Papers by Keyword: Micro-Lens Array

Abstract: This paper presents the design and fabrication of a micro-optic concentrator for optical radiation based on coupled micro-lenses and micro-prism (micro – mirrors) arrays. This type of micro-optic concentrator is suitable for both terrestrial and spatial applications where optical radiation is redirected and coupled to small area photovoltaic cells or detection devices located in front of the waveguide edges. Analysis and design were performed for the 0.4-1.06µm spectral range using the COMSOL Multiphysics program and the Ray Optics geometric optics module. Simulations for ray-tracing have been modeled in order to optimize the geometries of micro-optics elements taking into account the optical parameters of the materials to be used (polymers and glass) in the process of micro-optic concentrator fabrication. Micro-lenses and micro-prism arrays were fabricated by the technique of molding in silicon molds and replication in polymeric materials using OrmoClear30 elastomer (n=1.56, UV exposure) and in UV-PDMS, KER4690 polymer, respectively. Assembling and the fabrication process of micro-optic concentrator allowed the achievement of an optical efficiency of 70 % efficiency.

Abstract: This paper presents the fabrication of a micro-lens array surface with a single-mask process and two etching steps with KOH water solution. Numerical analysis of optics was used to determine the optimal design parameters such as curvature sagitta and radius. The dimension of each lens is 20μm x 20μm. We used anisotropic etching of <100> silicon through a circular and squar mask to produce a pyramidal pit formed by four (111) planes. The oxide mask is stripped and the immersion of the sample in the etchant solution favors the etching of (411) plane transforming the pit into a smooth hemispherical cavity. An intermediate stage exists when a wider 19.47⁰ <411> - face pyramid replaces the initial 54.74⁰ inverted pyramid. The dependence of surface roughness on concentration and temperature of KOH is investigated in the range of 25%-40% and 60°C-80°C, respectively, and compared between them. The surface profiles and roughness was characterized by AFM. The etching depth and radius of micro-lens array was obtained from the SEM images and AFM data. Also, the array of concave depressions was directly used as a mould for replication of KER-2500 transparent polymeric silicon from Shin-Etsu with a refractive index n=1.41. The perfectly matched array of micro-lenses can be detached from substrate and used as a local solar concentrator. Optical properties such as the focal length of the plano-convex micro-lens array, obtained by replication, are measured and analyzed.

Abstract: This paper analyzes the tool path generation of the microlens arrays by the single point diamond (FTS) turning,while focuses on the algorithm of tool radius compensation. Firstly, the mechanism of the fast tool servo machining process is introduced. Secondly, the tool path generation for FTS is calculated. The algorithm of tool radius compensation and the form error of the microlens is analyzed. Subsequently, the transitional zone is research, base on the algorithm of tool radius compensation, the optimized algorithm is proposed. Finally, using the optimized algorithm generate the tool path. Modeling of the tool path with the optimized algorithm of tool radius compensation is simulated with MATLAB. The simulation of the 3-D microlens arrays with the algorithm of tool radius compensation has done. According to the modeling of the simulation, algorithm of the radius compensation is discussed. The results show the optimized algorithm can improve the form accuracy of the microlens. The optimized algorithm is practical significant in the tool path generation.

Abstract: Microlens arrays have been fabricated by 3D diffuser lithography in this study. The method mainly adopts two kinds of diffuser films with different transmittances and hazes, integrated by photolithography, polydimethylsiloxane (PDMS) molding and UV forming techniques, to get microlens arrays with different parameters and geometries. The features, such as height, geometry and fill factor of microlens arrays, are controlled by photolithography, using a photomask with circular holes and different exposure doses. The microlens arrays can also be duplicated and transferred to the surface of flexible polyethylene terephthalate (PET) substrate through PDMS molding and UV forming processes. Finally, the outcoupling efficiency of microlens arrays attached to organic light-emitting devices (OLEDs) can be measured and analyzed. More than 60% enhancement of luminous current efficiency can be obtained in experimental results.

Abstract: In this paper, a 3-axis stage consisted of a XY stage and Z-axis feeding tool holder is proposed for the application of fast tool servo (FTS). The XY stage actuated by six piezoelectric (PZT) actuators is designed with symmetric flexural hinges featuring low interference motions, high stiffness, and fast response. Numerical design using the finite element method (FEM) was conducted to investigate the steady characteristics (displacement, stiffness, stress, and strain) and dynamic characteristic of resonance frequency. According to calculation results, the major characteristics obtained along XYZ axes are as follows: displacements induced are 10.06, 10.28, and 20.31 μm due to the applied voltage being 50 V; stiffness are 112.84, 110.31, and 223.34 kN/mm; the maximum stresses at the hinges are 9.78, 10.9, and 100.56 N/mm², which are lower than the allowable stress of aluminum used; and the resonant frequencies are 1.0, 0.64, and 0.4 kHz, respectively. Experimental examinations regarding to the resonant frequencies were performed with a maximum deviation of 16% along the Z-axis compared to the simulation result. As a result of the investigation, it is expected that the 3-axis stage can be effectively applied to implement a FTS.

Abstract: Comparing to the single aperture imaging system, Artificial Compound-Eyes (ACE) imaging system has some nice features, such as small size and stereo vision. This paper introduces our multiple-focus ACE imaging system. The system mainly consists of (a) a micro-lens array fabricated by Micro-Electro-Mechanical-System (MEMS) technology, (b) a CMOS chip, (c) a 3D mechanical moving stage, and (d) an auto-focus software module. It can simultaneously observe the object by several channels with different focus, therefore the focal length of the system can be adjusted by selecting different channels. Besides, a software module is developed to carry out auto-focus. The system is applicable to the fields of industry inspection, bio-medical imaging and robot vision.

Abstract: Compact compound imaging system with large CCD target surface has been researched. The target surface reaches 50mmX50mm, and reduces the system processing and installation difficulty. We present the system overall plan and discuss the imaging characteristics. The imaging results for sector resolution target show that the system can image with multi channel crosstalk free. The results show that whether the single convex lens system or double convex lens system, the definition and contrast of single channel graphs are poor. However we can get the super resolution image by POCS algorithm. The reconstructed results show that image quality has been obviously improved compared with the single channel image, which proof the availability of the compact compound imaging system with large CCD target surface. Key words: Compact ompound imaging system, Microlens array, Doublet lens, POCS

Abstract: A simple and easy method is demonstrated for the fabrication of the shape controllable micro-lenses, which are widely used in biomedical systems for improving the image quality as their ability to efficiently focus light into the devices. The micro-lenses were drop on demand printed on the glass micro-holes based on a simple drop on demand printing technique. The shape controllable micro-lenses with a fixed diameter resulting from boundary confinement effect of the micro-holes and the surface wetting conditions are controlled by printing different numbers of drops per micro-lens. The influence of the geometrical shape changes on the optical properties is also investigated. The micro-lens array with different numerical apertures (NA) can be fabricated by controlling the number of drops of the micro-holes as the boundary confinement and hydrophobic effect of the micro-holes.

Abstract: In recent years, micro lens arrays have played a crucial role in optical illumination systems. The function of micro lens arrays (MLAs) is to create a uniform light intensity or shape the light profile. Polymers that are commonly used as MLAs have several advantages, such as cost effectiveness, light weight, and easy formation. In general, the ultra-precision diamond-turning technique and plastic injection molding technique have been combined to fabricate MLAs with polymer materials. However, residual stress and non-balance injection pressure are produced on MLAs during injecting processing. Therefore, this paper presents the fabrication of MLAs using a direct molding method (DMM). The STAVAX with electroless nickel coating and PMMA were used as the mold and polymer preform, respectively. First, a mold of MLA with 100% filling factor was fabricated using the ultra-precision diamond-turning technique. A high filling factor can decrease the non-effective area of the MLA in an optical system. Subsequently, an MLA was formed on the PMMA surface using DMM processing. This paper shows the DMM process parameters, including molding temperature, molding force, and cooling rate. Moreover, the profile of the MLA was measured using a laser confocal microscope. Finally, a high filling factor MLA with a diameter of 11.5 mm, and lenses with a height of 8.5 μm and a radius of 470 μm were formed on PMMA.

Abstract: This study proposed a light trapping module to improve the light path in a solar cell in order to increase its light absorption efficiency. The microlens on a transparent substrate concentrates incident light into several light beams, which it leads into the optical channel on the back side. The optical channel is designed by coating highly reflective metals on the same transparent substrate, then an optical channel opening is made at the light beam focus so the light beams can pass through the optical channel and irradiate the solar cell. The light reflected by the solar cell is reflected again by the metal surface to the upper film of the solar cell, thus, increasing the absorption efficiency of the solar cell and reducing the film thickness of the solar cell to obtain better electrical properties. In this simulation the refractive index of the microlens was set as 1.43, the optical channel was 25 μm and the spacing was 0.27 mm, thus, the simulated absorption efficiency reached over 80%. The feasibility of this study was thus proved.