JP7484348B2 - Optical device, image display device, and optometry device - Google Patents

Description

The present invention relates to an optical device, an image display device, and an optometry device.

In recent years, technologies and products related to virtual reality (VR) and augmented reality (AR) have been attracting attention. AR technology in particular is expected to be applied to the industrial sector as a means of displaying added-value digital information in real space, and head-mounted displays (HMDs) that can be used in active (working) environments have been developed.

The mainstream HMDs are see-through types that allow users to view both the image and the image of objects in real space at the same time. Types that display a virtual image in front of the eyes via a partially reflective film or image guide structure, as well as retinal imaging types that directly image the image on the retina via a partially reflective film, are beginning to appear on the market.

Also disclosed is a device that projects scanned light onto the retina of a user's eyeball via an optical component, allowing the user to view an image produced by the projected light (see, for example, Patent Document 1).

However, with the device of Patent Document 1, there were cases where the image produced by the projected light and the real space could not be properly viewed.

The disclosed technology aims to improve the visibility of images produced by projected light and real space.

An optical device according to one aspect of the disclosed technology includes a projection unit that projects scanning light, which is light of a predetermined polarization state, and the projection unit includes an optical element that selectively reflects the light of the predetermined polarization state, and the optical element is a first reflective liquid crystal optical element that reflects and focuses the light toward a surface onto which it is projected, and the first reflective liquid crystal optical element includes at least two or more regions within the element surface having different magnitudes of focusing action.

The disclosed technology allows images projected by light to be properly viewed.

1 is a diagram showing an example of the configuration of a video display device according to a first embodiment; 3A and 3B are diagrams illustrating an example of the configuration of a scanning mirror according to the embodiment. 2 is a block diagram showing an example of a hardware configuration of a control unit according to the embodiment; FIG. 4 is a block diagram showing an example of a functional configuration of a control unit according to the embodiment; FIG. 1 is a diagram showing an example of the configuration of a reflective liquid crystal optical element according to an embodiment; 1A to 1C are diagrams illustrating an example of the operation of a reflective liquid crystal optical element according to an embodiment. FIG. 2 is a diagram illustrating an example of the operation of the image display device according to the first embodiment. FIG. 11 is a diagram illustrating an example of the configuration of a video display device according to a second embodiment. 11A and 11B are diagrams illustrating the operation of an image display device according to a comparative example. 13A and 13B are diagrams illustrating an example of the operation of the image display device according to the second embodiment.

Below, a description of the embodiment of the invention will be given with reference to the drawings. In each drawing, the same components are given the same reference numerals, and duplicated explanations may be omitted.

In the embodiment, the scanning light of a predetermined polarization state is selectively reflected by the optical element to project an image based on the scanning light. The image based on the scanning light is selectively reflected with high efficiency, and is therefore projected with little loss. On the other hand, light from an object in real space that contains a large amount of light other than the predetermined polarization state is transmitted through the optical element with high efficiency. As a result, on the surface onto which the scanning light is projected, both the image and the image of the object in real space are visually recognized as bright.

In the embodiment, an image display device equipped with an optical device will be described as an example. In addition, as an image display device, a retinal projection type head mounted display (HMD) that is a wearable terminal and projects an image or video directly onto the user's retina using Maxwellian vision will be described as an example.

In the embodiment, an image display device that displays an image on the user's left eyeball is described as an example, but this image display device can also be applied to the right eyeball. In addition, two image display devices can be provided and the device can be applied to both eyeballs.

In the description of the embodiments, an image is synonymous with a still image, and a video is synonymous with a moving image. A laser beam is synonymous with a laser beam. A laser beam is an example of "light."

[First embodiment]
<Configuration of image display device 100>
The configuration of an image display device 100 according to the first embodiment will be described with reference to Fig. 1. Fig. 1 is a diagram showing an example of the configuration of the image display device 100.

As shown in FIG. 1, the image display device 100 includes a laser light source 1, a lens 2, an aperture member 301, a dimming element 302, a polarizer 41, a quarter-wave plate 42, a scanning mirror 5, a reflecting mirror 6, and a reflective liquid crystal optical element 7. The image display device 100 also includes a glasses frame 8 and a control unit 20.

The eyeglass frame 8 includes temples 81 and rims 82, and the rims 82 hold eyeglass lenses (not shown). The lens 2, aperture member 301, dimming element 302, polarizer 41, quarter-wave plate 42, scanning mirror 5, and reflecting mirror 6 are provided inside the temples 81. The reflective liquid crystal optical element 7 is provided on the surface of the eyeglass lens 8c held by the rims 82. The user can wear the image display device 100 on the head by placing the eyeglass frame 8 on the ears.

The laser light source 1 is a semiconductor laser that emits a laser beam of a single or multiple wavelengths. The laser light source 1 emits a time-modulated laser beam in response to a drive signal from the control unit 20. When drawing a monochrome image, a laser light source that emits a laser beam of a single wavelength is used, and when drawing a color image, a laser light source that emits laser beams of multiple wavelengths is used. Here, the laser light source 1 is an example of a "light source".

The aperture member 301 is a member that has an opening that allows light to pass through, and shapes the laser beam into a desired cross-sectional shape or diameter by passing a part of the incident laser beam and blocking the rest. The diameter of the opening of the aperture member 301 is equal to or smaller than the diameter of the laser beam collimated by the lens 2 at a light intensity of 1/ ^e2 . Here, "e" is the base of the natural logarithm.

The diameter of the aperture member 301 is determined so that the cross-sectional diameter of the laser beam that passes through the aperture member 301 and enters the scanning mirror 5 is smaller than the effective diameter of the scanning mirror 5. In the embodiment, a circular aperture is assumed, but it may be an elliptical or partially distorted aperture. The aperture member 301 can make the cross-sectional light intensity distribution uniform, etc., so that the laser beam can be brought into a desired state, thereby improving the quality of the image beam and image.

The dimming element 302 is an optical element that reduces the light intensity of the passing laser beam so that the light intensity is appropriate while taking into consideration the safety of the user's eyes. The dimming element 302 is an ND (Neutral Density) filter or the like, which is made of a resin plate-shaped member on which an optical thin film with a predetermined transmittance is formed.

Here, appropriate light intensity that takes into consideration the safety of the user's eyes refers to a light intensity below Class 1 as defined by IEC (International Electrotechnical Commission) 60825-1, an international standard regarding the safety of laser light. By using the dimming element 302 to dim the laser beam emitted from the laser light source 1 to a desired intensity, a safe laser beam is projected onto the retina, ensuring the safety of the user's eyes.

The polarizer 41 is an optical element that converts the polarization state of incident light into linearly polarized light that vibrates only in a specific direction. A polarizing film sandwiched between a pair of transparent plates can be used as the polarizer 41. A polarizing film is made by adding iodine to a polarizing film such as polyvinyl alcohol (PVA) and stretching it to align the direction of the polymer molecules. The pair of transparent plates can be made of glass or a resin such as triacetyl cellulose.

The quarter-wave plate 42 is an optical element that converts the incident linearly polarized light into either right-handed circularly polarized light or left-handed circularly polarized light. The quarter-wave plate 42 is a wave plate made of an inorganic crystal material having birefringence, such as quartz. Here, the configuration including the polarizer 41 and the quarter-wave plate 42 is an example of a "polarizing section."

The scanning mirror 5 is a mirror that rotates around two different axes. The scanning mirror 5 rotates to change the angle, thereby scanning the incident light in two different directions. In the example of FIG. 1, the scanning mirror 5 scans the incident laser beam in the X direction (horizontal direction) and Y direction (vertical direction). The laser beam is synchronized and scanned in the X and Y directions, so that an image or video is projected onto the retina of the user's eyeball via the reflective liquid crystal optical element 7. Here, the scanning mirror 5 is an example of a "scanning unit."

Although not shown in FIG. 1, the image display device 100 can be equipped with a known synchronous detection optical system or the like to synchronize the scanning of the laser beam in the X and Y directions.

The X direction indicated by the arrow in Figure 1 corresponds to the main scanning direction in which pixels are drawn successively in time to form a series of pixel groups, and the Y direction corresponds to the sub-scanning direction, which is perpendicular to the main scanning direction and lines up a series of pixel groups. The scanning speed in the main scanning direction is set faster than the scanning speed in the sub-scanning direction.

A two-axis MEMS (Micro Electro Mechanical System) mirror can be used as the scanning mirror 5. The details of the configuration of the scanning mirror 5 will be described later with reference to FIG. 2.

The reflection mirror 6 is a mirror that reflects the laser beam scanned by the scanning mirror 5 toward the reflective liquid crystal optical element. The surface of the reflection mirror is not limited to a flat surface, and may be any shape, such as a concave or convex surface.

The reflective liquid crystal optical element 7 is a flat optical element made of a liquid crystal film containing liquid crystal molecules. The reflective liquid crystal optical element 7 utilizes the liquid crystal molecular orientation structure, including the helical molecular arrangement, helical pitch, and local orientation changes of the liquid crystal molecules, to selectively reflect (diffract) either the right-handed circularly polarized light or the left-handed circularly polarized light that is incident with high efficiency, and to focus the light near the center of the pupil 52 of the eyeball 50.

As shown in regions P1 to P3 in FIG. 1, the reflective liquid crystal optical element 7 reflects the laser beam toward the eyeball 50 in different directions depending on the region in the XY plane. In this way, the reflective liquid crystal optical element 7 has the characteristic that the magnitude of the focusing effect it has on the reflected light varies depending on the region, so that the light is focused near the center of the pupil 52. The greater the focusing effect, the more effective the lens function is, in other words, the equivalent of a shorter focal length, and the smaller the focusing effect, the more effective the lens function is, the equivalent of a longer focal length. In the example of FIG. 1, the focusing effect increases from region P1 to region P3.

The above-mentioned effect is due to the liquid crystal molecular orientation structure contained in the reflective liquid crystal optical element 7, and is achieved by adjusting the orientation distribution of the liquid crystal molecules on the element surface. The configuration and effect of such a reflective liquid crystal optical element 7 will be described in detail later with reference to Figures 5 to 7.

The reflective liquid crystal optical element 7 is an example of a "first reflective liquid crystal optical element." The reflective liquid crystal optical element 7 is also an example of an "optical member," and further an example of a "projection unit." The element surface of the reflective liquid crystal optical element 7 is also an example of a "reflective surface."

The control unit 20 is a control device that inputs image data that is the source of the image to be drawn, and controls the emission of laser light from the laser light source based on the input image data. The control unit 20 also controls the driving of the scanning mirror 5, thereby controlling the scanning of light by the scanning mirror 5.

In FIG. 1, an example is shown in which the laser light source 1 and the dimming element 302 are provided inside the temple 81, but this is not limiting. The laser light source 1 and the dimming element 302 may be provided outside the temple 81, and the laser beam emitted from the laser light source 1 and dimmed by the dimming element 302 may be guided inside the temple 81. Furthermore, the control unit 20 may be provided inside the temple 81, or the control unit 20 may be provided outside the temple 81, and a drive signal from the control unit 20 may be supplied to the inside of the temple 81.

In addition, while FIG. 1 shows an example in which the dimming element 302 is disposed between the aperture member 301 and the scanning mirror 5, the present invention is not limited to this. The dimming element 302 may be disposed between the aperture member 301 and the lens 2, or may be disposed in multiple locations. If the safety of the intensity of the light projected onto the user's retina is ensured, the dimming element does not necessarily have to be provided. By optimizing the positioning of the dimming element 302, the image display device 100 can be made smaller.

In addition, in FIG. 1, an example is shown in which the polarizer 41 and the quarter-wave plate 42 are arranged between the light-attenuating element 302 and the scanning mirror 5, but the polarizer 41 and the quarter-wave plate 42 may be arranged between the aperture member 301 and the light-attenuating element 302, or between the aperture member 301 and the lens 2.

In addition, while FIG. 1 shows an example in which the reflective liquid crystal optical element 7 is provided on the surface of the eyeglass lens 8c, this is not limiting. When the eyeglass lens 8c is configured as a light guide plate, the reflective liquid crystal optical element 7 may be provided inside or on the surface of the eyeglass lens 8c.

The laser light source 1 is not limited to a semiconductor laser, and a solid-state laser or a gas laser may be used. In addition, the polarizer 41 may be provided on the outermost surface of a transparent plate with a protective film for improving durability or an anti-reflective coating layer for preventing reflection. When a higher extinction ratio is required, it is preferable to use a wire grid polarizer or a metal dispersion type polarizing film.

The quarter-wave plate 42 is not limited to a wave plate made of an inorganic crystalline material, but may be a resin film made of an organic material such as polycarbonate that has been given birefringence by stretching, or a retardation plate in which a polymer liquid crystal phase is sandwiched between a pair of transparent plates.

The scanning mirror 5 is not limited to a MEMS mirror, but may be an optical element capable of scanning light, such as a polygon mirror or a galvanometer mirror, or a combination of these. However, using a MEMS mirror is preferable because it allows the image display device 100 to be made smaller and lighter. The driving method of the MEMS mirror may be electrostatic, piezoelectric, electromagnetic, or other.

<Behavior of Laser Beam in Image Display Device 100>
Next, the operation of the laser beam in the image display device 100 will be described.

In FIG. 1, a diverging laser beam (diverging beam not shown) emitted from a laser source 1 is converted into a substantially parallel beam by a lens 2. The action of the lens is not limited to substantially parallelization, and the light after passing through the lens may be in a convergent or divergent state. The substantially parallelized laser beam passes through an aperture member 301 and a dimming element 302, and is converted into a right-handed circularly polarized laser beam by a polarizer 41 and a quarter-wave plate 42. Here, right-handed circularly polarized light is an example of a "polarization state having chirality".

The laser beam converted into right-handed circularly polarized light is scanned in two axial directions by the scanning mirror 5, reflected by the reflecting mirror 6, and enters the reflective liquid crystal optical element 7.

The reflective liquid crystal optical element 7 selectively reflects, for example, an incident right-handed circularly polarized laser beam and allows it to enter the inside of the eyeball 50. The light incident on the inside of the eyeball 50 is first focused near the center of the pupil 52 by the focusing function of the reflective liquid crystal optical element 7, and then forms an image on the retina 53 located at the back of the eyeball 50. Here, the retina 53 is an example of a "surface onto which light is projected."

The above viewing state is generally called Maxwellian vision, and since light passing near the center of the pupil 52 reaches the retina 53 regardless of the focusing of the crystalline lens, it is ideal that the user can clearly view the projected image in focus no matter where in real space the eye is focused. On the other hand, in the real world, the laser beam entering the eyeball 50 has a small but finite diameter, so the lens action of the crystalline lens has a significant effect. Therefore, in the embodiment of the present invention, the lens 2 and the reflective liquid crystal optical element 7 are designed to focus the laser beam so that the diameter of the laser beam entering the eyeball 50 is 350 μm or more and 500 μm or less, and the beam divergence angle is a positive finite value, i.e., diverging light.

As a result, the image drawn by the laser beam scanned by the scanning mirror 5 reaches the retina 53 via the reflective liquid crystal optical element 7 without being affected by the focusing of the crystalline lens, so the user can always clearly view the projected image no matter where in real space the eye is focused. In other words, the image drawn by the laser beam scanned by the scanning mirror 5 is viewed by the user in a focus-free state.

The image display device 100 can change the light intensity of the emitted laser beam by changing the current or voltage applied to the laser light source 1. This allows the brightness of the image or video to be adjusted according to the brightness of the surrounding environment in which the image display device 100 is used.

<Details of the Configuration of Scanning Mirror 5>
Next, the details of the configuration of the scanning mirror 5 will be described with reference to Fig. 2. Fig. 2 is a diagram illustrating an example of the configuration of the scanning mirror 5. In Fig. 2, the directions indicated by the arrows are the α direction, the β direction, and the γ direction, respectively. As shown in Fig. 2, the scanning mirror 5 includes a support substrate 91, a movable portion 92, a serpentine beam portion 93, a serpentine beam portion 94, and an electrode connection portion 95.

Of these, the serpentine beam portion 93 is formed in a serpentine manner with multiple folded sections, one end of which is connected to the support substrate 91 and the other end of which is connected to the movable portion 92. The serpentine beam portion 93 includes a beam portion 93a including three beams and a beam portion 93b including three beams. The beams of the beam portion 93a and the beams of the beam portion 93b are formed alternately. Each of the beams included in the beam portion 93a and the beam portion 93b is independently equipped with a piezoelectric member.

Similarly, the serpentine beam portion 94 is formed in a serpentine manner with multiple folded portions, one end of which is connected to the support substrate 91, and the other end of which is connected to the movable portion 92. The serpentine beam portion 94 includes a beam portion 94a including three beams and a beam portion 94b including three beams. The beams of the beam portion 94a and the beams of the beam portion 94b are formed alternately. Each beam included in the beam portion 94a and the beam portion 94b is independently provided with a piezoelectric member. Note that the number of beams in the beam portions 93a and 93b is not limited to three and may be any number.

The piezoelectric members provided in beam portions 93a, 93b, 94a, and 94b are not shown in FIG. 2, but are provided as piezoelectric layers in, for example, a portion of the layers of each beam formed in a multi-layer structure. Hereinafter, the piezoelectric members provided in beam portions 93a and 94a may be collectively referred to as piezoelectric member 95a, and the piezoelectric members provided in beam portions 93b and 94b may be collectively referred to as piezoelectric member 95b.

When voltage signals of opposite phases are applied to the piezoelectric members 95a and 95b, causing warping of the serpentine beam portion 94, adjacent beam portions bend in different directions. This bending accumulates, generating a rotational force for rotating the reflecting mirror 92a back and forth around the A axis in FIG. 2.

The movable part 92 is formed so as to be sandwiched between the serpentine beam part 93 and the serpentine beam part 94 in the β direction. The movable part 92 includes a reflection mirror 92a, a torsion bar 92b, a piezoelectric member 92c, and a support part 92d.

The reflecting mirror 92a is formed, for example, by evaporating a thin metal film containing aluminum, gold, silver, etc. onto a substrate. The torsion bar 92b is connected at one end to the reflecting mirror 92a and extends in the positive and negative α directions to rotatably support the reflecting mirror 92a.

One end of the piezoelectric member 92c is connected to the torsion bar 92b, and the other end is connected to the support portion 92d. When a voltage is applied to the piezoelectric member 92c, the piezoelectric member 92c is bent and deformed, causing a twist in the torsion bar 92b. The twist in the torsion bar 92b becomes a rotational force, and the reflecting mirror 92a rotates around the B axis.

By rotating the reflecting mirror 92a around the A axis, the laser beam incident on the reflecting mirror 92a is scanned in the α direction. By rotating the reflecting mirror 92a around the B axis, the laser beam incident on the reflecting mirror 92a is scanned in the β direction.

The support portion 92d is formed to surround the reflecting mirror 92a, the torsion bar 92b, and the piezoelectric member 92c. The support portion 92d is connected to the piezoelectric member 92c and supports the piezoelectric member 92c. The support portion 92d also indirectly supports the torsion bar 92b connected to the piezoelectric member 92c, and the reflecting mirror 92a.

The support substrate 91 is formed to surround the movable portion 92, the serpentine beam portion 93, and the serpentine beam portion 94. The support substrate 91 is connected to and supports the serpentine beam portion 93 and the serpentine beam portion 94. The support substrate 91 also indirectly supports the movable portion 92 connected to the serpentine beam portion 93 and the serpentine beam portion 94.

The MEMS mirror that constitutes the scanning mirror 5 is formed by micromachining silicon or glass. By using micromachining technology, a highly accurate and tiny movable mirror can be formed on a substrate, integrated with a driving section such as a serpentine beam section.

Specifically, a single SOI (Silicon On Insulator) substrate is shaped by etching or other processes. The reflective mirror 92a, serpentine beams 93-94, piezoelectric members 95a-95b, electrode connections, and other components are integrally formed on the shaped substrate to form the MEMS mirror. The reflective mirror 92a and other components may be formed after or during the shaping of the SOI substrate.

An SOI substrate is a substrate in which a silicon oxide layer is provided on a silicon support layer made of single crystal silicon (Si), and a silicon active layer made of single crystal silicon is provided on the silicon oxide layer. The silicon active layer is thinner in the γ direction than in the α or β directions, so a member made only of the silicon active layer functions as an elastic part.

The SOI substrate does not necessarily have to be planar, and may have curvature, etc. Furthermore, the material used to form the MEMS mirror is not limited to the SOI substrate, as long as it is a substrate that can be integrally molded by etching or the like and can be made partially elastic.

When scanning in the main scanning direction, a sinusoidal voltage is applied in opposite phase to the piezoelectric members 95a and 95b of the scanning mirror 5 as a drive signal from the control unit 20. The frequency of the sinusoidal voltage is a frequency that corresponds to the resonance mode of the movable part 92 around the A axis. By applying the sinusoidal voltage, the scanning mirror 5 rotates back and forth at a low voltage and with a very large rotation angle.

A voltage signal with a sawtooth waveform can be used as the drive signal. A sawtooth waveform can be generated by superimposing sine wave waveforms. However, the waveform is not limited to a sawtooth waveform, and a waveform with rounded peaks or a waveform with curved linear regions of a sawtooth waveform can also be used.

<Hardware configuration of control unit 20>
Next, a hardware configuration of the control unit 20 according to the embodiment will be described with reference to Fig. 3. Fig. 3 is a block diagram showing an example of the hardware configuration of the control unit 20.

As shown in FIG. 3, the control unit 20 includes a CPU (Central Processing Unit) 22, a ROM (Read Only Memory) 23, a RAM (Random Access Memory) 24, a light source drive circuit 25, and a scanning mirror drive circuit 26. These are electrically connected to each other via a system bus 27.

Of these, the CPU 22 controls the overall operation of the control unit 20. The CPU 22 uses the RAM 24 as a work area and executes programs stored in the ROM 23 to control the operation of the entire control unit 20 and realize various functions.

The light source driving circuit 25 is an electric circuit that is electrically connected to the laser light source 1 and applies a current or voltage to the laser light source 1 to drive the laser light source 1. The laser light source 1 turns the emission of the laser beam ON or OFF and changes the light intensity of the emitted laser beam according to the driving signal output by the light source driving circuit 25.

The scanning mirror drive circuit 26 is an electric circuit that is electrically connected to the scanning mirror 5 and applies a voltage to drive the scanning mirror 5. The scanning mirror 5 changes the angle of rotation of the reflecting mirror 92a of the movable part 92 in response to the drive signal output by the scanning mirror drive circuit 26.

<Functional configuration of control unit 20>
Next, the functional configuration of the control unit 20 according to the embodiment will be described with reference to Fig. 4. Fig. 4 is a block diagram illustrating an example of the functional configuration of the control unit 20. As shown in Fig. 4, the control unit 20 includes an emission control unit 31, a light source driving unit 32, a scanning control unit 33, and a scanning mirror driving unit 34.

Of these, the functions of the emission control unit 31 and the scanning control unit 33 are realized by the CPU 22, etc. The function of the light source driving unit 32 is realized by the light source driving circuit 25, etc., and the function of the scanning mirror driving unit 34 is realized by the light source driving circuit 25, etc.

Of the above, the emission control unit 31 inputs image data that is the source of the image to be drawn, and outputs a control signal for driving and controlling the laser light source 1 to the light source driving unit 32 based on the input image data.

The scanning control unit 33 inputs image data that is the source of the image to be drawn, and outputs a control signal for driving and controlling the scanning mirror 5 to the scanning mirror driving unit 34 based on the input image data.

In addition, if the image viewed at a suitable position has distortion, etc., the emission control unit 31 and the scanning control unit 33 may perform control to correct the distortion, etc.

The light source driver 32 applies a current or voltage to the laser light source 1 based on the control signal input from the emission controller 31 to drive the laser light source 1. The scanning mirror driver 34 also drives the scanning mirror 5 with a voltage based on the control signal input from the scanning controller 33.

<Details of the configuration of the reflective liquid crystal optical element 7>
Next, the details of the configuration of the reflective liquid crystal optical element 7 will be described with reference to Fig. 5. Fig. 5 is a diagram for explaining an example of the configuration of the reflective liquid crystal optical element 7, where (a) is a perspective view of the reflective liquid crystal optical element 7, (b) is a diagram for explaining a part of the cross-sectional spatial distribution of the liquid crystal director 71 included in the reflective liquid crystal optical element 7, and (c) is a diagram for explaining a part of the in-plane spatial distribution on the element surface of the liquid crystal director 71 included in the reflective liquid crystal optical element 7.

As shown in FIG. 5, the element surface of the reflective liquid crystal optical element 7 refers to the x-y plane, which is a plane parallel to the liquid crystal director 71 or the substrate surface, and the cross section refers to a plane perpendicular to the element surface, for example, the x-z plane.

As shown in FIG. 5(a), the reflective liquid crystal optical element 7 is composed of a flat liquid crystal film. The reflective liquid crystal optical element 7 is produced by forming a desired molecular orientation structure using a photopolymerizable liquid crystal material, fixing the molecular orientation structure by UV light irradiation, and removing the substrate. Note that the orientation and position of the liquid crystal molecules are hardened by polymerization while maintaining the state before polymerization, so the liquid crystal molecular orientation structure can refer to the state before and after polymerization.

As shown in Figures 5(b) and (c), a liquid crystal molecular orientation structure in which the liquid crystal director 71 has three-dimensional periodicity is enclosed inside the reflective liquid crystal optical element 7. The liquid crystal director 71 refers to the average molecular orientation direction in which the liquid crystal molecules are aligned with their long axis direction.

The liquid crystal material in the embodiment of the present invention is a cholesteric liquid crystal in which a chiral agent is added to a nematic liquid crystal composed of achiral molecules, or a cholesteric liquid crystal that is expressed when the liquid crystal molecules themselves have chirality. In the cholesteric liquid crystal, a twist is induced in the molecular orientation between adjacent molecules, forming a helical periodic structure that has chirality in a direction perpendicular to the liquid crystal director 71. That is, the liquid crystal director 71 formed by the liquid crystal molecules sealed in the reflective liquid crystal optical element 7 in the embodiment of the present invention forms a helical molecular arrangement that has chirality in the depth direction perpendicular to the element surface, i.e., in the z direction. The cholesteric liquid crystal has the property of selectively Bragg reflecting circularly polarized light with synchronous chirality depending on the chirality of this helix.

In addition, in the reflective liquid crystal optical element 7, the starting position of the helical structure, i.e., the orientation direction of the liquid crystal director 71 on the element surface, is adjusted. That is, as shown in FIG. 5(c), the in-plane orientation distribution of the liquid crystal director 71 on the element surface of the reflective liquid crystal optical element 7 has a periodic arrangement in which the molecular orientation changes periodically radially from approximately the center of the element surface on the element surface. More specifically, the liquid crystal director 71 periodically rotates the orientation direction along a radial direction that can take any arbitrary direction from the center of the element, and the period gradually becomes smaller from the center toward the edge, that is, the orientation distribution has a period that changes nonlinearly.

Note that FIG. 5(c) merely shows a schematic representation of a portion of the in-plane spatial distribution, and is not limited to this, and may have any suitable number of periods based on the element size and required functions.

Due to such an in-plane orientation distribution, for example, as shown in FIG. 5(b), a phase distribution can be formed in the reflective liquid crystal optical element 7 in which the equiphase surface 72 in the helical molecular arrangement is curved concavely with respect to the positive z direction, which is the direction of light incidence. In other words, the locally varying molecular orientation distribution described above causes a concave phase shift in the reflected light. Therefore, the reflective liquid crystal optical element 7 has a reflecting and focusing effect on light incident in the positive z direction.

As described in FIG. 1, in the reflective liquid crystal optical element 7, the direction in which the laser beam is reflected toward the eyeball differs depending on the region in the xy plane. Therefore, in the reflective liquid crystal optical element 7, the above-mentioned in-plane orientation distribution is configured to be asymmetric in the first region (x- region with respect to the a-axis) and the second region (x+ region with respect to the a-axis) that are bisected by the a-axis parallel to the xy plane. More specifically, the period of the second region including the P3 region can be configured to be smaller overall than that of the first region including the P1 region shown in FIG. 1. That is, the second region has a smaller radius of curvature of the concave phase shift caused in the reflected light over the region, in other words, the second region has a larger focusing effect. In this way, the reflective liquid crystal optical element 7 includes at least two or more regions with different focusing effects within the element surface. As a result, the reflective liquid crystal optical element 7 can reflect the incident laser beam so as to focus it near the center of the pupil 52. In other words, the reflective liquid crystal optical element 7 functions as an aspheric mirror, or even a free-form mirror, making it possible to realize Maxwellian vision.

In addition, if the number of spiral pitches 73 (number of periods) shown in Figure 5 (b) is 6 or more, it is preferable because it can reflect light with high efficiency, for example, with a peak reflection intensity of more than 90%.

In addition, since known techniques can be applied to the technology for realizing optical functions by the phase distribution formed by the liquid crystal molecular orientation structure described above (e.g. Nature Photonics Vol. 10 (2016) p. 389), further detailed explanation will be omitted here.

The phase distribution in the reflective liquid crystal optical element 7 can be adjusted by adjusting the initial alignment direction of the liquid crystal director 71 on the element surface. A photo-alignment method can be used for such adjustment. In the photo-alignment method, the alignment film applied to the substrate is spatially divided, and linearly polarized light polarized in a specific direction is exposed to each region, so that the initial alignment direction of the liquid crystal molecules can be spatially adjusted.

The liquid crystal material may be either a polymerizable liquid crystal material or a non-polymerizable liquid crystal material. The chiral agent may be either polymerizable or non-polymerizable, and may be one type only, or two or more types may be combined, or may not be used if the liquid crystal molecules have chirality.

In the embodiment of the present invention, the method of manufacturing the reflective liquid crystal optical element 7 is described as forming a desired molecular orientation structure using a photopolymerizable liquid crystal material, then fixing the structure by irradiating with UV light, and removing the substrate, but the method is not limited to this. The form may be changed as required, such as a form in which the liquid crystal film is laminated on a transparent support substrate, or a form in which the film is sandwiched between transparent support substrates. In addition, in a form in which the liquid crystal film is in contact with air, a protective film or the like may be provided on the outermost surface to improve durability.

The shape of the reflective liquid crystal optical element 7 is not limited to a flat plate, and may be changed to any suitable shape, such as a curved shape, depending on the shape of the eyeglass lens 8c. In this case, the liquid crystal orientation structure of the reflective liquid crystal optical element 7 is adjusted depending on the shape of the eyeglass lens 8c, and the incident laser beam can be reflected so as to be focused near the center of the pupil 52.

<Function of Reflective Liquid Crystal Optical Element 7>
Next, the operation of the reflective liquid crystal optical element 7 will be described with reference to Fig. 6. Fig. 6 is a diagram for explaining an example of the operation of the reflective liquid crystal optical element 7. Fig. 6 shows an example in which right-handed circularly polarized light 61 and left-handed circularly polarized light 62 are incident on the reflective liquid crystal optical element 7 in which the liquid crystal molecules form a right-twisted helical arrangement.

As described above, the reflective liquid crystal optical element 7 Bragg reflects light of a specific wavelength band, which is circularly polarized light having the same chirality as the helical rotation direction of the liquid crystal molecules, with high diffraction efficiency due to the chiral helical arrangement. Here, the bandwidth Δλ of the specific wavelength band is determined by Δλ = Δnp cos θ, where Δn is the birefringence of the liquid crystal composition, p is the helical pitch of the liquid crystal, and θ is the angle of incidence of the light beam. The bandwidth Δλ can be adjusted by the birefringence of the liquid crystal composition, and is approximately 30 to 100 nm. This is very narrow compared to the bandwidth of visible light, which is 380 to 780 nm.

As shown in FIG. 6, when the laser beam incident on the reflective liquid crystal optical element 7 is right-handed circularly polarized light 61 that has the same chirality as the helical rotation direction of the liquid crystal molecules, the incident laser beam is selectively reflected with ideal efficiency.

The reflective liquid crystal optical element 7 transmits light outside the specified wavelength band, and light in the specified wavelength band that is circularly polarized light with the opposite chirality to the helical rotation direction of the liquid crystal molecules. Therefore, in FIG. 6, the left-handed circularly polarized light 62 is transmitted through the reflective liquid crystal optical element 7.

On the other hand, the phase shift caused by the reflected light is determined by the orientation distribution of the liquid crystal director 71 on the element surface, but the selective reflection property of the cholesteric liquid crystal is not lost by this change in the molecular orientation direction. Therefore, the reflective liquid crystal optical element 7 reflects only circularly polarized light of a specified wavelength band that has the same chirality as the helical arrangement of the liquid crystal molecules, and can focus the reflected circularly polarized light near the center of the pupil 52 by the focusing effect caused by the phase shift determined by the in-plane molecular orientation distribution.

In addition, since the helical pitch of cholesteric liquid crystal changes with temperature, it is preferable to construct the reflective liquid crystal optical element 7 with a liquid crystal film whose structure is fixed so that the specified wavelength band does not change with temperature.

Note that while FIG. 6 shows an example of a reflective liquid crystal optical element 7 in which the liquid crystal molecules form a right-handed helical arrangement, in the embodiment, a reflective liquid crystal optical element 7 in which the liquid crystal molecules form a left-handed helical arrangement may also be used. In this case, the reflective liquid crystal optical element 7 selectively reflects and focuses left-handed circularly polarized light that has the same chirality as the helical rotation direction of the liquid crystal molecules, and transmits light other than left-handed circularly polarized light.

<Operation of the image display device 100>
Next, the operation of the image display device 100 will be described with reference to Fig. 7. Fig. 7 is a diagram for explaining the operation of the image display device 100.

In FIG. 7, the right-handed circularly polarized laser beam is scanned by the scanning mirror 5 and reflected by the reflecting mirror 6 toward the reflective liquid crystal optical element 7. It is then selectively reflected by the reflective liquid crystal optical element 7 with ideal efficiency, and once focused near the center of the pupil 52 of the user's eyeball 50, it is projected onto the user's retina 53. The user can view the image formed by the laser beam projected onto the retina 53.

On the other hand, the light propagating in the negative Z direction from the object 70 in real space is randomly polarized light with a wide wavelength band. Therefore, light from the object 70 that is outside the specified wavelength band passes through the reflective liquid crystal optical element 7, and even if it is light within the specified wavelength band, light other than the right-handed circularly polarized component passes through the reflective liquid crystal optical element 7.

The bandwidth of the specified wavelength band in the reflective liquid crystal optical element 7 is very narrow compared to visible light, so the reflective liquid crystal optical element 7 has excellent transparency. Therefore, most of the light propagating from the object 70 in real space toward the eyeball 50 passes through the reflective liquid crystal optical element 7 and reaches the user's retina 53. This allows the image of the object 70 in real space to be viewed with sufficient brightness.

In this way, a user wearing the image display device 100 can view the image and the image of an object in real space in parallel, and can view both the image and the image in real space in a bright state.

<Effects of the image display device 100>
Conventionally, a device has been disclosed that projects scanned light onto the retina of a user's eyeball through an optical component, and allows the user to view an image produced by the projected light. However, in conventional image display devices such as a transmission-type HMD that allows the user to view an image of an object in real space in parallel with the image, there is a trade-off between the brightness of the image of the object in real space that passes through the eyeglass glasses and the brightness of the image reflected by the eyeglass glasses. Therefore, when the image of the object in real space is brightened, the projected image becomes dark, and there are cases where the image cannot be properly viewed.

In this embodiment, the reflective liquid crystal optical element 7 selectively reflects the right-handed circularly polarized scanning light to project an image based on the scanning light. Meanwhile, the reflective liquid crystal optical element 7 transmits light from real space with high efficiency. This allows a user who has an image projected onto their retina to see both the image and the image of an object in real space as bright images. In other words, the visibility of the image based on the projected light and the real space can be improved.

In addition, in this embodiment, images are rendered directly on the user's retina using Maxwell's vision, so the user can view the images in parallel and clearly regardless of where the focus is set in real space. As a result, for example, if the user is a worker at a manufacturing site, the clear field of vision does not impede work in real space, allowing the user to clearly view digital content such as work instructions, and the focus-free environment allows for visually stress-free work.

In addition, in this embodiment, by using a flat, thin reflective liquid crystal optical element 7, the image display device 100 can be made smaller and the image display device 100 can be easily mounted.

In addition, in this embodiment, the reflective liquid crystal optical element 7 includes a liquid crystal molecular orientation structure in which the magnitude of the light-focusing effect varies depending on the region. This allows the laser beam to be appropriately focused near the center of the pupil 52, realizing Maxwellian vision.

In addition, it is preferable to set the number of helical pitches 73 of the helical arrangement of liquid crystal molecules to 6 or more, since this allows for more efficient reflection.

In this embodiment, an HMD has been described as an example of an image display device, but an image display device such as an HMD may not only be worn directly on the user's head, but may also be worn indirectly on the user's head via a member such as a fixing part.

In addition, in this embodiment, an example is shown in which a reflective liquid crystal optical element 7 in which the liquid crystal molecules form a right-handed twisted helical arrangement is used, but a reflective liquid crystal optical element 7 in which the liquid crystal molecules form a left-handed twisted helical arrangement may also be used. In this case, the laser beam from the laser light source 1 is converted into left-handed circularly polarized light by the polarizer 41 and the quarter-wave plate 42, and is then incident on the reflective liquid crystal optical element 7, thereby obtaining the same effect as described above.

In addition, although the present embodiment shows an example in which one layer of the reflective liquid crystal optical element 7 is used, a stack of multiple reflective liquid crystal optical elements 7 may also be used. For example, if the reflective liquid crystal optical element 7 is made up of three layers, one with a reflective liquid crystal optical element having a predetermined wavelength band of red (R), another with a reflective liquid crystal optical element having a predetermined wavelength band of green (G), and another with a reflective liquid crystal optical element having a predetermined wavelength band of blue (B), a full-color image can be projected onto the retina by using an RGB laser light source.

Second Embodiment
Next, an image display device 100a according to a second embodiment will be described.

Due to the function of focusing reflected light by the reflective liquid crystal optical element, the state of the laser beam incident on the eyeball may change within the field of view. Here, the state of the laser beam includes the diameter of the laser beam and the beam spread angle. When projecting an image at a viewing angle where vignetting due to eyeball movement does not occur, it is desirable that the state of the laser beam incident on the eyeball is uniform within the range where the image is projected onto the retina.

In this embodiment, a laser beam is incident on the reflective liquid crystal optical element via a corrective reflective liquid crystal optical element, so that the state of the laser beam that is reflected by the reflective liquid crystal optical element and incident on the eyeball is made uniform.

<Configuration of image display device 100a according to second embodiment>
The configuration of an image display device 100a according to the second embodiment will be described. Fig. 8 is a diagram illustrating an example of the configuration of the image display device 100a. The image display device 100a includes a corrective reflective liquid crystal optical element 9. Here, the corrective reflective liquid crystal optical element 9 is an example of a "second reflective liquid crystal optical element."

The corrective reflective liquid crystal optical element 9, like the above-mentioned reflective liquid crystal optical element 7, is a flat optical element that reflects and focuses circularly polarized light having the same chirality as the helical rotation direction of the liquid crystal molecules in a specific wavelength band with high efficiency. The focusing effect, which is determined by the in-plane orientation distribution of the liquid crystal molecules contained in the corrective reflective liquid crystal optical element 9, is adjusted so as to uniform the state of the laser beam entering the eyeball 50 within the range in which the image is projected onto the retina 53.

<Function of the image display device 100a according to the second embodiment>
Before describing the operation of the corrective reflective liquid crystal optical element 9, an image display device according to a comparative example will be described with reference to Fig. 9. Fig. 9 is a diagram for explaining the operation of the image display device according to the comparative example.

In FIG. 9, each of the laser beams L1 to L3 is scanned by the scanning mirror 5, reflected by the reflecting mirror 6, and then enters the reflective liquid crystal optical element 7. Here, the laser beam L2 is a laser beam that corresponds to the center of the image. The laser beam L1 is a laser beam that corresponds to one end of the image in the X direction, and the laser beam L3 is a laser beam that corresponds to the other end of the image in the X direction. In other words, the laser beam L1 corresponds to one end of the range in which the image is projected onto the retina 53, and the laser beam L3 corresponds to the other end of the range in which the image is projected onto the retina 53.

Laser beam L1 is reflected by region P1 of the reflective liquid crystal optical element 7 and enters the eyeball 50. Laser beam L2 is reflected by region P2 of the reflective liquid crystal optical element 7 and enters the eyeball 50. Laser beam L3 is reflected by region P3 of the reflective liquid crystal optical element 7 and enters the eyeball 50.

As described above, in the reflective liquid crystal optical element 7, the laser beam is reflected toward the eyeball 50, focused near the center of the pupil, and then projected onto the retina 53, so that the magnitude of the focusing effect increases in the positive X direction from region P1 to region P3.

In addition, as shown in Figure 9, when a reflective liquid crystal optical element is placed in front of the eyeball 50, the optical path length of the laser beams L1 to L3 becomes longer, and the state of the laser beams when they enter the eyeball 50 differs between the laser beams L1 to L3.

For example, if we assume that laser beam L2 passing through the center of the field of view is incident on eyeball 50 in a state approximately parallel to the Z axis in the figure, laser beam L1 is incident on the eyeball in a more divergent state than laser beam L2. On the other hand, laser beam L3 is incident on the eyeball in a more convergent state than laser beam L2. Thus, in the image display device of the comparative example, the state of the laser beam incident on eyeball 50 becomes non-uniform within the range in which the image is projected, and the resolution characteristics and focus characteristics may not be uniform.

Next, the operation of the image display device 100a according to this embodiment will be described with reference to FIG. 10. FIG. 10 is a diagram illustrating an example of the operation of the image display device 100a.

In FIG. 10, the laser beam reflected by region C1 of the correction reflective liquid crystal optical element 9 is incident on region P1 of the reflective liquid crystal optical element 7. The laser beam reflected by region C2 of the correction reflective liquid crystal optical element 9 is incident on region P2 of the reflective liquid crystal optical element 7, and the laser beam reflected by region C3 of the correction reflective liquid crystal optical element 9 is incident on region P3 of the reflective liquid crystal optical element 7.

Here, the reflective liquid crystal optical element 7 and the corrective reflective liquid crystal optical element 9 are each formed from the same liquid crystal material, and the liquid crystal molecules form a right-twisted helical arrangement that has the same chirality as the polarization, corresponding to the incident right-handed circularly polarized laser beam. As described above, the corrective reflective liquid crystal optical element 9 has a liquid crystal molecular orientation structure designed to cancel out the difference in the magnitude of the light-gathering effect of the reflective liquid crystal optical element 7 and to homogenize the state of the laser beam incident on the eyeball 50 within the range where the image is projected.

More specifically, the in-plane orientation distribution of the liquid crystal molecules is specified so that the light-collecting effect of the reflective liquid crystal optical element 7 increases in the positive X direction from regions P1 to P3, while the light-collecting effect of the corrective reflective liquid crystal optical element 9 increases in the negative X direction from regions C3 to C1.

By adopting such a configuration, the laser beam L1 reflected from the region C1 where the focusing effect of the correction reflective liquid crystal optical element 9 is large is incident on the region P1 where the focusing effect of the reflective liquid crystal optical element 7 is small, and the laser beam L3 reflected from the region C3 where the focusing effect of the correction reflective liquid crystal optical element 9 is small is incident on the region P3 where the focusing effect of the reflective liquid crystal optical element 7 is large.

This adjusts the balance of the magnitude of the focusing effect in each region, and as shown in Figure 10, the state of the laser beam reflected by the reflective liquid crystal optical element 7 and incident on the eyeball 50, for example the diameter and beam spread angle of the laser beam, is made uniform within the range in which the image is projected.

In the image display device 100a according to this embodiment, as in the image display device 100 described above, the light incident on the inside of the eyeball 50 is first focused near the center of the pupil 52 by the focusing function of the reflective liquid crystal optical element 7, and then an image is formed on the retina 53 at the back of the eyeball 50, so that an image is projected using Maxwellian vision. Therefore, in this embodiment, the focusing action of the lens 2, the corrective reflective liquid crystal optical element 9, and the reflective liquid crystal optical element 7 is designed so that the diameter of the laser beam when it enters the eyeball 50, which is a suitable condition for Maxwellian vision, is 350 μm or more and 500 μm or less, and the beam divergence angle is a positive finite value, i.e., diverging light.

<Advantages of the image display device 100a according to the second embodiment>
As described above, in this embodiment, a laser beam is incident on the reflective liquid crystal optical element 7 via the corrective reflective liquid crystal optical element 9. This makes it possible to uniformize the state of the laser beam reflected by the reflective liquid crystal optical element 7 and incident on the eyeball 50, allowing the user to view an image with uniform resolution characteristics and focus characteristics within the range in which the image is projected.

In addition, in this embodiment, by using a flat, thin corrective reflective liquid crystal optical element 9, the image display device 100a can be made smaller and lighter, and the image display device 100a can be easily mounted. Note that other effects are the same as those described in the first embodiment.

[Third embodiment]
Next, an optometry apparatus according to a third embodiment will be described.

For example, the optical device and image display device of the present invention can be used in an eye examination device. An eye examination device refers to a device that can perform various tests such as visual acuity tests, eye refractive power tests, intraocular pressure tests, and axial length tests. An eye examination device is a device that can perform tests without contacting the eyeball, and has a support unit that supports the subject's face, an eye examination window, a display unit that projects test information onto the subject's eyeball during eye examination, a control unit, and a measurement unit. The subject fixes his or her face on the support unit and stares at the test information projected by the display unit through the eye examination window. At this time, the optical device of this embodiment can be used as the display unit. In addition, by using the image display device of this embodiment, it is possible to realize an eye examination device in the form of glasses. This eliminates the need for space or a large eye examination device required for the test, and allows the test to be performed with a simple configuration regardless of location.

The optical device, image display device, and eye examination device according to the embodiments have been described above, but the present invention is not limited to the above embodiments, and various modifications and improvements are possible within the scope of the present invention.

In this embodiment, a glasses-type HMD has been described as an example of an image display device, but an image display device such as an HMD may not only be worn directly on a person's head, but may also be worn indirectly on a person's head via a member such as a fixing part.

1 Laser light source 2 Lens 301 Aperture member 302 Dimming element 41 Polarizer 42 ¼ wavelength plate 5 Scanning mirror (an example of a scanning unit)
6 Reflection mirror 7 Reflection type liquid crystal optical element (an example of an optical member, an example of a projection unit, an example of a first reflection type liquid crystal optical element)
71 Liquid crystal director 72 Equiphase surface 8 Glasses frame 81 Temple 82 Rim 9 Corrective reflective liquid crystal optical element (an example of a second reflective liquid crystal optical element)
20 Control unit 22 CPU
23 ROM
24 RAM
25 Light source driving circuit 26 Scanning mirror driving circuit 27 System bus 31 Emission control unit 32 Light source driving unit 33 Scanning control unit 34 Scanning mirror driving unit 35 Pupil position estimation unit 36 Attitude control unit 37 Stage driving unit 50 Eyeball 52 Pupil 53 Retina 61 Right-handed circularly polarized light 62 Left-handed circularly polarized light 100 Image display device P Reflection point

Patent Publication No. 6209662

Claims (14)

A projection unit projects scanning light that is light in a predetermined polarization state,
the projection unit includes an optical member that selectively reflects light in the predetermined polarization state ,
the optical member is a first reflective liquid crystal optical element that reflects and collects the light toward a surface onto which the light is projected;
The first reflective liquid crystal optical element includes at least two or more regions having different light-collecting effects within the element surface.
Optical device. 2. The optical device according to claim 1, wherein the light in the predetermined polarization state is light in an chiral polarization state. The light in the chiral polarized state is either right-handed circularly polarized light or left-handed circularly polarized light.
3. The optical device according to claim 2 . 4. The optical device according to claim 1, wherein the optical member has a surface that selectively reflects the light. 5. The optical device according to claim 4, wherein the optical member transmits light having a polarization state that is paired with the chirality from a surface opposite to the surface that selectively reflects the light . 6. The optical device according to claim 1, wherein the optical member is made of a polymerizable liquid crystal material. the first reflective liquid crystal optical element has a liquid crystal molecular orientation structure having three-dimensional periodicity;
the liquid crystal molecular orientation structure has a helical molecular arrangement having chirality in a depth direction of the element,
The element has a periodic arrangement in which the molecular orientation changes periodically along the element plane from the center of the element,
7. The optical device according to claim 1, wherein the period of the periodic array changes nonlinearly from a center of the element along an element surface. the periodic array includes a first region and a second region that are divided into two by a center portion of the element,
The optical device according to claim 7 , wherein the periodic arrays in the first region and the second region are asymmetric. 9. The optical device according to claim 7 , wherein the periodicity of the helical molecular arrangement is 6 or more. A scanning unit that generates the scanning light and irradiates the scanning light on the projection unit ,
The scanning unit includes a scanning mirror that rotates around two different axes;
The optical device according to claim 1 , further comprising: a reflecting mirror that reflects the light reflected by the scanning mirror. 11. The optical device according to claim 10, wherein the reflecting mirror is a second reflective liquid crystal optical element having a reflecting surface that reflects and collects either right-handed circularly polarized light or left-handed circularly polarized light. The optical device described in claim 11, wherein the second reflective liquid crystal optical element includes at least two or more regions within the element surface having different magnitudes of focusing effect, and among the regions having different magnitudes of focusing effect , the regions having a smaller magnitude of focusing effect are located closer to the surface onto which light is projected by the projection unit than the regions having a larger magnitude of focusing effect. A light source;
a polarizing unit that converts the light from the light source into the predetermined polarization state;
An image display device comprising: an optical device according to claim 1 . An optometric apparatus comprising: an optical device according to claim 1 ; or an image display device according to claim 13 .

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