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CN-115398284-B - Non-polarized light grating in-coupler

CN115398284BCN 115398284 BCN115398284 BCN 115398284BCN-115398284-B

Abstract

In an exemplary embodiment, a diffraction element is provided. The diffraction element may comprise a substrate. A plurality of grating elements is provided on a substrate. Each grating element includes a first ridge region including a first ridge body region and a first core element, a second ridge region including a second ridge body region and a second core element, and a saddle region extending between the first ridge region and the second ridge region. In some embodiments, the first ridge body, the second ridge body, and the saddle region have a first refractive index (n 2), and the first core element and the second core element have a second refractive index (n 4) that is greater than the first refractive index.

Inventors

  • Oksana sramkova
  • Walter Drazick
  • LAURENT BLOND

Assignees

  • 交互数字CE专利控股有限公司

Dates

Publication Date
20260508
Application Date
20210322
Priority Date
20200323

Claims (13)

  1. 1. A diffraction element, the diffraction element comprising: A substrate; A plurality of grating elements on the substrate, each grating element having a U-shaped cross-section and comprising: a first ridge region; a second ridge region, and A saddle region extending between the first and second ridge regions, the saddle region having a first height (H 1 ) that is lower than a second height (H 3 ) of the first and second ridge regions; Wherein the first ridge region comprises a first ridge body region having a first refractive index (n 2 ) and a first core element located inside the first ridge body region, the first core element having a second refractive index (n 4 ) greater than the first refractive index, and The second ridge region includes a second ridge body region having the first refractive index (n 2 ) and a second core element located inside the second ridge body region, the second core element having the second refractive index (n 4 ).
  2. 2. The diffraction element of claim 1, wherein the first and second core elements are in contact with the substrate.
  3. 3. The diffraction element of claim 1, wherein the substrate has a third refractive index (n 3 ) that is less than the first refractive index (n 2 ).
  4. 4. The diffraction element of any one of the preceding claims, wherein the grating elements are periodically arranged on the substrate at a grating pitch.
  5. 5. The diffraction element of claim 4, wherein the saddle regions have a first width (W 4 ), the ridge regions each have a second width (W 3 ), and a sum of twice the second width (W 3 ) and the first width (W 4 ) is less than the grating spacing.
  6. 6. The diffraction element of claim 1, wherein the first and second core elements are comprised of silicon.
  7. 7. The diffraction element of claim 1, wherein the substrate is in contact with a base medium between successive grating elements in the diffraction element.
  8. 8. The diffraction element of claim 1, wherein the substrate is a waveguide of a waveguide display.
  9. 9. A method for a diffraction element, the method comprising: will have a first wavelength [ ] ) Is directed onto the diffraction element, wherein the diffraction element comprises: A substrate; A plurality of grating elements on the substrate, each grating element comprising: a first ridge region; a second ridge region, and A saddle region extending between the first and second ridge regions, the saddle region having a first height (H 1 ) that is lower than a second height (H 3 ) of the first and second ridge regions; Wherein the first ridge region comprises a first ridge body region having a first refractive index (n 2 ) and a first core element located inside the first ridge body region, the first core element having a second refractive index (n 4 ) greater than the first refractive index, and The second ridge region includes a second ridge body region having the first refractive index (n 2 ) and a second core element located inside the second ridge body region, the second core element having the second refractive index (n 4 ).
  10. 10. The method of claim 9, wherein the substrate has a third refractive index (n 5 ), wherein the method further comprises diffracting the light to a diffraction order And wherein the grating elements are arranged substantially periodically with a spacing between And (3) with 。
  11. 11. The method of claim 10, wherein 。
  12. 12. The method of claim 9, wherein the saddle regions have a first width (W 4 ), the ridge regions each have a second width (W 3 ), and a sum of twice the second width (W 3 ) and the first width (W 4 ) is less than the grating spacing.
  13. 13. The method of claim 9, wherein the first core element and the second core element are comprised of silicon.

Description

Non-polarized light grating in-coupler Cross Reference to Related Applications The present application claims priority from european patent application No. 20315043.8 entitled "Unpolarized LIGHT GRATING IN-Coupler" filed 3/23 in 2020, which is hereby incorporated by reference in its entirety. Background The present disclosure relates to the field of optics and photons, and more particularly to planar optics. More particularly, but not exclusively, the present disclosure relates to diffraction gratings widely used in various devices, such as, among other examples, displays including in-coupling and out-coupling of light in waveguides for glasses electronics and head-mounted displays for AR (augmented reality) and VR (virtual reality) glasses, head-up displays (HUD) in the automotive industry, optical sensors for photo/video/light field cameras, bio/chemical sensors including lab-on-chip sensors, microscopes, spectroscopy and metrology systems, and solar panels. This section is intended to introduce the reader to various aspects of art, which may be related to various aspects of the present disclosure that are described and/or claimed below. This discussion is believed to be helpful in providing the reader with background information to facilitate a better understanding of the various aspects of the present invention. Accordingly, it should be understood that these statements are to be read in this light, and not as admissions of prior art. AR/VR glasses are considered a new generation of human-machine interfaces. The development of AR/VR glasses (and more generally glasses protection electronics) is associated with a number of challenges, including reducing the size and weight of such devices and improving image quality (in terms of contrast, field of view, color depth, etc.) that should be sufficiently realistic to achieve a truly immersive user experience. The trade-off between optical image quality and physical size has motivated the search for ultra-compact optical components that can be used as building blocks for more complex optical systems such as AR/VR glasses. It is desirable that such optical components be easy to manufacture and replicate. In such AR/VR glasses, various types of refractive and diffractive lenses and beam forming components are used to direct light from a micro-display or projector to the human eye, allowing a virtual image to be formed that is superimposed (in the case of AR glasses) or captured by a camera (in the case of VR glasses) with an image of the physical world seen with the naked eye. Some types of AR/VR glasses utilize optical waveguides, where light propagates into the optical waveguide by TIR (total internal reflection) only within a limited range of internal angles. The FoV (field of view) of a waveguide depends on the material of the waveguide, etc. In WO2017180403, a waveguide with an extended field of view is proposed, in which dual mode image propagation is used. In this method, the diffraction mode +1 is used to carry the right hand side image in one direction (negative angle of incidence on the in-coupler) and the-1 mode is used to propagate the positive angle of incidence to the opposite direction in the waveguide. The two half images are combined by a pupil expander and an outcoupler at the exit of the waveguide so that the user sees one image. The purpose of this system is to double the field of view because each half image can use the full angular bandwidth of the waveguide in each propagation direction. Some optical waveguides include one or more diffraction gratings. The period d of the diffractive structure (also referred to as the grating pitch) may be selected based on the wavelength λ of the incident light and the refractive index n 3 of the waveguide material. For example, it may be desirable to select the grating spacing d to be twice the wavelength of light in the waveguide medium, as follows: If the ratio between grating pitch and wavelength is considered d/lambda, 3/2<n 2 <2 and 2/3<d/lambda <4/5 can be made in the case of equation 1 above, and in any case d/lambda <1 is a value that can be defined as a sub-wavelength. Equation 1 in any case shows that the diffraction grating has a sub-wavelength structure. In US20160231568 a waveguide for a wearable display is disclosed, wherein the grating pitch of the structure is between 250nm and 500 nm. Very fine pitch gratings can be difficult to manufacture. When the structure is sub-wavelength, a sufficiently small pitch grating is not reachable by lithographic techniques, and the required accuracy even challenges electron beam lithography. An overview of the existing optical waveguide design concept shows that there is a lack of a reliable solution that can provide strong responses for both polarizations (transverse electric wave TE and transverse magnetic wave TM) simultaneously. It is therefore desirable to provide diffraction gratings for optical waveguides or other optical components. It is further