Resonant Liquid Crystal Device

Abstract

A tunable liquid crystal (LC) device includes an LC layer between a pair of reflectors forming an optical cavity. The reflector includes a conductive layer for applying an electrical signal to the LC layer. One of the conductive layers may include an array of conductive pixels for selectively controlling the effective refractive index of the LC layer spatially. By placing the LC layer into the optical cavity, the phase delay introduced by the LC layer can be greatly increased or amplified. This enables a significant reduction in the thickness of the LC layer, which in turn enables very close spacing of the LC pixels, while reducing inter-pixel crosstalk caused by fringing electric fields, and achieving faster switching times. Closely spaced fast LC devices can be used as configurable holograms or spatial light modulators.

Description

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS

[0002] This application claims priority to U.S. Provisional Application No. 62 / 976,788, filed on February 14, 2020, entitled “RESONANT LIQUIDCRYSTAL DEVICES,” which is incorporated herein by reference in its entirety. Technical Field

[0003] The present disclosure relates to a tunable optical device, in particular to a tunable liquid crystal device, and to a display panel, a spatial light modulator, a beam control device, etc. based on the tunable liquid crystal device. Background Art

[0004] Head-mounted displays (HMDs), helmet-mounted displays, near-eye displays (NEDs), stereoscopic displays, and other types of displays are used to display content, such as virtual reality (VR) content, augmented reality (AR) content, mixed reality (MR) content, etc. Such displays find applications in a variety of fields including entertainment, education, training, engineering, biomedical sciences, to name just a few examples. The VR / AR / MR content displayed can be three-dimensional (3D) to improve the experience and match virtual objects with real objects observed by the user.

[0005] In many applications, particularly for head mounted displays, compact display devices are desired. Because the display of an HMD or NED is typically worn on the user's head, a large, bulky, unbalanced and / or heavy display device would be cumbersome and may be uncomfortable for the user to wear. Micro liquid crystal panels may be used for image generation in an HMD or NED. It may be desirable to improve the spatial resolution and switching speed of liquid crystal panels and other devices based on tunable liquid crystal cells to enable a wider range of display applications. Summary of the invention

[0006] The present invention therefore relates to an orientationally tunable liquid crystal (LC) device, a configurable hologram comprising the LC device, and a system according to the accompanying claims.

[0007] In one aspect, the present invention relates to a tunable liquid crystal (LC) device comprising: a first substrate; a first reflector above the first substrate, the first reflector comprising a first electrode layer; an LC layer above the first reflector; a second reflector above the LC layer, the second reflector comprising a second electrode layer; and a second substrate above the second reflector; wherein the LC layer is tuned by applying an electrical signal to at least one of the first electrode layer or the second electrode layer.

[0008] In an embodiment of the LC device according to the invention, the first substrate may comprise a silicon substrate supporting circuitry for providing electrical signals for tuning the LC layer.

[0009] In an embodiment of the LC device according to the present invention, the LC layer may further include a nematic LC having positive dielectric anisotropy, and the LC device may further include: 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 and the second alignment layer may be configured to uniformly align the LC at a pretilt angle of less than 10 degrees.

[0010] In an embodiment of the LC device according to the present invention, the LC layer may include a nematic LC having negative dielectric anisotropy, and the LC device may further include: a first alignment layer between the first reflector and the LC layer; and

[0011] a second alignment layer between the LC layer and the second reflector; wherein the first alignment layer and the second alignment layer may be configured to vertically align the LC at a pre-tilt angle greater than 85 degrees.

[0012] In an embodiment of an LC device according to the present invention, the LC layer may include a nematic LC having positive dielectric anisotropy, and the LC device may further include: 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 may be configured to align the LC at a first pretilt angle less than 10 degrees, and the second alignment layer may be configured to align the LC at a second pretilt angle greater than 85 degrees, so that the LC adopts a hybrid orientation configuration.

[0013] In embodiments of the LC device according to the invention, the LC layer may have a thickness of 2 micrometers or less.

[0014] In an embodiment of the LC device according to the invention, the first reflector may be a total reflector and the second reflector may be a partial reflector having a reflectivity of at least 6%.

[0015] In an embodiment of the LC device according to the present invention, the first reflector can be a total reflector and the second reflector can be a partial reflector with a reflectivity of at least 6%, wherein the reflectivity of the partial reflector can be less than the reflectivity of the total reflector minus the round-trip absorption loss in the optical cavity formed by the total reflector and the partial reflector.

[0016] In an embodiment of the LC device according to the invention, the first reflector may be a total reflector and the second reflector may be a partial reflector having a reflectivity of at least 6%, wherein the partial reflector may comprise a distributed Bragg reflector.

[0017] In an embodiment of the LC device according to the invention, the first reflector may be a total reflector and the second reflector may be a partial reflector having a reflectivity of at least 6%, wherein the partial reflector may comprise a high contrast sub-wavelength grating.

[0018] In an embodiment of the LC device according to the present invention, the first reflector may be a total reflector and the second reflector may be a partial reflector having a reflectivity of at least 6%, wherein the partial reflector may include a metasurface including at least one of a dielectric subwavelength structure or a metallic subwavelength structure.

[0019] In an embodiment of the LC device according to the present invention, the first reflector may be a total reflector and the second reflector may be a partial reflector with a reflectivity of at least 6%, wherein the first electrode layer may include an array of conductive layer segments, wherein at least some of the conductive layer segments in the array of conductive layer segments can be independently excited by applying an electrical signal thereto.

[0020] In an embodiment of the LC device according to the present invention, the first reflector can be a total reflector and the second reflector can be a partial reflector with a reflectivity of at least 6%, wherein the first electrode layer can include an array of conductive layer segments, wherein at least some of the conductive layer segments in the array of conductive layer segments can be independently excited by applying an electrical signal thereto, and wherein the array of conductive layer segments can have a pitch of 2 microns or less.

[0021] In an embodiment of the LC device according to the present invention, the first reflector can be a total reflector and the second reflector can be a partial reflector with a reflectivity of at least 6%, wherein the first electrode layer may include an array of conductive layer segments, wherein at least some of the conductive layer segments in the array of conductive layer segments can be independently excited by applying an electrical signal thereto, and wherein the array of conductive layer segments may include a conductive oxide with a visible light transmittance of at least 50%.

[0022] In an embodiment of the LC device according to the present invention, the first reflector can be a total reflector and the second reflector can be a partial reflector with a reflectivity of at least 6%, wherein the first electrode layer can include an array of conductive layer segments, wherein at least some of the conductive layer segments in the array of conductive layer segments can be independently excited by applying electrical signals thereto, and wherein at least some of the conductive layer segments in the array of conductive layer segments can be reflective.

[0023] In an embodiment of the LC device according to the present invention, the first reflector may be a total reflector, and the second reflector may be a partial reflector having a reflectivity of at least 6%, wherein the first electrode layer may include an array of conductive layer segments, wherein at least some of the conductive layer segments in the array of conductive layer segments may be independently excited by applying an electrical signal thereto, and wherein the total reflector further includes a reflective layer supported by the first substrate, wherein each conductive layer segment in the array of conductive layer segments may be supported by the reflective layer. In addition, the reflective layer may include at least one of the following: a distributed Bragg reflector; a subwavelength grating; or a metasurface including at least one of a dielectric subwavelength structure or a metallic subwavelength structure

[0024] In one aspect, the invention relates to a configurable hologram comprising an LC device as described above.

[0025] In one aspect, the present invention relates to a system comprising:

[0026] Any LC device as described above, in particular a LC device comprising:

[0027] A first substrate; a first reflector above the first substrate, the first reflector comprising a first electrode layer; an LC layer above the first reflector; a second reflector above the LC layer, the second reflector comprising a second electrode layer; and a second substrate above the second reflector; wherein the LC layer is capable of being tuned by applying an electrical signal to at least one of the first electrode layer or the second electrode layer, wherein the first reflector can be a total reflector and the second reflector can be a partial reflector having a reflectivity of at least 6%, wherein the first electrode layer can include an array of conductive layer segments, wherein at least some of the conductive layer segments in the array of conductive layer segments are capable of being independently excited by applying an electrical signal thereto; and a light source coupled to the LC device for providing a light beam to the LC device, wherein the LC device is configured to spatially modulate the light beam in at least one of phase or amplitude by applying an electrical signal to the conductive layer segments in the array of conductive layer segments.

[0028] In an embodiment of the system according to the invention, the system may further comprise an optical block arranged downstream of the LC device and configured to redirect the spatially modulated light beam for forming an image. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Exemplary embodiments will now be described with reference to the accompanying drawings, in which:

[0030] Figure 1 is a side cross-sectional view of a liquid crystal (LC) device of the present disclosure;

[0031] Figure 2A and Figure 2Bare side cross-sectional views of an LC device of the present disclosure in OFF and ON states, respectively, the LC having positive dielectric anisotropy;

[0032] Figure 2C and Figure 2D are side cross-sectional views of an LC device of the present disclosure in OFF and ON states, respectively, the LC having negative dielectric anisotropy;

[0033] Figure 3 is a schematic side view of a single-pass reflective LC cell;

[0034] Figure 4 is a schematic side view of a multi-pass reflective LC cell with a top partial reflector;

[0035] Figure 5A and Figure 5B The output field amplitude and phase shift are respectively given by the different reflectivity values ​​of the top reflector and the non-zero cavity loss as Figure 1 and Figure 4 A graph of the optical path length of the LC device as a function of FIG.

[0036] Fig. 6A , Figure 6B and Figure 6C are graphs of output phase shift, minimum reflection intensity, and ratio of minimum to maximum reflection intensity as a function of the reflectivity of the top reflector at different effective reflectivity values ​​of the bottom reflector, respectively;

[0037] Fig. 7A yes Figure 1 A side cross-sectional view of an embodiment of an LC device having a metal reflector;

[0038] Figure 7B yes Figure 1 A side cross-sectional view of an embodiment of an LC device having a reflective high contrast sub-wavelength grating serving as a top partial reflector;

[0039] Figure 7C yes Figure 1 A side cross-sectional view of an embodiment of an LC device having a distributed Bragg reflector that functions as a total reflector and a partial reflector;

[0040] Figure 8 yes Figure 7C A graph of output amplitude and phase of an LC device as a function of the effective refractive index of the LC material;

[0041] Fig.9A , Fig. 9B and Fig. 9C yes Figure 1 Schematic cross-sectional views of an embodiment of an LC device having a π-cell LC configuration at different applied voltages;

[0042] Fig. 10A and Fig. 10B They are Figure 1 Schematic cross-sectional views of an embodiment of an LC device having a hybrid alignment of LC molecules before and after application of a voltage;

[0043] Fig.11 is a schematic diagram of a configurable hologram based on an LC device of the present disclosure;

[0044] Fig.12 is a schematic diagram of a near-eye display that generates a virtual image using the LC device of the present disclosure;

[0045] Fig.13A is a perspective view of a head mounted display of the present disclosure; and

[0046] Fig. 13B Yes Fig.13A Block diagram of a virtual reality system for a head-mounted device. DETAILED DESCRIPTION

[0047] Although this teaching is described in conjunction with various embodiments and examples, this teaching is not intended to be limited to these embodiments. On the contrary, this teaching encompasses various alternatives and equivalents, as understood by those skilled in the art. All statements of the principles, aspects and embodiments of the present disclosure and their specific examples herein are intended to encompass their structural and functional equivalents. In addition, these equivalents are intended to include currently known equivalents and equivalents developed in the future, i.e., any element that performs the same function developed, regardless of structure.

[0048] As used herein, the terms "first", "second", etc. are not intended to imply a sequential order, but are intended to distinguish one element from another unless explicitly stated. Similarly, the sequential order of method steps does not imply a sequential order of execution unless explicitly stated.

[0049] In a liquid crystal (LC) cell, an electric field is applied to control the orientation of the LC molecules in a thin LC layer. An array of transparent electrodes may be provided on one side of the LC layer. A single transparent electrode may be provided on the other side of the LC layer. This electrode structure with one common continuous electrode and one segmented electrode may be used to apply an electric field to the LC layer in a spatially selective manner. The spacing of the transparent electrode array depends on the desired spatial resolution. At the low end, the spacing is limited by the thickness of the LC layer. When the spacing is less than the thickness, the electric field edges into adjacent pixels, causing crosstalk between adjacent LC pixels.

[0050] The required thickness of the LC layer is determined by the effective refractive index change of the LC at different orientations of the LC molecules, which is caused by the change in the amplitude of the applied electrical signal. Typical values ​​for the refractive index change Δn are about 0.2 to 0.3. In most applications, the LC cell is typically required to provide a phase shift of half-wave (π) to full-wave (2π) of the incident light. In order to provide this phase shift in a single pass of the light across the LC cell, the thickness of the typical LC layer needs to be at least ~1.5 microns. The requirement for minimum LC layer thickness may be contrary to the requirement for tight pixel pitch. For example, the pixel pitch required for wide-angle beam control and holographic applications is approximately 300nm to 500nm, where the useful thickness range extends to about 3 microns, which is less than the typical LC layer thickness of 5 to 6 microns. For a close-pitch LC cell, the aspect ratio, defined as the ratio of thickness to pitch, can be greater than 1. When the aspect ratio is greater than 1, a strong fringe field is generated at the pixel electrode boundary, resulting in significant crosstalk between adjacent pixels in the LC array.

[0051] According to the present disclosure, the required LC layer thickness can be reduced by placing the electrically responsive LC layer under optical resonant conditions. As a non-limiting example, the LC layer can be placed in an optical cavity or resonator formed by a pair of reflectors on either side of the LC layer. Light entering the optical cavity can propagate multiple times within the optical cavity, effectively increasing the achievable phase shift of the output light. The increased phase shift results in a significant reduction in the required LC layer thickness, resulting in smaller pitches and faster switching times.

[0052] According to the present disclosure, a tunable liquid crystal (LC) device is provided, which includes a first substrate and a first reflector above the first substrate. The first reflector includes a first electrode layer. The LC layer is arranged above the first reflector. The second reflector is arranged above the LC layer. The second reflector includes a second electrode layer. The second substrate is arranged above the second reflector. The LC layer is tuned by applying an electrical signal to at least one of the first electrode layer or the second electrode layer. Herein, the term "above..." is about the substrate rather than gravity. In other words, it does not assume a specific orientation of the substrate. The first substrate may include, for example, a silicon substrate that supports a circuit system for providing an electrical signal to tune the LC layer.

[0053] In some embodiments, the LC device may further include 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. In embodiments where the LC layer includes a nematic LC having a positive dielectric anisotropy, the first alignment layer and the second alignment layer may be configured to uniformly align the LC at a pretilt angle of less than 10 degrees; or, for example, the first alignment layer may be configured to align the LC at a first pretilt angle of less than 10 degrees, and the second alignment layer may be configured to align the LC at a second pretilt angle of greater than 85 degrees, so that the LC adopts a hybrid orientation configuration. In embodiments where the LC layer includes a nematic LC having a negative dielectric anisotropy, the first alignment layer and the second alignment layer may be configured to homeotropically align the LC at a pretilt angle of greater than 85 degrees.

[0054] In some embodiments, the LC layer has a thickness of 2 microns or less. The first reflector may be a total reflector, and the second reflector may be a partial reflector (e.g., having a reflectivity of at least 6%). The reflectivity of the partial reflector may be less than the reflectivity of the total reflector minus the round-trip absorption loss in the optical cavity formed by the total reflector and the partial reflector. The partial reflector may include a distributed Bragg reflector, a high contrast subwavelength grating, a metasurface including at least one of a dielectric or metal subwavelength structure, and the like.

[0055] The first electrode layer may include an array of conductive layer segments. At least some of the conductive layer segments in the array of conductive layer segments may be independently excited by applying electrical signals to the segments. The array of conductive layer segments may have a pitch of 2 microns or less. The array of conductive layer segments may include a conductive oxide having a visible light transmittance of at least 50%. At least some of the conductive layer segments in the array of conductive layer segments may be reflective. In some embodiments, the total reflector further includes a reflective layer supported by the first substrate, wherein each conductive layer segment in the array of conductive layer segments is supported by the reflective layer. The reflective layer may include at least one of the following: a distributed Bragg reflector; a subwavelength grating; or a metasurface including at least one of a dielectric or metallic subwavelength structure.

[0056] According to one aspect of the present disclosure, a configurable hologram based on the tunable LC device disclosed herein is provided.

[0057] According to one aspect of the present disclosure, a system is also provided, the system comprising a tunable LC device disclosed herein and a light source, the light source being coupled to the LC device for providing a light beam to the LC device, the LC device being configured to spatially modulate the light beam in at least one of phase or amplitude by applying an electrical signal to a conductive layer segment in an array of conductive layer segments. An optical block may be disposed downstream of the LC device and configured to redirect the spatially modulated light beam for forming an image.

[0058] Reference now Figure 1 , the LC device 100 of the present disclosure includes a bottom (first) substrate 104, a first reflector (e.g., a total reflector 101) above the bottom substrate 104, an LC layer 106 above the total reflector 101, a second reflector (e.g., a partial reflector 102) above the LC layer 106, and an optional top (second) substrate 134. Herein, the term "total reflector" refers to a reflector that reflects most of the incident light, so that the transmission of the incident light through the total reflector can be ignored. Therefore, the term "partial reflector" refers to a reflector that reflects only a portion of the incident light and allows a non-negligible portion of the incident light to propagate through the partial reflector. The portion of light reflected by the partial reflector is also a non-negligible portion, that is, it is greater than the small portion of light reflected at the optical interface, where the refractive index is not completely matched, or an anti-reflection (AR) coating is not provided. For the sake of certainty, the non-negligible portion of light is at least 6%; or in some embodiments, at least 12% of the optical power of the incident light. In other words, the reflectivity of the partial reflector is at least 6%; or in some embodiments, at least 12%. It should be noted that the full reflector and partial reflector need not be a single element, and can each include multiple layers or components for performing various functions (such as reflecting light, conducting electricity, etc.).

[0059] exist Figure 1 In the configuration shown, the LC layer 106 is confined between a bottom (first) alignment layer 118 and a top (second) alignment layer 120 supported by a total reflector 101 and a partial reflector 102, which are in turn supported by a bottom substrate 104 and a top substrate 134, respectively. The gap between the bottom alignment layer 118 and the top alignment layer 120 can be maintained by spacers (e.g., glass beads or microfabricated spacers or spacer arrays, not shown). The bottom substrate 104 and the top substrate 134 with all the intermediate layers (including the LC layer 106) are referred to as an LC cell. In this embodiment, the LC layer 106 is a thin layer of anisotropic fluid in an aligned monodomain state. The alignment configuration of the LC in the cell can be antiparallel, parallel, perpendicular, twisted, etc. For example, heterogeneous configurations of LC layers are also possible in different composite systems such as polymer dispersed LC (polymer dispersion of LC droplets), polymer network LC (LC in which a polymer network is formed), filled LC (LC filled with nanoparticles), etc. Polymer dispersed LC can be used to provide spatial modulation of, for example, the amplitude of a light beam.

[0060] The total reflector 101 may include a first electrode layer for applying an electric field to the LC layer 106. In the embodiment shown, the first electrode layer includes an array of coplanar conductive layer segments 108 supported by a total reflective layer 110. The array may be one-dimensional, i.e. extending in one direction, or two-dimensional, i.e. extending in two perpendicular directions in the plane of the segmented conductive layer. For example, the conductive layer segments 108 may transmit at least 50% of incident visible light. For the sake of simplicity, such a layer that transmits at least 50% of the incident light is referred to herein as "transparent", i.e. the term "transparent" includes semi-transparency. The partial reflector 102 may include a partially reflective layer 112 supported by a common transparent electrode layer 114. The conductive layer segments 108 define an array of LC pixels 122, which may be one-dimensional or two-dimensional. The LC pixels 122 may be individually addressable or excitable, i.e. may be provided with individual independent electrical signals, such as voltages, for independently controlling the underlying portions of the LC layer 106. To this end, the individual LC pixels may be provided with one or several thin film transistors (TFTs; for the sake of simplicity, Figure 1 104 or 134). In displays, this configuration is called an active matrix LC display (AMLCD).

[0061] A bottom alignment layer 118 and a top alignment layer 120 may be disposed at the boundaries between the LC layer 106 and the segmented 108 and common 114 transparent electrode layers, respectively, to provide a predetermined LC molecular alignment at the respective boundaries. The conductive layer segments 108 and / or the common electrode layer 114 may be made of a conductive oxide material, such as indium tin oxide (ITO) or another conductive oxide such as indium zinc oxide, aluminum zinc oxide, barium stannate, strontium vanadate, calcium vanadate, etc. As mentioned above, the term "transparent" is understood herein to mean fully or partially transparent, i.e., semi-transparent, e.g., at least 50%; 60%; 70%; 80%; 90% optical power transmission of visible light. It should also be noted that the term "layer" does not necessarily refer to a single layer, but may also refer to a layer comprising a stack of sub-layers.

[0062] In operation, an electrical signal, such as a voltage, may be applied between the segmented transparent electrode layer 108 and the common transparent electrode layer 114. The applied voltage generates an electric field 124 that reorients the LC molecules in the LC layer 106, thereby changing the effective refractive index for an incident light beam 126 emitted by the light source 151 and causing a phase delay of a reflected output light beam 128 to change. The electric field 124 Figure 1106, except for the fringe fields 124A at the boundaries between the LC pixels 122. The size of the fringe fields 124A depends on the aspect ratio of the LC pixels 122. The aspect ratio is defined as the ratio of the thickness d of the LC layer 106 to the LC pixel pitch p. The thickness of the LC layer 106 is also referred to as the cell gap. When the aspect ratio is large enough, i.e., when the LC pixel pitch p is similar in size to or smaller than the cell gap d, the fringe fields 124A may be unacceptably large because they drive the LC molecules of adjacent LC pixels 122, causing undesirable crosstalk between adjacent LC pixels 122. In some embodiments, the pitch of the conductive layer segments 108, and accordingly the pitch of the LC pixels 122, is less than 2 microns; less than 1 micron; less than 500 nm; for example, for wide-angle beam steering and holographic applications, even less than 300 nm.

[0063] The total reflector 101 and the partial reflector 102 form an optical cavity, i.e., a Fabry-Perot etalon or an optical resonator. The LC layer 106 is disposed in the optical cavity formed by the total reflector 101 and the partial reflector 102. By reflecting from the total reflector 101 and the partial reflector 102, the incident light beam 126 can propagate multiple times in the optical cavity, effectively increasing the achievable phase shift of the output light beam 128. This can significantly reduce the cell gap d, thereby reducing the fringe electric field 124A and the associated crosstalk, and reducing the switching time.

[0064] In some embodiments, substrate 104 may be an active substrate, such as a silicon substrate that supports circuitry for providing electrical signals to tune LC layer 106. Active substrates also enable miniaturization and integration of LC devices into compact spatial light modulators, configurable holograms, display panels, etc. Other active types of substrates may include, for example, but not limited to, active matrix TFTs on glass or similar transparent or non-transparent substrates.

[0065] It should be understood that Figure 1 The structure of the LC device 100 shown in is by way of example only. Many variations of the reflectors 101, 102, the LC layer 106 and the reflective layers 110, 112 etc. are possible. Some of these variations will be considered in more detail below.

[0066] Figure 2A , Figure 2B , Figure 2C and Figure 2D The basic operation of an LC cell with a nematic LC is shown. Figure 2A and Figure 2B LC cell 200A with nematic LC molecules having positive dielectric anisotropy is described. Voltage V can be applied to LC cell 200A via switch 201. When switch 201 is open ( Figure 2A), no voltage is applied, and the LC molecule 202A is in Figure 2A 200A, forming a planar configuration. The orientation is defined by the alignment layer, which can be configured (e.g., polished or illuminated with polarized UV light) to orient the adjacent LC accordingly. When the switch 201 is closed ( Figure 2B ), voltage V is applied to LC cell 200A, LC molecules 202A become oriented along the electric field E, that is, almost perpendicular to substrates 204, 206, causing Figure 2A 227, as indicated by electric field vector 227. The reorientation of the LC molecules 202A is caused by the electrostatic interaction between the applied electric field and the electric dipoles induced by the electric field in the LC molecules 202A. It should also be noted that for the LC cells 200A and 200C, the applied voltage V is preferably an alternating current (AC) voltage. Using an AC voltage, as opposed to a direct current (DC) voltage, helps reduce undesirable electrochemical effects at the layer interfaces. The optical path length ΔL achievable in the LC cell 200A is max The maximum change in is given by

[0067] ΔL max =(n e -n o )d (1)

[0068] n e and n o are the extraordinary and ordinary refractive indices of the LC, respectively, and d is the cell gap ( Figure 2A ).

[0069] Figure 2C and Figure 2D It refers to the LC cell 200C having a nematic LC (having negative dielectric anisotropy). When the switch 201 is turned on ( Figure 2C ), no voltage is applied, and the LC molecules 202C assume a near vertical orientation, i.e., almost perpendicular to the LC cell 200C substrates 204, 206, forming an antiparallel tilted vertical configuration in the absence of an electrical signal. The orientation is defined by the alignment layer configured to promote the vertical orientation of the LC molecules 202C. When the switch 201 is closed ( Figure 2D ), a voltage V is applied to the LC cell 200C, and the LC molecules 202C become oriented perpendicular to the electric field E, that is, almost parallel to the substrates 204, 206, causing the Figure 2C and Figure 2D The change in the effective refractive index of the incident light beam 226 polarized in the plane of , as shown by the optical electric field vector 227.

[0070] Figure 3A single-pass reflective LC cell 300 is shown, which may include a nematic LC having positive or negative dielectric anisotropy, such as FIG. 2A to FIG. 2B or Figure 2C to Figure 2D LC cell 200A or 200C. Figure 3 The single-pass reflective LC cell 300 includes an LC layer 306 above a total reflector 308 and a top substrate 334 above the LC layer 306. An incident light beam 326 propagates through the LC layer 306, is reflected by the total reflector 308, propagates back through the LC layer 306, doubling the phase retardation introduced by the LC layer 306 on the first pass, and exits the single-pass reflective LC cell 300 as an output light beam 328 (shifted laterally for clarity). A transparent electrode (not shown) may be provided to vary the optical phase retardation introduced by the LC layer 306.

[0071] Figure 4 A resonant multi-pass reflective LC cell 400 is shown, which may include a nematic LC having a positive dielectric anisotropy or a negative dielectric anisotropy, as respectively considered above. FIG. 2A to FIG. 2D The LC cells 200A and 200C. Figure 4 The resonant multi-pass LC cell 400 includes an LC layer 406 between a bottom reflector 408 and a top partial reflector 412, which form an optical resonator or optical cavity. A transparent electrode (not shown) may be provided to vary the optical phase delay introduced by the LC layer 406 over a single pass.

[0072] In operation, an incident light beam 426 is partially reflected by the top partial reflector 412, forming a first sub-beam 4281. The remaining portion of the incident light beam 426 propagates through the LC layer 406, is reflected by the total reflector 408, propagates through the LC layer 406 again, and is partially reflected to propagate back through the LC layer 406. Thus, a plurality of sub-beams 4281, 4282, 4283, 4284 are formed. For clarity, the sub-beams 4281, 4282, 4283, and 4284 are shown offset; in an actual device, they may overlap to form the output light beam 428. The phase shift of the output light beam 428 is determined by the phases of the individual sub-beams 4281, 4282, 4283, 4284. When certain conditions are met, the phase shift of the output light beam 428 may be greater than 4281 upon double-pass propagation through the LC layer 306. Figure 3 The phase shift of the output beam 328 is much larger. At high reflectivity values, very small changes in the cavity phase around the π value (resonant condition) result in significantly larger changes in the output phase shift, enabling the cell gap of the LC cell 400 to be significantly reduced.

[0073] The response time of the LC cell 400 is given by

[0074]

[0075] in

[0076] Where V is the drive voltage, K is the orientation elastic constant, γ is the rotational viscosity, W is the anchoring coefficient, d is the cell gap, and Δε is the dielectric anisotropy. It follows from equations (2) to (3) that, at typical values ​​of the above parameters, a 40-fold improvement in the cell gap will give a refresh rate of about 8 kHz. This enables color sequential LC on silicon (LCoS) displays with high refresh rates. Cell gaps d as small as 2 microns; 1 micron; 500 nanometers; and even as low as 300 nanometers can provide, for example, a phase delay of at least π (or even at least 2π) in the visible spectrum ranging from 380 nm to 720 nm and / or in the near infrared spectrum from 740 nm to about 1100 nm. Small cell gaps can provide tight pixel spacings of less than 2 microns; less than 1 micron; less than 500 nm; or in some embodiments, less than 300 nm.

[0077] In the presence of optical loss, the output phase Figure 4 The dependence of the cavity phase of the resonant multi-pass reflective LC cell 400 on Figure 5A and Figure 5B For ease of calculation and illustration, the round-trip cavity losses have been rolled into the bottom mirror reflectivity, for example due to non-zero round-trip absorption of the top and bottom transparent electrodes. In this particular example, a 10% round-trip absorption loss is accounted for by reducing the reflectivity of the bottom total reflector by 10%, i.e., from 1.0 to 0.9.

[0078] exist Figure 5A In FIG. 1 , the output electric field amplitude is plotted as a function of the optical path length (OPL) of the LC layer 306, which is measured at the wavelength of the incident light (at a top (partial) reflector with zero reflectivity (for comparison; zero reflectivity is Figure 3 0.45; 0.72; 0.85; 0.91; and 0.99 (non-zero reflectivity and Figure 4 The field amplitude does not depend on the OPL of the LC layer when the reflectivity of the top reflector is zero. As the reflectivity of the top reflector increases, an absorption peak appears at an OPL value of 0.5, which corresponds to a cavity phase shift of π. The amplitude of the peak increases, while the width of the peak decreases as the top reflectivity goes from 0.45 to 0.72 to 0.85 to 0.91. Then, the peak amplitude is observed to decrease again at a top reflectivity of 0.99.

[0079] exist Figure 5B, for the same value of the reflectivity of the top reflector, the output phase shift is plotted as a function of the OPL. It can be seen that the phase diagram is decomposed into two groups corresponding to the two working mechanisms defined by the relationship between the reflectivity of the top reflector and the reflectivity of the bottom reflector. For the first group 501, the reflectivity of the top reflector is less than the effective reflectivity of the bottom (total) reflector, and the effective reflectivity of the bottom (total) reflector is defined as the difference between the reflectivity of the total reflector and the round-trip absorption loss in the optical cavity formed by the top and bottom reflectors. Since more light is coupled into the optical cavity formed by the top and bottom reflectors at the lower reflectivity of the top reflector, this working mechanism is referred to as the "over-coupling" working mechanism in this article. The first group 501 shows a steep slope of 0.5 for the curve around the cavity OPL. For the second group 502, the reflectivity of the top reflector is higher than the effective reflectivity of the bottom (total) reflector, that is, for the second group 502, the reflectivity of the top reflector is greater than the reflectivity of the bottom reflector minus the round-trip light loss. This working mechanism is referred to as the "under-coupling" working mechanism in this article. The slope of the phase curve of the undercoupled LC cell is inverted and smaller in magnitude than the slope in the overcoupled LC cell.

[0080] Figure 4 The two working mechanisms of the resonant multi-pass reflective LC cell 400 are Fig. 6A , Figure 6B and Figure 6C First, refer to Fig. 6A , the phase shift of the wavelength of the incident light beam is plotted relative to the top mirror reflectivity at effective bottom mirror reflectivity values ​​of 0.5; 0.6; 0.7; 0.8; 0.9; 0.95; and 0.99 (i.e., the round-trip light loss is concentrated in the bottom mirror reflectivity). Each phase shift curve has a steep drop when the reflectivity of the top mirror reaches the effective reflectivity of the bottom mirror. On the left side of the drop, the resonant LC cell is in an over-coupled regime; and on the right side of the drop, the resonant LC cell is in an under-coupled regime.

[0081] In order to operate a pixelated resonant LC device as a pure phase spatial light modulator, it is desirable to increase the phase shift introduced into the light beam by the LC device while avoiding as much as possible excessive light losses and variations in the reflected beam amplitude. In other words, the minimum reflectivity needs to be increased, or at least the variation in the reflectivity of the LC device needs to be reduced. The minimum reflectivity of the LC device is plotted relative to the reflectivity of the top mirror of the LC device at Figure 6B In. From Figure 6B and Fig. 6A As can be seen from the comparison of , at low bottom reflectivity values ​​(i.e. high cavity losses), high reflectivity of the LC device can be achieved by increasing the reflectivity of the top mirror, albeit due to reduced phase change. Large phase changes can be achieved simultaneously with low reflectivity changes, but this requires that the effective reflectivity of the bottom mirror is high, i.e. the optical cavity losses need to be low. Figure 6C This conclusion was confirmed. Figure 6C The ratio of minimum to maximum reflectivity is plotted as a function of the reflectivity of the top mirror.

[0082] FIG. 7A to FIG. 7C Some exemplary configurations of tunable LC devices having an LC layer disposed in an optical cavity formed by a pair of reflectors are depicted. Fig. 7A , the tunable LC device 700A includes, from bottom to top: a bottom metal reflector 710A, an optional bottom conductive electrode 708, an LC layer 706, a top conductive electrode 714, and a top semi-transparent metal reflector 712A. For simplicity, the LC cell substrate is omitted. In a practical device, the bottom metal reflector 710A and the bottom conductive electrode layer 708 can be arranged on opposite sides of one (bottom) transparent substrate; and the top conductive electrode 714 and the top metal semi-transparent reflector 712A can be arranged on opposite sides of the other (top) transparent substrate. Metal reflectors may be too lossy for full phase light modulators, but can be used in amplitude modulators. So-called "enhanced metal" coatings, combining a metal layer with a single dielectric layer or multiple dielectric protective layers, can be used to enhance reflectivity and provide compatibility with adjacent layers.

[0083] refer to Figure 7B , the tunable LC device 700B includes a bottom distributed Bragg reflector (DBR) 710B as a total reflector, a bottom conductive electrode 708, an LC layer 706, a top conductive electrode 714, and a high contrast subwavelength grating 712B as a top partial reflector. The DBR 710B may include a sandwich structure of alternating refractive index layers, which are parallel to the LC layer 706. These layers form a Bragg grating with a predetermined reflection coefficient (e.g., 96% to 100%) in the wavelength band of interest. In some embodiments, the refractive index difference is less than 0.2, and / or the number of layers is at least 12 layers. The subwavelength grating 712B may use a metamaterial to obtain a desired dielectric constant and refractive index at optical frequencies. For example, a metasurface including a dielectric or metal subwavelength structure may be used instead of the high contrast subwavelength grating 712B, or in addition to the high contrast subwavelength grating 712B, a metasurface including a dielectric or metal subwavelength structure may also be used. Subwavelength gratings can be thinner than DBR reflectors of similar reflectivity, but are more challenging to manufacture, especially on a base substrate. In this article, the term "high contrast" refers to gratings with a refractive index contrast (greater than 0.2), which is defined as the difference between the refractive index of the diffraction grating fringe and the refractive index of the substrate / filler material. Figure 7BAs shown, the stripes 715 of the sub-wavelength grating 712B extend in the plane of the sub-wavelength grating 712B and may include continuous lines parallel to each other and to the LC layer 706, and / or a 2D array of features (e.g., dots, squares, polygons, etc.) having sub-wavelength spacing in two dimensions.

[0084] refer to Figure 7C , the tunable LC device 700C includes a bottom distributed Bragg reflector (DBR) 710B as a bottom full (ie, 100%) reflector, a bottom conductive electrode 708, an LC layer 706, a top conductive electrode 714, and a top DBR 712C as a partial reflector. FIG. 7A to FIG. 7C Reflectors of can be used in any combination. Furthermore, one or both reflectors can be made of several transparent conductive oxide (TCO) layers in a stack optimized to have the desired reflectivity value. One advantage of a TCO stack is that one or both reflectors of a reflective LC cell can be used as (multiple) LC cell electrodes, resulting in a simpler structure.

[0085] Go to Figure 8 , Figure 7C The amplitude and phase of a tunable LC device 700C have been calculated as a function of the effective refractive index of the LC layer 706 at a wavelength of 632 nm, where the LC layer 706 is 180 nm thick, the ITO electrode is 50 nm thick, the bottom DBR 710B includes 10 layer pairs of quarter-wavelength thick silicon nitride and quarter-wavelength thick silicon dioxide, and the top DBR 712C includes 4 such layer pairs. It can be seen that the amplitude of the reflected beam changes only by about 15%, i.e., the optical power of the beam changes by about 28%, while achieving a phase sweep of about 0.88 of the entire full wavelength.

[0086] Various types of LC and alignment configurations may be used in the intracavity LC cells of the present disclosure. 9A to 9C An LC cell 900 is depicted, which includes a bottom reflective substrate 910 and a top reflective substrate 912 coated with a bottom (first) alignment layer 918 and a top (second) alignment layer 920, respectively. The LC cell 900 is filled with a nematic LC that forms an LC layer 906 and includes elongated LC molecules 902 in a parallel tilted planar alignment configuration (also known as electrically controlled birefringence (ECB)) or a π-cell configuration. The bottom alignment layer 918 is disposed between the bottom reflective substrate 910 and the LC layer 906, and the top alignment layer 920 is disposed between the LC layer 906 and the top reflective substrate 912. The orientation of the LC molecules 902 in the absence of a driving voltage is determined by the alignment layers 918, 920. In 9A to 9C , the LC orientation under different driving conditions is shown: when no voltage is applied to the LC layer 906 ( Fig.9A ) When a voltage of 4 to 5 V is applied ( Fig. 9B ); when the full voltage of 20V is applied. The orientation of the LC molecules 902 can be characterized by a pretilt angle θ, which is the angle between one of the alignment layers 918, 920 and the LC director (a line drawn along the local alignment direction of the LC molecules 902) near the alignment layer, provided that the LC alignment is only affected by the alignment layers. For example, this condition is met in a thick LC cell when the influence of a second alignment layer near the first alignment layer can be ignored. In the case of anti-parallel alignment in an LC cell with two identical alignment layers, the alignment is consistent across the LC cell so that the tilt angle of the LC director is constant and equal to the pretilt angle at the alignment layer. In Figure 2A In the case of the parallel configuration shown, the tilt angles of the LC directors are not uniform. Typically, alignments with pretilt angles less than 5 to 6 degrees are called planar alignments or tilted-planar alignments. When the value of the pretilt angle θ is greater than 85 degrees, the alignment is called vertical or homeotropic or zero pretilt or tilted-vertical alignment.

[0087] When no voltage is applied to the LC layer 906 ( Fig.9A ), the LC molecules 902 adopt an eight-shaped configuration, which is determined by the alignment direction and pretilt angle of the LC molecules 902. Fig.9A At the top surface of the LC layer 906 in FIG. 1 , the LC molecules 902 are pre-tilted clockwise about the top surface, and at the bottom surface of the LC layer 906, the LC molecules 902 are pre-tilted counter-clockwise about the bottom surface. In this example, the alignment layers 918, 920 are configured to uniformly align the LC at a pre-tilt angle of less than 10 degrees.

[0088] When an intermediate voltage of 4 to 5 V is applied to the LC layer 906 ( Fig. 9B ), the LC molecules 902 begin to align along the applied electric field, i.e., Fig. 9B This is because the electric dipoles induced by the electric field along the LC molecules 902 are affected by the momentum of the electrostatic force generated by the electric field. The LC molecules 902 disposed close to the middle of the LC layer 906 rotate at a larger angle, almost vertically, while the LC molecules 902 in the boundary region 915 rotate less due to the alignment force tending to keep them closer to a horizontal orientation.

[0089] When the full voltage of 20V is applied to the LC layer 906 ( Fig. 9C ), all LC molecules 902 are oriented along the direction of the electric field, i.e. Fig. 9C The voltage-dependent rotation of the LC molecules 902 results in a change in the Fig.9A LC molecules 902 in Fig.9A The effective refractive index of light polarized in the x-direction (in the x-direction).

[0090] Many other LC configurations and orientations can be used, such as the electrically controlled birefringence (ECB) configuration. The ECB configuration is similar to the π-cell configuration, except that in the ECB configuration the pre-tilt direction of the LC molecules at the interface of the two LC cells is the same, e.g. Figure 2A As shown, Figure 2A An antiparallel configuration of the LC is depicted. Another LC configuration is vertical alignment (VA), in which the LC is almost vertically (homeotropically) aligned with a small (0.5° to 3°) deviation in the same direction at both interfaces. In the VA configuration, the LC with negative dielectric anisotropy is switched from homeotropic to planar orientation by a vertically applied electric field, as Figure 2C and Figure 2D As shown, Figure 2A and Figure 2B The switching in the ECB configuration shown is reversed.For the homeotropic configuration, the alignment layers 918, 920 may be configured to uniformly align the LC at a pretilt angle greater than 85 degrees.

[0091] Hybrid type or hybrid LC configurations are also possible. As a non-limiting example, refer to Fig. 10A , the hybrid LC cell 1000 includes a bottom reflective substrate 1010 and a top reflective substrate 1012. The top surface of the LC layer 1006 has a vertical alignment of the LC molecules 1002 (having a positive dielectric anisotropy). The alignment of the LC molecules near the top reflective substrate 1012 is defined by a vertical alignment layer 1017, which causes the nearby LC molecules 1002 to become substantially perpendicular to the vertical alignment layer 1017 in the absence of an applied voltage (e.g., at a pretilt angle θ greater than 85 degrees). H The bottom surface of the LC cell 1000 has a planar alignment of the LC molecules 1002 defined by the planar alignment layer 1019, where the boundary LC molecules 1002 are oriented almost parallel to the planar alignment layer 1019 in the boundary region 1015 when no voltage is applied (e.g., at a pretilt angle θ of less than 10 degrees). P ). The configuration of the hybrid LC cell 1000 may be flipped, ie the bottom interface of the LC layer 1006 may be vertically aligned in the absence of an electric field, and the top interface of the LC layer 1006 may have a planar alignment (with a small pretilt angle).

[0092] Fig. 10B 1 shows the orientation of the LC molecules 1002 when a voltage of 10V is applied across the hybrid LC cell 1000. Under an applied voltage of 10V, the bottom LC molecules 1002 are vertically oriented, such that the LC molecules 1002 are vertically or nearly vertically oriented across the entire LC layer 1006. For the same type of LC fluid, Fig. 10A and Fig. 10BThe switchable portion of the LC cell 1000 ( Fig. 10A The area 1015 in 9A to 9C The switchable portion of the LC cell 900 is much thinner. This is advantageous for reducing inter-pixel crosstalk at smaller pixel pitches, since the fringe fields do not significantly affect the orientation of the LC molecules 1002 near the top reflective substrate 1012. It should be noted that when driven in such a way that only the thin electrode-proximal LC sublayer is switched, for example when the LC cell 900 is driven between a drive voltage of 5 V and 20 V, FIG. 9A to FIG. 9C The LC cell 900 may also be thinned.

[0093] Various LC fluid types may be used in the LC devices described herein. As non-limiting examples, nematic LCs with Δε>0 (positive dielectric anisotropy) may include E7, E44, E49, ZLI-2293, MLC-12100-000, MLC-7500-000, TL-205, TL-213, etc. manufactured by Merck & Co. Nematic LCs with Δε<0 (negative dielectric anisotropy) may include MLC-6608, MLC-6609, MLC-66010, etc. manufactured by Merck & Co. Dual-band nematic LCs (with a low dielectric anisotropy at some critical frequency f) may also be used. C The following has Δε>0, and for f>f C , Δε<0). An example of a dual-band LC is the MLC 2048 manufactured by Merck & Co. In some embodiments, a ferroelectric LC operating in, for example, a deformed helical FLC (DH-FLC) mode or a Kerr effect mode may be used. In some cases, a cholesteric polymer-stabilized blue phase mode LC may also be used.

[0094] The LC devices described herein can be used in a variety of applications. The tight pixel spacing and associated small unit gap provided by the resonant configuration are useful in applications such as configurable holograms (i.e., phase-only or phase and amplitude spatial light modulators with sub-micron pixel spacing, configured for operation in a holographic projector such as a 3D holographic display). The tight spacing can also allow the light beam to be steered at large steering angles (e.g., 60 degrees or greater). For example, such large steering angles may be required in scanning projector displays including scanning projector near-eye displays, and / or in general beam scanners that can be used in barcode scanners, LIDAR, 3D mappers, and the like. Spatial light modulators based on the LC devices disclosed herein can be used to generate predetermined, dynamically switchable light patterns, such as structured light that can be used in 3D mapping applications, and the like.

[0095] In a broader aspect, large amplitude and / or large range changes in optical phase can be provided by placing an electrically responsive LC layer, a nematic LC layer, a ferroelectric LC layer, etc. in any configuration disclosed herein in an optical cavity configured to provide multiple passes of an optical beam across the LC layer. Also, in a broader aspect, the electrically responsive LC layer can be configured to have an optical resonance at a specific value of an electrical signal applied to the LC layer. For example, resonant particles (such as nanostructure particles having plasmon resonances at predetermined wavelengths) can be placed in the electrically responsive LC layer to effectively amplify the phase response of the LC layer. Another option is to provide a resonant dielectric nanostructure filled with liquid crystal. Many other configurations are also possible.

[0096] refer to Fig.11 , the configurable hologram 1100 includes a resonant LC device 1102 (such as, for example Figure 1 LC device 100), Figure 4 The resonant multi-pass reflective LC unit 400, or respectively Fig. 7A , Figure 7B and Figure 7C 100A, 100B, 100C, etc. in the resonant LC device 1102. The resonant LC device 1102 is operably coupled to a controller 1104. The resonant LC device 1102 has a sub-micron pixel pitch, e.g., less than 600 nm, less than 400 nm, less than 300 nm, or less than 200 nm, with a kilohertz refresh rate, both provided by a thin cell gap in a resonant optical cavity. The controller 1104 may be configured to obtain an image of a 3D object to be displayed to a viewer, and may be configured to obtain a digital holographic frame (e.g., by performing optical interferometry calculations on a light field scattered by the 3D object using an analog reference beam having some predefined characteristics). The controller 1104 can then configure the resonant LC device 1102 to display a frame containing a digital hologram by setting individual pixels of the resonant LC device 1102 to values ​​of phase delay and / or attenuation corresponding to an actual hologram, and simulating the optical interference of scattered light using a light beam (the light beam having characteristics used by the controller 1104 to perform calculations). The actual hologram can be obtained in a holographic recording setup that involves illuminating a 3D object with a light beam. When the resonant LC device 1102 is illuminated with an actual light beam 1106 having the same or similar characteristics, a holographic image 1108 is obtained that can be observed by a user. In some embodiments, to facilitate observation, an optional pupil replica waveguide 1110 can be used to provide multiple offset copies 1108' of the angular distribution of light corresponding to the holographic image 1108.

[0097] Go to Fig.12, the near eye display 1200 includes a frame 1201 having the form factor of a pair of glasses. The frame 1201 supports for each eye: a light source 1205, a spatial light modulator 1208 optically coupled to the light source 1205, a pupil replica waveguide 1210 optically coupled to the projector 1208, an eye tracking camera 1204, a plurality of illuminators 1206, and an eye tracking camera controller 1207. The illuminators 1206 ( Fig.12 ) may be supported by a pupil replica waveguide 1210 for illuminating an eye box 1212. The spatial light modulator 1208 may include any tunable LC device disclosed herein, such as Fig.11 configurable hologram 1100. The light beam provided by the light source 1205 is diffracted in the spatial light modulator 1208 to form a fan of light beams carrying the image in the angular domain to be projected into the user's eye. The pupil replica waveguide 1210 receives the fan beam and provides multiple laterally offset parallel copies of each beam in the fan beam, thereby expanding the projected image on the eye box 1212. The eye box 1212 is a geometric area in which an image of acceptable quality is formed for observation by the user's eye. For augmented reality (AR) applications, the pupil replica waveguide 1210 can be transparent to enable the user to view the outside world as well as the image projected into each eye and superimposed with the view of the outside world.

[0098] The purpose of eye tracking camera 1204 is to determine the position and / or orientation of the user's eyes. Once the position and orientation of the user's eyes are known, the gaze convergence distance and direction can be determined. The imagery generated by spatial light modulator 1208 can be dynamically adjusted to account for the user's gaze to more realistically immerse the user in the displayed augmented reality scene and / or to provide specific functionality for interacting with augmented reality.

[0099] The illuminator 1206 can be arranged in an unobtrusive manner at the periphery of the pupil replica waveguide 1210 so as not to obstruct the view of the outside world or within the field of view. In operation, the illuminator 1206 illuminates the eye at the corresponding eye box 1212 to enable the eye tracking camera to obtain an image of the eye, as well as provide a reference reflection, i.e., a flash. The flash can be used as a reference point in the captured eye image to facilitate eye gaze direction determination by determining the position of the eye pupil image relative to the flash image. In order to avoid distracting the user with the illumination light, the illumination light can be made invisible to the user. For example, infrared light can be used to illuminate the eye box 1212.

[0100] The function of the eye tracking camera controller 1207 is to process the images obtained by the eye tracking camera 1204 to determine the eye gaze direction of the user's eyes in real time. In some embodiments, the image processing and eye position / orientation determination functions can be performed by a central controller (not shown) of the near eye display 1200. Based on the determined eye position, eye orientation, gaze direction, eye vergence, etc., the central controller can also provide control signals to the spatial light modulator 1208 to generate an image to be displayed to the user. It should be noted that the near eye display 1200 is only one example of a visual display in which the resonant tunable LC device of the present disclosure can be used. Other types of visual displays using resonant tunable LC devices include projection displays, display panels, etc.

[0101] Embodiments of the present disclosure may include an artificial reality system or be implemented in conjunction with an artificial reality system. The artificial reality system adjusts the sensory information about the external world obtained through sensations such as visual information, audio, touch (somatosensory) information, acceleration, balance, etc. in some way before presenting it to the user. As a non-limiting example, artificial reality may include virtual reality (VR), augmented reality (AR), mixed reality (MR), hybrid reality, or some combination and / or derivative thereof. Artificial reality content may include fully generated content or content generated in combination with captured (e.g., real world) content. Artificial reality content may include video, audio, somatic or tactile feedback, or some combination thereof. Any of the content may be presented in a single channel or multiple channels, such as in a stereoscopic video that produces a three-dimensional effect on the viewer. In addition, in some embodiments, artificial reality may also be associated with an application, product, accessory, service, or some combination thereof, which is used, for example, to create content in artificial reality and / or otherwise used for artificial reality (e.g., performing activities in artificial reality). Artificial reality systems that provide artificial reality content can be implemented on a variety of platforms, including wearable displays such as HMDs connected to a host system, standalone HMDs, near-eye displays with eyeglass form factors, mobile devices or computing systems, or any other hardware platform capable of providing artificial reality content to one or more viewers.

[0102] Reference Fig.13A, HMD 1300 is an example of an AR / VR wearable display system that surrounds the user's face for greater immersion in an AR / VR environment. HMD 1300 may use any of the LC devices disclosed herein. The function of HMD 1300 is to enhance the view of a physical, real environment with computer-generated images, and / or to generate a completely virtual 3D image. HMD 1300 may include a front body 1302 and a strap 1304. The front body 1302 is configured to be placed in front of the user's eyes in a secure and comfortable manner, and the strap 1304 may be stretched to secure the front body 1302 on the user's head. A display system 1380 may be disposed in the front body 1302 for presenting AR / VR images to the user. For example, the display system 1380 may include Fig.11 Configurable hologram 1100. Side 1306 of front body 1302 can be opaque or transparent.

[0103] In some embodiments, the front body 1302 includes a positioner 1308 and an inertial measurement unit (IMU) 1310 for tracking the acceleration of the HMD 1300, and a position sensor 1312 for tracking the position of the HMD 1300. The IMU 1310 is an electronic device that generates data indicating the position of the HMD 1300 based on measurement signals received from one or more of the position sensors 1312, which generate one or more measurement signals in response to the movement of the HMD 1300. Examples of the position sensor 1312 include: one or more accelerometers, one or more gyroscopes, one or more magnetometers, another suitable type of sensor that detects movement, a type of sensor used for error correction of the IMU 1310, or some combination thereof. The position sensor 1312 can be located outside the IMU 1310, inside the IMU 1310, or some combination thereof.

[0104] The localizer 1308 is tracked by an external imaging device of the virtual reality system so that the virtual reality system can track the position and orientation of the entire HMD 1300. The information generated by the IMU 1310 and the position sensor 1312 can be compared with the position and orientation obtained by tracking the localizer 1308 to improve the tracking accuracy of the position and orientation of the HMD 1300. As the user moves and turns in 3D space, accurate position and orientation are important for presenting an appropriate virtual scene to the user.

[0105] The HMD 1300 may also include a depth camera assembly (DCA) 1311 that captures data describing depth information for a local area surrounding some or all of the HMD 1300. To this end, the DCA 1311 may include a laser radar (LIDAR) or similar device. The depth information may be compared with information from the IMU 1310 to more accurately determine the position and orientation of the HMD 1300 in 3D space.

[0106] The HMD 1300 may also include an eye tracking system 1314 for determining the orientation and position of the user's eyes in real time. The position and orientation of the eyes obtained also allow the HMD 1300 to determine the user's gaze direction and adjust the image generated by the display system 1380 accordingly. In one embodiment, the vergence, i.e., the convergence angle of the user's eye gaze, is determined. The determined gaze direction and vergence angle can also be used to compensate for visual artifacts that depend on the viewing angle and eye position in real time. In addition, the determined vergence and gaze angle can be used to interact with the user, highlight objects, bring objects to the foreground, create additional objects or pointers, etc. An audio system may also be provided, including, for example, a set of small speakers built into the front body 1302.

[0107] Reference Fig. 13B , the AR / VR system 1350 includes Fig.13A The HMD 1300 may be "tethered" to the console 1390 using a physical cable, or may be connected to the console 1390 via a computer such as a computer. A wireless communication link such as Wi-Fi is connected to the console 1390. There may be multiple HMDs 1300, each with an associated I / O interface 1315, wherein each HMD 1300 and (multiple) I / O interfaces 1315 communicate with the console 1390. In alternative configurations, different and / or additional components may be included in the AR / VR system 1350. Additionally, in some embodiments, in combination with Fig.13A and Fig. 13B One or more of the components shown may be combined with the described functionality. Fig.13A and Fig. 13B The described approaches are distributed between components in different ways. For example, some or all of the functionality of the console 1390 may be provided by the HMD 1300, and vice versa. The HMD 1300 may be provided with a processing module capable of implementing such functionality.

[0108] As mentioned above Fig.13AAs described, HMD 1300 may include eye tracking system 1314 ( Fig. 13B ) (for tracking eye position and orientation, determining gaze angle and convergence angle, etc.), IMU 1310 (for determining the position and orientation of HMD 1300 in 3D space), DCA 1311 (for capturing the external environment), position sensor 1312 (for independently determining the position of HMD 1300), and display system 1380 (for displaying AR / VR content to the user). Display system 1380 includes ( Fig. 13B ) electronic display 1325, such as, but not limited to, a liquid crystal display (LCD), an organic light emitting display (OLED), an inorganic light emitting display (ILED), an active matrix organic light emitting diode (AMOLED) display, a transparent organic light emitting diode (TOLED) display, a projector, or a combination thereof. The display system 1380 also includes an optical block 1330, the function of which is to transmit the image generated by the electronic display 1325 to the user's eyes. The optical block may include various lenses, such as a refractive lens, a Fresnel lens, a diffractive lens, an active or passive Pancharatnam-berry phase (PBP) lens, a liquid lens, a liquid crystal lens, etc., a pupil replica waveguide, a grating structure, a coating, etc. The display system 1380 may also include a zoom module 1335, which may be part of the optical block 1330. The function of the zoom module 1335 is to adjust the focus of the optical block 1330, such as compensating for vergence accommodation conflict, correcting for visual defects of a specific user, offsetting aberrations of the optical block 1330, etc.

[0109] The I / O interface 1315 is a device that allows a user to send an action request and receive a response from the console 1390. An action request is a request to perform a specific action. For example, an action request may be an instruction for starting or ending the capture of an image or video data or an instruction for performing a specific action within an application. The I / O interface 1315 may include one or more input devices, such as a keyboard, a mouse, a game controller, or any other suitable device for receiving an action request and transmitting the action request to the console 1390. The action request received by the I / O interface 1315 is transmitted to the console 1390, and the console 1390 performs an action corresponding to the action request. In some embodiments, the I / O interface 1315 includes an IMU that captures calibration data indicating an estimated position of the I / O interface 1315 relative to the initial position of the I / O interface 1315. In some embodiments, the I / O interface 1315 may provide tactile feedback to the user according to the instruction received from the console 1390. For example, tactile feedback may be provided when an action request is received, or the console 1390 may transmit instructions to the I / O interface 1315 to cause the I / O interface 1315 to generate tactile feedback when the console 1390 performs an action.

[0110] The console 1390 may provide content to the HMD 1300 for processing based on information received from one or more of the following: the IMU 1310, the DCA 1311, the eye tracking system 1314, and the I / O interface 1315. Fig. 13B In the example shown, the console 1390 includes an application store 1355, a tracking module 1360, and a processing module 1365. Some embodiments of the console 1390 may have a Fig. 13B Similarly, the functions described further below may be combined with Fig.13A and Fig. 13B The described methods are distributed among the components of console 1390 in different ways.

[0111] Application storage 1355 may store one or more applications executed by console 1390. An application is a set of instructions that, when executed by a processor, generates content for presentation to a user. The content generated by the application may be responsive to input received from the user via movement of HMD 1300 or I / O interface 1315. Examples of applications include: gaming applications, presentation and conferencing applications, video playback applications, or other suitable applications.

[0112] The tracking module 1360 may track the movement of the HMD 1300 or the movement of the I / O interface 1315, the IMU 1310, or some combination thereof. For example, the tracking module 1360 may determine the location of a reference point of the HMD 1300 in a map of the local area based on information from the HMD 1300. The tracking module 1360 may also determine the location of the reference point of the HMD 1300 or the reference point of the I / O interface 1315 using data from the IMU 1310 indicating the location of the HMD 1300 or using data from an IMU included in the I / O interface 1315 indicating the location of the I / O interface 1315, respectively. Furthermore, in some embodiments, the tracking module 1360 may use a portion of the data from the IMU 1310 indicating the location of the HMD 1300 and the representation of the local area from the DCA 1311 to predict the future location of the HMD 1300. The tracking module 1360 provides the estimated or predicted future position of the HMD 1300 or the I / O interface 1315 to the processing module 1365 .

[0113] The processing module 1365 may generate a 3D map of an area (“local area”) surrounding some or all of the HMD 1300 based on information received from the HMD 1300. In some embodiments, the processing module 1365 determines depth information for the 3D map of the local area based on information related to a technique for calculating depth received from the DCA 1311. In various embodiments, the processing module 1365 may use the depth information to update a model of the local area and generate content based in part on the updated model.

[0114] The processing module 1365 executes an application within the AR / VR system 1350 and receives position information, acceleration information, velocity information, predicted future position, or some combination thereof of the HMD 1300 from the tracking module 1360. Based on the received information, the processing module 1365 determines content to provide to the HMD 1300 for presentation to the user. For example, if the received information indicates that the user has looked to the left, the processing module 1365 generates content for the HMD 1300 that reflects the user's movement in a virtual environment or in an environment that enhances a local area with additional content. In addition, the processing module 1365 performs an action within an application executed on the console 1390 in response to an action request received from the I / O interface 1315, and provides feedback to the user that the action has been performed. The feedback provided may be visual or auditory feedback via the HMD 1300 or tactile feedback via the I / O interface 1315.

[0115] The hardware for implementing the various illustrative logics, logic blocks, modules, and circuits described in conjunction with the aspects disclosed herein may be implemented or executed using a general purpose processor, a digital signal processor (DSP), an application specific integrated circuit (ASIC), a field programmable gate array (FPGA) or other programmable logic device, discrete gate or transistor logic, discrete hardware components, or any combination thereof designed to perform the functions described herein. The general purpose processor may be a microprocessor, but in an alternative, the processor may be any conventional processor, controller, microcontroller, or state machine. The processor may also be implemented as a combination of computing devices, such as a combination of a DSP and a microprocessor, a combination of multiple microprocessors, a combination of one or more microprocessors and a DSP core, or any other such configuration. Alternatively, some steps or methods may be performed by circuit systems specific to a given function.

[0116] The present disclosure is not limited to the scope of the specific embodiments described herein. In fact, according to the foregoing description and the accompanying drawings, in addition to the embodiments and modifications described herein, various other embodiments and modifications will be apparent to those of ordinary skill in the art. Therefore, these other embodiments and modifications are intended to fall within the scope of the present disclosure. In addition, although the present disclosure has been described herein in the context of a specific implementation in a specific environment for a specific purpose, those skilled in the art will recognize that its usefulness is not limited thereto, and the present disclosure can be advantageously implemented in any number of environments for any number of purposes. Therefore, the claims set forth below should be interpreted according to the full scope and spirit of the present disclosure described herein.

Claims

1. A tunable liquid crystal (LC) device, comprising: a first substrate; a first reflector above the first substrate, the first reflector comprising a first electrode layer; an LC layer above the first reflector; a second reflector above the LC layer, the second reflector comprising a second electrode layer; and a second substrate above the second reflector; wherein the LC layer is tuned by applying an electrical signal to at least one of the first electrode layer or the second electrode layer; Features: The first reflector is a total reflector and the second reflector is a partial reflector having a reflectivity of at least 6%; and The first electrode layer comprises an array of conductive layer segments, wherein at least some of the conductive layer segments in the array of conductive layer segments can be independently excited by applying an electrical signal thereto.

2. The tunable LC device of claim 1, wherein the first substrate comprises a silicon substrate supporting circuitry for providing the electrical signal to tune the LC layer.

3. The tunable LC device of claim 1 , wherein the LC layer comprises a nematic LC having positive dielectric anisotropy, the LC device further comprising: a first alignment layer between the first reflector and the LC layer; as well as a second alignment layer between the LC layer and the second reflector; The first alignment layer and the second alignment layer are configured to uniformly align the LC at a pre-tilt angle less than 10 degrees.

4. The tunable LC device of claim 1, wherein the LC layer comprises a nematic LC having a negative dielectric anisotropy, the LC device further comprising: a first alignment layer between the first reflector and the LC layer; as well as a second alignment layer between the LC layer and the second reflector; The first alignment layer and the second alignment layer are configured to vertically align the LC at a pre-tilt angle greater than 85 degrees.

5. The tunable LC device of claim 1, wherein the LC layer comprises a nematic LC having positive dielectric anisotropy, the LC device further comprising: a first alignment layer between the first reflector and the LC layer; as well as a second alignment layer between the LC layer and the second reflector; The first alignment layer is configured to align the LC at a first pretilt angle less than 10 degrees, and the second alignment layer is configured to align the LC at a second pretilt angle greater than 85 degrees, so that the LC adopts a hybrid alignment configuration.

6. The tunable LC device of claim 1, wherein the LC layer has a thickness of 2 microns or less.

7. The tunable LC device of claim 1, wherein a reflectivity of the partial reflector is less than a reflectivity of the total reflector minus a round-trip absorption loss in an optical cavity formed by the total reflector and the partial reflector.

8. The tunable LC device of claim 1 , wherein the partial reflector comprises: Distributed Bragg reflectors, High contrast sub-wavelength gratings, or A metasurface comprising at least one of a dielectric subwavelength structure or a metallic subwavelength structure.

9. The tunable LC device of claim 1, wherein the array of conductive layer segments has a pitch of 2 microns or less, or comprises a conductive oxide having a visible light transmission of at least 50%.

10. The tunable LC device of claim 1, wherein at least some of the array of conductive layer segments are reflective.

11. The tunable LC device of claim 1 , wherein the total reflector further comprises a reflective layer supported by the first substrate, wherein each conductive layer segment in 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 a dielectric subwavelength structure or a metallic subwavelength structure.

12. A configurable hologram comprising the LC device according to claim 1.

13. A system comprising: The LC device according to claim 1; A light source is coupled to the LC device for providing a light beam to the LC device, wherein the LC device is configured to spatially modulate the light beam in at least one of phase or amplitude by applying an electrical signal to a conductive layer segment in an array of conductive layer segments, and optionally, the system also includes an optical block, which is arranged downstream of the LC device and is configured to redirect the spatially modulated light beam for forming an image.

Images