WO2022155612A1

WO2022155612A1 - Aperture heating for liquid crystal beam steering systems

Info

Publication number: WO2022155612A1
Application number: PCT/US2022/012824
Authority: WO
Inventors: Douglas J. Mcknight; Jay Stockley
Original assignee: Boulder Nonlinear Systems, Inc.
Priority date: 2021-01-18
Filing date: 2022-01-18
Publication date: 2022-07-21

Abstract

This disclosure describes systems, methods, and apparatus for heating liquid crystal layers in a non-mechanical beam steering assembly. One or more of the stages can include an adjacent heating element, such as the peripheral stages and optionally one or more stages in the bulk of the stack. The assembly may also comprise edge heaters arranged at or near edges of the stages. Power can be provided to the peripheral heating elements and the bulk heating element(s) until an optimum temperature range is approached, at which point power can be reduced to the heating elements, but more so to the bulk heating element, which is primarily used during warm-up. In some embodiments, heating elements distinct from liquid crystal control electrodes can be used, while in others, the control electrodes can also perform heating.

Description

TITLE: APERTURE HEATING FOR LIQUID CRYSTAL BEAM STEERING

SYSTEMS

CLAIM OF PRIORITY UNDER 35 U.S.C. §119

[0001] The present Application for Patent claims priority to Provisional Application No. 63/138,735 entitled “APERTURE HEATING FOR LIQUID CRYSTAL BEAM STEERING SYSTEMS” filed January 18, 2021, and assigned to the assignee hereof and hereby expressly incorporated by reference herein.

FIELD OF THE DISCLOSURE

[0002] The present disclosure relates generally to beam steering. In particular, but not by way of limitation, the present disclosure relates to systems, methods and apparatuses for beam steering using polarization gratings and related methods of operation.

DESCRIPTION OF RELATED ART

[0003] Passive liquid crystal polarization gratings (LCPGs) are thin birefringent films that steer light to one of two deflection angles, depending on the polarization handedness of the input light. LCPGs are similar to traditional diffraction gratings utilizing a periodic structure to steer light, however, they use polarization modulation instead of pure phase or amplitude modulation, resulting in high first-order efficiencies exceeding 99.8%. The high efficiency and compact size makes LCPG’s a natural candidate for coherent beam steering and active and passive image scanning systems such as LIDAR (e.g., mapping, autonomous driving, ), LADAR, and long-range communications, to name just a few. Because each element in a stack can be switched off, added, or subtracted from the net deflection, a relatively small stack can provide a large set of deflection angles, enabling a wide range of angles in two dimensions to be achieved with a small number of stack elements. High quality, large aperture gratings (e.g., 100mm and more) have been demonstrated with large steer angles for wavelengths from visible to MWIR. These devices are optically efficient, rugged, and capable of being placed on remote platforms, where size, weight and power (SWaP) can represent a significant system constraint.

[0004] Non-mechanical steering of electromagnetic radiation has numerous applications, with one exemplary method being described in U.S. Patent No. 8,982,313. This type of system comprises, typically, several stages, each comprising a single liquid crystal cell to control the polarization of the light passing through it, and one or more polarization grating steering elements. The polarization gratings output light at a different angle depending on the polarization of incident light. Thus, by adjusting the incident polarization with the liquid crystal cell, the pair of liquid crystal cell and polarization grating form a non-mechanical beam steering stage. By stacking additional stages, one can achieve greater numbers of output angles, and thus greater beam steering precision, as well as wider angles of steering.

[0005] In general, this type of beam steering system is best thought of as a multilayer “sandwich”, or “stack”, of liquid crystal cells and liquid crystal polarization grating steering elements.

[0006] Figure 1 illustrates a simplified view of components of a typical liquid crystal assembly or cell. A transparent conductor 108 is arranged on a substrate 106, and these conductor-substrate pairs are arranged on opposing sides of the liquid crystal cell/layer 104 with the transparent conductors 108 facing the liquid crystal layer 104. Each of the conductor-substrate pair is offset from its opposing pair to allow for bonding to the conductors 108, which are arranged on inward facing surfaces of the substrates 106. For instance, connections such as wire or flex can be bonded to the transparent conductors 108.

[0007] Figure 2 illustrates the liquid crystal assembly of Figure 1 coupled to a polarization grating 202 via one of the two transparent substrates 106. Bonding between the substrate 106 and polarization grating 202 is performed via transparent bonding agent 204. The assembly of Figure 2 can be referred to as a stage of an LCPG stack.

[0008] Figure 3 illustrates an LCPG stack comprising six LCPG stages, such as the one illustrated in FIG. 2, bonded together via a transparent bonding material, the same or similar to the transparent bonding agent 204 described relative to FIG. 2.

[0009] Properties of these stacks that may be important, depending on the application of the system, include aperture size, uniformity of performance over the aperture, losses (due to reflection, absorption, or scatter), crosstalk, thickness, cost, weight, and switching speed. The speed with which a beam can be switched from one steering direction to another is determined by the speed with which the liquid crystal cell(s) can switch the polarization state of the beam. Liquid crystal cells have a temperature range over which they will operate normally. This range may be many 10’ s or even over 100 degrees Celsius but there are differences in the material characteristics over this range that lead to significant performance changes. One of the differences is that the liquid crystal material becomes more viscous, and so switches more slowly, at lower temperatures. For this reason, in many use cases it is desirable to warm the stages in the LCPG stack above ambient temperature. The prior art is replete with arrangements of heaters in liquid crystal cells, stretching back over the last 25 years, though many of these have focused on display devices with numerous pixels, rather than stacks of LCPGs. Nonetheless, these heaters have long been arranged outside of one of the two liquid crystal substrates, such as U.S. Patent No. 5,088,806 (Honeywell), U.S. Patent No. 5,247,374, U.S. Patent No. 8,009,262 (American Panel Corp), within one of the two liquid crystal substrates, such as U.S. Patent No. 6,157,432 (Hewlett Packard), and arranged on the inside of the cell, such as U.S. Patent No. 4,773,735, U.S. Patent No. 5,559,614 (Motorola), U.S. Patent No. 6,943,768, U.S. Patent No. 7,495,714, U.S. Patent No. 7,324,176 and 7,750,994 (American Panel Corp). Despite this long history of heating liquid crystals to optimum temperatures via various structures, the industry has always used a heater distinct from the liquid crystal biasing circuitry.

[0010] Another property of liquid crystal materials that is generally affected by temperature is the retardance. This, in turn, affects the choice of optimum drive voltage. So, if a liquid crystal cell exhibits a temperature variation across its aperture, it may be difficult or impossible to find a single drive voltage that is simultaneously acceptable for all locations across the aperture. Applying different drive voltages in different locations is possible but at the cost of reduced optical efficiency and greatly increased complexity. This is especially important for LCPG stacks, where the liquid crystal aperture is often tens of millimeters across rather than mere microns per pixel as seen in pixelated display applications.

[0011] These fundamental liquid crystal properties mean that it is desirable to be able to controllably increase the temperature of a beam steering stack while maintaining good temperature uniformity across the device aperture.

SUMMARY OF THE DISCLOSURE [0012] The following presents a simplified summary relating to one or more aspects and/or embodiments disclosed herein. As such, the following summary should not be considered an extensive overview relating to all contemplated aspects and/or embodiments, nor should the following summary be regarded to identify key or critical elements relating to all contemplated aspects and/or embodiments or to delineate the scope associated with any particular aspect and/or embodiment. Accordingly, the following summary has the sole purpose to present certain concepts relating to one or more aspects and/or embodiments relating to the mechanisms disclosed herein in a simplified form to precede the detailed description presented below.

[0013] According to some aspects of the disclosure a beam steering apparatus includes one or more heating elements arranged to elevate the device temperature above the ambient temperature, while causing the temperature to be substantially uniform across the device’s aperture.

[0014] According to other aspects of the disclosure a beam steering apparatus may include means for driving different heating elements with different powers depending on whether the apparatus is undergoing a warm-up or is maintaining a steady state temperature.

[0015] According to other aspects of the disclosure a transparent conductor sheet resistance is chosen that is higher than normally used for heaters.

[0016] According to other aspects of the disclosure a beam steering apparatus may include transparent heating elements with peripheral regions of low resistance.

[0017] According to other aspects of the disclosure a beam steering apparatus may include transparent electrodes used for both heating and supplying the drive voltage to the liquid crystal layer. These functions may be used sequentially or simultaneously. [0018] According to some aspects of the disclosure a liquid crystal stage includes a liquid crystal layer, first and second transparent conductors, a liquid crystal driver, and a heater driver. The transparent conductors can be on opposing sides of the liquid crystal layer, for instance, the first transparent conductor being on a first side of the liquid crystal layer, and the second transparent conductor being on a second side of the liquid crystal layer. The first transparent conductor can include first and second low-resistance regions spaced from each other, for instance, on opposing ends of the first transparent conductor. In some embodiments, more than two low-resistance regions can be spaced in opposing orientations across the first transparent conductor. The second transparent conductor can include third and fourth low-resistance regions spaced from each other, for instance, on opposing ends of the second transparent conductor. In some embodiments, more than two low-resistance regions can be spaced in opposing orientations across the second transparent conductor. The liquid crystal driver can be electrically coupled to the first and second low-resistance regions (or to any number of low -resistance regions), and the heater driver can be electrically coupled to the first and third low-resistance regions. An orientation of the liquid crystal layer and a temperature of the liquid crystal layer can be controlled via the first and second transparent conductors, and more specifically, by voltages across (heating) and between (liquid crystal orientation) these two conductors.

[0019] According to some aspects of the disclosure an optical assembly can include a plurality of optical stages, a first peripheral heating element, and drive circuitry. Each of the plurality of optical stages can include a liquid crystal layer surrounded by a first transparent conductor on a first side of the liquid crystal layer and a second transparent conductor on a second side of the liquid crystal layer. A polarization grating can also be part of each stage and can be arranged next to or near either of the first and second transparent conductors. The first peripheral heating element can be adjacent to a first of the plurality of optical stages (e.g., a stage at a surface of the device aperture), and can be configured to provide surface heating for the optical assembly. In some embodiments, a second peripheral heating element can be adjacent to a second of the plurality of optical stages (e.g., a stage at an opposing surface of the device aperture) and can be configured to provide surface heating for the optical assembly. The drive circuitry can include a first heater circuit and liquid crystal drive circuits. The first heater circuit can be configured to provide a controlled current to the first peripheral heating element. Optionally, a second heater circuit can be configured to provide a controlled current to the second peripheral heating element. The liquid crystal drive circuits can be configured to provide a drive signal to each of the liquid crystal layers to control an orientation of each of the liquid crystal layers. In some embodiments, one or more bulk heating elements can be implemented toward a middle of the optical stack, or between the first and second peripheral heating elements where both are used.

[0020] According to other aspects of the disclosure a method of heating a non-mechanical beam-steering optical stack can include providing power to one or more peripheral heating elements in the optical stack and one or more bulk heating elements in the optical stack during a warm-up period as a temperature of the optical stack moves toward an optimal temperature range (e.g., optimal temperature range is 60°-80°F), and reducing power to the one or more bulk heating elements in the optical stack at a greater rate than a reduction in power to the one or more peripheral heating elements when a temperature of the optical stack approaches or reaches the optimal temperature range. The method may further include removing power from the one or more bulk heating elements when the temperature of the optical stack reaches the optimal temperature range.

BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Various objects and advantages and a more complete understanding of the present disclosure are apparent and more readily appreciated by referring to the following detailed description and to the appended claims when taken in conjunction with the accompanying drawings:

[0022] Figure 1 shows the construction of a typical liquid crystal cell.

[0023] Figure 2 shows a liquid crystal cell assembled to a polarization grating to form a single stage of a beam steering device.

[0024] Figure 3 shows a typical beam steering stack, including six stages with liquid crystal cells and polarization gratings.

[0025] Figure 4 shows a simplified view of an LCPG stack formed from 4 stages, where each stage comprises a liquid crystal cell and a polarization grating (individual transparent conductors are not visible in this simplified view).

[0026] Figure 5 shows the heat flow with edge mounted heating elements, which can maintain a steady-state temperature, but there is center-to-edge temperature variation.

[0027] Figure 6 shows area heating elements on the front and back apertures maintaining steady state, and uniform, temperature.

[0028] Figure 7A shows the heat flux as peripheral heating elements and one or more bulk heating elements are together being used to warm a stack from low temperature.

[0029] Figure 7B shows the heat flux when equilibrium has been reached.

[0030] Figure 7C shows another optical stack where a peripheral heating element is used on a front of the stack. [0031] Figure 7D shows another optical stack where peripheral heating elements are used on the front and back of the stack.

[0032] Figure 7E shows another optical stack where a peripheral heating element is used on a front of the stack and a bulk heating element within the stack.

[0033] Figure 7F shows another optical stack where peripheral heating elements are used on the front and back of the stack as well as a bulk heating element within the stack.

[0034] Figure 8 shows low-resistance regions on the edges of transparent conducting heating element.

[0035] Figure 9 shows a six-stage stack with heating elements at the front and back apertures, plus an extra heating element in the bulk of the stack.

[0036] Figure 10 shows a simplified illustration of connections to a traditional liquid crystal cell.

[0037] Figure 11 shows a new addressing scheme with two connections on each cell electrode. This approach allows a current to be driven through each cell electrode for the purposes of heating the device.

[0038] Figure 12A shows an overhead view of the liquid crystal layer and drive mechanism for controlling polarization while also controlling application of heat to the liquid crystal layer.

[0039] Figure 12B shows a circuit diagram of the drive scheme of Figure 12A.

[0040] Figure. 13 illustrates a control circuit for an LCPG stack.

[0041] Figure 14 shows uniformly-spaced equipotential lines, which causes uniform power dissipation per unit area on substrates with uniform sheet resistance.

[0042] Figure 15 shows a seven-stage stack with heating elements at the front and back apertures plus an extra heating element in the bulk of the stack, where the heating elements use the same transparent electrodes as the liquid crystal control electrodes. [0043] Figure 16 shows a method of uniformly heating an LCPG optical stack using peripheral and bulk heating elements and optional edge heater(s).

[0044] Figure 17A shows a timing diagram for low-resistance regions of a first transparent conductor with a pulsed or AC liquid crystal orientation control signal and a DC heating bias.

[0045] Figure 17B shows a timing diagram for low-resistance regions of a second transparent conductor with a pulsed or AC liquid crystal orientation control signal and a DC heating bias.

[0046] Figure 17C shows a timing diagram for low-resistance regions of a first transparent conductor with a pulsed or AC liquid crystal orientation control signal provided alternately to the first and second transparent conductors and a DC heating bias.

[0047] Figure 17D shows a timing diagram for low-resistance regions of a second transparent conductor with a pulsed or AC liquid crystal orientation control signal provided alternately to the first and second transparent conductors and a DC heating bias.

[0048] Figure 18A shows a timing diagram for low-resistance regions of a first transparent conductor with a pulsed or AC liquid crystal orientation control signal provided alternately to the first and second transparent conductors and a pulsed heating bias.

[0049] Figure 18B shows a timing diagram for low-resistance regions of a second transparent conductor with a pulsed or AC liquid crystal orientation control signal provided alternately to the first and second transparent conductors and a pulsed heating bias

[0050] Figure 18C shows a timing diagram of the heating bias of Figures 18A and 18B in isolation.

[0051] Figure 19A shows a first embodiment of a circular transparent electrode having two curved low-resistance regions. [0052] Figure 19B shows a second embodiment of a circular transparent electrode having six curved low-resistance regions.

[0053] Figure 20 shows a block diagram depicting physical components that may be utilized to realize a controller of a liquid crystal driver and/or heater drive according to an exemplary embodiment.

DETAILED DESCRIPTION

[0054] The present disclosure relates generally to non-mechanical beam steering. In particular, but not by way of limitation, the present disclosure relates to systems, methods and apparatuses for non-mechanical beam steering using liquid crystals and polarization gratings and related methods of operation.

[0055] The word “exemplary” is used herein to mean “serving as an example, instance, or illustration.” Any embodiment described herein as “exemplary” is not necessarily to be construed as preferred or advantageous over other embodiments.

[0056] Preliminary note: the flowcharts and block diagrams in the following Figures illustrate the architecture, functionality, and operation of possible implementations of systems, methods and computer program products according to various embodiments of the present disclosure. In this regard, some blocks in these flowcharts or block diagrams may represent a module, segment, or portion of code, which comprises one or more executable instructions for implementing the specified logical function(s). It should also be noted that, in some alternative implementations, the functions noted in the block may occur out of the order noted in the figures. For example, two blocks shown in succession may, in fact, be executed substantially concurrently, or the blocks may sometimes be executed in the reverse order, depending upon the functionality involved. It will also be noted that each block of the block diagrams and/or flowchart illustrations, and combinations of blocks in the block diagrams and/or flowchart illustrations, can be implemented by special purpose hardware-based systems that perform the specified functions or acts, or combinations of special purpose hardware and computer instructions.

[0057] It will be understood that, although the terms first, second, third etc. may be used herein to describe various elements, components, regions, layers and/or sections, these elements, components, regions, layers and/or sections should not be limited by these terms. These terms are only used to distinguish one element, component, region, layer or section from another region, layer or section. Thus, a first element, component, region, layer or section discussed below could be termed a second element, component, region, layer or section without departing from the teachings of the present disclosure.

[0058] Spatially relative terms, such as “beneath,” “below,” “lower,” “under,” “above,” “upper,” and the like, may be used herein for ease of description to describe one element or feature's relationship to another element(s) or feature(s) as illustrated in the figures. It will be understood that the spatially relative terms are intended to encompass different orientations of the device in use or operation in addition to the orientation depicted in the figures. For example, if the device in the figures is turned over, elements described as “below” or “beneath” or “under” other elements or features would then be oriented “above” the other elements or features. Thus, the exemplary terms “below” and “under” can encompass both an orientation of above and below. The device may be otherwise oriented (rotated 90 degrees or at other orientations) and the spatially relative descriptors used herein interpreted accordingly. In addition, it will also be understood that when a layer is referred to as being “between” two layers, it can be the only layer between the two layers, or one or more intervening layers may also be present.

[0059] The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the disclosure. As used herein, the singular forms “a,” “an,” and “the” are intended to include the plural forms as well, unless the context clearly indicates otherwise. It will be further understood that the terms “comprises” and/or “comprising,” when used in this specification, specify the presence of stated features, integers, steps, operations, elements, and/or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and/or groups thereof. As used herein, the term “and/or” includes any and all combinations of one or more of the associated listed items, and may be abbreviated as “/”.

[0060] It will be understood that when an element or layer is referred to as being “on,” “connected to,” “coupled to,” or “adjacent to” another element or layer, it can be directly on, connected, coupled, or adjacent to the other element or layer, or intervening elements or layers may be present. In contrast, when an element is referred to as being “directly on,” “directly connected to,” “directly coupled to,” or “immediately adjacent to” another element or layer, there are no intervening elements or layers present. Likewise, when light is received or provided “from” one element, it can be received or provided directly from that element or from an intervening element. On the other hand, when light is received or provided “directly from” one element, there are no intervening elements present. [0061] Embodiments of the disclosure are described herein with reference to cross-section illustrations that are schematic illustrations of idealized embodiments (and intermediate structures) of the disclosure. As such, variations from the shapes of the illustrations as a result, for example, of manufacturing techniques and/or tolerances, are to be expected. Thus, embodiments of the disclosure should not be construed as limited to the particular shapes of regions illustrated herein but are to include deviations in shapes that result, for example, from manufacturing. Accordingly, the regions illustrated in the figures are schematic in nature and their shapes are not intended to illustrate the actual shape of a region of a device and are not intended to limit the scope of the disclosure.

[0062] Unless otherwise defined, all terms (including technical and scientific terms) used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this disclosure belongs. It will be further understood that terms, such as those defined in commonly used dictionaries, should be interpreted as having a meaning that is consistent with their meaning in the context of the relevant art and/or the present specification and will not be interpreted in an idealized or overly formal sense unless expressly so defined herein.

[0063] This disclosure describes systems, methods, and apparatus for heating a liquid crystal polarization grating (“LCPG”) and achieving uniform heating across the LCPG aperture as well as its thickness (Section I). This disclosure also describes using a single pair of transparent conductors on opposing sides of a liquid crystal to bias and control the liquid crystal orientation while simultaneously heating the liquid crystal to an optimal temperature range (Section II). In other words, while the industry has for over 25 years used distinct circuits and electrodes to perform liquid crystal heating and switching, this disclosure simplifies that long-held standard using a single pair of conductors to both bias and heat the liquid crystal. Nor has the industry seen this as a possible solution since there was a belief that heating bias needed to be insulated from liquid crystal control bias (see U.S. Patent No. 8,089,440 at column 3, lines 34-36). Along these same lines, this disclosure describes using a higher-resistivity conductor, with greater optical transmission, to bias the liquid crystal (and since a single pair of conductors is used, to heat the liquid crystal) (Section IV).

I. Uniform Heating

[0064] Steady-state operation is the equilibrium operation state at which the temperature of each part of the assembly remains stable over time. In this state, heat flows from heat sources to heat sinks through the effect of temperature gradients that have become established over time. Figure 4 shows a simplified view of an LCPG stack formed from 4 stages, and this simplified stack will be shown and described in Figures 5-7, even though this discussion is equally applicable to any number of stages. Figure 5 shows the use of “edge heaters” 502 in the art and the resulting thermal gradient that results, where less thermal energy reaches a center of the stack and the edges tend to be cooler than the bulk of the stack. The edge heaters 502 can be arranged within a housing 504 that encapsulates an outer edge of the stack (i.e., an outer edge of each stage) as well as electrical connections to the plurality of stages (not shown).

[0065] These temperature gradients across the optical device (e.g., an LCPG stack) aperture can be mitigated by using a combination of peripheral (or surface) heaters and optionally edge heaters, where the peripheral heaters are arranged at or near the outerfacing edges or surfaces of the device (e.g., outer-facing stages of the stack) as shown in Figures 6 and 7. More specifically, the device can include an LCPG stack 601 for non-mechanical beam steering formed from stages, where each stage includes a liquid crystal layer, control electrodes, and an adjacent polarization grating layer. A peripheral heating element 602, 604 can be arranged near both outermost LCPG stages of the stack 601 and optional edge heating elements 605 may be arranged within the housing 610 as shown. The peripheral heating elements 602, 604 can span the entire aperture thereby avoiding the thermal gradients seen in Figure 5. Insulation in the housing 610 or use of optional edge heating elements 605 can be used to prevent heat loss out of the edges of the stack 601 through the housing 610. The edges of the optical stack 601 may be insulated from the outside environment by use of conventional techniques to establish a thermal break. For example, instead of being mounted in contact with metal holders, the stack 601 may be “potted” in an epoxy material which serves both as a mechanical mount, and thermal insulation from a metal or polymer housing. Additionally, the housing 610 may only contact the outermost stages of the stack 601 thereby providing an air or even vacuum barrier at the edges of most stages. This air or vacuum gap may contain an insulator such as foam or rubber.

[0066] In some embodiments, the two peripheral heating elements 602, 604 can be operated at different thermal powers, for instance, to address different ambient temperatures on the two opposing sides of the stack 601. Alternatively, where one side of the stack 601 is at or near an optimum temperature range, a peripheral heater for that side of the stack 601 may not be needed, and in these embodiments, a single peripheral heating element on the colder side may be used. The heating elements can be controlled, for instance, via a circuit similar to the one shown in Figure 13.

[0067] While the above solution is sufficient in moderate climates, for certain lower- temperature applications (e.g., vehicle LIDAR in winter or satellite-based communications in the near-vacuum of space), there may be a desire to rapidly bring the stack 601 up to an optimal temperature before steady-state operation (e.g., 40°C). At the beginning of the rapid warm-up process the stack 601 is at the same temperature as the environment, so no heat is being lost to the environment. Essentially all the heat that is being supplied has the effect of increasing the temperature of the stack 601. As the surface of the stack 601 becomes warmer, more heat is lost to the environment until, ultimately, an equilibrium is reached at an operating temperature at which time little to no more heat is used to increase the temperature of the stack 601. At this steady-state period, heat only needs to be added in sufficient quantity to equal the heat lost to the environment (i.e., the heating elements can be turned down). While peripheral heating elements 602, 604 can heat the bulk of the stack 601 (i.e., the stages toward a middle of the stack 601), the thermal transfer from the peripheral heating elements 602, 604 toward the middle of the stack 601 through stage by stage diffusion is slow.

[0068] To more rapidly bring the bulk of the stack to temperature, Figures 7A and 7B show a “bulk” heating element 706. Although only one bulk heating element 706 is shown, any number of bulk heating elements could be implemented between the peripheral heating elements 702, 704. By using one or more bulk heating elements 706 distributed through the bulk of the stack 701 the assembly can be warmed more quickly than in Figure 6 without exposing the stack 701 to excessive thermal stress. Typically, a warm-up sequence would begin with all heating elements 702, 704, 706 operating together (Block 1602 in Figure 16), and then the bulk heating element(s) 706 would have its (their) power reduced at a greater rate than a reduction in the power to the peripheral heating elements 702, 704 (Block 1606). This reduction could occur once equilibrium is reached or in an incremental reduction as equilibrium is approached (Decision 1604). Optionally, edge heating elements can be used to better achieve uniform heating across the optical stack 701.

[0069] Figure 7A shows an assembly during a startup phase where peripheral heating elements 702, 704 as well as a bulk heating element 706 are used to quickly ramp the stack 701 temperature up to an operating temperature. Once a steady state is achieved, the bulk heating element 706 can be turned down or turned off (or gradually reduced as steady state is approached), as shown in Figure 7B. At steady state the peripheral heating elements 702, 704 can be set to dissipate enough heat to match heat loss out of the outer surfaces 708, 710 of the stack 701, such that the bulk heater 706 can be reduced to a greater extent in power than the peripheral heating elements 702, 704 if not turned off entirely. The peripheral heaters 702, 704 can be operated at different powers if the temperatures on opposing sides of the stack 701 are different. The small horizontal arrows indicate movement of thermal energy where all heating elements are turned on in FIG. 7 A, and the bulk heating element 706 is turned down or off in FIG. 7B.

[0070] In some embodiments, the two peripheral heating elements 702, 704 can be operated at different thermal powers, for instance, to address different ambient temperatures on the two opposing sides of the stack 701. Alternatively, where one side of the stack 701 is at or near an optimum temperature range, a peripheral heater for that side of the stack 701 may not be needed, and in these embodiments, a single peripheral heating element on the colder side may be used (e.g., see Figures 7C and 7D). The heating elements can be controlled, for instance, via a circuit such as the one shown in Figure

13. [0071] In some embodiments, use of the bulk heating element 706 allows the peripheral heating elements 702, 704 to be run at a higher power than steady state, during warmup, to more quickly ramp the stack up to a steady state temperature. Without the bulk heater 706 this could lead to excessive thermal stress on the stack as the bulk of the stack 701 could see much lower temperatures than regions near the peripheral heating elements 702, 704. This stress could be detrimental to the materials close to the peripheral heating elements 702, 704 and differential expansion could be damaging to the stack 701 and/or the entire assembly. However, with bulk heating element 706, lower thermal gradients result during rapid warm-up and thus the peripheral heating elements 702, 704 can be operated at higher-than-steady-state during rapid warm-up. This operation is equally applicable to embodiments where more than one bulk heating element 706 is used.

[0072] While Figures 7 A and 7B show use of peripheral heating elements on both sides of the stack as well as a bulk heating element, in other embodiments, different arrangements of these heating elements may be used. For instance, Figure 7C shows an optical stack with a first peripheral heating element 702 arranged on a front of the optical stack 701 and Figure 7D shows an optical stack with a first peripheral heating element 702 arranged on a front of the optical stack 701 and a second peripheral heating element 704 arranged on a back of the optical stack 701. These stacks can be formed of a plurality of stages including transparent conductors 710, liquid crystal cells/layers 714, and polarization gratings 712.

[0073] Figure 7E shows an optical stack with a first peripheral heating element 702 arranged on a front of the optical stack 701, and a bulk heating element 706 arranged toward a middle of the optical stack 701. Figure 7F shows an optical stack with a first peripheral heating element 702 arranged on a front of the optical stack 701, a second peripheral heating element 704 arranged on a back of the optical stack 701, and a bulk heating element 706 arranged toward a middle of the optical stack 701

[0074] While Figures 7C, 7D, 7E, and 7F use “front” and “back” references, it should be appreciated that one of skill in the art could easily swap these orientations without departing from the scope of the disclosure. Further, while these figures show six LCPG stages, any number of stages could be implemented including more or fewer than those shown. It should also be understood that while the bulk heating elements 706 in Figures 7E and 7F are shown in a specific position within the stack, any position toward a middle stages of the stack will be operable. However, where more than one bulk heating element is used, the bulk heating elements may be distributed throughout the stack in a spacing that is not necessarily weighted toward a middle of the stack (e.g., equally distributed through the stack). Furthermore, while the peripheral heating elements 702, 704 are illustrated on an outside of the first and last stages, they could also be arranged inside the first and last stages.

[0075] As will be described in more detail relative to Figures 11 and 12, in some embodiments, the heating elements 602, 604, 702, 704, 706 can provide thermal energy to the stack as well as provide a controlling field for controlling a state of the liquid crystal. In other embodiments, the heating elements 602, 604, 702, 704, 706 can provide thermal energy to the stack but be distinct from liquid crystal controlling biases.

[0076] Figure 8 shows a single transparent substrate coated with a transparent conductor, such as ITO, and two low-resistance regions at opposing edges of the top surface of the substrate 808. Electrical connections 804 can be made to these low-resistance regions 806 and a bias between the two low-resistance regions 806 can be established such that thermal energy is equally dissipated as heat across the transparent conductor 802. This arrangement can be used to implement the heating elements 602, 604, 702, 704, and 706, though connections other than wire bonds can be used to provide power to the low-resistance regions 806 (e.g., flex circuit).

[0077] Figure 9 shows a cross sectional view of an LCPG stack that could be used as the stack 601 or 701. It should be appreciated that while six stages are shown and three heating elements, other numbers of stages and heating elements could also be implemented. For instance, where two peripheral heating elements 902, 904 are used, then at least one stage is implemented. Where two peripheral heating elements 902, 904 are used and at least one bulk heating element 906, then at least two stages are implemented. Here, the bulk heating element 906 is separated from each of the peripheral heating elements 902, 904 by three stages. In another non-limiting variation, three additional stages could be arranged between two bulk heating elements and those two bulk heating elements each separated from a closest peripheral heating element by three stages. Although the illustrated example and the examples described above use an equal number of stages between heating elements, in other embodiments, thermal gradients and/or the composition and size of the stages may lead to an optimization wherein unequal numbers of stages are arranged between heating elements. For instance, where two bulk heating elements are used, and X stages are arranged between the two bulk heating elements, Y stages may be arranged between each of the bulk heating elements and a corresponding peripheral heating element where Y < X. In the illustrated embodiment, each LCPG stage has a different pair of electrical connections, and the heater connections are distinct from the LCPG control connections. [0078] All three or more heating elements can be turned on during a warm-up phase, and the bulk heating element(s) can be turned down or off when the stack reaches a steady state or incrementally reduced in power as the stack approaches a steady state.

[0079] In some embodiments, the two peripheral heating elements 902, 904 can be operated at different thermal energies, for instance, to address different ambient temperatures on the two opposing sides of the stack 901.

II. Heating and Controlling Liquid Crystal with the Same Electrodes

[0080] According to another aspect of this disclosure, the transparent electrodes that are used to drive the liquid crystal layer may be used also to heat the stack. These electrodes may be used as heaters separately from their liquid crystal drive function during a non-operation warm-up phase, or they may be used as heaters simultaneously with normal liquid crystal driving operation. One advantage of this approach is that fewer transparent conductors are used in the beam path than is seen in the art, where distinct heaters and drive electrodes are used. This results in less optical loss in the stack. Another advantage is that fewer components reduce bulk, weight, and assembly cost. Another advantage is that by applying heat directly at the location of the liquid crystal layer, without having to pass that heat through a liquid-crystal biasing layer, the liquid crystal layer is the first part of the assembly to warm, further reducing the time that the liquid crystal takes to reach operating temperature.

[0081] This aspect of the disclosure is explained with the help of Figures 10 through 12. Figure 10 shows a simplified view of transparent biasing electrodes for a liquid crystal cell (the liquid crystal layer is hidden for simplicity). A bias applied to one of the two leads biases the corresponding transparent electrode, which in turn generates a corresponding electric field between the electrodes. The strength of this field controls the liquid crystal orientation, and thus the polarization of the light that reaches an adjacent polarization grating of the optical stage. However, Figure 10 does not allow heating and biasing of the liquid crystal layer.

[0082] Figure 11 shows a simplified view of biasing electrodes of a liquid crystal cell that can perform both biasing and heating. In particular, two transparent electrodes are used as liquid crystal biasing and heating elements. These functions may be used sequentially or simultaneously through the choice of drive signals. Each of the two transparent electrodes of the liquid crystal cell is equipped with two low-resistance regions 1102, such as those seen in Figure 8. Due to their low resistance, these regions 1102 can also be referred to as equipotential areas since current can pass through these regions with relatively little voltage drop as compared to current flow between low-resistance regions 1102 on the same transparent electrode. The equipotential areas 1102 enhance the goal of substantially uniform current flow across each transparent electrode and in the direction of the arrows. Each transparent electrode has heater current flowing in it such that there is a voltage drop along the path of the current flow between the equipotential areas 1102 on a given electrode. The current directions are chosen to be the same in both substrates. For example, if current is flowing from connection Fl to F2, then current is also flowing from Bl to B2. Because the current is flowing in the same direction, and assuming that the voltage difference between Fl and Bl and between F2 and B2 is the same, there will be a voltage drop between the two electrodes, across the liquid crystal cell (hidden in this simplified illustration) that will be the same at all points on the two electrodes (when viewed from above or beneath). Biasing of the liquid crystal can be governed by Equation 1 as follows:

Equation 1

[0083] When Equation 1 is true, the liquid crystal will have the same voltage across each part of the liquid crystal film. To adjust the liquid crystal orientation and thus its optical effect, a bias can be applied to both VFI and VF2. The bias for liquid crystal cells is often an AC signal, though DC can be used in some situations. See Figure 12B for more detail, which shows an embodiment where an AC liquid crystal control signal is used.

[0084] To adjust heating in the conductors, a heating bias can be applied to the higher potential equipotential region of each of the two conductors (i.e., at VFI and VBI). Equation 2 shows the relation between heater voltage and the biases on the equipotential regions.

Equation 2

[0085] Heater voltage should be applied to both VFI and VBI, or else the liquid crystal bias will be altered (i.e., the field between the two conductors will change). In other words, where equal heating bias is applied to both conductors, the liquid crystal drive voltage can be controlled independent from the heater control for the liquid crystal cell. The heater power, for each conductor, can be written as: p > heater

‘ heaters _R Equation 3

[0086] where R is the resistance of the conductor. [0087] The liquid crystal film responds to the difference in voltage between the conductors because the lateral electric field created by practical heater drive conditions is tiny compared to the liquid crystal drive electric field between the closely spaced conductors. Note that many, but not all, liquid crystal cells are driven with AC voltages. AC liquid crystal drive can be combined with either AC or DC heater drive depending on factors such as convenience of drive scheme design or contact reliability considerations.

[0088] In Figure 11, the top and bottom conductors are offset (right and left in the figure) to allow space for connections Bl, B2 to be made to the conductors, since the gap between the conductors may only be a few microns. If connections to the equipotential regions, 1102, can be made from the edge or the back of the substrates, for example with deposited “wrap around” conductive layers, then the substrates need not be offset.

[0089] Figure 15 shows a seven-stage stack with heating elements at the front and back apertures plus an extra heating element in the bulk of the stack, where the heating elements use the same transparent electrodes as the liquid crystal control electrodes. This illustration shows that an optical stack with peripheral heating elements and a bulk heating element can be formed, where, unlike Figure 9, the heating elements are not distinct from the liquid crystal control electrodes. In other words, the heating elements in Figure 15 can be formed and controlled in the same fashion as described in Figures 11 and 12 where the control and heating electrodes are one in the same. It should be understood that while Figures 6 and 7 were largely described in terms of heating elements that were separate from the control electrodes for the liquid crystal layers, the embodiment exemplified by Figure 15 could be implemented in the stacks of Figures 6 and 7 — where heating electrodes and control electrodes are one and the same.

[0090] While Figure 15 only shows a single bulk heating element, in other embodiments, additional bulk heating elements could be implemented. Further, while this embodiment shows stages between those stages having heating elements, in other embodiments, all stages could include heating elements, or at least a greater ratio of stages than see in this illustration. For instance, a half, or a third of the stages could include heating elements. It is also conceived that certain stages can use the integrated heating elements as shown here and in Figures 11 and 12, while other stages could use the independent heating elements shown in Figure 9.

[0091] Figure 15 is shown in a DC driving arrangement, but those of skill in the art will appreciate how to modify this driving scheme to use non-DC or AC drive.

III. Heater and Liquid Crystal Control System

[0092] Figure 12A shows a simplified view of a liquid crystal cell with two transparent conductors providing driving and heating signals. In previous embodiments, with the addition of an LCPG, this assembly could be referred to as an optical stage of a stack, such as the stacks 601 and 701. Current flows between connections Fl and F2 through the “front” electrode, and between connections Bl and B2 through the “back” electrode. This current flow through the resistive transparent conductive electrodes dissipates heat to warm the liquid crystal cell. At the same time, the potential difference, V(LC), between the front and back electrodes controls an electric field through the liquid crystal and thereby controls the polarization of transmitted light.

[0093] Figure 12B shows an embodiment of a generalized control topology that could be used to drive a conductor on either side of a liquid crystal cell to control both the liquid crystal drive voltage and heating. For instance, the Fl, F2, Bl, and B2 connections could be those shown in Figures 11 or 12 A. In this embodiment, the liquid crystal drive signal is a pattern of AC pulses that is delivered to connections Fl and F2 via driver circuits (e.g., voltage regulators). The heating control signal is added to the liquid crystal drive (or liquid crystal polarization control signal) before the Fl connection and to the opposing electrode at Bl (without summing with another signal). The liquid crystal drive signal is not delivered to either of the Bl or B2 connections. In other words, the liquid crystal control or bias is provided primarily to the front conductor. The heating signal is provided to the higher potential connections of both conductors. The B2 connection can be grounded, while the F2 connection can be driven by the liquid crystal drive. Note that it may be electrically convenient to periodically exchange the roles of the F and B connections to allow for a driver that requires a lower supply voltage.

[0094] Although Figures 11-12 refer to “front” and “back” sides of the liquid crystal cell, these are exemplary uses only, and in practice, either the front or back side of the liquid crystal cell could receive incident light and the opposing side could be coupled to a polarization grating or other output layer.

[0095] Figure 12B is shown in a DC driving arrangement, but those of skill in the art will appreciate how to modify this driving scheme to use non-DC or AC drive. For instance, Figures 17A and 17B show timing charts in terms of voltage for the four connections Fl, F2, Bl, and B2 shown in Figures 12A and 12B. These charts show the signals reaching the low-resistance regions, and thus include the combined effect of liquid crystal orientation control signals as well as heating signals. Here, an AC or pulsed liquid crystal orientation control signal is provided to the Fl and F2 connections, while B2 is grounded and a DC heating signal is provided equally to Fl and B 1 (see the positive DC offset at both of these connections while F2 is centered around 0 V).

[0096] Figure 17C shows a similar timing chart, but where the liquid crystal orientation control signal is provided to both transparent electrodes, one half cycle apart. In particular, both Fl and F2 see the same liquid crystal orientation control signal, and Bl and B2 also see this same signal, but a half a cycle out of phase with the other electrode. Thus, the voltage difference across the liquid crystal is twice the amplitude of the signal provided to both electrodes. This driving scheme can allow lower power hardware while still achieving equivalent liquid crystal orientation control as the driving scheme seen in Figures 17A and 17B. The liquid crystal orientation control signal of these embodiments can be implemented as an AC signal. The amount of thermal energy generated can be determined by the amplitude of the DC drive signal.

[0097] In some embodiments, a pulsed heating signal can be used, or pulsed heating can be used to control an amount of heating power delivered (e.g., reducing duty cycle reduces heating power delivered as the electrodes approach or reach an optimum temperature range). For instance, Figure 18A shows exemplary timing charts in terms of voltage for providing drive signals to the Fl and F2 connections. Figure 18B shows exemplary timing charts in terms of voltage for providing control signals to the Bl and B2 connections. In particular, Figure 18B shows a pulsed heating signal (e.g., 50% duty cycle), which is provided to Fl and Bl, but not F2 and not B2. Thus, the signals at Fl and Bl show a summing of control and heating signals. Low-resistance regions on the same transparent conductor receive the same liquid crystal orientation control signal (i.e., Fl and F2 receive the same orientation signal and Bl and B2 receive the same orientation signal).

[0098] Each of these figures corresponds to Equations 1 and 2.

[0099] Figure 13 shows another example of a drive system. This system could drive a stack such as the ones shown in Figures 6, 7, and 9, where the heating elements and the electrodes for controlling liquid crystal polarization are distinct. The liquid crystal cells are driven with AC square waves, and the heating elements are driven with pulse-width modulated currents. One or more temperature sensor(s) provides information for heater and/or liquid crystal cell control. The controller 1302 may be a conventional computer, microcontroller, FPGA, or ASIC, to name a few non-limiting examples. The controller 1302 can control a steering angle of an LCPG stack, can control power of the stack, and report status and temperature. The controller 1302 has two main functions: (1) to drive appropriate voltages to the liquid crystal cells so that they condition the polarization state of the light so that the LCPG elements steer the beam appropriately; and (2) to drive the heating elements with the appropriate powers to warm the stack to operating temperature, and to maintain it at that temperature. Control can be based on temperature feedback from a temperature sensor at the liquid crystal cells of one or more stages of the stack. If the operating environment is not known in advance of system deployment, the temperature sensor(s) will allow closed- loop operation to achieve and maintain an acceptable operating temperature. If, on the other hand, the system is designed to operate in an environment with a fairly well- known temperature, such as “room temperature”, then it may be acceptable to operate open loop. In this case the controller 1302 would run a pre-programmed heater drive sequence for the warm-up, and then maintain steady heater drive powers thereafter.

The drive currents may be predetermined by experiment or calculation.

[00100] Figure 13 shows the heater drive implemented using a conventional pulsewidth modulation (PWM) scheme. This is known to be an electrically efficient way to achieve an effectively analog response from resistive heating elements, but this method is not intended to be limiting, and other approaches may also be used. If one or more temperature sensors are being used, the controller 1302 may use a Proportional, Integral, Differential (PID) controller or other conventional feedback mechanism, which may be implemented in software.

[00101] The controller 1302 can have outputs for liquid crystal polarization control and others for the heaters. On the liquid crystal polarization control side, each control signal from the controller 1302 can pass through a DAC 1304, or be digitized at the controller 1302 (in an embodiment different from the one shown), and then passed to drivers 1308 and on to corresponding connections of the liquid crystal cells 1 through N. The same digitized control signals can be inverted by inverters 1306, or other inverting means, and passed to the corresponding liquid crystal connections via drivers 1310. In some embodiments, the inverter 1306 functionality can be part of the driver 1310. Heating control is performed via pulse width modulation in this example, but other control mechanism could also be used. One low-resistance region of a transparent conductor can be coupled to a heater supply 1312 (e.g., a voltage source) and each opposing transparent conductor can be selectively grounded via a switch 1314, such as a gated transistor. The PWM signals from the controller 1302 can control these switches and in turn an amount of power passing through these heater conductors. The 1^st and 2^nd peripheral heaters can correspond to 602 and 604 or 702 and 704, for instance. The bulk heater(s) can correspond to 706 for instance. The edge heater(s) can correspond to 605, or the edge heaters shown in Figure 7, for instance.

[00102] A typical temperature control system will have one or more temperature probe(s) at representative part(s) of the system to be maintained under temperature control. With this information, heater power can be modulated in a number of different ways. Simple systems may simply switch heaters on and off, under the control of a simple on/off thermostat, while a more complex, high-performance system may use a proportional-integral-derivative controller (PID) that calculates heater drive strength using terms that are proportional to the error value (target temperature - actual temperature), the integral of the error value, and the time- derivative of the error value. The heater drive voltage (and so heater current) may be continuously modulated or pulsed, with pulse-width modulation likely being both practical and efficient.

[00103] While it may be possible to locate temperature sensor(s) in the aperture of the device, it is likely preferable to instead monitor the temperature outside of the active area, for example at the edge of the stack inside the housing (e.g., 610 in Figure 6). By monitoring ambient temperature, the stack temperature along with the knowledge of the history of these parameters, the appropriate drive voltages can either be calculated or read from a look-up-table. The calculation parameters or look-up table entries would be established for a new system design during a characterization process. Temperatures during warm-up cycles and/or operation under various cold conditions could be established by instrumenting a representative test assembly with multiple temperature sensors. With this information it is possible to determine a set of control programs to rapidly, and evenly warm up the stack. It is also possible to characterize the offset, over a range of conditions, between temperature sensor(s) in the housing and the temperature of the stack.

[00104] The details of the temperature control scheme will depend on the specifics of the system that one desires to control, including the performance specifications, the operating conditions, the physical geometry of the stack and the budget available for complexity. In some situations, it may be beneficial to measure the temperature near the front and back of the stack if, for example, the front is exposed to an outside environment and the back faces the inside of an enclosure containing other hardware. In other cases, a single measurement may be an acceptable proxy for the entire stack temperature. In some cases, a separate sensor may be helpful to track the temperature between the front and back of the stack.

[00105] While control has so far been described in terms of bringing temperature up to optimal to enhance liquid crystal switching speed, in other embodiments, biasing of the liquid crystal can be adjusted based on temperature. For instance, higher voltages may be needed to carry out switching at lower temperatures. The correlation of bias voltage to temperature could be empirically determined prior to operation (e.g., at the factory or during a calibration phase with a delivered product). In other embodiments, a combination of heating the liquid crystal and adjusting bias voltages based on the resulting stack temperature could be used. These two methods may also be used at different times during operation, for instance pure heating during warm-up and then bias adjustment during steady state operation, or vice versa. For instance, there may be a desire to operate at lower power than optimal in order to save power, and in this case adjusting control biases to match the resulting temperature may be implemented. IV. High Sheet Resistance Conductor Acting as Both Liquid Crystal Bias and Heater

[00106] Transparent conductors, such as Indium-Tin Oxide (ITO), have been used as heating elements attached to the front of displays for applications such as for automotive displays. These applications typically use low resistance ITO with sheet resistances of approximately 10 to 20 ohms/square. Thin Film Devices of Anaheim, CA is an example of a supplier of transparent conductors for this application. This standard choice of sheet resistance allows an effective heater to be constructed using relatively low voltage drivers. However, low-resistance conductors also tend to be less transparent in visible (approximately 380nm to 750nm) and near- infrared (approximately 750nm to 2500nm) wavelengths, than high-resistance conductors. For most display applications, the resulting loss of 5-10% of brightness is not concerning. However, in non-mechanical beam steering applications, such as LIDAR or optical communication, such losses can be significant and thus there is a desire to both heat liquid crystals in a non-mechanical beam steering assembly while also using more transparent heating elements.

[00107] In one embodiment, this disclosure uses a transparent conductor (e.g., ITO), of much higher sheet resistance than used in the art, such as 300 to 1000 ohms/square, which results in better light transmission than low-resistance conductors. The choice of higher sheet resistance leads to a higher drive voltage, such as 25V or more depending on the situation, along with a commensurately lower current. For example, a square electrode with a sheet resistance of 400 ohms/square, will dissipate 1W with a 20V drive voltage and 4W with a 40V drive voltage, drawing 100mA. However, these increased drive requirements can be designed into the system without great increase in complexity, cost, size, or reduced switching speed. Thus, with little disadvantages, increased sheet resistance conductors and their corresponding increased transmission in the visible and infra-red are advantageous for a nonmechanical beam steering device (e.g., an LCPG stack) that may use more than one heater to achieve good uniformity, and/or rapid warm-up.

[00108] Independent of the above-noted choice of transparent conductor/electrode, two low-resistance regions (e.g., < 50 ohm/square) can be fabricated at opposing edges of both conductors/electrodes to act as an equipotential bonding pad/region, and the shape of these low-resistance regions can be selected to provide substantially uniform current flow across the substrate (see Figures 8, 11, and 14). In one embodiment, these low-resistance regions can be arranged to be substantially parallel to each other and close to opposing edges of a conductor or the device aperture (where the conductor is wider than the aperture). The resistance of these low-resistance regions can be lower than a resistance of the rest of the conductor. They can be fabricated by depositing a low-resistance conductor (e.g., sputter or vapor deposition), such as aluminum, Chromium, Nickel, or Silver, to name a few non-limiting examples, in a region at or near an edge of the conductor, or by bonding a bulk material to the conductor edge such as a wire, silver epoxy, copper tape, or flex connector near the edge of the aperture, to name a few non-limiting examples. If the sheet resistance of the transparent conductor is substantially uniform, and drive electronics are bonded to the conductor at the low-resistance regions, then the current density across each electrode will be substantially uniform from one low-resistance region to the opposing low-resistance region as shown, for instance, in Figure 14. Similarly, the heat dissipation will also be substantially uniform. [00109] Note that in some system designs the stack may be exposed to different temperatures at the “front” and “back” sides of the stack if, for example, one side is exposed to the outside world and the other side is exposed to the inside of an enclosure containing system hardware. In this situation it may be preferable to use a temperature sensor to monitor the temperature of the outside world and another temperature sensor to monitor the temperature inside the system enclosure. This will allow the control system to set appropriate, different, heater currents for the front and back aperture heaters.

[00110] Although this application has used ITO as an exemplary conductive film and though it is a commonly used transparent conductor for visible and near infra-red wavelengths, other transparent conductors may also be used or may be preferred at other wavelengths. For example, Indium-Molybdenum Oxide (IMO) may be chosen for short wave infra-red (SWIR) applications and Carbon Nanotube fabrication and deposition is an area of active research. Carbon Nanotube films may become commercially viable for these devices in future.

[00111] Although this disclosure has largely discussed square or rectangular apertures and electrodes, other shapes are also envisioned. As just one non-limiting example, the aperture and/or electrodes could have a circular form as shown in Figures 19A and 19B. Achieving uniform heater current in such a shape is more challenging than in a square or rectangular shape, and an ideal uniformity may not be possible. Thus, novel low-resistance regions and combinations of different biases can be used to approximate uniform current flow. For instance, while Figure 19A has a single arched low-resistance region 1902 at the top and bottom of a transparent circular electrode, Figure 19B may provide more uniform current by using additional low- resistance regions and applying different voltages to these different low-resistance regions based on distances between opposing low-resistance regions. For instance, the smaller low-resistance regions 1906 may have a lower voltage bias than the larger low-resistance regions 1904.

[00112] The methods described in connection with the embodiments disclosed herein may be embodied directly in hardware, in processor-executable code encoded in a non-transitory tangible processor readable storage medium, or in a combination of the two. Referring to FIG. 20 for example, shown is a block diagram depicting physical components that may be utilized to realize a controller of the LC driver and/or heater drive in Figure 12 or the controller 1302 (and the controller of liquid crystal drive signals and heater signals generally) according to an exemplary embodiment. As shown, in this embodiment a display portion 2012 and nonvolatile memory 2020 are coupled to a bus 2022 that is also coupled to random access memory ("RAM") 2024, a processing portion (which includes N processing components) 2026, an optional field programmable gate array (FPGA) 2027, and a transceiver component 2028 that includes N transceivers. Although the components depicted in FIG. 20 represent physical components, FIG. 20 is not intended to be a detailed hardware diagram; thus many of the components depicted in FIG. 20 may be realized by common constructs or distributed among additional physical components. Moreover, it is contemplated that other existing and yet-to-be developed physical components and architectures may be utilized to implement the functional components described with reference to FIG. 20.

[00113] This display portion 2012 generally operates to provide a user interface for a user, and in several implementations, the display is realized by a touchscreen display. In general, the nonvolatile memory 2020 is non-transitory memory that functions to store (e.g., persistently store) data and processor-executable code (including executable code that is associated with effectuating the methods described herein). In some embodiments for example, the nonvolatile memory 2020 includes bootloader code, operating system code, file system code, and non-transitory processorexecutable code to facilitate the execution of a method described with reference to Figure 16 described further herein.

[00114] In many implementations, the nonvolatile memory 2020 is realized by flash memory (e.g., NAND or ONENAND memory), but it is contemplated that other memory types may be utilized as well. Although it may be possible to execute the code from the nonvolatile memory 2020, the executable code in the nonvolatile memory is typically loaded into RAM 2024 and executed by one or more of the N processing components in the processing portion 2026.

[00115] The N processing components in connection with RAM 2024 generally operate to execute the instructions stored in nonvolatile memory 2020 to enable a method for controlling liquid crystal orientation and liquid crystal heating. For example, non-transitory, processor-executable code to effectuate the methods described with reference to Figure 16 may be persistently stored in nonvolatile memory 2020 and executed by the N processing components in connection with RAM 2024. As one of ordinarily skill in the art will appreciate, the processing portion 2026 may include a video processor, digital signal processor (DSP), micro-controller, graphics processing unit (GPU), or other hardware processing components or combinations of hardware and software processing components (e.g., an FPGA or an FPGA including digital logic processing portions). [00116] In addition, or in the alternative, the processing portion 2026 may be configured to effectuate one or more aspects of the methodologies described herein (e.g., the method described with reference to Figure 16). For example, non-transitory processor-readable instructions may be stored in the nonvolatile memory 2020 or in RAM 2024 and when executed on the processing portion 2026, cause the processing portion 2026 to perform a method of controlling liquid crystal orientation and heating. Alternatively, non-transitory FPGA-configuration-instructions may be persistently stored in nonvolatile memory 2020 and accessed by the processing portion 2026 (e.g., during boot up) to configure the hardware-configurable portions of the processing portion 2026 to effectuate the functions of the controllers for liquid crystal orientation and heating.

[00117] The input component 2030 operates to receive signals (e.g., a desired liquid crystal operating temperature) that are indicative of one or more aspects of the desired state of the liquid crystal optical stack. The signals received at the input component may include, for example, a desired temperature, temperature feedback from a temperature sensor, or a desired beam-steering angle. The output component generally operates to provide one or more analog or digital signals to effectuate an operational aspect of the liquid crystal optical stack. For example, the output portion 2032 may provide the drive signal for the transparent conductors to control liquid crystal orientation and/or heating described with reference to Figures 7A-7F and 12A and 12B.

[00118] The depicted transceiver component 2028 includes N transceiver chains, which may be used for communicating with external devices via wireless or wireline networks. Each of the N transceiver chains may represent a transceiver associated with a particular communication scheme (e.g., WiFi, Ethernet, Profibus, etc.).

[00119] Some portions are presented in terms of algorithms or symbolic representations of operations on data bits or binary digital signals stored within a computing system memory, such as a computer memory. These algorithmic descriptions or representations are examples of techniques used by those of ordinary skill in the data processing arts to convey the substance of their work to others skilled in the art. An algorithm is a self-consistent sequence of operations or similar processing leading to a desired result. In this context, operations or processing involves physical manipulation of physical quantities. Typically, although not necessarily, such quantities may take the form of electrical or magnetic signals capable of being stored, transferred, combined, compared or otherwise manipulated. It has proven convenient at times, principally for reasons of common usage, to refer to such signals as bits, data, values, elements, symbols, characters, terms, numbers, numerals or the like. It should be understood, however, that all of these and similar terms are to be associated with appropriate physical quantities and are merely convenient labels. Unless specifically stated otherwise, it is appreciated that throughout this specification discussions utilizing terms such as “processing,” “computing,” “calculating,” “determining,” and “identifying” or the like refer to actions or processes of a computing device, such as one or more computers or a similar electronic computing device or devices, that manipulate or transform data represented as physical electronic or magnetic quantities within memories, registers, or other information storage devices, transmission devices, or display devices of the computing platform. [00120] The terms and expressions employed herein are used as terms and expressions of description and not of limitation, and there is no intention, in the use of such terms and expressions, of excluding any equivalents of the features shown and described or portions thereof. Each of the various elements disclosed herein may be achieved in a variety of manners. This disclosure should be understood to encompass each such variation, be it a variation of an embodiment of any apparatus embodiment, a method or process embodiment, or even merely a variation of any element of these. Particularly, it should be understood that the words for each element may be expressed by equivalent apparatus terms or method terms — even if only the function or result is the same. Such equivalent, broader, or even more generic terms should be considered to be encompassed in the description of each element or action. Such terms can be substituted where desired to make explicit the implicitly broad coverage to which this invention is entitled.

[00121] As but one example, it should be understood that all action may be expressed as a means for taking that action or as an element which causes that action. Similarly, each physical element disclosed should be understood to encompass a disclosure of the action which that physical element facilitates. Regarding this last aspect, by way of example only, the disclosure of a “protrusion” should be understood to encompass disclosure of the act of “protruding” — whether explicitly discussed or not — and, conversely, were there only disclosure of the act of “protruding”, such a disclosure should be understood to encompass disclosure of a “protrusion”. Such changes and alternative terms are to be understood to be explicitly included in the description.

[00122] As will be appreciated by one skilled in the art, aspects of the present invention may be embodied as a system, method or computer program product. Accordingly, aspects of the present invention may take the form of an entirely hardware embodiment, an entirely software embodiment (including firmware, resident software, micro-code, etc.) or an embodiment combining software and hardware aspects that may all generally be referred to herein as a "circuit," "module" or "system." Furthermore, aspects of the present invention may take the form of a computer program product embodied in one or more computer readable medium(s) having computer readable program code embodied thereon.

[00123] As used herein, the recitation of "at least one of A, B and C" is intended to mean "either A, B, C or any combination of A, B and C." The previous description of the disclosed embodiments is provided to enable any person skilled in the art to make or use the present disclosure. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the generic principles defined herein may be applied to other embodiments without departing from the spirit or scope of the disclosure. Thus, the present disclosure is not intended to be limited to the embodiments shown herein but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims

WHAT IS CLAIMED IS:

1. A liquid crystal stage comprising: a liquid crystal layer; a first transparent conductor on a first side of the liquid crystal layer; a second transparent conductor on a second side of the liquid crystal layer; the first transparent conductor comprising first and second low- resistance regions spaced from each other; the second transparent conductor comprising third and fourth low- resistance regions spaced from each other; a liquid crystal driver coupled to the first and second low-resistance regions; a heater driver coupled to the first and third low-resistance regions, wherein an orientation of the liquid crystal layer and a temperature of the liquid crystal layer are controlled via the first and second transparent conductors.

2. The liquid crystal stage of Claim 1, wherein the fourth low-resistance region is coupled to ground.

3. The liquid crystal stage of Claim 2, wherein signals from the heater driver and the liquid crystal driver are summed at or before the first low-resistance region.

4. The liquid crystal stage of Claim 1, wherein signals from the heater driver and the liquid crystal driver are summed at or before the first low-resistance region.

42

5. The liquid crystal stage of Claim 1, wherein the first and second transparent conductors have a high sheet resistance between 300 and 1000 ohms/square.

6. The liquid crystal stage of Claim 5, wherein the low-resistance regions have a low sheet resistance less than 50 ohms/square.

7. The liquid crystal stage of Claim 1, wherein the liquid crystal driver is DC.

8. The liquid crystal stage of Claim 1, wherein the liquid crystal driver is AC.

9. The liquid crystal stage of Claim 1, wherein the liquid crystal stage is circular.

10. The liquid crystal stage of Claim 1, further comprising a polarization grating.

11. The liquid crystal stage of Claim 10, wherein the liquid crystal stage is part of a multi-stage liquid crystal polarization grating non-mechanical beam steering optical stack.

12. An optical assembly comprising: a plurality of optical stages, each of the stages comprising a liquid crystal layer surrounded by a first transparent conductor on a first side of the liquid crystal layer, a second transparent conductor on a second side of the liquid crystal layer, and a polarization grating; a first peripheral heating element adjacent to a first of the plurality of optical stages and configured to provide surface heating for the optical assembly; and drive circuitry comprising:

43 a first heater circuit configured to provide a controlled current to the first peripheral heating element; and liquid crystal drive circuits configured to provide a drive signal to each of the liquid crystal layers to control an orientation of each of the liquid crystal layers.

13. The optical assembly of Claim 12, further comprising: a second peripheral heating element adjacent to a last of the plurality of optical stages and configured to provide surface heating for the optical assembly; and a second heater circuit configured to provide a controlled current ot eh second peripheral heating element.

14. The optical assembly of Claim 13, further comprising one or more bulk heating elements in between the first and second peripheral heating elements and arranged toward a middle stage of the plurality of optical stages.

15. The optical assembly of Claim 13, wherein the first and second heater circuits are configured to provide different power levels to the first and second peripheral heating elements.

16. The optical assembly of Claim 12, further comprising one or more bulk heating elements arranged toward a middle stage of the plurality of optical stages.

17. The optical assembly of Claim 16, wherein once the optical assembly reaches the optimal temperature range, power to the one or more bulk heating elements is reduced to a greater extent than power is reduced to the first and second peripheral heating elements.

18. The optical assembly of Claim 12, wherein the first peripheral heating element spans most or all of an aperture of the optical assembly.

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19. The optical assembly of Claim 12, wherein the first and second transparent conductors are transparent in the visible and/or near infra-red spectrum.

20. The optical assembly of Claim 12, wherein the first and second heater circuits are configured to heat the optical assembly to an optimal temperature range and then reduce power to maintain that optimal temperature range.

21. The optical assembly of Claim 20, wherein the first and second heater circuits are configured to, during a warm-up period, heat the optical assembly with more power than is necessary to maintain the optimal temperature range, and then reduce power once the optimal temperature range is reached.

22. The optical assembly of Claim 12, wherein the first and second transparent conductors have a high sheet resistance between 300 and 1000 ohms/square.

23. The optical assembly of Claim 22, wherein the first transparent conductor comprises at least two low-resistance regions configured to receive the drive signal from the first heater circuit, wherein the at least two low-resistance regions have a low sheet resistance less than 50 ohms/square.

24. The optical assembly of Claim 12, further comprising an edge heating element adjacent to or in contact with edges of the optical stages and configured to provide edge heating for the optical assembly.

25. A method of heating a non-mechanical beam-steering optical stack, the method comprising: providing power to one or more peripheral heating elements in the optical stack and one or more bulk heating elements in the optical stack during a warm-up period as a temperature of the optical stack moves toward an optimal temperature range; reducing power to the one or more bulk heating elements in the optical stack at a greater rate than a reduction in power to the one or more peripheral heating elements when a temperature of the optical stack approaches or reaches the optimal temperature range.

26. The method of Claim 25, further comprising adjusting a bias to a liquid crystal layer in the optical stack based on the temperature of the optical stack along with a desired orientation of the liquid crystal layer and where the temperature of the optical stack is below the optimal temperature range.

27. The method of Claim 25, wherein the one or more peripheral heating elements and the one or more bulk heating elements are transparent conductors.

28. The method of Claim 27, wherein the one or more peripheral heating elements and the one or more bulk heating elements have a sheet resistance of between 300 and 1000 ohms/square.

29. The method of Claim 25, further comprising providing thermal energy to edges of stages in the optical stack to optimize equal distribution of thermal energy throughout the optical stack.

30. The method of Claim 25, wherein the optimal temperature range is

60°-80°F.

31. The method of Claim 25, further comprising removing power from the one or more bulk heating elements when the temperature of the optical stack reaches the optimal temperature range.

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