可调谐光纤环滤波器

本文提出了一种利用相位调制器和光纤环的可调谐滤波器,运用部分相干光理论分析得到滤波因子,分析了诸滤波器性质,介绍了调谐试验结果.     

一种基于液晶技术的可调谐滤波器研究

首先介绍了一种新型液晶可调谐滤波器(LCTF)的基本结构,分析了其工作原理,然后用琼斯矩阵理论推导了其光传输矩阵,理论上得出了其幅度、相位电压调制范围,并对其进行数值分析。最后实验上制作了该器件,实验结果与理论分析相符。     

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。     

高温超导滤波器的低温调谐技术

本文给出了高温超导滤波器的一种低温机械调谐方法,通过调谐滤波器的电场来达到优化性能的目的.此方法可以很好的改善滤波器的性能和提高产品的合格率,使基片厚度的不均匀性以及介电常数的误差对高温超导滤波器性能的影响降到最低,从而最大程度地使测试结果和计算机仿真结果相一致.文中以一个4节的高温超导微带滤波器为例,叙述了该方法的实现过程.其带宽为15MHz,中心频率为2.868GHz,带内插损为-0.04dB,反射损耗为-21dB.文中给出了带外抑制,带内特性等的调谐结果.制备完成的超导滤波器在调谐前的性能较设计结果有较大的偏差.主要表现在带内插入损耗、反射损耗特性和带外抑制的偏差.通过调谐,带内特性和带外抑制有明显的改善.带内插入损耗由调谐前的-0.44dB改善到-0.21dB;反射损耗由调谐前低端带边的-8.2dB改善到-14.27dB,但在高频端没有改善;带外抑制由实测的-28dB最大可以改善为-47dB.理论预测该调谐方法会使通带中心频率向低频端移动,我们也观察到了该现象,中心频率向低频端最大偏移了大约3.1MHz.综合各项参数,调谐后,整体性能更接近设计结果.     

二氧化碲非同向声光可调谐滤波器的设计分析

在分析非同向声光可调谐滤波器器件设计理论的基础上，同时考虑声光晶体的双折射和旋光特征，分析和计算了二氧化碲声光可调谐滤波器的超声波极角θａ和入射光波极角θｉ之间的关系以及超声波频率ｆａ和光波波长λ０之间的调谐关系。     

窄带集成声光可调谐滤波器的研制

利用模式耦合理论分析了声光模式转换,并对声光可调谐滤波器的滤波带宽、调谐范围、驱动功率等性能参数进行分析计算。设计并制作出窄带集成声光可调谐滤波器(IAOTF)样品,搭建相应的IAOTF测试平台,得到中心波长在1.55μm,滤波带宽达到0.85 nm,波长调谐范围达到80 nm,驱动功率低于40mW的IAOTF。并对进一步压缩滤波带宽和旁瓣效应提出了解决途径。     

通信用声光可调谐滤波器

介绍了以LN为基底的集成型和以TeO2为材料的体型通信用声光可调谐滤波器(AOTF)的工作机制,并对其结构和性能进行了比较分析,指出了各自需要解决的主要问题。讨论了用作OADM的声光可调谐滤波器对偏振分束器的要求及偏振分束器对滤波器性能的影响。提出了有必要对TeO2器件应用于通信领域的可能性进行更为深入的研究。     

光子晶体多通道可调谐偏振滤波器的理论研究

通过对设计的一维掺杂光子晶体的数值计算和理论分析,得出了两个偏振态缺陷模透射峰的变化特征为:P-偏振波其缺陷模透射峰在入射角大于0.75(rad)范围内有多条明显的缺陷模透射峰带,而S-偏振波在入射角大于0.75 (rad) 范围内没有缺陷模透射峰;P-偏振波缺陷模在同一杂质光学厚度可以截到多个波长不同的透射峰.以此为基础设计出滤波通道波长可调范围大于60 nm 、滤波通道的半高宽可调范围在1~5 nm、滤波通道透射峰值大于0.98的一维光子晶体三通道可调谐偏振滤波器.     

光子晶体多通道可调谐滤波器的理论研究

为了实现光子晶体的多通道滤波,对设计出的一维掺杂光子晶体进行了数值计算和理论分析。结果表明：多通道透射峰的波长与空气膜厚度呈线性变化,不同厚度的空气膜可以截到数目不同的透射峰,多通道透射峰的半高宽随光子晶体折射率n₂的增加而减小。以此为基础,设计出滤波通道波长的可调范围达60nm,滤波通道半高宽的可调范围为1nm～5nm,滤波通道透射峰值大于0.98的一维光子晶体三通道可调谐滤波器。     

VHF波段超窄带超导滤波器的设计及其时域调谐

低频超窄带滤波器要求谐振器间的耦合极弱,设计受到薄膜面积限制,其性能对基片介电常数的均匀性极为敏感且受制作和封装精度的限制.这些因素将导致的滤波器中心频率偏移和带内性能恶化.对此,时域调谐提供了很好的解决途径.我们采用嵌套双螺旋型谐振器,在37mm×12mm的MgO基片上设计制作了4节超导滤波器,中心频率为166.9 MHz,相对带宽仅为0.29%.由于基片厚度或介电常数的偏差及不均匀性会导致滤波器中各谐振的谐振频率偏移,使通带性能受到很大影响.我们提出了将机械调谐与时域分析相结合的方法,通过机械调谐纠正各谐振器的谐振频率,改善滤波器性能.同时为了解决多信道滤波器系统中,各滤波器工作于同一温度下,系统频率一致性问题,通过时域调谐获得频率可调范围信息.对上述0.5 MHz带宽的VHF波段滤波器应用时域调谐方法,得到的可调范围为0.7 MHz,测试结果表明该滤波器具有优异性能,带内插损小于0.4 dB,反射损耗达到14.8 dB,带外抑制大于-70 dB.     

C-band three-port tunable band-pass thin film optical filter with low polarization-sensitivity

According to the oblique incidence characteristics of thin film narrowband filter, the stack of 100 GHz DWDM four cavities angle-tuned thin film filter has been designed and optimized. The two polarization modes’ central wavelengths of the thin film filter can be centered at the same one in oblique incidence, and it has a stable tuning range of 20 nm without the phenomenon of polarization central wavelength separation. Using this kind of angle-tuned thin film filter and the polarization beam-splitters, the tuning range of the angle-tuned thin film filter can be further expanded due to the reason that it can transmit only the s-polarization light. In this paper we also developed a three-port bandpass tunable filter device with new structure, which tuning range can cover the whole C-band and its adjacent channel isolation degree is high. The experiments show that the three-port tunable filter has an effective tuning range of 33 nm, and its adjacent channel isolation degree is more than 35 dB. It has a bright application opportunity for its flexibility and effective performance.     

Phase diagram of ferroelectric thin film with diluted surface

We study the influence of the surface of the ferroelectric films on the properties of the intrinsic ferroelectric polarization state in frame of statistical Transverse Ising Model (TIM). The quality of the surface is modelled by the dilution parameter q$q$ that reflects the relative weight of the paraelectric impurities vs. ferroelectric ions. Using the effective field approach the variation of the average value of spontaneous polarization as function of temperature for different film thicknesses has been investigated as function of dilution parameter q$q$. The phase diagram of the system and crossover from the ferroelectric to the paraelectric phase is discussed.     

基于压电聚合物薄膜可调谐Fabry-Perot滤波器的研究

采用DBR/电极/间隔层/电极/DBR的结构形式制作滤波器,器件透光部分刻蚀以消除电光效应.测试滤波器透过率光谱,并通过加电压对滤波器中心波长进行调制.据实际结果得到腔的光学厚度为8.04μm,腔长在电场作用下收缩.在140V电压下,腔长收缩量约为0.757%.实验证明电致伸缩效应在调制中起作用.     

Nanogroove array on thin metallic film as planar lens with tunable focusing

Numerical results for the distributions of light transmitted through metallic planar lenses composed of symmetric nanogroove arrays on the surfaces of a gold film are presented and explained. Both the near- and far-field distributions of the intensity of light transmitted are calculated by using a Green?s function formalism. Results for an optimal transverse focus based on a quadratic variation of groove width are obtained. Meanwhile, a significant dependence of the focal length on the wavelength of light incident from the air side through the gold film into a dielectric substrate is found for this detector configuration.     

Phase transition behaviors of a ferroelectric thin film with long-range interactions

Within the framework of the mean-field approximation, the transverse-field Ising model is used to investigate the surface parameter modification of interaction constants and transverse fields on phase transition behaviors of a ferroelectric thin film with long-range interactions. The variation of Curie temperature as a function of the surface transverse field for different surface interaction constants or thickness is discussed. Meanwhile, the variation of Curie temperature as a function of the surface exchange interaction for different surface transverse fields is examined. In addition, the dependence of Curie temperature on the film thickness for different surface exchange interactions and surface transverse fields is obtained.     

YMnO_3薄膜的铁电行为及其纳米尺度铁电畴的研究

六方YMnO_3是一种特殊的多铁性材料,因其具有介电常数低、单一极化轴、无挥发性元素等特点,在磁电领域具有独特的优势,但目前关于YMnO_3薄膜的铁电性特别是畴结构的研究相对较少.本文采用溶胶-凝胶法在Si(100)基片上制备了多铁性YMnO_3薄膜,利用掠入射X-射线衍射、原子力显微镜对薄膜的结构及表面形貌进行了分析,用压力显微镜(PFM)技术研究了纳米尺度畴结构及微区电滞行为,并通过I-V,P-E曲线进一步研究了薄膜的漏电流和宏观电滞行为.结果表明,该薄膜为六方钙钛矿结构,YMnO_3晶粒大小均匀并且结晶性较好,薄膜表面粗糙度为7.209 nm.PFM图显示出清晰的电畴结构,结合典型的微区振幅蝴蝶曲线和相位电滞回线,证实该YMnO_3薄膜具有较好的铁电性.由于受内建电场的作用,振幅曲线和相位曲线都向正向偏移,表现出非对称特征.该薄膜的漏电流密度低于10~(-6)A·cm~(-2),因而其电滞回线基本能够达到饱和.     

Polarization reversal behavior of an asymmetric ferroelectric thin film

Using the Landau–Khalatnikov equation of motion, the polarization reversal behavior in an asymmetric ferroelectric thin film has been studied. Our model first introduces a third power of polarization to describe the asymmetry of a ferroelectric thin film with surface transition layer, which originates from the difference between the surfaces. Interestingly, vertical drift of polarization switching behaviors was found in this system. The properties consisting of hysteresis loop, spontaneous polarization, switching current of an asymmetric ferroelectric thin film with surface transition layer are discussed.     

Effect of electrodes on the properties of a thin ferroelectric film

The effect of various metal electrodes on the properties of thin ferroelectric films is considered using the phenomenological Ginzburg-Landau theory. The electric field produced by charges on electrodes is taken into account (with allowance for the screening of the charges in the metals) in the free energy functional and in the Euler-Lagrange equation for the film polarization. This equation is solved using the variational method, and the free energy functional is reduced to the conventional free energy with a renormalized coefficient of P ². This coefficient is dependent on the properties and thickness of the film and the properties of the electrode. Therefore, the physical characteristics of the size effect can be found by merely substituting the renormalized coefficient into the usual formulas from phenomenological theory. The calculations are shown to be in good agreement with the experimental data for Pt, Ir, IrO₂, and SrRuO₃.     

Design of non-polarization angle-tuned narrowband thin film filter

Angle-tuned thin film bandpass filter is widely used in DWDM system. In oblique incidence, the bandwidths and central wavelengths of the P-polarization and S-polarization light will separate obviously, which will cause serious polarization dependent loss. These phenomena of the polarization sensitivities are analyzed and a novel non-polarization 100 GHz four-cavity narrowband dielectric thin film stack used in oblique incidence is proposed. The simulation results show that it can eliminate the polarization bandwidths and central wavelengths separation within the incident angle from 0° to 25°, and its tunable range can cover the whole C-band.