for reflecting the multi-colored light from the light source 20 are multiplexed in the image projection device 1 using a retinal projection method. As a result, an eye-box may be enlarged with respect to multi-colored (e.g., full color) light while suppressing the complexity of hardware and software configurations.

Alternatively, the optical element group 35 may be configured in consideration of stray light. The optical element group 35 may be configured as illustrated in FIG. 11. FIG. 11 is a diagram illustrating a configuration of the optical element group 35 according to a fourth modification example of the embodiment. It should be noted that a polarization direction turning clockwise when being viewed from the plus X side is referred to as right-handed circular polarization and a polarization direction turning counterclockwise when being viewed from the plus X side is referred to as left-handed circular polarization.

The optical element group 35 includes a plurality of optical elements HOE_A" , HOE_B" , and HOE_C" instead of the plurality of optical elements HOE_A, HOE_B, and HOE_C (see FIG. 2) , and further includes a filter element FE and a conversion element CE.

The optical element (first optical element) HOE_A" is arranged at a position corresponding to the optical element HOE_A, and extends in a flat plate shape in the Y and Z directions. The optical element HOE_A" is, for example, a stacked-type holographic optical element in which hologram having the recorded interference fringe pattern and cholesteric liquid crystal having left-handed reflection characteristics are stacked. The optical element HOE_A" includes cholesteric liquid crystal having a helical structure turning counterclockwise when being viewed from the plus X side. For this reason, among components of the incident light, the optical element HOE_A" reflects a circularly-polarized component (e.g., left-handed circularly-polarized component) in the same direction as the helical structure in the cholesteric liquid crystal, and transmits a circularly-polarized component (e.g., right-handed circularly-polarized component) in the opposite direction.

The optical element (second optical element) HOE_B" is arranged at a position corresponding to the optical element HOE_B, and extends in a flat plate shape in the Y and Z directions. The optical element HOE_B" is, for example, a stacked-type holographic optical element in which hologram having the recorded interference fringe pattern and cholesteric liquid crystal having right-handed reflection characteristics are stacked. Alternatively, the optical element HOE_B" may be a liquid-crystal holographic optical element on which an interference fringe pattern itself is recorded. The optical element HOE_B" includes cholesteric liquid crystal having a helical structure turning clockwise when being viewed from the plus X side. For this reason, among components of the incident light, the optical element HOE_B" reflects a circularly-polarized component (e.g., right-handed circularly-polarized component) in the same direction as the helical structure in the cholesteric liquid crystal, and transmits a circularly-polarized component (e.g., left-handed circularly-polarized component) in the opposite direction.

The optical element (third optical element) HOE_C" is arranged at a position corresponding to the optical element HOE_C, and extends in a flat plate shape in the Y and Z directions. The optical element HOE_C" is, for example, a stacked-type holographic optical element in which hologram having the recorded interference fringe pattern and cholesteric liquid crystal having left-handed reflection characteristics are stacked. The optical element HOE_C" includes cholesteric liquid crystal having a helical structure turning counterclockwise when being viewed from the plus X side. For this reason, among components of the incident light, the optical element HOE_C" reflects a circularly-polarized component (e.g., left-handed circularly-polarized component) in the same direction as the helical structure in the cholesteric liquid crystal, and transmits a circularly-polarized component (e.g., right-handed circularly-polarized component) in the opposite direction.

The filter element FE is arranged to intersect with the optical axis PA, between the optical element HOE_A" and the optical element HOE_B" in the X direction. The filter element FE is also arranged to intersect with the optical axis PA, between the optical element HOE_A" and the conversion element CE in the X direction. The filter element FE has a filter function for selectively passing appropriately-polarized light. The filter element FE is, for example, a right-handed circular polarizing filter in which a linear polarizing plate and a quarter-wave plate are stacked. Among components of the incident light, the filter element FE transmits a right-handed circularly-polarized component, converts a linearly-polarized component into a right-handed circularly-polarized component to transmit the converted component as right-handed circularly-polarized light, and blocks a left-handed circularly-polarized component.

The conversion element CE is arranged to intersect with the optical axis PA, between the optical element HOE_A" and the optical element HOE_B" in the X direction. The conversion element CE is also arranged to intersect with the optical axis PA, between the filter element FE and the optical element HOE_B" in the X direction. The conversion element CE converts a polarized state of light into another polarized state to assist the filter function of the filter element FE. The conversion element CE is a quarter-wave plate, for example. If incident light is circularly-polarized light, the conversion element CE converts the circularly-polarized light into linearly-polarized light and emits the converted light.

It should be noted that the filter element FE may be arranged to intersect with the optical axis PA between the optical element HOE_B" and the optical element HOE_C" in the X direction. In this case, the conversion element CE is arranged to intersect with the optical axis PA between the filter element FE and the optical element HOE_C" in the X direction.

For example, as illustrated in FIG. 11, when the linearly-polarized light is incident onto the optical element HOE_A" from the plus X side, some components are reflected as left-handed circularly-polarized light to head for the eyeball 100. Other components are converted into right-handed circularly-polarized light and are transmitted. The right-handed circularly-polarized light passes through the filter element FE and is converted into linearly-polarized light by the conversion element CE, and the converted light is incident onto the optical element HOE_B" .

When the linearly-polarized light is incident onto the optical element HOE_B" from the plus X side, some components are reflected as right-handed circularly-polarized light, and other components are converted into left-handed circularly-polarized light and are transmitted. The right-handed circularly-polarized light reflected by the optical element HOE_B" is converted into linearly-polarized light by the conversion element CE. The linearly-polarized light is converted into right-handed circularly-polarized light by the filter element FE, and the converted light is incident onto the optical element HOE_A" from the minus X side. The right-handed circularly-polarized light passes through the optical element HOE_A" to head for the eyeball 100. In other words, the light reflected by the optical element HOE_B" may be prevented from being re-reflected by the optical element HOE_A" .

Assume other polarized light different from the right-handed circularly-polarized light is incident onto the optical element HOE_A" from the filter element FE as illustrated by a dotted arrow. In this case, the other polarized light is reflected by the optical element HOE_A" as left-handed circularly-polarized light and thus the reflected light is blocked by the filter element FE. As a result, even if light re-reflected by the optical element HOE_A" is generated, the re-reflected light may be blocked by the filter element FE and the influence of the re-reflected light may be suppressed.

On the other hand, almost all components of the left-handed circularly-polarized light transmitted through the optical element HOE_B" are reflected as left-handed circularly-polarized light and are incident onto the optical element HOE_B" from the minus X side. The left-handed circularly-polarized light passes through the optical element HOE_B" and is converted into linearly-polarized light by the conversion element CE. The linearly-polarized light is converted into right-handed circularly-polarized light by the filter element FE, and the converted light is incident onto the optical element HOE_A" from the minus X side. The right-handed circularly-polarized light passes through the optical element HOE_A" to head for the eyeball 100. In other words, the light reflected by the optical element HOE_C" may be prevented from being re-reflected by the optical element HOE_A" .

If other polarized light different from the right-handed circularly-polarized light is incident onto the optical element HOE_A" from the filter element FE as illustrated by a dotted arrow, the other polarized light is reflected by the optical element HOE_A" as left-handed circularly-polarized light and thus the reflected light is blocked by the filter element FE. As a result, even if light re-reflected by the optical element HOE_A" is generated, the re-reflected light may be blocked by the filter element FE and the influence of the re-reflected light may be suppressed.

In this way, the optical element group 35 includes the filter element FE that is provided between the plurality of optical elements HOE_A" to HOE_C" in the X direction to selectively pass appropriately-polarized light. As a result, because light reflected by each of the optical elements HOE_A" to HOE_C" may be prevented from being reflected by the other optical element HOE, stray light may be removed.

[Explanations of Letters or Numerals]

1 Image projection device

10 Controller

20 Light source

30 Optical system

31 Lens

32 Mirror

33 Mirror

34 Scanning drive unit

35 Optical element group

35A to 35C Optical element group

DOE_A_B to DOE_C_G Optical element

HOE_A to HOE_C Optical element

HOE_A_BG to HOE_C_R Optical element

HOE_A' to HOE_C' Optical element

HOE_A" to HOE_C" Optical element

Claims

An image projection device comprising:

a light source configured to be able to project light;

an optical system configured to be able to transmit outside light from an outside world and reflect the light from the light source;

wherein the optical system concentrates the light in a vicinity of a pupil of an eyeball of a user to project an image created according to the light from the light source on a retina of the eyeball.
The image projection device according to claim 1, wherein

the optical system comprising:

a first optical element configured to concentrate the light from the light source at a first concentrating point; and

a second optical element configured to concentrate the light from the light source at a second concentrating point, the second concentrating point being located at a position different from the first concentrating point.
The image projection device according to claim 2, wherein

the first optical element and the second optical element are located separately from each other in a first direction along an optical axis of transmitted light.
The image projection device according to claim 3, wherein

the first optical element and the second optical element are located at positions shifted each other in the first direction so as to intersect with the optical axis of the transmitted light.
The image projection device according to claim 4, wherein

the first concentrating point and the second concentrating point are located at positions shifted each other in a second direction.
The image projection device according to claim 5, wherein

the second direction is a direction intersecting with the optical axis of the transmitted light.
The image projection device according to claim 5, wherein

one of the first concentrating point and the second concentrating point is located in a vicinity of the optical axis of the transmitted light.
The image projection device according to claim 2, wherein

an optical characteristic of the first optical element and an optical characteristic of the second optical element are substantially equal to one another.
The image projection device according to claim 2, wherein

an optical characteristic of the first optical element and an optical characteristic of the second optical element are adjusted so that the first concentrating point and the second concentrating point are located in a vicinity of a plane that passes through the pupil and that is perpendicular to an optical axis of transmitted light.
The image projection device according to claim 2, wherein

the optical system further comprises a third optical element configured to concentrate the light from the light source at a third concentrating point, the third concentrating point being located at a position different from the first concentrating point and the second concentrating point.
The image projection device according to claim 10, wherein

the first optical element, the second optical element, and the third optical element are located separately from each other in a first direction along an optical axis of transmitted light.
The image projection device according to claim 11, wherein

the third optical element is arranged on an opposite side of the first optical element in the first direction while placing the second optical element therebetween such that the first optical element, the second optical element and third optical element are intersect with an optical axis of the transmitted light.
The image projection device according to claim 12, wherein

the third concentrating point is arranged on an opposite side of the first concentrating point in a second direction while placing the second concentrating point therebetween.
The image projection device according to claim 13, wherein

the second direction is a direction intersecting with the optical axis of the transmitted light.
The image projection device according to claim 13, wherein

one of the first concentrating point, the second concentrating point and the third concentrating point is located in a vicinity of the optical axis of the transmitted light.
The image projection device according to claim 10, wherein

an optical characteristic of the first optical element, an optical characteristic of the second optical element, and an optical characteristic of the third optical element are substantially equal to one another.
The image projection device according to claim 10, wherein

an optical characteristic of the first optical element, an optical characteristic of the second optical element, and an optical characteristic of the third optical element are adjusted so that the first concentrating point, the second concentrating point, and the third concentrating point are located in a vicinity of a plane that passes through the pupil and that is perpendicular to an optical axis of transmitted light.
The image projection device according to claim 10, wherein

an interval between the first optical element and the second optical element in a first direction is substantially equal to an interval between the second optical element and the third optical element in the first direction, and

a distance between the first concentrating point and the second concentrating point in a second direction is substantially equal to a distance between the second concentrating point and the third concentrating point in the second direction.
The image projection device according to claim 2, wherein

the optical system further comprises, between the first optical element and the second optical element, a filter element configured to selectively pass appropriately-polarized light.
A retinal projection method comprising:

generating a light;

transmitting outside light through an optical system;

reflecting the generated light at the optical system; and

concentrating, by the optical system, the light in a vicinity of a pupil of an eyeball of a user to project an image created according to the light from the light source on a retina of the eyeball.