可调谐液晶滤波器的调谐性能研究

在电调谐液晶法布里一珀罗腔滤波器的连续调谐过程中,存在“透射峰跳跃”现象,影响器件的单调调谐性。为了改善器件的单调调谐性能,对此现象进行了分析,表明这是由于法布里—珀罗腔干涉级次在调谐过程中发生改变引起的;进而给出了法布里一珀罗腔透射波长λ,干涉级次m与腔内介质折射率n的关系,以及器件实际的有效调谐范围。当腔长为10μm、折射率差为0．05时,就可以使器件的单调调谐范围达到整个C波段。数值模拟与实验结果相吻合。并针对改善器件的单调调谐性能,提出了几种可行的方案。     

可调谐液晶红外滤光片的光学特性分析

可调谐红外滤光片是高分辨率红外成像仪谱段识别和分光的重要光学器件。采用琼斯矩阵方法对平行向列相和90°扭曲向列相液晶法-珀红外滤光片的本征偏振态及光学特性进行了研究。结果表明,当非偏振光垂直入射时,平行向列相液晶法-珀滤光片在任何电压下两组本征偏振态均不发生模式混合,具有偏振敏感性;90°扭曲向列相液晶法-珀滤光片在电压较低时具有偏振敏感性,当电压大于三倍Freedericksz阈值电压时,两组本征偏振态发生模式混合,偏振敏感性消除。     

利奥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利奥滤波器的原理设计了利奥型液晶电光调谐滤波器,并且从理论上和实验上证明了其可行性;为了克服其在红外波段的缺点,设计了法布里-珀罗腔液晶可调谐滤波器,并且给出了理论模拟。理论模拟证明法布里-珀罗腔液晶可调谐滤波器具有调谐范围大、带宽窄的优点。     

液晶法布里-玻罗滤波器可调谐特性分析

分析了液晶法布里－玻罗可调滤波器中介质反射镜反射相位引起的峰值波长漂移. 液晶法－玻滤波器通过外加电压调谐峰值波长, 反射相位会导致峰值波长漂移使器件不能达到DWDM系统的使用要求. 本文推导了一套计算反射镜反射相位的公式,将它应用于液晶法-玻可调滤波器的理论设计, 模拟结果定量表示了反射相位对峰值波长造成的影响. 这对确定液晶可调滤波器峰值波长和设计器件电驱动装置具有重要意义. 由此设计了一个在光通讯波段可单调调谐的液晶法-玻滤波器.     

一种新型微机电系统法布里-珀罗滤波器的设计与分析

基于微机电系统(MEMS)技术,提出了一种光栅与法布里-珀罗(F-P)腔相结合的新型MEMS F-P滤波器结构,这种滤波器既能保证较宽的自由光谱范围又能够获得较窄的半峰全宽。从实现机理、参数设计和选择对F-P滤波器的结构进行了深入分析,并着重对微桥桥面的机电性能进行了仿真计算。通过选择不同的微桥桥面厚度(0.5,0.6,0.7,0.8,0.9,1μm),比较微桥在静电力作用下的平整度,发现当微桥表面厚度为1μm时,得到了一个较优结果,在5V电压下,上反射镜的倾斜位移ΔL为9.11nm,最大腔长变化量为242nm,这样能保持前后腔面反射光的平行要求,从而保证滤波器的滤波效率和对选择光的利用率。该滤波器能够解决传统微型滤波器自由光谱范围与半峰全宽相互限制的矛盾,提高微型滤波器的性能。     

可调谐F-P谐振腔的研究进展

可调谐法布里-珀罗谐振腔目前是在光通信、传感器和激光器等领域被广泛应用的光学器件。按照调谐方式可分为光纤型F-P腔、微机械型F-P腔和电光型F-P腔,每种均有相应的优点和优势领域。综述了可调谐F-P腔的研究进展,包括器件结构、性能参数两方面,并分析了各类可调谐F-P腔器件的性能差异和未来的应用前景。     

反射相移对MEMS滤波器半峰全宽影响分析

以典型的基于MEMS的FP腔结构为例,用传输矩阵方法推导了考虑反射相移的半峰全宽的解析表达式.利用此解析表达式分别模拟了考虑反射相移的半峰全宽与干涉级次和FP腔两反射镜间距的关系,并将其与不考虑反射相移的半峰全宽进行了对比;同时将反射相移和反射率对半峰全宽的影响进行了比较分析.     

一种用于密集波分复用系统中的可调谐液晶法布里-珀罗滤光片

基于液晶分子的双折射特性，设计并制作了一种结构简单的可用于波分复用系统中的可调谐液晶法布里-珀罗滤光片。对器件的光谱调谐特性进行了分析和模拟，并得到了液晶分子的折射率调制与其分子在电场作用下产生的转动角度之间的关系式。最后，对所设计的结构进行了制作和实验，测试结果显示了滤光片的性能受液晶分子的排列特性和法布里-珀罗腔的反射镜参量的影响较大，同时实验表明了这种利用向列型液晶分子作为法布里-珀罗腔内介质的可调谐滤光片在加电压调试下其调谐性能良好，调谐范围可覆盖C波段，透过峰的半峰全宽达到了0．8nm，实验结果与设计相吻合。     

一种新型可调谐红外滤光片的设计和应用

可调谐红外滤光片是高分辨率红外成像仪谱段识别和分光的重要光学器件.本文介绍了一种新型可调红外滤光片———液晶法布里-珀罗滤光片的基本原理、设计参数、制作方法,分析了这种滤光片的透射光谱、精细度、带宽、镜面反射率和腔长之间的关系,以及外加电压和温度对透射波长的影响,给出了消除偏振效应的几种方案.并对液晶法布里-珀罗滤光片在空间遥感,特别是红外探测方面的应用前景进行了展望.     

一种新型可调谐锁模光纤激光器

利用法布里-珀罗腔的激光二极管作为调制器件，实现环形腔光纤激光器的主动锁模。并利用法布里-珀罗腔的激光二极管的多纵模特性，把激光二极管当作一梳状滤波器，通过偏振控制器来调整入射到激光二极管内光的偏振态，同时均衡腔内增益，得到波长大范围可调谐的锁模激光，其脉冲宽度约为48ps，脉冲重复速率2GHz。     

基于液晶可调滤光片的广角多光谱成像光学系统设计

基于液晶可调滤光片(Liquid Crystal Tunable Filter,LCTF)的分光原理,设计一种工作谱段为400~720nm,焦距4.5mm,视场角140°,F数为1.28的广角多光谱成像光学系统。该光学系统由前端光学镜头、LCTF和成像镜头组成,其中前端光学系统镜头将入射光束进行扩束,同时将入射光束的广角视场缩小至LCTF可接收角度范围内;LCTF利用液晶材料的电控双折射效应,实现对某一波长光信号的选择透过。根据多光谱成像系统的总体方案,对光学系统的各光学参数进行合理选取。设计结果表明,整个系统在120lp/mm的空间频率处轴上及轴外的调制传递函数MTF均大于0.4。     

声光可调谐滤波器成像光谱仪非球面光学系统设计

基于声光可调谐滤波器(AOTF)的工作原理,设计了一套工作在440～780nm的光谱成像光学系统。该光学系统通过引入一面偶次非球面提高了系统的成像质量,简化了镜头的结构,提高了光学系统的透射率。前置光学系统采用由一组双胶合透镜构成的像方远心光路。后置成像光学系统由一组三胶合透镜构成,其中包含一面非球面,根据非球面变形系数与初级像差间的贡献关系,完成了非球面及其位置的优化和对AOTF的+1级衍射光成像。光学系统在32lp/mm的空间频率下的调制传递函数(MTF)大于0.6,像质优良,加工装调公差适中。     

Shift-tolerance Property of Optical Security System using Phase-based Virtual Image

The shift-tolerance property of the encrypted image or the Fourier decrypting key in the Fourier space is proposed based on a phase-encoded virtual image. The encrypted data is obtained by the Fourier transform of the product of a phase-encoded virtual image to camouflage the original one and a random phase image. Therefore, even if unauthorized users analyze the encrypted image, they cannot reconstruct the required image. This virtual image protects the original one from being counterfeited and from unauthorized access. We demonstrate the robustness to data loss and shift of the encrypted data or the Fourier decrypting key in the proposed decryption technique using an interferometer.     

Numerical Analysis of the Crosstalk on an Integrated Acousto-Optic Tunable Filter (AOTF) for Network Applications

In this article, we did a study of the crosstalk level (Xtalk) and extinction ratio (Xratio) of an acousto-optic tunable filter (AOTF) operating with ultra-short light pulses (2 ps). It is clear that the transmission bandwidth decreases as the length of the device increases. The compression factor was studied for the switched pulse in an AOTF without loss considering five nonlinearity profiles. One can observe that there is always an optimum value for β (final value of the nonlinearity) that one can obtain a switched pulse with the same time duration of the input pulse. The study of the crosstalk level, of this device, considering the optimum values of β obtained from the compression studies, as a function of the pump power (P₀) was done. For the soliton profile at 1 W of pump power one can notice that the Gaussian profile presents the lower Xtalk value (-13 dB), and the constant profile presents the worst value (-9.8 dB). However, if one is looking for a specific Xtalk value, one can conclude that with the constant profile one can obtain this value with a lower power. For the quasi-soliton profile of the same device, with low pump power (1 W), one can notice again that the Gaussian profile presents the lower Xtalk value (-13 dB) and the constant profile presents the worst value (-9.87 dB). This fact can be explained because, with pump power at 1 W, soliton and quasi-soliton profiles lead equivalent input pulses and under the same conditions produce equal results. The Xtalk level, considering all the profiles as a function of the β value, was studied. For all the profiles one has a strong increase of the Xtalk level with the increase of the final β value of the nonlinearity profile. Comparing all the profiles one can conclude that the Gaussian profile presents the lower Xtalk value in the range of β values in use. At the same time the value of the Xtalk for this profile does not change much with the change in the β value, presenting values in interval (-13 dB; -11.7 dB).

The studies of the Xratio of the same device operating with the input pulses with the soliton and quasi-soliton profiles reveal that for all the nonlinearity profiles the Xratio increases with an increase in pump power. For the quasi-soliton profile one can notice that there is a minimum of the Xratio as a function of the pump power. The Xratio considering all the profiles as a function of the β value shows that for all the profiles one has a strong increase of the Xratio level with the increase of the final β value of the nonlinearity profile. Comparing all the profiles one can conclude that the Gaussian profile presents the lower Xratio value in the range of β values in use. One can conclude that the operation of the AOTF in a switching configuration is worse for high pump power as observed for Xtalk.

The study of the crosstalk level and the extinction ratio on the AOTF operating with ultra-short optical solitons provides possibilities for achieving high efficiency in ultra fast all-optical signal processing, especially for optical switches, filters, and optical transistors. The acoustic-optic tunable filter (AOTF) has attracted great attention in recent years, in part because it appears to be a suitable basis for multi-wavelength optical cross-connects. It is probably the only known tunable filter that is capable of selecting several wavelengths simultaneously. This capability can be used to construct a multi-wavelength router.     

厚度偏差对VCSEL的反射谱和反射相移的影响

采用光学传输矩阵方法分析了厚度偏差对VCSEL的反射谱和反射相移产生的影响。结果表明,反射镜和VCSEL中各层厚度的偏大,将使反射镜的中心波长以及VCSEL的模式波长向长波方向移动,而反射镜和VCSEL中各层厚度的偏小,将使反射镜的中心波长以及VCSEL的模式波长向短波方向移动。将键合界面离有源区稍微远一些,有利于减小其厚度偏差对VCSEL的模式波长的影响。