Cylindrical Microlens Array Research Articles

Cylindrical Liquid Crystal Microlens Array With Rotary Optical Power and Tunable Focal Length

A novel cylindrical liquid crystal microlens array with rotary power and tunable capability is proposed and experimentally demonstrated. This structure is capable of generating tunable cylindrical microlenses in two different axis by low voltage control. For this, complex electrical signals are required (electrical phase shift of 180°). A control over the maximum phase shift from $4\pi $ to $34\pi $ radians has been demonstrated. This effect modifies the effective focal length (from 0.2 to 1.2 mm). Moreover, an OFF-state is also possible (behaving like a transparent medium). The structure is simple and does not require a complex fabrication process. The proposed device has several advantages over the existing microlens arrays and is simple and low cost. The device could contribute to developing new applications and to reducing the fabrication costs of current devices. For example, this device can be used in the next generation of mobile displays with autostereoscopic capability.

Design, fabrication, characterisation of optical imaging cylindrical micro-lens array based on liquid crystal

The electrical adjustment of the optical performance of liquid crystal cylindrical micro-lens array of 128×128, which is based on the field controlling effect of liquid crystal dielectric behaviour, is realised through constructing smart liquid crystal electro-optic structure, and orderly modulating the refractive index of liquid crystal material and its spatial distribution. According to the elastic continuum theory of liquid crystal, it is firstly described on the formation of specific refractive index spatial distribution of liquid crystal molecules, which is driven by applied electric-field. Furthermore, the white-light focusing, the far-field white-light interference and the monochromatic laser interference are all measured extensively and discussed in details.

High-integrated spectral splitting solar concentrator with double-light guide layers

Individual secondary optical components in a spectral splitting solar concentrator utilizing a microlens array require multiple photovoltaic (PV) cells, which leads to the complexity of system alignment and a high cost. In order to improve the integration of the PV cells and thermal management, a spectral splitting concentrator coupled to double-light guide layers has been proposed. Using one-axis tracking, we further investigate the optical performance of the concentrator combined with a cylindrical microlens array with double vertically staggered light guide layers in detail. The results show that this solar concentrator maintains a good acceptance angle of ±2 deg in the east-west direction and an acceptable angle of ±14 deg in the perpendicular direction on both low and high spectrums, achieving a concentration ratio of 10×. Finally, the capability of lateral displacement tracking has been explored for an aperture angle of ±24 deg in this concentrator.

Multiple lateral photo-Dember terahertz emitters illuminated by a cylindrical micro-lens array

We demonstrate a terahertz multiple emitter design based on the lateral photo-Dember effect and illuminated with a cylindrical micro-lens array. The multiple emitter produces an average of 5.2 times the output power of a single lateral photo-Dember emitter and is capable of reaching bandwidth comparable to that of a single commercial photoconductive antenna.

P.1: Distinguished Student Poster Paper: Submillisecond‐response Polymer Network Liquid Crystal Cylindrical Microlens Array for 3D Displays

AbstractWe demonstrate a submillisecond‐response tunable‐focus cylindrical microlens array based on polymer network liquid crystal. The focal length can be tuned from 1.9 cm to 5 cm by increasing the voltage from 0 to 80V. This microlens array has potential applications in autostereoscopic 3D displays.

Concentrating microlens array mounted on an InGaP/GaAs/Ge solar cell for photovoltaic performance enhancement

We present a technique of mounting a microlens array (MLA) on a solar cell to serve as both an incident light manipulator and an encapsulation layer. The cylindrical MLA with a uniform element is fabricated through micromachining processes. The MLA mounted on a triple-junction InGaP/GaAs/Ge solar cell enhances the optical efficiency and the resultant photovoltaic performance, which is mainly attributed to the solar light micro-concentration effect and the elimination of optical shading. The MLA effect is maximized under the optimal mounting condition, resulting in the 17.2% and 18.5% increases in photocurrent and power conversion efficiency (PCE), respectively, in comparison with those of the bare glass-covered cell. The efficiency of the MLA-encapsulated solar cell remained almost unchanged for a long time.

Planar waveguide concentrator used with a seasonal tracker

Solar concentrators offer good promise for reducing the cost of solar power. Planar waveguides equipped with a microlens slab have already been proposed as an excellent approach to produce medium to high concentration levels. Instead, we suggest the use of a cylindrical microlens array to get useful concentration without tracking during the day. To use only a seasonal tracking system and get the highest possible concentration, cylindrical microlenses are placed in the east-west orientation. Our new design has an acceptance angle in the north-south direction of ±9° and ±54° in the east-west axis. Simulation of our optimized system achieves a 4.6× average concentration level from 8:30 to 16:30 with a maximum of 8.1× and 80% optical efficiency. The low-cost advantage of waveguide-based solar concentrators could support their use in roof-mounted solar panels and eliminate the need for an expensive and heavy active tracker.

Process Modeling and Fabrication of Microlens Array in Thick Photoresist

In this work, the design and fabrication of a low f-number cylindrical microlens array is presented. The lenses were fabricated in thick photo resist of 12 μm thickness, using a contact printer exposure through a mask with a repetitive 6 μm line - 4 μm space pattern. Numerical calculations based on scalar diffraction theory were employed to model the light propagation inside the resist, determining the aerial image as a function of its thickness. Than the resist response characteristics, expressed by its contrast curve, and absorption rate were used to obtain a cross section profile. A good match between numerical and experimental results were found.

Fabrication and characterization of linear diffusers based on concave micro lens arrays

We present a new approach of beam homogenizing elements based on a statistical array of concave cylindrical microlens arrays. Those elements are used to diffuse light in only one direction and can be employed together with fly's eye condensers to generate a uniform flat top line for high power coherent light sources. Conception, fabrication and characterization for such 1D diffusers are presented in this paper.

Three-dimensional shape measurement of micro-lens arrays using full-field swept-source optical coherence tomography

We report three-dimensional (3D) shape measurement of refracting samples using full field swept-source optical coherence tomographic (FF-SS-OCT) system. The optical arrangement of FF-SS-OCT consists of a swept-source system containing super-luminescent diode as low coherence light source and an acousto-optic tunable filter as electronically controlled frequency tuning device, a compact Michelson interferometer and an area detector. Refracting samples, such as, cylindrical lens and micro-lens arrays were used as object. By means of sweeping the frequency of the light source, multiple interferograms were recorded and both amplitude and phase map of the interference fringe signal were then reconstructed. Experimental results of optically sectioned images (tomography) of the cylindrical lens and micro-lens arrays obtained by means of selective Fourier filtering and 3D-surface profile retrieved from the phase-map are demonstrated. The proposed system does not require any mechanical scanning. In addition, a common optical path enables this proposed technique to be highly stable.

Fabrication of microlens arrays in photosensitive glass by femtosecond laser direct writing

This article reports the fabrication of high-fill-factor plano-convex cylindrical and spherical microlens arrays horizontally and vertically embedded in a photosensitive Foturan glass chip by femtosecond (fs) laser micromachining. The microlens arrays were fabricated by modifying the microstructure of Foturan glass using fs laser direct writing followed by thermal treatment, wet etching, and additional annealing. The focusing ability and image quality of the microlens arrays were examined, showing that the lens arrays not only can focus light well but also provide an imaging capability that holds great potential for lab-on-a-chip applications.

Efficiency improvement and image quality of organic light-emitting display by attaching cylindrical microlens arrays

In this paper, cylindrical microlens arrays with two different alignments were proposed to be applied in a commercial mobile phone having an organic light-emitting diode (OLED) panel. It was found that the parallel-aligned cylindrical array had better performance than the vertical-aligned one for the OLED panel. The parallel-aligned cylindrical microlens array can increase the luminous current efficiency at surface normal and the luminous power efficiency of the OLED panel by 45% and 38%, respectively. Besides, it can also make the spectrum of the OLED panel more insensitive to the viewing angle. Though it can slightly blur the image on the OLED panel, the universal image quality index can be maintained at a level of 0.8630.

Micro-optical polarizer with high efficiency

Based on liquid crystal polymers (LCP) a compact micro-optical polarizer with high efficiency has been designed and realized. By using cylindrical microlens arrays made of LCP and index matching layer, a complete separation of both polarization components of the unpolarized input light is achieved. Combined with a patterned twisted nematic (TN) cell, allowing a rotation of only one polarization component, a polarizer with high efficiency (72,5% (measured) is realized. Simulations and measurements are presented.

7.3: Giant‐grain Poly‐Si by CW Laser Annealing of a‐Si with Cylindrical Microlens Array

AbstractWe have developed a super large grain poly‐Si on glass by CW laser crystallization using cylindrical microlens array. A giant‐grain poly‐Si with average grain size of 15 μm × 15 μm was achieved. The n‐channel TFT using the poly‐Si exhibited the field‐effect mobility, on/off current ratio, threshold voltage and gate voltage swing of 470 cm2/Vs, ∼108, 0.1 V and 0.4 V/dec., respectively. On the other hand, the p‐channel TFT exhibited 192 cm2/Vs, ∼108, −2.2 V and 0.5 V/dec., respectively. A single crystalline Si on glass can be achieved with this technique.

Shack-Hartmann sensor based on a cylindrical microlens array

We present a Shack-Hartmann wavefront sensor (SHWS) based on a cylindrical microlens array as a device for measuring highly aberrated wavefronts. Instead of the typical spot pattern created by a conventional SHWS, two orthogonal line patterns are detected on a CCD and are superimposed. A processing algorithm uses the continuity of the focal line to extend the dynamic range of measurement by localizing the line, even if it leaves the CCD area confined by the corresponding microcylinder. The measurement of a wavefront from a progressive addition lens with an 80 lambda peak-to-valley value reveals the capabilities of the sensor.

Analysis of microlens array with long focal depth and smallf-number by improved first Rayleigh–Sommerfeld method

The improved first Rayleigh?Sommerfeld method (IRSM1) is applied to analyse the focusing performance of dual-?and tri-cylindrical microlens arrays with long focal depth and small f-number for the TE polarization. The real extended focal depth, the diffraction efficiency, the spot size, and the real position of the focal plane of the microlens array with different f-numbers and the preset extended focal depths are calculated by the IRSM1, rigorous boundary element method (BEM), and original Rayleigh?Sommerfeld method (ORSM1), respectively. The accuracies of the IRSM1 and the ORSM1 are evaluated along the longitudinal direction. The results indicate that the IRSM1 can be used for analysing the cylindrical microlens array with long focal depth and small f-number, but the ORSM1 completely fails for those microlens arrays with small f-number. It is expected that this investigation will provide useful information in the design of the micro-optical elements for realizing longitudinal optical field modulation.

Polyvinylidene fluoride—piezoelectric polymer for integrated infrared optics applications

The suitability of polyvinylidene fluoride films for IR integrated optics applications was demonstrated. Polyvinylidene fluoride is a piezoelectric polymer, which demonstrates high transparency in the middle-IR and has several transparent windows in the far-IR. The fabrication of cylindrical microlenses and microlens arrays by CO2 laser irradiation of polyvinylidene fluoride substrates has been demonstrated. Pseudo-spherical microlenses were also fabricated by direct laser writing. Strong piezoelectric properties, high chemical resistance, stability to UV radiation and high continuous-use temperature make PVDF suitable for various IR integrated optics applications.

Analysis of a cylindrical microlens array with long focal depth by a rigorous boundary-element method and scalar approximations.

We investigated the focal characteristics of open-regional cylindrical microlens arrays with long focal depth by using a rigorous boundary-element method (BEM) and three scalar methods, i.e., a Kirchhoff and two Rayleigh-Sommerfeld diffraction integral forms. Numerical analysis clearly shows that the model cylindrical microlens arrays with different f-numbers can generate focusing beams with both long focal depth and high transverse resolution. The performance of the cylindrical microlens arrays, such as extended focal depth, relative extended focal depth, diffraction efficiency, and focal spot size, is appraised and analyzed. From a comparison of the results obtained by the rigorous BEM and by scalar approximations, we found that the results are quite similar when the f-number equals f/1.6; however, they are quite different for f/0.8. We conclude that the BEM should be adopted to analyze the performance of a microlens array system whose f-number is less than f/1.0.

Micro-optical 1 x 4 fiber switch for multimode fibers with 600-microm core diameters.

The design, manufacture, and test of a 1 x 4 micro-optical fiber switch for multimode fibers with 600-microm core diameters are described. Microlens array telescopes allow for variable and fast beam deflection when the positions of the cylindrical microlens arrays relative to each another are altered by specially designed piezomechanical actuators. Standard achromats are used for collimation of light emitted by the input multimode fiber and for focusing of the deflected light onto a linear array of output multimode fibers. Design and assembly of micro-optical as well as of optomechanical components are discussed. Insertion loss and cross talk are measured, and the results are compared with those of numerical optical simulations. Measurements of switching time and long-term stability, as well as of thermal behavior, are also presented.

Simple fabrication of cylindrical sol-gel microlens array by reflowing technique

In this paper, we report the fabrication of a 128-x 1024-element cylindrical microlens array in a low-cost inorganic-organic SiO 2 /ZrO 2 sol-gel glass using reflowing technique. The fabricated microlens array had excellent surface smoothness and dimension uniformity. The prime advantages of the hybrid sol-gel material are its suitability as an etching-free negative-tone UV-sensitive material, uniformity, and other excellent optical properties. Microfabrication in sol-gel glass using the reflowing technique is demonstrated as a cost-effective and high-volume production technology for micro-optical elements.