基于偏振分束器的C波段可调谐薄膜滤波器

针对多腔窄带薄膜滤光片在倾斜入射时会产生严重的偏振相关损耗问题,研制了一种基于双折射晶体偏振分束器、信道间隔为100 GHz的角度可调薄膜滤波器.该方法可简化倾斜入射时多腔窄带薄膜滤光片消偏振膜系结构,通过对入射光信号偏振态的控制,仅使用常规窄带滤光片就能实现角度调谐其中心透射波长.该可调谐滤波器件具有结构简单、成本低...     

LP模型分析涂覆长周期光纤光栅复折射率传感器

对于涂覆长周期光纤光栅(LPG)传感元件,涂覆层折射率大于包层折射率时将具有很高的灵敏度.然而在涂覆层厚度为纳米量级时,涂覆层的折射率将具有一定的吸收,吸收将对LPG传感元件产生一定的影响.本文在线偏振(LP)模近似理论和耦合模理论(CMT)的理论模型基础上,通过数值计算对这一情况进行研究讨论.详细分析了模式转变点附近和远离模式转变点区域涂覆LPG的模式结构和透射谱情况.在无吸收的理想模型基础上,详细分析了消光系数对模式转变和重新组合的影响,以及模式结构的转变对LPG透射谱的影响,得出吸收将会导致LPG灵敏度、可测量的动态范围的变化.最后,文章给出了一种新型的LPG吸收传感元件的模型.     

可调谐手征超表面电磁特性研究进展

手征超表面是由具有特定电磁响应的平面手征单元结构构成的超薄超材料,由于其具有自由控制电磁波的奇异能力而引起了极大的关注。通过在超表面设计中加入可调谐材料,可以实现其功能受外部激发控制的可调谐或可重构的超器件,为动态调谐电磁波开辟了新的道路。本文介绍了可调/可重构手征超表面电磁特性的一些理论基础,当线偏振光进入可调谐手征超表面时,会被分解为左旋圆偏振(LCP)波和右旋圆偏振(RCP)波,通过外部环境改变介质的介电常数和磁导率,超表面光器件可以动态地控制各种偏振光特别是圆偏振光的响应特性如折射率、二色性、旋光性、不对称传输等。按照可调谐手征超表面所控制的负折射率、圆二色性和旋光性、不对称传输性质,对其最新的研究进展进行了综述。最后,对可调谐手征超表面这一快速发展领域未来可能的发展方向和存在的挑战提出了自己的看法。     

双MMI型微环谐振器的传输特性分析

建立平行双MMI型微环谐振器的数学模型,分析MMI损耗系数和输入光谱的偏振状态对系统传输特性的影响。损耗系数减小时,系统透射谱相对于传统微环谐振器仅是整体向下平移,且幅度较小,证明二者理想传输特性具有高度的一致性;改变输入光谱的偏振状态,透射谱也仅是整体左右移动。结论表明平行双MMI型微环谐振器相对于传统微环谐振器具有更大的设计容差,可进一步降低器件制造工艺成本、提高器件的成品率和工作可靠性。     

亚波长金属光栅偏振器设计

针对仿生微纳导航传感器敏感波段380～520nm的要求，基于严格耦合波理论，设计了一种适用于蓝紫光波段的金属光栅偏振器，并应用等效介质理论直观地分析了金属光栅偏振器的工作原理．所设计的金属光栅偏振器与传统的金属光栅偏振器的不同之处在于：在基底和金属线栅之间增加了氟化镁薄膜，并且刻蚀一部分氟化镁薄膜．在垂直入射条件下，在整个可见光波段，金属光栅偏振器TN透射效率大于61．5％，消光比大于370；数值计算和理论分析表明，所设计的金属光栅偏振器是一种宽带宽、高TN透射效率和高消光比的偏振器件．     

可调缺陷层等离子体光子晶体的滤波特性分析

等离子体光子晶体中引入另一种缺陷等离子体层,构成一种新的等离子体光子晶体滤波器.在不需改变等离子体光子晶体几何外形尺寸的情况下,通过改变缺陷等离子体层的参数,实现缺陷等离子体等效折射率改变,使等离子体光子晶体缺陷层的谐振频率发生偏移,实现了滤波器的可调谐特性.数值模拟中采用时域有限差分算法,计算了电磁波通过等离子体光子晶体的透射谱.结果表明通过调控缺陷层等离子体参数,使缺陷层的谐振频率发生偏移,从而实现等离子体光子晶体可调滤波特性.     

可调谐半导体激光吸收光谱测温谱线选择

可调谐半导体激光吸收光谱(Tunable Diode Laser Absorption Spectroscopy,TDLAS)作为非接触光学测量手段,在燃烧诊断、推进系统研发中应用广泛,而吸收谱线对的选择是采用TDLAS技术进行燃气温度测量的基础和关键一步。在扫描波长-直接吸收法测量H_2O温度的实验中,首先系统地研究了谱线选择的基本原则和实现步骤,对选择原则中各指标的量化进行了重点分析;然后对中心频率在7000～7500 cm~(-1)范围内的水分子吸收谱线进行研究和筛选;最后结合数值模拟进行分析,选择了7022. 7091,7444. 3707 cm~(-1)和7185. 5962,7444. 3707cm~(-1)两对谱线,为TDLAS温度测量系统设计提供依据。     

双泵浦SOA四波混频效应全光波长变换的研究

本文报道了半导体光放大器 (SOA)在偏振方向相互垂直的双泵浦光作用下 ,利用其四波混频 (FWM )效应实现的全光波长变换实验 ,其变换效率和信噪比在很宽的调谐范围内较高并且基本稳定。     

动力调谐陀螺锁定回路解耦控制一体化设计

针对动力调谐陀螺(DTG)模型锁定回路设计中陀螺真实模型与理论模型差异带来的问题,提出基于陀螺辨识模型的解耦、控制一体化控制器设计方案.首先,构建动力调谐陀螺模型辨识系统,获取动力调谐陀螺自回归(ARX)模型参数,为控制器设计提供设计依据.然后,按照系统指标要求在单独通道设计(ICD)框架下分析动力调谐陀螺参数模型的耦合特征并设计对角控制器,将解耦设计纳入到回路控制器设计当中.最后,针对某型号动力调谐陀螺进行实验验证,实验结果表明:设计得到的锁定回路阶跃响应上升时间小于50 ms,超调量小于5%,回路之间耦合量小于5%.依据动力调谐陀螺辨识模型设计对角控制器可以保证动力调谐陀螺锁定回路性能达到指标要求,为进一步深入探索先进控制技术在动力调谐陀螺锁定回路中的应用奠定基础.     

不同晶粒尺寸Mg掺杂(Ba0.6Sr0.4)0.925K0.075TiO3薄膜的直流场介电性能研究

采用溶胶凝胶工艺,在Pt/Ti/SiO2/Si衬底制备了Mg掺杂(Ba0.6Sr0.4)0.925K0.075TiO3(BSKT)薄膜.X射线衍射(XRD)和扫描电镜(SEM)分析测定了物相微结构和薄膜表面形貌,研究了Mg掺杂含量对BSKT晶粒尺寸和直流场介电调谐性能的影响,讨论了直流场介电损耗谱演变的原因.结果表明,Mg掺杂BSKT使薄膜表面粗糙度、晶粒尺寸、介电常量、介电损耗和调谐量都降低;在室温1MHz下,BSKT薄膜有最大的调谐量73.6%;6%(摩尔分数)Mg掺杂BSKT薄膜有最低的介电损耗为0.0088;发现直流场下薄膜的介电损耗谱演变一方面可能与薄膜的晶粒尺寸有关,另一方面也可能与测试温度有关.     

Demonstration of an all-digital 7-bit 33-channel photonic delay line for phased-array radars

A 7-bit multichannel photonic delay line for phased-array antenna control is demonstrated. Multichannel (33-pixel) ferroelectric liquid-crystal (FLC) devices are used as polarization rotation elements, and polarization beam-splitter cubes are used as polarization elements that route the optical signals to different paths. The controller is remotely fed by a unique fiber-optic-array design that uses gradient-index lens collimators for the input single-mode polarization-maintaining fibers. The optical signal is collected by a similar fiber array that uses multimode fibers for improved coupling efficiency. Photonic delay-line (PDL) design issues such as multiport assemblies, multipixel FLC designs, and delay-line architectures are discussed. Furthermore, various PDL parameters are examined. High electrical isolation numbers are obtained for both the within-channel leakage noise (e.g., less than -70 dB) and the interchannel cross talk (e.g., less than -90 dB). Optical and electrical insertion loss is examined for the PDL as well as for the overall system. A high-compression dynamic range of 149 dB . Hz and a spurious free dynamic range of 105 dB . Hz(2/3) are presented.     

Transformation equation in three-dimensional photoelasticity

Optical phenomena that occur when polarized light passes through an inhomogeneous birefringent medium are complicated, especially when the principal directions of the dielectric tensor rotate on the light ray. This case is typical in three-dimensional photoelasticity, in particular in integrated photoelasticity by stress analysis on the basis of measured polarization transformations. Analysis of polarization transformations in integrated photoelasticity has been based primarily on a system of two first-order differential equations. Using a transformed coordinate in the direction of light propagation, we have derived a single fourth-order differential equation of three-dimensional photoelasticity. For the case of uniform rotation of the principal directions we have obtained an analytical solution.     

Multichannel‐Independent Information Encoding with Optical Metasurfaces

Optical metasurfaces, as an emerging platform, have been shown to be capable of effectively manipulating the local properties (amplitude, phase, and polarization) of the reflected or transmitted light and have unique strengths in high‐density optical storage, holography, display, etc. The reliability and flexibility of wavefront manipulation makes optical metasurfaces suitable for information encryption by increasing the possibility of encoding combinations of independent channels and the capacity of encryption, and thus the security level. Here, recent progress in metasurface‐based information encoding is reviewed, in which the independent channels for information encoding are built with wavelength and/or polarization in one‐dimensional/two‐dimensional (1D/2D) modes. The way to increase information encoding capacity and security level is proposed, and the opportunities and challenges of information encoding with independent channels based on metasurfaces are discussed.     

Power law analysis estimates of analyte concentration and particle size in highly scattering granular samples from photon time-of-flight measurements

Optical measurements of particle size and composition in granular samples are difficult to make due to complex light scattering from particles. These multiple scattering events bias absorption estimates and complicate the calculation of scattering and absorption coefficients used to estimate sample properties. Time series data, such as chromatograms and photon time-of-flight (TOF) profiles, contain self-repeating (fractal) characteristics. Power law analysis of photon TOF profiles allows the determination of absorption coefficients and particle sizes in a single experiment. A correlation dimension algorithm was used on photon TOF data from scattering samples. MLR models were then obtained from correlation dimension plots for the estimation of sample properties. Estimates of particle sizes and absorption coefficients were shown to agree well with theoretical values when compared using independent validation sets. Results show close to a 3-fold and up to a 5-fold decrease in the errors of estimation of dye concentration and particle size, respectively, as compared to steady-state measurements. The power law approach provides a useful means of determining sample properties in highly scattering media.     

Wurtzite InP/InAs/InP core-shell nanowires emitting at telecommunication wavelengths on Si substrate

Optical properties of wurtzite InP/InAs/InP core-shell nanowires grown on silicon substrates by solid source molecular beam epitaxy are studied by means of photoluminescence and microphotoluminescence. The growth conditions were optimized to obtain purely wurtzite radial quantum wells emitting in the telecom bands with a radiative lifetime in the 5-7 ns range at 14 K. Optical studies on single nanowires reveal that the polarization is mainly parallel to the growth direction. A 20-fold reduction of the photoluminescence intensity is observed between 14 and 300 K confirming the very good quality of the nanowires.     

Basic spectroscopic properties of bismuth tellurium oxide,Bi2TeO5

Optical absorption measurements in the visible and infrared and reflectivity measurements in the visible and ultraviolet are reported for single crystals of bismuth tellurium oxide (Bi₂TeO₅). Strong dependence of these measurements on the light polarization is found for this recently grown non-linear material. Deviation from the Urbach rule (see Appendix) is believed to result from non-stoichiometry; approximate values of the Urbach parameters are given for the [0 1 0] polarization.     

Digital time-of-flight measurement for ultrasonic sensors

Ultrasonic sensor measurements are mostly based on the determination of the time of flight (TOF). The development of a digital algorithm for pulse-echo measurement applications, based on the use of a cross-correlation function to determine the TOF, is presented. Some experimental results are presented, and the possibility to realize a low-cost real-time measurement system is considered     

光纤隔离器隔离度偏振敏感性的实验研究

本文采用了 1 80°输入测量的新方法研究了光纤隔离器隔离度随着输入线偏振光偏振方向变化。并对其进行了详细的讨论与分析。研究的结果对于该类光纤隔离器的设计和测试具有一定的参考价值     

Polarization-based vision through haze

We present an approach for easily removing the effects of haze from passively acquired images. Our approach is based on the fact that usually the natural illuminating light scattered by atmospheric particles (airlight) is partially polarized. Optical filtering alone cannot remove the haze effects, except in restricted situations. Our method, however, stems from physics-based analysis that works under a wide range of atmospheric and viewing conditions, even if the polarization is low. The approach does not rely on specific scattering models such as Rayleigh scattering and does not rely on the knowledge of illumination directions. It can be used with as few as two images taken through a polarizer at different orientations. As a byproduct, the method yields a range map of the scene, which enables scene rendering as if imaged from different viewpoints. It also yields information about the atmospheric particles. We present experimental results of complete dehazing of outdoor scenes, in far-from-ideal conditions for polarization filtering. We obtain a great improvement of scene contrast and correction of color.     

Reconfigurable Plasmonic Chirality: Fundamentals and Applications

Molecular chirality is a geometric property that is of great importance in chemistry, biology, and medicine. Recently, plasmonic nanostructures that exhibit distinct chiroptical responses have attracted tremendous interest, given their ability to emulate the properties of chiral molecules with tailored and pronounced optical characteristics. However, the optical chirality of such human-made structures is in general static and cannot be manipulated postfabrication. Herein, different concepts to reconfigure the chiroptical responses of plasmonic nano- and micro-objects are outlined. Depending on the utilized strategies and stimuli, the chiroptical signature, the 3D structural conformation, or both can be reconfigured. Optical devices based on plasmonic nanostructures with reconfigurable chirality possess great potential in practical applications, ranging from polarization conversion elements to enantioselective analysis, chiral sensing, and catalysis.