Piezo-optical element and piezo-optical system

Abstract

The optical element has a first piezoelectric layer of a fluorinated polymer with a piezoelectric coefficient d 31 of at least 25 pC / N, and an electrode layer disposed on the first piezoelectric layer. When the first piezoelectric layer is deformed upon application of a voltage in the electrode layer, the optical characteristics of the optical element change.

Description

Technical Field

[0001] Cross - Reference to Related Applications This application claims the benefit of priority under 35 U.S.C.§119(e) to U.S. Provisional Patent Application No. 63 / 352,199, filed on June 14, 2022, which is hereby incorporated by reference in its entirety. This application further claims the benefit of priority under 35 U.S.C.§119(e) to U.S. Provisional Patent Application No. 63 / 406,613, filed on September 14, 2022, which is hereby incorporated by reference in its entirety.

Background Art

[0002] In order to focus or disperse light rays, optical elements such as lenses and mirrors may be used. The optical operation of an optical element can be affected by the shape of the optical element. For example, a spherical lens has different optical properties from a concave optical lens. Therefore, by adjusting the shape of a non - rigid optical element, the optical properties of the optical element can be changed. A piezoelectric material can be used to cause a mechanical actuation to adjust the shape.

Summary of the Invention

Means for Solving the Problems

[0003] This summary is provided to introduce various concepts that are further described in the following detailed description. This summary is not intended to identify key or essential features of the claimed subject matter, nor is it intended to be used as an aid in limiting the scope of the claimed subject matter.

[0004] Generally, in one aspect, an embodiment is an optical element comprising a first piezoelectric layer of a fluorinated polymer having a piezoelectric coefficient d31 of at least 25 pC / N and an electrode layer disposed on the first piezoelectric layer, wherein when the first piezoelectric layer deforms upon application of a voltage in the electrode layer, the optical properties of the optical system change.

[0005] Generally, in one aspect, an embodiment is an optical element comprising a first piezoelectric layer of a fluorinated polymer having a piezoelectric coefficient d31 of at least 25 pC / N and an electrode layer disposed on the first piezoelectric layer, wherein when a voltage is applied across the electrode layer and the first piezoelectric layer deforms, the optical properties of an optical system change. The present disclosure relates to a piezo-optical system comprising such an optical element.

[0006] Other aspects and advantages of the claimed subject matter will become apparent from the following description and the appended claims.

[0007] Next, specific embodiments of the technology of the present disclosure will be described in detail with reference to the accompanying drawings. Like components in the various drawings are denoted by like reference numerals for consistency. BRIEF DESCRIPTION OF THE DRAWINGS

[0008]

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DETAILED DESCRIPTION OF THE INVENTION

[0009] In the following detailed description of embodiments of the present disclosure, numerous specific details are set forth in order to provide a more thorough understanding of the present disclosure. However, it will be apparent to those of ordinary skill in the art that the present disclosure may be practiced without these specific details. In other instances, well-known features have not been described in detail so as not to unnecessarily complicate the description.

[0010] Throughout this application, ordinal numbers (e.g., first, second, third, etc.) may be used as adjectives with respect to elements (i.e., any nouns in this application). The use of ordinal numbers is not for suggesting or creating any particular order of the components, nor for limiting that any component is only a single component, unless explicitly disclosed by using terms such as "before", "after", "single", and other such terms. Rather, the use of ordinal numbers is for distinguishing components. For example, the first component is different from the second component, the first component includes two or more components, and may follow (or precede) the second component in the ordering of the components.

[0011] Generally, embodiments of the present disclosure include a piezoelectric optical system and a piezoelectric optical element. The piezoelectric optical system according to an embodiment of the present disclosure includes at least one optical element having an adjustable shape. The optical element may be a lens or a mirror, and may include non-rigid components such as a deformable elastic solid, a fluid, a gas, etc. The mechanical actuation that brings about the shape adjustment may be provided by an actuator. In one or more embodiments, the actuator is based on a piezoelectric material that changes shape when electrically driven.

[0012] A piezoelectric optical system provided with one or more piezoelectrically adjustable optical elements may be an optical system of any type and for any application, for example, a projection system for virtual reality (VR), augmented reality (AR), or mixed reality (MR) applications of any form factor such as head-mounted or stationary. Other applications include, but are not limited to, cameras, video cameras, microscopes, optical medical devices, and vision correction devices.

[0013] Figures 1A, 1B, and 1C provide introductory examples of scenarios including a viewer observing a visual stimulus. Based on these examples, one possible use of the optical element according to an embodiment of the present disclosure is described.

[0014] Referring to FIG. 1A, the first scenario (100) includes an observer (102) observing a stimulus (104) under natural stereoscopic viewing conditions. For example, the observer (102) can see objects in the surrounding environment. The stimulus (104) can be a physical object, such as a cup on a table in front of the observer (102). Three different stimuli (104) are presented at different distances from the observer (102). The stimuli (104) are represented by different symbols (rectangle, circle, and triangle). The stimuli are presented with respect to accommodation (filled symbols) and convergence (hollow symbols). Accommodation is the process by which the eye changes its refractive power to maintain a sharp image or focus on an object as the distance of the object varies. Convergence is the simultaneous movement of the pupils of the eyes towards or away from each other during focusing. Under natural viewing conditions, as shown in FIG. 1A, convergence occurs in conjunction with accommodation, as indicated by the convergence symbol aligned with the accommodation symbol. A physiological control system coordinates convergence and accommodation to occur together when observing objects at different distances (e.g., the three stimuli shown in FIG. 1A).

[0015] Referring to FIG. 1B, the second scenario (120) includes an observer (102) observing a stimulus (124) in a stereoscopic virtual reality (VR) environment. Thus, the stimulus (124) is a virtual object rather than a physical object. The stimulus (124) can be projected by a VR system optical system (126). The VR system optical system (126) can include various optical elements such as projectors, lenses, mirrors, etc. There are various configurations of the VR system optical system, and any configuration can be used. The VR system optical system (126) is a fixed VR system optical system that defines a non-dynamically changing focal length. As a result, in order for the stimulus (124) to appear in focus, the visual system of the observer (102) needs to be adjusted to a plane at a fixed distance from the user indicated by the filled circle symbol. However, the fixed VR system optical system (126) can change the depth of the virtual object (as indicated by the arrow associated with the unfilled symbol), thereby changing the convergence and providing a stereoscopic three-dimensional cue. When the observer (102) receives a cue of mismatch between the distance (convergence) of the virtual 3D stimulus and the focal length (accommodation) required for the eye to focus on that stimulus, i.e., when the depth of the virtual object is in front of or behind the fixed plane determined by the fixed VR system optical system (126), a contradiction in convergence adjustment can occur. As a result, problems of visual focusing, visual fatigue, and eye strain during viewing of the stereoscopic image, as well as visual effects that remain even after stopping viewing the image, can occur.

[0016] The contradiction in convergence adjustment can be particularly severe for stimuli close to the observer, which occurs because the visual system relies on the accommodation-convergence reflex that provides coordination between the optical focus (accommodation) of the eye based on the perceived distance (convergence) to the object being viewed by the eye.

[0017] Referring to FIG. 1C, a third scenario (140) includes an observer (102) observing a stimulus (144) in a stereoscopic virtual reality (VR) environment according to one or more embodiments. Similar to the scenario (120) of FIG. 1B, the stimulus (144) is a virtual object rather than a physical object. The stimulus (144) can be projected by a VR system optical system (146). The VR system optical system can include various elements such as a projector, lenses, mirrors, etc. In one or more embodiments, unlike the VR system optical system (126) of FIG. 1B, the VR system optical system (146) is an adjustable VR system optical system not limited to a fixed focal length. Thus, for example, by adjusting the focal length in conjunction with the depth of the virtual object being displayed or based on other cues such as the current focal depth of the eye when available, the vergence adjustment conflict can be avoided.

[0018] Optical elements according to embodiments of the present disclosure can be used in an adjustable VR system optical system (146) as described later.

[0019] The use of the optical elements according to embodiments of the present disclosure is not intended to be limited by the scenario of FIG. 1C. The scenario of FIG. 1C is used to illustrate the unique advantages associated with embodiments of the present disclosure, but there are also various other advantages. The advantages can vary depending on the application. Detailed descriptions will be provided later.

[0020] FIGS. 2A, 2B, and 2C show optical elements according to one or more embodiments. FIGS. 2A, 2B, and 2C introduce the optical elements at a conceptual level and show minimal components, but the actual implementation of the optical elements is shown with reference to the drawings described later.

[0021] There are two basic groups of optical elements, transmissive optical elements (such as lenses and prisms) and reflective optical elements (such as mirrors). The optical element can be at least one of a partially transmissive and partially reflective type.

[0022] An optical lens is a transmissive optical element that converges or diverges light rays by refraction. A single lens consists of one transparent material, while a compound lens usually consists of several single lenses (elements) arranged along a common axis. Lenses are manufactured from materials such as glass or plastic and are ground, polished, or molded into the desired shape. Unlike a prism that refracts light without converging it, a lens can converge light to form an image. The optical properties of a lens are determined by multiple factors including the refractive index of the lens material, the curvature of the two lens surfaces, the thickness of the lens, etc. Additionally, different optical properties can be obtained based on the position of the lens in the optical path (e.g., in an adjustable zoom lens arrangement consisting of multiple lenses).

[0023] An optical mirror is a reflective optical element that reflects light. Metals such as silver or aluminum can be used for the reflective surface of the mirror. Curved mirrors, including non-planar mirrors, i.e., concave and convex mirrors, can provide optical properties of divergence and convergence similar to those of an optical lens. By changing at least one of the curvature and position of the optical mirror, the optical properties of the optical mirror can change.

[0024] Optical elements such as lenses and mirrors can be designed for at least one of the visible spectrum of light and any other wavelengths including the non-visible spectrum and microwaves.

[0025] Optical elements according to embodiments of the present disclosure, such as lenses and mirrors, can be used in a variety of applications, including display technologies including virtual reality and augmented reality displays, stationary or wearable imaging devices, etc.

[0026] Optical elements according to embodiments of the present disclosure are deformable in a controllable manner, thereby providing adjustable optical properties. Examples of adjustable optical properties include not only adjustment of focal length but also other adjustments for correcting wavefront aberration, such as those related to myopia, hyperopia, astigmatism, and higher-order wavefront aberration. FIGS. 2A, 2B, and 2C provide a basic description of the components related to the deformability of the optical element. Additional components and configurations are described with reference to other drawings.

[0027] Referring to FIG. 2A, an optical element (200) according to one or more embodiments is shown. In one or more embodiments, the optical element (200) has a plurality of layers including a piezoelectric layer (202) and an electrode layer (204) adjacent to the piezoelectric layer. These layers are disposed on a substrate (240). Without departing from the present disclosure, additional layers may be included. The functions of these layers are described below. In the case of a transmissive optical element, the piezoelectric layer (202), the electrode layer (204), and the substrate (240) may have a minimum required transparency. In the case of a reflective optical element, the piezoelectric layer (202), the electrode layer (204), and the substrate (240) do not necessarily have a minimum required transparency.

[0028] In one or more embodiments, the electrode layer (204) and the piezoelectric layer (202) are arranged in a sandwich structure in which the piezoelectric material is sandwiched between two electrode layers. Due to the piezoelectric effect associated with the piezoelectric material, when a voltage is applied to the piezoelectric layer (204) by, for example, a voltage source (206), the charge balance across the piezoelectric layer (204) changes. The change in the charge balance can result in deformation of the piezoelectric layer (such as shown in FIGS. 2B and 2C). In one embodiment, the piezoelectric layer is a polyvinylidene fluoride (PVDF) piezoelectric film. Piezoelectric materials used include, but are not limited to, PVDF homopolymers, copolymers (such as poly(vinylidene fluoride-co-trifluoroethylene) (P(VDF-TrFE) copolymer), poly(vinylidene fluoride-co-chlorofluoroethylene) (P(VDF-CFE) copolymer), poly(vinylidene fluoride-co-chlorotrifluoroethylene) (P(VDF-CTFE) copolymer), poly(vinylidene fluoride-co-hexafluoropropylene) (P(VDF-HFP) copolymer), poly(vinylidene fluoride-co-tetrafluoroethylene) (P(VDF-TFE) copolymer), P(VDF-TrFE-CFE) terpolymer, P(VDF-TrFE-CTFE) terpolymer), P(VDF-TFE-HFP) terpolymer, P(VDF-TFE-CTFE) terpolymer, P(VDF-TFE-CFE) terpolymer, polylactic acid piezobiopolymer, polyurea, polyurethane, polyamide, polyacrylonitrile, polyimide, polypropylene, etc. Among these, films formed from PVDF homopolymers or P(VDF-TFE) copolymers are preferred.

[0029] In one or more embodiments, the substrate (240) mechanically supports a sandwich structure of a piezoelectric layer (202) between two electrode layers (204). The mechanical properties of the substrate (240) can affect the deformation of the optical element (200). Thus, the selection of at least one of the substrate (240) and the shape of the substrate can be a design parameter of the optical element (200). For example, a more rigid substrate can cause a smaller deformation of the optical element in response to the application of a voltage to the piezoelectric layer (204), while a less rigid substrate can cause a larger deformation. In one or more embodiments, as further described below, the substrate can include or form an optical layer or an optical medium that can be deformed, for example, in the form of a lens, and the rigidity can be selected to achieve the desired deformation of the sandwich structure including the piezoelectric layer(s) and the optical layer.

[0030] Additional layers can be added to the piezoelectric film. The additional layer(s) can include, for example, one or more of a hard coat layer, a refractive index matching layer, an antistatic layer, etc. An explanation of the piezoelectric film is provided in PCT patent application number PCT / JP2021 / 013199. PCT / JP2021 / 013199 is hereby incorporated by reference in its entirety.

[0031] The piezoelectric film can be manufactured using extrusion, a solvent casting method, or a hot press process. The polarization that causes the piezoelectric operation of the piezoelectric film can be obtained by at least one of elongation and exposure to a high electric field, which can be performed separately or simultaneously. The elongation can be performed uniaxially or biaxially. An explanation of the manufacturing process is provided in U.S. Patent No. 8,356,393. U.S. Patent No. 8,356,393 is hereby incorporated by reference in its entirety.

[0032] In one or more embodiments, the piezoelectric layer (204) is based on a piezoelectric film polarized by exposure to a high electric field during the manufacture of the piezoelectric film without the need for the mechanical elongation that would otherwise be used to obtain polarization. The electric field strength during the polarization process can be 200 to 600 MV / m, and the polarized polymer includes a polar α-type crystal structure. The resulting piezoelectric film is less likely to shrink, bend, peel, or a combination thereof when laminated with the electrode layer. Japanese Patent Application Laid-Open No. 2011-192665 provides an explanation of a piezoelectric film manufactured in this manner. Japanese Patent Application Laid-Open No. 2011-192665 is hereby incorporated by reference in its entirety. Alternatively, the piezoelectric film can be directionally oriented by either uniaxial or biaxial elongation.

[0033] The piezoelectric film according to an embodiment of the present disclosure may have one or more of the following characteristics. The sensitivity (the charge in response to the applied force, i.e., represented as the piezoelectric coefficient d31) may be more than 10 pC / N or more than 20 pC / N, or at least 25 pC / N. Various methods can be used to obtain a fluorinated polymer with a high d31, such as using a copolymer / terpolymer or hybrid polymer with a higher piezoelectric effect, using a strong poling treatment, increasing the elongation ratio, adding a nucleating agent to increase the amount of β-crystals, etc. The piezoelectric film may have an arbitrary thickness in the range of, for example, 5 to 200 μm. The thickness of the laminated layers may be uniform, or layers of different thicknesses may be combined according to the desired direction of deformation. The light transmittance of the piezoelectric film may be at least 80%, 90%, or 95%. The transmission haze of the piezoelectric film may be less than 10% or less than 5%. The piezoelectric film may have a Young's modulus of at least 1500 MPa. The piezoelectric film may have an electromechanical coupling coefficient k31 of at least 0.1. The piezoelectric film may have a thermal shrinkage rate of 2% or less after exposing the piezoelectric layer to a temperature of 75 °C for 30 minutes. The piezoelectric film may have a surface roughness (Ra) of 350 nm or less. The piezoelectric film may have a lightness value (L*) of at least 95%, a green-red component (a*) of less than 0.1, and a blue-yellow component (b*) of less than 0.5. The piezoelectric film may have a Poisson's ratio ν31 in the range between 0.15 and 0.8. The piezoelectric film may contain agents such as ammonium salts, polymethyl methacrylate (PMMA), graphene, carbon nanotubes (CNTs), and fullerene crystal nucleating agents useful for increasing the proportion of β-type crystals.

[0034] In one or more embodiments, the electrode layer (204) includes one or more electrodes as either a uniform layer or a patterned layer, as discussed below with reference to FIGS. 4A, 4B, and 4C. The electrodes can consist of transparent conductive coatings such as indium tin oxide (ITO), CNTs, doped CNTs, a mixture of CNTs and metal nanowires (e.g., silver nanowires), conductive polymers (e.g., poly(3,4-ethylenedioxythiophene) polystyrene sulfonic acid or PEDOT:PSS), graphene, metal mesh, etc. For applications where transparency is not required (e.g., when the optical element is a mirror), an opaque material can be used for the electrodes. For example, metals, inorganic oxides, carbon, conductive polymers, etc. can be used.

[0035] The electrodes of the electrode layer (204) according to embodiments of the present disclosure can have one or more of the following characteristics. The sheet resistance of the entire electrode layer can be kept low. The sheet resistance can be less than 300 Ω / sq., less than 100 Ω / sq., or less than 50 Ω / sq. The light transmittance of the electrode layer can be at least 90% or at least 95%. The transmission haze of the electrode layer can be less than 10% or less than 5%.

[0036] In one or more embodiments, the combination of the piezoelectric layer (202) and the electrode layer (204) forms a piezoelectric actuator (208). The piezoelectric actuator (208) generates a mechanical output, such as motion, in the presence of an electrical input, such as a voltage.

[0037] In one or more embodiments, the combination of the piezoelectric layer (202) and the electrode layer (204) forms a piezoelectric stripe actuator, also referred to as a bending actuator. The stripe actuator can be designed to generate a relatively large mechanical deflection in response to the application of a voltage. The stripe actuator can include two piezoelectric layers coupled together. As shown in FIGS. 2B and 2C, the two piezoelectric layers are provided such that when a voltage is applied, one piezoelectric layer expands while the other piezoelectric layer contracts or does not change in length, thereby causing curvature.

[0038] Although not shown, the piezoelectric actuator according to the embodiment may be deformed in other ways. For example, the piezoelectric actuator may be lengthened or shortened, buckled or twisted in one or more directions.

[0039] In one or more embodiments, the piezoelectric actuator (208) provides an actuation to change one or more optical properties of the optical element (200). The change in the optical property may be a result of the deformation of the element shown in FIG. 2. For example, when the piezoelectric layer (202) and the electrode layer (204) are substantially transparent, they may form a tunable lens. Alternatively, additional components may be involved in the change of the optical property. For example, the addition of a light reflecting layer may provide a tunable mirror. Other combinations of elements will be described below. A variety of types of tunable optical elements, including but not limited to active diffraction gratings, tunable lenses, and tunable mirrors, may be formed in this manner.

[0040] Looking at FIG. 2B, the optical element (200) of FIG. 2A is shown. Different from FIG. 2A where the voltage source (206) is not operating (there is no voltage between the electrodes of the electrode layer), in FIG. 2B, the voltage source (206) is operating.

[0041] In FIG. 2B, the optical element (200) is fixed on one side by an anchor (212). Therefore, the application of a voltage through the electrodes of the electrode layer (204) results in the deformation (210) of the optical element (200). In FIG. 2B, the deformation includes the curvature of the optical element (200) that results in the displacement of the free end of the optical element (200). As a result of the deformation (210), the optical properties of the optical element (200) may change. For example, a change in the optical property may be brought about by a change in the curvature along the optical element (200) as a result of the curvature of the optical element (200). Further, a change in the optical property may also be brought about by an offset of the translational motion at the free end of the optical element.

[0042] Referring to FIG. 2C, the optical element (200) of FIG. 2A is shown. Different from FIG. 2A where the voltage source (206) is not operating (there is no voltage between the electrodes of the electrode layer), in FIG. 2C, the voltage source (206) is operating.

[0043] In FIG. 2C, the optical element (200) is fixed on both sides by anchors (222A, 222B). Therefore, by applying a voltage through the electrodes of the electrode layer (204), deformation (220) of the central region of the piezoelectric element (200) is brought about. In FIG. 2C, the deformation includes bending or buckling of the piezoelectric element (200). As a result of the deformation (220), the optical characteristics of the optical element (200) may change. For example, a change in the optical characteristics may be brought about by a change in the curvature along the optical element (200) as a result of the bending of the optical element (200). The simulation results of the optical element shown in FIG. 2C are summarized below with reference to FIGS. 5A - M.

[0044] FIGS. 2B and 2C show individual rigid anchors (212, 222A, 222B), but other types of anchors may be used without departing from the present disclosure. For example, the anchor may be flexible instead of rigid. Materials such as polymers, gels, foams, gases, or liquids or combinations thereof may be used. Further, the anchor may extend over a part or all of the surface of the optical element (200).

[0045] The deformations (210, 220) shown in FIGS. 2B and 2C can be stepwise. As the voltage from the voltage source (206) becomes higher, a greater deformation can be brought about. By reversing the voltage, a deformation in the opposite direction can be brought about. Depending on the design of the optical element (200), the voltage supplied by the voltage source can reach different values, for example up to 10 V, up to + / - 10 V, up to 2,000 V, up to + / - 2,000 V or any voltage in between. When applying a voltage to the optical element (stacked layers), the voltage can be applied in series, in parallel or to individual layers. When applying the voltage individually, the same voltage may be applied to each layer, or different voltages may be applied depending on the shape to be deformed. To achieve the desired amount of deformation, the optical element can be driven at a voltage of 50 V or more for each layer. Higher voltages can sufficiently deform the electro-optic element, but it may be preferable to drive at a lower voltage in terms of power consumption. Since the piezoelectric coefficient d31 greatly affects the amount of deformation, the driving conditions can be selected based on the combination of the voltage and d31 in order to obtain sufficient deformation while keeping the voltage low. In one or more embodiments, the product of the absolute value of d31 (pC / N) and the voltage (V) applied to each piezoelectric layer is 4,000 or more (pC / N*V). To precisely control the deformation of the optical element, various electrode patterns described below with reference to FIGS. 4A to 4C can be further used.

[0046] FIGS. 3A, 3B, and 3C show a stack of an optical element according to one or more embodiments. The stacks of FIGS. 3A to 3C show how the aforementioned layers can be arranged and further how additional layers can be included in the stack.

[0047] Referring to FIG. 3A, the stack (300) includes a piezoelectric layer (302) similar to that shown in FIGS. 2A to 2C and two electrode layers (304).

[0048] Referring to FIG. 3B, laminate (310) includes a polyethylene terephthalate (PET) layer (314) and an adhesive layer (316) in addition to the elements of laminate (300) of FIG. 3A. The PET layer (314) can be used to facilitate the manufacture of optical elements. In particular, the electrodes of the electrode layer (304) can be disposed on the PET layer (314) instead of on the piezoelectric layer (302). The adhesive (316) can permanently bond the PET layer (314) with electrodes to the piezoelectric layer (302). The laminate (310) can be similar to the laminate (300) in other respects.

[0049] Referring to FIG. 3C, laminate (320) includes a plurality of arrangements of the layers of laminate (300). Any number of laminates (300) can be stacked. An adhesive (326) can mechanically connect the individual laminates. Stacking as shown in FIG. 3C can increase the magnitude of the generated motion, and the overall magnitude of the motion can be the sum of the displacements of each piezoelectric layer. Stacking can further enable more complex motion patterns, including any combination of compression, elongation, torsion, and bending.

[0050] The piezoelectric layers of laminate (320) can be uniaxially oriented in respective unique directions. Thus, each piezoelectric layer can have a unique directional deformation pattern, such as the curvature described with reference to FIGS. 2B and 2C. The deformation of an individual piezoelectric layer can be anisotropic (e.g., as shown in FIG. 2B), but a combination of multiple piezoelectric layers can result in an isotropic deformation. For example, the resulting deformation can be symmetric with respect to the axis of rotation. Such deformation patterns can be particularly beneficial in lenses, mirrors, etc., which are often circular. Four or more layers with different orientations can be used to create symmetric concentric circular deformations in a rectangular element.

[0051] Figures 3A - 3C show various laminations, but other laminations may be implemented without departing from the present disclosure. For example, any component shown in one of the laminations may be present in any of the other laminations. Also, although the laminations of Figures 3A - 3C are shown with all layers being flat, the laminations may instead be pretensioned and may have, for example, curvature or any other deviation from being substantially flat. Pretensioning can be achieved during the layer lamination process. The lamination may further include layers of a single fluorinated polymer, multiple different fluorinated polymers, or a blend of multiple different fluorinated polymers or combinations thereof. Fluorinated polymer layers with different properties (d31, mechanical properties, thickness, etc.) may be laminated, or the same fluorinated polymer layer may be laminated. Examples of fluorinated polymers and other electroactive materials that can be stacked include ceramic materials such as K0.5Na0.5NbO3 ("KNN"), barium titanate, lithium niobate, lithium tetraborate, quartz, Pb(Mg1 / 3Nb2 / 3)3 - PbTiO3 ("PMN - PT"), Pb(Zn1 / 3Nb2 / 3)O3 - PbTiO3 ("PZN - PT"), and lead zirconate titanate ("PZT"), other piezoelectric polymers such as polylactic acid piezobiopolymer, polyurethane, polyurea, polyamide, polyacrylonitrile membrane, polyimide, and polypropylene, or other electroactive polymers such as dielectric electroactive polymers, ferroelectric polymers, electrostrictive polymers, ionic electroactive polymers, and stimulus - responsive gels, or combinations thereof.

[0052] The selection of a particular lamination can be based on various considerations. For example, a more basic lamination (fewer layers) can be at least one of more cost - effective and more compact. Other laminations can be easier to manufacture. For example, instead of placing an electrode directly on the surface of a piezoelectric film, an additional PET layer can be used to support the electrode. Further, a certain lamination may be more suitable for achieving a particular type of deformation required or desired for a particular optical application. Specific types of deformation can also be obtained by selectively driving the piezoelectric layer(s) using patterned electrodes.

[0053] Figures 4A, 4B, and 4C show electrode patterns according to one or more embodiments. The electrode patterns can be used to selectively expose limited regions of the piezoelectric layer to voltage. A basic electrode pattern can include two electrodes, one on each side of the piezoelectric layer. With this electrode pattern, the entire piezoelectric layer can be driven non-selectively all at once. The following description refers to electrode patterns that enable selective driving of the piezoelectric layer. Some piezoelectric embodiments use an array of electrodes or other regular or irregular patterns to drive the piezoelectric material at different locations throughout the piezoelectric layer.

[0054] Referring to FIG. 4A, a first electrode pattern (400) according to one or more embodiments is shown. The electrode pattern includes a row of first electrodes (402) and a column of second electrodes (404). The first electrodes (402) can be located on one of the two electrode layers (204) of the optical element (200) of FIGS. 2A-2C. Similarly, the second electrodes (404) can be located on the other of the two electrode layers (204). In the electrode pattern (400), the first electrodes (402) and the second electrodes (404) have a rectangular shape. The electrodes can have different shapes without departing from the present disclosure. For example, interconnected diamond-shaped electrode pads can be arranged in a row or column. Although not shown, the piezoelectric layer (202) can be located between the first electrodes (402) disposed on one surface of the piezoelectric layer and the second electrodes (404) disposed on the other surface of the piezoelectric layer as described above.

[0055] At the intersection of the first electrode (402) and the second electrode (404), a voltage can be applied in a pattern localized in the piezoelectric layer. This region of localized driving of the piezoelectric layer can be referred to as a "driving element" (406). In FIG. 4A, only a single driving element (406) is identified, but driving elements (406) can exist at each intersection of the first electrode (402) and the second electrode (404). By applying a voltage to each of the driving elements (406), the operation (e.g., deformation) of the piezoelectric layer can be locally controlled over the entire (or a part of) the piezoelectric layer as a result. The application of the voltage can be performed in a scanning operation, for example, in at least one of row-by-row and column-by-column until all the driving elements (406) are driven. Different voltages can be applied to different driving elements (406) to obtain a desired mechanical operation of the piezoelectric layer. If the driving of different driving elements is performed at a sufficiently high frequency over time, a quasi-static mechanical operation of the piezoelectric layer can be obtained. The driving operation can be performed by a driving circuit (not shown). The driving circuit can drive each driving element with a voltage specific to that driving element.

[0056] The electrode pattern (400) is for a substantially rectangular region, but the electrode pattern may be modified to have different shapes. For example, the contour of the electrode pattern (400) may be circular.

[0057] Looking at FIG. 4B, an electrode pattern (420) is shown. This electrode pattern includes a pattern of a first electrode (422) and a single second electrode (424) extending over the region of the first electrode (422). The first electrode (422) can be located in one of the two electrode layers (204) of the optical element (200) in FIGS. 2A - 2C. Similarly, the second electrode (424) can be located in the other of the two electrode layers (204). In this electrode pattern (420), each of the first electrodes (422) is a pad that can have an arbitrary shape.

[0058] A driving element (426) is formed on each of the first electrodes (422). The design of the electrode pattern (420) is different from the design of the electrode pattern (400), but the driving of the piezoelectric layer by voltage can be performed in a similar manner.

[0059] Figures 4A and 4B show two types of electrode patterns, but other types of electrode patterns may be used without departing from the present disclosure. Also, non-patterned electrodes (e.g., electrodes on a solid surface) may be used. Further, the electrode pattern may have at least one of its size and resolution changed without departing from the present disclosure.

[0060] Referring to FIG. 4C, a third electrode pattern (440) according to one or more embodiments is shown. The third electrode pattern may be particularly suitable for generating non-uniform deformations of lenses and other optical elements. For example, the third electrode pattern (440), while being in an axially symmetric manner, may be used to provide the curvature, curvature variation, and combinations of curvature and curvature variation shown in FIG. 2C. As shown in FIG. 4C, the axially symmetric electrode pattern (440) may be used to induce axially symmetric or substantially axially symmetric deformations. In this example, the first electrode is ring-shaped while the second electrode is not patterned. The axial symmetry of the electrode pattern can produce a substantially axially symmetric curvature change for adjusting the refractive power. Any number of ring-shaped first electrodes may be used. Although FIG. 4C shows a completely axially symmetric embodiment, other embodiments need not be completely axially symmetric. For example, the electrode pattern (440) may include one or more first electrodes that are not circular. FIG. 4C shows a single second electrode (444), but in other embodiments, a second electrode set may be patterned, for example, as radially oriented spokes or in other patterns. The patterned second electrode may enable correction of optical aberrations by deviating from a strict axially symmetric deformation of the optical element.

[0061] Based on the introduction of the optical element, the stack, and the electrode pattern, additional configurations of the optical element will be described later.

[0062] In one embodiment, the optical element includes a sandwich structure of a plurality of optical layers and a plurality of piezoelectric layers. This optical element may include, from bottom to top, an optical layer, two or more piezoelectric layers, and another optical layer. The piezoelectric layers may be driven together or individually using electrode layers that can be patterned to cause a desired deformation of the optical element.

[0063] In one embodiment, a Fresnel lens can be integrated with an optical element such as an optical element having a bimorph structure. For example, the optical element may include one or more piezoelectric layers and a Fresnel lens in a sandwich-like structure. The piezoelectric layers may be driven together or individually using electrode layers that can be patterned to cause a desired deformation of the Fresnel lens. Due to the deformation, the optical properties of the Fresnel lens can change. For example, the deformation can change the pitch within the active diffraction grating during elongation, or change the curvature during bending to vary the refractive power, selectively reflect or refract light, and / or provide beam steering.

[0064] Other embodiments may include deformable optical media such as gases (e.g., air, nitrogen, etc.), liquids (e.g., water, saline solution, high refractive index liquids, etc.), polymer materials, gels (e.g., silicone gel), foams (e.g., silica aerogel), etc.

[0065] Although various different optical elements are described, many other combinations can be used without departing from the present disclosure. Further examples include combinations of a Fresnel lens or a pancake lens with a piezoelectric actuator. In one embodiment, one or more piezoelectric actuators are combined with a pancake lens. The resulting pancake lens assembly can be used to fold the optical path from a light source to a detector in an optical system. For example, the pancake lens assembly can be used in a head-mounted display (HMD) to fold the optical path, thereby shortening the back focal length in the HMD. The pancake lens assembly can include a first optical element, a piezoelectric actuator (variable focus lens), and a second optical element. The first optical element and the second optical element may form a cavity, and the variable focus lens may be disposed inside or outside the cavity. In one embodiment, one or more piezoelectric actuators are combined with an alvarez lens. The piezoelectric actuator(s) can drive the lateral displacement of two lens elements of the alvarez lens relative to each other to perform focus or defocus adjustment.

[0066] Regardless of the particular embodiments being considered, the use of piezoelectric actuators can provide various advantages. For example, PVDF (and similar materials) are flexible, thus being strong against repeated deformation, providing a rapid response time and a wide frequency response. Further, the properties of PVDF (and similar materials) can be controlled by adjusting the manufacturing process, by copolymerization, and / or by mixing with other polymers or other materials. The optical elements according to embodiments of the present disclosure are suitable for numerous applications and can have properties that can be detailed. For example, the properties of the optical elements can include a deformation that can be realized of at least 200 μm, the performance of correcting spherical aberration of second order or higher, an adjustable focal length ranging from 10 cm to ∞, etc.

[0067] Also, FIGS. 2A-2C, 3A-3C, and 4A-4C show the configurations of the components, but other configurations may be used without departing from the scope of the present disclosure. For example, one component may be created by combining various components. As another example, the functions performed by a single component may be performed by two or more components.

[0068] FIGS. 5A-5M show simulations according to one or more embodiments.

[0069] Referring to FIG. 5A, a finite element analysis (FEA) model configuration according to one or more embodiments is shown. The FEA model configuration (500) is used in the simulations described below. The FEA model configuration (500) includes a rectangular (3 cm × 4.5 cm) piezoelectric base lens having a piezoelectric layer with a thickness of 40 micrometers, a Poisson's ratio of 0.3, and a density of 1.78 g / cm3. Another FEA model configuration (not shown) includes a circular (3 cm in diameter) piezoelectric base lens having a piezoelectric layer with a thickness of 40 micrometers, a Poisson's ratio of 0.3, and a density of 1.78 g / cm3. In one configuration, the piezoelectric layer of the circular lens is 20 micrometers thick.

[0070] Referring to FIG. 5B, two FEA model configurations according to one or more embodiments are shown. The first FEA model configuration (510) includes a single piezoelectric layer (left), and the second FEA model configuration (510) includes four piezoelectric layers (right). Two additional FEA model configurations (shown here) include two and eight piezoelectric layers. In the simulations, each of the two-layer, four-layer, and eight-layer configurations can be connected using a tie constraint (e.g., representing bonding or adhesion in an actual implementation).

[0071] FEA of optical element deformation under different conditions was performed. The parameters varied included d31, Young's modulus, voltage, number of layers, and layer thickness.

[0072] In the first simulation scenario (520) shown for eight layers in FIG. 5C, a voltage was applied across the entire stack. Each layer of the stack was in direct contact, and the stack could have any number of layers. The following results were obtained: (1) As the voltage increased and the d31 value increased, the maximum deformation and curvature of the stack increased. (2) When a constant voltage was applied across the entire stack, the deformation resistance increased as the number of layers increased. (3) As the Young's modulus of the layer(s) increased, the displacement increased until the optimal value of the Young's modulus was reached. No further continuous increase in displacement was observed beyond the optimal value. It was found that, when compared directly, d31 had a greater effect on deformation than the Young's modulus. Also, the smaller the Young's modulus of the substrate (anchor) in contact with the bottom surface, the greater the deformation. In the second simulation scenario (530) shown in FIG. 5D, a voltage was applied to individual layers (the potential difference across both sides of each layer was 1000 V). In this configuration, a thin (e.g., 1 μm) insulating layer could separate the stacked layers. The insulating layer could have a rigidity similar to that of the layers. The increase in voltage resulted in greater layer deformation and curvature. Also, assuming the same material properties and charging, a rectangular lens produced greater deformation than a circular lens. In contrast, a circular lens with a smaller number of layers achieved a smoother and more uniform curvature than a rectangular lens. In the simulation, thinner lenses produced greater deformation than thicker lenses, and there was no adverse effect on the smoothness of the lens curvature. It was further determined that at least four layers might be required to create a symmetric circular deformation in a rectangular optical element.

[0073] Figures 5E to 5I show simulation results according to embodiments of the present disclosure. The simulation results are for a first simulation scenario using a rectangular model. Displacements in response to various voltages are shown for various configurations, such as eight-layer, four-layer, two-layer, and one-layer configurations including a 40-micrometer-thick layer using PVDF and a rigid substrate. The simulation results are for several different d31 values. Further, Figures 5J to 5L show additional simulation results according to embodiments of the present disclosure using a circular model in the first simulation scenario. Figure 5M shows additional simulation results according to embodiments of the present disclosure using a circular model in the second simulation scenario. Displacements in response to 1000 V are shown for an eight-layer configuration including a piezoelectric layer that is 40 micrometers or 20 micrometers thick and a thin insulating layer that is 1 micrometer thick.

[0074] Referring to FIG. 6, an optical system according to one or more embodiments is shown. The optical system (600) of FIG. 6 is a head-mounted display (HMD) in the form of glasses or a more immersive helmet-type configuration. The HMD may include one or more display assemblies (610) according to embodiments of the present disclosure. The display assembly (610) is located within the transparent aperture of the HMD (600) and may be configured to present media to a user (698). In this example, the display assembly (610) includes a display device, such as an image projector (612). The image projector (612) may be mounted on the temple arm (620) of the HMD (600). Projection light (614) is directed by a beam steerer (not shown) and reflected by a combiner (616), and the resulting reflected light (618) may be focused onto the pupil of the user (698). In an AR system, the user can simultaneously view real objects through at least a partially transparent combiner (616). In one or more embodiments, the combiner (616) is or includes the aforementioned optical element. For example, the combiner (616) may include a Fresnel combiner or a pancake combiner, and may include the aforementioned optical element, an ellipsoidal mirror, one or more tunable waveguides, or a holographic combiner. By operating the optical element, the focal length of the HMD can be increased or decreased, and the eye relief can be adjusted. The HMD may include additional components. For example, additional optical elements different from the combiner (616) may be adjustable using piezoelectric actuators. In some embodiments, the HMD or AR glasses are configured to provide augmented reality content to the wearer of the display device. For example, the HMD may include an eye tracker (not shown). The eye tracker is used to track the position and focal length of the user's pupil, thereby enabling closed-loop operation of the AR or VR glasses and avoiding convergence adjustment conflicts. Based on the detected pupil position and the estimated focal length, the focal length of the lens or mirror can be adjusted in the x and / or y directions, or in the x, y, and / or z directions. The adjustment can be performed in real time.The HMD may also include one or more audio speakers to enhance the level of immersion. The audio speaker may be a piezoelectric film-based audio speaker. In one embodiment, the audio speaker is a bone conduction-based speaker.

[0075] Only a few exemplary embodiments have been described in detail above, but those skilled in the art will readily understand that numerous modifications are possible in the exemplary embodiments without substantially departing from the present invention. Accordingly, it is intended that all such modifications be included within the scope of the present disclosure as defined by the following claims.

Claims

1. Piezoelectric coefficient d ３１ a first piezoelectric layer of a fluorinated polymer having a piezoelectric coefficient d of at least 25 pC / N, and An electrode layer disposed on the first piezoelectric layer, An optical element comprising: When the first piezoelectric layer deforms upon application of a voltage in the electrode layer, the optical characteristics of the optical element change, Optical element.

2. The optical element according to claim 1, wherein the fluorinated polymer is a polyvinylidene fluoride (PVDF) homopolymer, a poly(vinylidene fluoride-co-trifluoroethylene) (P(VDF-TrFE) copolymer), a poly(vinylidene fluoride-co-chlorofluoroethylene) (P(VDF-CFE) copolymer), a poly(vinylidene fluoride-co-chlorotrifluoroethylene) (P(VDF-CTFE) copolymer), a poly(vinylidene fluoride-co-hexafluoropropylene) (P(VDF-HFP) copolymer), a poly(vinylidene fluoride-co-tetrafluoroethylene) (P(VDF-TFE) copolymer), a P(VDF-TrFE-CFE) terpolymer, a P(VDF-TrFE-CTFE) terpolymer), a P(VDF-TFE-HFP) terpolymer, a P(VDF-TFE-CTFE) terpolymer, and a P(VDF-TFE-CFE) terpolymer, and an optical element comprising at least one selected from the group consisting of.

3. The optical element according to claim 1, wherein the first piezoelectric layer is one selected from the group consisting of a uniaxially oriented film, a biaxially oriented film, or an unoriented film.

4. The optical element according to claim 1, wherein the first piezoelectric layer has a light transmittance of at least 80%.

5. The optical element according to claim 1, wherein the first piezoelectric layer has a thickness in the range between 5 μm and 200 μm.

6. The optical element according to claim 1, wherein the first piezoelectric layer has a Young's modulus of at least 1500 MPa.

7. The optical element according to claim 1, wherein the first piezoelectric layer has an electromechanical coupling coefficient k of at least 0.1 ３１ The optical element having the same.

8. The optical element according to claim 1, wherein the first piezoelectric layer has a thermal shrinkage rate of 2% or less after exposing the piezoelectric layer to a temperature of 75 ° C for 30 minutes.

9. The optical element according to claim 1, wherein the first piezoelectric layer has a surface roughness (Ra) of 350 nm or less.

10. The optical element according to claim 1, wherein the first piezoelectric layer has a lightness value (L ＊ of at least 95%, a green-red component (a ＊ of less than 0.1, and a blue-yellow component (b ＊ of less than 0.5).

11. The optical element according to claim 1, wherein d ３１ the product of the absolute value of (pC / N) and the voltage (V) applied to each piezoelectric layer is 4,000 or more (pC / N ＊ V), and the optical element is driven so as to be.

12. The optical element according to claim 1, wherein the fluorinated polymer contains a drug selected from at least one of the group consisting of an ammonium salt, polymethyl methacrylate (PMMA), graphene, carbon nanotubes (CNTs), and fullerene as a crystal nucleating agent.

13. The optical element according to claim 1, further comprising a hard coat layer disposed on the first piezoelectric layer.

14. The optical element according to claim 1, wherein the electrode layer is one selected from the group consisting of ITO, metal nanowires, metal meshes, CNTs, graphene, and poly(3,4-ethylenedioxythiophene) polystyrenesulfonic acid.

15. The optical element according to claim 1, wherein the voltage ranges between 10 V and 2,000 V.

16. The optical element according to claim 1, further comprising a second piezoelectric layer of a fluorinated polymer.

17. The optical element according to claim 16, wherein the first piezoelectric layer and the second piezoelectric layer are stacked with different orientations.

18. The optical element according to claim 1, wherein the optical element is one selected from the group consisting of a tunable lens and a tunable mirror.

19. The optical element according to claim 18, wherein the tunable lens is one selected from the group consisting of a pancake lens, an alvarez lens, and a fresnel lens.

20. The optical element according to claim 18, wherein the tunable lens has an adjustable focal length in the range of 10 cm to ∞.

21. The optical element according to claim 1, wherein the deformation is at least 50 μm.

22. The optical element according to claim 1, which corrects wavefront aberrations of the second order or higher.

23. Piezoelectric coefficient d ３１ a first piezoelectric layer of a fluorinated polymer having at least 25 pC / N, and An electrode layer disposed on the first piezoelectric layer, An optical element comprising: A piezoelectric optical system comprising an optical element in which when the first piezoelectric layer deforms upon application of a voltage to the electrode layer, the optical characteristics of the optical system change.

24. The piezoelectric optical system according to claim 23, wherein the piezoelectric optical system is one selected from the group consisting of a headset and glasses.

25. A piezoelectric-optical system according to claim 24, further comprising an eye tracker that identifies a current focusing distance of a user using the optical system, wherein the optical characteristics are adjusted based on the current focusing distance. **Claim 26** A piezoelectric-optical system according to claim 24, further comprising a piezoelectric film-based audio speaker. **Claim 27** A piezoelectric-optical system according to claim 23, wherein the optical characteristic is a focal length of the optical element. **Claim 28** A piezoelectric-optical system according to claim 23, wherein the piezoelectric-optical system is integrated into one selected from the group consisting of augmented reality (AR) applications, virtual reality (VR) applications, and mixed reality (MR) applications.

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