Optical film for augmented reality device

Abstract

An optical element includes a first wavelength band filter film including a diffractive optical structure, where the diffractive optical structure diffracts light including light in a first wavelength band so as to form a first optical focus array. The wavelength band filter film selectively reflects or transmits one of the light in the first wavelength band, and selectively reflects or transmits the other of the light outside the first wavelength band.

Description

Technical Field

[0001] The present invention relates to an optical element for augmented reality (AR) and virtual reality (VR) head mounted displays (HMD) and heads up displays (HUD). Background Art

[0002] Augmented reality (AR) devices allow users to experience and / or interact with virtual information without losing situational awareness of the real world. Such devices typically include a display device positioned close to the user's eyes that displays images to the user while still allowing the user to see the displayed images to maintain awareness of the external environment. AR devices typically take the form of a head-mounted display (HMD), which is worn on the user's head in the same way as a pair of glasses or a helmet. The display is located in front of one or both of the user's eyes and is typically in the form of a partially transparent film through which the image is projected. The user can then see the image projected through the film to the outside world.

[0003] Existing AR HMD products include Google Glass (RTM) and Microsoft Hololens (RTM). HMD applications require AR displays to be compact, non-intrusive, comfortable, and capable of producing high-quality images.

[0004] On the other hand, a heads-up display (HUD) is a transparent display located at the windshield of a car or aircraft to present data without requiring the driver or pilot to look away from his or her usual viewpoint. Several car manufacturers, including BMW (RTM) and Bentley (RTM), offer HUDs.

[0005] Each HMD device has an eye range, which is defined as the area in which a user can move their eyes relative to the display and still see the full projected image. It is desirable to have a large eye range so that the user can see the image from different eye positions, especially when the HMD may be misplaced during movement. In addition, a large eye range ensures that a greater proportion of users can view the projected image without having to readjust the HMD, while taking into account the natural variations in face shape and eye spacing between users.

[0006] The field of view (FOV) of a display is defined as the angle within which the eyes are open and within which the user can see the displayed content. A large FOV increases the realism of virtual content and the sense of immersion provided by an AR device, as well as enabling the display of larger and more detailed images. A small FOV is one of the most common complaints about existing AR displays, with many currently available HMDs only implementing a diagonal FOV of less than 56°, and current HUDs providing a FOV of less than 11°.

[0007] Free space combiners are optical elements in an AR HMD that are located directly in front of the user’s eyes. Through these optical elements, the user can see digital content superimposed on the real world. Free space combiners can also perform other optical functions, such as lens functions, making them critical to the FOV and eye-tracking size of the AR device in which they are placed.

[0008] Unlike free-space combiners, waveguide combiners are based on total internal reflection and are widely used in AR glasses to integrate multiple optical functions into a thin, transparent and lightweight substrate. Waveguide combiners usually include a diffractive optical element (DOE) or a holographic optical element (HOE) to relay images from the image engine of the AR device to the eye.

[0009] It is desirable for an AR device to have a transparent and lightweight combiner that can produce a large FOV and eye range. It is desirable to place the combiner as close to the eye as possible to improve the FOV of the device and also make the AR device more compact. There are also conflicting requirements for the combiner, namely, allowing the user to view light from the real world with as little distortion as possible while modifying light from the image engine of the AR device to reflect and focus the light.

[0010] A beam combiner composed of conventional diffractive structures is compact and can meet the above requirements of AR device combiners to a certain extent. However, existing beam combiners produce visually obtrusive rainbow-like dispersion when used with generated AR images containing multiple colors or when used for viewing bright ambient light. In addition, it is challenging to realize such diffractive structures with multiple colors. Summary of the invention

[0011] According to an aspect of the present invention, an optical element is provided, which includes a first wavelength band filter film, the first wavelength band filter film includes a diffractive optical structure, wherein the diffractive optical structure diffracts light including light in a first wavelength band to form a first optical focus array, the wavelength band filter film selectively performs one of reflection or transmission of light in the first wavelength band, and selectively performs the other of reflection or transmission of light outside the first wavelength band.

[0012] The combination of a diffractive structure and a narrowband film provides a compact film that can meet the optical functions required by the combiner of an AR device, including a lens function to produce multiple exit pupils. These optical functions can be provided by the diffractive patterning of the film. At the same time, the film appears transparent to visible light, and the rainbow-like dispersion effect is significantly reduced due to the presence of the narrowband filter.

[0013] The film of the present invention realizes a transparent and clear AR display with a large FOV and a large eye range while maintaining the image always in focus. When used as a reflector, the film can have high transparency when only reflecting a very narrow band due to the presence of a narrow band filter. The film can be used both in free space and in waveguide optical combiners.

[0014] Preferably, the optical focus forms an array of spots located in a manifold separated from the surface of the membrane.

[0015] Preferably, the focal points are regularly spaced from one another.

[0016] Preferably, the diffractive optical structure comprises a pattern of grooves or holes formed in the waveband film.

[0017] Preferably, the wavelength filter film has a wavelength band falling within one or both of the visible light band and the infrared light band.

[0018] Preferably, the wavelength band filter film is a transmission filter having a wavelength band with a full width at half maximum transmission of 50 nm or less.

[0019] Preferably, the wavelength band filter film is a reflective filter that reflects a wavelength band with a full width at half maximum of 50 nm or less.

[0020] Suitably, the band filter is a notch filter.

[0021] Preferably, the band filter film is a narrow band reflector film.

[0022] Preferably, the wavelength filter film comprises a superstructure.

[0023] More preferably, the superstructure is a supersurface having a unit structure, which unit structure includes one of the following groups: elliptical nanocolumn pairs, rectangular nanocolumns with notches, hollow nanocolumns distributed in a square two-dimensional lattice, circular nanocolumns periodically arranged in a square two-dimensional lattice, nanocolumns with elliptical cross-sections periodically arranged in a square lattice, and multilayer nanocolumns with circular cross-sections.

[0024] Preferably, the nanopillars of the metasurface are made of TiO2.

[0025] Preferably, one or more nanorods in the unit structure are disposed in air.

[0026] Alternatively, one or more nano-pillars in the unit structure are encapsulated in an organic polymer material.

[0027] In one embodiment, the metasurface has a unit structure including one or more multilayer nanocolumns, wherein each multilayer nanocolumn includes an Al2O3 bottom layer, a TiO2 middle layer formed on the bottom layer, and a SiO2 top layer formed on the middle layer.

[0028] Preferably, the band filter film has a layer structure, which includes one of alternating Al2O3 / SiO2 layers, alternating HfO2 / SiO2 layers, alternating TiO2 / SiO2 layers and alternating Ta2O5 / SiO2 layers.

[0029] Preferably, the optical structure also includes a second wavelength band filter film, which has a second diffractive optical structure, wherein the second diffractive optical structure diffracts light including light in the second wavelength band to form a second optical focus array, the second wavelength band filter film selectively performs one of reflection or transmission of light in the second wavelength band, and selectively performs the other of reflection or transmission of light outside the second wavelength band, and the second wavelength band does not overlap with the first wavelength band.

[0030] Suitably, the optical structure also includes a third wavelength band filter film, which has a third diffractive optical structure, wherein the third diffractive optical structure diffracts light including light in a third wavelength band to form a third optical focus array, the third wavelength band filter film selectively performs one of reflection or transmission of light in the third wavelength band, and selectively performs the other of reflection or transmission of light outside the third wavelength band, and wherein the third wavelength band does not overlap with the first wavelength band or the second wavelength band.

[0031] Preferably, the diffractive optical structure is a holographic optical structure.

[0032] According to another aspect of the present invention, a free space combiner for an augmented reality or virtual reality device is provided, comprising the above optical element.

[0033] According to another aspect of the present invention, there is provided a waveguide combiner for an augmented reality or virtual reality device, comprising the above optical element.

[0034] According to another aspect of the present invention, an augmented reality or virtual reality device is provided, comprising the combiner as described above and a light source configured to project light onto the combiner to form an image, wherein the light source is configured to project light having a wavelength within the first wavelength band.

[0035] According to another aspect of the present invention, an augmented reality or virtual reality device is provided, comprising: a combiner comprising the above-mentioned optical element; a first light source configured to project light onto the combiner to form an image, wherein the first light source is configured to project light having a wavelength within the first wavelength band; and a second light source configured to project light onto the combiner to form an image, wherein the second light source is configured to project light having a wavelength within the second wavelength band.

[0036] Preferably, the above-mentioned augmented reality or virtual reality device also includes a third light source, which is configured to project light onto the combiner to form an image, wherein the third light source is configured to project light having a wavelength within a third wavelength band, wherein the third wavelength band does not overlap with the first wavelength band or the second wavelength band.

[0037] Preferably, there is provided a virtual reality device as described above, further comprising a light shield configured to block external light from reaching the combiner. BRIEF DESCRIPTION OF THE DRAWINGS

[0038] Embodiments of the invention will now be described, by way of further example only, and with reference to the accompanying drawings, in which:

[0039] Figure 1 is a perspective view of a film acting as a combiner in an AR device according to an embodiment;

[0040] Figure 2 is a top plan view of AR glasses including a film of an embodiment that acts as a combiner;

[0041] Figure 3 a front view showing an eye field according to an embodiment, illustrating the focal point created by the membrane;

[0042] Figure 4 is a perspective view of a film acting as a combiner in a VR device according to an embodiment;

[0043] Figure 5 is a perspective view of a membrane acting as a combiner in an alternative VR device according to an embodiment;

[0044] Figure 6 is an example of a full-color display device using a film including three hologram layers according to the embodiment;

[0045] Figure 7 is a perspective view of a film acting as a combiner in AR glasses according to an embodiment, showing an image engine projecting light onto the film;

[0046] Figure 8 showing cross-sectional views of a unit structure in the XY and XZ planes of the metasurface design used in the first example;

[0047] Fig. 9 shows the reflectance spectrum of the metasurface of the first example;

[0048] Fig.10 showing cross-sectional views of a unit structure in the XY and XZ planes of a metasurface design used in a second example;

[0049] Fig.11 shows the reflectance spectrum of the metasurface of the second example;

[0050] Fig.12 showing cross-sectional views of a unit structure in the XY and XZ planes of a metasurface design used in a third example;

[0051] Fig.13 shows the reflectance spectrum of the metasurface of the third example;

[0052] Fig.14 showing cross-sectional views of a unit structure in the XY and XZ planes of a metasurface design used in a fourth example;

[0053] Fig.15 shows the reflection spectrum of the metasurface of the fourth example;

[0054] Fig.16 shows cross-sectional views of a unit structure in the XY and XZ planes of a metasurface design used in a fifth example;

[0055] Fig.17 shows the reflection spectrum of the metasurface of the fifth example;

[0056] Fig.18 shows cross-sectional views of a unit structure in the XY and XZ planes of a metasurface design used in a sixth example;

[0057] Fig.19 shows the reflection spectrum of the metasurface of the sixth example;

[0058] Fig. 20 showing cross-sectional views of a unit structure in the XY and XZ planes of a metasurface design used in a seventh example;

[0059] Fig.21 shows the reflection spectrum of the metasurface of the seventh example; DETAILED DESCRIPTION

[0060] Embodiments of the present invention include a band filter film. Examples of suitable band filter films include narrow band reflectors, notch filter films, and films including superstructures.

[0061] An example of a suitable commercially available notch filter film suitable for use as a substrate for an optical element is the product code NF514-17 produced by Thorlabs (RTM). The film reflects a band centered at 514 nm and having a full width at half maximum (FWHM) of 17 nm. For the purposes of this description, a narrowband filter is defined as a filter that reflects or transmits a band with a FWHM of 50 nm or less and preferably 20 nm or less. In a more preferred embodiment, the filter has a FWHM of 15 nm or less. The effective reflected light intensity of a desired wavelength can be adjusted by varying the depth of the diffraction pattern imprinted on the narrowband film, which can be a holographic pattern.

[0062] The present inventors have discovered that a notch filter having particularly advantageous optical properties can be formed from a plurality of alternating Al2O3 / SiO2 layers. Other preferred materials for the notch filter include a plurality of alternating hafnium (IV) dioxide (HfO2) / silicon dioxide (SiO2) layers, titanium dioxide (TiO2) / SiO2 layers, or tantalum pentoxide (Ta2O5) / SiO2 layers.

[0063] Suitable band filters can also be formed by superstructures such as metasurfaces. A metastructure is a structure consisting of an array of unit structures whose size and spacing are less than the wavelength of light for which the surface is designed. Superstructures for visible wavelengths typically have structure sizes less than 1 micron. A metasurface is a superstructure that includes a surface consisting of an array of unit structures discussed above.

[0064] Depending on the design of the unit structure, the metasurface can provide multi-dimensional light modulation of properties such as polarization, phase, amplitude, and orbital angular momentum. In the present invention, the metasurface can be used to provide a film with highly saturated structural color, which is equivalent to a narrow-band wavelength filter.

[0065] Suitable metasurfaces can be formed from various known materials including TiO2, SiO2 and Al2O3. The inventors have found that a metasurface having particularly advantageous optical properties can be formed from a TiO2 layer. To achieve the narrowband filtering effect of the present invention, these materials are used to form unit structures having various possible designs that will be discussed in detail below.

[0066] The band filter film is patterned to produce a diffractive and preferably holographic lens structure, which includes multiple diffractive lenses in an array across the surface of the film. These lenses focus the incident light at different points, which allows the creation of an expanded eye range when the film is used as a combiner in an AR HMD device. The focal points of the multiple lenses are usually arranged on a manifold away from the surface of the film. These points correspond to the possible positions of the user's eyes to correctly view the virtual image in the AR HMD.

[0067] In this example, the surface of the film contains a pattern of grooves or holes of various predetermined depths formed in the film, thereby producing a two-dimensional hologram. The grooves or holes of the film and the unpatterned portions effectively form pixels in a relief image on the surface of the film, thereby forming a hologram. This type of pattern can be created by known computer-generated holographic techniques to produce the desired diffractive lens array on the film. The pattern can be physically created on the film by performing electron beam lithography or other nanofabrication techniques.

[0068] Existing holographic lenses cause different wavelengths of light to bend when they hit the lens at different angles, creating chromatic aberration images. This is undesirable because such lenses cannot be used in devices that operate in multiple colors. In addition, users see rainbow-like dispersion when viewing any external strong light through the lens. This limits the practicality of holographic lenses in applications such as AR devices.

[0069] In the present invention, these chromatic aberration problems are minimized by making the hologram from narrowband reflectors, notch filters (thin films based on distributed Bragg reflectors), or metasurfaces as discussed above. Such layers are designed to reflect only a narrow bandwidth of light (e.g., less than 15nm per color), while being transparent to the rest of the visible spectrum.

[0070] Figure 1 is a perspective view of a film acting as a combiner in an AR device according to an embodiment, showing the eye range formed by the film when light is projected onto the holographic surface of the film. In a typical AR device, a light engine (such as one or more scanning laser projectors) projects light onto the combined film, and then the light in the wavelength band selected by the filter film is reflected and focused by a diffractive lens formed by patterning the film. Other light engines, such as micro-LED (light emitting diode) and OLED (organic light emitting diode) light sources, can also be used. The resulting focus itself forms an array across the eye range of the device.

[0071] Figure 2 Shows a pair of AR glasses viewed from above Figure 1 Similar devices. Figure 2 In FIG. 5 , two light engines are shown projecting light onto the combiner film, but a single light engine may also be used.

[0072] Figure 3 is a view of the eye-tracking range showing the focus or convergence point produced by the film according to the present invention from the perspective of the user's eye. The focus forms an array of points located in a manifold separated from the surface of the film. The manifold can be flat, but a curved surface is preferred in order to match the focus position across the eye-tracking range with the likely position of the user's eye.

[0073] When the combiner is used in a VR device instead of an AR device, a light shield is placed on the side of the combiner away from the eye-tracking range to block light from the outside. This means that only light from the light engine reaches the user's eyes via the combiner in the VR device. Figure 4 , which is a VR device, the VR device includes a sunshade and a projector placed between the sunshade and the combiner. Similarly, Figure 5 A VR device is shown having a projector and a projection lens between a sunshade and a combiner.

[0074] For multicolor displays, the present invention uses a combination of several band filters that are tuned to different visible light wavelengths that match the colors of the display. In a complete AR device, multiple light sources with different wavelengths are used to project images onto the film. The band filters within the optical element are tuned to the same wavelength as the laser, respectively. Typically three light sources and three corresponding band filters are used, each of which is tuned to a band that matches one of the red (about 640nm), green (about 525nm), and blue (about 450nm) display colors. This produces a conventional RGB display type.

[0075] Figure 6 An example of a full-color display device using a film according to the present invention is shown. The three holographic film layers reflect red light, green light, and blue light from an image projector, respectively. Since each film layer reflects only a narrow band of light near the wavelength of the light from the projector, almost all external light is transmitted through the film layer to the user's eyes. This means that the user sees the outside world clearly. Even with three reflective films according to the present invention, the total bandwidth of wavelengths reflected by these films is typically less than 50 nm, i.e., a small portion of the entire visible light band, which extends from about 400 nm to about 700 nm.

[0076] Figure 7 Shown with Figure 6 A similar full-color display device incorporated into a pair of AR glasses. The light engine is shown projecting red, green, and blue light onto the three holographic film layers that make up the combiner film, which in turn reflects and diffracts the light to form a color image on the user's eye.

[0077] In an alternative embodiment, a color display may be provided by using three different color light sources and only two band filter films, one of which has two bands corresponding to the bands of two of the light sources.

[0078] Example

[0079] Notch Filter Examples

[0080] In a first example, a diffractive optical element comprising a 2D grating with a pitch of 100 μm was written on a notch filter by laser ablation. The notch filter is product code NF514-17 produced by Thorlabs (RTM). Product NF514-17 is designed to reflect 514 nm wavelength (full width at half maximum of 17 nm) and transmit the rest of the visible wavelengths.

[0081] Tests on the examples showed that the diffraction pattern (i.e., 2D grating) written on the wavelength selective reflective layer (i.e., notch filter) will only diffract light with the designed wavelength. Red laser light (wavelength 632.8nm) and green laser light (wavelength 515nm) were diffracted successively by the optical element to demonstrate this. It was found that the green pattern produced by the optical element diffracting the green laser light was 28 times brighter than the red pattern produced by the optical element diffracting the red laser light. The red laser light produced a weak diffraction pattern, which is believed to be caused by specular reflection.

[0082] Metasurface Examples

[0083] The inventors have developed several metasurface designs that implement the narrowband optical filtering of the present invention. The holographic lenses formed using these metasurfaces reflect light with a narrow band width and work under vertical or oblique incident light with a specific angle of incidence (AOI).

[0084] The material used for these metasurface designs is titanium dioxide (TiO2) due to its high energy bandgap and relatively high refractive index (refractive index is about 2.5). Alternatively, gallium nitride (GaN) or another high refractive index material can be used to replace TiO2 in the metasurface.

[0085] The substrate material on which the metasurface is formed is glass, which has a refractive index of approximately 1.5.

[0086] Each metasurface consists of unit cells periodically arranged in a planar square lattice. These figures show the unit cell structure of the design, not the entire lattice. Other lattice structures, such as hexagonal lattices, can also be used.

[0087] Metasurface Example 1

[0088] Figure 8 A cross-sectional view of a unit structure in the XY and XZ planes of a first metasurface design suitable for use in the present invention is shown. The angle of incidence (AOI) of incident light E is shown at the top of the figure. The metasurface includes pairs of elliptical TiO2 nanopillars in air.

[0089] The composite unit structure consists of a pair of elliptical nanocolumns, which refers to a column with an elliptical cross-section and an elliptical plan view. Each nanocolumn has a height h, a short axis length d1, and a long axis length d2. Each nanocolumn is oriented at an angle θ between its long axis and the global Y axis. The center of each nanocolumn is located at the coordinates dx, dy relative to the center of the unit structure. The design parameters used in this example are listed in Table 1 below. The polarization direction is along the Y axis, and the incident light is located in the YZ plane.

[0090] Fig. 9 The reflectance spectrum of the metasurface of this example is shown. This symmetry-breaking and symmetry-preserving design suppresses a major portion of the metasurface scattering losses, thus resulting in the narrow reflectance bandwidth required for the film of the present invention.

[0091] Table 1

[0092] Height(h) 140nm Diameter 1 (d1) 90nm Diameter 2 (d2) 190nm Center X coordinate (dx) 90nm Center y coordinate (dy) 0nm Period 1 (p1) 360nm Period 2 (p2) 230nm Angle (θ) 25 degrees

[0093] Metasurface Example 2

[0094] Fig.10 A cross-sectional view of a unit structure in the XY and XZ planes of a second metasurface design suitable for use in the present invention is shown. The angle of incidence (AOI) of incident light E is shown at the top of the figure. The metasurface includes pairs of rectangular TiO2 nanopillars with recesses in air.

[0095] The unit structure consists of a TiO2 nanocolumn with a notch having a rectangular cross section. The notch also has a rectangular cross section in plan view and is located at one corner of the column in cross section. This results in the column being L-shaped in plan view.

[0096] Ignoring the notch, the height of the column is h and the width in the X and Y directions is w1 and w4, respectively. The nanocolumn is located at the center of the unit structure. On one side of the nanocolumn, a notch with a width of w2 and (w4-w3) is created in the X and Y directions, respectively, to break the rotational symmetry of the column. In this example, the notch is formed throughout the entire height of the column.

[0097] The design parameters used in this example are listed in Table 2 below.

[0098] Fig.11 The reflection spectrum of the metasurface of this example is shown. The presence of the notch destroys the rotational symmetry of the unit structure and induces destructive interference between different damping modes within the same nanopillar. The non-radiative attenuation of this design is small, and this results in a narrow reflection bandwidth.

[0099] Table 2

[0100] Height(h) 140nm Width 1 (w1) 230nm Width 2 (w2) 50nm Width 3 (w3) 50nm Width 4 (w4) 180nm Period (p) 340nm

[0101] Metasurface Example 3

[0102] Fig.12 A cross-sectional view of a unit structure in the XY and XZ planes of a third metasurface design suitable for use in the present invention is shown. The angle of incidence (AOI) of incident light E is shown at the top of the figure. The metasurface includes hollow TiO2 nanopillars with a diameter of d1 and a height of h, distributed in a square 2-dimensional lattice with a period p in air.

[0103] The center of each TiO2 nanorod forming the unit structure forms a cylindrical empty volume with a diameter of d2. The hollow volume of the nanorod effectively changes the refractive index at the center of the nanorod. From another perspective, the hollow volume affects the distribution of the induced displacement current and changes the mode excited in the nanorod.

[0104] The position of the circular void volume can also be offset from the center of the TiO2 nanorod. The cross-sectional area of ​​the TiO2 nanorod and the void volume therein can be freely modified. In addition to other possible shapes, the cross-section of the TiO2 nanorod can also be square.

[0105] The design parameters used in this example for an AOI of 30 degrees are listed in Table 3 below.

[0106] Fig.13 The reflectance spectrum of the metasurface of this example is shown.

[0107] Table 3

[0108] Height(h) 250nm Diameter 1 (d1) 290nm Diameter 2 (d2) 210nm Period (p) 380nm

[0109] Metasurface Example 4

[0110] Fig.14 A cross-sectional view of a unit structure in the XY and XZ planes of a fourth metasurface design suitable for use in the present invention is shown. The angle of incidence (AOI) of incident light E is shown at the top of the figure. The metasurface includes circular TiO2 nanopillars of height h and diameter d, which are periodically arranged in a square lattice with a lattice constant or period p.

[0111] The metasurface is in an ambient air environment. Although the unit structure in this example has a circular cross section, square cross sections of pillars of height h and side length d are possible as well as other shapes. This example is based on Mie scattering, where the incident light excites different modes inside the nanopillars (the fundamental mode is a magnetic dipole mode) through the excitation of a displacement current.

[0112] The design parameters used in this example for an AOI of 45 degrees are listed in Table 4 below.

[0113] Fig.15The reflectance spectrum of the metasurface of this example is shown.

[0114] Table 4

[0115] Height(h) 140nm Diameter(d) 180nm Period (p) 340nm

[0116] Metasurface Example 5

[0117] Fig.16 A cross-sectional view of a unit structure in the XY and XZ planes of a fifth metasurface design suitable for use in the present invention is shown. The angle of incidence (AOI) of incident light E is shown at the top of the figure. The metasurface includes TiO2 nanopillars with a diameter of d and a height of h having a circular cross section, which are periodically arranged in a square lattice with a lattice constant or period p.

[0118] This metasurface differs from Example 4 in that the nanopillars are encapsulated in polymethyl methacrylate (PMMA) using a vacuum process. The refractive index of PMMA is 1.48, which is close to the refractive index of the glass substrate. In modified examples, other organic polymers such as polydimethylsiloxane (PDMS) can be used instead of PMMA. By substantially matching the refractive index of the packaging environment of the metasurface and the substrate, reflections at unwanted wavelengths can be minimized. This helps to further narrow the bandwidth of light reflected from the metasurface.

[0119] The design parameters used in this example for an AOI of 45 degrees are listed in Table 5 below.

[0120] Fig.17 The reflectance spectrum of the metasurface of this example is shown.

[0121] Table 5

[0122]

[0123]

[0124] Metasurface Example 6

[0125] Fig.18 A cross-sectional view of a unit structure in the XY and XZ planes of a sixth metasurface design suitable for use in the present invention is shown. The angle of incidence (AOI) of incident light E is shown at the top of the figure. The metasurface includes TiO2 nanopillars having an elliptical cross-section with a major axis d1, a minor axis d2 and a height h. The nanopillars are periodically arranged in a square lattice with a lattice constant or period p.

[0126] In this example, the nanopillars forming the metasurface have an asymmetric cross-sectional shape. On the one hand, this increases the dependence of the optical properties of the metasurface on the polarization of the incident light. On the other hand, this property of the metasurface provides a narrower reflection bandwidth and reduces the dependence of the reflection properties on the AOI.

[0127] The design parameters used in this example for an AOI of 45 degrees are listed in Table 6 below.

[0128] Fig.19 The reflectance spectrum of the metasurface of this example is shown.

[0129] Table 6

[0130] Height(h) 140nm Diameter 1 (d1) 180nm Diameter 2 (d2) 160nm Period (p) 300nm

[0131] Metasurface Example 7

[0132] Fig. 20 Cross-sectional views of unit structures in the XY and XZ planes of a seventh metasurface design suitable for use in the present invention are shown. The metasurface comprises multiple layers of nanopillars having a circular cross-section with a diameter d and a total height of h=h1+h2+h3.

[0133] In the multilayer nanopillar structure, a TiO2 middle layer with a height of h2 is sandwiched between a SiO2 upper layer with a refractive index of about 1.46 and a height of h1 and an Al2O3 lower layer with a refractive index of about 1.68 and a height of h3. The SiO2 upper layer is used to match the refractive index of air and the TiO2 middle layer. The Al2O3 lower layer is used to match the refractive index of the substrate and the TiO2 middle layer.

[0134] The multilayer nanorods are distributed in a square lattice with a period of p. In modified examples, the cross-section of the multilayer nanorods may also be a square or other shapes.

[0135] The design parameters used in this example are listed in Table 7 below.

[0136] Fig.21 The reflectance spectrum of the metasurface of this example is shown.

[0137] Table 7

[0138] <![CDATA[Height (h1) of SiO2]]> 100nm <![CDATA[Height (h2) of TiO2]]> 140nm <![CDATA[Height (h3) of Al2O3]]> 60nm Diameter(d) 190nm Period (p) 380nm

[0139] The following description is given by way of example only, and it will be appreciated by those skilled in the art that modifications may be made to the invention without departing from the scope of the invention as defined by the claims.

Claims

1. An optical element, comprising a first wavelength band filter film, wherein the first wavelength band filter film comprises a diffractive optical structure, wherein The diffractive optical structure diffracts light including light in a first wavelength band to form a first optical focus array, The wavelength filter film selectively performs one of reflecting or transmitting the light in the first wavelength band, and selectively performs the other of reflecting or transmitting the light outside the first wavelength band.

2. An optical element as claimed in claim 1, wherein the optical focus forms an array of spots located in a manifold separated from the surface of the film.

3. An optical element as claimed in claim 2, wherein the focal points are regularly spaced from each other.

4. An optical element as claimed in any one of the preceding claims, wherein the diffractive optical structure comprises a pattern of grooves or holes formed in the waveband film.

5. The optical element according to any one of the preceding claims, wherein the wavelength filter film has a wavelength band falling within one or both of a visible light band and an infrared light band.

6. The optical element according to any one of the preceding claims, wherein the wavelength band filter film is a transmission filter that transmits a wavelength band having a full width at half maximum of 50 nm or less.

7. The optical element as claimed in any one of the preceding claims, wherein the wavelength band filter film is a reflective filter reflecting a wavelength band having a full width at half maximum of 50 nm or less.

8. An optical element as claimed in any one of the preceding claims, wherein the wavelength filter is a notch filter.

9. The optical element of any one of the preceding claims, wherein the wavelength filter film is a narrow band reflector film.

10. The optical element of any one of the preceding claims, wherein the wavelength filter film comprises a superstructure.

11. The optical element of claim 10, wherein the metastructure is a metasurface having a unit structure, the unit structure comprising one of the group consisting of: an elliptical nanopillar pair, a rectangular nanopillar with a notch, a hollow nanopillar distributed in a square two-dimensional lattice, a circular nanopillar periodically arranged in a square two-dimensional lattice, a nanopillar with an elliptical cross-section periodically arranged in a square lattice, and a multilayer nanopillar with a circular cross-section.

12. An optical element as described in claim 11, wherein the nanopillars of the metasurface are made of TiO2.

13. The optical element according to claim 11 or 12, wherein the one or more nanorods in the unit structure are disposed in air.

14. The optical element of claim 11 or 12, wherein the one or more nanorods in the unit structure are encapsulated in an organic polymer material.

15. An optical element as described in claim 10, wherein the metasurface has a unit structure including one or more multilayer nanocolumns, wherein each multilayer nanocolumn includes an Al2O3 bottom layer, a TiO2 middle layer formed on the bottom layer, and a SiO2 top layer formed on the middle layer.

16. The optical element of any one of claims 1 to 9, wherein the band filter film has a layer structure, the layer structure comprising one of alternating Al2O3 / SiO2 layers, alternating HfO2 / SiO2 layers, alternating TiO2 / SiO2 layers, and alternating Ta2O5 / SiO2 layers.

17. An optical element as described in any one of the preceding claims, further comprising a second wavelength band filter film, the second wavelength band filter film having a second diffractive optical structure, wherein the second diffractive optical structure diffracts light including light in a second wavelength band to form a second optical focus array, the second wavelength band filter film selectively performs one of reflection or transmission of the light in the second wavelength band, and selectively performs the other of reflection or transmission of light outside the second wavelength band, and the second wavelength band does not overlap with the first wavelength band.

18. The optical element as described in claim 17, further comprising a third wavelength band filter film, the third wavelength band filter film having a third diffractive optical structure, wherein the third diffractive optical structure diffracts light including light in a third wavelength band to form a third optical focus array, the third wavelength band filter film selectively performs one of reflection or transmission of the light in the third wavelength band, and selectively performs the other of reflection or transmission of light outside the third wavelength band, and wherein the third wavelength band does not overlap with the first wavelength band or the second wavelength band.

19. An optical element as claimed in any preceding claim, wherein the diffractive optical structure is a holographic optical structure.

20. A free space combiner for an augmented reality or virtual reality device comprising an optical element as claimed in any preceding claim.

21. A waveguide combiner for use in an augmented reality or virtual reality device comprising an optical element as claimed in any preceding claim.

22. An augmented reality or virtual reality device, comprising: A combiner as claimed in claim 19 or 20; as well as A light source is configured to project light onto the combiner to form an image, wherein the light source is configured to project light having a wavelength within the first wavelength band.

23. An augmented reality or virtual reality device, comprising: A combiner comprising the optical element according to claim 17; a first light source configured to project light onto the combiner to form an image, wherein the first light source is configured to project light having a wavelength within the first wavelength band; as well as A second light source is configured to project light onto the combiner to form an image, wherein the second light source is configured to project light having a wavelength within the second wavelength band.

24. The augmented reality or virtual reality device of claim 23, further comprising a third light source configured to project light onto the combiner to form an image, wherein the third light source is configured to project light having a wavelength within a third wavelength band, wherein the third wavelength band does not overlap with the first wavelength band or the second wavelength band.

25. The virtual reality device of claim 22, further comprising a light shield configured to block external light from reaching the combiner.

Images