Patent Publication Number: US-2022214595-A1

Title: Beam steering devices

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application is a continuation of U.S. application Ser. No. 16/783,863 filed Feb. 6, 2020, titled “BEAM STEERING DEVICES,” which is a bypass continuation of PCT Application No. PCT/US2019/062110 filed Nov. 19, 2019, titled “BEAM STEERING DEVICES,” which claims priority to U.S. Provisional Application No. 62/769,052 filed Nov. 19, 2018, titled “FAST BEAM STEERING DEVICE USING MULTI-DIMENSIONAL ELECTRIC FIELDS AND OVER-DRIVING,” the entire disclosures of which are incorporated herein by reference. 
    
    
     BACKGROUND 
     Current liquid crystal-based beam steering devices use an electric field to alter the orientation of the liquid crystal molecules. The liquid crystal molecules align with the direction of the electric field. Anchoring forces created by an alignment layer return the liquid crystal molecules to their original orientation when the electric field is removed. Increasing the amplitude of the electric fields increases the speed of rotation of the liquid crystal molecules, but the alignment layer forces are fixed, so the change in orientation when the electric field is removed occurs relatively slowly, regardless of the field amplitude. This causes a conventional liquid-crystal beam steering device to switch slowly from an “ON” state to an “OFF” state, regardless of how quickly the device switches from “OFF” to “ON.” 
     SUMMARY 
     A beam steering device includes a substrate defining a cavity and having a first refractive index, and an electroactive material, disposed within the cavity and having a variable refractive index. The beam steering device also includes a first overlay, coupled to the substrate, to receive an incident light beam orthogonal to a first plane of the first overlay and to couple the incident light beam into the electroactive material. The beam steering device also includes a second overlay coupled to the substrate and defining a second plane tilted with respect to the first plane to define a tilt angle between the first plane and the second plane. The second overlay receives the incident light beam from the electroactive material and outputs, after refraction, the incident light beam as an output light beam. 
     A method for projecting a light beam on a retina of a user via eyewear worn by the user includes receiving, via a network overlay of the eyewear, image data and/or video data from a remote device. The method further includes converting, via a source of the eyewear, the image data and/or video data into a light beam. The method further includes coupling, into a beam steering device of the eyewear, the light beam as an incident light beam orthogonal to a first plane of a first overlay of the beam steering device. The first overlay is coupled to a substrate of the beam steering device. The substrate has a first refractive index and defines a cavity having an electroactive material disposed therein, the electroactive material exhibiting a variable refractive index. The method also includes receiving, at a second overlay of the beam steering device, the incident light beam from the electroactive material, the second overlay defining a second plane titled with respect to the first plane to define a tilt angle. The method further includes applying a first electric field to the electroactive material between the first overlay and the second overlay, and a second electric field to the electroactive material between a third overlay and a fourth overlay of the beam steering device. The third overlay and the fourth overlay each define a plane orthogonal with respect to the first plane, such that the electroactive material attains a second refractive index based on a strength of the first electric field and the second electric field. The method also includes outputting, after refraction by the second overlay, the incident light beam as an output light beam onto the retina of the user. 
     A scanning system includes a set of beam steering devices in cascade. Each beam steering device includes a substrate defining a cavity and having a first refractive index and an electroactive material, disposed within the cavity and having a variable refractive index. Each beam steering device further includes a first overlay, coupled to the substrate, to receive an incident light beam orthogonal to a first plane of the first overlay and to couple the incident light beam into the electroactive material. Each beam steering device further includes a second overlay coupled to the substrate and defining a second plane tilted with respect to the first plane to define a tilt angle between the first plane and the second plane, to receive the incident light beam from the electroactive material and to output, after refraction, the incident light beam as an output light beam. A first beam steering device receives the incident light beam and outputs the output light beam as a first output light beam. Each subsequent beam steering device receives the output light beam of a previous beam steering device as its input light beam. Each beam steering device outputs is output light beam as refracted along a different axis than each other beam steering device of the set of beam steering devices. 
     All combinations of the foregoing concepts and additional concepts discussed in greater detail below (provided such concepts are not mutually inconsistent) are part of the inventive subject matter disclosed herein. In particular, all combinations of claimed subject matter appearing at the end of this disclosure are part of the inventive subject matter disclosed herein. The terminology used herein that also may appear in any disclosure incorporated by reference should be accorded a meaning most consistent with the particular concepts disclosed herein. 
    
    
     
       BRIEF DESCRIPTIONS OF THE DRAWINGS 
       The skilled artisan will understand that the drawings primarily are for illustrative purposes and are not intended to limit the scope of the inventive subject matter described herein. The drawings are not necessarily to scale; in some instances, various aspects of the inventive subject matter disclosed herein may be shown exaggerated or enlarged in the drawings to facilitate an understanding of different features. In the drawings, like reference characters generally refer to like features (e.g., functionally similar and/or structurally similar elements). 
         FIG. 1  illustrates light refraction according to Snell&#39;s Law. 
         FIG. 2A  illustrates a beam steering device having a liquid crystal material with its molecules aligned perpendicular to the device&#39;s optical axis in the absence of an electric field. 
         FIG. 2B  illustrates the beam steering device of  FIG. 2A  upon application of an electric field along the device&#39;s optical axis, with the molecules of the liquid crystal material rotated with respect to the device&#39;s optical axis. 
         FIG. 2C  illustrates the beam steering device of  FIG. 2A  upon application of an electric field along the device&#39;s optical axis with a higher voltage than in  FIG. 2B , with the molecules of the liquid crystal material rotated more with respect to the device&#39;s optical axis. 
         FIG. 3A  shows an inventive beam steering device with an electroactive material whose molecules are aligned with the device&#39;s optical axis in the absence of an electric field. 
         FIG. 3B  illustrates the beam steering device of  FIG. 3A  upon application of an electric field, with the molecules of the liquid crystal material in a second alignment. 
         FIG. 3C  illustrates the beam steering device of  FIG. 3A  upon application of an electric field with a higher voltage than in  FIG. 3B , with the molecules of the liquid crystal material in a third alignment. 
         FIG. 4A  illustrates the beam steering device of  FIG. 3A  in use, with an output beam refracted by a first degree. 
         FIG. 4B  illustrates the beam steering device of  FIG. 3A  in use, with an output beam refracted by a second degree which is greater than the first degree of  FIG. 4A . 
         FIG. 4C  illustrates the beam steering device of  FIG. 3A  in use, with an output beam refracted by a third degree which is greater than the second degree of  FIG. 4A . 
         FIG. 5A  is a perspective view of the beam steering device of  FIG. 4A  with front and back covers removed. 
         FIG. 5B  is a perspective view of the beam steering device of  FIG. 4A  with front and back covers in place. 
         FIG. 6A  illustrates a smart contact lens with a beam steering device like the one shown in  FIGS. 3A-3C . 
         FIG. 6B  is a magnified view of the portion of the smart contact lens of  FIG. 6A  showing the beam steering device. 
     
    
    
     DETAILED DESCRIPTION 
     Light beams can be redirected, or steered, by utilizing materials where the effective birefringence may be changed, resulting in a change in the index of refraction. When light travels through one material and encounters another material of a different index of refraction, its speed changes as it propagates into the other material. If the light exits one material and enters the next material at an angle perpendicular to the overlay between the materials, the light will change speed but not propagation direction. However, if the light enters the second material at an angle with respect the overlay between the materials, the propagation direction of the light will change too. This phenomenon is called refraction and is described by Snell&#39;s Law 
       FIG. 1  illustrates refraction of light at the interface/boundary between two media of different refractive indices n 2  and n 1 , with n 2 &gt;n 1 . Since the velocity in the second medium (v 2 ) is lower than in the first medium (v 1 ), i.e., v 2 &lt;v 1 , the angle of refraction θ 2  is less than the angle of incidence θ 1 . Said another way, the light ray/beam in the higher-index medium is closer to the surface normal. Snell&#39;s law (also known as Snell-Descartes law and the law of refraction) is a formula used to describe the relationship between the angles of incidence and refractive indexes, when referring to light or other waves passing through a boundary between two different isotropic media, such as water, glass, or air. In optics, Snell&#39;s law is used in ray tracing to compute the angles of incidence or refraction, and in experimental optics to find the refractive index of a material. 
     Snell&#39;s law states that the ratio of the sines of the angles of incidence and refraction is equivalent to the ratio of phase velocities in the two media, or equivalent to the reciprocal of the ratio of the indices of refraction: 
     
       
         
           
             
               
                 sin 
                 ⁢ 
                 
                   θ 
                   1 
                 
               
               
                 sin 
                 ⁢ 
                 
                   θ 
                   2 
                 
               
             
             = 
             
               
                 
                   v 
                   1 
                 
                 
                   v 
                   2 
                 
               
               = 
               
                 
                   n 
                   2 
                 
                 
                   n 
                   1 
                 
               
             
           
         
       
     
     with each θ as the angle measured from the normal of the boundary, v as the velocity of light in the respective medium (SI units are meters per second, or m/s), λ as the wavelength of light in the respective medium and n as the refractive index (which is unitless) of the respective medium. 
     In an example inventive beam steering device, two different materials are abutted to one another at an interface/boundary. A light beam, or other electromagnetic beam, encounters this interface at an angle. At least one of the materials is an electroactive material that can change its index of refraction. At one value of the index of refraction of the electroactive material at this interface the beam changes its angle of direction by one amount, while at a second value of an index of refraction the light beam changes its angle of direction by a second amount. If the index of refraction can be changed in discrete steps, then the light beam can be redirected in discrete angles. If the index of refraction can be changed in an analog or continuous manner, then the light beam&#39;s angle can also be changed in an analog/continuous manner. 
     Electroactive materials, for example, liquid crystals (LC), possess the ability to change their index of refraction when the molecules are oriented in certain directions, i.e., they have a variable refractive index. If, for example, a nematic liquid crystal with elongated molecules that are oriented such that the long axis of the molecules is perpendicular to the direction of the light traveling through them, the index of refraction may be 1.7 if the polarization of light is parallel to the long axis of the molecules. If the molecules are then reoriented such that the long axis is parallel to the direction of the light traveling through them, the index of refraction may change to 1.5. 
       FIGS. 2A-2C  illustrate an example beam steering device  200  having substrates  205  placed parallel to each other with a small gap between them that can be less than about 1 μm, from about 1 μm to about 10 μm, greater than 10 μm, including all values and sub-ranges in between. An electrically conductive but optically transmitting material, for example, Indium Tin Oxide (ITO), is coated on the surfaces of the substrates that are facing each other. These electrically conductive layers are sometimes referred to as electrodes or electrode layers  210 . Over the top of these electrodes is a layer of material that causes liquid crystal molecules to align parallel to the surface, or possibly vertically if using a negative dielectric liquid crystal. Negative dielectric liquid crystals are available from Merck in Darmstadt, Germany. Such an alignment surface may be polyimide that has parallel micro-grooves rubbed into its surface or other materials and processes to achieve the same effect, for example, UV-cured alignment materials produced by Rolic of Basel Switzerland, a BASF Company, or polyimides produced by Nissan Chemical of Japan. These surfaces are sometimes referred to as alignment layers  215 . The combination of an electrode/electrode layer and its alignment layer can sometimes be referred to as an overlay. 
       FIG. 2A  illustrates how, when no electric field is applied by a circuit  225  across the electrodes  210 , the anchoring force of the alignment layer  15  causes the LC molecules  220  to align their long axes parallel to the substrates  205  and perpendicular to the optical axis  230  of the beam steering device  200 . In this condition, the index of refraction of the LC material  220  is a first value, for example, n=1.7. 
     In  FIG. 2B , a small electric field is applied by the circuit  225  across the electrodes  210 , causing the long axis of the LC molecules  220  to partially rotate away from the alignment layers  15  and towards the direction of the electric field, which is perpendicular to the substrates  205  and parallel to the optical axis  230  of the beam steering device  200 . When the electric field is of a relatively low value, for example, 0.5 volts, the change-of-rotation force of the alignment layers  215  upon the LC molecules  220  is greater than the force of the electric field, so the LC molecules  220  rotate by a relatively small amount. In this state, the long axes of the LC molecules  220  are aligned more towards the plane of the alignment layer  215  than in the direction of the electric field (i.e., perpendicular to rather than parallel to the substrates  205 ). In this situation, the index of refraction changes by a small amount its total permissible range, for example, it may change from 1.7 to 1.62, generally, an example permissible range in refractive index for any of the beam steering devices disclosed herein can be less than 0.25, from about 0.25 to about 0.40, or greater than 0.40, including all values and sub-ranges in between. 
     In  FIG. 2C , a higher voltage than that applied in  FIG. 2B  is applied by the circuit  225 , which creates a higher rotational force on the LC molecules  220  than the force being applied by the alignment layers  215 . As a result, the long axes of the LC molecules  220  align themselves relatively more with the direction of the electric field, and parallel to the optical axis  230 , than with the plane(s) of the alignment layers  215 . In this situation, the index of refraction changes/reduces further, for example, it may change to 1.55. When the electric field is returned to a lower voltage, or zero voltage, the anchoring force of the alignment layers  215  returns the LC molecules  220  to their initial state of orientation shown in  FIG. 2A . 
     The rate/speed of changing the orientation of the LC molecules from one where they are substantially parallel to the plane(s) of the alignment layers to substantially parallel to the direction of the electric field can be influenced by the level of the voltage applied. If a higher-than-required electric field is applied, i.e., higher than required to rotate the LC molecules to a maximum permissible degree of rotation, the rotation is faster than if the minimum-required voltage is applied for attaining the maximum permissible degree of rotation. Generally, the minimum-required voltage can be a voltage required for affecting rotation of the LC molecules, and can be from about 0.5 V to about 3 V. In some cases, the minimum-required voltage can be lower than 0.5 V, or can be higher than 3 V (e.g., 40 V or more), such as is the case for some LC materials. 
     For example, if a beam steering device requires 5 V to fully rotate the LC Molecules to their maximum permissible orientation (e.g., 90 degrees) with the electric field, the time to rotate from the alignment layer orientation to the electric field orientation may be, for example, 300 ms. However, if 10 V (i.e., greater than the minimum-required voltage of 5 V) were applied, the time to rotate will be lower, for example, as low as 100 ms. If 20 volts were applied, the time to rotate would be even lower. 
     In another example, if the voltage required to rotate the LC material from the alignment-layer orientation to midway between the two states (i.e., between alignment-layer orientation and electric-field orientation, as illustrated in  FIG. 2B ) is 2.3 V, and 2.3 V is applied, it may take, for example, 250 ms to complete this rotation. However, if a higher voltage is applied, such as 5 V, it may traverse this rotation in 100 ms. To take advantage of this response without rotating the LC molecules farther than desired, 5 V may be applied for 100 ms as the “speed” voltage, then switched to 2.3 V as the “holding voltage.” These “speed up” methods/approaches are sometimes known as overdriving the LC material to attain a desired orientation. Despite overdriving, the speed at which the LC material returns towards its orientation with the plane of the alignment layer can be slow because the anchoring force of the alignment layer is weaker than the electric energy, and due to the elastic constants (e.g., the elastic modulus) of the LC material. For example, the molecules of a stiffer or more viscous material with a higher elastic modulus will likely be slower in changing their orientation to be with that of the alignment layer than one with a lower elastic modulus. The result is that the speed of switching the lens from the OFF position (i.e., when the LC material is aligned with the plane of the alignment layer) to an ON position (i.e., when the LC material is at least partially aligned with the direction of the electric field) may be increased by overdriving, but the speed of switching from ON to OFF cannot be increased in the beam steering device  200  by overdriving because the only force that reorients the LC material is the relatively weak force exerted by the alignment layer. 
     Beam Steering Devices 
     Disclosed herein are beam steering devices that can speed up the change in orientation of the liquid crystal molecules (and generally, any electroactive material that may be employed) when the orientation of the liquid crystal molecules is being adjusted in both directions. To accomplish this, two additional, similar substrates are attached to two substrates like those in  FIGS. 2A-2C  to form an LC cavity with a trapezoidal cross section, where the parallel sides are parallel to the device&#39;s optical axis. The alignment layer is optional for these additional substrates. One of the facets/substrates is not parallel to its opposite substrate and is instead at an angle or tilted with respect to it by, for example, less than about 1 degree, between about 1 degree and about 60 degrees, greater than 60 degrees, including all values and sub-ranges in between. The substrates can be assembled such that their respective electrode layers are electrically insulated from each other. 
       FIGS. 3A-3C  illustrate a beam steering device  300  that includes a first overlay  330 , a second overlay  335 , a third overlay  340 , and a fourth overlay  345  are shown. Each overlay may be coupled to a substrate, and may include an electrode layer  360  (e.g., composed of an electrically conductive and preferably optically transparent coating, such ITO, silver nanowires, PEDOT (poly(3,4-ethylenedioxythiophene), etc.) and an optional alignment layer  355  (e.g., composed of rubbed polyimide, though any suitable material capable of affecting the alignment of the electroactive material can be employed) as described for  FIGS. 2A-2C . An alignment layer on one or more of the overlays  330 ,  335 ,  340  and  345  aligns the liquid crystal material when the beam steering device  300  is in an unpowered state (i.e., when there is no electric field) and reduces discontinuities in the electroactive molecule/material arrangement. 
     The substrate(s) that couple to the overlays  330 ,  334 ,  340 ,  345  can be a singular, continuous substrate or composed of multiple, discontinuous substrates; each of these possible substrate layouts is sometimes collectively referred to as a ‘substrate’ as well. Such a substrate can also include any additional components (not shown), made of the same or different material from the substrate, needed or desired to form a sealed internal cavity  370  for holding an electroactive material. For example, the substrate can encompass or be coupled to the seals  350  that may be placed at each of the four corners of the device  300  to electrically isolate the electrode layers of the overlays  330 ,  335 ,  340  and  345  from each other, and to seal the cavity inside the device  300  for the electroactive material  365 , such as a liquid crystal material. Each substrate itself can have a characteristic, fixed refractive index (e.g., from about 1.3 to about 2.5, including all values and sub-ranges in between), and be composed of materials such as Glass, PMMA (polymethyl methacrylate), a polycarbonate, quartz, fused silica, and combinations thereof. An example electroactive material within the cavity is a liquid crystal (e.g., Merck MLC-2140). 
     As shown in  FIG. 3A , each overlay defines a plane, such that the first overlay  330  defines a plane P 1 , the second overlay  335  defines a plane P 2 , the third overlay  340  defines a plane P 3 , and the first overlay  345  defines a plane P 4 . As illustrated, the plane P 4  of the fourth overlay  345  is not parallel to, and is tilted with respect to, the plane P 3  of its opposite overlay  340 . On the other hand, the plane P 1  of the first overlay  330  is substantially parallel to the plane P 2  of its opposite overlay  335 . As also illustrated in  FIG. 3A , the device  300  can define an optical axis  375  with respect to which the orientation of the electroactive material can be measured. 
     During example use of the beam steering device  300 , an electric field may be applied between any set of opposing overlays (e.g., the overlays  330 ,  335 ) to induce liquid crystal rotation at a fast speed by utilizing the overdriving method. Then that electric field may be removed and another electric field may be applied to the other two opposing overlays (e.g., the overlays  340 ,  345 ), causing the liquid crystal to align along the axis of the new electric field. This can be accomplished, for example, by using a single electric source, the output of which is switched to affect generation of one electric field or the other. In some cases, two sources can be used such that both electric fields are generated/present at the same time. 
     In the configuration of the device  300 , overdriving can be applied in two different directions (i.e., between both sets of overlays), allowing faster rotation changes in both directions as compared to the device  200  of  FIGS. 2A-2C , where it is available in only one direction. The two electric fields can be present as one at any given time, in both directions simultaneously, or in a temporally overlapping manner. The two electric fields can be generated using a single source, or with a different source for each electric field. 
     If both electric fields are substantially equal to each other in amplitude, the liquid crystal molecules can be held at an interim rotation within their total available/permissible rotation. If one electric field is greater than the other, the liquid crystal molecules will rotate and align to a greater degree in the direction of the stronger electric field. If one electric field is slightly greater than the other, the alignment direction will be slightly more along the direction of the stronger electric field. As the stronger electric field is increased in strength relative to the weaker electric field, more rotation toward the stronger electric field occurs. By varying the relative strengths of the electric field in an analog fashion, rotation of the liquid crystal may be adjusted also in an analog fashion. Overdriving may also be used in the above described analog control, where a brief, larger-than-required voltage is applied. 
     If there is a homogenous alignment layer formed on overlays  330  and  335 , the liquid crystal material  365  will align as shown in  FIG. 3A , parallel to the planes P 1 , P 2  of the overlays  330 ,  335 , and along the optical axis  375 . If an electric field is now applied between the overlays  340 ,  345 , then the liquid crystal molecules  365  will still align in the same direction, but the electric field will be in addition to the alignment forces provided by the alignment layer of overlays  330 ,  335 . If the alignment layer is not present on overlays  330 ,  335 , the electric field between the overlays  340 ,  345  would perform the alignment, however some discontinuities may present themselves. In the orientation of the material  365  shown in  FIG. 3A , the index of refraction of the material  365  experienced by light traveling from left to right (i.e., from the overlay  340  to the overlay  345 ) is at a minimum for the material  365  if polarized appropriately, and the index of refraction of the material  365  to the same light traveling from top to bottom (i.e., between the overlays  330 ,  335 ) is at its maximum. 
       FIG. 3B  illustrates that the electric field between the overlays  340 ,  345  is removed, while an electric field strong enough to cause full rotation of the material  365  is applied across the overlays  330 ,  335 , causing the molecules to align parallel to the plane P 3  of the overlay  340 . The index of refraction of the liquid crystal to light traveling from left to right (i.e., from the overlay  340  to the overlay  345 ) is now at its maximum if polarized appropriately, while the index of refraction to the same light traveling from top to bottom (i.e., between the overlays  330 ,  335 ) in the figure would be at its minimum. 
       FIG. 3C  illustrates that the electric field between the overlays  340 ,  345  is removed, while an electric field strong enough to cause half rotation of the material  365  is applied across the overlays  330 ,  335 , causing the molecules of the material  365  to align halfway between being vertically and horizontally aligned, i.e., tilted between the angles of planes P 1 , P 3 .  FIG. 3C  is, however, also illustrative of the state of the molecules of the material  365  when the field between the overlays  340 ,  345  as well as the field between the overlays  330 ,  335  is present, and interact to align the molecules as illustrated. The index of refraction of the liquid crystal experienced by light traveling both horizontally (i.e., from the overlay  340  to the overlay  345 ) and vertically (i.e., between the overlays  330 ,  335 ) is approximately equal. As illustrated in  FIG. 3B , a combination of a power source  380  and a controller  385  can be used for generating and controlling application of the electric fields. The controller can be any suitable processing device configured to run and/or execute a set of instructions or code associated with operating the beam steering device  300 . The controller can be, for example, a general purpose processor, a Field Programmable Gate Array (FPGA), an Application Specific Integrated Circuit (ASIC), a Digital Signal Processor (DSP), and/or the like. 
       FIGS. 4A-4C  illustrate how variable beam steering can be accomplished with a beam steering device  400  that can be structurally and/or functionally similar to the device  300 . In FIG.  4 A, the electric field is in the same condition/state as described in  FIG. 3A , applied between overlays  440 ,  445 . The index of refraction of the electroactive material (e.g., liquid crystal) inside of chamber/cavity  420  is equal to the index of refraction at the overlay  440  (which is essentially the same as the refractive index of the underlying substrate) for the incident light beam  480 . The light beam  480  can be coupled into the overlay  440  in any suitable manner, including free-space coupling and the use of coupling optics such as optical fibers. Light beam  480  enters into, or is incident on, the overlay  440  perpendicular to its surface, so even though the index of refraction of the medium (typically air with an index of 1) outside of overlay  440  is less than the index of refraction at the overlay  440 , no refraction of light occurs because the angle of incidence of the light onto the substrate is perpendicular. The light beam  480  can include one or more wavelengths, including visible wavelengths (e.g., from about 400 nm to about 700 nm, including all values and sub-ranges in between), UV wavelengths (e.g., from 10 nm to about 400 nm, including all values and sub-ranges in between), and IR wavelengths (e.g., from 800 nm to about 1 mm, including all values and sub-ranges in between). 
     The light beam  480  then travels through overlay  440  and enters the liquid crystal within cavity  420 . Because the light beam  480  is still perpendicular to the interface between the liquid crystal within the cavity  420  and the overlay  440 , no refraction takes place, regardless of the index of refraction of the liquid crystal. Light beam  480  travels through the liquid crystal within cavity  420  and enters the overlay  445 . Although the overlay  445  is at a non-perpendicular angle of incidence to light beam  480  (i.e., is tilted at a tilt angle α 1  with respect to the overlay  440  as illustrated), no refraction occurs because the index of refraction of the liquid crystal and the overlay  445  are equal. When light beam  80  exits the overlay  445 , it encounters a different index of refraction (e.g., air again), so the angle between the exit surface of the overlay  445  and the light beam causes the light beam to be refracted at an angle  495 . Input/incident light beam  480  is thus redirected into output light beam  490 . Angle  495 , sometimes referred to as the angle of refraction, is relatively small compared to those illustrated in  FIGS. 4B and 4C , described further below. 
     In  FIG. 4B , the electric field is in the same condition/state as described in  FIG. 3B , applied between overlays  430 ,  435 . The electric field applied is not sufficient to fully align the liquid crystal molecules to the electric field, and only partial rotation occurs. The index of refraction of the liquid crystal inside of chamber/cavity  320  is now higher than the index of refraction at the overlay  440  for the light beam  480 . The light beam  480  enters into the overlay  440  perpendicular to its surface, so even though the index of refraction of the medium outside of the overlay  440  is less than the index of refraction at the overlay  440 , no refraction of light occurs because the angle of incidence of the light onto the overlay  440  is perpendicular. The incident/input light beam  480  then travels through the overlay  440  and enters the liquid crystal within cavity  420 . Because it is still perpendicular to the overlay between the liquid crystal within the cavity  420  and the overlay  440 , no refraction takes place, regardless of the index of refraction of the liquid crystal. Light beam  80  travels through the liquid crystal within the cavity  420  and enters the overlay  445 . The overlay  445  is at a non-perpendicular angle to the direction of light beam  480 , and the index of refraction of the liquid crystal within cavity  420  is now higher than that of the overlay  445 , resulting in refraction of the light upward at the interface between the liquid crystal and the overlay  445 . When the light beam  480  exits the overlay  445 , it again encounters a different index of refraction of the new medium it enters (e.g., air), so the angle between the exit surface of the overlay  445  and the light beam  480  causes the light beam to be refracted further by an angle  405 . Light beam  480  is thus redirected into light beam  425 . Angle  405  is larger than angle  495  in  FIG. 4A  because angle  405  is now the sum of the change in propagation from refraction of light that occurred at the liquid crystal—to—overlay  445  boundary, plus the refraction of light that occurred at the overlay  445 —to—exit medium boundary, whereas the refraction of the light in  FIG. 4A  occurred only at the overlay  445 —to—exit medium boundary. 
     In  FIG. 4C , the electric field is in the same condition/state as described in  FIG. 3C , applied to the overlays  430 ,  435 . The electric field applied between the overlays  430 ,  435  is now stronger than the same field applied in  FIG. 4B , and is sufficient in strength to fully align the liquid crystal molecules with that electric field. The index of refraction of the liquid crystal inside of chamber/cavity  420  is now even higher than the index of refraction in the condition described in  FIG. 4B , and also higher than the overlay  430  for the incident/input light beam  480 . Light beam  480  enters into overlay  440  perpendicular to its surface, so even though the index of refraction of the medium outside of overlay  440  is less than the index of refraction at the overlay  440 , no refraction of the light occurs because the angle of incidence of the light onto the substrate is perpendicular. The light beam  480  then travels through overlay  440  and enters the liquid crystal within the cavity  420 . Because the light beam  480  is still perpendicular to the boundary between the liquid crystal within the cavity  120  and overlay  440 , no refraction takes place, regardless of the index of refraction of the liquid crystal. The light beam  480  travels through the liquid crystal within the cavity  420  and enters the overlay  445 . The substrate  445  is at an angle to the direction of the light beam  480 , and the index of refraction of the liquid crystal within the cavity  420  is now much higher than that of overlay  445 , resulting in refraction of the light at the boundary between the liquid crystal and the overlay  445 . Due to the higher different in refractive index between the two materials, there is more refraction than that seen in  FIG. 4B . When the light beam  480  exits the overlay  445 , it again encounters a different index of refraction of the new medium it enters, so the angle between the exit surface of the overlay  445  and the light beam causes the light beam to deflect at an angle  415 . The input light beam  480  is thus redirected/steered into output light beam  410 . Angle  115  is larger than angle  105  in  FIG. 7B  because angle  115  is now the sum of a greater amount of the refraction of light that occurred at the liquid crystal-to-overlay, plus the refraction of light that occurred at the substrate-to-exit medium interface. 
       FIGS. 4A-4C  illustrate three discrete settings that result in three different values of refractive index for the liquid crystal material, resulting in three discrete angles of refraction of the output beam. However, the electric field applied to either set of overlays can be changed in an analog and continuous manner, resulting in an analog change in the amount of output beam steering that can be done. For example, one or both of the electric fields applied between the pairs of overlays can be swept such that the refractive index varies between a minimum or lower value to a maximum or higher value. The corresponding change in refractive index can be linear or non-linear. Further, the overdrive method described above can also be employed for any of the electric fields described in  FIGS. 4A-4C , resulting in much faster light beam angle changing/beam steering than could be accomplished without using the overdrive method. 
       FIGS. 5A and 5B  illustrate a 3D perspective view of a beam steering device  500  (which can be structurally and/or functionally similar to the devices  300 ,  400 ) formed as a 3D right trapezoid. The device  500  includes overlays  530 ,  535  with planes that are parallel to each other, and an overlay  545  having a plane that is tilted with respect to that of its opposing overlay  540 . During use, the overlay  545  received an incident light beam, while the overlay  545  outputs an output light beam as explained with respect to  FIGS. 3A-3C, 4A-4C . The interior of the device  500  defines a cavity  570  for holding the electroactive material. As illustrated in  FIG. 5B , covers  580  may be placed at either end of the device  500  to seal the cavity  570 , and at least one of the covers  580  may be removable. The distance between the overlays  530 ,  535 , the distance between the overlays  540 ,  545 , and/or the distance between the covers  580 , can independently be from about 1 μm to about 15 μm, including all values and sub-ranges in between. The switching speed for changing the degree of refraction for any of the beam steering devices  300 ,  400 ,  500  can be from about 1 μs to about 5 ms, including all values and sub-ranges in between. 
     As an example of comparative switching speeds, the beam steering device  200  in  FIGS. 2A-2C  may be able to change the orientation of the LC molecules  220  from alignment layer-orientation ( FIG. 2A ) to electric field-orientation ( FIG. 2C ) in 10 ms in overdrive. However, it takes 50 ms, upon removal of the electric field, for the LC molecules  220  to change their orientation from electric field-orientation ( FIG. 2C ) back to alignment layer-orientation ( FIG. 2A ). In contrast, the beam steering device  300  in  FIGS. 3A-3C  may be able to change the orientation of the LC molecules  365  from alignment layer-orientation ( FIG. 3A ) to electric field-orientation ( FIG. 3C ) in 10 ms in overdrive, similar to the device  200 . However, upon removal of one electric field and application of the other (i.e., between the other pair of interfaces), the LC molecules  365  now change their orientation from electric field-orientation ( FIG. 3C ) back to alignment layer-orientation ( FIG. 3A ) more quickly, and at a similar rate due to the application of another field. So this change of orientation back to the alignment layer-orientation can also occur in about 10 ms in overdrive mode for the device  300 . 
     Applications 
     An example application of such beam steering devices is for multi-axis scanning (e.g., 2D/XY, or 3D, or generally nD scanning), which can find use in various applications that would benefit from the improved beam steering speeds achieved with these devices. In such applications, two or more of these beam steering devices can be used in series/in a cascade, with a first beam steering device receiving the initial input light beam and outputting an output light beam for consumption by the next beam steering device, and so on. Each beam steering device can refract its input light beam along a different axis that each other beam steering device. For example, a first beam steering device in the cascade can receive the input light beam and output light beam as refracted along (say) an X-axis. A second beam steering device is positioned to receive this output light beam as orthogonal to its surface and refract it along (say) a Y-axis. A third beam steering device is positioned to receive this output light beam from the second beam steering device as orthogonal to its surface and refract it along (say) a Z-axis. The resulting output beam then can have specific XYZ addressability that is independently controllable for each axis. 
     Another example application of such beam steering devices is for multi-stage beam steering, such as for, for example, in an optical demultiplexing approach. A first stage can include a first beam steering device that can be operated to receive an incident light beam and output it as an output light beam (i.e., by selectively changing the refractive index of the electroactive material of the first beam steering device) that is refracted by discrete, predetermined amounts. For each degree of refraction that the output light beam can attain, the output light beam is coupled into a different beam steering device of a second stage, which can in turn be operated in any suitable manner depending on the application (e.g., to discard the light beam, to couple it to additional downstream optical components, etc.). 
     Yet another example application or use of such a beam steering device can be as a component in eyewear for generated virtual images. For example, such beam steering devices may be useful in smart contact lens, spectacle glasses, or head-mounted displays, to project a scanned image into the eye, such as in mixed or augmented reality (AR). AR devices create a virtual image that a user sees in addition to what is seen in the real world. Conventional AR devices typically include a small display screen in conjunction with reflectors or mirrors to relay the image to the eye. Adding such display screens to spectacle frames adds bulk and weight to the frames, while adding such display screens to contact lenses is impossible. The present device replaces the display screen and overcome these limitations. 
     In the case of using the present technology in a smart contact lens, the beam steering device can be fabricated such that the overall thickness (e.g., the distance between the overlays  540 ,  545  in  FIGS. 5A-5B ) can be less than the thickness of the contact lens, which is typically about 0.1 mm thick. This device could include the light source, beam steering device, and any collimating optics either as a single stack in line with the optical axis of the eye, or with the use of mirrors if it is desired that some components be thicker and would cause the overall device to be thicker than required. For example, the light source could project the light “sideways” or perpendicular to the eye&#39;s optical axis on the user&#39;s retina, then be redirected along the eye&#39;s optical axis and into the beam steering device. Any or all the components could be arranged perpendicular to the eye&#39;s optical axis, then redirected to the eye&#39;s optical axis with a mirror or reflecting component. 
       FIGS. 6A-6B  illustrate example use of such a beam steering device within a smart contact lens  600 , though it is readily applicable to any suitable eyewear, such as any kind of lens (e.g., an intra-ocular lens), spectacles, and head-mounted displays to either project the beam directly into the eye, or project the beam onto a surface outside of the eye to paint/display the image. Here, the lens  655 , in which a light source  670  and beam steering device  665  (which can be structurally and/or functionally similar to the devices  300 ,  400 ,  500 ) are embedded, coupled to, and/or formed as a stack  665  embedded at location  650 . The light source  670  can be configured, with or without coupling optics, to generate a light signal as a spot (e.g., of image or video data) for projection on the retina  660  of the user. The light signal can be generated, for example, based on data received from a remote source, such as via an antenna coil or other network interfaces that is embedded or coupled to the lens  655 . A combination of a power source and a controller, either of which may be embedded in or coupled to the lens  655 , can be used for controlling operation of the source  670  and the beam steering device  665 , and particularly for controlling generation of the light signal based on the received data. In addition to the beam steering device being controlled by the controller to steer the beam, the controller could also switch the light source on and off so as to create individual points of light rather than continuous lines being painted. For clarity, one beam steering device is illustrated, but two or more can be stacked in sequence as described above. 
     Then the beam steering device  665  can receive the light signal from the source  670  directly or via coupling optics and steer/scan the spot around to paint an image, or to render a video, on the retina  660 , as described for  FIGS. 3A-3C, 4A-4C , and similar to how CRT television tubes painted an image onto a phosphorous screen. As described above, more than one beam steering device  665  can be employed to accomplish 2D scanning of the image/video onto the retina  660 . The orientation of the tilted surfaces can be positioned such that one device would steer the beam in one direction while the other device steers the beam in the other direction, and can be generally orthogonal to each other. The power source and the controller can control generation of the electric fields of the beam steering device  665  for manipulating the refractive index of the electroactive material within the beam steering device  665 . 
     CONCLUSION 
     While various inventive embodiments have been described and illustrated herein, those of ordinary skill in the art will readily envision a variety of other means and/or structures for performing the function and/or obtaining the results and/or one or more of the advantages described herein, and each of such variations and/or modifications is deemed to be within the scope of the inventive embodiments described herein. More generally, those skilled in the art will readily appreciate that all parameters, dimensions, materials, and configurations described herein are meant to be exemplary and that the actual parameters, dimensions, materials, and/or configurations will depend upon the specific application or applications for which the inventive teachings is/are used. Those skilled in the art will recognize, or be able to ascertain using no more than routine experimentation, many equivalents to the specific inventive embodiments described herein. It is, therefore, to be understood that the foregoing embodiments are presented by way of example only and that, within the scope of the appended claims and equivalents thereto, inventive embodiments may be practiced otherwise than as specifically described and claimed. Inventive embodiments of the present disclosure are directed to each individual feature, system, article, material, kit, and/or method described herein. In addition, any combination of two or more such features, systems, articles, materials, kits, and/or methods, if such features, systems, articles, materials, kits, and/or methods are not mutually inconsistent, is included within the inventive scope of the present disclosure. 
     Also, various inventive concepts may be embodied as one or more methods, of which an example has been provided. The acts performed as part of the method may be ordered in any suitable way. Accordingly, embodiments may be constructed in which acts are performed in an order different than illustrated, which may include performing some acts simultaneously, even though shown as sequential acts in illustrative embodiments. 
     All definitions, as defined and used herein, should be understood to control over dictionary definitions, definitions in documents incorporated by reference, and/or ordinary meanings of the defined terms. 
     The indefinite articles “a” and “an,” as used herein in the specification and in the claims, unless clearly indicated to the contrary, should be understood to mean “at least one.” 
     The phrase “and/or,” as used herein in the specification and in the claims, should be understood to mean “either or both” of the elements so conjoined, i.e., elements that are conjunctively present in some cases and disjunctively present in other cases. Multiple elements listed with “and/or” should be construed in the same fashion, i.e., “one or more” of the elements so conjoined. Other elements may optionally be present other than the elements specifically identified by the “and/or” clause, whether related or unrelated to those elements specifically identified. Thus, as a non-limiting example, a reference to “A and/or B”, when used in conjunction with open-ended language such as “comprising” can refer, in one embodiment, to A only (optionally including elements other than B); in another embodiment, to B only (optionally including elements other than A); in yet another embodiment, to both A and B (optionally including other elements); etc. 
     As used herein in the specification and in the claims, “or” should be understood to have the same meaning as “and/or” as defined above. For example, when separating items in a list, “or” or “and/or” shall be interpreted as being inclusive, i.e., the inclusion of at least one, but also including more than one, of a number or list of elements, and, optionally, additional unlisted items. Only terms clearly indicated to the contrary, such as “only one of” or “exactly one of,” or, when used in the claims, “consisting of,” will refer to the inclusion of exactly one element of a number or list of elements. In general, the term “or” as used herein shall only be interpreted as indicating exclusive alternatives (i.e. “one or the other but not both”) when preceded by terms of exclusivity, such as “either,” “one of,” “only one of,” or “exactly one of.” “Consisting essentially of,” when used in the claims, shall have its ordinary meaning as used in the field of patent law. 
     As used herein in the specification and in the claims, the phrase “at least one,” in reference to a list of one or more elements, should be understood to mean at least one element selected from any one or more of the elements in the list of elements, but not necessarily including at least one of each and every element specifically listed within the list of elements and not excluding any combinations of elements in the list of elements. This definition also allows that elements may optionally be present other than the elements specifically identified within the list of elements to which the phrase “at least one” refers, whether related or unrelated to those elements specifically identified. Thus, as a non-limiting example, “at least one of A and B” (or, equivalently, “at least one of A or B,” or, equivalently “at least one of A and/or B”) can refer, in one embodiment, to at least one, optionally including more than one, A, with no B present (and optionally including elements other than B); in another embodiment, to at least one, optionally including more than one, B, with no A present (and optionally including elements other than A); in yet another embodiment, to at least one, optionally including more than one, A, and at least one, optionally including more than one, B (and optionally including other elements); etc. 
     In the claims, as well as in the specification above, all transitional phrases such as “comprising,” “including,” “carrying,” “having,” “containing,” “involving,” “holding,” “composed of,” and the like are to be understood to be open-ended, i.e., to mean including but not limited to. Only the transitional phrases “consisting of” and “consisting essentially of” shall be closed or semi-closed transitional phrases, respectively, as set forth in the United States Patent Office Manual of Patent Examining Procedures, Section 2111.03.