Electrically switchable holographic liquid crystal/polymer Fresnel lens using a Michelson interferometer

A holographic technique for fabricating an electrically switchable liquid crystal/polymer composite Fresnel lens is reported. A Michelson interferometer is used to produce the required Fresnel pattern, by placing a convex lens into one path of the interferometer. Simplicity of the method and the possibility of fabricating different focal length lenses in a single arrangement are advantages of the method. The performance of the fabricated lens was demonstrated and its electro-optical properties were investigated for its primary focal length.     

Experimental study on polarization lens formed by asymmetrical metallic hole array

A polarization bifocal lens based on the polarization effect caused by asymmetrical hole arrays had been designed, fabricated, and characterized experimentally. By considering the fact that the skin depth of an infrared electromagnetic field inside metal is much shorter than the incident wavelength, a polarization bifocal lens composed of high deep-width ratio metallic holes was realized by using a gold-coated silicon structure to replace the one directly formed on a thick metal film. An infrared optical experiment setup is built based on the secondary imagery method for characterizing the focal length of the designed bifocal lens. The measured focal lengths of the fabricated bifocal lens coincide well with the designed values, which proves the validity for realizing the polarization elements with the proposed structure and the feasibility of the fabrication process.     

Variable Focusing Microlens Chip for Potential Sensing Applications

A variable focusing microlens chip, which has the capability of adjusting its focal length over a wide range without any mechanical driving parts, is reported in this paper. The packaged microlens chip consists of a flexible polymer lens, a fluidic chamber, an integrated sensor, and an actuator. A thermal actuator is introduced into this variable focusing microlens to obtain relatively large actuation force and displacement. The hemispheric convex polymer lens provides an initial focal point without being actuated. The focal length change is controlled by varying the voltage applied to the thermal actuator. A 1.9-mm-diameter polymer lens is made to test the performance of the device. The focal length of this chip varies from 14.658 to 2.782 mm, which corresponds to the change of numerical aperture from 0.078 to 0.412. Based on the working mechanism and constructing method of the single lens chip, a variable focusing microlenses array has been fabricated for future testing and application. Potential sensing applications for single lens and array include cell detection and immobilization, optical sensors, lab-on-a-chip, ophthalmic lens systems, microphotonics, high throughput scanning, and confocal imaging system     

Design of a dual-effect lens on lanthanum-modified lead zirconate titanate for continuous variation of focal length

The design of a Fresnel lens with continuous focal length is proposed for use in optical processing. A convex lens is induced in lanthanum-modified lead zirconate titanate through the application of an electric-field profile supplied by the indium tin oxide electrodes that make up the zones of a Fresnel lens. The use of a numerical method based on fast Fourier transform algorithms was required to analyze accurately the induced field inside a Fresnel lens with an initial focal length of 0.4 m (at 470 nm) and 20 indium tin oxide electrodes. The effective focal location obtained by the combined mechanisms is derived. This design is expected to produce continuous variations of ~16% in focal length; the ability of previous designs to achieve focal length switching is maintained.     

Liquid tunable lens integrated with a rotational symmetric surface for long depth of focus

A liquid tunable lens with an extended depth of focus (DOF) is proposed. By integrating a phase plate with rotational symmetric quartic function (QF) contour into the liquid lens cavity, the lens can achieve higher tolerance to the defocus aberration. The liquid lens was fabricated with a convenient and low-cost process that combined single-point diamond turning (SPDT) with soft lithography using polydimethylsiloxane (PDMS). Experimental results demonstrate that both focal length tunability and extended DOF can be achieved with the proposed liquid lens.     

Modeling microlenses by use of vectorial field rays and diffraction integrals

A nonparaxial vector-field method is used to describe the behavior of low-f-number microlenses by use of ray propagation, Fresnel coefficients and the solution of Maxwell equations to determine the field propagating through the lens boundaries, followed by use of the Rayleigh-Sommerfeld method to find the diffracted field behind the lenses. This approach enables the phase, the amplitude, and the polarization of the diffracted fields to be determined. Numerical simulations for a convex-plano lens illustrate the effects of the radii of curvature, the lens apertures, the index of refraction, and the wavelength on the variations of the focal length, the focal plane field distribution, and the cross polarization of the field in the focal plane.     

Liquid-crystal lens with a focal length that is variable in a wide range

A liquid-crystal (LC) lens driven by two voltages is reported. The lens has a focal length that is electrically tunable. The range of the variable focusing power is very wide, covering approximately 0.8-10.7 D. In the entire focal range the LC lens maintains high optical quality. The LC lens can be driven in a simple way to prevent the occurrence of a disclination line. The use of the LC lens in image formation is demonstrated.     

High-performance fluidic adaptive lenses

High-performance fluidic lenses with an adjustable focal length spanning a very wide range (30 mm to infinite) are demonstrated. We show that the focal length, F-number, and numerical aperture can be dynamically controlled by changing the shape of the fluidic adaptive lens without moving the lens position mechanically. The shortest focal length demonstrated is less than 30 mm for a 20-mm lens aperture. The fluidic adaptive lens has a nearly perfect spherical profile and shows a resolution better than 40 line pairs/mm in a plano-convex structure and 57 line pairs/mm in a biconvex structure.     

Long-distance optical guiding of colloidal particles using holographic axilens

We report the use of an aspheric holographic optical element (axilens) that essentially combines the properties of the long focal depth of an axicon and the high energy concentration of a conventional spherical lens for long-distance guiding of microscopic objects. With the use of the axilens, polystyrene spheres (~6 μm diameter) could be transported over a distance of ~16 mm that was ~3 times longer compared with that obtained using a spherical lens of focal length identical to the mean focal length of the axilens. Further, due to the availability of good on-axis power density, even objects having very marginally higher refractive index than the medium (differing only at third decimal place) could be guided with a guiding speed of ~5 μm/s.     

Fast response varifocal lenses using KTa(1-x)Nb(x)O3 crystals and a simulation method with electrostrictive calculations

We fabricated cylindrical varifocal lenses with fast responses by using the strong Kerr effect of KTa(1-x)Nb(x)O(3) (KTN) single crystals. We observed focus shifts of up to 87 mm with the assistance of a 250 mm focal length lens, which corresponds to a focus shift from infinity to 720 mm by the KTN lens itself. The response time was as fast as 1 μs. We also present a simulation method for calculating refractive index distributions in KTN single crystals, which is essential when designing the lens. The method is characterized by the strain contribution, which has not conventionally been typical of electro-optic simulations. We used this method to explain the refractive index modulations that are characteristic of the varifocal lenses.     

Electromechanically driven variable-focus lens based on transparent dielectric elastomer

Dielectric elastomers with low elastic stiffness and high dielectric constant are smart materials that produce large strains (up to 300%) and belong to the group of electroactive polymers. Dielectric elastomer actuators are made from films of dielectric elastomers coated on both sides with compliant electrode material. Poly(3,4-ethylenedioxythiophene) (PEDOT), which is known as a transparent conducting polymer, has been widely used as an interfacial layer or polymer electrode in polymer electronic devices. In this study, we propose the transparent dielectric elastomer as a material of actuator driving variable-focus lens system using PEDOT as a transparent electrode. The variable-focus lens module has light transmittance up to 70% and maximum displacement up to 450. When voltage is applied to the fabricated lens module, optical focal length is changed. We anticipate our research to be a starting point for new model of variable-focus lens system. This system could find applications in portable devices, such as digital cameras, camcorder, and cell phones.     

Efficient Raman laser system using stimulated Brillouin scattering with different confocal parameters for CH(4)

We report the efficient Raman laser system with the wavelength of 1.54 microm from a passively Q-switched Nd:YAG laser with high-pressure methane gas. It has been known that the stimulated Brillouin scattering (SBS) prevents the Raman conversion. The efficiency of the Raman conversion, however, has been greatly enhanced with a specially designed lens to use a backward-stimulated Brillouin in our scheme. The special lens has a focal length of 12 cm, and a maximum conversion efficiency of 51% has been obtained with the first-Stokes energy of 32 mJ and the residual pump energy of 30 mJ at 1,400 psi. Comparing two resonators with different focal lengths of the lenses, we have found that backward-SBS can be greatly enhanced by use of the shorter focal length of 12 cm, and the enhanced backward-SBS helps to increase the conversion efficiency.     

Measurement of parameters of simple lenses using digital holographic interferometry and a synthetic reference wave

The use of digital holographic intrerferometry in the testing of simple thin lenses is explored. Focal length, radius of curvature, and refractive index are the lens parameters that can be determined using this method. The digital holograms using the lens under test are recorded at various positions of the test lens using off-axis geometry. This is combined with a digitally computed plane wavefront to determine the curvature of the light beam emerging from the test lens. Focal length is the position of the test lens where a single fringe results. The radius of curvature of the test lens is also determined similarly using a long focal length lens to concentrate a collimated beam onto the test lens. The nonuniformities on the lens surface could also be found by using this method. The implementation of the method is shown by using computer simulations in the case of biconvex lenses. The method can be utilized to measure the parameters of plano-convex and concave lenses also.     

Simple focal-length measurement technique with a circular Dammann grating

A novel technique for focal-length measurements with a circular Dammann grating is presented. In the back focal plane of the lens under test, a one-order circular Dammann grating with limited aperture will produce double-humped radial rings. The separation between the two lobes varies with the displacement of the observed plane from the focal plane of the lens. By searching for the position at which the separation is minimal, the focal point of the lens can be located and hence the back focal length can be determined. Experimental results demonstrated that this method is efficient and can be used effectively for a quick check of focal length.     

Implementation of a hybrid lens

Details are presented of the design, fabrication, and use of a hybrid lens employed to interconnect two-dimensional arrays of optical transceivers. The hybrid lens consists of a custom-designed, 42-mm focal length, ?/5 compound lens followed by an array of afocal telescope compound microlenses.     

Electrowetting-driven variable-focus microlens on flexible surfaces

We demonstrate a flexible, electrowetting-driven, variable-focus liquid microlens. The microlens is fabricated using a soft polymer polydimethylsiloxane. The lens can be smoothly wrapped onto a curved surface. A low-temperature fabrication process was developed to reduce the stress on and to avoid any damage to the polymer. The focal length of the microlens varies between -15.0?mm to +28.0?mm, depending on the applied voltage. The resolving power of the microlens is 25.39 line pairs per mm using a 1951 United States Air Force resolution chart. The typical response time of the lens is around 50?ms.     

Mechanically tunable aspheric lenses via additive manufacture of hanging elastomeric droplets for microscopic applications

Abstract

Mechanically deformable lenses with dynamically tunable focal lengths have been developed in this work. The fabricated five types of aspheric polydimethylsiloxane (PDMS) lenses presented here have an initial focal length of 7.0, 7.8, 9.0, 10.0 and 10.2 mm. Incorporating two modes of operation in biconvex and concave–convex configurations, the focal lengths can be tuned dynamically as 5.2–10.2, 5.5–9.9, 6.6–11.9, 6.1–13.5 and 6.6–13.5 mm respectively. Additive manufacturing was utilized to fabricate these five types of aspheric lenses (APLs) via sequential layering of PDMS materials. Complex structures with three-dimensional features and shorter focal lengths can be successfully produced by repeatedly depositing, inverting and curing controlled PDMS volume onto previously cured PDMS droplets. From our experiments, we empirically found a direct dependence of the focal length of the lenses with the amount (volume) of deposited PDMS droplets. This new mouldless, low-cost, and flexible lens fabrication method is able to transform an ordinary commercial smartphone camera into a low-cost portable microscope. A few microscopic features can be readily visualized, such as wrinkles of ladybird pupa and printed circuit board. The fabrication technique by successively applying hanging droplet and facile mechanical focal-length-tuning set-up can be easily adopted in the development of high-performance optical lenses.     

Characteristics of the thick,compound refractive lens

A compound refractive lens (CRL), consisting of a series of N closely spaced lens elements each of which contributes a small fraction of the total focusing, can be used to focus x rays or neutrons. The thickness of a CRL can be comparable to its focal length, whereupon a thick-lens analysis must be performed. In contrast with the conventional optical lens, where the ray inside the lens follows a straight line, the ray inside the CRL is continually changing direction because of the multiple refracting surfaces. Thus the matrix representation for the thick CRL is quite different from that for the thick optical lens. Principal planes can be defined such that the thick-lens matrix can be converted to that of a thin lens. For a thick lens the focal length is greater than for a thin lens with the same lens curvature, but this lengthening effect is less for the CRL than for the conventional optical lens.     

Transient thermal lens formed by short laser pulse in condensed medium

The problem of relaxation is solved for a thermal lens which has been formed by a short laser pulse in a condensed medium. An expression is obtained for the focal length of such a lens and the asymptotic trend of the focal length as time increases is determined.Translated from Inzhenerno-Fizicheski Zhurnal, Vol. 45, No. 6, pp. 983–987, December, 1983.     

Drop‐on‐Demand Inkjet Printing of Thermally Tunable Liquid Crystal Microlenses

In this letter, the authors demonstrate Drop‐on‐Demand printing of variable focus, polarization‐independent, liquid crystal (LC) microlenses. By carefully selecting the surface treatment applied to a glass substrate, the authors are able to deposit droplets with a well‐defined curvature and contact angle, which result in micron‐sized lenses with focal lengths on the order of 300–900 µm. Observations with an optical polarizing microscope confirm the homeotopic alignment of the LC director in the droplets, which is in accordance with the polarization independent focal length. Results show that microlenses of different focal lengths can be fabricated by depositing successive droplets onto the same location on the substrate, which can then be used to build up programmable and arbitrary arrays of microlenses of various lens sizes and focal lengths. Finally, the authors utilize the thermal dependency of the order parameter of the LC to demonstrate facile tuning of the focal length. This technique has the potential to offer a low‐cost solution to the production of variable focus, arbitrary, microlens arrays.