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EP-4104012-B1 - RESONANT LIQUID CRYSTAL DEVICES

EP4104012B1EP 4104012 B1EP4104012 B1EP 4104012B1EP-4104012-B1

Inventors

  • MAIMONE, Andrew
  • JIANG, Yingfei
  • SHIPTON, ERIK
  • YAROSHCHUK, OLEG
  • COLBURN, Shane
  • WEI, GUOHUA
  • PARSONS, MAXWELL

Dates

Publication Date
20260513
Application Date
20210211

Claims (12)

  1. A tunable liquid crystal (LC) device comprising: a first substrate; a first reflector over the first substrate, the first reflector comprising a first electrode layer; an LC layer over the first reflector; a second reflector over the LC layer, the second reflector comprising a second electrode layer; and a second substrate over the second reflector; wherein the LC layer is tunable by applying an electrical signal to at least one of the first or second electrode layers; wherein the first reflector is a full reflector, and the second reflector is a partial reflector having reflectivity of at least 6%; the first electrode layer comprises an array of conductive layer segments, wherein at least some conductive layer segments of the array of conductive layer segments are independently energizable by applying electrical signals thereto; and the array of conductive layer segments comprises a conductive oxide having at least 50% transmission of visible light.
  2. The tunable LC device of claim 1, wherein the first substrate comprises a silicon substrate supporting a circuitry for providing the electrical signal for tuning the LC layer.
  3. The tunable LC device of claim 1, wherein the LC layer comprises a nematic LC with positive dielectric anisotropy, the LC device further comprising: a first alignment layer between the first reflector and the LC layer; and a second alignment layer between the LC layer and the second reflector; wherein the first and second alignment layers are configured to uniformly align the LC with a pretilt angle of less than 10 degrees.
  4. The tunable LC device of claim 1, wherein the LC layer comprises a nematic LC with negative dielectric anisotropy, the LC device further comprising: a first alignment layer between the first reflector and the LC layer; and a second alignment layer between the LC layer and the second reflector; wherein the first and second alignment layers are configured to homeotropically align the LC with a pretilt angle of greater than 85 degrees.
  5. The tunable LC device of claim 1, wherein the LC layer comprises a nematic LC with positive dielectric anisotropy, the LC device further comprising: a first alignment layer between the first reflector and the LC layer; and a second alignment layer between the LC layer and the second reflector; wherein the first alignment layer is configured to align the LC with a first pretilt angle of less than 10 degrees, and the second alignment layer is configured to align the LC with a second pretilt angle of greater than 85 degrees, causing the LC to adopt a hybrid orientational configuration.
  6. The tunable LC device of claim 1, wherein the LC layer has a thickness of 2 micrometers or less.
  7. The tunable LC device of claim 1, wherein a reflectivity of the partial reflector is less than a reflectivity of the full reflector minus a round-trip absorption loss in an optical cavity formed by the full and partial reflectors.
  8. The tunable LC device of claim 1, wherein the partial reflector comprises: a distributed Bragg reflector, a high-contrast subwavelength grating, or a metasurface that comprises at least one of dielectric or metallic subwavelength structures.
  9. The tunable LC device of claim 1, wherein at least some conductive layer segments of the array of conductive layer segments are reflective.
  10. The tunable LC device of claim 1, wherein the full reflector further comprises a reflective layer supported by the first substrate, wherein each conductive layer segment of the array of conductive layer segments is supported by the reflective layer, and, optionally, wherein the reflective layer comprises at least one of: a distributed Bragg reflector; a subwavelength grating; or a metasurface comprising at least one of dielectric or metallic subwavelength structures.
  11. Use of the LC device of claim 1 for configuring a hologram.
  12. A system comprising: the LC device of claim 1; a light source coupled to the LC device for providing a light beam thereto, wherein the LC device is configured to spatially modulate the light beam in at least one of phase or amplitude by applying electrical signals to conductive layer segments of the array of conductive layer segments, and, optionally, the system further comprising an optics block disposed downstream of the LC device and configured to redirect the spatially modulated light beam for forming an image.

Description

TECHNICAL FIELD The present disclosure relates to tunable optical devices, and in particular to tunable liquid crystal devices, as well as display panels, spatial light modulators, beam steering devices, etc., based on tunable liquid crystal devices. BACKGROUND Head mounted displays (HMDs), helmet mounted displays, near-eye displays (NEDs), stereoscopic displays, and other types of displays are used for displaying content, e.g. virtual reality (VR) content, augmented reality (AR) content, mixed reality (MR) content, etc. Such displays are finding applications in diverse fields including entertainment, education, training, engineering, biomedical science, to name just a few examples. The displayed VR / AR / MR content can be three-dimensional (3D) to enhance the experience and to match virtual objects to real objects observed by the user. Compact display devices are desired in many applications, especially for head-mounted displays. Because a display of an HMD or NED is usually worn on the head of a user, a large, bulky, unbalanced, and/or heavy display device would be cumbersome and may be uncomfortable for the user to wear. Miniature liquid crystal panels may be used for image generation in HMD or NED. It may be desirable to improve spatial resolution and switching speed of liquid crystal panels and other devices based on tunable liquid crystal cells to enable a broader range of display applications. US 2016/291405 A1 describes a spatial light modulator for modulating the phase, retardation or polarization state of an incident optical signal propagating in a first dimension. The optical phase modulator includes a liquid crystal material and a pair of electrodes for supplying an electric potential across the liquid crystal material to drive liquid crystals in a predetermined configuration. Modulator also includes a diffractive optical element disposed adjacent a first electrode. Element includes a first array of diffractive elements formed of a first material having a first refractive index and extending in a second dimension substantially perpendicular to the first dimension. Elements are at least partially surrounded by a second material formed of a lower refractive index SUMMARY OF THE INVENTION Accordingly, the present invention is directed tunable liquid crystal (LC) devices, configurable hologram comprising the LC devices, and systems according to the appended claims. The scope of the present invention is set out in the claims appended hereto. BRIEF DESCRIPTION OF THE DRAWINGS Exemplary embodiments will now be described in conjunction with the drawings, in which: FIG. 1 is a side cross-sectional view of a liquid crystal (LC) device of this disclosure;FIGs. 2A and 2B are side cross-sectional views of an LC device of this disclosure in OFF and ON states, respectively, the LC having positive dielectric anisotropy;FIGs. 2C and 2D are side cross-sectional views of an LC device of this disclosure in OFF and ON states, respectively, the LC having negative dielectric anisotropy;FIG. 3 is a schematic side diagram of a single-pass reflective LC cell;FIG. 4 is a schematic side diagram of a multipass reflective LC cell having a top partial reflector;FIGs. 5A and 5B are graphs of output field amplitude and phase shift, respectively, as a function of optical path length of the LC devices of FIG. 1 and 4 at different values of reflectivity of the top reflector and a non-zero cavity loss;FIGs. 6A, 6B, and 6C are graphs of output phase shift, minimum reflected intensity, and a ratio of minimum to maximum reflected intensity, respectively, as a function of top reflector reflectivity at different values of effective reflectivity of the bottom reflector;FIG. 7A is a side cross-sectional view of an embodiment of the LC device of FIG. 1 with metal reflectors;FIG. 7B is a side cross-sectional view of an embodiment of the LC device of FIG. 1 with a reflective high-contrast subwavelength grating used as the top partial reflector;FIG. 7C is a side cross-sectional view of an embodiment of the LC device of FIG. 1 with distributed Bragg reflectors used as full and partial reflectors;FIG. 8 is a graph of output amplitude and phase of the LC device of FIG. 7C as a function of effective refractive index of the LC material;FIGs. 9A, 9B, and 9C are schematic cross-sectional views of an embodiment of the LC device of FIG. 1 with a π-cell LC configuration at different applied voltages;FIGs. 10A and 10B are schematic cross-sectional views of an embodiment of the LC device of FIG. 1 with a hybrid alignment of LC molecules before and after application of voltage, respectively;FIG. 11 is a schematic view of a configurable hologram based on an LC device of this disclosure;FIG. 12 is a schematic view of a near-eye display using an LC device of this disclosure to generate virtual imagery;FIG. 13A is an isometric view of a head-mounted display of this disclosure; andFIG. 13B is a block diagram of a virtual reality system including the headset o