The Fabry-Perot interferometer (FP) can be used as a kind of filter for obtaining spectral information of targets in several wavelength ranges such as in the visible or infrared regions. Micro-electro-mechanical systems (MEMS) are generally micro-structures that integrate micro-sensors for converting incident microbeams into arrayed electronic signals and micro-actuators. The MEMS-FP filter constructed by combining the MEMS and FP functions, can be further integrated into a chip-level imaging spectrometer to achieve spectral imaging operation. In our design, the MEMS-FP filter is also mounted a liquid-crystal microlens array with a high filling-factor. The key micro-bridges of each MEMS-FP unit are modeled and simulated in this paper. We have designed two types of supporting structures and simulated them with the simulation software COMSOL Multiphysics 5.2. The key factors include tuning range, filling-factor, and parallelism of the bridges. After calculating and analyzing, we found that the tuning range can be optimized by changing the thickness of the micro-bridge and the arm width of the cantilever beam. The filling-factor is already increased by geometry design. The parallelism of the bridge in the two micro-structures differs greatly, which is related to the shape of the bridge itself. According to the simulations, a tuning range of 160 nm has been achieved in the visible and near-infrared wavelength range, with a maximum filling-factor of more than ~80%.
Generally optical micro-nano-antenna can be used to modulate lightwaves in the sub-wavelength scale, which is a hot and difficult research issue. Patterned metal nano-antenna array can be utilized to stimulate intense surface plasmon polaritons (SPPs), so as to realize sub-wavelength focusing by breaking through diffractive limit, and thus remarkably improving THz imaging efficiency. In this article, firstly, based on SPPs, the Drude dispersion model for metallic film is analyzed, and the dispersion relations and excitation modes of the SPPs are discussed, and the numerical analysis methods of the metallic micro-nano-antenna are also presented including a time-domain finite integral method and a frequency-domain finite element method. According to related literature, the key optical micro-nano-antenna unit is modeled, and a metasurface formed by etching a gold thin film on a silicon substrate is designed. Through regulating parameters including the number and size of the openings and the line width, the SPP excitation in THz band is studied. Using finite element and adaptive mesh division method, the common electromagnetic properties such as transmission intensity and electric field distribution are simulated and analyzed. The simulations show that the optical micro-nano-antenna element can resonantly induct terahertz wave, and demonstrate a resonant electric-field at the aperture gap, which will move towards high frequencies end as increasing the gap size or line width, so as to lay a concrete foundation for continuously fabrication THz-SPPs devices.
Approaches for realizing a small scale tunable liquid-crystal microlens array (LCMLA) with several independent driving channels of applying voltage signal has been investigated in recent year. However, current requirements based on electrically tuning focus function are further increasing array scale of LCMLA and continuously improving driving efficiency of electric-signal setup so as to acquire more optical information of objects. The conventional point-to-point electrically driving (PTPED) method, which has disadvantages such as high power dissipation, lots of external wirings connections, and complicated electric-structure matching, cannot be used to accomplish a real-time independent driving control of arbitrary electrode end in a patterned electrode array of a LCMLA. In this paper, an addressably electric-scanning driving (ESD) approach for a 4×4 zoned LCMLA with sixteen electrode zone divided so as to reduce the number of driving signal lines, is proposed. Simultaneously, key functions such as the amplitude and frequency of a square-wave voltage signal for driving arbitrary electrode with needed RMS voltage value, which can be programmable processed so as to independently control zoned electrodes, can be effectively achieved. The principle of ESD of LCMLA, the simulation and design of hardware circuit, and the fabrication of ESD device are presented. According to our experiences in LCMLA, the ESD approach will exhibit possibility for construction and application of large-scale LCMLA. Besides, scene scanning automatically and three-dimension object reconstruction based on addressable LCMAL with multi-focuses is also predicted.
Liquid-crystal material demonstrates a special property of optical anisotropy. So far, it is widely used in many fields including flat panel displaying and other various optoelectronic devices. Electrically controlled liquid-crystal microlenses have presented some unique capabilities such as swinging focus over the focal plane and tuning focal length only by electrical signals applied over them. According to the typical electro-optical characteristics of nematic liquid-crystal materials, a liquid-crystal microlens array (LCMLA) with a featured zoned quasi-single-microhole electrode with more controlling area than the past microelectrode structure developed by us, which is applied by a multiplexed controlling signals according to an electrically scanning fashion, is proposed for realizing a new type of dual-mode imaging including one addressable wavefront measurement and correction through sensor array zoned by LCMLA, and another intensity image. Each sub-electrode in a quasi-single-microhole electrode can be individually driving and adjusting. So, two operations of adjusting focus and swinging focus can be achieved only by applying suitable voltage signals over each subelectrode. However, to successfully achieve a dynamic compensation of the aberrated wavefront measured so as to minimize target image distortion, hundreds of LC microlenses are needed for measuring and reconstructing wavefront corresponding to realtime image acquired. This will lead to a problem: a large number of conductive wires cannot be effectively arranged and connected to the LC microlens. In this paper, a LCMLA based on an electrically scanning approach is proposed. An "active matrix" for applying voltage signal over different structural unit is used so as to realize a active control of wavefront measurement and correction corresponding to a target image.
In this study, a kind of electronically controlled liquid-crystal microlens array (LCMLA) with plane swing focus and tunable focal length instead of a commonly microlens array with a fixed focal length and then focus distribution for highresolution image acquisition, wavefront measurement, and distortion wavefront correction, is proposed. The LCMLA mainly consists of two glass substrates coated with a film of indium-tin-oxide (ITO) transparent material on one side. Each sub-unit top layer is composed of four sub-square electrodes, and the bottom layer is a circular electrode. The key technological steps in electrode fabrication contain an ultraviolet lithography, a dry etching (ICP etching), and final electron beam evaporation and overlay. The current LCMLA can be realized in three operating modes under external driving circuitry, including intensity image acquiring, wavefront measurement and distortion wavefront correction. The LCMLA is only in the image acquisition mode under the condition of no driving electrical signal. As the same driving electrical signals are applied onto the top four sub-electrodes of each sub-unit, the LCMLA is in the wavefront measurement mode. The LCMLA is in the key wavefront correction mode when different driving electrical signals are simultaneously applied onto the top four sub-electrodes of each sub-unit. Experiments show that the focal point of the LCMLA can be moved along the optical axis and over the focal plane by applying appropriate driving voltage signals.
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