Lyot型可调谐液晶电光滤波器的特性分析

根据液晶的电光效应和Lyot滤波器的原理设计了Lyot型液晶电光滤波器，并且从理论和实验上证明了其可行性。为了扩展其在红外波段的应用，设计了FP腔液晶可调谐滤波器，并且给出了其理论模拟。理论模拟证明FP腔液晶可调谐滤波器具有调谐范围大、带宽窄、精细度高等优点。     

基于铁电液晶电控双折射的调谐滤波器的研究

将铁电液晶作为缺陷层引入一维光子晶体中,基于液晶的电控双折射,形成快速窄带调谐滤波器.用传输矩阵法研究了铁电液晶缺陷光子晶体的可调谐滤波特性,计算了电场对滤波器透射峰的位置、强度、个数和带宽的影响,结果表明该滤波器呈现良好的滤波功能.     

基于液晶的可调谐太赫兹双折射滤波器的设计

液晶双折射滤波器具有室温下工作,调谐简单方便,带宽窄等优点。为了达到设计不同调谐范围和带宽的这种滤波器的目的,以满足实际应用的需要,扩大其应用范围,采用数值模拟的方法,进行参数计算和设计思路的总结,并设计了一套窄带输出的滤波器实例。结果表明,通过对影响滤波器调谐范围和输出带宽的关键参数的数值模拟和分析,为设计不同调谐范围的液晶双折射滤波器提供了依据;设计实例基本上满足预期的设计要求,调谐范围0.691~0.866 THz。     

温度对铁电液晶电调谐滤波特性影响的研究

在改变外加电场实现铁电液晶电调谐滤波中,由于铁电液晶的螺距和自发极化强度对温度变化很敏感,从而为铁电液晶电调谐滤波器的应用和准确度的提高带来了困难。从铁电液晶的螺距和自发极化强度与温度的关系出发,讨论了温度对铁电液晶双折射的影响,给出了铁电液晶电调谐滤波器的透射率随温度变化的关系式,并进行了数值计算。结果表明,温度升高时,透射率和带宽增大,透射峰波长向短波长方向移动,温度变化对铁电液晶电调滤波特性的影响远小于电场变化的影响。     

基于液晶材料的带宽可重构毫米波滤波器

根据液晶材料在毫米波段良好的介电特性和调谐能力,设计了一款基于液晶材料的毫米波带宽可重构宽带带通滤波器。滤波器使用一个高通滤波器和一个低通滤波器级联实现带通效果;在低通部分加载液晶材料,通过调谐液晶材料的等效介电常数改变低通滤波器的响应频率,实现带宽的可重构。仿真结果表明,当调谐液晶介电常数从2.4变化到3.8时,滤波器的高频截止频率从52 GHz下降至48 GHz,相对带宽从84.9%变为78.3%。     

液晶可调谐光滤波器的实验研究

对液晶可调谐光滤波器进行了实验研究,初步研制出带宽0.3～0.5 nm,精细度为100～200,连续可调谐范围大于70 nm的液昌F-P腔光滤波器.     

红外波段液晶电调谐滤波器

将液晶作为内腔物质的电调谐滤波器，测量了在红外波段不同条件下的透射特性，给出了大约１００ｎｍ的可调谐范围和约４０ｎｍ的自由光谱区，通过对透射谱的测定和计算得到了液晶折射率随驱动电压的变化曲线。     

一维光子晶体波长可调谐滤波器

介绍了一种将液晶作为缺陷引入到一维光子晶体结构中,实现波长可调谐的滤波器.通过对光子晶体的滤波特性的分析清晰地说明这种光可调谐滤波器的原理和可行性.同时选用手征近晶型液晶,利用电压对这种液晶折射率的调制快于向列液晶的特性,得到符合现在光通信网要求的体积小、阻带区对透光抑制力强、损耗低和开关速度快的可调滤波器.最后,对滤波结构中的重要参数进行了探讨.     

新型光子晶体调谐滤波器的研究

提出了一种在光子晶体中引入液晶缺陷层的光子晶体调谐滤波器.用传输矩阵法给出了含液晶层时光子晶体的光谱透过率公式,对电压和液晶材料参数对调谐滤波器透射谱的影响进行了数值计算.结果表明,改变电压时光子晶体滤波器的透射峰波长和带宽作周期性变化,在适当电压作用下光子晶体具有多通道滤波功能,而液晶的厚度和固有双折射的改变几乎不能实现光子晶体滤波器的调谐作用.     

液晶分子取向对液晶/聚合物光栅电光特性以及激光出射特性的影响

报道了液晶分子不同取向对液晶/聚合物光栅电光特性以及激光出射的影响。通过扫描电子显微镜观察液晶/聚合物光栅的截面,成功观察到了光栅的体光栅结构。液晶分子垂直光栅矢量排列时,由于光栅形貌变差,衍射效率由液晶分子沿光栅矢量排列时的83.2%降低至72%,同时散射损耗由11.8%增加至19.1%。液晶分子垂直光栅矢量时,液晶/聚合物光栅的调谐电场由液晶分子沿光栅矢量时的13.6V/μm下降至3.1V/μm。液晶沿光栅矢量排列时,激光出射阈值更低,为利于激光出射的方向。本文工作为进一步加深对液晶/聚合物光栅以及染料掺杂分布式反馈选频的理解和认识,提供了指导和借鉴。     

A double-element broad-band liquid crystal tunable filter-factorsaffecting contrast ratio

A double-element broad-band liquid crystal tunable filter consisting of a high-order quartz wave plate in series with a very-low-order electrooptically tunable liquid crystal phase plate and placed between crossed polarizers is described. A possible application for such a device is protection against intrusive laser radiation. The advantage of this double-element filter over a single-element low-order LC filter is that it increases the wavelength resolution of the device, which, when operated in the protect mode, allows continued sensing of the scene. Experimental and theoretical studies were made of the contrast ratios obtainable with such a filter     

Tunable liquid crystal phase shifter for microwave frequencies

A tunable phase shifter using liquid crystal (LC) is presented. The device is fabricated in a fashion similar to LC displays which makes fabrication very simple compared, for example, to MEMS approaches. At the targeted operation frequency of 20 GHz the device offers a performance of above 60 differential phase shift per dB insertion loss and a minimum tuning speed of 340 ms.     

含氟三环NCS液晶材料的介电性能研究

为了探究液晶材料的介电性能,本文研究了4PPTGS和4PUTGS两种含氟三环NCS类液晶材料的介电各向异性和介电损耗。首先用精密LCR表(Agilent E4980A)测量液晶盒的电容并用双盒模型和液晶盒电容模型得到4PPTGS和4PUTGS两种液晶材料的平行和垂直介电常数,再由电压-电容特性曲线得到它们的阈值电压,并进一步探讨了介电各向异性和阈值电压对温度的依耐性;然后,在20 Hz~10kHz范围内研究了外加电压频率对液晶材料介电损耗的影响,两种液晶材料在1kHz左右都存在介电损耗峰值,为了减小器件的功耗和提升器件的质量,液晶材料应选择在介电损耗小的频率下工作;最后,通过对平行和垂直排列向列相盒中液晶材料在不同电压下介电损耗的测试与分析,介电损耗的变化是由于在外加电场下液晶分子固有偶极矩的取向极化引起的,介电损耗值的大小与液晶分子的排列状态密切相关。此项研究对提升液晶材料在应用中的介电性能具有一定的指导意义。     

低电压驱动的MEMS F-P可调光学滤波器研究

基于微机电系统（MEMS）技术,研制了一种新颖的光学腔与静电驱动器分离的Fabry-Pérot（F-P）可调谐滤波器。从光学设计、MEMS结构设计、制造工艺与器件测试等开展了F-P可调谐滤波器的研究,成功制备了工作在以1550 nm波长为中心、调谐范围为40 nm和驱动电压低于30 V的MEMS F-P可调滤波器。测试...     

High-speed continuously tunable liquid crystal filter for WDMnetworks

We describe a high-speed wavelength tunable liquid crystal filter which can be utilized as the tuning element at the receiving end of wavelength division multiaccess (WDMA) optical networks. The filter uses chiral smectic A electroclinic liquid crystals as the active cavity material in a Fabry-Perot etalon in order to obtain a microsecond switching speed. Using the commercially available BDH764E liquid crystal material, we demonstrate a tunable optical filter both in a bulk Fabry-Perot and a fiber Fabry-Perot (FFP) configuration. A bandwidth of about 0.7 mm and effective finesse of 70 were obtained in the FFP configuration. A FFP tuning range of 13 nm with a switching time of less than 10 μs were measured at the operating wavelength of 1.55 μm. A theoretical analysis of the expected filter performance in the FFP configuration is given. Diffraction in the Fabry-Perot cavity is identified as the dominant loss factor, resulting in reduced throughput and finesse broadening. It is calculated theoretically that an effective finesse of 130 and a throughput loss of 2.2 dB are achievable for a mirror finesse of 200 and a liquid crystal cavity thickness of 5 μm. A short waveguide piece is assumed to be included in the cavity. Other expected loss sources for the filter in the FFP configuration have been calculated, showing negligible effect on the filter performance     

A novel dual-band tunable notch filter with controllable center frequencies and bandwidths

This article proposes a new dual-band tunable bandstop filter. This tunable filter is composed of two separate parts, the transmission line, and coupled stubs that each connect to three varactors. The center frequency and bandwidth in each band can be controlled individually. Moreover, the LC equivalent circuit of the proposed filter is calculated, and the results are simulated. In the proposed filter, the simulations show that the first stopband can be tuned in a frequency range from 1.2 to 1.9 GHz with 10-dB absolute bandwidth 310 ± 30 MHz, whereas the second stopband varies from 2.5 to 3.3 GHz with the 10-dB absolute bandwidth 720 ± 20 MHz. These two stopbands can also be tuned independently. Furthermore, the bandwidth of each fixed center frequency can be changed easily. The fabricated proposed filter validates the simulation results. The compact filter has an effective size of 9 × 27.5 mm².     

Polarization sensitive performance of one dimensional photonic crystal filters with a liquid crystal layer

A tunable photonic crystal (PC) filter is proposed with the twisted nematic (TN) liquid crystal (LC) as a defect layer. The polarization sensitive performance and the eigenmodes are analyzed. The results show that there are two kinds of transmission modes, namely o and e, when the voltage is low. The different modes can be selected by rotating the filter axially. The e mode shifts toward the shorter wavelength side as the applied voltage increases. Then the peaks of two modes merge into each other and the polarization sensitive performance disappears. The photonic band gap is insensitive to the voltage. The tunable range of the filter is 53 nm.     

New structure of tunable wavelength-selective filters with a liquid crystal for FDM systems

To decrease the bandwidth of liquid-crystal Fabry-Perot interferometers (LC-FPIs), LC-FPIs having a double-layer cavity were devised where the intracavity consists of the LC layer and a glass layer. This filter is shown to have a very narrow bandwidth (full width at half maximum <10 GHz), low loss (4 dB), and a large tunability (9 nm). It is also shown to have the potential to select over 50 channels for FDM (frequency division multiplexing) systems.<>     

Electronically tunable external-cavity laser diode using a liquid crystal deflector

A novel external-cavity wavelength tunable laser based on a liquid crystal (LC) deflector is proposed. This device consists of a gain chip, collimating lens, LC deflector, and diffraction grating. By controlling the voltage applied to the LC deflector, a maximum wavelength variation of 12 nm and a sidemode suppression ratio higher than 30 dB are obtained.