Liquid Crystal Devices

Abstract

The liquid crystal device (400) comprises a liquid crystal layer having a thickness, the liquid crystal layer including a liquid crystal material and a plurality of polymer structures (414a, 414b) including polymerized liquid crystal material. Each polymer structure (414a, 414b) is disposed at a different depth in the thickness of the liquid crystal layer. Electrodes are provided that are configured to apply an electric field to the liquid crystal layer. Each polymer structure (414a, 414b) has a different selected locked-in liquid crystal state.

Description

[Technical field]

[0001] The present invention relates to liquid crystal devices, and in particular, but not exclusively, to liquid crystal devices and methods for manipulating the spatial distribution of light. [Background technology]

[0002] A diffractive optical element (DOE) is an optical component designed to manipulate the spatial distribution of light. DOEs range from simple gratings that split a light beam into multiple diffracted light beams, to computer generated holograms (CGHs) that diffract light into recognizable images. Applications of DOEs span numerous industries and include holographic displays, augmented reality (AR) and virtual reality (VR), spectroscopy, aberration correction, beam steering, beam shaping, and 3D depth sensing.

[0003] Due to a combination of high birefringence and sensitivity to external electric fields, liquid crystals (LCs) have found use as switchable optical materials in spatial light modulators and single-pixel DOEs.

[0004] Liquid Crystal on Silicon (LCOS) SLMs allow the switching of arbitrary pixelated DOE designs with switching speeds of a few milliseconds. However, these pixelated devices are complex and require CMOS backplane electronics to drive the individual pixels of the LC layer.

[0005] For many tasks, it is more convenient to use single-pixel LC-DOEs. However, conventional single-pixel devices have simple device architectures and offer significantly less flexibility than SLMs, typically only allowing switching between an off state and a single on state. The earliest implementations of such optical elements employed a variety of conventional lithographic methods to pattern surface relief structures into standard negative photoresists, which were then converted into active devices by adding a layer of refractive index-matched liquid crystal material. However, the fabrication of useful devices using this principle is limited by the complex, multi-step fabrication process required. Furthermore, challenges exist in controlling the alignment of LC on the fabricated polymer structures, with undesirable defects impeding device performance.

[0006] One on / off switchable LC-DOE technology is holographic polymer dispersed LC (H-PDLC), which is formed by exposing a device containing a mixture of LC and photosensitive isotropic monomers to a UV interference pattern. A major drawback of H-PDLC is that compared to bulk LC, a large electric field (15-20 V / μm) is required to switch off the diffraction due to the confinement of LC into droplets with micrometer or nanometer sizes.

[0007] In response, a variation of H-PDLC called POLICRYPS (Polymer Liquid CRYstal Polymer Slices) was developed by Caputa et al., which switches with an external electric field of only a few V / μm and provides high diffraction efficiency. The interference lithography fabrication process for H-PDLC / POLICRYPS is flexible and fast, but is limited to producing gratings that are on (i.e., produce a diffraction pattern) in the absence of an applied electric field. For some optical applications, including AR / VR, it is desirable to use gratings that consume no power in the off state and are therefore hidden and operate in a reversed mode (non-diffracting at 0 V by default). The H-PDLC / POLICRYPS technology is currently unable to provide a solution for such applications.

[0008] Previously reported reversed-mode LC-DOEs have been fabricated using interference of a UV laser to generate modulated intensity patterns that are encoded directly into devices containing UV-sensitive polymerizable LC / reactive mesogen mixtures. After fabrication, application of a voltage to these devices reorients the LCs in the unpolymerized channels, creating a refractive index mismatch between the polymer structure and the LC, resulting in diffraction. However, employing such holographic interference fabrication methods limits grating designs to simple periodic structures. Within these constraints, the most complex LC-DOEs thus created are two-dimensional (2D) hexagonal lattices of micropillars.

[0009] The present invention has been devised in consideration of the above. Summary of the Invention [Means for solving the problem]

[0010] According to a first aspect of the present invention, there is provided a liquid crystal device. The liquid crystal device may comprise a liquid crystal layer having a thickness. The liquid crystal layer may comprise a liquid crystal material. The liquid crystal layer may also comprise a plurality of polymer structures comprising polymerized liquid crystal material. Each polymer structure may be provided at a different depth in the thickness of the liquid crystal layer. The liquid crystal device may also comprise electrodes configured to apply an electric field to the liquid crystal layer.

[0011] The depth of the polymer structure may be the depth of the center of gravity of the volume of the polymer structure. Each polymer structure may be formed within or comprise a separate or distinct sublayer of the liquid crystal layer, for example, through the thickness of the liquid crystal layer.

[0012] Writing multiple polymer structures into a single liquid crystal device can enhance the functionality and utility of the device. The device may be switchable between multiple different active states, rather than simply on and off. Each polymer structure may provide or correspond to a distinct active state. Additionally or alternatively, multiple polymer structures can work in conjunction with each other to tune or control the spatial phase modulation of light incident on the device.

[0013] This increased functionality can be controlled simply by increasing or decreasing the voltage applied to or across the device, rather than using complex backplane electronics typically required with switchable SLMs. This functionality can provide a compromise between fully programmable SLM devices and fixed optical elements, and can be employed in a wide range of applications. The device can also support multiple modes of operation, such as conventional mode operation (optically active by default with no applied voltage) and reversed mode operation (optically inactive with no applied voltage).

[0014] At least two of the polymer structures may at least partially spatially overlap one another in a direction extending through the thickness of the liquid crystal layer.

[0015] Two or more polymer structures may have different selected locked-in liquid crystal states. Optionally, each polymer structure may have a different selected locked-in liquid crystal state. Alternatively, two or more polymer structures may have the same locked-in liquid crystal state.

[0016] The polymer structures can be disposed at different depths in the thickness of the liquid crystal composition to provide device functionality without increasing the footprint of the device, which can be reduced or minimized if two or more of the polymer structures at least partially overlap each other in a direction extending through the thickness of the liquid crystal layer.

[0017] Each polymer structure can be configured to provide a different spatial phase modulation of light incident on the device, thereby increasing the number of different (e.g., distinct) optical states or functions provided by the device. Additionally or alternatively, the spatial phase modulations provided by two or more polymer structures can operate together to provide a single optical state or function.

[0018] The electrodes may be configured to apply an electric field across at least a portion of the liquid crystal layer. The electrodes may include a first electrode and a second electrode configured to apply an electric field across a thickness of the liquid crystal layer.

[0019] The electrodes are operable to apply a substantially uniform electric field.

[0020] At least one of the electrodes may include a plurality of individually addressable electrode elements, each of which may be configured to apply an electric field across a different portion of the liquid crystal layer. At least one of the electrodes may include a patterned electrode or may include an electrode array. The patterned electrode array or electrode array may be or include a plurality of concentric rings.

[0021] Each of the various liquid crystal states of the polymer structure may correspond to a state of the liquid crystal material at a different predetermined electric field strength.

[0022] At least one of the polymer structures may include multiple domains of polymerized liquid crystal material.

[0023] At least one of the polymer structures may be or include a diffractive optical element. Two or more of the polymer structures may work in combination with one another to function as a single diffractive optical element.

[0024] At least one of the polymer structures may be or may include a diffractive optical element. At least one diffraction grating may be configured to generate a hexagonal diffraction pattern. At least one diffraction grating may be or may include a triangular mesh. Additionally or alternatively, at least one diffraction grating may be configured to generate a one-dimensional (1-D) diffraction pattern. At least one diffraction grating may be or may include a plurality of posts or walls.

[0025] At least one of the polymer structures may be or include a hologram.

[0026] The polymer structure may be or include multiple stacked layers or sub-layers through the thickness of the liquid crystal device. One or more layers may be or include a substantially continuous layer. Additionally or alternatively, one or more layers may be or include a discontinuous layer. Two or more layers may be in substantially direct contact with each other. The polymer structure may be or include multiple stacked disks. Alternatively, the polymer structure may be or include multiple concentric rings. Each ring may have or include a different height or thickness.

[0027] The liquid crystal device may further comprise a first substrate and a second substrate. At least one of the polymer structures may be coupled or anchored to the first substrate or the second substrate. The plurality of polymer structures may include a first polymer structure coupled or anchored to the first substrate and a second polymer structure coupled or anchored to the second substrate. The first polymer structure may be at a first depth and the second polymer structure may be at a different second depth. Alternatively or additionally, one or more polymer structures may be at least partially coupled or anchored to one or more of the other polymer structures.

[0028] According to a second aspect, there is provided an optical aberration correction device comprising a liquid crystal device according to the first aspect. This allows switching between different (e.g. distinguishable) phase profiles, e.g. to correct various aberration modes. Its operation can be controlled by increasing or decreasing an applied voltage to switch between various phase profiles, allowing significantly easier control than conventional devices, such as SLMs. Additionally or alternatively, it allows variable control of the magnitude of the phase modulation provided by the phase profile, e.g. to correct one or more aberration modes. Furthermore, its operation can be controlled by increasing or decreasing an applied voltage to adjust the magnitude of the phase modulation provided by the phase profile.

[0029] According to a third aspect, there is provided an optical device comprising the apparatus of aspect 2. The optical device may be a lens, a microscope, a telescope, binoculars, or any suitable optical device.

[0030] According to a fourth aspect, there is provided a distance sensing and / or depth mapping device comprising a liquid crystal device according to the first aspect.

[0031] Each of the polymer structures can be configured to create a different structured light illumination pattern. Many applications using distance sensing and / or depth mapping techniques require significant miniaturization of the devices and have stringent power consumption requirements. Thus, the combination of multiple optical functions in the switchable liquid crystal devices of the present disclosure can provide devices with multiple selectable active states within a compact device structure with a reduced footprint.

[0032] According to a fifth aspect, there is provided a holographic display device comprising the liquid crystal device of the first aspect. Stacked or cascaded holograms have been used for applications including multiplexed information display, color images, and multi-wavelength optical interconnects. Furthermore, stacked holograms are employed to improve image resolution and diffraction efficiency compared to conventional single-layer holograms. The liquid crystal device of the first aspect can provide these advantages in a single device that is easily controllable by adjusting the applied voltage.

[0033] According to a sixth aspect there is provided a virtual reality or augmented reality device comprising a liquid crystal device according to the first aspect and / or an optical aberration correction device according to the second aspect.

[0034] According to a seventh aspect, there is provided a beam steering and / or beam shaping device comprising a liquid crystal device of the first aspect and / or an aberration correction apparatus of the second aspect.

[0035] According to an eighth aspect, there is provided a method of electrically controlling spatial phase modulation of light incident on a liquid crystal device. The liquid crystal device may comprise a liquid crystal layer having a thickness and electrodes for applying an electric field to the liquid crystal layer. The liquid crystal layer may comprise a liquid crystal material. The liquid crystal layer may comprise a plurality of polymer structures comprising polymerised liquid crystal material. Each polymer structure may be provided at a different depth in the thickness of the liquid crystal layer. The method may comprise applying an electric field across the liquid crystal layer to selectively control the spatial phase modulation of light incident on the device.

[0036] The method of the eighth aspect may be carried out on or with a liquid crystal device of the first aspect.

[0037] Features described in the context of individual aspects and embodiments of the invention can be used together and / or interchangeably wherever possible. Similarly, where features are described in the context of a single embodiment for brevity, they can also be provided separately or in any subcombination. Features described in relation to the liquid crystal device of the first aspect may have corresponding features definable in relation to the apparatus of the second to seventh aspects and the method of the eighth aspect, and vice versa, and those embodiments are specifically envisaged. [Brief description of the drawings]

[0038] The invention will now be described, by way of example only, with reference to the accompanying drawings, in which:

[0039] [Figure 1] 1 shows a schematic diagram of a liquid crystal device. [Figure 2A] 1 shows a schematic diagram of a liquid crystal device containing a single layer grating under an applied voltage of 0 V, including the orientation of the liquid crystal molecules. [Figure 2B] 1 shows a schematic diagram of a liquid crystal device containing a single layer grating under an applied voltage of 10 V, including the orientation of the liquid crystal molecules. [Figure 2C] 2B shows a polarized optical microscope image of the liquid crystal device shown in FIG. 2A. [Figure 2D] 2C shows a polarized optical microscope image of the liquid crystal device shown in FIG. 2B. [Figure 2E] Pixel intensity as a function of position (μm) for the liquid crystal devices of FIGS. 2A and 2B under an applied voltage of 10 V. [Figure 2F] The relationship between the position (μm) of the polymer wall and the number of peaks in the liquid crystal devices of FIGS. 2A and 2B under an applied voltage of 10 V is shown. [Figure 2G] 2A and 2B show the far-field diffraction patterns produced by the liquid crystal device of FIG. 2A and FIG. 2B under an applied voltage range of 0 V to 10 V. [Figure 2H]The diffraction efficiency of the liquid crystal device of Figures 2A and 2B is shown as a function of voltage. [Figure 3A] 1 shows a schematic diagram of another liquid crystal device containing a single layer grating under an applied voltage of 0 V, including the orientation of the liquid crystal molecules. [Figure 3B] 1 shows a schematic diagram of another liquid crystal device containing a single layer grating under an applied voltage of 10 V, including the orientation of the liquid crystal molecules. [Figure 3C] 3B shows a polarized optical microscope image of the liquid crystal device shown in FIG. 3A. [Figure 3D] 3C shows a polarized optical microscope image of the liquid crystal device shown in FIG. 3B. [Figure 3E] 3A and 3B show far-field diffraction patterns produced by the liquid crystal device of FIG. 3A and FIG. 3B under an applied voltage range of 0.5 V to 9.5 V. [Figure 3F] The diffraction efficiency of the liquid crystal device of Figures 3A and 3B is shown as a function of voltage. [Figure 4A] FIG. 2 shows a schematic diagram of another liquid crystal device with two diffraction gratings according to an embodiment of the present invention. [Figure 4B] 4B shows a schematic cross-sectional view of the liquid crystal device 400 of FIG. 4A during the manufacturing process. [Figure 4C] 4B shows a schematic cross-sectional view of the liquid crystal device 400 of FIG. 4A during the manufacturing process. [Figure 4D] FIG. 4B shows a schematic diagram of the switching behavior of the liquid crystal device of FIG. 4A. [Figure 4E] FIG. 4B shows a schematic diagram of the switching behavior of the liquid crystal device of FIG. 4A. [Figure 5A] 4 shows a plot of transmittance as a function of voltage for another liquid crystal device according to an embodiment of the invention. [Figure 5B] 4 shows a plot of the phase as a function of voltage for light passing through a liquid crystal device. [Figure 5C] 5A and 5B show a sequence of polarized optical microscope images of the liquid crystal device characterized in FIG. 5A and FIG. 5B after fabrication of the two diffraction gratings. [Figure 6]11 shows a sequence of polarized optical microscope images of another liquid crystal device with two diffraction gratings in accordance with an embodiment of the present invention. [Figure 7A] 13 illustrates the fabrication of another liquid crystal device with two computer generated holograms, according to an embodiment of the present invention. [Figure 7B] 13 illustrates the fabrication of another liquid crystal device with two computer generated holograms, according to an embodiment of the present invention. [Figure 7C] [Figure 7D] [Figure 8] 11 shows a sequence of polarized optical microscope images of another liquid crystal device including two computer generated holograms in accordance with an embodiment of the present invention. [Figure 9] FIG. 1 shows the optical setup used to characterize the liquid crystal devices. [Figure 10A] 1 shows another liquid crystal device with multiple polymer structures forming an array of concentric rings. [Figure 10B] 1 shows another liquid crystal device with multiple polymer structures forming an array of concentric rings.

[0040] Like reference numbers and designations in the various drawings indicate like elements. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0041] FIG. 1 shows a schematic diagram of a liquid crystal device 100 used in the embodiments described herein. The device 100 comprises transparent substrates 105a, 105b spaced apart from each other using spacer beads. The substrates 105a, 105b are coated with a planar alignment layer. A liquid crystal composition 110 is provided between the substrates 105a, 105b. At least some of the liquid crystal composition 110 is polymerized to form a polymer structure 112 having a selected locked-in liquid crystal state. The device 100 comprises transparent electrodes 115a, 115b configured to apply an electric field between the substrates 105a, 105b. In the illustrated example, the electrodes 115a, 115b are disposed on the outer side of the substrates 105a, 105b (e.g., on the opposite side of the substrates 105a, 105b with respect to the liquid crystal composition 110), although this is not required. Alternatively, the electrodes 115a, 115b may be disposed on the inner side of the substrates 105a, 105b.

[0042] In the illustrated example, the liquid crystal composition 110 includes a mixture of a nematic liquid crystal host, a reactive mesogen, and a photoinitiator. In a particular example, the liquid crystal host is E7, although other materials or compositions can be used instead. The reactive mesogen is RM257 (Merck) at a concentration of about 30% by weight, although other compositions and / or concentrations can be used if the director of the liquid crystal host can realign in the presence of an electric field. The photoinitiator is Irgacure 819 (Merck) at a concentration of about 1% by weight, although other compositions and / or concentrations can be used instead.

[0043] In the illustrated example, the transparent substrates 105a, 105b comprise glass, although any transparent material could alternatively be used. The substrates 105a, 105b are separated by spacer beads (not shown) forming a gap between the substrates 105a, 105b. The alignment layers are rubbed in anti-parallel directions (indicated by arrows on the substrates 105a, 105b) to place the liquid crystal material in a homogeneous planar alignment, although this is not required. The alignment layers comprise polyimide, although any suitable material or composition could alternatively be used. The electrodes 115a, 115b comprise indium tin oxide (ITO), although any transparent electrode material could alternatively be used. In the illustrated example, the device 100 comprises an anti-parallel rubbed liquid crystal cell manufactured by Instec Inc., although other cells could alternatively be used.

[0044] In the illustrated example, the polymerizable liquid crystal composition 110 was disposed between the transparent substrates 105a, 105b by capillary filling to form a liquid crystal cell. The liquid crystal composition 110 was prepared by thermal mixing at substantially 70° C. before being disposed between the substrates 105a, 105b, although this is not required.

[0045] A direct laser writing (DLW) system was used to directly form the polymer structures in the liquid crystal device 100. The liquid crystal device 100 was mounted on a translation stage and connected to a waveform generator, allowing an electric field to be applied to the device 100 during fabrication of the polymer structures in the device 100. By forming the polymer structures 112 directly in the liquid crystal device 100, the specific orientation (described by a unit vector known as the director) of the liquid crystal molecules at the precise moment of exposure to the laser beam can be controlled. This provides access to a wider range of director profiles that can be held or fixed by the DLW process than if the director profile was controlled solely by alignment layers at the substrates 105a, 105b.

[0046] The DLW process used femtosecond laser pulses with 100 fs pulse width from a Spectra-Physics Tsunami Ti:Sapphire oscillator emitting at a wavelength of 780 nm with a repetition rate of 80 MHz. The laser pulses were focused into the liquid crystal composition using an Olympus 0.46 NA objective lens. The power of the fabrication laser used in the examples described here was just above the polymerization threshold (delivering the lowest required energy to the sample for polymerization) and was experimentally found to be 41 mW at a writing speed of 100 μm / s. The polarization of the laser was oriented perpendicular to the rubbing direction of the device 100 with the assistance of a half-wave plate. The device 100 was mounted on top of a stack of high-resolution stages (Aerotech ANT-95XY and ANT95V-3) with a positioning resolution of 1 nm. A halogen light source with a 550 nm long-pass filter was used to provide transmitted illumination of the device, allowing the fabrication to be monitored in-situ using a color CCD without affecting the photocuring process. The polymer walls were fabricated by moving the sample under continuous exposure to a pulsed laser beam at a speed of 100 μm / s. During the fabrication of the polymer structure 112, a square wave AC voltage with a frequency of 1 kHz was applied to the device 100 using an arbitrary waveform function generator (Tektronix AFG3021).

[0047] When a laser pulse is incident on the liquid crystal composition 110 during the DLW process, two-photon absorption by the photoinitiator induces crosslinking of reactive mesogens via a free radical polymerization reaction, which stabilizes the molecular alignment of the liquid crystal via the formation of a polymer network upon exposure to the laser beam. The polymerized liquid crystal composition 110 holds or fixes the voltage-dependent director of the liquid crystal molecules upon exposure to form a polymer structure 112. By exposing the liquid crystal device 100 to different voltage amplitudes during the DLW process, different liquid crystal alignments can be held or fixed. The unpolymerized surrounding bulk liquid crystal material is free to reorganize or reorient in the presence of an applied electric field after fabrication.

[0048] The two-photon absorption process that occurs when a laser pulse is incident on a liquid crystal composition results in absorption that occurs exclusively within the focus of the laser in a small volume called a voxel. By translating the sample relative to the laser focus, three-dimensional structures can be constructed on a voxel-by-voxel basis.

[0049] 2A and 2B show schematic diagrams of a liquid crystal device 200 including a single layer grating 212 fabricated by the DLW process described above. The grating 212 includes a number of parallel polymer walls 214 with a period of 5 μm. To generate a hidden or reversed mode grating, the walls were fabricated with a writing voltage of 0 V, which provides no diffraction in the default state. FIG. 2A shows the liquid crystal device 200 with an applied voltage of 0 V, while FIG. 2B shows the liquid crystal device 200 with an applied voltage of 10 V.

[0050] 2A and 2B show the ideal operating principle behind the illustrated switchable diffraction grating. With no applied voltage, there is expected to be no difference in the liquid crystal orientation between the polymerized and unpolymerized regions (see FIG. 2A). In this state, the device 200 behaves as a uniform birefringent layer and no diffraction occurs. When a voltage above a certain threshold is applied, the unpolymerized regions switch and as the voltage is increased, the liquid crystal director (the vector describing the average molecular orientation of the liquid crystal) tends to approach perpendicular (see FIG. 2B). In this switched state, light polarized parallel to the rubbing direction experiences an effective refractive index n eff In the overlap region, we see a modulation of n eff The value of n eff At infinite voltage, if the director is perfectly vertical, the unpolymerized region is n o (normal refractive index). When light is incident on device 200, this spatial modulation of the refractive index results in diffraction. Note that no diffraction occurs for light polarized perpendicular to the rubbing direction. In this geometry, regardless of the applied voltage, light experiences a normal refractive index n o Thus, there is no spatial modulation of the refractive index, and no diffraction occurs.

[0051] Figures 2C and 2D show polarized optical microscope (POM) images at 50x of the grating 12 in device 200 at 0V and 10V, respectively. The scale bar in the lower right corner of Figure 2C is 50 μm. Figures 2A and 2B are inset into Figures 2C and 2D, respectively, showing the orientation of the liquid crystal molecules in the grating 212 (the shaded area indicates the polymer network corresponding to the polymer walls 214).

[0052] Microscopy was performed using an Olympus BX51 polarized optical microscope equipped with a Qlmaging Retiga R6 camera attached to a phototube. An Olympus objective lens was used and the cover glass correction collar was set to the thickness of the glass substrate of the liquid crystal device 200 to improve the quality of the images by reducing aberrations. A long-pass filter with a cutoff wavelength of 550 nm was inserted between the halogen bulb and the sample to avoid polymerization of unreacted reactive mesogen molecules. The device 200 was oriented so that the rubbing direction was at 45° to the transmission axis of the crossed polarizers (indicated by the white arrow in Figure 2C) by rotating the sample until a bright state was found. A MATLAB script was written to automate the process of acquiring microscope images at a range of different voltages by controlling an arbitrary function generator (Tektronix AFG3021) with SCPI commands. The microscope camera was controlled by a command library provided by the manufacturer.

[0053] The POM images show that the spacing of the walls is quite uniform, with the width of the walls themselves remaining approximately 0.9 μm. The POM images also show that at 0 V the device 200 behaves as a substantially uniform birefringent layer, with the polymer walls 214 being substantially indistinguishable from the surrounding unpolymerized liquid crystal composition, and little diffraction occurs. However, at 10 V the anchoring of the polymer walls 214 is broken and the director becomes nearly vertical. Due to the anchoring of the homogeneous planar director state within the polymer walls 214, the polymer walls 214 remain in a birefringent state even as the surrounding unpolymerized liquid crystal composition switches to the vertical state. Thus, the diffraction grating 212 becomes active at 10 V, and diffraction occurs due to spatial modulation of the refractive index.

[0054] Image analysis was performed to evaluate the uniformity and width of the walls. Image analysis was performed by performing horizontal line scans across a grayscale version of the POM image of the grating 212 under an applied electric field of 10 V, as shown in FIG. 2D. These line scans were averaged to reduce noise, and the results are plotted in FIG. 2E, where each polymer wall 214 is represented by a peak. The scale was calibrated using a microscope calibration slide with an etched scale. The MATLAB function "findpeaks" was used to find the locations of the peaks, and the values ​​were plotted against the peak number, as shown in FIG. 2F. An optional output from the "findpeaks" function that calculates the full width of the peaks at half ridges was then used to obtain an estimate of the polymer wall width.

[0055] The straightness shown in FIG. 2F indicates that there is a consistent spacing between each of the polymer walls 214 that form part of the diffraction grating 212. The average distance between adjacent walls 214 is 5.00 μm with a standard deviation of 0.08 μm, which is on the order of the image resolution of 0.09 μm / pixel. The uniformity of the peaks themselves in FIG. 2E indicates that the polymer walls 214 have a highly uniform structure. The estimated width of the polymer walls 214 averages 0.87 μm with a standard deviation of only 0.02 μm, indicating a very high uniformity of the polymer walls 214.

[0056] FIG. 2G shows the far-field diffraction pattern generated by device 200 and projected onto a screen at applied voltages ranging from 0V to 10V in 1V increments, while FIG. 2H shows the diffraction efficiency of the first four diffraction orders as a function of voltage. The diffraction efficiency is defined here as the ratio of the intensity of the diffraction order to the incident intensity. In the off state at 0V, the polymer network in the polymer walls 214 is in the same state as the unpolymerized liquid crystal composition, so there is no contrast in the effective refractive index and no diffraction occurs. As the voltage is increased, the unpolymerized liquid crystal composition starts to switch, creating a refractive index contrast between the polymer walls 214 and the unpolymerized liquid crystal composition, and a diffraction pattern appears. The diffraction grating 212 clearly generates multiple diffraction orders due to its Raman-Nath domain properties. The maximum diffraction efficiency of the first order of 33.2% is comparable to the value of about 34% previously reported by Kossyrev et al. for polymer-stabilized reverse-mode LC gratings fabricated by UV interference.

[0057] Examining the behavior of the diffraction orders at low voltages (<1V) reveals that there are low non-zero intensities associated with the first and second orders. This means that the formation of a polymer network within the polymer walls 214 slightly disturbs the alignment of the liquid crystals and reduces the effective refractive index from the unpolymerized liquid crystal composition at 0V. As a result, the n eff The small difference in n causes weak diffraction at 0 V. As the voltage is increased, the first order disappears at 1.2 V, and the unpolymerized liquid crystal composition starts to switch, causing the n eff This means that the formation of the polymer network corresponds to n eff This means that the

[0058] The study of the Freedericksz transition allows one to observe the elastic influence of the polymer walls 214 on the switching behavior of the liquid crystal composition. In the fabricated device 200, the effective Freedericksz threshold voltage is 1.2 V, which is higher than the pre-polymerization value of 0.7 V. This indicates that the effect of the polymer walls 214 is to increase the magnitude of the electric field required to reorient the liquid crystal director.

[0059] 3A and 3B show schematic diagrams of another liquid crystal device 300 including a single layer grating 312 fabricated by the DLW process described above. The grating 312 comprises a plurality of parallel polymer walls 314 with a period of 5 μm and is substantially similar to the device 200 described above. However, the polymer walls 314 were fabricated with a write voltage of 1.55 V to provide a conventional mode grating where diffraction is generated at 0 V. FIG. 3A shows the liquid crystal device 300 at an applied voltage of 0 V, while FIG. 3B shows the liquid crystal device at an applied voltage of 1.55 V.

[0060] When no voltage is applied, there is a difference in the alignment of the liquid crystal between the polymerized and unpolymerized regions (see Figure 3A). In this state, light polarized parallel to the rubbing direction is polarized by n of the unpolymerized liquid crystal composition. eff and the higher value of n for the polymer wall 314 eff When a voltage of 1.55V (approximately equal to the write voltage of the polymer wall 314) is applied, there is no difference in the alignment of the liquid crystal between the polymerized and unpolymerized regions (see FIG. 3B). At this stage, the device 300 behaves as a uniform birefringent layer and virtually no diffraction occurs.

[0061] Figures 3C and 3D show polarized optical microscope (POM) images at 50x of the grating 212 of device 200 at 0V and 1.55V, respectively. The scale bar in the lower right corner of Figure 3C is 50 μm. Figures 3A and 3B are inset into Figures 2C and 2D, respectively, and show the orientation of the liquid crystal molecules in the grating 312 (the shaded area indicates the polymer network corresponding to the polymer walls 314). Similar to device 200, the grating 312 has a period of 5 μm.

[0062] FIG. 3E shows the far-field diffraction pattern produced by device 300 and projected onto a screen at voltages ranging from 0.5V to 9.5V in 1V increments, while FIG. 3F shows the diffraction efficiency of the first four diffraction orders as a function of voltage. Diffraction efficiency is defined here as the ratio of the intensity of the diffraction order to the incident intensity. In the off state at about 1.5V (1.55V), the polymer network in the polymer walls 314 is in the same state as the unpolymerized liquid crystal composition, so there is no contrast in the effective refractive index and no diffraction occurs. As the applied voltage is increased or decreased from the 1.55V off state, the unpolymerized liquid crystal composition begins to switch, creating a refractive index contrast between the polymer walls 314 and the unpolymerized liquid crystal composition, and a diffraction pattern appears. The diffraction grating 312 clearly produces multiple diffraction orders due to its properties in the Raman-Nath domain.

[0063] FIG. 4A shows another liquid crystal device 400. The liquid crystal device 400 is similar in structure to the liquid crystal devices 200 and 300 described above. However, the liquid crystal device 400 includes a first diffraction grating 412a and a second diffraction grating 412b, each of which includes a number of parallel polymer walls 414a and 414b. In the illustrated embodiment, the diffraction gratings 412a and 412b are orthogonal to each other. This configuration is advantageous because it is easy to resolve the diffraction patterns from each diffraction grating 412a and 412b, and their orthogonality is very obvious. However, it is not essential that the diffraction gratings 412a and 412b are orthogonal to each other.

[0064] In the illustrated embodiment, the polymer walls 414a of the first grating 412a are fabricated to be coupled to (e.g., fabricated on) the first transparent substrate 405a of the liquid crystal device 400. The polymer walls 414b of the second grating 412b are fabricated to be coupled to (e.g., fabricated on) the second transparent substrate 405b of the liquid crystal device. The substrates 405a, 405b are separated by a thickness d. However, this is not required and the polymer walls 414a, 414b of one or both of the gratings 412a, 412b may be formed at an intermediate position through the thickness d of the liquid crystal composition between the substrates 405a, 405b without being coupled to the substrates. For example, one or more of the polymer walls 414a, 414b of each grating 412a, 412b may be at least partially coupled or secured to one or more of the polymer walls 414a, 414b of another grating 412a, 412b. By forming different polymer structures, such as sets of polymer walls, at different depths through the thickness d of the liquid crystal composition between the substrates 405a, 405b, different polymer structures can be formed in the same area or region of the device 400 and allow the polymer structures to operate (e.g., spatially modulate the phase of light incident on the device) independently of one another. Each polymer structure can be formed within or include a separate or distinct sublayer of a liquid crystal layer (e.g., a liquid crystal layer disposed between the substrates 405a, 405b).

[0065] 4B and 4C show schematic cross-sectional views of the liquid crystal device 400 during the fabrication process. The focal depth of the laser is varied during fabrication to couple the polymer walls 414a, 414b to the opposing substrates 405a, 405b. Using a 0.46 NA objective lens results in an expected voxel size of approximately 11 μm. To ensure strong coupling of the polymer walls 414a, 414b to the respective substrates 405a, 405b, the focal depth of the fabrication laser was adjusted so that approximately half of the voxel was within the substrates 405a, 405b. However, as mentioned above, it is not essential that the polymer walls 414a, 414b be coupled to the substrates 405a, 405b. In addition to the variation in fabrication height, the voltage applied to the liquid crystal composition is also varied during the process, with the polymer walls 414a, 414b including each grating being written with different voltages. For clarity, in the illustrated example, the second grating 412b is shown written at 0V and the first grating 412a is shown written at any voltage above the Fredericks threshold voltage of the device 400. However, one of the fabrication voltages need not be 0V, and the first and second gratings 412a, 412b may be written at any two sufficiently different voltages.

[0066] 4D and 4E show the switching behavior of the double-layer grating device 400 after fabrication of the two gratings 412a, 412b. At the write voltage (0V) of the second grating 412b, the first grating 412a is active because the polymer walls 414a of the first grating 412a have a locked-in non-zero voltage liquid crystal state. This creates a refractive index modulation of the first grating 412a between the polymer walls 414a and the unpolymerized liquid crystal composition, while for the second grating 412b, the directional alignment is uniform across both the polymer walls 414b and the unpolymerized liquid crystal composition. To switch or activate the second grating 412b, an applied voltage having a magnitude equal to the write voltage for the first grating 412a is applied to the device 400. This deactivates the first grating 412a (due to the uniform liquid crystal director orientation at the first grating 412a) and switches the second grating 412b to an active state. There is no refractive index modulation for the first grating 412a because the unpolymerized liquid crystal composition is in the same liquid crystal state as that of the polymer walls 414a of the first grating 412a. However, there is a refractive index modulation for the second grating 412b due to the difference in director orientation between the polymer walls 414b and the switched unpolymerized liquid crystal composition.

[0067] The individual write voltages used to fabricate the first and second gratings 412a, 412b of the device 400 can be selected to maximize the diffraction efficiency of each grating 412a, 412b, but this is not required. For example, maximum diffraction efficiency in a binary phase grating requires that the phase difference be equal to π. By elucidating the phase vs. voltage relationship of the device 400, the polymer structure or gratings 412a, 412b of the device 400 can be written with two different voltages with a phase difference equal to π. The phase vs. voltage relationship depends on several variables, including the wavelength of the incident light, the thickness of the liquid crystal device 400, and the birefringence of the liquid crystal composition. The phase vs. voltage relationship of the device 400 can be experimentally and straightforwardly established by studying the transmission behavior of the device 400 when oriented between crossed polarizers before the polymer walls 414a, 414b are written.

[0068] 5A and 5B show the electro-optical properties of the liquid crystal device 500 before the polymer walls 514a, 514b are written. In the illustrated embodiment, the device 500 has substantially the same structure as the liquid crystal device 400, and like reference numbers indicate like features. In the illustrated embodiment, the device 500 has a thickness (distance d between the substrates 505a, 505b) of 20 μm. This allows for spatial separation of the first and second gratings 512a, 512b in the direction perpendicular to the substrates 505a, 505b, but this is not required. For the device 500 having a thickness of 20 μm and illuminated at a wavelength of 635 nm, writing voltages of 3.7 V and 6.7 V were selected for the first and second gratings 412a, 412b, respectively, to maximize the diffraction efficiency, but this is not required.

[0069] FIG. 5A shows a plot of the transmittance as a function of voltage for a device 500 oriented between crossed polarizers. The device 500 was oriented with its optical axis at 45° to the polarizers and illuminated with a laser diode (Thorlabs PL202) having a wavelength of 635 nm. Peak and valley voltages are selected in the transmittance vs. voltage plot. The peak indicates where the device 500 effectively acts as a half-wave plate, where the polarization is rotated by 90° from the polarizer axis to the analyzer axis. The valley indicates where the device 500 effectively acts as a full-wave plate (lambda plate), where the polarization direction is unchanged from the original orientation of the polarizer and vanishes after the analyzer.

[0070] The transmission T of a birefringent layer between crossed polarizers, whose optical axis is at 45° to the polarizer axis, is given by the formula T=sin 2 The phase can be related to the phase φ by (φ / 2). In this relationship, the transmittance is normalized to the maximum transmittance through the device. Using this equation, the phase can be extracted from the plot of transmittance as a function of voltage shown in FIG. 5A. FIG. 5B shows a plot of phase as a function of voltage for light passing through device 500, showing that device 400 illuminated using a wavelength of 635 nm experiences a phase difference π at voltages of 3.7 V and 6.7 V.

[0071] FIG. 5C shows a sequence of polarized optical microscope images of the liquid crystal device 500 at various applied voltage conditions (ranging from 0V to 9V in 1V increments, with additional images at 3.7V and 6.7V) with inset images of the corresponding diffraction patterns. The second grating 512b coupled to the second substrate 505b was written at 3.7V with a grating period of 20 μm, and the polymer walls 514b were vertically oriented in the POM image. The first grating 512a coupled to the first substrate 505a was written at 6.7V with a grating period of 10 μm, and the polymer walls 514a were horizontally oriented in the POM image. Thus, the polymer walls 514a, 514b of the first and second gratings 512a, 512b are positioned orthogonal to each other (although this is not required). However, it will be understood that the polymer walls 514a, 514b may be written at other voltages, or at 0V. The scale bar in the lower right corner of the image at 0 V is 50 μm.

[0072] At applied voltages close to the writing voltage of the second grating 512b (3.7V), the second grating is not visible in the POM image due to the uniformity between the director alignment of the polymer walls 514b and the unpolymerized liquid crystal composition. The first grating 512a is visible in the POM image at these voltages. This is because the polymer walls 514a are written at 6.7V and have a locked-in director profile that is different from the director profile of the unpolymerized liquid crystal composition. The horizontally aligned polymer walls 514a of the first grating 512a are clearly visible at voltages around 3.7V in FIG.

[0073] At applied voltages close to the write voltage of the first grating 512a (6.7V), the first grating 512a becomes invisible because the director orientations of the unpolymerized liquid crystal composition and the polymer walls 514a are the same. Therefore, at these voltages, the vertically aligned polymer walls 514b of the second grating 512b are visible due to the different director orientations in the polymer walls 514b and the unpolymerized liquid crystal composition.

[0074] Upon closer inspection, it can be seen that the diffraction pattern produced by the second grating 512b is in fact best seen at 3.0 V, rather than the write voltage of 3.7 V. This effect is caused by the polymer walls 514a of the first grating 512a, which was written at 6.7 V, exerting an elastic influence on the unpolymerized liquid crystal composition in the device 500. The locked-in director alignment at the higher voltage can create an anchoring surface within the device 500, influencing the unpolymerized liquid crystal composition to match its alignment at 6.7 V, effectively lowering the index matching voltage of the second grating 512b.

[0075] FIG. 6 shows a sequence of polarized optical microscope images of another liquid crystal device 600. The liquid crystal device 600 is similar to the device 500 described above, and like reference numbers indicate like features. In the device 600, the second grating 612b includes a triangular mesh of polymer walls 614b that produces a hexagonal diffraction pattern in the far field. The first grating 612a is a conventional one-dimensional grating including polymer walls 614a, as described above. The same cell thickness and writing voltages were used as in the device 500 described above. The second grating 612b is written at 3.7V and includes periodic triangular elements with a pitch of 5 μm, while the first grating 612a is written at 6.7V and includes multiple polymer walls 614a with a grating period of 5 μm. However, it will be understood that the polymer walls 614a, 614b may be written at other suitable voltages, or even at 0V. The scale bar in the lower right corner of the image at 0V is 50 μm.

[0076] At applied voltages close to the write voltage of the triangular second grating 612b (3.7 V), only the 1D diffraction pattern produced by the first grating 612a is visible. As the applied voltage is increased towards the write voltage of the first grating 612a (6.7 V), the observed diffraction pattern changes to the hexagonal diffraction pattern produced by the second grating 612b.

[0077] 7A and 7B show the fabrication of another liquid crystal device 700. The liquid crystal device 700 is similar to the devices 500, 600 described above, and like reference numbers indicate like components. However, instead of the first and second diffraction gratings, the device 700 comprises first and second holograms 712a, 712b. Holograms are diffractive optical elements that generate a recognizable image in the far-field diffraction pattern. The phase map that defines the hologram is highly aperiodic. The direct laser writing process described above is well suited to the task of fabricating such structures due to the ability to arbitrarily control the exposure pattern of the writing laser.

[0078] The fabrication procedure is substantially the same as described above for device 500. First, a voltage V1 is applied to device 700 to fabricate a second binary phase computer generated hologram (CGH) 712b (also denoted as A). In the illustrated embodiment, the polymer structures representing the pixels of the second CGH 712b are coupled to a second substrate 705a, although this is not required. Subsequently, a voltage V2 is applied to device 700 and the position of the laser focus is adjusted upward to fabricate a first binary phase CGH (712a (also denoted as B)). In the illustrated embodiment, the polymer structures representing the pixels of the first CGH 712a are coupled to a first substrate 705a, although this is not required. Application of a voltage changes the director orientation in the liquid crystal composition and stabilizes the director orientation at a given voltage when a polymer network is formed.

[0079] After fabrication, the device 700 is operated by illuminating the device with a collimated laser beam that is linearly polarized in a direction parallel to the optical axis of the liquid crystal composition. The far-field diffraction pattern can be observed and studied on a screen. As shown in Figures 7C and 7D, when a voltage V1 is applied to the device 700, there is no contrast in director orientation between the polymerized pixels of the second CGH 712b and the unpolymerized liquid crystal composition written with V1. Thus, the incident light sees a uniform refractive index profile for the second CGH 712b, and no diffraction occurs. In contrast, with an applied voltage V1, there is a difference in director orientation between the polymerized pixels of the first CGH 712a and the unpolymerized liquid crystal composition. This is manifested as the incident light seeing the spatially varying effective refractive index of the first CGH 712a, producing a diffraction pattern corresponding to the first CGH 712a in the far field.

[0080] Conversely, at an applied voltage V2, the situation is reversed, the first CGH 712a is inactive, the second CGH 712b is active, and the far-field diffraction pattern switches to a pattern generated only by the second CGH 712b. In this way, the device 700 can be switched between two different diffraction patterns after fabrication by simply applying to the device 700 the write voltages used in fabrication.

[0081] 8 shows a sequence of polarized optical microscope images of another liquid crystal device 800 under various applied voltage conditions (from 0V to 9V in 1V increments, with additional images at 3.7V and 6.7V). The liquid crystal device 800 comprises two binary CGHs 812a, 812b, similar to device 700 above. The corresponding diffraction patterns or images generated by the CGHs are inserted in the images.

[0082] The second CGH 812b was designed to reproduce an image of the Oxford University logo and was written at 3.7V, while the first CGH 812a was designed to reproduce an image of the Somerville College coat of arms and was written at 6.7V, although it will be appreciated that CGHs 812a, 812b may be written at voltages other than 3.7V and 6.7V. Device 800 represents an actual example of device 700, as illustrated generally in Figures 7A-7D and described above.

[0083] The operation of device 800 is similar to devices 500-700 described above and shown in Figures 5-7, with application of a write voltage for the CGH deactivating it. At an applied voltage close to the write voltage for the second CGH 812b, only the diffraction pattern from the first CGH 812a is visible (image of Somerville College crest). At an applied voltage close to the write voltage for the first CGH 812a, only the diffraction pattern from the second CGH 812b is visible in the far field (image of Oxford University logo). The diffraction pattern or image generated by device 800 can thus be switched between two different images by varying the magnitude of the voltage applied to device 800.

[0084] In the illustrated embodiment, the CGH was generated using the Gerchberg-Saxton (GS) algorithm implemented in MATLAB. The target images for the dual-layer CGH were a 512×512 pixel image of the Oxford University logo and a 300×300 pixel image of the Somerville College coat of arms. These images were resized to 128×128 pixel images before being placed in the top left corner of a 256×256 pixel black image. The reason for placing the desired target in the top corner of the input to the GS algorithm was to prevent overlap with the zero-order spot and conjugate image in the replay field. The output of the GS algorithm was a 256×256 pixel binary hologram. The hologram was written over an area of ​​1024×1024 μm using the direct laser writing process described above, so that each pixel of the hologram was 4×4 μm in size. Fabrication was performed on devices with a substrate spacing or thickness of 20 μm. A MATLAB script converted the hologram design into an AeroBasic manufacturing script, which wrote the hologram row by row with 1 μm spacing between adjacent rows. The replay field was captured using a Fourier lens to deliver the far-field diffraction pattern to the plane of the CCD, although it will be appreciated that the CGH may be generated using any suitable method.

[0085] The diffractive structures or DOEs of the devices 200-800 described above were characterized using a custom built optical setup 900 shown in Figure 9. The light source was a 635 nm laser diode 902 (Thorlabs PL202) with a beam diameter of 3 mm and optical power of 1 mW. To selectively illuminate specific DOEs within the device, the beam was reduced by two lenses 904a, 904b in a telescope configuration. For some DOEs written in very small areas, the beam had to be focused using a 300 mm lens to produce a beam size small enough to fit completely within the area of ​​a structure. The output power of the laser diode was reduced to 100 μW using a variable neutral density filter to provide adequate power for the CCD and photodiode. To allow targeting and positioning of the laser beam, the sample was mounted on a stack of precision manual translation stages (Thorlabs PT1) with a travel range of 25 mm in the x and y directions. To aid in locating and identifying the DDEs within the device, a simple optical microscope was constructed with illumination provided by a fiber-coupled 660 nm LED 906. The optical path of the 635 nm laser diode 902 is shown by the red line in FIG. 9, while the illumination path of the 660 nm LED 906 is shown by the purple dashed line in FIG. 9. A full-color CCD camera 908 (Thorlabs DCC1240C) was used to provide a magnified image of the device and allow navigation to the correct position. Diffraction patterns could be recorded either by i) taking an image of the screen 910 using a full-color CCD 912 (Thorlabs DCU224C) fitted with a camera lens, or ii) directly recording the diffraction intensity using a photodiode 914 (Thorlabs PDA36A-EC). A MATLAB script was written to automate the experimental process of running voltage sweeps and acquiring diffraction data from the DOE. An arbitrary function generator 916 (Tektronix AFG 3021) controlled the supply of AC drive voltages to the DOE, and data was recorded by either a CCD 912 or a photodiode 914 focused on the screen 910 .In the latter method, the voltage sweep was repeated for each diffraction order, realigning the photodiode 914 between each measurement. The MATLAB script interfaced with the CCD camera 912 via a .NET library, while the photodiode 914 was connected to a digital oscilloscope (Tektronix TDS2024C) which read out the voltage signal from the photodiode 914 via SCPI commands.

[0086] The liquid crystal devices 500-800 described above demonstrate how the functionality and utility of the device can be increased by writing multiple diffractive structures or diffractive optical elements (DOEs) within a single device. The devices 500-800 are not simply switched on and off (i.e., producing either a diffractive pattern or not producing a diffractive pattern) as in conventional liquid crystal switchable diffractive optics, but rather are switchable between multiple different diffractive states. Although the devices 500-800 described above each comprise two DOEs written with different voltages, it will be appreciated that more than two diffractive structures or DOEs can be written into the device with different write voltages. This increased functionality can also be provided by simple control of switching between diffractive states by increasing or decreasing the voltage applied to the device, rather than the complex backplane electronics typically required by switchable SLMs. Intermediate states combining spatial phase modulation contributions from two or more polymer structures (with the same or different selected locked-in liquid crystal states) can also be achieved. Furthermore, by writing the polymer structures of each DOE at different depths in the thickness of the liquid crystal composition within the device, increased functionality can be provided without increasing the footprint of the device. The diffractive structures may at least partially spatially overlap one another in a direction extending through the thickness of the device.

[0087] Another advantage of the switchable devices 500-800 described above is that they can support multiple modes of operation. In many previously reported liquid crystal gratings, including H-PDLC technology, the fabricated devices are optically active by default (i.e., with no voltage applied), and therefore a voltage is required to switch the device off. This is known as conventional mode operation. This limitation means that H-PDLC devices consume power in the off state, which can be an undesirable characteristic for many applications where power consumption is a critical design parameter. In contrast, in the switchable devices described above, the diffractive structure can be designed to operate in the inverted mode and be optically inactive without an applied voltage by writing the polymer structure at 0V during fabrication. Additionally, the devices described above may also include a diffractive structure designed to operate in the conventional mode (where diffraction is generated at 0V by default) by fabricating the polymer structure at an applied voltage above the Fredericks threshold.

[0088] Potential applications of the liquid crystal devices described herein include 3D distance sensing and / or depth mapping, using diffraction gratings to create structured light illumination patterns. Conventional depth mapping technologies, such as Apple's Face ID system and Microsoft's Kinect, generate a fixed grid of dots to illuminate a scene. For high-resolution depth sensing, required to process subtle changes in individual finger movements or facial expressions, an illumination grid of thousands of infrared dots is projected onto the target scene and processed by a camera and a dedicated ASIC. The liquid crystal devices described above can be employed as switchable dot projectors capable of projecting two different illumination patterns onto a scene. Many applications using 3D depth mapping technologies, including head-mounted displays, require significant miniaturization and have stringent power consumption requirements, so it may be advantageous to combine multiple optical functions into a single switchable device.

[0089] The liquid crystal devices described above also have great potential for the use of holography in advanced applications. Stacked or cascaded CGHs are used for applications including multiplexed information display, color images, and multi-wavelength optical interconnects. Furthermore, stacked CGHs are employed to improve image resolution and diffraction efficiency compared to conventional single-layer CGHs. The liquid crystal devices of the present disclosure can provide these advantages within a single device that can be easily controlled by adjusting the applied voltage.

[0090] Another potential application of the liquid crystal devices described above is aberration correction, significantly simplifying the operation of such devices compared to the complex active matrix backplane electronics required to drive pixels in, for example, conventional SLMs, by switching between different phase profiles using a uniformly applied voltage. Liquid crystal devices can be incorporated into or used in conjunction with optical devices (e.g. lenses, microscopes, etc.) to provide aberration correction for these optical devices. Each diffractive element within a liquid crystal device can be configured to address a different aberration mode and can be selectively activated and / or deactivated by controlling the applied voltage as required.

[0091] FIG. 10A shows a schematic diagram of another liquid crystal device 1000. The liquid crystal device 1000 is similar to the devices 500-800 described above, and like reference numerals indicate like functions. The device 1000 comprises a plurality of polymer structures 1012a-1012d. Each polymer structure 1012a-1012d is disposed at a different depth in the thickness of a liquid crystal layer disposed between the substrates 1005a, 1005b. Each polymer structure 1012a-1012d may alternatively be considered to be formed in or to comprise a separate or different sub-layer within the liquid crystal layer. In the illustrated embodiment, the plurality of polymer structures 1012a-1012d may also be considered to together form a plurality of stacked plates or disks of varying diameters and thicknesses, and / or an arrangement of concentric rings each having a different height or thickness (shown in plan view in FIG. 10B). However, this is not required and other arrangements of polymer structures may be used. In the illustrated embodiment, polymer structure 1012a is coupled to a first substrate 1005a and polymer structure 1012d is coupled to a second substrate 1005b. Polymer structure 1012b is coupled to polymer structures 1012a and 1012c and polymer structure 1012c is coupled to polymer structures 1012b and 1012d.

[0092] However, in device 1000, each of the polymer structures 1012a-1012d are written with the same voltage (rather than different voltages as in devices 500-800 described above), as indicated by the common director orientation shared by the liquid crystal molecules within the polymer structures 1012a-1012d. In the illustrated embodiment, each of the polymer structures 1012a-1012d are written with 0V, although alternatively the polymer structures 1012a-1012d may be written with any suitable voltage.

[0093] Rather than switching between various active states by varying an applied voltage, device 1000 is configured to provide a variable phase change in various areas within device 1000. When a voltage is applied across device 1000, the liquid crystal molecules within the unpolymerized liquid crystal composition realign in response to the applied voltage. In the illustrated embodiment, the arrangement of polymer structures 1012a-1012d effectively provides a different thickness of polymerized liquid crystal composition at each lateral or radial location (e.g., the x-direction shown in FIG. 10A) within device 1000. The different thicknesses of polymerized liquid crystal composition at each location are configured to modulate the phase of light incident on device 100 by a different amount at each location. Furthermore, the magnitude of the phase modulation can be adjusted (e.g., increased or decreased) by adjusting (e.g., increasing or decreasing) the voltage applied across device 1000. However, the relative amount of phase modulation between each of the different locations may remain constant due to the ratio of thicknesses of polymerized and unpolymerized liquid crystal composition at each location. Thus, the polymer structures 1012a-1012d can work in conjunction with each other to tune or control the spatial phase modulation of light incident on the device.The polymer structures 1012a-1012d can together form a diffractive optical element.

[0094] Device 1000 can be used to correct one or more specific aberration modes, such as one or more Zernike modes. As discussed above, the flexibility in fabricating polymer structures allows device 1000 to be fabricated to correct one or more aberration modes specific to a particular optical system.

[0095] One or both of the electrodes 1015a, 1015b may alternatively include multiple individually addressable electrode elements. For example, one or both of the electrodes 1015a, 1015b may comprise a patterned electrode or electrode array rather than a single planar electrode. For example, one or both of the electrodes 1015a, 1015b may be or include an array of concentric rings substantially corresponding to the concentric rings formed by the polymer structures 1012a-1012d described above. However, alternatively, any suitable electrode array may be used. Each element (e.g., ring, etc.) of the array or patterned electrode may be separately or individually addressable. This allows for voltage application across only a portion of the device 1000, allowing finer spatial control of the magnitude of phase modulation at each radial or lateral location within the device 1000. The electrode array may be or may include elements having any suitable shape, arrangement, and / or size, and may substantially complement or correspond to the shape, arrangement, and / or size of the polymer structure.

[0096] Alternatively, the device 1000 may comprise two multiple polymer structures. For example, the first multiple polymer structures 1012a-1012d may be written with a first voltage (e.g., 0V as described above). The second multiple polymer structures may be written with a second voltage different from the first voltage, substantially similar to that described above with respect to the devices 500-800. The first multiple polymer structures may be written to a first multiple distinct depths in the thickness of the liquid crystal layer. The second multiple polymer structures may be written to a second multiple distinct depths, although this is not required. The second multiple distinct depths may be different from the first multiple distinct depths. The second multiple polymer structures may function to correct one or more particular aberration modes different from those addressed by the first multiple polymer structures. A voltage equal to the write voltage of one of the multiple polymer structures may be applied across the device 1000 to optically inactivate the multiple polymer structures, substantially similar to that described above. This enables device 1000 to be switchable between various active states (eg, aberration correction) in substantially the same manner as described above for devices 500-800.

[0097] Other potential applications of the liquid crystal devices described above include augmented reality (AR) and / or virtual reality (VR) applications, beam steering and beam shaping, spectroscopy, etc.

[0098] The multilayer DOE device described here enables the switching of multiple different phase patterns in a simple single-pixel liquid crystal device. This functionality fills an important gap between fully programmable SLM devices and fixed diffractive optical elements, and can be adopted in a wide range of applications.

[0099] Further variations and modifications will be apparent to persons skilled in the art upon reading the present disclosure, and may include equivalent and alternative structures already known in the art of liquid crystal devices, which may be used instead of or in addition to structures already described herein.

[0100] Although the appended claims are directed to specific combinations of features, it should be understood that the scope of the present disclosure also includes, explicitly or implicitly, any novel feature or combination of any novel features disclosed herein, or any generalization thereof, whether or not it relates to the same invention as currently claimed in any claim, and whether or not it alleviates some or all of the same technical problems as the present invention.

[0101] Features that are described in the context of separate embodiments may also be provided in combination in a single embodiment. Conversely, various features that are, for brevity, described in the context of a single embodiment may also be provided separately or in any suitable subcombination. Applicant hereby notifies that new claims may be formulated to such features and / or combinations of such features upon prosecution of this application or any further application derived therefrom.

[0102] For the sake of completeness, it is also clarified that the term "comprising" does not exclude other elements or steps, and the terms "a" or "an" do not exclude a plurality, such that a single processor or other unit may fulfill the functions of several means recited in the claims, and that reference signs in the claims are not to be interpreted as limiting the scope of the claims.

Claims

1. a liquid crystal layer having a thickness, the liquid crystal layer including a liquid crystal material and a plurality of polymer structures including polymerized liquid crystal material, each polymer structure being disposed at a different depth within the thickness of the liquid crystal layer; electrodes configured to apply an electric field to the liquid crystal layer; Each polymer structure has a different selected locked-in liquid crystal state, liquid crystal device.

2. 10. The liquid crystal device of claim 1, wherein at least two of the polymer structures at least partially spatially overlap one another in a direction extending through the thickness of the liquid crystal layer.

3. 10. The liquid crystal device of claim 1, wherein each polymer structure is configured to provide a different spatial phase modulation of light incident on the device.

4. 10. The liquid crystal device of claim 1, wherein the electrodes are configured to apply an electric field across at least a portion of the liquid crystal layer.

5. 5. The liquid crystal device of claim 4, further comprising first and second electrodes configured to apply an electric field across the thickness of the liquid crystal layer.

6. 5. A liquid crystal device according to claim 4, wherein the electrodes are operable to apply a substantially uniform electric field.

7. 5. A liquid crystal device according to claim 4, wherein at least one of the electrodes comprises a plurality of individually addressable electrode elements.

8. 10. The liquid crystal device of claim 1, wherein each of the different liquid crystal states of the polymer structure corresponds to a state of the liquid crystal material at a different predetermined electric field strength.

9. 10. The liquid crystal device of claim 1, wherein at least one of the polymer structures comprises multiple domains of polymerized liquid crystal material.

10. 10. The liquid crystal device of claim 1, wherein at least one of the polymer structures is or comprises a diffractive optical element.

11. 11. The liquid crystal device of claim 10, wherein at least one of the polymer structures is or includes a diffraction grating.

12. 12. A liquid crystal device according to claim 11, wherein at least one diffraction grating is configured to generate a hexagonal diffraction pattern, and optionally at least one diffraction grating comprises a triangular mesh.

13. 12. A liquid crystal device according to claim 11, wherein at least one diffraction grating is configured to generate a one-dimensional diffraction pattern, and optionally at least one diffraction grating comprises a plurality of posts or walls.

14. 11. The liquid crystal device of claim 10, wherein at least one of the polymer structures is or includes a hologram.

15. 10. The liquid crystal device of claim 1, further comprising a first substrate and a second substrate, wherein at least one of the polymer structures is coupled or fixed to the first substrate or the second substrate.

16. 16. The liquid crystal device of claim 15, wherein the plurality of polymer structures includes a first polymer structure attached or anchored to the first substrate and a second polymer structure attached or anchored to the second substrate.

17. 10. The liquid crystal device of claim 1, wherein at least one of the polymer structures is at least partially linked or anchored to one or more other polymer structures.

18. An aberration correction device comprising the liquid crystal device according to claim 1.

19. An optical device comprising the apparatus of claim 18.

20. A distance sensing and / or depth mapping device comprising a liquid crystal device according to claim 1.

21. 21. The distance sensing and / or depth mapping device of claim 20, wherein each of the polymer structures is configured to create a different structured light illumination pattern.

22. A holographic display device comprising the liquid crystal device of claim 13.

23. A virtual reality or augmented reality display device comprising a liquid crystal device according to claim 1.

24. A beam steering and beam shaping device comprising the liquid crystal device of claim 1.

25. 1. A method for electrically controlling spatial phase modulation of light incident on a device comprising a liquid crystal layer having a thickness and electrodes for applying an electric field to the liquid crystal layer, comprising: the liquid crystal layer includes a liquid crystal material and a plurality of polymer structures including polymerized liquid crystal material, each polymer structure being disposed at a different depth in the thickness of the liquid crystal layer; The method includes applying an electric field across a liquid crystal layer to selectively control spatial phase modulation of light incident on the device; Each polymer structure has a different selected locked-in liquid crystal state.

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