Including a stepped cavity high color uniformity dual-material diffraction grating

Abstract

In an exemplary embodiment, the diffraction grating includes a substrate having an outer surface and a first refractive index. A plurality of grating elements are provided on the substrate. The grating elements may have a stepped structure. In some embodiments, each grating element includes a stepped channel inserted into the substrate. The stepped channel has a second refractive index greater than the first refractive index. In some embodiments, the stepped channel is a two-step channel having a first step along the outer surface of the substrate and a second step extending inwardly from the first step. In some embodiments, the width of the first step is greater than the width of the second step.

Description

[0001] Cross-reference to related applications

[0002] This application claims priority to European Patent Application No. 20305538.9, filed on May 22, 2020, entitled "High Color Uniformity Double Material Diffraction Grating Comprising Step-Like Cavities", the entire contents of which are incorporated herein by reference. Background Technology

[0003] This disclosure relates to the fields of optics and photonics, and more specifically to optical devices comprising at least one diffraction grating. It can be applied in the field of conformal and wearable optics (e.g., AR / VR glasses (augmented reality / virtual reality)) and in a variety of other consumer electronics products including displays and / or lightweight imaging systems (including head-up displays (HUDs)), such as in the automotive industry.

[0004] This section is intended to introduce the reader to various aspects of the art that may relate to the various aspects of this disclosure described below and / or claimed. This discussion is intended to help provide the reader with background information to facilitate a better understanding of the various aspects of the systems and methods described herein. Therefore, it should be understood that these statements should be interpreted in this context, rather than as an admission of prior art.

[0005] With the advent of nanotechnology, interest in exploring the nanoscale optical world has been growing, leading to the desire to manipulate visible light at subwavelength scales. To this end, researchers have made considerable efforts to reduce the size of optical lenses to the micrometer and submicrometer scales; however, their efforts are hampered by the diffraction limit, as the size of the lens approaches the wavelength of light.

[0006] Planar lenses, due to their small thickness and excellent focusing ability, have been developed to replace their thicker dielectric counterparts as typical nanophotonic components. To date, several types of planar lenses have been studied, such as zone plates, nanoslits and nanopore arrays, photonic crystals, and metasurfaces. Although different terms are used in these techniques, they share the same focusing principle: generating constructive interference at the focal point by bending the phase wavefront of an incident plane wave. In effect, the focusing (or beamforming) of electromagnetic waves is a method of establishing a localized increase in the amplitude of an electric field, thereby improving the efficiency of sensors, such as photoelectric sensors, whose operating principle relies on converting energy propagating in space as electromagnetic waves into an output voltage or current.

[0007] The performance of plane lenses has been improved through sophisticated designs. However, to date, most proposals lack the ability to control the focal position or change the orientation of the electromagnetic beam.

[0008] There are many optical devices that include components that perform light focusing and deflection functions. These include digital image sensors used in various cameras / camcorders, optical combiners used in AR / VR glasses, and light guide systems that are a major part of various light-capturing and light-processing devices. There are also some components that can perform two functions simultaneously, such as asymmetric dielectric lenses, diffractive lenses, and diffraction gratings.

[0009] Transform optics (TO) allows for the control of electromagnetic (EM) fields using carefully designed materials with spatially varying parameters. This flexibility in controlling EM waves appears to be advantageous for designing novel devices with performances that are difficult to achieve or with specific desired properties.

[0010] The lens that provides the possibility of changing the propagation direction of electromagnetic radiation beams was proposed by J. Yi et al. in “Coherent beam control with an all-dielectric transformation optics based lens” (Science & Technology Report, Vol. 6, Article No.: 18819 (2016)).

[0011] The excitation source is transmitted through a lens corresponding to the transformed medium, which deflects the beam away from the normal direction. A prototype of an all-dielectric, compact, low-cost lens exhibiting a gradient dielectric constant profile is fabricated using three-dimensional (3D) multi-spot jet printing. The radiator array consists of four planar microstrip antennas, implemented using standard photolithography, and serves as the excitation source for the lens.

[0012] One possible method for manipulating visible light at the subwavelength scale is the use of surface plasmons; these surface plasmon-based lenses, or so-called plasmonic lenses, can achieve subwavelength-scale focusing regions. However, to fully realize the potential of plasmonic lenses, not only is focusing the light required, but also the manipulation and precise positioning of the light at small scales. In "Beam bending via plasmonic lenses" by Ya. Zhao et al. (Optics Letters, Vol. 18, No. 22 23458 (2010)), a more practical method for achieving directional modulation using plasmonic lenses was proposed. The design principle of a plasmonic lens that can bend light along a direction transverse to the propagation direction was proposed. Light bending is achieved by constructing a carefully designed bent phase wavefront for the plasmonic lens. Control of the phase wavefront profile is achieved through two mechanisms: the phase delay caused by the width and shape of the individual slits in the lens, and the position of these slits. The proposed single-layer lens can be conveniently fabricated using focused ion beam (FIB) technology.

[0013] Recently, the use of plasmonic antenna structures for near-field optical trapping of objects has attracted attention. However, metallic nanostructures also provide a compact platform for general wavefront engineering of mid- and far-field beams. Yo.C. Jun et al., in "Optical Manipulation with Plasmonic BeamShaping Antenna Structures" (Advances in Optoelectronics, Vol. 2012, Article No. 595646), analyzed the optical forces generated by plasmonic beamshaping antenna structures and showed that these optical forces can be used for general optical manipulation, such as guiding dielectric particles along linear or curved trajectories. An asymmetric slit-groove structure generates a collimated beam at a specific angle. Different groove periods on either side generate constructive interference in the off-axis direction. The authors also demonstrated that different wavelengths lead to different interference conditions and beam directions.

[0014] Metasurfaces can provide solutions for realizing complex optical systems with compact and planar configurations. In M. Khorasaninejad et al.'s paper, "Super-Dispersive Off-Axis Meta-Lenses for Compact High Resolution Spetrcoscopy" (Nano Letters, Vol. 16, No. 6, 3732 (2016)), off-axis metalenses that simultaneously focus and disperse light of different wavelengths at high spectral resolution were proposed. These off-axis metalenses are designed based on geometric phase via rotating silicon nanofins and can focus light at an angle of 80°.

[0015] Various strategies have emerged to achieve tunability of planar lenses, with the aim of manipulating the transmitted phase wavefront from a predetermined structure. For example, Liu Z. et al. demonstrated in the following article: "Tuning the focus of a plasmonic lens by the incident angle" (Applied Physics Letters, Vol. 88, 171108 (2006)). Active tunability in static plasmonic devices can enhance their functionality. Variable refractive index materials are commonly incorporated into plasmonic devices and optical metasurfaces, including liquid crystals, vanadium dioxide, silicon, and other materials. Therefore, the optical phase of the guided mode excited in a gradient refractive index metalens can be manipulated to achieve a degree of tunability in the focusing behavior of the photonic device. In the following article, Y. Chen et al. also proposed designing far-field focusing patterns using planar superlenses composed of slit arrays filled with phase-change material Ge2SB2Te5 (GST): "Engineering the phasefront of light with phase-change material based planar lenses" (Science & Technology Report, Vol. 5, Article No.: 8660 (2015)).

[0016] Plasmonic lenses may suffer from high absorption losses in the optical wavelength range. There are also fabrication difficulties that reduce the effectiveness of the proposed topology. It has been found that using dielectric materials may solve the problem of achieving the desired functionality of controlling the position and deviation of the electromagnetic beam.

[0017] There are also several near-field focusing components that achieve subwavelength resolution but cannot fully generate light deflection functionality. Photonic nanojet (NJ) is a narrow, high-intensity optical radiation flux formed near the shaded surface of an irradiated transparent dielectric symmetric body, with a diameter comparable to or slightly larger than the wavelength of the incident light radiation. The physical origin of photonic nanojet formation comes from the interference (both constructive and destructive interference) of the net flux of radiation passing through the diffracted particles (see, for example, SCKong et al., “Photonic nanojet-enabled optical data storage” (Optics Letters, Vol. 16, No. 18, 2008), V. Pacheco-Pena et al., patent document US 7,394,535, “Terajets produced by dielectric cuboids” (Applied Physics Letters, Vol. 105, 084102, 2014), and V. Pacheco-Pena et al., “Multifrequency focusing and wide angular scanning of terajets” (Optics Letters, Vol. 40, No. 2, pp. 245-248, 2015)).

[0018] A key characteristic of photonic nanojet is the high spatial localization of the light field in the longitudinal direction (relative to the incident direction), which, compared to conventional high NA (numerical aperture) focusing optics, can lead to subwavelength scale photonic jets. The shared interest in the nanojet effect stems primarily from its promising practical applications in nanophotonics, biology, medicine, and nanoelectronics. Some devices operate based on the ability of nanojet to provide high-intensity electromagnetic fields in localized spatial regions near the microparticle, and on high sensitivity to perturbations of both the field and the material source.

[0019] The manipulation of the properties of controlled nanojet and the generation of thinner or longer and stronger jets through variations in the properties of optical elements have attracted increasing attention. The shape and intensity of nanojet are significantly dependent on the size and optical properties of the generating particles (see, for example, "Optics of photonic nanojets" by AVItagi et al. (Journal of the Optical Society of America A, Vol. 22, 2847 (2005)), "Subdiffraction optical resolution of a gold nanosphere located within the nanojet of a Mie-resonant dielectric microsphere" by A. Heifetz et al. (Optics Letters, Vol. 15, 17334 (2007)), and "Three-dimensional subwavelength confinement of light with dielectric microspheres" by A. Devilez et al. (Optics Letters, Vol. 17, 2089 (209)).

[0020] Furthermore, if nanojet is generated from materials consisting of composite radially inhomogeneous particles composed of several concentric shells with different refractive indices (see, for example, Yu Shen et al., “Ultralong photonic nanojet formed by a two-layer dielectric microsphere” (Optics Letters, Vol. 39, No. 14, 4120 (2014), CM Riuz et al., “Detection of embedded ultra-subwavelength-thin dielectric features using elongated photonic nanojets” (Optics Letters, Vol. 18, No. 16, 16805 (2010), Yu E. Geints et al., “Photonic nanojet calculations in layered radially inhomogeneous micrometer-sized spherical particles”). In the case of particles ("Journal of the Optical Society of America B", Vol. 28, No. 8, 1825 (2011), and G. Gu et al. "Super-long photonic nanojet generated from liquid-filled hollow microcylinder" (Optics Letters, Vol. 40, No. 4, 625 (2015)); or gradient refractive index materials (X. Mao et al. "Tunable photonic nanojet formed by generalized Luneburglens" (Optics Letters, Vol. 23, No. 20, 026426 (2015)), the characteristics of nanojet can be significantly altered. Specifically, it will become possible to abnormally elongate the photon jet and further amplify the electric field.

[0021] AR / VR glasses are considered the next generation of human-computer interfaces. The development of AR / VR glasses (and more generally, protective electronic devices for glasses) is associated with many challenges, including reducing the size and weight of such devices and improving image quality (in terms of contrast, field of view, color depth, etc.) to achieve a truly immersive user experience.

[0022] The trade-off between image quality and physical size in optics has spurred research into ultracompact optical components that could serve as building blocks for more complex optical systems, such as AR / VR glasses. It is hoped that such optical components will be easy to manufacture and replicate.

[0023] In such AR / VR glasses, various types of refractive and diffractive lenses and beam-forming components are used to guide light from a microdisplay or projector toward the human eye, thereby allowing the formation of a virtual image superimposed on an image of the physical world seen with the naked eye.

[0024] Some types of AR / VR glasses utilize optical waveguides, where light propagates into the waveguide only within a limited internal angle range via TIR (Total Internal Reflection). The FoV (Field of View) of the waveguide depends on the waveguide material and other factors.

[0025] For example, WO2017180403 proposes a waveguide with an extended field of view, employing dual-mode image propagation. In this method, the +1 diffraction mode is used to carry the right-hand side image (negative incident angle at the in-coupler) in one direction, and the -1 mode is used to propagate the positive incident angle in the opposite direction within the waveguide. In WO2017180403, these two half-images are combined due to a pupil dilator and an out-coupler at the waveguide exit, allowing the user to see a single image. The goal of this system is to double the field of view, as each half-image can utilize the entire angular bandwidth of the waveguide in each propagation direction.

[0026] Using a diffraction order higher than one has the effect of multiplying the wavelength by the diffraction order used in the diffraction equation. Since the grating spacing is directly a function of the product Mλ, this means the grating spacing is multiplied by M. A lower grating density with fewer lines per millimeter can be used, and the manufacturing process can be simplified by using overwavelength structures instead of subwavelength structures.

[0027] An optical waveguide with a diffraction order of ±2 provides a FoV of approximately 60°, where the refractive index is 1.52. Therefore, it is possible to obtain a 60° field of view using a material with a refractive index of 1.52 instead of 2 in the single-mode. However, the 60° FoV is still limited relative to the total human field of view, in which stereoscopic vision is effective for human vision and is approximately 114°.

[0028] Waveguide-based AR / VR glasses can exhibit a wide field of view along one direction (e.g., horizontal) but may have a narrower field of view along another direction (e.g., vertical). However, since AR / VR applications typically require a specific aspect ratio, for practical purposes, limiting the field of view along one direction may effectively limit the field of view along another direction. Summary of the Invention

[0029] The terms "an embodiment," "implementation," or "exemplary embodiment" used in the specification describe embodiments that may include specific features, structures, or characteristics; however, not every embodiment necessarily includes specific features, structures, or characteristics. Furthermore, such phrases do not necessarily refer to the same embodiment. Additionally, when a specific feature, structure, or characteristic is described in conjunction with an embodiment, such feature, structure, or characteristic may be used in conjunction with other embodiments, whether or not it is explicitly described.

[0030] A diffraction grating according to some embodiments includes: a substrate having an outer surface and a first refractive index; and a plurality of grating elements, each grating element including a stepped channel inserted into the substrate, the stepped channel having a second refractive index greater than the first refractive index. In some embodiments, the stepped channel is a two-step channel having a first step along the outer surface of the substrate and a second step extending inwardly from the first step, the width of the first step being greater than the width of the second step.

[0031] A method for fabricating a diffraction grating according to some embodiments includes: forming a plurality of stepped channels in the outer surface of a substrate having a first refractive index; and filling each stepped channel with a material having a second refractive index greater than the first refractive index. In some embodiments, each stepped channel is a two-step channel having a first step along the outer surface of the substrate and a second step extending inward from the first step, the width of the first step being greater than the width of the second step.

[0032] In some implementations, the outer surface of the stepped channel is substantially coplanar with the outer surface of the substrate.

[0033] In some implementations, the width of the first step is essentially twice the width of the second step.

[0034] In some implementations, the side edges of the first step are substantially aligned with the side edges of the second step.

[0035] In some implementations, the first step has a width W and a height h1, wherein

[0036]

[0037] And among them, in Where n L It is the first refractive index, and n H It is the second refractive index.

[0038] In some implementations, the height h2 of the stepped passage is less than twice the height h1 of the first step.

[0039] In some implementations, the substrate is a waveguide in a waveguide display. Attached Figure Description

[0040] Figure 1A This is a schematic diagram of the cross-section of a waveguide display.

[0041] Figure 1B This is a schematic diagram of a binocular waveguide display with a first layout featuring diffractive optical components.

[0042] Figure 1C This is a schematic diagram of a binocular waveguide display with a second layout featuring diffractive optical components.

[0043] Figure 1D This is a schematic exploded view of a dual-waveguide display based on some implementation schemes.

[0044] Figure 1E This is a cross-sectional schematic diagram of a dual-waveguide display according to some implementation schemes.

[0045] Figure 2 This is a cross-sectional view showing two cells in a diffraction grating according to some embodiments. The grating element can be described as a stepped optical element.

[0046] Figure 3A It is a cross-sectional view of a cell in a diffraction grating according to some implementation schemes.

[0047] Figure 3B It is a cross-sectional view of a cell in a diffraction grating according to an additional implementation scheme.

[0048] Figure 4A This is a cross-sectional view of a portion of a diffraction grating according to some implementation schemes. Although in Figure 4A The diagram shows three cells, but diffraction gratings according to some implementations may include arrays of dozens, hundreds, or thousands of cells.

[0049] Figure 4B It is based on some implementation plans, such as Figure 4A A schematic cross-sectional perspective view of a portion of a diffraction grating.

[0050] Figures 5A to 5CThis is a graph showing the simulation results of reflectivity and transmittance for an incident angle α of the electromagnetic wave. In all simulations, λ = 625 nm, d = 494 nm, n1 = 1.0, n3 = 1.5154. Figure 5A In the given information, n2 = 2.8, W = 300 nm, h1 = 255 nm, and h2 = 475 nm. Figure 5B In the given information, n2 = 2.6, W = 300 nm, h1 = 295 nm, and h2 = 500 nm. Figure 5C In the given information, n2 = 2.4, W = 380nm, h1 = 420nm, and h2 = 680nm.

[0051] Figures 6A to 6D This is a schematic cross-sectional view of a portion of a diffraction grating and substrate in a progressive stage of the manufacturing process, according to some implementation schemes.

[0052] Figure 7A and 7B Simulated values ​​of reflectivity and transmittance relative to the electromagnetic wave incident angle (α) (shown here in radians) are shown for n1 = 1.0, n2 = 2.8, and n3 = 1.5154. Figure 7A In the given information, λ = 460 nm, d = 365.7 nm, W = 220 nm, h1 = 190 nm, and h2 = 350 nm. Figure 7B In the given information, λ = 530 nm, d = 421.4 nm, W = 260 nm, h1 = 220 nm, and h2 = 400 nm. Detailed Implementation

[0053] Overview of waveguide displays

[0054] This article describes systems and methods that can be used in optical waveguide devices. Figure 1A An exemplary waveguide display device is shown in the figure. Figure 1A This is a schematic cross-sectional side view of the waveguide display device in operation. The image is projected by image generator 102. Image generator 102 can project the image using one or more of a variety of technologies. For example, image generator 102 can be a laser beam scanning (LBS) projector, a liquid crystal display (LCD), a light-emitting diode (LED) display (including organic LED (OLED) or micro LED (μLED) displays), a digital light processor (DLP), a liquid crystal on silicon (LCoS) display, or other types of image generators or light engines.

[0055] Light representing image 112 generated by image generator 102 is coupled into waveguide 104 via diffraction inner coupler 106. Inner coupler 106 diffracts the light representing image 112 into one or more diffraction orders. For example, a ray 108 representing part of the bottom of the image is diffracted by inner coupler 106, and one of the diffraction orders 110 (e.g., second order) is positioned at an angle that allows it to propagate through waveguide 104 via total internal reflection.

[0056] At least a portion of the light 110 coupled into waveguide 104 via diffractive inner coupler 106 is coupled out of the waveguide via diffractive outer coupler 114. At least some of the light coupled out of waveguide 104 replicates the angle of incidence of the light coupled into the waveguide. For example, in the illustration, the externally coupled rays 116a, 116b, and 116c replicate the angle of the internally coupled ray 108. Since the light leaving the outer coupler replicates the direction of the light entering the inner coupler, the waveguide essentially replicates the original image 112. The replicated image is visible to the user's eye 118.

[0057] exist Figure 1A In the example, the external coupler 114 allows a single input beam (such as beam 108) to generate multiple parallel output beams (such as beams 116a, 116b, and 116c) by reflecting only a portion of the externally coupled light each time. In this way, even if the eye is not perfectly aligned with the center of the external coupler, at least some light from each part of the image may reach the user's eye. For example, if the eye 118 moves downwards, beam 116c can enter the eye even if beams 116a and 116b do not, so the user can still perceive the bottom of image 112 despite the positional shift. Therefore, the external coupler 114 partially operates as an exit pupil dilator in the vertical direction. The waveguide may also include one or more additional exit pupil dilators (…). Figure 1A (not shown in the image) to expand the exit pupil in the horizontal direction.

[0058] In some implementations, waveguide 104 is at least partially transparent to light originating from outside the waveguide display. For example, at least some light 120 from a real-world object (such as object 122) passes through the waveguide 104, allowing the user to see the real-world object while using the waveguide display. Since the light 120 from the real-world object also passes through diffraction grating 114, there will be multiple diffraction orders and therefore multiple images. To minimize the visibility of multiple images, it is desirable that the zeroth order diffraction (not deflected by 114) has a high diffraction efficiency for light 120, while higher diffraction orders have lower energy. Therefore, in addition to extending and externally coupling virtual images, external coupler 114 is preferably configured to pass through the zeroth order of the actual image. In such implementations, the image displayed by the waveguide display may appear to be superimposed on the real world.

[0059] In some implementations, as described further in detail below, the waveguide display includes more than one waveguide layer. Each waveguide layer can be configured to preferentially deliver light with a specific wavelength range and / or angle of incidence from the image generator to the viewer.

[0060] like Figure 1B and Figure 1C As shown, waveguide displays with internal couplers, external couplers, and pupil expanders can have various different configurations. Figure 1B An exemplary layout of a binocular waveguide display is shown. Figure 1B In the example, the display includes waveguides 152a and 152b for the left and right eyes, respectively. The waveguides include inner couplers 154a and 154b, pupil dilators 156a and 156b, and components 158a and 158b, which operate as outer couplers and horizontal pupil dilators. The pupil dilators 156a and 156b are arranged along an optical path between the inner and outer couplers. An image generator (not shown) can be provided to each eye and is arranged to project light representing the image on the corresponding inner coupler.

[0061] Figure 1C Another exemplary layout of a binocular waveguide display is shown in the image. Figure 1C In the example, the display includes waveguides 160a and 160b for the left and right eyes, respectively. The waveguides include inner couplers 162a and 162b. Light from different parts of the image can be coupled by the inner couplers 162a and 162b to different directions within the waveguides. Inner-coupled light traveling to the left passes through pupil dilatators 164a and 164b, while inner-coupled light traveling to the right passes through pupil dilatators 166a and 166b. Having passed through the pupil dilatators, light is coupled out of the waveguides using components 168a and 168b, which operate as both outer couplers and vertical pupil dilatators to substantially replicate the image provided at the inner couplers 162a and 162b.

[0062] In different implementations, different features of the waveguide display can be disposed on different surfaces of the waveguide. For example (e.g.) Figure 1AIn some configurations, both the inner and outer couplers can be positioned on the front surface of the waveguide (away from the user's eye). In other embodiments, the inner and / or outer couplers can be positioned on the rear surface of the waveguide (facing the user's eye). The inner and outer couplers can be positioned on opposite surfaces of the waveguide. In some embodiments, one or more of the inner coupler, outer coupler, and pupil dilator can be present on both surfaces of the waveguide. The image generator can be positioned facing either the front or rear surface of the waveguide. The inner coupler is not necessarily on the same side of the waveguide as the image generator. Any pupil dilator in the waveguide can be positioned on the front, rear, or both surfaces of the waveguide. In displays with more than one waveguide layer, different layers can have different configurations of inner couplers, outer couplers, and pupil dilators.

[0063] Figure 1D This is a schematic exploded view of a dual-waveguide display according to some embodiments, including an image generator 170, a first waveguide (WG1) 172 and a second waveguide (WG2) 174. Figure 1E This is a schematic side view of a dual-waveguide display according to some embodiments, including an image generator 176, a first waveguide (WG1) 178, and a second waveguide (WG2) 180. The first waveguide includes a first transmission diffraction inner coupler (DG1) 180 and a first diffraction outer coupler (DG6) 182. The second waveguide has a second transmission diffraction inner coupler (DG2) 184, a reflection diffraction inner coupler (DG3) 186, a second diffraction outer coupler (DG4) 188, and a third diffraction outer coupler (DG5) 190. Different embodiments may use different arrangements of optical components (such as different arrangements of pupil dilatators) on the first and second waveguides.

[0064] Although Figures 1A to 1E The example demonstrates the use of waveguides in near-eye displays, but the same principle can be applied to other display technologies, such as head-up displays for automobiles or other applications.

[0065] Overview of diffractive optical elements

[0066] This disclosure relates to the fields of optical devices and photonics, and more specifically to planar optical devices.

[0067] More specifically, but not entirely, this disclosure relates to a diffraction grating comprising near-field focusing and forming a beam in a near-field region element, which can be used in a wide range of devices, such as displays (including input and output coupling of light in waveguides for eyeglass electronics and head-mounted displays for AR (augmented reality) and VR (virtual reality) glasses), optical sensors for cameras / camcorders / light field cameras, biological / chemical sensors (including on-chip laboratory sensors), microscopes, spectroscopic and metrological systems, solar panels, etc.

[0068] Some embodiments described herein provide a topology for a dual-material dielectric diffraction grating. In some embodiments, this topology provides good diffraction efficiency and diffraction uniformity. In some embodiments, it protects optical elements from mechanical damage and degradation.

[0069] With the advent of nanotechnology, the interest in exploring the nanoscale optical world has led to the desire to manipulate visible light at the subwavelength scale. To this end, researchers have made considerable efforts to reduce the size of optical lenses to the micrometer and submicrometer scales; however, their efforts are hampered by the diffraction limit, as the size of the lens approaches the wavelength of light.

[0070] Planar lenses, due to their small thickness and excellent focusing ability, have been developed to replace their dielectric counterparts as typical nanophotonic components. To date, several types of planar lenses have been studied, such as zone plates, nanoslits and nanopore arrays, photonic crystals, and metasurfaces. Although different terms are used in these techniques, they all share the same principle of focusing coherent waves: constructive interference is generated at the focal point by bending the phase wavefront of the incident plane wave. The performance of planar lenses has been improved through sophisticated designs. However, when using planar lenses, it can be difficult to control the focal position or change the orientation of the electromagnetic beam.

[0071] There is a need to provide optical components that enable focusing and deflection. Available solutions for achieving such functions (typically used in optical applications) may not fully meet the requirements due to the performance characteristics (e.g., chromatic aberration and limited resolution) and manufacturing difficulties of emerging nanophotonics applications.

[0072] Therefore, introducing new components to achieve the desired light focusing and deflection functions has practical significance. Additional desirable features of such devices are subwavelength resolution and simple topologies compatible with established micron and nanometer fabrication techniques.

[0073] Diffraction gratings optimized to achieve good grating efficiency in diffraction orders other than zero can provide light deflection functionality in the far-field region. Some implementations include dual-material optics that deflect and focus incident light in the near-field region for the purpose of targeted light distribution in the far-field region.

[0074] WO2019175010A1, "Diffraction grating comprising double-material structures," proposes near-field focusing components based on nanojet-based structures with different material combinations. Some embodiments described therein utilize the nanojet (NJ) concept. The nanojet beam-forming optical element is formed from a combination of at least two dielectric materials with different refractive indices, which have an asymmetric system in the vertical cross-section. This transformation results in the deflection of the focused nanojet beam. It has been shown that such properties for deflecting light through a double-material system can be advantageously used in diffraction gratings. Changing the refractive index of the constituent parts has the potential to alter the grating's performance and significantly increase the refractive transmittance by ±1 order. Known diffraction grating profiles include those illustrated in US 2016 / 0231568, where the diffraction grating consists of a deeply tilted structure.

[0075] It is also expected that a novel optical device will be provided that fully meets the needs of emerging nanophotonic applications in terms of performance characteristics and manufacturing difficulties. In other words, it is also expected that a novel optical device will have a topology compatible with established micron and nanofabrication technologies.

[0076] Overview of Nanojet Optical Focusing

[0077] Exemplary embodiments provide a focusing element based on nanojet spraying, which enables the focused beam to be deflected in both the near and far regions. This property of deflecting light through a single element is advantageous for applications with asymmetric intensity distributions (T0). j ≠T- j R j ≠R -j In a diffraction grating (where j is the diffraction order), high grating efficiency is provided for the desired diffraction order. With the proposed element having W ≤ λ, the maximum input corresponds to ±1 order. An exemplary embodiment provides high diffraction uniformity and first-order efficiency.

[0078] Exemplary embodiments provide a topology for the diffraction element to control the position of the focused nanojet beam and change the orientation of the nanojet beam. Some embodiments use optical elements with a stepped geometry. In some embodiments, the stepped topology provides a combination of nanojet beams originating from the system edge, thereby contributing to the formation of a final nanojet beam deflected from the normal direction. The cross-section and focusing function are schematically represented in... Figure 2 The characteristics of the generated nanojet beam are controlled by parameters of the corresponding parts of the stepped system, such as the refractive index ratio between the dielectric materials forming the system, the cavity size, and the incident angle of the irradiation wave.

[0079] Some embodiments include a diffraction grating for diffracting light, the grating comprising multiple grating cells with stepped optical elements. In some embodiments, the optical elements are positioned on a substrate surface. In other embodiments, the stepped optical elements comprise stepped cavities or channels in the substrate filled with a dielectric material having a high refractive index. A second variant of the diffraction grating represents an optical element protected from mechanical damage and may have a simpler manufacturing process.

[0080] Exemplary implementations have been numerically validated by full-wave electromagnetic analysis of 2D and 3D dual-layer optical elements. For simplicity, the analysis assumes all materials are non-destructive and non-dispersive. The analysis shows that diffraction of plane waves on optical elements based on combinations of different dielectric materials can cause nanojet beams to deviate from the normal direction under normal incidence. The position of the focal point, the deviation angle, the intensity and shape of the nanojet beam can be controlled by changing the refractive index and size of the constituent parts / blocks. A stepped diffraction grating achieves an asymmetric distribution of intensity, resulting in high grating efficiency for the desired diffraction order. In some implementations using elements with W≤λ, the maximum input corresponds to ±1 order. Some implementations exhibit very high diffraction homogeneity (approximately 95%) for the first diffraction order.

[0081] Topology of an exemplary implementation

[0082] Figure 2 The general topology of a dual-material optical element in some embodiments is shown. Figure 2 A cutaway portion of the optical component is shown, illustrating two grating elements 202 and 204 inserted into a substrate 206. Each grating element can be described as a stepped channel within the substrate. The grating element has a refractive index n2, which in some embodiments is greater than the refractive index n3 of the substrate. The ambient medium may have a refractive index n1. In this embodiment, each grating element has two steps, a first step 208 arranged along the outer surface of the substrate (e.g., substantially coplanar with it), and a second step 210 extending inward from the first step (in... Figure 2(Middle, downwards) Extending. The first and second steps can be connected to each other. Figure 2 The dashed lines are shown only for clarity. Figure 2 In one implementation, the width of the first step is greater than the width of the second step. In an exemplary implementation, the side edge of the first step ( Figure 2 Align the left edge of the first step with the corresponding side edge of the second step.

[0083] therefore, Figure 2 The cross-sectional view corresponds to a stepped element of a single material with a refractive index of n2, embedded in a homogeneous dielectric with a refractive index of n3 (n2>n3). The entire system is situated within a homogeneous master medium with a refractive index of n1. In some cases, n1 can be equal to n3. The materials and dimensions of the constituent parts can be selected below to manage the location of the nanojet hotspots and the intensity, direction, and deviation angle of the nanojet beam. Some embodiments use a vertical edge parallel to the z-axis and a top / bottom surface parallel to the xy-plane, corresponding to a base angle α = 90°. However, in some embodiments, prismatic structures (with arbitrary base angles) can also be used. Variations in the base angle value provide additional degrees of freedom in controlling the radiation of the nanojet beam.

[0084] The topology of the two diffraction grating cells in Figures 3A to 3B As shown in the image. Figure 3A A diffraction grating with stepped elements, such as element 302 with a refractive index of n2, is shown, which is contained in a homogeneous medium with a refractive index of n1 and placed in a medium with a refractive index of n3 (n 2,3 The grating element 302 is located on the substrate surface 304, where n1 > n2. In some embodiments, n2 > n3. The grating element 302 has a stepped structure, wherein the width of the first step 306 is greater than the width of the second step 308. The second step 308 is located on the outer surface of the substrate 304, and the first step extends outward from the second step (on the substrate surface 304). Figure 3A (Middle, upward). In an exemplary embodiment, the side edge of the first step ( Figure 3A Align the left edge of the first step with the corresponding side edge of the second step. Figure 3B A periodic array of stepped optical elements corresponding to a refractive index of n2, which are embedded in a substrate with a refractive index of n3 (n2>n3>n1), such as... Figure 2 As shown. The grating constant or grating period is d. A linearly polarized plane wave can be incident on the grating from the top in a plane perpendicular to the grating. Figures 4A to 4B An implementation of a raster with a second type of cell is shown in the figure.

[0085] In some implementations, the stepped element is made of a material with a refractive index greater than that of the substrate. Examples of materials used for stepped elements include titanium dioxide (TiO2) and silicon nitride (Si3N4).

[0086] In some implementations, the diffraction grating may be configured for, for example, λ = 625 nm or other wavelengths. In some examples, the grating may have the following parameters: d = 494 nm, W = 300 nm, h1 = 295 nm, h2 = 500 nm, n1 = 1.0, n2 = 2.6, n3 = 1.5154.

[0087] Figures 6A to 6D The diagram illustrates methods for fabricating diffraction gratings according to several implementation schemes. For example... Figure 6A As shown, a substrate 600 is provided. The substrate 600 has a first refractive index n3. The substrate 600 may be, for example, a waveguide for a waveguide display. Figure 6B As shown, for example, multiple stepped channels are formed in the outer surface of the substrate 600 by chemical or mechanical etching. Figure 6C As shown, each stepped channel is filled with a material having a second refractive index n2, which is greater than the first refractive index n3. In some embodiments, optional polishing or other smoothing methods may be performed to provide, for example, Figure 6D The flush outer surface shown is more resistant to scratches and damage than surfaces with protruding grating elements. Optionally, it can be... Figure 6D An additional protective layer or optical layer or coating (e.g., an anti-reflective coating) is applied to the diffraction grating structure shown.

[0088] Performance of exemplary implementations

[0089] The combination of materials and dimensions for the grating elements used to deflect nanojet beams can be selected according to the formulas and techniques described below.

[0090] The overall response of a diffraction grating is affected by edge diffraction phenomena in individual elements entering the period, as described in the following article: A. Boriskin, V. Drazic, R. Keating, M. Damghanian, O. Shramkova, L. Blondé, “Near field focusing by edge diffraction,” Optics Letters, 2018 (“Boriskin et al.”). The data shown below were obtained using COMSOL Multiphysics software. The proposed analysis of the field and power distributions within the meta-element of the grating helps to explain the physics of this phenomenon and allows for the selection of topologies that provide the desired properties. This analysis assumes that the system is illuminated by a linearly polarized plane wave E = {0,0,1}. The influence of the parameters of individual meta-elements on the system function is considered.

[0091] As described by Boriskin et al., the beam formation phenomenon is associated with the edges of the system, and the radiation angle of the nanojet beam is defined by Snell's law. For normal incidence of the incident wave, the radiation angle of the nanojet beam for the constituent parts of the nanojet optical element can be determined by the refractive index n of the medium housing the element. L (for Figure 3A n L =n1, and for Figure 3B n L =n3) and the refractive index n of the material of the optical element H (n H =n2) is a function of the ratio between the base angle of the element and the refractive index. (This analysis is for elements with vertical edges, where the base angle is equal to 90°). For elements with a refractive index of n... H The main component of a nanojet optical element, the radiation angle of the nanojet beam, can be determined using the following approximate formula:

[0092]

[0093] in This is the critical angle of refraction. For an exemplary embodiment, the two opposing edges of a large step with width W and height h1 on the top of the element will produce two similar nanojet patterns, such as... Figure 2As shown. One nano-jet (NJ2) will penetrate into the second step with a width of W / 2 without deformation. Another nano-jet (NJ1) will be reflected by the right edge of the lower step. The combination of these two nano-jets and the nano-jets generated by the second step will increase the intensity of the final light beam obtained at the bottom surface of the superlens. The following is an exemplary formula for the element parameters that can be used to obtain such a combination of nano-jets within the element. The intersection point (hot spot) of the two symmetric nano-jets NJ1 and NJ2 generated by the outer edge of the bulk on the top of the element can be used to select the approximate height of the bulk, which can be estimated as:

[0094]

[0095] Here, W is the full width of the larger step on the top, which can be selected considering the full size of the system or the cell width (W < d) in the case of a diffraction grating. The height of the second step can be selected to correspond to a value that provides the desired deviation angle for the total nano-jets generated outside the element. To prevent additional reflection of the nano-jets by the left outer wall of the optical element, the height can be selected such that (h2 - h1) < h1.

[0096] Using these optical elements to form a diffraction grating, the dimensions of the stepped element can be selected to increase the diffraction uniformity for the oblique incidence of electromagnetic waves. For this purpose, it can be considered that for oblique incidence, the deviation angles of NJ1 and NJ2 may not be equal, and depending on the angle of incidence, there may be multiple nano-jet reflections at the edges of the optical element.

[0097] The diffraction grating based on the stepped element can have the following performance characteristics. The following provides the results of numerical simulations for the case of the cells presented in Figure 3B The simulation assumes that a linearly polarized plane wave is incident on the grating from the top in a plane perpendicular to the grating. The angle of the diffracted light beam is not affected by the structure of the optical element. Instead, the angle of the diffracted light beam is determined by the grating period, the wavelength of the incident plane wave, and the wave incident angle, and can be calculated according to the grating equation.

[0098] Figure 4A is a cross-sectional view of a part of a diffraction grating configured according to Figure 3B Although three cells are shown in Figure 4A the diffraction grating according to some embodiments may include an array of dozens, hundreds, or thousands of cells. Figure 4B is a schematic cross-sectional perspective view of a part of the diffraction grating as in Figure 4A which shows four cells.

[0099] The performance of a diffraction grating depends on the polarization of the incident wave and the parameters of the elements (size, form, and material). Unlike diffraction gratings that contain symmetrical, single-material optical elements (regularly spaced structures), exemplary diffraction gratings based on dual-material elements achieve an asymmetric intensity distribution (T0). j ≠Tj, R j ≠R -j , where j is the diffraction order, thus resulting in the maximum grating efficiency for the desired diffraction order. The maximum input corresponds to ±1 order when the element has W ≤ λ.

[0100] Figures 5A to 5C The calculated reflectivity and transmittance of incident TE are plotted. These graphs show the results for a substrate with n3 = 1.5154 ( Figure 3B , Figures 4A to 4B A grating with a period of d = 494 nm and stepped optical elements configured for the element's refractive index n2 are presented. The reflectivity for the zeroth order (R0) and the transmittance for the negative first order (T⁻¹), zeroth order (T⁰), and positive first order (T⁁) are measured at λ = 625 nm. A full-wave electromagnetic analysis is performed on the 2D array of the two-material elements. This calculation assumes the system is infinite in the X and Y directions. It can be seen that changing the refractive index n2 alters the grating's performance and changes the refractive transmittance of the first order. The diffraction uniformity of the systems with n2 = 2.8 and n2 = 2.6 is approximately 95%. Such properties of the proposed diffraction grating topology can be used to couple light into waveguides. Figures 5A to 5C It is evident that the maximum intensity of the first-order diffraction corresponds to the element with a higher refractive index n2 (n2 = 2.8) and a smaller component size. This can be interpreted as a result of the nanojet deviating at a larger angle.

[0101] Figures 5A to 5C This is a graph showing the simulation results of reflectivity and transmittance for an incident angle α of the electromagnetic wave. In all simulations, λ = 625 nm, d = 494 nm, n1 = 1.0, n3 = 1.5154. Figure 5A In the given information, n2 = 2.8, W = 300 nm, h1 = 255 nm, and h2 = 475 nm. Figure 5B In the given information, n2 = 2.6, W = 300 nm, h1 = 295 nm, and h2 = 500 nm. Figure 5C In the given information, n2 = 2.4, W = 380nm, h1 = 420nm, and h2 = 680nm.

[0102] like Figures 6A to 6CAs shown, by comparing the power distribution of exemplary diffraction gratings with stepped elements at different incident angles, it can be observed that the nanojet redistribution due to element edge reflection provides uniform intensity for the first transmission order. It can be seen that the refraction of the nanojet by the walls of the element with a refractive index of n2 can alter the position and direction of the nanojet beam at the bottom boundary (the bottom edge of the second block with width W / 2 and height h2-h1), resulting in a redistribution of diffraction efficiency between the positive and negative diffraction orders. For position (X and Z coordinates, where the bottom edge of the optical element corresponds to Z=0 and the axis of symmetry of the cell corresponds to X=d / 2), in Figures 6A to 6C The correlation analysis of the peak power intensity of the nanojet hotspot (in the case of a single cell) and the nanojet hotspot shows that the nanojet hotspot is located inside the second smaller block of the element near the bottom edge of the optical element.

[0103] For use in waveguide systems for true-color imaging, it may be desirable to configure a structure for at least three wavelengths. Figure 7A and Figure 7B The calculated reflectance and transmittance for blue and green wavelengths are plotted in the figure. Figure 7A and Figure 7B The diagram shows simulated values ​​for reflectivity and transmittance at the zeroth order (R0) and transmittance at the negative first order (T-1), zeroth order (T0), and positive first order (T1) for the electromagnetic wave incident angle (α), with n1 = 1.0, n2 = 2.8, and n3 = 1.5154. Figure 7A In the given information, λ = 460 nm, d = 365.7 nm, W = 220 nm, h1 = 190 nm, and h2 = 350 nm. Figure 7B In the given information, λ = 530 nm, d = 421.4 nm, W = 260 nm, h1 = 220 nm, and h2 = 400 nm.

[0104] Furthermore, the diffraction uniformity of these systems with n² = 2.8 is approximately 95%. The simulations presented above assume that all materials are non-destructive and non-dispersive. The presented simulations can be adapted to dispersive materials without significant variations in refractive index for the three colors. The system exhibits very high transmittance for all colors. In some implementations, this three-waveguide system can be used as an internal coupler for augmented reality displays without color correction. The high uniformity of all three colors avoids dedicating portions of the image signal to correcting brightness and color uniformity.

[0105] An exemplary implementation includes a stepped micro-element that deflects the focused beam in the near region.

[0106] In some embodiments, a periodic array of stepped elements embedded in a dielectric substrate can be considered as a diffraction grating with an asymmetric intensity distribution, resulting in high grating efficiency for the desired diffraction order. Some embodiments provide high diffraction uniformity (e.g., >95%) for the corresponding order.

[0107] Due to the flat surface of the diffraction grating, some implementations offer relative ease of fabrication and robustness of the structure. For example, fabrication can be performed by chemically or mechanically etching or otherwise forming a stepped channel in the substrate and filling the stepped channel with a material having a refractive index greater than that of the substrate.

[0108] In some implementations, a grating configuration for three wavelengths allows the three-waveguide system to be used as an internal coupler for augmented reality displays without color correction.

[0109] Exemplary implementations can be achieved through various optical systems that operate to deflect an image or some light from the microstructure, offering advantages including simplicity and robustness in fabrication. Exemplary application areas include head-mounted displays, solar panels for maximizing light collection, light extraction in OLED displays, and so on.

[0110] While the examples above primarily involve the use of devices configured for visible light, other embodiments are configured to use longer or shorter wavelengths, such as infrared or ultraviolet light, or other portions of the electromagnetic spectrum. Such embodiments may employ materials that are transparent to their designed wavelengths.

[0111] A diffraction grating according to some embodiments includes: a substrate having an outer surface and a first refractive index; and a plurality of grating elements, each grating element including a stepped structure having a second refractive index greater than the first refractive index, and wherein the stepped structure includes a first step and a second step, the width of the first step being greater than the width of the second step; wherein the second step is located on the outer surface of the substrate, and the first step extends outward from the second step.

[0112] In some implementations of diffraction gratings, the inner surface of the stepped channel is substantially coplanar with the outer surface of the substrate.

[0113] In some implementations of diffraction gratings, the width of the first step is essentially twice the width of the second step.

[0114] In some implementations of the diffraction grating, the side edges of the first step are substantially aligned with the side edges of the second step.

[0115] In some implementations of the diffraction grating, the first step has a width W and a height h1, wherein

[0116]

[0117] And among them, in Where n L It is the first refractive index, and n H It is the second refractive index.

[0118] In some implementations of the diffraction grating, the height h2 of the stepped channel is less than twice the height h1 of the first step.

[0119] A diffraction grating according to some embodiments includes: a substrate having an outer surface and a first refractive index; and a plurality of grating elements, each grating element including a stepped structure having a second refractive index greater than the first refractive index.

[0120] In some implementations of diffraction gratings, each grating element includes a stepped channel inserted into a substrate.

[0121] In some implementations of the diffraction grating, the stepped channel is a two-step channel having a first step along the outer surface of the substrate and a second step extending inward from the first step, the width of the first step being greater than the width of the second step.

[0122] In some implementations of diffraction gratings, the outer surface of the stepped channel is substantially coplanar with the outer surface of the substrate.

[0123] In some embodiments of the diffraction grating, the stepped structure includes a first step and a second step, the width of the first step being greater than the width of the second step; wherein the second step is located on the outer surface of the substrate, and the first step extends outward from the first step.

[0124] A method for manufacturing a diffraction grating according to some embodiments includes: etching the outer surface of a substrate to form a plurality of stepped channels in the substrate, the substrate having a first refractive index; and filling each of the stepped channels with a material having a second refractive index greater than the first refractive index to generate a plurality of stepped channel inserts.

[0125] Although the features and elements have been described above in specific combinations, those skilled in the art will understand that each feature or element may be used alone or in any combination with other features and elements.

Claims

1. A diffraction grating, the diffraction grating comprising: A substrate having an outer surface and having a first refractive index; Multiple grating elements, each grating element including a stepped channel inserted into the substrate, the stepped channel having a second refractive index greater than the first refractive index; The stepped channel is a two-step channel, having a first step along the outer surface of the substrate and a second step extending inward from the first step, wherein the width of the first step is greater than the width of the second step; and The height of the stepped passage is less than twice the height of the first step.

2. The diffraction grating according to claim 1, wherein the outer surface of the stepped channel is substantially coplanar with the outer surface of the substrate.

3. The diffraction grating of claim 1, wherein the width of the first step is substantially twice the width of the second step.

4. The diffraction grating according to claim 1, wherein the side edge of the first step is substantially aligned with the side edge of the second step.

5. The diffraction grating according to any one of claims 1 to 4, wherein the first step has a width W and a height h1, wherein And among them, in Where n L It is the first refractive index, and n H It is the second refractive index.

6. The diffraction grating according to any one of claims 1 to 4, wherein the substrate is a waveguide in a waveguide display.

7. A method for fabricating a diffraction grating, the method comprising: Multiple stepped channels are formed in the outer surface of a substrate having a first refractive index. Each stepped channel is a two-step channel, the two-step channel having a first step along the outer surface of the substrate and a second step extending inward from the first step, the width of the first step being greater than the width of the second step. as well as Each of the stepped channels is filled with a material having a second refractive index greater than the first refractive index, and The height of each stepped passage is less than twice the height of the first step.

8. The method of claim 7, wherein the width of the first step is substantially twice the width of the second step.

9. The method of claim 7, wherein the side edge of the first step is substantially aligned with the side edge of the second step.

10. The method according to any one of claims 7 to 9, wherein the first step has a width W and a height h1, wherein And among them, in Where n L It is the first refractive index, and n H It is the second refractive index.

11. The method according to any one of claims 7 to 9, wherein the substrate is a waveguide in a waveguide display.

12. An optical device, the optical device comprising: At least one waveguide, the at least one waveguide comprising a substrate having an outer surface, the substrate having a first refractive index, and the waveguide having an internal coupler; and An image generator that operates to direct light representing an image onto the inner coupler; The internal coupler includes a plurality of grating elements, each grating element including a stepped channel inserted into the substrate, the stepped channel having a second refractive index greater than the first refractive index, the stepped channel being a two-step channel having a first step along the outer surface of the substrate and a second step extending inward from the first step, the width of the first step being greater than the width of the second step, and wherein the height of the stepped channel is less than twice the height of the first step.

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