In this paper, we propose a new type of liquid-crystal cylindrical microlens arrays (LCCMAs) with nonuniform microcoil electrodes (NMEs). The key functional microstructure of the LCCMAs includes two ~500-μm-thick glass substrates with indium-tin-oxide (ITO) films for shaping the top and the bottom electrodes and a thin LC layer with a typical thickness of 20μm. The ITO film of the upper substrate is etched into the shape of nonuniform microcoil by traditional lithography process and inductively coupled plasma etching (ICP etching). By simply adjusting voltage signal applied on the NMEs, the LCCMAs exhibit relatively sharp point spread functions (PSFs) at the focal plane of different spectral beams including red (635-671nm), green (501-561nm) and blue (430-473nm) lasers at relatively low signal voltages (even less than 3Vrms).
To focusing ion beam etching (FIB) machine, the maximum effective processing size in x- and y-direction is still in ~100 micron scale during a single manufacturing cycle, generally. Considering the performances of existing equipments, it is a core operation that a high-precision and small-volume stepping displacement microplatform with a larger manufacturing size of more than that of existing equipments, is constructed effectively for fabricating optical antenna with a size in centimeter scale. The designed setup can be used to conduct a two-dimensional displacement with very high precision of few tens of nanometers for processing sample with structural size scope in centimeter level or even more, is to attach to the working plate of the FIB machine. In this paper, the 80C51 single-chip microcomputer is used as the control setup. Based on the analysis of the three closed-loop DC speed regulation system, the key parameters of the controller are designed according to the dynamic and static performance indicators of the system. Using Matlab's Simulink and Power System toolbox, a three-mode closed-loop DC speed control system for positioning and current generating is built. The model and the key parameter setting of the positioning loop, the speed loop and the current generating loop, are introduced. The simulation model and results of the DC reversible speed control system are given. The simulations verify the model, which can be effectively utilized to correct the parameter setting. It should be noted that the current change rate is suppressed while maintaining a maximum allowable changing rate, so as to make the entire current waveform being closer to the ideal waveform.
We propose a foveated imaging system (FIS) implementing by effectively correcting wavefront aberration, which mimics the human visual system to obtain a high resolution image for the regions of interest (ROI) while keeping a wide field of view (FOV). It is flexibly tuning the variation of the refractive index of liquid-crystal (LC) materials through adding variable AC voltage signals. A novel liquid-crystal microlens array (LCMLA) with three concentric ringelectrodes are presented, where three different AC voltage signals can be applied to corresponding ring-electrodes. There are three hexagon arrangement patterned electrode arrays with different diameters (equivalent to 98μm, 112μm and 140μm from the center to the periphery) in the concentric circles. The diameter of the MLA in the central field is the smallest, where the spatial resolution may be the highest. If appropriate AC voltage signals are added, the wavefront aberration of the incident light of ROI could be well adjusted. An experiment is developed to validate the performance of the FIS using LCMLA. The example images show that the proposed FIS can obtain local high resolution image of the ROI by dynamically controlling AC voltage signals and a total low resolution image over a wide FOV.
In this paper, a new type of electrically controlled liquid-crystal microlens arrays (ECLCMAs) based on plane nonuniform spiral microcoils (PNSMs) is proposed. The microlens array is based on a nematic liquid-crystal material, which presents a special characteristics of optical anisotropy and birefringence, and is fabricated by common ultraviolet lithography and dry ICP etching process to form needed PNSMs pattern. In the ECLCMAs, a glass substrate precoated by a film of indium tin oxide (ITO) on both surfaces of substrate is adopted. The key center electrode for shaping each functioned LC cell is drilled using a laser etching and emery polishing process. Metallic indium particles are selected to connect the upper and lower ITO layers. The design can guarantee the continuity of the upper and lower plates and does not affect the electric and magnetic fields generated by spiral microcoils, which are utilized to drive LC film to present needed functions of further controlling and adjusting incident microbeam distribution, which is preprocessed by main objective lens system. After an AC voltage signal is applied across the microcoil, an effective electromagnetic field can be formed in LC cell so as to drive LC molecules to rotate and thus demonstrates an electrically tuning focus. The simulations show that the design of patterned PNSMs can be effectively used to form a sufficient electric and magnetic fields that are directly used to rotate LC molecules and thus form a gradient refractive index distribution for converging incident microbeams so as to show a higher controlling-light efficiency than that of traditional patterned microelectrodes. The proposed method laid a solid foundation for future smart ECLCMAs.
This paper presents a polarization insensitive infrared filter based on a liquid-crystal Fabry-Perot (LC-FP) developed for electrically tunable spectrum and performing high efficient imaging detection. Generally, the LC-FP filters are polarization sensitive optical devices, which means that filtering effect will be enormously influenced by ray polarization so as to lead to a low utilizing efficiency of incident energy. Therefore, it is of great significance to find an approach to improve or even solve the problem. The new type of infrared filter designed by us is mainly consists of a FP resonant cavity with a layer of zinc selenide (ZnSe) material as its substrate and a thin film of nano-aluminum (Al) material acting as its electrode and high-reflection mirror. Particularly, compared to the common filters, it has a multi-directional layer of ployimide (PI) film which can make the LC distributed along two mutually perpendicular directions so that the incident infrared light in different polarization orientations are able to be modulated. The experiment results indicate that the filter’s polarization insensitivity is substantially improved, thus it can work well in various polarized infrared radiations, and obviously will have a broader prospect of application.
In this paper, a new liquid-crystal microlens array (LCMLA) with patterned ring-electrode arrays (PREAs) is investigated, which has an ability to acquire multiple-mode two-dimensional images with better electrically tunable efficiency than common liquid-crystal devices. The new type of LCMLA can be used to overcome several remarkable disadvantage of conventional liquid-crystal microlens arrays switched and adjusted electrically by relatively complex mechanism. There are two layer electrodes in the LCMLA developed by us. The top electrode layer consists of PREAs with different featured diameter but the same center for each single cell, and the bottom is a plate electrode. When both electrode structures are driven independently by variable AC voltage signal, a gradient electric field distribution could be obtained, which can drive liquid-crystal molecules to reorient themselves along the gradient electric field shaped, so as to demonstrate a satisfactory refractive index distribution. The common experiments are carried out to validate the performances needed. As shown, the focal length of the LCMLA can be adjusted continuously according to the variable voltage signal applied. According to designing, the LCMLA will be integrated continuously with an image sensors to set up a camera with desired performances. The test results indicate that our camera based on the LCMLA can obtain distinct multiple-mode two-dimensional images under the condition of using relatively low driving signal voltage.
Under the condition of existing intense turbulence, the object's wavefront may be severely distorted. So, the wavefront sensors based on the traditional microlens array (MLA) with a fixed focal length can not be used to measure the wavefront effectively. In order to obtain a larger measurement range and higher measurement accuracy, we propose a liquid-crystal microlens array (LCMLA) with needed ability of swing focus over the focal plane and further adjusting focal length, which is constructed by a dual patterned ITO electrodes. The main structure of the LCMLA is divided into two layers, which are made of glass substrate with ITO transparent electrodes. The top layer of each liquid-crystal microlens consists of four rectangular electrodes, and the bottom layer is a circular electrode. In common optical measurements performed, the operations are carried out such as adding the same signal voltage over four electrodes of each microlens to adjust the focal length of the lens cell and adding a signal voltage with different RMS amplitude to adjust the focus position on the focal plane. Experiments show that the LCMLA developed by us demonstrate a desired focal length adjustable function and dynamic swing ability, so as to indicate that the method can be used not only to measure wavefront but also correct the wavefront with strong distortion.
In this paper, a kind of electronically controlled liquid crystal microlens arrays (LCMAs) with non-uniform coil electrodes arrays (NCEAs) is presented. The focal length of the electronically controlled LCMAs can be easily adjusted by applying the appropriate AC signal. The structure of the LCMAs is designed as a NCE array, which can then produce non-uniform electric field to drive liquid crystal molecules. The top electrode is fabricated by depositing an indium-tinoxide (ITO) semiconductor transparent conductive film based on a non-uniform electrode coil, and the bottom electrode is a conventional plate electrode. Due to the design of non-uniform electrode coil array is small, in addition to the traditional lithography process, the etching process we used is dry etching (ICP etching). The simulation results show that, the focal length of the LCMAs with the NCEAs can be tuned easily by applying the appropriate AC signal.
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