Optical elements, optical systems, and display devices

Abstract

There is a need for optical elements that enable good image display and good imaging in a compact optical system. [Solution] The optical element 11 has a first power for the first light RY1 and a second power for the second light RY2, which has a wavelength and polarization direction that differ from the first light in at least one respect. When the first power is ψ1 and the second power is ψ2, the condition |ψ2 / ψ1|≦0.025 is satisfied.

Description

Technical Field

[0001] The present invention relates to an optical element suitable for an optical system used in a display device such as a head-mounted display (HMD).

Background Art

[0002] As disclosed in Patent Document 1, there is an optical system used in an HMD that guides image light from a display element to an observer's eye and guides light from the eye to an imaging element for line-of-sight detection.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] For an optical system as described above, an optical element is required that enables good image display and good eye imaging while being small.

Means for Solving the Problems

[0005] An optical element as one aspect of the present invention has a first power with respect to first light and a second power with respect to second light that is different from the first light in at least one of wavelength and polarization direction. When the first power is ψ1 and the second power is ψ2, |ψ۲ / ψ۱|≦0.025 It is characterized by satisfying the condition. The optical system also includes a first optical element as the above optical element and a display optical system that guides second light from the display surface to the observation side, and an optical system that guides first light from the observation side to the imaging surface through the first optical element, which constitutes another aspect of the present invention. Further, a display device having the above optical system, a display element having a display surface, and an imaging element having an imaging surface also constitutes another aspect of the present invention.

Advantages of the Invention

[0006] According to the present invention, it is possible to provide an optical element suitable for enabling compact and high-quality image display and imaging. [Brief explanation of the drawing]

[0007] [Figure 1] Diagram showing the optical element of the embodiment. [Figure 2] Magnified view of the optical surface of the above optical element [Figure 3] Cross-sectional view showing the display device of Example 1 [Figure 4] Cross-sectional view showing the display device of Example 2 [Figure 5] Cross-sectional view showing the display device of Example 3 [Figure 6] Diagram showing the polarization state and optical path in Example 3 [Figure 7] Cross-sectional view showing the display device of Example 4 [Figure 8] Cross-sectional view showing the display device of Example 5 [Figure 9] Cross-sectional view showing the display device of Example 6 [Figure 10] Cross-sectional view showing the display device of Example 7 [Figure 11] Figure showing an HMD including the display optical system of the embodiment. [Modes for carrying out the invention]

[0008] The following describes embodiments of the present invention with reference to the drawings.

[0009] Figures 1(a) and 1(b) show the optical element 1 of the embodiment. Figure 1(a) shows the case when a first light r1 is incident on the optical element 1, and Figure 1(b) shows the case when a second light r2 is incident on the optical element 1. The first light r1 and the second light r2 differ from each other in at least one of their wavelengths and polarization directions. Here, differing wavelengths means that the wavelengths as single wavelengths (e.g., 800 nm and 550 nm) are different, or that the wavelength ranges (e.g., near-infrared region 750-1000 nm and visible region 400-700 nm) are different. Also, different polarization directions mean that the polarization directions are orthogonal to each other or opposite to each other.

[0010] The optical element 1 has a first surface s1 and a second surface s2 as optical surfaces. In Figure 1(a), the first light r1 incident on the optical element 1 from the first surface s1 is focused to a focal position x1 by the focusing effect of at least one of the first surface s1 and the second surface s2. On the other hand, in Figure 1(b), the second light r2 incident on the optical element 1 from the first surface s1 is focused to a focal position x2 that is different from the focal position x1 (further from the optical element 1) by the focusing effect of at least one of the first surface s1 and the second surface s2.

[0011] Figures 1(a) and 1(b) show the case where the optical element 1 has positive power, but it may also have negative power. In Figure 1(b), the optical element 1 does not have to have power with respect to the second light r2. Figures 1(a) and 1(b) show the optical element 1 that transmits the first light r1 and the second light r2, but the optical element 1 may also reflect the first light r1 and the second light r2.

[0012] At least one of the first surface s1 and the second surface s2 is not limited to a plane, but may also be a curved surface (spherical, non-curved), a diffracted surface, or a metasurface.

[0013] Figure 2 shows a configuration example of a metasurface. The metasurface is formed by two-dimensionally arranging nanopillars Mp as structures that are sufficiently smaller than the wavelength of light on a substrate Ms. In the figure, one nanopillar Mp is shown. The metasurface forms a phase difference between the first light r1 and the second light r2 according to the height Mh, depth Md, width Mw, material, direction, and pitch of the nanopillar Mp. Thereby, the actions on the first light r1 and the second light r2 can be controlled. [[ID=**1**]] [[ID=**2**]]

[0014] [[ID=**3**]] For example, in Optics Letters, Vol. 46, 6, 1193 (2021), Xiang et al. reported a metasurface that can form different foci for lights with polarization directions orthogonal to each other in a wide wavelength range. Further, U.S. Patent No. 11977950 discloses a metalens that changes the optical path in different wavelength ranges. [[ID=**5**]] [[ID=**6**]]

[0015] [[ID=**7**]] Note that in Fig. 2, the case where the nanopillar Mp has a rectangular parallelepiped shape is shown, but the shape of the nanopillar may be changed according to the wavelength range and polarization state. The periphery of the nanopillar may be covered with air or other media. [[ID=**9**]] [[ID=**10**]]

[0016] [[ID=**11**]] Furthermore, the optical element 1 may be formed by joining a plurality of elements, or may be formed by laminating a plurality of films. [[ID=**13**]]

Example

[0017] [[ID=**18**]] Figure 3 shows the configuration of the display device OU1 of Example 1. The display optical system LU1 used in this example enables the observation of an enlarged image (display image) of the original image by guiding the image light from the display surface PNL on which the original image is displayed to the pupil EP of the observer's eye EYE. The display surface PNL is the modulation surface of a display element (optical modulation element) such as an LCD (Liquid Crystal Display) or an OLED (Organic Light Emitting Diode) display. A cover glass CL as a parallel flat plate having no refractive power is disposed between the display optical system LU1 and the display surface PNL. The display system is constituted by the display optical system LU1 and the display surface PNL. [[ID=**20**]]<[ [[ID=**21**]]

[0018] Furthermore, the display device OU1 captures a corneal image by focusing imaging light (light reflected by the cornea) from the cornea of ​​the eye (EYE) onto the imaging surface IM through the display optical system LU1 and the first optical element 11. The first optical element 11 has the function of optical element 1 as described in Figures 1(a) and (b). The first optical element 11 and the imaging surface IM are located on the display side of the display optical system LU1. The imaging surface IM is the light-receiving surface of an image sensor such as a CCD (Charge Coupled Device) sensor, CMOS (Complementary Metal Oxide Semiconductor), or SPAD (Single Photon Avalanche Diode) sensor. The display optical system LU1 and the first optical element 11 constitute the imaging optical system, and the imaging optical system and the image sensor constitute the gaze detection camera as an imaging system.

[0019] In this embodiment, the first light reaching the imaging surface IM1 from the eye EYE is defined as imaging light RY1, and the second light reaching the pupil EP from the display surface PNL is defined as image light RY2.

[0020] At least a portion of the power-generating region of the first optical element 11 is positioned within the optical path of the image light RY2. That is, a portion of the image light RY2 passes through the power-generating region of the first optical element 11. This reduces the tilt angle of the optical axis of the gaze detection camera relative to the cornea of ​​the eye, thereby reducing vignetting of the imaging light RY1 caused by the orientation of the eye and the thickness of the observer's eyelids. As a result, the accuracy of gaze detection can be improved.

[0021] Image light RY2 is visible light with wavelengths that allow the observer to view the displayed image, while imaging light RY1 is near-infrared light with wavelengths outside the visible range for line-of-sight detection. An image sensor with an imaging surface IM is sensitive in the near-infrared region.

[0022] In this embodiment, in order for the observer to view a good display image, the power of the first optical element 11 with respect to the image light RY2 is smaller than the power with respect to the imaging light RY1 (conversely, the power with respect to the imaging light RY1 is larger than the power with respect to the image light RY2). Because it has different powers depending on the wavelength, it is desirable that the first optical element 11 uses a metasurface.

[0023] Furthermore, by allowing at least a portion of the image light RY2 to pass through the first optical element 11, that is, by arranging at least a portion of the first optical element 11 within the optical path on the image light RY2, the display device OU1 can be made smaller compared to the case where the first optical element 11 is located outside the optical path on the image light RY2.

[0024] According to this embodiment, despite its compact size, it is possible to achieve high eye-tracking accuracy while allowing the observer to view a good display image with minimal distortion.

[0025] In this embodiment, the display optical system LU1 is composed of three lenses, but the number of lenses may be increased to correct various aberrations or decreased to reduce the size.

[0026] Furthermore, as shown in Figure 3, a portion of the imaging light RY1 passes through the peripheral portion of the display optical system LU1 and enters the image sensor IM. In this case, it is desirable that the first optical element 11 includes an asymmetrical (non-rotationally symmetrical) optical surface in order to correct the eccentricity aberration caused by the display optical system LU1.

[0027] Furthermore, it is desirable that the imaging surface IM be arranged parallel to or on the same plane as the display surface PNL. This allows the imaging surface IM and the display surface PNL to be placed in close proximity on the same element (or the same substrate), thereby enabling miniaturization of the entire display device OU1.

[0028] Here, we will explain the relationship between the power of the first optical element 11 (optical element 1) and the imaging light RY1 and the image light RY2. Let ψ1 be the power of the first optical element 11 with respect to the imaging light RY1 (first power), and ψ2 be the power of the first optical element 11 with respect to the image light RY2 (second power). In this case, |ψ2 / ψ1|≦0.025 (1) It is preferable that the following conditions be satisfied.

[0029] Since power is the reciprocal of the focal length (ψ1=1 / f1, ψ2=1 / f2), when the focal length of the first optical element 11 with respect to the imaging light RY1 is f1 and the focal length of the first optical element 11 with respect to the image light RY2 is f2, equation (1) can be rewritten as follows.

[0030] |f1 / f2|≦0.025 (2) By satisfying the conditions of equation (1) or equation (2), the power of the first optical element 11 relative to the image light RY2 is small, and the power of the first optical element 11 relative to the imaging light RY1 is small, allowing the observer to see a good display image with little distortion.

[0031] Furthermore, if the first optical element 11 has no power relative to the image light RY2, then ψ2 is set to 0 and f2 to infinity, and |ψ2 / ψ1|=0.000 and |f1 / f2|=0.000. It is more preferable to set the upper limits of equations (1) and (2) to 0.020, 0.015, or 0.010. The preference for satisfying the conditions of equations (1) and (2) is the same in other embodiments described later. [Examples]

[0032] Figure 4 shows the configuration of the display device OU2 of Example 2. The display device OU2 uses the same display optical system LU1 as in Example 1, but uses a first optical element 21 that is different from the first optical element 11 of Example 1.

[0033] The first optical element 21 is located on the lens surface closest to the observer (eye) among the three lenses that constitute the display optical system LU2. The imaging light from the cornea of ​​the eye is reflected by the first optical element 21 and guided to the imaging surface IM. In other words, the first optical element 21 and the imaging surface IM are located on the observer side of the display optical system LU1.

[0034] In this embodiment as well, at least a portion of the power-generating region of the first optical element 21 is positioned within the optical path of the image light RY2. This reduces the tilt angle of the optical axis of the gaze detection camera relative to the observer's cornea. Furthermore, the power of the first optical element 21 to the image light RY2 is smaller than the power to the imaging light RY1. It is also desirable that the first optical element 21 utilizes a metasurface.

[0035] In this embodiment, despite its compact size, it achieves high eye-tracking accuracy while allowing the observer to view a good display image with minimal distortion. [Examples]

[0036] Figure 5 shows the configuration of the display device OU3 of Example 3. The display device OU3 has a display optical system LU2 composed of two lenses and a first optical element 31 included in the imaging optical system. The display optical system LU2 includes a polarization section FL positioned on the observation side of the display surface PNL. The polarization section FL is composed of a polarizing plate and a quarter-wave plate (λ / 4 plate), as will be described later.

[0037] The first optical element 31 and the imaging surface IM are positioned on the display surface side of the display optical system LU2. In this embodiment as well, at least a portion of the power-generating region of the first optical element 31 is positioned within the optical path of the image light RY2. Furthermore, the power of the first optical element 31 with respect to the image light RY2 is smaller than the power it generates with respect to the imaging light RY1.

[0038] The display optical system LU2 has a first transmissive reflective surface HM1 and a second transmissive reflective surface HM2. In this embodiment, the first transmissive reflective surface HM1 is provided on the display-side lens surface of the display-side lens, and the second transmissive reflective surface HM2 is provided on the observation-side lens surface of the same lens. However, at least one of the first and second transmissive reflective surfaces HM1 and HM2 may be provided on the observation-side lens. The ratio of the transmittance to reflectance of the first and second transmissive reflective surfaces HM1 and HM2 may be 50:50, or it may be a different ratio.

[0039] Figure 6 shows the polarization state and optical path in the display device OU3. The polarization section FL is composed of a first polarizer PL1 and a first λ / 4 plate QWP1. The first polarizer PL1 transmits linearly polarized light in a polarization direction parallel to its transmission axis and absorbs linearly polarized light in a polarization direction perpendicular to the transmission axis. Note that if the display surface PNL can control the polarization state by the orientation of the liquid crystal, as in an LCD, the polarization section FL may be omitted. In addition, a first λ / 4 plate QWP1 is also placed between the first optical element 31 and the imaging surface IM. This first λ / 4 plate QWP1 may be integrated with the first λ / 4 plate QWP1 of the polarization section FL.

[0040] The second transmission / reflection surface HM2 is composed of a second λ / 4 plate QWP2 and a polarization-selective polarization-separating element PBS. The polarization-separating element PBS transmits linearly polarized light in a polarization direction parallel to its transmission axis and reflects linearly polarized light in a polarization direction perpendicular to the transmission axis. Note that the second λ / 4 plate QWP2 and the polarization-separating element PBS do not have to be placed on the same lens surface, but may be placed on separate lens surfaces.

[0041] Of the unpolarized image light RY2, the linearly polarized light transmitted through the first polarizer PL1 of the polarizing section FL is converted to right-handed circular polarization by the first λ / 4 plate QWP1. A portion of the right-handed circular polarization transmitted through the first transmission / reflection surface HM1 is converted to linear polarization (S polarization) by the second λ / 4 plate QWP2, and this linear polarization is reflected by the polarization separation element PBS. A portion of the right-handed circular polarization reflected by the first transmission / reflection surface HM1 becomes left-handed circular polarization, and this left-handed circular polarization is converted to linear polarization with a polarization direction perpendicular to the transmission axis of the first polarizer PL1 by the first λ / 4 plate QWP1, and this linear polarization is absorbed by the first polarizer PL1.

[0042] Linearly polarized light reflected by the polarization separation element PBS is converted to right-handed circularly polarized light by the second λ / 4 plate QWP2, and a portion of this right-handed circularly polarized light is reflected by the first transmission reflective surface HM1 to become left-handed circularly polarized light. Of the right-handed circularly polarized light, a portion that passes through the first transmission reflective surface HM1 is converted to linearly polarized light with a polarization direction perpendicular to the transmission axis of the first polarizer PL1 by the first λ / 4 plate QWP1, and this linearly polarized light is absorbed by the first polarizer PL1.

[0043] The left-handed circularly polarized light reflected by the first transmission / reflection surface HM1 is converted to linearly polarized light (P-polarized light) by the second λ / 4 plate QWP2, passes through the polarization separator element PBS, and reaches the pupil EP of the observer's eye (EYE).

[0044] Thus, the image light RY2 follows an optical path that reflects twice within the display optical system LU2 before reaching the pupil EP. This makes it possible to expand the field of view and effectively correct various aberrations while keeping the thickness of the display optical system LU2 in the optical axis direction low.

[0045] On the other hand, the imaging light RY1 passes through the second transmission reflective surface HM2 and the first transmission reflective surface HM1 in that order, passes through the first optical element 31, and forms an image on the imaging surface IM. By guiding the imaging light RY1 onto the imaging surface IM without reflecting it within the display optical system LU2, the number of times the imaging light RY1 passes through the first and second transmission reflective surfaces HM1 and HM2 is reduced, thereby suppressing a decrease in the amount of light incident on the imaging surface IM.

[0046] In this embodiment, the polarization state PS1 when the image light RY2 from the display surface PNL passes through the first polarizing plate PL1 of the polarizing unit FL, and the polarization state PS4 when the imaging light RY1 from the pupil EP passes through the first λ / 4 plate QWP1 and is directed toward the imaging surface IM, have mutually orthogonal polarization directions. Furthermore, the polarization state PS2 after the image light RY2 has passed through the first λ / 4 plate QWP1 and the polarization state PS3 when the imaging light RY1 passes through the first transmissive semi-reflective surface HM1 and is incident on the first λ / 4 plate QWP1 are mutually oppositely polarized circularly. In this embodiment, a first optical element 31 is used that has a metasurface whose power to the image light RY2 is smaller than the power to the imaging light RY1 due to these differences in polarization states. This allows the first optical element 31 to be placed in the optical path of the image light RY2.

[0047] The first optical element 31 may have a metasurface that has different powers on the image light RY2 and the imaging light RY1 depending on their wavelength difference. Furthermore, the first optical element 31 may have a metasurface that has different powers on the image light RY2 and the imaging light RY1 depending on their polarization state and wavelength difference.

[0048] Alternatively, the first and second transmissive reflective surfaces HM1 and HM2 may be provided on the surface of a substrate that is a parallel plate without refractive power.

[0049] Furthermore, the optical paths of the polarized states shown in Figure 6 are merely examples, and the orientation of the transmission axes of the polarizer and polarization separator, as well as the polarization state conversion effect of the λ / 4 plate, may be changed. Also, the polarization separator is not limited to elements that transmit and reflect according to the polarization direction of linearly polarized light; elements that transmit and reflect according to the polarization direction of circularly polarized light may also be used. The first transmission and reflection surface may also be changed to a surface that transmits and reflects according to the polarization direction.

[0050] In this embodiment, despite its compact size, it achieves high eye-tracking accuracy while allowing the observer to view a good display image with minimal distortion. [Examples]

[0051] Figure 7 shows the configuration of the display device OU4 of Example 4. The display device OU4 has the same display optical system LU2 as in Example 3 and two first optical elements 41 and 42 included in the imaging optical system.

[0052] In this embodiment as well, the first optical elements 41 and 42 and the imaging surface IM are positioned on the display surface side of the display optical system LU2. Both the first optical elements 41 and 42 have the functions of optical element 1 as described in Figures 1(a) and (b). At least a portion of the power-generating regions of the first optical elements 41 and 42 are positioned within the optical path of the image light RY2. The combined power of the first optical elements 41 and 42 with respect to the image light RY2 is smaller than the combined power with respect to the imaging light RY1. The imaging system may include multiple first optical elements.

[0053] Furthermore, the display device OU4 includes a light source LS, such as an LED, which is positioned on the display surface side of the display optical system LU2 and emits illumination light RY3 as a third light in the near-infrared region, and an illumination optical element 43, which is a second optical element positioned between the light source LS and the display optical system LU2. The illumination light from the light source LS is irradiated onto the observation side (eye) via the illumination optical element 43 and the display optical system LU2. The illumination system is composed of the light source LS, the illumination optical element 43, and the display optical system LU2. The illumination optical element 43 also has the function of optical element 1 as described in Figures 1(a) and (b). At least a portion of the region of the illumination optical element 43 that has power for illumination light is positioned within the optical path of the image light RY2.

[0054] According to this embodiment, despite its compact size, it includes an illumination system for eye-tracking detection, achieving high eye-tracking accuracy while allowing the observer to view a good display image with minimal distortion.

[0055] Alternatively, the light source LS may be placed on the observation side of the display optical system LU2, and the illumination light RY3 from the light source LS may be reflected by the illumination optical element 43 placed on the lens surface closest to the observation side of the display optical system LU2 and illuminated on the observation side. [Examples]

[0056] Figure 8 shows the configuration of the display device OU5 of Embodiment 5. The display device OU5 has the same display optical system LU2 as in Embodiments 3 and 4, and a first optical element 51 included in the imaging optical system. In this embodiment, the polarization unit FL is configured to be included in the imaging optical system and the illumination optical system.

[0057] In this embodiment as well, the first optical element 51 and the imaging surface IM are positioned on the display surface side of the display optical system LU2. The first optical element 51 has the function of optical element 1 as described in Figures 1(a) and (b). At least a portion of the power-generating region of the first optical element 51 is positioned within the optical path of the image light RY2. The power of the first optical element 51 with respect to the image light RY2 is smaller than the power with respect to the imaging light RY1. The first optical element 51 is provided on the observation-side surface of the polarization section FL.

[0058] Furthermore, the display device OU5 includes a light source LS that emits illumination light RY3, and an illumination optical element 52 as a second optical element positioned between the light source LS and the display optical system LU2. The illumination light from the light source LS is irradiated onto the observation side via the illumination optical element 52 and the display optical system LU2. The illumination optical element 52 also has the functions of optical element 1 as described in Figures 1(a) and (b). At least a portion of the power region of the illumination optical element 52 is positioned within the optical path of the image light RY2. The illumination optical element 52 is provided on the observation side surface of the polarization section FL.

[0059] In this embodiment, despite its compact size, it includes an illumination system for gaze detection, achieving high gaze detection accuracy while allowing the observer to view a good display image with minimal distortion. Furthermore, in this embodiment, by integrating the first optical element 51 and the illumination optical element 52 with the polarization unit FL, the increase in the number of components constituting the display device OU5 can be suppressed. [Examples]

[0060] Figure 9 shows the configuration of the display device OU6 of Example 6. The display device OU6 has a display optical system LU3 composed of three lenses, and a first optical element 61 and an optical element (lens in the figure) 62 included in the imaging optical system. The display optical system LU3 includes a polarization section FL similar to that of Example 3.

[0061] The imaging plane IM is located on the display plane side of the display optical system LU3. The first optical element 61 has the function of optical element 1 as described in Figures 1(a) and (b). At least a portion of the power region of the first optical element 61 is located within the optical path of the image light RY2. The power of the first optical element 61 with respect to the image light RY2 is smaller than the power with respect to the imaging light RY1. The first optical element 61 is located at the cemented surface of the cemented lens included in the display optical system LU3.

[0062] On the other hand, the optical element 62 is located outside the optical path of the image light RY2 and does not have the function of the optical element 1 described in Figures 1(a) and (b). The optical element 62 is not limited to a biconvex lens as shown in the figure, but may also be a biconcave lens, a meniscus lens, a diffracting element, a mirror, etc. Furthermore, multiple optical elements may be provided as the optical element 62. [Examples]

[0063] Figure 10 shows the configuration of the display device OU7 of Example 7. The display device OU7 has the same display optical system LU3 as in Example 6 and a first optical element 71 included in the imaging optical system.

[0064] The imaging sensor (IM) is located behind the display panel (PNL) (on the opposite side from the observation side of the display panel). This configuration is also called an under-display camera.

[0065] The first optical element 71 has the function of optical element 1 as described in Figures 1(a) and (b). The entire power-bearing region of the first optical element 71 is located within the optical path of the image light RY2. The power of the first optical element 71 with respect to the image light RY2 is smaller than the power with respect to the imaging light RY1. The first optical element 71 is located on the lens surface closest to the display surface in the display optical system LU3.

[0066] According to this embodiment, the degree of freedom in arranging the first optical element 71 and the display surface PNL is improved, making it possible to make the entire display device OU7 thinner and suppress the increase in the number of components.

[0067] [Head-mounted display (HMD)] Figure 11 shows an HMD100 that utilizes the display devices of Examples 1 to 7. The HMD100 has a right optical system 101 and a left optical system 201, and a right display unit 102 and a left display unit 202. Optical systems 101 and 201 each have the display system and imaging system (and illumination system) described in each example.

[0068] The display light from the display surfaces (original images) of the right and left display units 102 and 202 is guided to the observer's right and left eyes, respectively, through the right and left optical systems 101 and 201. This allows the observer to view the magnified display image. By introducing parallax into the original images displayed on the right and left display units 102 and 202, the observer can observe a display image that can be viewed in stereoscopic form. The display units or optical systems may be made different for the left and right sides depending on the observer's visual acuity.

[0069] Furthermore, the HMD100 is connected to a processing unit 301 that detects the gaze of the observer's right and left eyes based on corneal images captured by the right and left imaging systems. The processing unit 301 can change the resolution of the original images displayed on the display units 102 and 202, or operate the displayed user interface (menu image), according to the gaze detected. Alternatively, the observer may be authenticated using the iris image obtained by the imaging system. The imaging system that acquires the corneal and iris images may be provided only on one eye side.

[0070] Furthermore, the display devices of Examples 1 to 7 are not limited to HMDs, but can be used as various display devices that guide light from the display surface to the observer's eye, such as electronic viewfinders.

[0071] The above embodiments include the following configuration.

[0072] (Composition 1) Possessing first power relative to first light, A second light has a second power for a second light whose wavelength and polarization direction are different from the first light, When the first power is ψ1 and the second power is ψ2, |ψ2 / ψ1|≦0.025 An optical element characterized by satisfying the following conditions. (Configuration 2) The optical element according to configuration 1, characterized by transmitting or reflecting the first light and the second light. (Composition 3) The second light is light with wavelengths in the visible range, The optical element according to configuration 1 or 2, characterized in that the first light is light with a wavelength outside the visible range. (Composition 4) The optical element according to any one of configurations 1 to 3, characterized in that the polarization directions of the first light and the second light are orthogonal to each other or opposite to each other. (Composition 5) The optical element is characterized by having a metasurface, as described in any one of configurations 1 to 4. (Composition 6) Possessing first power relative to first light, A second light has a second power for a second light whose wavelength and polarization direction are different from the first light, An optical element characterized in that the second power is smaller than the first power. (Composition 7) A first optical element as the optical element described in any one of configurations 1 to 6, It has a display optical system that guides the second light from the display surface to the observation side, An optical system characterized by guiding the first light from the observation side to the imaging surface via the first optical element. (Composition 8) The optical system according to configuration 7, characterized in that at least a portion of the regions having the first and second powers in the first optical element is arranged in the optical path of the second light. (Composition 9) The optical system according to configuration 7 or 8, characterized in that the first light is guided to the imaging surface via the display optical system and the first optical element. (Composition 10) The display optical system includes two transmissive reflective surfaces that transmit and reflect the second light, The optical system according to any one of configurations 7 to 9, characterized in that the two transmission and reflection surfaces transmit the first light from the observation side without reflecting it and direct it toward the imaging surface. (Composition 11) The optical system according to configuration 10, characterized in that one of the two transmission and reflection surfaces is composed of a polarization separation element that transmits and reflects the second light according to its polarization state. (Composition 12) The optical element has a second optical element, The optical system according to any one of configurations 7 to 11, characterized in that it guides the third light from the light source to the observation side via the second optical element. (Composition 13) The optical system according to configuration 12, characterized in that at least a portion of the region in the second optical element that has power for the third light is located within the optical path of the second light. (Composition 14) The optical system according to configuration 12 or 13, characterized in that the third light is guided to the observation side via the second optical element and the display optical system. (Composition 15) An optical system according to any one of configurations 12 to 14, characterized in that the third light reflected on the observation side is guided to the imaging surface as the first light. (Composition 16) The optical system described in any one of configurations 7 to 15, A display device having the display surface, A display device characterized by having an image sensor having the aforementioned imaging surface. (Composition 17) The display device according to configuration 16, characterized in that the image sensor performs imaging for detecting the observer's line of sight.

[0073] The embodiments described above are merely representative examples, and various modifications and changes can be made to each embodiment when implementing the present invention. [Explanation of Symbols]

[0074] 1,11,21,31,41,42,43,51,52,61,71 (First) Optical element LU1,LU2,LU3 Display optical system PNL display surface IM imaging surface

Claims

1. Having first power relative to first light, The second light has a second power for a second light whose wavelength and polarization direction are different from the first light, When the first power is ψ1 and the second power is ψ2, |ψ2 / ψ1|≦0.025 An optical element characterized by satisfying the following conditions.

2. The optical element according to claim 1, characterized in that it transmits or reflects the first light and the second light.

3. The second light is light with wavelengths in the visible range, The optical element according to claim 1, characterized in that the first light is light with a wavelength outside the visible range.

4. The optical element according to claim 1, characterized in that the polarization directions of the first light and the second light are orthogonal to each other or opposite to each other.

5. The optical element according to claim 1, characterized in that the optical element has a metasurface.

6. Having first power relative to first light, The second light has a second power for a second light whose wavelength and polarization direction are different from the first light, An optical element characterized in that the second power is smaller than the first power.

7. The first optical element as the optical element according to claim 1 or 6, It has a display optical system that guides the second light from the display surface to the observation side, An optical system characterized by guiding the first light from the observation side to the imaging surface via the first optical element.

8. The optical system according to claim 7, characterized in that at least a portion of the regions having the first and second powers in the first optical element is arranged in the optical path of the second light.

9. The optical system according to claim 7, characterized in that the first light is guided to the imaging surface via the display optical system and the first optical element.

10. The display optical system includes two transmissive reflective surfaces that transmit and reflect the second light, The optical system according to claim 7, characterized in that the two transmission and reflection surfaces transmit the first light from the observation side without reflecting it and direct it toward the imaging surface.

11. The optical system according to claim 10, characterized in that one of the two transmission and reflection surfaces is composed of a polarization separation element that transmits and reflects the second light according to its polarization state.

12. The optical element has a second optical element, The optical system according to claim 7, characterized in that it guides the third light from the light source to the observation side via the second optical element.

13. The optical system according to claim 12, characterized in that at least a portion of the region of the second optical element that has power with respect to the third light is arranged in the optical path of the second light.

14. The optical system according to claim 12, characterized in that the third light is guided to the observation side via the second optical element and the display optical system.

15. The optical system according to claim 12, characterized in that the third light reflected on the observation side is guided to the imaging surface as the first light.

16. The optical system according to claim 7, A display device having the display surface, A display device characterized by having an image sensor having the aforementioned imaging surface.

17. The display device according to claim 16, characterized in that the image sensor performs imaging for detecting the observer's line of sight.

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