Institutional Repository of Xi'an Institute of Optics and Precision Mechanics, CAS
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Self-trapped spatially localized states in combined linear-nonlinear periodic potentials
No full textWe analyze the existence and stability of two kinds of self-trapped spatially localized gap modes, gap solitons and truncated nonlinear Bloch waves, in one- and two-dimensional optical or matter-wave media with self-focusing nonlinearity, supported by a combination of linear and nonlinear periodic lattice potentials. The former is found to be stable once placed inside a single well of the nonlinear lattice, it is unstable otherwise. Contrary to the case with constant self-focusing nonlinearity, where the latter solution is always unstable, here, we demonstrate that it nevertheless can be stabilized by the nonlinear lattice since the model under consideration combines the unique properties of both the linear and nonlinear lattices. The practical possibilities for experimental realization of the predicted solutions are also discussed.</p
Modified eigenvector-based feature extraction for hyperspectral image classification using limited samples
No full textClassical supervised feature extraction methods, such as linear discriminant analysis (LDA) and nonparametric weighted feature extraction (NWFE), and search for projection directions through which the ratio of a between-class scatter matrix to a within-class scatter matrix can be maximized. The two feature extraction methods can obtain good classification results when training samples are sufficient; however, the effect is nonideal when samples are insufficient. In this study, the eigenvector spectra of LDA and NWFE are modified using spectral distribution information, which is locally unstable under the condition of a few samples. Experiments demonstrate that the proposed method outperforms several conventional feature extraction methods.</p
Effect of cation vacancies on the optical and dielectric properties of KSr2Nb5O15: A first-principles study
No full textUsing first-principles calculations, the effect of cation vacancies on the electronic structures and optical characters of KSr2Nb5O15 (KSN) lead-free ferroelectrics are investigated. The calculated dielectric properties are demonstrated by the experimental results. The cation vacancies involve K+ vacancies (KSN-K), Sr2+ vacancies (KSN-Sr), and coexisting K+ and Sr2+ vacancies (KSN-K&Sr). When these cation vacancies exist in KSN, the unit cell volumes decrease, leading to phase transition from tetragonal to orthorhombic, and the cation vacancies show strong effects on the band gap of KSN, declining by 1.46%-9.46%. The optical properties including the static dielectric constants, refraction, and extinction coefficient of KSN-K, KSN-Sr, and KSN-K&Sr increase more than those of KSN without vacancies, but the reflectivity and loss function decrease. All structures with cation vacancies are mainly refractive in the 0-4 eV photon energy range and are reflective at 5-8 eV. The refractivity increases and reflectivity decreases after vacancies occur. KSN-Sr has the largest static dielectric constant while KSN-K&Sr has the smallest values. The dielectric constant can be adjusted in the range of 25% by controlling the cation vacancies. The calculated dielectric properties are in good agreement with the experimental results. The results pave the way to regulate the optical and dielectric properties of lead-free ferroelectrics by controlling different cation vacancies.</p
1D Solitons in Saturable Nonlinear Media with Space Fractional Derivatives
No full textTwo decades ago, standard quantum mechanics entered into a new territory called space-fractional quantum mechanics, in which wave dynamics and effects are described by the fractional Schrodinger equation. Such territory is now a key and hot topic in diverse branches of physics, particularly in optics driven by the recent theoretical proposal for emulating the fractional Schrodinger equation. However, the light-wave propagation in saturable nonlinear media with space fractional derivatives is yet to be clearly disclosed. Here, such nonlinear optics phenomenon is theoretically investigated based on the nonlinear fractional Schrodinger equation with nonlinear lattices-periodic distributions of either focusing cubic (Kerr) or quintic saturable nonlinearities-and the existence and evolution of localized wave structures allowed by the model are addressed. The model upholds two kinds of one-dimensional soliton families, including fundamental solitons (single peak) and higher-order solitonic structures consisting of two-hump solitons (in-phase) and dipole ones (anti-phase). Notably, the dipole solitons can be robust stable physical objects localized merely within a single well of the nonlinear lattices-previously thought impossible. Linear-stability analysis and direct simulations are executed for both soliton families, and their stability regions are acquired. The predicted solutions can be readily observed in optical experiments and beyond.</p
Fabrication of refractive silicon microlens array with a large focal number and accurate lens profile
No full textIn this paper, we demonstrate the fabrication of refractive silicon microlens array with a large focal number and almost perfect spherical lens shape. Through a modified thermal reflow, photoresist microlens array of a large focal number is fabricated, which is then transferred into the silicon substrate by ion beam milling. To reach an accurate spherical lens profile, we both theoretically and experimentally study the practical factors that harm the pattern transfer fidelity, which mainly include the etching selectivity and faceting effect. Other secondary etching effects, such as the trenching effect and re-deposition effect, are also discussed. Based on these studies, a silicon microlens array with a focal number of 1.35 has been successfully obtained, with the profile error controlled well-below 0.121 mu m, less than lambda/6 within the whole infrared wavelength band. Besides, the fabricated microlens array exhibits a good uniformity and fine surface smoothness. The fabricated silicon microlens arrays can be applied in minatured infrared and terahertz imaging devices, or used as the master mould for soft lithography.</p
Retrieval of marine inorganic particle concentrations in turbid waters using polarization signals
No full textThe polarization properties of water-leaving radiance (L-w) contains rich information about hydrosols, which has great potential to improve the retrieval accuracy of oceanic constituents. However, current ocean colour inversion algorithms are only based on the water-leaving radiation intensity, and the polarization properties have been ignored. Here, based on the radiative transfer simulations, the possibility of retrieving suspended particulate matter in turbid waters based on the polarization properties was investigated. The results showed that the degree of polarization (DOP) of the upward radiation just beneath the water surface has significant angular and spectral variations with respect to the observational geometries, inorganic particle concentrations, solar zenith angles and aerosol optical thicknesses (AOTs). The directional variations in DOP along with viewing zenith angles are typically characterized by a double peak feature with a maximum of 0.5 in the principal plane. In addition, the DOP in the visible bands is highly sensitive to inorganic particle concentrations. The DOP gradually decreases from 412 nm to 555 nm and increases with wavelengths beyond 555 nm, particularly for wavelengths larger than 620 nm. An empirical relationship between the DOP at 670 nm and the inorganic particle concentration was established for different viewing geometries with determination coefficient (R-2) up to 0.9996. Overall, our simulation results indicate that the polarization property of underwater upward radiance has great potential for suspended particulate matter retrieval in coastal waters.</p
Optimized design of an emerging optical imager using compressive sensing
No full textThe emerging optical imager utilizes Fourier-domain interferometry and can reduce system weight, size and power by an order of magnitude compared to conventional optical telescopes at the same resolution. The compressive sensing theory demonstrates that incomplete and noisy measurements may actually suffice for accurate reconstruction of compressible or sparse signals. In this paper, we propose an optimized design of the emerging optical imager based on compressive sensing theory. It simplifies data acquisition structure and reduces data transmission burden. In addition, the system robustness is improved.</p
一种焦面探测器安装单元
No full text本实用新型涉及一种焦面探测器安装单元，包括：焦面探测器、焦面法兰、焦面电路板、固定座及散热装置，固定座包括边部框架和中心支架，边部框架与焦面法兰固定连接；中心支架的两端设置有柔性连接臂，柔性连接臂的刚度既小于边部框架的刚度也小于中心支架的刚度，中心支架通过两端设置的柔性连接臂与边部框架连接；焦面电路板设置在边部框架中，焦面电路板与边部框架固定连接；散热装置及焦面探测器依次设置在中心支架的内侧，焦面探测器通过一侧两端设置的安装凸耳与散热装置及中心支架连接在一起,并通过探测器管脚与焦面电路板连接。本实用新型提供了一种焦面探测器安装单元，满足了焦面探测器安装的力学和热学稳定性要求
Comparison Investigation of the Three-dimensional Stiffness of Optical Tweezers with Different Polarization Fields
No full text为了研究激光偏振态对光阱刚度的影响,本文比较了四种不同偏振态光场（方位角偏振光、径向偏振光、线偏振光、圆偏振光）捕获不同尺寸SiO2微粒的三维光阱刚度.研究结果表明:当SiO2微粒的尺寸和激光波长相近时,圆偏振光和线偏振光的三维光阱刚度大于径向偏振光和方位角偏振光的三维光阱刚度;而随着SiO2微粒尺寸的增加,方位角偏振光和径向偏振光的三维光阱刚度大于圆偏振光和线偏振光的三维光阱刚度.此外,实验也表明:使用浸油物镜捕获微粒时,物镜匹配油的折射率和水的折射率不一致引起的球差,会降低系统对物镜数值孔径的利用.通过这些研究工作,可以为不同偏振态光场的测力研究提供一定的指导和参考. </p
一种双摆轴激光加工头的多级防撞系统
No full text为了对双摆轴激光加工头进行全方位防护，本发明提供了一种双摆轴激光加工头的多级防撞系统，包括第一防撞单元、第二防撞单元和比较单元；第一防撞单元包括用于监测双摆轴激光加工头中电机电流的电流检测装置；比较单元用于将电流检测装置测得电机电流变化量分别与电流变化阈值相比较，当任一电机电流变化量大于或等于电流变化阈值时，比较单元向激光加工机床的数控系统发送碰撞信号；第二防撞单元包括复位装置和压力检测单元；压力检测单元中任一压力传感器的输出信号大于或等于压力变化阈值时，比较单元向所述数控系统发送碰撞信号；数控系统收到第一防撞单元或第二防撞单元发出的碰撞信号后，进行激光器关闭和机床运动轴去使能操作