Effects of low polymer content in a liquid-crystal microlens

A small number of bifunctional monomers are mixed with a nematic liquid crystal (LC) and cured with a distributed electric field, which is produced by a circular-hole-patterned electrode structure. A gradient type of lens, that is, a LC microlens, is investigated for various polymer concentrations. Addition of 3% polymer is enough to freeze the gradient-index properties of the structure in the form of a convex lens, and a polymer-stabilized LC microlens is demonstrated. Although a lower concentration of polymer cannot hold the distribution properties in a curing process, it can maintain the variable focus as a nematic material can. The polymer networks can also eliminate the disclination line that usually appears and causes the lens in this type of LC device to deteriorate.     

Optimization of Device Parameters for Minimizing Spherical Aberration and Astigmatism in Liquid Crystal Microlenses

The aberration properties of liquid crystal (LC) microlenses with various diameters, thicknesses and shapes (circles or ellipses) are evaluated by analyzing fringe patterns generated by interference between ordinary and extraordinary rays. It is found that the astigmatism and the spherical aberration can be minimized by adjusting the ellipticity of the hole pattern and the applied voltage, respectively. Based on the experimental results, we propose a design scheme for minimizing the spherical aberration and astigmatism. It is confirmed that the LC microlens obtained by the proposed design scheme shows a good focusing spot whose value of full width half maximum is close to that of the diffraction limit.     

非球面液滴微透镜固化控制和焦斑测量研究

利用电场改变液滴透镜的面形得到非球面,并实时检测其面形和焦斑图像,在适当的时候用紫外光固化液滴制作具有良好光学性能的非球面微透镜.比较了非球面液滴微透镜在固化前后面形、焦斑的变化和对透镜性能的影响,讨论了液滴透镜在固化过程中变形的机理和相应的解决方法.用分辨率50 nm的光斑探针扫描仪精确测量了固化后的非球面微透镜的聚焦光斑,测得了光斑轴向分布曲线和均方根直径3.384μm的聚焦光斑,经图像处理计算了透镜的点扩散函数和光学传递函数,评价了所制作的非球面微透镜的聚光和成像能力,并给出了透镜的实际成像图像,对于完善高品质非球面微透镜及其阵列的制作工艺具有重要意义.     

平面交叉玻璃波导型微透镜阵列光学性能研究

介绍了平面交叉玻璃光波导型半球形微透镜阵列的制作方法.利用积分形式的光线方程式讨论了半球形微透镜的光学特性,得到了半球形微透镜的光线轨迹方程式和焦距表示式,理论结果与实验数据是一致的.     

Three-dimensional integration of microoptical components buried inside photosensitive glass by femtosecond laser direct writing

We report the three-dimensional (3D) integration of microoptical components such as microlenses, micromirrors and optical waveguides in a single glass chip by femtosecond (fs) laser direct writing. First, two types of microoptical lenses were fabricated inside photosensitive Foturan glass by forming hollow microstructures using fs laser direct writing followed by thermal treatment, successive wet etching and additional annealing. One type of lens is the cylindrical microlens with a curvature radius R of 1.0 mm, and the other is the plano-convex microlens with radius R of 0.75 mm. Subsequently, by the continuous procedure of hollow microstructure fabrication, a micromirror was integrated with the plano-convex microlens in the single glass chip. Further integration of waveguides was performed by internal refractive index modification using fs laser direct writing after the hollow structure fabrication of the microlens and the micromirror. A demonstration of the laser beam transmission in the integrated optical microdevice shows that the 3D integration of waveguides with a micromirror and a microoptical lens in a single glass chip is highly effective for light beam guiding and focusing. PACS 42.62.-b; 81.05.Kf; 42.82.Cr; 82.50.Pt; 42.79.Gn     

Numerical analysis and design of patterned electrode liquid crystal microlens array with dielectric slab

The phase profile of hole patterned electrode liquid crystal (LC) microlens array (MLA) was studied by a numerical method. It indicated that the formation of inverse domain and tilt wall in the liquid crystal cell limits the optical performance of the microlens array. The physical mechanism that determines the formation of inverse domain and tilt wall was elucidated by analyzing the phase profile and the liquid crystal director distribution. According to our numerical results, a new configuration for hole patterned electrode liquid crystal microlens array was proposed by introducing a dielectric slab between the patterned electrode and the liquid crystal. The physical parameters that influence the optical performance of this new configuration LC MLA were studied, which provide fundamental information for the design. The results indicate that the phase profile and focusing power of the new configuration is greatly improved.     

Design and simulation of single-electrode liquid crystal phased arrays

Liquid crystal (LC) phased arrays and gratings have been employed in optical switching and routing [1]. These diffractive optic elements are of great interest because they can be scaled up to a large number of elements and their optical properties can be electrically addressed with a low driving voltage. LC phase gratings have been achieved either by periodic addressing of pixels or by using periodically-modified structures. The latter approach leads to less reconfigurable devices but the addressing is simpler. In this paper we focus on optical phased arrays where the phase is varied either continuously or discretely and where the periodicity is induced by electrode configuration. We first describe a possible structure based on a conductive silicon wafer. We argue that this structure can induce either continuously or discretely varying arrays while applying single voltage to the array. In the second part we simulate the behaviour of such arrays. We base the simulation on a LC synthesized at the Military University of Technology, this high-birefringence nematic LC shows in a 4-μm thick cell a linear phase shift range of more than 360° between 1.2 V and 1.8 V. We calculate the distribution of the LC molecule director and assess the performance of the array with respect to the applied voltage. Finally, the relevance of such technology for switchable phased arrays is discussed.     

Optical Properties of a Polarization Converting Device Using a Nematic Liquid Crystal Cell

A radially and homogeneously aligned LC cell as a polarization controlling device is fabricated using a memory effect in an axially symmetric electrical field. Optical properties and the molecular orientation of the LC cell are investigated and the conversion property of the polarization states of the cell is discussed in detail from the molecular orientation in the cell.On leave from Advantest Laboratories, Ltd., 48-2 Matsubara, Kamiayashi, Aoba-ku, Sendai, 989-31 Japan.     

大变焦范围电调谐液晶变焦透镜的研究

基于向列相液晶指向矢随施加电场作用发生变化的特性, 结合几何光学和液晶理论提出了一种液晶透镜结构模型, 研究了电极大小、隔垫物厚度等液晶透镜参数对液晶透镜焦距的影响. 通过优化参数, 得到结构简单、变焦范围较大的新型液晶透镜样品, 在驱动电压0 V_RMS–250 V_RMS下可调的焦距范围为75–230 mm, 达到155 mm.     

微透镜阵列线性光学扫描器

本文介绍了一种新型的线性扫描光学系统，它由一对处于望远型结构的微透镜阵列和一个普通的会聚透镜组成。微透镜阵列采用二元光学技术进行设计和制作。该装置具有扫描灵敏度高（～１０００）、扫描范围大（±１００ｍｍ）、结构紧凑、价格低廉等优点。     

紫外衍射微透镜阵列的设计与制备

为了提高紫外焦平面阵列的填充因子,可以通过微透镜阵列与紫外焦平面阵列的集成,以改善紫外焦平面阵列的探测性能。根据标量衍射理论设计了用于日盲型紫外焦平面阵列的128×128衍射微透镜阵列,其工作中心波长为350nm,单元透镜F数为F/3.56。采用组合多层镀膜与剥离的工艺方法制备了128×128衍射微透镜阵列,对具体的工艺流程和制备误差进行了分析,测量了衍射微透镜阵列的光学性能。实验结果表明:衍射微透镜阵列的衍射效率为88%,与理论值95%有偏差,制备误差主要来自对准误差和线宽误差。紫外衍射微透镜阵列具有均匀的焦斑分布,与紫外焦平面阵列单片集成能较好地改善器件的整体性能。     

Research on micro-optical lenses fabrication technology

We present a detail investigation on the development of a series of gradient index (GRIN) optical glass microlens and polymer microlens and microlens arrays in our laboratory in recent years. The special glass material GRIN lenses have been fabricated mainly by using ion-exchange technology, which are applied to construct micro-optic devices and other applications. On one hand, we demonstrated the light propagation and imaging properties of GRIN lenses and the results analyzed. On the other hand, we have explored a drop-on-demand ink-jet printing method to produce microlens array using nano-scale polymer droplets involved with a uniform ultraviolet light and heat solidifying process. The experimental setup for manufacturing polymer microlens array and the performance of refractive microlens elements are also given in this paper.     

柔性液晶微透镜阵列的制备与性能研究

针对集成成像视场角狭小的问题,设计并制备了一种柔性圆孔驱动电极控制液晶分子偏转的可弯曲和焦距可调的柔性液晶微透镜阵列。利用光刻技术在柔性ITO基板表面刻蚀并形成规则的圆孔阵列电极,旋涂工艺制备柔性聚酰亚胺(PI)膜层,PI膜层经60℃加热5 min后,再利用等离子体在功率630 W条件下处理5 min固化成PI取向层。利用液晶盒成盒工艺将上、下基板组装成液晶透镜,研究未弯曲和弯曲曲率半径7.5 cm条件下液晶微透镜阵列的光学性能。实验结果表明,所制备的液晶透镜在未弯曲和曲率半径为7.5 cm的情况下均可实现聚焦功能,且液晶微透镜阵列的干涉圆环均匀,聚焦光斑小。在驱动电压3~5.3 Vrms下,弯曲曲率半径为7.5 cm的液晶微透镜阵列焦距可调的范围为0.43~1.05 mm。     

Ultrathin Planar Microlens Arrays Based on Geometric Metasurface

Ascribing to the properties of two dimensional parallel focusing and imaging, low propagation loss, integration and miniaturization, microlens array has been widely used in imaging, optical communication, organic light emitting devices, adaptive optics, photolithography, biomedical and other applications. However, the existing traditional microlens array suffers from difficulty in fabrication, large‐thickness, curved surface, non‐uniformity of light spots, or requirement of additional discrete components to control the microlens. Herein, a planar microlens array is experimentally demonstrated based on the geometric metasurface. The single microlens is composed of space‐variant subwavelength metallic gratings with high polarization conversion efficiency and thus exhibits gradient phase distribution. The focused spot diameter of 22.5 μm with radius of 350 μm, focal length of 1 cm and the light spots intensity uniformity of 0.9885 (standard deviation 0.0115) at the focal plane are obtained. Moreover, the broadband property of microlens array is also confirmed. The novel design strategy for microlens array would facilitate the miniaturization of optical devices and be easily integrated in the optical interconnected devices.     

Optical compensator with switchable modes using polymer stabilized liquid crystals

We propose an optical compensator configuration with switchable modes by combining the polymer stabilized liquid crystal (PSLC) technology with the novel electrode design. It could be applied to a fixed-focus lens module for providing the defocus compensation of an optical imaging system. The device has two operation modes that can be switched by the electrode connection and provide respective optical retardation effects. It was designed by using the optical simulation tool and fabricated by using the standard photolithographic processes, the liquid crystal (LC) cell assembly procedure, and the particular ultra-violet (UV) exposure steps. The device was implemented and experimental results qualitatively showed its feasibility for realizing the capability of switching different compensation modes.     

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.     

Design and Fabrication of Microlens Array for Near-Field Vertical Cavity Surface Emitting Laser Parallel Optical Head

A GaP microlens for collecting laser light was developed in the tip of a near-field probe. It is important to realize a near-field optical probe head with high throughput and a small spot size. The design and fabrication results of the GaP microlens array are described. The most suitable GaP microlens with a probe was calculated as having a 10 μm radius using the two-dimensional finite difference time domain (2-D FDTD) method. The full width half maximum (FWHM) spot size variation and optical power density tolerance were calculated as 157 nm ± 5 nm and 7%, respectively. A spherical GaP microlens was fabricated with a radius of 10 μm by controlling the Cl₂/Ar gas mixture ratio. The difference between the theoretical spherical shape and the fabricated GaP microlens was evaluated as 40 nm at peak to valley. The FWHM spot size and optical throughput of the fabricated microlens were measured as 520 nm and 63%, respectively. The microlens was the same as a theoretical lens with a 10 μm radius. The micron-lens array fabrication process for a near-field optical head was demonstrated in this experiment.     

Optical Pickup with a Spherical Aberration Compensator Using a Crossed-Stripe Liquid Crystal Device

To increase recording density in an optical disk system, a two-lens system which enlarge its numerical aperture (NA) has been developed. When NA becomes larger, however, the spherical aberration due to disk thickness error increases. We propose an optical pickup with a spherical aberration compensator using nematic liquid crystal (LC). Our LC device is composed of two LC cells each of which has X and Y stripe electrodes, respectively. We discussed how the spherical aberration due to the disk thickness error can be compensated by combination of two crossed cylindrical phase distributions induced by the LC cells, and confirmed the compensation effect in a design example by simulation. We have also fabricated the crossed stripe LC device actually, and have obtained the experimental result which shows that amount sufficient to compensate the aberration is achieved.     

凹折射微透镜阵列的离子束刻蚀制作

利用光刻热熔成形工艺及离子束刻蚀制作 12 8× 12 8元凹微透镜阵列。所制硅及石英凹微透镜的典型基本图形分别为凹球冠形、凹柱形和矩顶凹面形。分析了在光致抗蚀剂柱凹微透镜图形制作过程中的膜系匹配特性 ,与制作该种微透镜有关的光掩模版的主要结构参数 ,以及光致抗蚀剂掩模工艺参数的控制依据等。探讨了在凹微透镜器件制作基础上利用成膜工艺开展平面折射微透镜器件制作的问题。采用扫描电子显微镜 (SEM)和表面轮廓仪测试了所制石英凹微透镜阵列的表面微结构形貌。给出了所制石英凹微透镜阵列远场光学特性的测试结果。     

Fabrication and characterization of polydimethylsiloxane concave microlens array

Concave microlens array is fabricated with PDMS (polydimethylsiloxane) material. Resist thermal reflow method and reverse pattern replication method are employed to fabricate the concave microlens array. The optical performance of the PDMS concave microlens array is analyzed with ray-trace method. Profile of the PDMS concave microlens array is observed by metallographic microscope and Talystep. It is indicated by the results that the surface profile of the PDMS concave microlens array is clear and distinct. Optical properties are also tested with Beamprofiler system. The shine spots on the focal plane of the microscope objective are of highly uniformity, and essentially coincide well with the simulation result. The PDMS concave microlens array has potential application in many optoelectronic devices, such as diffusers and scanners.