WO2021233877A1 - Réseaux de diffraction transmissifs et réfléchissants en matériau à indice de réfraction élevé à uniformité élevée - Google Patents

Réseaux de diffraction transmissifs et réfléchissants en matériau à indice de réfraction élevé à uniformité élevée Download PDF

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WO2021233877A1
WO2021233877A1 PCT/EP2021/063079 EP2021063079W WO2021233877A1 WO 2021233877 A1 WO2021233877 A1 WO 2021233877A1 EP 2021063079 W EP2021063079 W EP 2021063079W WO 2021233877 A1 WO2021233877 A1 WO 2021233877A1
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diffraction grating
refractive index
optical
diffraction
layer
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PCT/EP2021/063079
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English (en)
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Oksana SHRAMKOVA
Valter Drazic
Laurent Blonde
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Interdigital Ce Patent Holdings, Sas
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    • G—PHYSICS
    • G02—OPTICS
    • G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
    • G02B27/00—Optical systems or apparatus not provided for by any of the groups G02B1/00 - G02B26/00, G02B30/00
    • G02B27/01—Head-up displays
    • G02B27/017—Head mounted
    • G02B27/0172—Head mounted characterised by optical features
    • G—PHYSICS
    • G02—OPTICS
    • G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
    • G02B27/00—Optical systems or apparatus not provided for by any of the groups G02B1/00 - G02B26/00, G02B30/00
    • G02B27/0081—Optical systems or apparatus not provided for by any of the groups G02B1/00 - G02B26/00, G02B30/00 with means for altering, e.g. enlarging, the entrance or exit pupil
    • G—PHYSICS
    • G02—OPTICS
    • G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
    • G02B27/00—Optical systems or apparatus not provided for by any of the groups G02B1/00 - G02B26/00, G02B30/00
    • G02B27/01—Head-up displays
    • G02B27/0101—Head-up displays characterised by optical features
    • G02B2027/0112—Head-up displays characterised by optical features comprising device for genereting colour display
    • G—PHYSICS
    • G02—OPTICS
    • G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
    • G02B27/00—Optical systems or apparatus not provided for by any of the groups G02B1/00 - G02B26/00, G02B30/00
    • G02B27/01—Head-up displays
    • G02B27/0101—Head-up displays characterised by optical features
    • G02B2027/0123—Head-up displays characterised by optical features comprising devices increasing the field of view
    • G—PHYSICS
    • G02—OPTICS
    • G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
    • G02B27/00—Optical systems or apparatus not provided for by any of the groups G02B1/00 - G02B26/00, G02B30/00
    • G02B27/01—Head-up displays
    • G02B27/017—Head mounted
    • G02B27/0172—Head mounted characterised by optical features
    • G02B2027/0174—Head mounted characterised by optical features holographic

Definitions

  • the present disclosure relates to the field of optics and photonics, and more specifically to optical device comprising at least one diffraction grating. It may find applications in the field of conformable and wearable optics (e.g. AR/VR glasses (Augmented Reality/Virtual Reality)), as well as in a variety of other electronic consumer products comprising displays and/or lightweight imaging systems, including head up displays (HUD), as for example in the automotive industry.
  • conformable and wearable optics e.g. AR/VR glasses (Augmented Reality/Virtual Reality)
  • HUD head up displays
  • the present disclosure relates to diffraction gratings, containing near-field focusing and beam forming in the near-field zone elements, that can be used in a wide range of devices (as for example displays, including in and out coupling of light in waveguides for eyewear electronic devices and head-mounted displays for AR (Augmented Reality) and VR (Virtual Reality) glasses, optical sensors for photo/video/lightfield cameras, bio/chemical sensors, including lab-on-chip sensors, microscopy, spectroscopy and metrology systems, solar panels, etc.).
  • devices as for example displays, including in and out coupling of light in waveguides for eyewear electronic devices and head-mounted displays for AR (Augmented Reality) and VR (Virtual Reality) glasses, optical sensors for photo/video/lightfield cameras, bio/chemical sensors, including lab-on-chip sensors, microscopy, spectroscopy and metrology systems, solar panels, etc.
  • planar lens thanks to its small thickness and excellent focusing capability, has been developed to replace its thick dielectric counterpart as a nanophotonic component.
  • planar lenses have been studied so far, for example zone plates, nano-slit and nano-hole arrays, photonics crystals and metasurfaces.
  • different terminologies are used in the aforementioned techniques, they share the same principle of focusing coherent waves, which is to generate a constructive interference at the focal point by curving the phase front of an incident plane wave.
  • the performance of planar lenses has been optimized through sophisticated designs. However, most of the proposals do not allow for satisfactory control over the focal spot position and do not satisfactorily allow for changes to the orientation of an electromagnetic beam.
  • the available solutions may not fully satisfy the needs of emerging nano- photonic applications due to their performance characteristics (e.g. chromatic aberrations and limited resolution) and fabrication difficulties.
  • An optical see-through head mounted display is a device used for augmented/virtual reality (AR/VR) applications.
  • AR/VR augmented/virtual reality
  • Some AR-based HMDs use a waveguide structure in order to reduce the overall size and weight of the device.
  • Some such structures include in- and out-couplers which are fabricated by diffractive optical elements or holographic volume gratings. To couple light into the waveguide and provide good color uniformity, diffracted non-zero order light should have high intensity across a wide angular range.
  • a photonic nano jet is a narrow high-intensity optical radiation flux formed in the proximity to the shadow surface of an illuminated transparent dielectric particle with relatively small refractive index and a diameter that is comparable to or somewhat larger than the wavelength of the incident optical radiation.
  • the physical origin of photonic nanojet formation arises from the interference of the radiation net fluxes diffracted and transmitted through a particle.
  • One feature of a photonic nanojet is the high spatial localization of the light field in the transverse direction.
  • the physics of photonic nanojet formation by spherical particles has been studied by means of the Mie theory. Studies have shown that the focusing properties of the arbitrary-shaped microstructures are affected by the edge diffraction phenomenon.
  • the diffraction of light on the edge of a dielectric microstructure forms a tilted focused beam having a deviation angle that depends on the index ratio between the structure material and host medium.
  • references in the specification to “one embodiment,” “an embodiment,” “an example embodiment,” and the like indicate that the embodiment described may include a particular feature, structure, or characteristic; but not every embodiment necessarily includes that particular feature, structure, or characteristic. Moreover, such phrases are not necessarily referring to the same embodiment. Further, when a particular feature, structure, or characteristic is described in connection with an embodiment, such feature, structure, or characteristic may be used in connection with other embodiments whether or not explicitly described.
  • An optical system comprises an optical substrate, a plurality of diffraction grating elements arranged periodically on the substrate, and a phase-modifying optical layer between the optical substrate and the diffraction grating elements, the phase-modifying layer having a refractive index greater than a refractive index of the optical substrate.
  • the diffraction grating elements have a refractive index greater than 3.0.
  • the diffraction grating elements comprise a semiconductor. In some such embodiments, the diffraction grating elements comprise silicon. In some other embodiments, the diffraction grating elements comprise aluminum arsenide.
  • each grating element comprises a single component having a substantially rectangular cross section.
  • each grating element comprises a pair of components having substantially rectangular cross sections.
  • each grating element has a substantially U-shaped cross section.
  • the phase-modifying optical layer has a refractive index greater than 2.0.
  • the phase-modifying optical layer comprises titanium dioxide.
  • Some embodiments of the optical system further include a stop layer between the phase- modifying optical layer and the diffraction grating elements.
  • the optical substrate is a waveguide in a waveguide display.
  • the diffraction grating elements are configured to operate as a reflective diffraction grating.
  • the diffraction grating elements are configured to operate as a transmissive diffraction grating.
  • a method includes directing light on an optical system as described herein.
  • the method includes propagating the light through the optical substrate by total internal reflection.
  • the light may comprise an image.
  • FIG. 1 A is a cross-sectional schematic view of a waveguide display.
  • FIG. 1 B is a schematic illustration of a binocular waveguide display with a first layout of diffractive optical components.
  • FIG. 1 C is a schematic illustration of a binocular waveguide display with a second layout of diffractive optical components.
  • FIG. 1 D is a schematic exploded view of a double-waveguide display.
  • FIG. 1 E is a cross-sectional schematic view of a double-waveguide display.
  • FIGs. 2A-2B illustrate cross-sectional views of a unit cell of a high refractive index material regular diffraction grating (FIG. 2A); and a high refractive index material U-shape diffraction grating (FIG. 2B).
  • FIGs. 4A-4B illustrate cross-sectional views of unit cells of diffraction gratings with a layer of high refractive index material.
  • FIG. 4A illustrates a high refractive index material regular diffraction grating with additional layers.
  • FIG. 4B illustrates a high refractive index material twin-shape diffraction grating with additional layers.
  • ⁇ 3°.
  • ⁇ 30°.
  • H 1 0nm
  • ⁇ angle of electromagnetic wave incidence
  • FIGs. 10A-10C illustrate cross-sectional views of a unit cell of: a regular reflective diffraction grating (FIG. 10A); high refractive index material regular reflective diffraction grating with additional layers (FIG. 10B); high refractive index material twin-shape reflective diffraction grating with additional layers (FIG. 10C).
  • FIG. 1A is a schematic cross-sectional side view of a waveguide display device in operation.
  • An image is projected by an image generator 102.
  • the image generator 102 may use one or more of various techniques for projecting an image.
  • the image generator 102 may be a laser beam scanning (LBS) projector, a liquid crystal display (LCD), a light-emitting diode (LED) display (including an organic LED (OLED) or micro LED ( ⁇ LED) display), a digital light processor (DLP), a liquid crystal on silicon (LCoS) display, or other type of image generator or light engine.
  • LBS laser beam scanning
  • LCD liquid crystal display
  • LED light-emitting diode
  • ⁇ LED micro LED
  • DLP digital light processor
  • LCDoS liquid crystal on silicon
  • Light representing an image 112 generated by the image generator 102 is coupled into a waveguide 104 by a diffractive in-coupler 106.
  • the in-coupler 106 diffracts the light representing the image 112 into one or more diffractive orders.
  • light ray 108 which is one of the light rays representing a portion of the bottom of the image, is diffracted by the in-coupler 106, and one of the diffracted orders 110 (e.g. the second order) is at an angle that is capable of being propagated through the waveguide 104 by total internal reflection.
  • At least a portion of the light 110 that has been coupled into the waveguide 104 by the diffractive in-coupler 106 is coupled out of the waveguide by a diffractive out-coupler 114.
  • At least some of the light coupled out of the waveguide 104 replicates the incident angle of light coupled into the waveguide.
  • out-coupled light rays 116a, 116b, and 116c replicate the angle of the in- coupled light ray 108. Because light exiting the out-coupler replicates the directions of light that entered the in-coupler, the waveguide substantially replicates the original image 112. A user’s eye 118 can focus on the replicated image.
  • the out-coupler 114 out-couples only a portion of the light with each reflection allowing a single input beam (such as beam 108) to generate multiple parallel output beams (such as beams 116a, 116b, and 116c). In this way, at least some of the light originating from each portion of the image is likely to reach the user’s eye even if the eye is not perfectly aligned with the center of the out-coupler. For example, if the eye 118 were to move downward, beam 116c may enter the eye even if beams 116a and 116b do not, so the user can still perceive the bottom of the image 112 despite the shift in position.
  • the out-coupler 114 thus operates in part as an exit pupil expander in the vertical direction.
  • the waveguide may also include one or more additional exit pupil expanders (not shown in FIG. 1A) to expand the exit pupil in the horizontal direction.
  • the waveguide 104 is at least partly transparent with respect to light originating outside the waveguide display. For example, at least some of the light 120 from real-world objects (such as object 122) traverses the waveguide 104, allowing the user to see the real-world objects while using the waveguide display. As light 120 from real-world objects also goes through the diffraction grating 114, there will be multiple diffraction orders and hence multiple images. To minimize the visibility of multiple images, it is desirable for the diffraction order zero (no deviation by 114) to have a great diffraction efficiency for light 120 and order zero, while higher diffraction orders are lower in energy.
  • the out-coupler 114 is preferably configured to let through the zero order of the real image.
  • images displayed by the waveguide display may appear to be superimposed on the real world.
  • Some waveguide displays include more than one waveguide layer. Each waveguide layer may be configured to preferentially convey light with a particular range of wavelengths and/or incident angles from the image generator to the viewer.
  • waveguide displays having in-couplers, out-couplers, and pupil expanders may have various different configurations.
  • An example layout of one binocular waveguide display is illustrated in FIG. 1 B.
  • the display includes waveguides 152a, 152b for the left and right eyes, respectively.
  • the waveguides include in-couplers 154a,b, pupil expanders 156a,b, and components 158a,b, which operate as both out-couplers and horizontal pupil expanders.
  • the pupil expanders 156a,b are arranged along an optical path between the in-coupler and the out-coupler.
  • An image generator (not shown) may be provided for each eye and arranged to project light representing an image on the respective in-coupler.
  • FIG.1C An layout of another binocular waveguide display is illustrated in FIG.1C. In the display of FIG.
  • the display includes waveguides 160a, 160b for the left and right eyes, respectively.
  • the waveguides include in-couplers 162a,b. Light from different portions of an image may be coupled by the in-couplers 162a,b to different directions within the waveguides. In-coupled light traveling toward the left passes through pupil expanders 164a,b and 165a,b, while in-coupled light traveling toward the right passes through pupil expanders 166a,b and 167a,b. Having passed through the pupil expanders, light is coupled out of the waveguides using out-couplers 168a,b to substantially replicate an image provided at the in- couplers 162a,b.
  • different features of the waveguide displays may be provided on different surfaces of the waveguides.
  • the in-coupler and the out-coupler may both be arranged on the anterior surface of the waveguide (away from the user’s eye).
  • the in-coupler and/or the out-coupler may be on a posterior surface of the waveguide (toward the user’s eye).
  • the in-coupler and out-coupler may be on opposite surfaces of the waveguide.
  • one or more of an in-coupler, an out-coupler, and a pupil expander may be present on both surfaces of the waveguide.
  • the image generator may be arranged toward the anterior surface or toward the posterior surface of the waveguide.
  • the in-coupler is not necessarily on the same side of the waveguide as the image generator. Any pupil expanders in a waveguide may be arranged on the anterior surface, on the posterior surface, or on both surfaces of the waveguide. In displays with more than one waveguide layer, different layers may have different configurations of in-coupler, out- coupler, and pupil expander.
  • FIG. 1 D is a schematic exploded view of a double waveguide display, including an image generator 170, a first waveguide (WG 1 ) 172, and a second waveguide (WG 2 ) 174.
  • FIG. 1 E is a schematic side-view of a double waveguide display, including an image generator 176, a first waveguide (WG 1 ) 178, and a second waveguide (WG 2 ) 180.
  • the first waveguide includes a first transmissive diffractive in-coupler (DG1) 180 and a first diffractive out-coupler (DG6) 182.
  • the second waveguide has a second transmissive diffractive in-coupler (DG2) 184, a reflective diffractive in-coupler (DG3) 186, a second diffractive out- coupler (DG4) 188, and a third diffractive out-coupler (DG5) 190.
  • DG2 transmissive diffractive in-coupler
  • DG3 reflective diffractive in-coupler
  • DG4 second diffractive out- coupler
  • DG5 third diffractive out-coupler
  • Different displays may use different arrangements of optical components (such as different arrangements of pupil expanders) on the first and second waveguides.
  • FIGs. 1A-1 E illustrate the use of waveguides in a near-eye display
  • the same principles may be used in other display technologies, such as head up displays for automotive or other uses.
  • Example embodiments include transmissive and reflective diffraction gratings using high refractive index material.
  • the described uses of high refractive index materials may increase the diffraction efficiency and diffraction uniformity of transmissive and reflective gratings with simple topologies.
  • an additional high refractive index thin layer and stop layer are provided between the substrate and elements of diffraction grating, which may further improve the diffraction uniformity of in- coupled diffraction order and simplify the fabrication process.
  • high refractive index material diffraction gratings can be employed to efficiently steer light in the visible range with substantially uniform efficiency over a wide range of incidence angles.
  • Use of additional layers on the top of waveguide may improve the diffraction uniformity of an in- coupled diffraction order and simplify the fabrication process.
  • high refractive index material for at least some of the components that make up the elements of the reflective/transmissive gratings.
  • example embodiments use an additional layer of high refractive index material on the top of the waveguide.
  • a stop layer is provided above this high refractive index material layer, which may simplify the fabrication process.
  • the present disclosure further describes diffraction gratings comprising a plurality of grating unit cells.
  • FIG. 2A-2B illustrate cross-sectional views of a unit cell of a high refractive index material regular diffraction grating (FIG. 2A); and a high refractive index material U-shape diffraction grating (FIG. 2B).
  • FIG. 2A The general topology of the unit cell of an example symmetrical transmissive diffraction grating is illustrated in FIG. 2A.
  • the grating element 202 in a unit cell 204 is a single high refractive index grating component.
  • This cross-section view may correspond to high refractive index ( n 2 ) component on the top of a homogeneous dielectric substrate medium 206 with a refractive index n 3 ( n 2 > n 3 ).
  • n 2 is at least 1.45 times as great as n 3 .
  • the full system is hosted by the homogeneous host medium with refractive index n 1 .
  • n 1 ⁇ n 3 The full system is hosted by the homogeneous host medium with refractive index n 1 .
  • W and H are the width and height of the high refractive index component.
  • the materials and size of the constitutive parts may be configured to manage the position, direction, phase and amplitude of the edge waves diffracted by the vertical edges of the high refractive index component.
  • the illustrations provided herein show structures with vertical edges parallel to the z-axis and top/bottom surfaces parallel to the xy- plane, which corresponds to the base angle being equal to 90°.
  • some embodiments use prismatic structures (with arbitrary base angles) or other shapes. Variation of the base angle value provides additional degree of freedom in the control of the edge wave radiation.
  • a periodic array of the unit cells is provided.
  • the grating constant or the period of the grating is d.
  • the period of diffraction grating may be selected to in-couple diffraction order M 1 .
  • the grating pitch may be selected based on the angular span that can be coupled into the waveguide to propagate by Total Internal Reflection (TIR).
  • TIR Total Internal Reflection
  • a linearly polarized plane wave may be incident on the grating from the top in a plane perpendicular to the grating.
  • Example embodiments may be used for both TE and TM polarizations, but different embodiments may be configured to improve efficiency by taking into account the polarization of an incident wave.
  • FIG. 2B illustrates a u-shape diffraction grating unit cell 206.
  • the unit cell in the grating of FIG. 2B may be described as two unit cells as in FIG. 2A with grating components 210, 212 together with an additional component 214 with the width W 1 and height H 1 between these unit cells.
  • the distance between the high index components may be W 1 ⁇ d-W.
  • twin-shape diffraction grating uses a unit cell similar to that of FIG. 2B but without the central block (the additional component with the width W 1 and height H 1 ).
  • Simulations were performed to determine the effects of the edge diffraction phenomenon in the single element of the period into the total response of the diffraction grating. The presented data were obtained using the COMSOL Multiphysics software.
  • the presented analysis of the fields and power distributions inside the elements of the gratings may be used in selecting grating topologies for different applications.
  • E ⁇ 0,0, 1 ⁇ .
  • the effect of the parameters of the single element on the functionality of the system is considered.
  • the beam-forming phenomenon is associated with the edge of the system, and the nanojet beam radiation angle is linked to Snell’s law, as described, for example, in A. Boriskin, V. Drazic, R. Keating, M. Damghanian, O. Shramkova, L. Blonde, “Near field focusing by edge diffraction,” Opt. Lett., 2018.
  • the nanojet beam radiation angle for constitutive parts of the element of the unit cell can be determined as a function of the ratio between the refractive indexes of the media hosting the element: n 1 and material of the element of diffraction grating n 2 , and the base angle of the element.
  • the nanojet beam radiation angle can be determined using the approximate formula: where is the critical angle of refraction.
  • two opposite edges of the element on the top of substrate with the width I/I/ and height H will generate two nanojets (the nanojets are similar only in a case of normal incidence).
  • the creation of a nanojet beam is the result of constructive interference between the edge wave diffracted by the vertical edge and refracted plane wave.
  • Two edge waves (EW1 and EW2) will propagate inside the element with the angle of deviation equal to (see FIG. 2A).
  • nanojet length and intensity depend significantly on the size of an element, as described, for example in B. Varghese, O. Shramkova, V. Drazic, V. Allie, L. Blonde , “Influence of an edge height on the diffracted EM field distribution,” ICTON 2019,
  • ⁇ is the angle of electromagnetic wave incidence. It may be desirable to select the height of the element of the diffraction grating to substantially satisfy the following equation:
  • the dimensions of the element in some embodiments may be configured to increase the diffraction uniformity for inclined incidence angles of the electromagnetic wave.
  • the angles of deviation of EWi and EW2 will not be equal and depending on the angle of incidence there may be multiple EW reflections by the edges of the element.
  • the performance of the grating is affected by the polarization of the incident wave and parameters (dimensions, form and material) of the elements.
  • the first diffraction order is in-coupled into the waveguide. So, maximal input for dual mode system (where the diffraction efficiency is configure for two diffraction modes) corresponds to the orders ⁇ 1.
  • FIGs. 3B and 3D illustrate results for a u-shaped transmissive diffraction grating (as in FIG.
  • FIGs. 3A-3D reflect the dependencies for different heights of the elements.
  • the numerical analysis of diffraction uniformity and power for different configurations are presented below in Table 1.
  • An alternative substrate material may be an episulfide material (such as those used in some eyeglasses) with a refractive index of around 1.716 at 532 nm.
  • the full-wave electromagnetic analysis was conducted for the 1 D periodic array of the elements.
  • a measure G of diffraction uniformity may be defined as:
  • the diffraction uniformity is about 86.93%.
  • the diffraction power which is the ratio of the total transmitted light to the incoming one over this angular range, of such grating is equal to 81.2%.
  • some embodiments use a modified topology of the elements.
  • the transmitted intensity corresponding to the low angles of incidence will be increased providing higher diffraction uniformity.
  • G will be equal to 91.85%.
  • the diffraction power of such grating is equal to 78.6%.
  • Example diffractive structures with additional layers are illustrated.
  • Some embodiments operate to increase the transmittivity of in-coupled diffraction order at low angles of incidence.
  • Some embodiments employ a high refractive index material diffraction grating with an additional thin layer ( H L 1 is the thickness of this layer with refractive index n L 1 ) placed on the top of the waveguide.
  • H L 1 is the thickness of this layer with refractive index n L 1
  • a stop layer is provided between this thin layer and elements of the grating.
  • the stop layer material refractive index is n L 2
  • H L 2 is the thickness of this layer.
  • Example topologies corresponding to regular and twin-shaped diffraction gratings are presented in FIGs. 4A and 4B, respectively.
  • the utilization of an additional high refractive index layer between the substrate and elements of diffraction grating modifies the phase of the refracted edge wave, providing higher transmissivity of the in-coupled order.
  • FIGs. 4A-4B illustrate cross-sectional views of unit cells of diffraction gratings with a layer of high refractive index material.
  • FIG. 4A illustrates a high refractive index material regular diffraction grating with additional layers.
  • FIG. 4A illustrates a diffraction grating unit cell 400 with element 402 on substrate 404.
  • the example of FIG. 4A includes a phase-modifying optical layer 406 with refractive index n L 1 .
  • the grating as illustrated further includes an optional stop layer 408 with refractive index n L 2 .
  • FIG. 4B illustrates a high refractive index material twin-shape diffraction grating with additional layers.
  • Unit cell 410 includes a pair of grating elements 412, 413 arranged on substrate 414.
  • the example of FIG. 4B includes a phase-modifying optical layer 416 with refractive index nu.
  • the grating as illustrated further includes an optional stop layer 418 with refractive index n L 2 .
  • the calculations assume that AI 2 O 3 is the material of stop layer.
  • the diffraction uniformity of depends in part on the thickness H L 1 and refractive index of material of this additional layer n L 1 .
  • ⁇ 3°.
  • ⁇ 30°.
  • the high refractive index layer may be titanium dioxide (TiO 2 ).
  • FIG. 6B illustrates the reflectivity and transmittivity for a twin-shaped diffraction grating with additional layers. [0079] FIG. 6A-6B illustrate reflectance and transmittance vs.
  • the utilization of an additional high refractive index layer together with the stop layer may also increase the diffraction uniformity of the in-coupled diffraction order in the case of a low refractive index material diffraction grating.
  • the utilization of the additional phase- modifying layer can provide better uniformity and utilization of the stop layer can simplify the fabrication process.
  • H L1 10 nm.
  • H L1 15 nm.
  • the utilization of an additional high refractive index layer together with the stop layer may increase (e.g. nearly double) the diffraction uniformity of the in-coupled diffraction order in the case of low refractive index material diffraction grating.
  • high refractive index material elements are used for fabrication of reflective diffraction gratings with high diffraction uniformity and efficiency for incoupled diffraction orders.
  • the constructive interference between the edge waves diffracted by the vertical edges and reflected by the top and walls of the high refractive index element and refracted plane wave will provide high intensity of reflected orders.
  • FIG. 10A shows positions and directions of edge waves generated by the single element of a regular reflective diffraction grating.
  • FIGs. 10A-10C illustrate cross-sectional views of a unit cell of: a regular reflective diffraction grating (FIG. 10A); high refractive index material regular reflective diffraction grating with additional layers (FIG. 10B); high refractive index material twin-shape reflective diffraction grating with additional layers (FIG. 10C).
  • a full-wave electromagnetic analysis was performed for a 1 D array of the elements. The analysis assumes that the system is infinite in X- and Y-directions. It can be seen that such a high refractive index material diffraction grating has a high intensity for reflected first order.
  • two additional layers are provided between the waveguide and elements of the diffraction grating to modify the reflectivity of the in-coupled order.
  • Reflectances and transmittances for two different reflective grating topologies presented in FIGs. 10B and 10C vs. angle of electromagnetic wave incidence are depicted in FIGs. 13A-13B. It may be observed that utilization of additional layers can also increase the diffraction uniformity in a case of reflective diffraction gratings.
  • Example embodiments provide diffraction grating devices with high efficiency and uniformity.
  • Some embodiments use high refractive index material for the elements of transmissive and reflective diffraction gratings.
  • the diffraction gratings in some embodiments contain symmetrical single- material elements using a regular structure of the same spacing, resulting in a symmetrical distribution of an intensity.
  • Use of high refractive index material provides high diffraction efficiency and diffraction uniformity of corresponding orders for gratings with a relatively simple topology. Parameters of the grating may be selected using, for example, Equation (3).
  • Some embodiments operate to increase the transmitted intensity of in-coupled diffraction order at low angles of incidence.
  • the pitch of the grating for the proposed u- and twin- shape topologies is increased to allow for in-coupling of the second diffraction order (instead of first diffraction order in the case of regular diffraction grating) into the waveguide.
  • example embodiments use an additional high refractive index thin layer and stop layer between the substrate and elements of diffraction grating.
  • Example embodiments may be used in any optical system that operates to deviate an image or light with a micro-structure, potential advantages including simplicity of fabrication and robustness.
  • Example application domains are head-up displays, solar cell panels for maximizing light collection, OLED display light extraction, among many others.
  • the above examples refer primarily to the use of devices configured for visible light, other embodiments are configured for use with longer or shorter wavelengths, such as infrared or ultraviolet light, or for use with waves in other parts of the electromagnetic spectrum. Such embodiments may employ materials that are transparent to the wavelengths for which they are designed.
  • an optical system includes an optical substrate; and a plurality of diffraction grating elements arranged periodically on the substrate, wherein the diffraction grating unit cells comprise at least one high refractive index component.
  • the high refractive index component has a refractive index greater than 2.5. In some embodiments, the high refractive index component has a refractive index greater than 3.0.
  • the high refractive index component comprises a semiconductor, such as silicon or aluminum arsenide, among others.
  • the high refractive index component comprises a high refractive index dielectric metasurface.
  • the respective grating elements comprise a single grating component having a substantially rectangular cross section.
  • the respective grating elements comprise a pair of grating components having a substantially rectangular cross section.
  • the respective grating elements have a substantially u-shaped cross section.
  • the optical substrate is a waveguide, such as a waveguide in a waveguide display.
  • the diffraction grating unit cells are configured to operate as a reflective diffraction grating. In some embodiments, the diffraction grating unit cells are configured to operate as a transmissive diffraction grating.
  • the optical system further includes a phase-modifying optical layer between the optical substrate and the diffraction grating unit cells.
  • the phase-modifying optical layer may be a substantially continuous layer.
  • the phase-modifying layer may have a refractive index greater than a refractive index of the optical substrate.
  • the phase-modifying optical layer may have a refractive index greater than 2.0.
  • an optical system includes an optical substrate, a plurality of diffraction grating elements arranged periodically on the substrate; and a phase-modifying optical layer between the optical substrate and the diffraction grating elements, where the phase-modifying layer has a refractive index greater than a refractive index of the optical substrate.
  • the phase-modifying optical layer may be a substantially continuous layer with a refractive index greater than 2.0.
  • the phase-modifying optical layer may have a refractive index greater than 2.5.
  • Some embodiments further include a stop layer between the phase-modifying optical layer and the diffraction grating elements.
  • Some embodiments include a method in which light is directed on an optical system as described herein.
  • the light may be light representing an image, for example in a waveguide display system.
  • the method may include coupling the light into the waveguide.
  • An optical system includes: an optical substrate; a plurality of diffraction grating elements arranged periodically on the substrate; and a phase-modifying optical layer between the optical substrate and the diffraction grating elements, the phase-modifying layer having a refractive index greater than a refractive index of the optical substrate.
  • the phase-modifying optical layer is a substantially continuous.
  • the phase-modifying optical layer has a refractive index greater than 2.0. In some embodiments, the phase-modifying optical layer has a refractive index greater than 2.5.
  • Some embodiments further include a stop layer between the phase-modifying optical layer and the diffraction grating elements.
  • a method is performed that includes directing light on the optical system.
  • the light may comprise an image.
  • the refractive index of the high refractive index component is at least 1.45 times as great as a refractive index of the substrate.
  • a diffractive system includes: a substrate that is transparent to at least a first wavelength of electromagnetic radiation; and a plurality of diffraction grating elements arranged periodically on the substrate; wherein the diffraction grating elements comprise at least one component having a refractive index at the first wavelength that is at least 1.45 times as great as a refractive index of the substrate at the first wavelength.

Abstract

Dans des modes de réalisation donnés à titre d'exemple, un système optique comprend un substrat optique et une pluralité d'éléments réseaux de diffraction agencés périodiquement sur le substrat, les éléments réseaux de diffraction comprenant au moins un composant à indice de réfraction élevé. Les éléments réseaux peuvent être symétriques, et peuvent avoir différentes configurations de section transversale dans différents modes de réalisation. Dans certains modes de réalisation, le système optique comprend une couche de modification de phase et une couche d'arrêt entre le substrat et les éléments réseaux de diffraction. Le substrat optique peut être un guide d'ondes dans un dispositif d'affichage à guide d'ondes.
PCT/EP2021/063079 2020-05-18 2021-05-18 Réseaux de diffraction transmissifs et réfléchissants en matériau à indice de réfraction élevé à uniformité élevée WO2021233877A1 (fr)

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