Classifications

• • G—PHYSICS
  • G02—OPTICS
  • G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
  • G02B3/00—Simple or compound lenses
  • G02B3/12—Fluid-filled or evacuated lenses
  • G02B3/14—Fluid-filled or evacuated lenses of variable focal length
• • G—PHYSICS
  • G02—OPTICS
  • G02C—SPECTACLES; SUNGLASSES OR GOGGLES INSOFAR AS THEY HAVE THE SAME FEATURES AS SPECTACLES; CONTACT LENSES
  • G02C7/00—Optical parts
  • G02C7/02—Lenses; Lens systems ; Methods of designing lenses
  • G02C7/08—Auxiliary lenses; Arrangements for varying focal length
  • G02C7/081—Ophthalmic lenses with variable focal length
  • G02C7/083—Electrooptic lenses
• • G—PHYSICS
  • G02—OPTICS
  • G02F—OPTICAL DEVICES OR ARRANGEMENTS FOR THE CONTROL OF LIGHT BY MODIFICATION OF THE OPTICAL PROPERTIES OF THE MEDIA OF THE ELEMENTS INVOLVED THEREIN; NON-LINEAR OPTICS; FREQUENCY-CHANGING OF LIGHT; OPTICAL LOGIC ELEMENTS; OPTICAL ANALOGUE/DIGITAL CONVERTERS
  • G02F1/00—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics
  • G02F1/01—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour 
  • G02F1/13—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour  based on liquid crystals, e.g. single liquid crystal display cells
• • G—PHYSICS
  • G02—OPTICS
  • G02F—OPTICAL DEVICES OR ARRANGEMENTS FOR THE CONTROL OF LIGHT BY MODIFICATION OF THE OPTICAL PROPERTIES OF THE MEDIA OF THE ELEMENTS INVOLVED THEREIN; NON-LINEAR OPTICS; FREQUENCY-CHANGING OF LIGHT; OPTICAL LOGIC ELEMENTS; OPTICAL ANALOGUE/DIGITAL CONVERTERS
  • G02F1/00—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics
  • G02F1/29—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the position or the direction of light beams, i.e. deflection
• • G—PHYSICS
  • G02—OPTICS
  • G02F—OPTICAL DEVICES OR ARRANGEMENTS FOR THE CONTROL OF LIGHT BY MODIFICATION OF THE OPTICAL PROPERTIES OF THE MEDIA OF THE ELEMENTS INVOLVED THEREIN; NON-LINEAR OPTICS; FREQUENCY-CHANGING OF LIGHT; OPTICAL LOGIC ELEMENTS; OPTICAL ANALOGUE/DIGITAL CONVERTERS
  • G02F1/00—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics
  • G02F1/29—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the position or the direction of light beams, i.e. deflection
  • G02F1/294—Variable focal length devices

Definitions

• Ophthalmic lenses are most useful if they have adjustable focusing power (i.e., the focusing power is not static). Adjustable focusing power provides the eye with an external accommodation to bring objects of interest at different distances into focus. Adjustable focusing power can be achieved using a mechanical zoom lens. However, the mechanical approach makes the spectacle bulky and costly.
• a new lens design and corresponding device and method for adjusting the focal length of a lens is provided.
• the new design is based on an individually addressable electrode pattern. Described here are two applications of the new design.
• the first application allows switching the focal length between discrete values. In one embodiment, the focal length is switched between an initial focal length and integer multiples of the initial focal length.
• the second application allows a more general use, where the focal length is continuously adjusted from the minimum possible value based on the design parameters to infinity.
• the new design overcomes the difficulties described above.
• an adjustable focusing electrically controllable electroactive lens More specifically, provided is an adjustable focusing electrically controllable electroactive lens. Also provided are methods for discretely or continuously adjusting the focal length of an electrically controllable electroactive lens. Electrically controllable electroactive lenses allow the focal length to be adjusted without bulky and inefficient mechanical movement. In contrast to the simultaneous vision lenses such as bifocal, trifocal, or progressive eyeglasses or contact lenses, in which the field of view for each vision is limited to a narrow corridor and the user is confronted with two images, and the monovision lenses in which the binocular depth perception is affected, the electro-active adjusts the focusing power and at each working condition the whole aperture has the same focusing power.
• simultaneous vision lenses such as bifocal, trifocal, or progressive eyeglasses or contact lenses
• Devices made from the adjustable focusing electrically controllable lenses provide adjustable focusing with a large field of view and high image quality without the need to switch between different physical lenses.
• Other advantages of this lens include compact, lighter weight, low cost, and easier operation with low voltages and low power dissipation.
• an adjustable focusing electrically controllable electroactive lens comprising: a liquid crystal layer positioned between a pair of transparent substrates; a Fresnel zone patterned electrode having M zones, each zone having L individually addressable subzones positioned between the liquid crystal layer and the inward-facing surface of the first transparent substrate, where M and L are positive integers; and a conductive layer between the liquid crystal layer and the inward-facing surface of the second transparent substrate.
• the individually addressable subzones of the Fresnel zone patterned electrode can be on the same horizontal plane, in which the subzones are separated by an insulator to prevent electrical shorting, or the individually addressable subzones of the Fresnel zone patterned electrode can be positioned on two or more horizontal planes, each separated by an insulating layer, or other configurations can be used as known in the art.
• a method of adjusting the focal length of a lens by integer multiples of an original focal length F comprising: providing a lens comprising a liquid crystal layer enclosed between a pair of transparent substrates; a Fresnel zone patterned electrode positioned between the liquid crystal layer and the inward-facing surface of the first transparent substrate, said patterned electrode having M zones, each zone having L subzones, said patterned electrode having a total of M-L individually addressable electrodes; a conductive layer between the liquid crystal layer and the inward-facing surface of the second transparent substrate; and an electrical control electrically connected to the electrode zones and the conductive layer; applying the same voltage to each k individually addressable electrodes to adjust the focal length to kF, where k is an integer from 1 to ML.
• the electrode zones are formed from patterned ITO (Indium Tin Oxide) electrodes.
• the phase retardation in each zone is modulated by reorientation of the liquid crystal using applied electrical fields, as known in the art.
• the adjustable focusing electrically controllable electroactive lens described herein provides many advantages over current approaches.
• One advantage is the ability to adjustably change the focusing power of the lens.
• the focal length of a diffractive lens is determined by the electrode zone spacing. In the lenses described herein, the electrode pattern is fixed and the focal length can be changed directly by changing the electronic driving connections to the electrodes and the voltage applied.
• the individually addressable electrode zones allow correction for different distance vision, including near- (e.g., reading), intermediate- (e.g., computer screen) and distance vision.
• the focusing power can be adjusted either directly by a range finder or manually by the user.
• microelectronic circuits are integrated with the lens, so the assembly is compact.
• the electrode structure is invisible, which provides a cosmetic advantage over the terraced liquid crystal approach. A loss of electrical power will not affect the distance vision (the focusing power provided when no current is provided). At each working condition the entire aperture has the same focusing power.
• the Fresnel zone structure described herein in one embodiment allows relatively large apertures, which is required for ophthalmic lens applications. Other advantages of the invention described herein include a compact design, lighter weight, low cost, easier operation with low voltages and low power dissipation.
• the focal length of the lenses described herein and the corresponding diopter values can be either positive or negative, depending on the voltages applied.
• adjustable focusing means the focal length of the lens is not fixed at one distance as in a conventional optical lens.
• the focal length of an adjustable focusing lens is adjusted by changing the voltage applied to electrodes by means known in the art. In one embodiment, the focal length is adjusted by the user to provide vision of an object at a desired distance.
• Individually addressable means the same or different voltage can be applied to different electrodes independently.
• Electrically controllable means a voltage is applied to control or change a parameter, such as the orientation state of a liquid crystal, as known in the art.
• Continuous adjusting means the focal length can be adjusted to many different values that are not strict multiples of the original focal length and does not necessarily mean that every different focal length is achievable, due to the physical limitations of the current patterned electrode fabrication techniques.
• layer does not require a perfectly uniform film. Some uneven thicknesses, cracks or other imperfections may be present, as long as the layer performs its intended purpose, as described herein.
• perpendicular means approximately perpendicular to the surface of the substrate. Note that the optical axis generally is approximately perpendicular to the surface of the substrate.
• no horizontal gap between electrodes includes the situation where the electrodes have no space between them when viewed in the perpendicular direction, and also includes the situation where there is a space between electrodes when viewed in the perpendicular direction that does not cause the diffraction efficiency of the optic to be reduced by more than 25% from the theoretical maximum, as well as all individual values and ranges therein.
• the devices of the invention can be used in a variety of applications known in the art, including lenses used for human or animal vision correction or modification.
• the lenses can be incorporated in spectacles, as known in the art.
• Spectacles can include one lens or more than one lens.
• the devices may also be used in display applications, as known to one of ordinary skill in the art without undue experimentation.
• the lenses of the invention can be used with conventional lenses and optics.
• the lenses of the invention can be used as a portion of a conventional lens, for example as an insert in a conventional lens, or a combination of conventional lenses and lenses of the invention can be used in a stacked manner.
• This invention is useful in preparing spectacles having lenses that adjust focusing strength based on distance from the object viewed.
• a range-finding mechanism, battery and control circuitry are housed in the spectacles or are part of a separate control system. These components and their use are known in the art.
• the range- finding mechanism is used to determine the distance between the spectacle and a desired object. This information is fed to a microprocessor which adjusts the voltage applied to the individually addressable electrodes, which gives the lens the desired phase transmission function to view the object.
• Various methods of applying voltage to the electrodes can be used, as known in the art.
• a battery can be used to supply the voltage, or other methods, as known in the art. It is known in the art that various methods of controlling all aspects of the voltage applied to electrodes can be used, including a processor, a microprocessor, an integrated circuit, and a computer chip. The voltage applied is determined by the desired phase transmission function, as known in the art.
• Figure 1 shows an illustration of a diffractive lens: graph (a) is a conventional refractive lens; graph (b) is a diffractive lens with continuous quadratic blaze profile; graph (c) is a binary diffractive lens; and graph (d) is a four-level approximation of the diffractive lens.
• Figure 2 shows a construction of a diffractive lens.
• Figure 3 shows a liquid crystal cell.
• Figure 4 shows general structure of an electro-active liquid crystal lens with patterned electrodes.
• Figure 5A illustrates a structure where all electrodes are on the same plane (one-layer structure), in which there is a small gap between neighboring subzones.
• Figure 5B illustrates a structure where odd-numbered electrodes and even-numbered electrodes are interleaved into two horizontal layers, and there is no gap between neighboring subzones (two-layer structure).
• Figure 6 shows an example of digital variable focal length using the individually addressable electrode pattern.
• Figure 7 shows continuous adjustment of the focal length using individually addressable circular array of electrodes with proper resolution.
• Diffractive lenses are known in the art.
• the function of a diffractive lens is based on near-field diffraction by a Fresnel zone pattern.
• Each point emerging from the structure serves as an emitter of a spherical wave.
• the optical field at a particular observing point is a summation of the contributions of the emitted spherical waves over the entire structure. Constructive interference of the spherical waves coming from the various points creates a high intensity at the observation point, corresponding to a high diffraction efficiency.
• Figure 1 shows an illustration of a diffractive lens: graph (a) is a conventional refractive lens; graph (b) is a diffractive lens with continuous quadratic blaze profile; graph (c) is a binary diffractive lens; and graph (d) is a four-level approximation of the diffractive lens.
• Figure 1 graph (a) shows a part of a conventional refractive lens.
• a diffractive lens is obtained as shown in Fig. 1 graph (b).
• the phase jump at each zone boundary is 2 ⁇ for the design wavelength ⁇ 0 , and the blazing profile in each zone makes perfect constructive interference at the focal point.
• Figure 1 graph (c) and Figure 1 graph (d) show different approximations of the desired phase profile in Fig. 1 (b), wherein multiple steps in each zone are used to approximate the desired phase profile.
• Figure 2 shows a construction of a diffractive lens.
• (f) is displayed along the optical axis.
• the radius (r m ) is displayed perpendicular to the optical axis. Note that the path traveled by light entering the lens at radius (r m ) to reach the focal point F is equivalent to the focal length (f) plus an integer number of wavelengths (m ⁇ ) in order to have constructive interference.
• the focal length (f) of the diffractive lens is determined by the period of the zones.
• the optical path length differences are multiples of the wavelength.
• f + m ⁇ is a hypotenuse of a right triangle in Figure 2:
• each zone consists of L subzones of equal size (area). Note that there are L subzones and each of the subzones has a different optical thickness, thus there are L phase levels.
• Table 1 gives various parameters for a 1 -diopter diffractive lens. As seen in Table 1 , the diffraction efficiency increases as the number of phase levels increases and the width of the last subzone decreases as the aperture of the lens increases.
• FIG. 3 shows an illustrative embodiment of an electro-active liquid crystal cell, where a layer of liquid crystal is sandwiched between two glass plates that have conductive inner surfaces. The surfaces of the plates are coated with an alignment layer such as polyvinylalcohol (PVA) or nylon 6,6 and are treated by rubbing to give a homogeneous molecular orientation. The alignment layers are buffed in the direction shown in the arrows, as known in the art. A voltage is applied to the inner conductive surfaces of the plates.
• PVA polyvinylalcohol
• nylon 6,6 nylon 6,6
• every zone has the same thickness, but the refractive index of the extraordinary beam is changed due to the reorientation of the liquid crystal molecule when a voltage is applied to the medium.
• the original orientation of the liquid crystal molecule is determined by the buffing direction.
• the long axis (optic axis) of the liquid crystal molecule is aligned vertically.
• the effective refractive index (n e ') is given by where n 0 and n e are the refractive indices for the ordinary and extraordinary beams, respectively, ⁇ is the angle between the optic axis of the molecule and the vertical axis.
• the extraordinary beam initially has the maximum refractive index n e .
• the effective refractive index n e ' becomes smaller, and when a saturation voltage is applied, the optic axis of the molecule is aligned horizontally and the effective refractive index of n e ' reaches the minimum and is equal to n 0 .
• the refractive index for the ordinary beam (horizontally polarized) is always the same. So the electro- optic effect modulates the effective refractive index of the extraordinary beam.
• the conductive material on one substrate does not form a homogeneous layer, rather a pattern of electrodes are formed, as further described herein.
• Figure 4 illustrates the general structure of an electro-active liquid crystal lens with patterned electrodes. From top to bottom, the layers comprise:
• Figure 4 illustrates the general structure of the electro- active liquid crystal lens used herein.
• a liquid crystal layer 430 is sandwiched between a patterned electrodes 420 and a ground electrode 460.
• the patterned electrode 430 may be fabricated by photolithographic processing of a conductive film deposited on a glass substrate, as known in the art, and the ground electrode 460 contains a uniform conductive layer, formed in any manner as known in the art.
• the patterned electrodes comprise a circular array of rings whose radii are determined by the focal length desired, as described herein.
• the electro-optic effect of the liquid crystals 440 results in electrically controllable birefringence.
• the phase profile across the lens is tailored by applying proper voltages to the patterned electrodes, as further described herein.
• the conductive material may be any suitable material, including those specifically described herein, and other materials known in the art. It is preferred that the conductive material be transparent, such as indium oxide, tin oxide or indium tin oxide (ITO).
• the substrate can be any material that can provide desired optical transmission and can function in the devices and methods described herein, such as quartz, glass or plastic, as known in the art.
• the thickness of the conducting layer is typically between 30 nm and 200 nm. The layer must be thick enough to provide adequate conduction, but not so thick as to provide excess thickness to the overall lens structure.
• the patterned electrodes 420 may be formed using photolithographic techniques, such as those described herein and known to one of ordinary skill in the art.
• Figure 5A illustrates a structure where all electrodes are on the same plane (one-layer structure), in which there is a small gap between neighboring subzones.
• the controller or Driver 510 is connected by Wires 520 to vias or Contacts 530, which in turn are connected to individually controllable Electrodes 540.
• the wires 520 may be electrically insulated from the electrodes 540 by an insulating layer (not shown), and then the wires may be selectively contacted to the electrodes through vias (holes or pathways in said insulating layer) or contacts 530. This type of contact fabrication is well known in manufacturing lithography, and in integrated circuit manufacture.
• Figure 5A illustrates a layout of concentric, individually addressable (individually controllable) ring shaped electrodes in one layer. Neglecting the wires 520 and the vias through the insulation, this layout is defined as a "one-layer" structure because all of the electrodes are in a single layer.
• the wires 520 may be ganged close together in a bus (not shown) running radially with respect to concentric ring electrodes.
• a bus (not shown) running radially with respect to concentric ring electrodes.
• other patterned electrode shapes may be used.
• a hexagonal array may contain hexagonal pixels, or a grid array may contain square pixels, or a set of irregular shapes may correct for non- symmetric refractive errors.
• Irregular or complex shaped electrodes may be fabricated to correct for a specific non-symmetric or non-conventional or high order refractive error.
• the electrodes may have variable thickness in the direction of the optical axis, in order to create more complex interactions with the liquid crystals.
• arrays with high pixel densities may be controlled to approximate the concentric rings of Figure 5A to create diffractive lenses, particularly if more than two pixels fit inside the width of one ring electrode. Such high pixel density arrays may also approximate more complex shapes.
• the innermost ring electrode as electrode number 1 , and count outwards to the 16 th and outermost electrode. Note that the innermost electrode may preferably be a full circle instead of a ring, but Figure 5A illustrates a ring for symmetry, and to more clearly illustrate the via or contact 530 with the innermost ring electrode.
• the innermost four rings are grouped into one zone.
• This first zone comprises electrodes 1-4, numbering from the innermost electrode outward.
• Each of these electrodes 1- 4 is a subzone of the first zone.
• the second zone is comprised by electrodes 5-8.
• the third zone is comprised by electrodes 9-12.
• the fourth zone is comprised by electrodes 13-16. This organization of a 16 electrodes yields a 4 level (or phase) diffractive lens with 4 zones.
• Each ring electrode 540 is independently addressable by wires 520 as discussed above. If all the electrodes are distributed in one layer, there must be electrically insulating gaps between neighboring electrodes. The gaps between the electrodes may cause phase distortion, and simulation of this design shows that this phase distortion may greatly affect the diffraction efficiency and other performance measures.
• the ring electrodes may be separated into two distinct layers, to create a "two-layer" design.
• the odd numbered rings may be placed in one electrode layer, and the even numbered rings may be placed in a separate second electrode layer. These two distinct electrode layers may be separated by an insulating layer such as SiO 2 .
• Figure 5B illustrates a structure where odd-numbered electrodes and even-numbered electrodes are interleaved into two horizontal layers and there is no gap between neighboring subzones (two-layer structure).
• the controller or Driver 510 communicates through wires 520 to the electrodes, and the electrodes are grouped into a layer with the even rings 542 and a layer with the odd rings 544. These two electrode layers are separated by an insulating layer SiO 2 544.
• Cr alignment marks 560 are also shown for photolithographic fabrication alignment.
• Zone m 580 and Zone m+1 590 are also shown, corresponding to adjacent zones from Figure 5A.
• Zone m 580 extends from r m to r m+ i and comprises a total of 4 electrodes. 2 of the 4 electrodes in Zone m 580 are even numbered and reside in layer 542, and the remaining 2 electrodes in Zone m 580 reside in layer 544.
• each ring electrode 540 may be individually addressed from an additional layer (not shown in Figure 5B) through vias as in the one- layer case.
• the wires 520 may be located in any convenient location or layer.
• alignment marks 560 are deposited on the conducting layer. Any suitable material may be used for the alignment marks, such as Cr.
• the alignment marks 560 allow proper alignment of the various photolithographic masks to the substrate and therefore of the patterns which are created in the processing steps associated with use of each mask from the "mask set" that was made in order to have the desired total photolithographic definition of the electrodes when the electrodes are patterned.
• One part of a zone of patterned electrodes is formed in the conducting layer using methods known in the art and described herein.
• a layer of insulator, such as SiO 2 550 is deposited onto the patterned conductor layer.
• a second layer of conductor is deposited onto the SiO 2 and the second part of the patterned electrodes zone is formed in the second layer of conductor.
• An alignment layer (not shown) is placed on the second layer of conductor and over the second substrate's conductor.
• the alignment layer is prepared by means known in the art such as unidirectional rubbing. Currently used alignment layers are spin coated polyvinyl alcohol or nylon 6,6. It is preferred that the alignment layer on one substrate is rubbed antiparallel from the alignment layer on the other substrate. This allows proper alignment of the liquid crystal, as known in the art.
• a layer of liquid crystal is placed between the substrates, and the substrates are kept at a desired distance apart (such as between 3 and 20 microns apart) with glass spacers, or other means known in the art. Spacers may be any desired material such as Mylar, glass or quartz, or other materials useful to provide the desired spacing.
• the liquid crystal layer In order to achieve efficient diffraction the liquid crystal layer must be thick enough to provide one wave of activated retardation (d > ⁇ / ⁇ n ⁇ 2.5 ⁇ m, where ⁇ n is the birefringence of the liquid crystal media), but thicker liquid crystal layers help to avoid saturation phenomena. Disadvantages of thicker cells include long switching times (varying as d 2 ) and loss of electroactive feature definition.
• the transparent substrates can be spaced any distance apart that allows for the desired number of patterned electrodes and the desired thickness of liquid crystal layer. In particular embodiments, the transparent substrates are spaced between three and 20 microns apart, and all individual values and ranges therein. One currently preferred spacing is 5 microns.
• the voltage required to change the index of refraction to a desired level is applied to the electrodes by a controller.
• a “controller” can include or be included in a processor, a microprocessor, an integrated circuit, an IC, a computer chip, and/or a chip. Typically, voltages up to about 2 Vrms are applied to the electrodes. Phase-synchronized, wave-form controlling drivers are connected to each electrode group in common-ground configuration. Driver amplitudes are simultaneously optimized for maximum focusing diffraction efficiency. The voltage function required to change the index of refraction to a desired level is determined by the liquid crystal or liquid crystal mixture used, as known in the art. [0067] Figure 6 shows an example of digital variable focal length using the individually addressable electrode pattern.
• Graph (a) corresponds to the basic focal length F, which is determined by the area of the original single electrode (i.e., the period of the original structure).
• the period of the structure is the area of the original single electrode.
• the focal length can be increased to multiples of F by increasing the period of the lens without affecting the diffraction efficiency.
• Graph (b) corresponds to the focal length 2F.
• the area of each zone (subzone) of Figure 6B is twice that of Figure 6A. The diffraction efficiency is the same for both cases.
• the voltages applied to the four electrodes of a particular 4-phase level lens are 1.1V, 1.31 V, 1.49V, and 1.72V, respectively.
• the voltages applied to the eight electrodes of a particular 8-phase level lens are 0.71 V 1 0.97V, 1.05V, 1.13V, 1.21 V, 1.30V, 1.37V, and 1.48V, respectively.
• the voltages applied to the electrodes are easily determinable by one of ordinary skill in the art without undue experimentation and are a function of the liquid crystal used, arrangement of the cell, and other factors, as known in the art.
• the voltages can be positive or negative, depending on the desired focal length, as known in the art.
• the voltages applied to the electrodes are positive or negative values between 0.5 and 2 V, and all individual values and subranges therein.
• the insulating material may be any suitable material, including those specifically described herein, and other materials known in the art.
• the conductive material and insulating material are arranged in alternating patterns, for example circles with increasing radius.
• the patterns may be any desired pattern, such as circular, semi-circular, square, angular, or any other shape that provides the desired effect, as described herein.
• the terms "circular, semi-circular, square, angular" and other shapes are not intended to mean a perfect shape is formed, rather, the shape is generally formed, and may include, as known in the art, bus lines or other methods of bringing current through the substrate.
• any liquid crystal can be used in the invention. It is preferred that the switching time is fast enough so that the user is not aware of a delay in switching from one focal length to another.
• a nematic liquid crystal is used as the electro-optic medium.
• the lens has an optical response to one of the two orthogonal polarization components of light.
• Polarization-insensitive cholesteric liquid crystal can also be used, in which case a polarizer is unnecessary.
• the liquid crystal used in the invention include those that form nematic, smectic, or cholesteric phases that possess a long-range orientational order that can be controlled with an electric field.
• the liquid crystal have a wide nematic temperature range, easy alignability, low threshold voltage, large electroactive response and fast switching speeds, as well as proven stability and reliable commercial availability.
• E7 a nematic liquid crystal mixture of cyanobiphenyls and cyanoterphenyls sold by Merck
• examples of other nematic liquid crystals that can be used in the invention are: pentyl- cyano-biphenyl (5CB), (n-octyloxy)-4-cyanobiphenyl (80CB).
• Electroactive polymers can also be used in the invention. Electroactive polymers include any transparent optical polymeric material such as those disclosed in "Physical Properties of Polymers Handbook" by J. E.
• chromophore molecules having unsymmetrical polarized conjugated ⁇ electrons between a donor and an acceptor group such as those disclosed in "Organic Nonlinear Optical Materials" by Ch. Bosshard et al., Gordon and Breach Publishers, Amsterdam, 1995.
• Examples of polymers are as follows: polystyrene, polycarbonate, polymethylmethacrylate, polyvinylcarbazole, polyimide, polysilane.
• Electroactive polymers can be produced by: a) following a guest/host approach, b) by covalent incorporation of the chromophore into the polymer (pendant and main-chain), and/or c) by lattice hardening approaches such as cross-linking, as known in the art.
• Polymer liquid crystals may also be used in the invention.
• Polymer liquid crystals are also sometimes referred to as liquid crystalline polymers, low molecular mass liquid crystals, self-reinforcing polymers, in situ-composites, and/or molecular composites.
• PLCs are copolymers that contain simultaneously relatively rigid and flexible sequences such as those disclosed in "Liquid Crystalline Polymers: From Structures to Applications" by W. Brostow; edited by A. A. Collyer, Elsevier, New- York-London, 1992, Chapter 1. Examples of PLCs are: polymethacrylate comprising 4- cyanophenyl benzoate side group and other similar compounds.
• PDLCs Polymer dispersed liquid crystals
• NCAP nematic curvilinear aligned phases
• TIPS thermally induced phase separation
• SIPS solvent-induced phase separation
• PIPS polymerization-induced phase separation
• BDH-Merck mixtures of liquid crystal E7
• NOA65 Norland products, Inc.
• PSLCs Polymer-stabilized liquid crystals
• PSLCs are materials that consist of a liquid crystal in a polymer network in which the polymer constitutes less than 10% by weight of the liquid crystal.
• a photopolymerizable monomer is mixed together with a liquid crystal and an UV polymerization initiator. After the liquid crystal is aligned, the polymerization of the monomer is initiated typically by UV exposure and the resulting polymer creates a network that stabilizes the liquid crystal.
• PSLCs see, for instance: C. M. Hudson et al. Optical Studies of Anisotropic Networks in Polymer-Stabilized Liquid Crystals, Journal of the Society for Information Display, vol.
• Self-assembled nonlinear supramolecular structures include electroactive asymmetric organic films, which can be fabricated using the following approaches: Langmuir-Blodgett films, alternating polyelectrolyte deposition (polyanion/polycation) from aqueous solutions, molecular beam epitaxy methods, sequential synthesis by covalent coupling reactions (for example: organotrichlorosilane-based self-assembled multilayer deposition). These techniques usually lead to thin films having a thickness of less than about 1 ⁇ m.
• lens and electrode configurations are useful for various applications.
• a lens can be immersed in a solution of liquid crystal or liquid crystal can be sandwiched between planar electrode plates with a gradient refractive index change. The latter makes the liquid crystal alignment easier and the cell thinner which permits faster switching.
• planar electrode plates with a gradient refractive index change. The latter makes the liquid crystal alignment easier and the cell thinner which permits faster switching.
• different electrode zone configurations can be used in the methods and devices of this invention. These different lens and electrode zone configurations and other configurations as known in the art are intended to be included in this disclosure.
• each electrode subzone of the patterned electrode must be individually addressed.
• two different exemplary applications are presented. One allows switching between the elementary focal length and multiples of the elementary focal length. The other is more general and allows continuous adjustment of the focal length from the minimum possible value to infinity.
• the focal length can be varied to 3F, 4F, ..., by increasing the zone period to 3T 1 2 , 4T 1 2 , ..., respectively.
• the focal length can be varied to kF (k is a positive integer) by increasing the zone period to kr t 2 .
• the lens has a diffraction efficiency of 95%.
• adjustable focal lengths are the elementary focal length F and multiples of the elementary focal length.
• the resolution of the adjustment is also F.
• the electrodes are designed for an elementary focal length of 10 cm, then the adjustable focal length would be 10 cm, 20 cm, 30 cm, and so on, to infinity. If other intermediate focal lengths are desired, a smaller elementary focal length can be used.
• F the feature size of the electrodes becomes very small for a large- aperture lens and it is difficult to make them with low cost with currently available techniques.
• the patterned electrodes are a circular array of rings of particular size. Each ring is individually addressable. A proper resolution of the ring is determined by the focal length range to be adjusted. For each desired focal length, the size of each subzone of all the zones can be calculated using Eqs. (2a) and (2b). A certain number of rings can be chosen to form each subzone and appropriate voltage can be applied. If the resolution of the rings is good enough, the lens can always have high efficiency with no significant change in efficiency as the focal length changes. The resolution necessary for the patterned electrodes is determined by the size of the subzones in the last few zones for the desired lenses, as described herein.
• Figure 7 shows continuous adjustment of the focal length using individually addressable circular array of electrodes with proper resolution.
• the four examples in Figure 7 show the electrode spacing in ⁇ m for a subset of electrodes.
• Geometric parameters for 3D, 2.5D, 2D, and 1 D focusing powers are depicted in examples A, B, C and D, respectively, r is the radius of the zone boundary.
• FIG. 7 An example of continuously changing the focal length from -30 cm to infinity is illustrated here. Assume the diameter of the lens is 10 mm and 8- level phase modulation is used. To illustrate the principle, the geometric parameters for the adjustable focusing powers of 3D, 2.5 D, 2D, and 1 D are depicted in Fig. 7, where the radius of each zone boundary and the width of each subzone for the last one or two zone are clearly shown. More detailed parameters for these lenses can be found in Tables 3-7. It is seen that for a particular focusing power, the variation of the width of each subzone is very small at the edges of these lenses, and the variation is even smaller as the aperture of the lens increases. For higher focusing power, the width as well as the area of each subzone is smaller.
• each electrode is 1 ⁇ m wide in this area.
• the width of each subzone is larger than 1 ⁇ m, several electrodes can be combined together to form one subzone and the boundary of each subzone can be rounded to the closest electrode boundary. Combining the electrodes means applying the same voltages to them.
• the lens can be used for all the subjects who need correction in this range for different distance vision.
• the zones close to the center have larger geometric size, the density of the electrodes can be smaller in that area (the size of the electrodes close to the center can be larger than those in the other area) in comparison with the area close to the edges. If the same density of electrodes is kept in the area close to the center, higher phase levels can be obtained and the diffraction efficiency will be increased.
• Another approach to achieve this goal is to use a pixilated spatial light modulator where small rectangular pixels are used. These pixels may be in multiple layers to reduce or eliminate gaps when viewed perpendicularly to the substrate, similar to the 2 layers of circular electrodes illustrated in Figure 5B.

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