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Chromatic aberration has been a functional distortion for the emerging microlens owing to phase mismatch, thus an extensive challenge is to achieve achromatic microlens over a broad wavelength range because it is difficult to achieve engineer simultaneous phase profiles at distinct wavelengths. For practical applications, a further challenge is to create an achromatic microlens with uncomplicated structure that can work in the transmission mode for incident light waves. In this work, we design a special and uncomplicated structure to achieve achromatic focusing based on the metallic silver subwavelength nanostructures, grating bars in our work, the structure can be regarded as a metal–insulator–metal (MIM) waveguide via exciting the surface plasmon polaritons (SPPs) mode to produce the phase retardation that could compensate and correct phase, thus we can obtain an achromatic microlens with uncomplicated structure over the whole visible, which do not need excessive requirement for the fabrication technology. The low-cost and manufacture compatibility make our achromatic microlens suitable for applications in nanophotonics and integrated optics in the visible.

We report a novel beam homogenizer for digital micromirror device lithography system. Such a beam homogenizer contains only one random freeform microlens array (rfMLA). And the rfMLA consists of different freeform microlenses. By the individual design and irregular arrangement of the microlenses, efficient and uniform beam shaping results have been obtained, and the interference patterns in particular are greatly weakened. Compared with traditional beam homogenizer, the energy efficiency has been increased from 62.00% to 69.70%, and the uniformity for incoherent light and coherent light have been improved from 91.93% to 97.60% and from 79.00% to 94.33%, respectively. rfMLA has great potential for enhancing the performance of DMD lithography system and other optical systems, particularly for the homogenization of the beam and the integration of the system.

Tomographic reconstruction of three-dimensional (3D) flow field is critical to achieve an accurate measurement of the complex flow field in tomographic particle image velocimetry (Tomo-PIV). Tomo-PIV based on the light field imaging has been used for 3D flow measurement due to its advantages of simple equipment system, low cost and overcoming the problems of complex synchronization and calibration of multi-cameras Tomo-PIV. However, the reconstruction quality such as the elongation and position error of the reconstructed particle, and the normalized correlation coefficient Q is closely related to the optical parameters of the light field camera, such as the inverse magnification and focal length of the main lens and the microlens, and the microlens pitch. Thus, the optimization of these optical parameters is desired for a better reconstruction quality. In this paper, the effects of these optical parameters on the light field image and reconstruction are numerically and experimentally investigated. In simulations, the light field images of the tracer particles are firstly generated for different the optical parameters by the ray tracing technique. The 3D tracer particle field is then reconstructed by the Expectation–Maximization (EM) algorithm. Simulation results show that the inverse magnification of the main lens and microlens, the focal length of the microlens, and the microlens pitch have important effects on the reconstruction quality, and thus the size and position of the measurement volume along the Z axis. Experiments are also carried out to verify the simulations. This study provides a basis for the optimization of the light field camera parameters for the accurate tomographic reconstruction of 3D flow field and the determination of the size and position of the measurement volume along the Z axis in the light field Tomo-PIV.

In this paper, we present an integral imaging microscopy, which can achieve continuous depth extraction. The multiple stereo matching algorithm is optimized with data point interpolation and calculation range correction, which can improve the computing efficiency and accuracy. A water suspension of silica-embedded magnetic particles in light-trap environment is used as a specimen. The elementary image array is obtained through sequentially imaging the specimen by the objective lens and microlens array, which contains continuous depth information that can give the optical tweezers a feedback for precise 3-D manipulation. Experimental and calculated results show the feasibility of our method.

A theoretical model based on ray optics is used to simulate the optical performance of organic light-emitting diodes (OLEDs) with spheroidal microlens arrays (MLAs) in a hexagonal array configuration using the Monte Carlo method. In simulations, ray tracing was performed until 20 reflections occurred from the metal cathode, with 10 consecutive reflections permitted in a single lens pattern. The parameters describing the shape and array of the lens pattern of a MLA are its radius, height, contact angle, and fill factor (FF). Many previous results on how these parameters affect light extraction efficiency (LEE) are inconsistent. In this paper, these contradictory results are discussed and explained by introducing a new parameter. To examine light extraction from an OLED through a MLA, the LEE enhancement is studied considering the effect of absorption by indium tin oxide during multiple reflections from the metal cathode. The device size where LEE enhancement is unchanged with changing lens pattern was identified for a fixed FF; under this condition, the optimal LEE enhancement, 84%, can be obtained using an OLED with a close-packed spheroidal MLA. An ideal maximum LEE enhancement of 120% was achieved with a device with an infinite-sized MLA. The angular intensity distribution of light emitted through a MLA is considered in addition to LEE enhancement for an optimized MLA.

A microlens array (MLA) is a key optical element for four-dimensional light-field analysis in a light-field camera. MLA manufacturing errors affect light-field imaging, but their effects, especially on the physical imaging process and image-degradation mechanism, have not entirely been studied. In this paper, we develop a manufacturing-error model for MLA and quantitatively analyze raw images and refocused images using image quality evaluation indexes. The results indicate that manufacturing errors cause changes in image features including brightness, resolution, and spot position. The image-features undergo changes and the degree of degradation caused by different error types showed great differences.

In this paper, a two-dimensional liquid gradient refractive index (L-GRIN) microlens is designed which can be used in adjusting focusing direction and focal spot of light beam. Finite element method (FEM) is used to simulate the convection diffusion process happening in core inlet flow and cladding inlet flow. And the ray tracing method shows us the light beam focusing effect including the extrapolation of focal length and output beam spot size. When the flow rates of the core and cladding fluids are held the same between the internal and external, left and right, and upper and lower inlets, the focal length varied from 313 μm to 53.3 μm while the flow rate of liquids ranges from 500 pL/s to 10,000 pL/s. While the core flow rate is bigger than the cladding inlet flow rate, the light beam will focus on a light spot with a tunable size. By adjusting the ratio of cladding inlet flow rate including Qright/Qleft and Qup/Qdown, we get the adjustable two-dimensional focus direction rather than the one-dimensional focusing. In summary, by adjusting the flow rate of core inlet and cladding inlet, the focal length, output beam spot and focusing direction of the input light beam can be manipulated. We suppose this kind of flexible microlens can be used in integrated optics and lab-on-a-chip system.

Three-dimensional information in the real world is observed not only by using the parallax cue created by the different positions of the two eyes, but also by using the depth cue created by adjustment of the crystalline lens. Here we describe a catadioptric light-field camera using two planar mirrors to imitate the process by which humans observe the world. Using a microlens array and planar mirrors, both parallax and accommodation information can be obtained. The design of the proposed system and calibration procedure of its computational model are presented in detail. The proposed method was verified using a prototype with digital refocusing; results were obtained by applying the acquired calibrated light field from both view positions.

An experimental system of spectral beam combining of 3 large-mode-area double-clad fiber lasers has been built on the basis of an external cavity with a microlens array. The analysis models of coupling and combining efficiency, as well as beam quality were established. According to the models, the influences of focal length of transform lens on the coupling, combining efficiency, as well as beam quality were analyzed. The results show that the longer focal length of transform lens increases the number of combined emitters, while hardly affects the combining efficiency. In the tunable experiment of individual fiber laser, the laser can be tuned in a range of 40.62 nm for using transform lens with focal length of 50 mm, slightly wider than that for another one with focal length of 100 mm (40.36 nm). In the combining experiment of three fiber lasers, the measured combining efficiency for the transform lens with focal length of 50 mm was about 77.0%, with the output power of about 1.01 W, and the beam quality factor ( M x 2 ) of 1.318. For another one with focal length of 100 mm, the measured combining efficiency was about 83.3%, with the output power of about 1.09 W, and the beam quality factor ( M x 2 ) of 1.312.

To meet the uniform dose exposure in optical lithography, it is desirable to get uniform illumination in the scanning direction on wafer for the step-and-scan lithographic system. We present a flat Gauss illumination for the step-and-scan lithographic system in this paper. Through flat Gauss illumination in scanning direction, pulse quantization effect could be reduced effectively. Correspondingly, the uniformity of the reticle and wafer is improved. Compared with the trapezoid illumination, flat Gauss illumination could keep the slit edge fixed, and pulse quantization effect will not be enhanced. Moreover flat Gauss illumination could be obtained directly without defocusing and blocking, which results in high energy efficiency and high throughput of the lithography. A design strategy for flat Gauss illumination is also proposed which offers high uniformity illumination, fixed slope and integral energy of flat Gauss illumination in different coherence factors. The strategy describes a light uniform device which contains first microlens array, second microlens array, one-dimensional Gauss diffuser and a Fourier lens. The device produces flat Gauss illumination directly at the scanning slit. The design and simulation results show that the uniformity of flat Gauss illumination in two directions satisfy the requirements of lithographic illumination system and the slope. In addition, slit edge of flat Gauss illumination does not change.

This paper describes numerical analysis of microlens assembly errors in light field cameras using the Monte Carlo method. Assuming that there were no manufacturing errors, home-built program was used to simulate images of coupling distance error, movement error and rotation error that could appear during microlens installation. By researching these images, sub-aperture images and refocus images, we found that the images present different degrees of fuzziness and deformation for different microlens assembly errors, while the subaperture image presents aliasing, obscured images and other distortions that result in unclear refocus images.

A compressive sensing (CS) approach is proposed for the complex wave retrieval algorithm from single off-axis digital Fresnel holography to improve the accuracy of quantitative phase measurement. The linear model of non-linear holographic process used in the complex wave retrieval algorithm is utilized to meet the linearity requirement of the proposed CS implementation presented in this paper. The error in object wave reconstruction due to the approximations used in complex wave retrieval algorithm is compensated by combining it with CS approach. A Mach–Zehnder interferometric geometry in transmission and off-axis mode in the Fresnel domain is used to record the digital hologram. The numerical simulations and experimental results are presented to demonstrate and validate the proof of the concept and to compare CS frame work with conventional complex wave retrieval algorithm. The proposed algorithm is tested for the microlens sample characterization by considering the parameters such as height, diameter and radius of curvature. A Haar wavelet based object wave sparsification is used in the experiment for the prudent phase reconstruction in the CS approach. The proposed method enables an improved and accurate object phase reconstruction, with minimal noise such as distortions or speckles with respect to the conventional complex wave retrieval method.

The light field micro-particle image velocimetry (LF- μ PIV) can record the instantaneous three-dimensional (3D) spatial position information of tracer particles in a single photographic exposure by a single camera, and thus achieve the instantaneous 3D velocity measurement of the micro-scale flow. The accuracy of the spatial positions of the reconstructed tracer particles is closely related to the spatial reconstruction resolution of the LF- μ PIV system, and determines the measurement accuracy of the 3D velocity distribution. In this paper, the effects of the optical parameters of the LF- μ PIV system and the spatial position of the tracer particle on the spatial resolution and reconstruction quality are numerically studied. The location of the measurement volume and the optical parameters of the LF- μ PIV system are further optimized. Based on the optimized parameters, a LF- μ PIV system is assembled. Finally, experiments are carried out to verify the feasibility of the optical parameters optimization from simulations and to evaluate the performance of the LF- μ PIV system for three-dimensional velocity field in a micro-scale convergent channel. Results indicate that the lateral and axial reconstruction resolutions are higher in the outside and inside regions away from the focal plane, compared with those in the region near the focal plane of the objective lens, and is less affected by the microlens aperture, CCD sensor pixel size and objective lens magnification. The spatial reconstruction resolution of the LF- μ PIV system at different depths is in good agreement with the simulation results, proving the effectiveness of the optical parameters optimization of the LF- μ PIV system. The measurement results of 3D velocity field in a micro-scale convergent channel are consistent with the simulation results by ANSYS Fluent, further verifying the feasibility of the optimized LF- μ PIV system for 3D velocity field.

In this paper, we propose a high-resistance (Hi-R) liquid crystal (LC) micro-lens arrays (MLAs) with a low operating voltage and a controllable focal length for integral imaging (II) 3D display. The focal lengths of the Hi-R LC MLAs can be effectively controlled by applying different operating voltages and driving frequencies. The experimental results indicate that the focal lengths can be adjusted from 4.27 mm to 2.88 mm when the operating voltage applied to the Hi-R LC MLAs increases from 1.8 Vrms to 2.8 Vrms at the driving frequency of 130 kHz. Compared with the II 3D display by using ITO circular-hole electrodes-based or Al circular-hole electrodes-based LC MLAs without Hi-R layer, the II 3D display based on the Hi-R LC MLAs with Al circular-hole electrodes can reveal clear 3D scenes at the corresponding center depth plane (CDP) when a low operating voltage is applied to the Hi-R LC MLAs. Furthermore, the generated elemental images with different depths can be reconstructed at different CDPs by electrically controllable focal lengths of the Hi-R LC MLAs, and these 3D scenes can be realized the switchable display in the same II 3D display system, which can effectively present the optical performance of the II 3D display.

In this research, design of artificial spherical superposition compound eye is presented. The imaging system consists of three layers of lens arrays. In each channel, two lenses are designed to control the angular magnification and a field lens is added to improve the image quality and extend the field of view. Aspherical surfaces are introduced to improve the image quality. Ray tracing results demonstrate that the light from the same object point is focused at the same imaging point through different channels. Therefore the system has much higher energy efficiency than conventional spherical apposition compound eye.

Most CCD imaging detectors integrated microlens arrays (MLAs) to increase fill factor and sensitivity. However, they also introduce spot calibration issues with the inconsistency of spot geometry center and intensity distribution center. We setup theoretical and experimental models to research the problem of centroid shifting. According to the Seidel and Zernike coefficients of the optical model, we analyze main aberrations of microlens. In “Chief Ray” and “Centroid” reference frames, centroid shift numerical value is calculated with Geometric Ensquared Energy (GEE). Based on pentaprism test for 8.4 m mirror segment, we conduct spot imaging experiment in interference system. Spots images are obtained, and two-dimensional centroid algorithm processing is performed on them to get the analog experiment values of centroid movements. The results show that the MLA placed in KAI‐16000 imaging detector causes the spot centroid to move. When there is a 14° (or −14°) angle of incident ray, the shifting values are about 1.46 μm in simulation and 2.18 μm in experiment. Our research makes a contribution to the compensation of calibrated error in metrology technology. We also prove that a significant portion of the shift comes from the low order aberration of microlens.

As microlens technology matures, studies of structural design and reconstruction algorithm optimization for light-field cameras are increasing. However, few of these studies address numerical physical simulation of the camera, and it is difficult to track lighting technology for forward simulations because of its low efficiency. In this paper, we develop a Monte Carlo method (MCM) based on ray splitting and build a physical model of a light-field camera with a microlens array to simulate its imaging and refocusing processes. The model enables simulation of different imaging modalities, and will be useful for camera structural design and error analysis system construction.

A new lithographic approach for the fabrication of an enticing optical diffuser with concave microlens array (MLA) is reported. A flexible photopolymerizable polymer mold is employed as an intermediate transferring template from nickel stamp and directly adopted to fabricate concave MLA diffuser films. The influence of the parameters (such as diameter, fill factor etc.) of concave MLA is analyzed experimentally and theoretically. The results verify that the optical gain can be reached as high as 53%, which has a similar fascinating diffusion effect compared with that of conventional convex MLA diffuser films. Additionally, it is found that diffusion angle could be manipulated by the profile of the concave elliptical MLA, leading to luminance increase in long axis larger than that in short axis. The approach demonstrated here affords the intriguing opportunity to large scale industrial processing for high-quality diffusers with low manufacturing and materials cost.

A novel freeform microlens array was designed for a multi-aperture camera to achieve a thin and compact system. A 3×3 microlens array has a field of view (FOV) of 24°×24°, with a thickness of only 2 mm. Optical freeform surface is used to steer the incident rays so that the principal axis of each channel is perpendicular to the surface of imaging sensor. To achieve a small sampling angle with the large FOV, the partial images of each adjacent pair of microlens are braided. The structure and principle of compact multi-aperture camera were analyzed, and the freeform microlens array was designed and simulated in details. The simulated partial images were reconstructed into one whole image with higher resolution, which proves the validity of the proposed design.

We experimentally demonstrate multiple imaging, multifocusing and 3D imaging through motheye kind of dual periodic rhombic-hexagonal and hexagonal-hexagonal gradient microlens multi-array based on photoresist coated glass substrate. FDTD based simulation study presents a bow-shape multifocus for broad spectrum of an unpolarized electromagnetic wave through these planar hexagonally packed microlens array. The multi-imaging and focusing property of the fabricated microlens array is expected to help collect real-time 3D depth information in bio-imaging. The principle of multi-focus is based on the gradient variation of the spatial dimension (diameter) of the micro-lenses leading to a different radius of curvatures and focal length in an array. This planar microlens arrays can be realized through a single step using a cost-effective phase-controlled interference lithography technique.

Microlens array and micropattern array are integrated on a sheet of polyester film aiming to give rise to a Glass moire pattern, which can be observed without any visual facilities. In this paper, we propose an elemental pattern capture method for obtaining a special presentation of an individual Glass moire pattern rather than moire patterns displayed in an array. The Glass moire pattern will appear and disappear with the viewing angle varying. The pickup process and reconstruction process are introduced in detail. Besides, optimization method has been proposed to solve the cross-interference. In addition, we put forward a way to control the viewing angle in which the moire pattern appears. Experiments are carried out to verify the validity of our method. This moire phenomenon shows a good application prospect in document security and authentication. The elemental pattern capture method can find potential applications in integral imaging.

Photosensitive TiO 2 /organically modified silane hybrid thin films were prepared by a low-temperature sol–gel spin-coating technique. Optical and structural properties of the hybrid films with different titanium contents were characterized by prism coupling technique, UV–visible spectroscopy, Fourier transform infrared spectroscopy, and thermal gravimetric analysis. Advantages for fabrication of elliptical concave micro-lens arrays (MLAs) based on the as-prepared hybrid films were demonstrated by combining polydimethylsiloxane soft mold with a UV-cured imprint technique. Results indicate that the as-prepared hybrid films have great applicability for the fabrication of photonic components, and the fabrication technique provides a simple and cost-effective way for the fabrication of the sol–gel elliptical concave MLAs.

The chromatic aberration effect of light focusing in a periodic nanoscale metallic waveguide array (NMWA) is investigated by using the coupled-mode theory and numerical simulations. The dispersion of the coupling coefficient in the periodic NMWA is calculated. The spreading angle of surface plasmon polaritons (SPPs) is derived from the distribution of the electric field density. The numerical results demonstrate that the light focusing in the periodic NMWA exhibits an anomalous chromatic property in an appropriate wavelength range compared to a conventional microlens.

Collimated beam shaping with freeform surface usually employs a predefined mapping to tailor one or multiple freeform surfaces. Limitation on those designs is that the source, the freeform optics and the target are in fixed one-to-one correspondence with each other. To overcome this drawback, this paper presents a kind of freeform microlens array module integrated with an ultra-thin freeform microlens array and a condenser lens to reshape any arbitrary-shape collimated beam into a prescribed uniform rectangular illumination and achieve color mixing. The design theory is explicitly given, and some key issues are addressed. Several different application examples are given, and the target is obtained with high uniformity and energy efficiency. This freeform microlens array module, which shows better flexibility and practicality than the regular designs, can be used not only to reshape any arbitrary-shape collimated beam (or a collimated beam integrated with several sub-collimated beams), but also most importantly to achieve color mixing. With excellent optical performance and ultra-compact volume, this optical module together with the design theory can be further introduced into other applications and will have a huge market potential in the near future.

A novel method to reduce the diffraction crosstalk for micro-lens based free space optical interconnects is presented. Instead of using microlenses with uniform transmittance apertures, the use of microlenses with non-uniform transmittance apertures is proposed. It is shown that the diffraction crosstalk which exists in the free space interconnects systems that use microlenses with uniform transmittance apertures can be substantially reduced by using microlenses with Gaussian transmittance. The optical field at the detectors array using both the uniform and Gaussian apertures have been derived and used to calculate the crosstalk. Numerical results have been introduced to show the improvement of the signal-to-crosstalk ratio when using the Gaussian transmittance for the microlens.

A new method for fabricating a novel dual-curvature microlens array with a high fill-factor using proximity printing in a lithography process is reported. The lens shapes include dual-curvature, which is a novel shape composed of triangles and hexagons. We utilized UV proximity printing by controlling a printing gap between the mask and substrate. The designed high density microlens array pattern can fabricate a dual-curvature microlens array with a high fill-factor in a photoresist material. It is due to the UV light diffraction which deflects away from the aperture edges and produces a certain exposure in the photoresist material outside the aperture edges. A dual-curvature microlens array with a height ratio of 0.48 can boost axial luminance up to 22%. Therefore, the novel dual-curvature microlens array offers an economical solution for increasing the luminance of organic light emitting diodes.

The aspherical microlens used for beam shaping of vertical-cavity surface emitting lasers (VCSELs) was designed and fabricated. The microlens designed as needed was directly fabricated and integrated in one step on the emitting surface of a VCSEL by femtosecond laser direct writing (FsLDW). By the microlens’ shaping the beam quality of VCSELs can be remarkably improved, especially the reduction of the divergence angle. The experiment results agree with the numerical modeling results. After integrating aspherical microlenses the far-field divergence angle of the VCSEL was reduced from 18.16° to 0.83°. This novel technique has great potential in the field of miniature and low power integrated optical system.

This paper presents a high-performance LED agricultural luminaire that uses a beam-shaping diffuser to achieve high optical efficiency and energy saving. The agricultural luminaire performs an optical efficiency as high as 84.2%. The beam shaping effect also obtains irradiance uniformity of 1/2.56 and excellent spatial color uniformity. The enhancement ratio of optical utilization factor in the proposed agricultural luminaire is 360% in comparison with traditional lighting. Under the designed case, the total utilization factor, including optical utilization factor and spectral utilization factor, of the B+R LED lamp can save 86.1% of power consumption in comparison with compact fluorescent bulbs.

A low cost and simple route was presented to fabricate large-scale ordered microlens arrays on gallium phosphide light emitting diodes with enhanced extraction efficiency. The different morphological microlens arrays were simply fabricated by controlling heat treatment temperature. Light extraction efficiency and light output power of gallium phosphide light emitting diodes were enhanced by different array structures of the polystyrene microlens. Compared to conventional gallium phosphide light emitting diodes, light intensity of the light emitting diodes covered by hemispherical polystyrene microlens shows 1.32 times enhancement under the forward current of 20 mA. The mechanism of enhanced light output with microlens arrays is discussed in detail.

Design and fabrication of optical films to increase visual brightness of OLED (Organic Light-Emitting Diode) lighting units are presented in this paper. This study explores a new fabrication process combining precision machining, photolithography, and micro forming techniques to make a double-sided optical film. One side of the optical film is made of micro triangular-pyramidal array (MTPA), and the other side is micro gapless hexagonal microlens array (GHMA). First, Taguchi Method is applied to determine the optimal microstructure configuration by the assistance of the commercial optical software, FRED. Second, tungsten (W) mold of MTPA as the first mold is manufactured by precision machining including optical projection grinding, lapping, and polishing processes. Nickel–cobalt (NiCo) mold of GHMA as the first mold of the other side is fabricated by using LIGA (Lithographie Galvanoformung Abformung)-like process. To obtain inverse molds, poly dimethylsiloxane (PDMS) is used to replicate W and Ni–Co molds, which are served as the secondary molds for two sides, respectively. With these molds, UV (ultraviolet) curable resin was used to make double-sided optical film. Then the optical film was packaged on OLED unit to measure its optical properties by PR 650 equipment. The result shows that both brightness and uniformity can be improved by using this film.

Novel structure of dual-focus microlens array with dual layers is proposed. Dual-focus microlenses formed by combination of dual layers of concentric spherical lenses are fabricated through photo lithography and dry etching processes. The dual lens is formed by combination of a thermally reflowed photo resist lens on a fused quartz lens which is formed by dry etching of the fused quartz substrate.

This study attempted to develop a detection system for lens sag of the microlens array in real time using an optical automatic inspection framework to link with the computer through a camera. An image processing technique was applied to detect the spherical microlens array, and then, the results were compared. The system light source used laser light and applied CCD to collocate with the microscope array to form an automatic optical detection system for an optical interferometric microscope. It applied the principle of the Fizeau interferometer, illuminated the surface of microlens array, and formed the phase difference required by the interference of two lights through the laser light reflected by the reference plane and the surface of the microlens array, thus, forming an interference fringe. When the sag of the microlens was much longer than the wave length of the detection light source, the fringe would be densely distributed, thus, only a few central fringes were clear in the microscopic image. An image processing method was used to search the center of the interference fringe and a creative algorithm was utilized to obtain the lens sag of the microlens. As proved by the experiment, lens sag of 4 microlens arrays were detected in real time, with a minimum detection error of 0.08 μm, and a maximum detection error of 4 μm (error value 1 ~ 9%), according to different sample processes. This system featured a simple structure and is applicable to non-contact detection and detection of different-sized microlens arrays.

Regular periodic textures e.g., microlens arrays, micro-pyramids, and cones on substrate surface have been used to enhance light out-coupling in light emitting devices. Photon randomization, often associated with surface roughening, has been suggested as the mechanism for out-coupling enhancement. This article analytically investigates the ray dynamics in a light emitting device when periodic texture is used as an external out-coupler. An attempt has been made to understand the relationship between enhancement in out-coupling and the surface inclination of these structures using classical ray optics.

Microlens array has been known to be effective in enhancing the out coupling efficiency of LEDs, OLEDs and other thin film light emitting devices. However, mechanism of efficiency enhancement by use of microlens arrays is still ambiguous, apart from suggestions that it leads to randomization of photons. We have studied the photon dynamics in the presence of microlens arrays and the effect of various parameters e.g. microlens contact angle, absorption and substrate refractive index using ray tracing simulations. Microlens array leads to extraction of a portion of photons outside the escape cone at the cost of reduced extraction from within the escape cone. The reduced extraction from within the escape cone is compensated by multiple reflections from the back surface. Increase in microlens contact angle reduces the number of reflections required for out-coupling hence reducing the absorption in the device.

An optical film with aspherical microlens array (A-MLA) by using multi-step lithography process for an OLED (Organic Light-Emitting Diode) package is fabricated, by which method the luminance of OLEDs can be enhanced. The method of design and fabrication of an A-MLA is explored in this study. In the design process, various parameters of an A-MLA such as curved profiles, layout template and dimensions of microlens are analyzed and characterized. Curved profiles include hyperbola, parabola, ellipse and sphere; and layout templates include square, hexagon, triangle and tangential circle. The profile of the A-MLA was determined by using a commercial optical simulation software, FRED. Based on the simulated result, a film with an A-MLA was fabricated using the LIGA-like (Lithographie Galvanoformung Abformung, LIGA) process, including lithography, sputtering, micro-molding with PDMS (Polydimethylsiloxane) and UV (Ultraviolet)-cured technology. The major challenge to this process is to use JSR-126N negative thick photoresist to manufacture an approximate A-MLA optical film with multi-step lithography method. Finally, the films with A-MLAs are attached to an OLED to measure their optical-electric properties. The effectsof A-MLA optical films on OLED luminance are analyzed. In addition, the measured results are compared with simulated ones. They show good agreement with each other.

Utilization of the zero space microlens technology can significantly improve the image quality of CMOS sensors. In this study, we present systematical data of design, simulation, characterization and silicon level testing during the initial stage of development of the zero space microlens based CMOS imaging technology. The optimal structure of zero space microlens was obtained based on the simulation results. Sample CMOS image sensors with a 2.8 μm pitch zero space microlens above each pixel have been successfully fabricated based on 0.18 μm CMOS technology. Using AFM (atomic force microscopy) and sensor test platform, the structural and optical properties of both space microlens and zero space microlens have been characterized, and their performances have been evaluated respectively. Both AFM results and silicon tests have demonstrated that the 2.8 μm pitch zero space microlens can remarkably improve the pixel sensitivity and pixel array non-uniformity, and reduce the optical crosstalk. Compared to the space 2.8 μm square microlens, the zero space microlens shows 78.83% (68.42% and 75.93%) enhancement of photosensitivity and increment of pixel non-uniformity up to 20% (45.6% and 30.77%) for R (G and B), and reduction of the optical crosstalk up to 44.49%, under 45 lux light and 30 ms exposure time. In addition, the zero space microlens has also shown a great potential in further reducing pixel size down to less than 2.8 μm and meanwhile improving imaging performance of CMOS image sensors.

We report the electro-optical properties of dielectric liquid droplets based on dielectrophoretic effect. Due to dielectric force, the surface of each droplet can be reshaped which in turn alters its focusing behaviors. Our experimental results show that a deformed droplet can recover to its original shape with a negligible hysteresis. Both amplitude and frequency of the applied voltage play important roles affecting the droplet's shape change. The rise time is mainly governed by the applied voltage: for a given frequency a higher voltage results in a faster rise time. On the other hand, the decay time is jointly determined by the interfacial surface tensions, droplet size, and viscosity of the employed liquids.

Microlens array (MLA) is microfabricated using Ultra Violet (UV) laser for display device applications. A colorless liquid photopolymer, Norland Optical Adhesive (NOA) 60, is spin-coated and pre-cured via UV light for completing the laser process. The laser energy controlled by a galvano scanner is radiated on the surface of the NOA 60. A rapid thermal volume expansion inside the material creates microlens array when the Gaussian laser energy is absorbed. The fabrication process conditions for various shapes and densities of MLA using a non-contact surface profiler are investigated. Furthermore, we analyze the optical and display characteristics for the Organic Light Emitting Diode (OLED) devices. Optimized condition furnishes the OLED with the enhancement of light emission by 15%. We show that UV laser technique, which is installed with NOA 60 MLA layer, is eligible for improving the performance of the next generation display devices.

This paper presents a technique that distortion aberrations of an optical imaging system can be reduced by using spherical lenses accompanying a microlens array. This technique is implemented by putting a microlens array on the intermediate image plane in the imaging system. Our experimental result confirmed that distortion aberrations can be obviously reduced after applying our proposed techniques.

Gaussian beam propagation through a novel high refractive index contrast nanostructured Gradient-Index (GRIN) microlens with an arbitrary refractive index distribution is investigated. The concept of the nanostructured GRIN microlenses is based on the effective medium theory and we show numerically, using the FDTD method, that nanostructured GRIN microlenses can focus Gaussian beams in an identical manner to conventional GRIN microlenses. Nanostructured GRIN microlenses have a reduced thickness by almost two orders of magnitude compared to conventional GRIN lenses. We also investigate the accuracy of the standard scalar and paraxial GRIN theory in the case of a very high contrast nanostructured GRIN microlens. The paraxial GRIN lens theory is shown only to give an approximate description of Gaussian beam propagation in such a high contrast nanostructured GRIN microlens.

We fabricated spherical microlenses on optical glasses by femtosecond laser direct writing (FLDW) in ambient air. To achieve good appearances of the microlenses, a meridian-arcs scanning method was used after a selective multilayer removal process with spiral scanning paths. A positive spherical microlens with diameter of 48 μm and height of 13.2 μm was fabricated on the surface of the glass substrate. The optical performances of the microlens were also tested. Compared to the conventional laser direct writing (LDW) technique, this work could provide an effective method for precise shape-controlled fabrication of three-dimensional (3D) microstructures with curved surfaces on difficult-to-cut materials for practical applications.

Focusing a radially polarized annular Gaussian beam with a gradient Mikaelian’s microlens is simulated using a radial version of the FDTD method (finite-difference time domain), in which Maxwell’s equations in the cylindrical coordinates are solved in the MATLAB 7.0 environment. We show that the focal spot size (the area with larger-than half-maximum intensity) can be made as small as 0.126λ2, with focal spot diameter being 0.40λ.