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.     

基于液晶光调制器的夏克-哈特曼波前探测技术

微透镜阵列是夏克-哈特曼波前探测器的关键器件。利用液晶器件的空间相位调制特性,可实现微透镜阵列功能,且具有孔径和焦距可变的优点。论述了基于液晶光调制的夏克-哈特曼波前探测校正技术的特征、技术进展、及应用前景。     

装置参数对狭缝天线激发的等离子体表面波传播的影响

采用时域有限差分法对矩形结构装置的等离子体表面波传播进行了三维数值模拟.研究了装置参数(如介质板相对介电常数、厚度以及介质板上方空气间隙)对天线阵列激发的等离子体表面波传播的影响,给出了合适的介质板相对介电常数和厚度,并指出空气间隙的存在会严重削弱天线阵列对表面波的激发.计算结果可为大面积矩形表面波等离子体源装置的优化设计提供参考. 关键词： 时域有限差分法 等离子体表面波 狭缝天线     

微透镜列阵提高红外探测器探测能力的方法研究

研究用微光学方法提高红外探测器探测能力的机理,通过实验将锗微透镜列阵耦合到180元HgCdTe焦平面红外探测器上,使耦合组件探测率提高到原来的2．8倍,提出的光学耦合效应概念为客观评价微光学聚能元件综合质量及耦合机构性能提供了一种新的方法。还对微透镜列阵的冷屏效应进行了讨论。     

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。     

Diffractive Microlens Array Monolithic Integration with PtSi Focal Plane array

Diffractive microlens arrays can completely collect the light at the focal plane and concentrate it into a smaller spot size on the detector plane, the photodetector area can be substantially reduced. Increased gamma radiation hardening and noise reduction result from the decrease in photodetector sensitive area. The diffractive microlens arrays have been designed by considering the correlative optical and processing parameters for PtSi focal plane array. They have been fabricated on the backside of PtSi focal plane array chip by successive photolithography and Ar⁺ ion-beam-etching technique. The alignment of microlens array with PtSi focal plane array was completed by a backside aligner with IR light source. The practical processes and fabrication method are discussed. The performance parameters of PtSi FPA with diffractive microlens array are presented.     

Three-dimensional photonic crystal of negative refraction achieved by interference lithography

A three-dimensional bicontinuous photonic crystal of a bcc lattice with all-angle negative refraction that can be achieved at optical frequencies by interference lithography is proposed. A numerical simulation of the focusing imaging of a slab of this crystal was performed to verify the property of all-angle negative refraction. The dependence of the negative-refraction frequency range on the threshold of photoresist development and on the dielectric constant is also discussed.     

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.     

Circular arc plasmonic waveguide couplers between two-dimensional dielectric slab waveguides and plasmonic waveguides

We investigate the properties of arc plasmonic waveguide coupler between two-dimensional dielectric slab waveguides and plasmonic waveguides with two-dimensional finite difference time domain methods. The simulation results show that transmission efficiency between high index dielectric slab waveguides with width 300 nm and silver-air-silver waveguides with width 40 nm connected by the coupler can reach to 90.4% at optical communication wavelength. And, by optimizing the shapes near the ends of the coupler, the transmission efficiency can be improved to 98.4%.     

Hybrid Integration Between Long Focus Microlens Array and IR Detector Array

A special method, named step simulation method, is proposed for fabricating Si microlens array to improve the performance of infrared focal plane array (IR FPA). The focus length of rectangle-based multistep microlens array with element dimension of 40 µm×30 µm is 885.4 µm by the method, which is much longer than the focus length of microlens array fabricated by conventional Fresnel binary optics technique., The large-scale 256×256 element microlens array is hybridintegrated with the PtSi Schottky-barrier IR FPA by optical adhesive. The test results show that diffractive spot size of the microlens is 17 µm×15 µm and the average optical response of the IR FPA is increased by a factor of 2.4.     

Efficiency improvement and spectral shift of an organic light-emitting device with a square-based microlens array

In this paper, we present and analyze the influences of the fill factor and the height ratio of square-based microlens arrays on the optical characteristics of an organic light-emitting device (OLED). These properties include spectral shift, CIE coordinates, viewing-angle dependence, luminous current efficiency and luminous power efficiency. Both the luminous current efficiency and luminous power efficiency of the OLED were found to increase linearly with increasing the fill factor of microlenses. It is also found that the full width at half maximum (FWHM) of the OLED spectra and CIE coordinate decreased linearly with increasing the fill factor of the microlenses. Besides, the efficiency improvement of the OLED increased with the height ratio of attached microlenses. Compared to the OLED, the luminous current efficiency and luminous power efficiency of the device can be enhanced by 42% and 47%, respectively, by attaching the microlens array having a fill factor of 90% and a height ratio of 0.57. We also observed blue shifts at different viewing angles when microlens arrays were attached to the OLED, which is the evidence that the waveguiding modes are being extracted. In our planar OLED, the peak wavelength blue shifted and the FWHM decreased with increasing the viewing angles due to the microcavity effect.     

Mode splitting in an optical slab waveguide filled with nematic liquid crystals

Mode splitting was observed when a He-Ne laser beam was reflected through a prism-coupled liquid-crystal slab waveguide under an applied electric field. The splitting manifests itself as the imposed voltage reaches a critical level, and diminishes when the voltage increases above a critical high value. If the applied voltage increases even further, mode splitting vanishes, attributing to the result that almost all the directors of the liquid crystal turn upright to the surface. The multi-layer matrix simulation can satisfactorily account for this phenomenon by exploiting the property of the anisotropic optical birefringence of a liquid crystal under applied voltages. Received: 2 December 2002 / Revised version: 24 January 2003 / Published online: 23 May 2003 RID="*" ID="*"Corresponding author. Fax: +886/3572-3052, E-mail: jtlue@phys.nthu.edu.tw     

Rigorous electromagnetic analysis of dual-closed-surface microlens arrays

In this paper, we investigated the focal performance of the dual-closed-surface microlens arrays (DCSMAs) based on rigorous electromagnetic theory and boundary element method (BEM) in the case of TE polarization. The DCSMAs are designed with different substrate thickness and different distance between microlenses. DCSMAs designed according to different wavelengths are surveyed. The DCSMAs with different incident angles are also studied. Several focusing performance measures, such as the focal spot size, the focal position on the preset focal plane, the diffraction efficiency and the normalized transmitted power, are presented. Numerical results indicate the DCSMAs with different parameters can implement focusing beams and the focal performance of DCSMAs is easily influenced by the substrate thickness and the incident wavelength. Furthermore, the optimal thickness for the maximal diffraction efficiency of the DCSMAs is given. It is expected that the DCSMAs may be used as a parallel processing device in micro-optics systems.     

Formation for Bass-Relief Microprofiles Based on an Analytic Formulation

A method of fast design and fabrication for bass-relief micro-profiles is developed by using an analytic formulation to determine the exposure distribution. Based on an equivalent exposure threshold model, the formulation is simplified for the case of bass-relief profile corresponding to the smaller exposure dose. The mask function for a microlens array is designed without iteration involved by the analytic formulation. The experiment is performed to validate the method, and the fabrication result is obtained with the profile error less than 30nm （rms）.     

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.     

Flat polymeric microlens array

A polymer-based flat microlens array is demonstrated. Within each pixel of the array, the polymer presents a circular central-symmetric inhomogeneous orientation. Pixel with such a structure behaves a lens-like character. A suitable amount of liquid crystal mixed in the polymer host can improve not only the lens flexibility but also the lens performance. Moreover, the polymer-based microlens array has the advantages of real planar surface, ultra-thin thickness, and can be designed with any aperture size.     

基于微透镜阵列匀束的激光二极管面阵抽运耦合系统分析

为了提升高功率固体激光器中激光二极管(LD)面阵抽运场性能,采用几何光学和数理统计分析的方法,建立了基于微透镜阵列匀束的LD面阵抽运耦合系统的数学与物理模型,对微透镜阵列参数与最终耦合输出抽运场参数之间的关系进行分析,明确了微透镜单元F数、微透镜通光单元数以及微透镜阵列空间周期参数的设计原则.经实验测试,优化设计完成的LD面阵抽运耦合系统光场不均匀度为7.9%,耦合效率为90.7%.     

Extraordinary Transmission through Metallic Grating with Subwavelength Slits for S-Polarization Illumination

Based on the rigorous coupled-wave analysis algorithm, we have systematically analysed the effect of the geometrical parameters of a dielectric film coated metallic grating with subwavelength slits on extraordinary optical transmission for s-polarization illumination. Results show that the dielectric film which sustains a waveguide electromagnetic mode on the top of the metallic lamellar grating can strongly enhance the transmittance, the positions of the transmission peaks are mainly determined by the period of the metallic grating, the thickness and refractive index of the dielectric film. This structure shows potential applications in excellent polarizers or polarization-isotropic devices at infrared spectral range by appropriately choosing the geometrical parameters.     

Generation of 60-GHz Millimetre Wave with 20-GHz DSB Optical

A new scheme to generate a 60-GHz millimetre （mm） wave by tripling the frequency of the 20-GHz DSB optical mm wave is proposed. According to our analysis and numerical simulation of transmission along a fibre, this scheme can not only eliminate code form distortion, but also reduces the influence of fading effect as it transmits along the fibre. Therefore, the radio-over-fibre link based on the generated optical ram-wave signal has better performance.     

Optical defect modes at an active defect layer in photonic liquid crystals

An analytic approach to the theory of the optical defect modes in photonic liquid crystals in the case of an active defect layer is developed. The analytic study is facilitated by the choice of the problem parameters related to the dielectric properties of the studied structures. The chosen models allow eliminating polarization mixing at the external surfaces of the studied structures. The dispersion equations determining the relation of the defect mode (DM) frequency to the dielectric characteristics of an isotropic, birefringent and absorbing (amplifying) defect layer and its thickness are obtained. Analytic expressions for the transmission and reflection coefficients of the defect mode structure (DMS) (photonic liquid crystal-active defect layer-photonic liquid crystal) are presented and analyzed. The effect of anomalously strong light absorption at the defect mode frequency for an absorbing defect layer is discussed. It is shown that in a distributed feed-back lasing at the DMS with an amplifying defect layer, adjusting the lasing frequency to the DM frequency results in a significant decrease in the lasing threshold and the threshold gain decreases as the defect layer thickness increases. It is found that, generally speaking, the layer birefringence and dielectric jumps at the interfaces of the defect layer and photonic liquid crystal reduce the DM lifetime in comparison with the DMS with an isotropic defect layer without dielectric jumps at the interfaces. Correspondingly, generally speaking, the effect of anomalously strong light absorption at the defect mode frequency and the decrease in the lasing threshold are not so pronounced as in the case of the DMS with an isotropic defect layer without dielectric jumps at the interfaces. The case of a DMS with a low defect layer birefringence and sufficiently large dielectric jumps are studied in detail. The options of effectively influencing the DM parameters by changing the defect layer dielectric properties, and the birefringence in particular, are discussed.