【作者】 连佳；

【导师】 刘永军；

【作者基本信息】 哈尔滨工程大学 ， 光学， 2009， 硕士

【摘要】 随着光纤通信技术的发展,密集波分复用(DWDM)逐渐成为光传输系统中的关键的技术。为适应DWDM的全面发展,减少通信中的光电转换环节,人们开始研究实用化的全光通信网络,而可调谐滤波器是全光通信中不可缺少的器件。因此对可调谐滤波器的要求也越来越高一要求具有稳定精确的波长,并且体积小,易于集成和低损耗等特性。光子晶体具有结构简单、可靠性好、便于集成和控制性强等优点,并且当光子晶体原有的周期性受到破坏时,可以在禁带中引入一个缺陷态,与缺陷态频率对应的光子将被局域在缺陷的位置,这为制作可调谐光滤波器提供了技术基础。目前,通过在光子晶体中引入缺陷来实现对光信号的滤波技术越来越引起人们的关注。液晶是一种各向异性光学材料,其电控双折射特性使液晶的双折射率对外界参量(电磁场、温度、压力)变化很敏感,基于这些特性,以液晶作为光子晶体缺陷的可调谐滤波器,具有成本低、功耗低、调谐范围大、调谐精度高、重复性能好,可实时控制等优点。因此,对液晶光子晶体滤波器的研究有着重要的意义。向列相液晶较胆甾相和近晶相液晶来说,比较容易获得而且其应用技术也比较成熟,具有较大的介电各向异性和折射率,极易受外界作用的电场、磁场和温度的影响,因此是很好的滤波器调谐材料。Fink等人从理论和实验上指出一维光子晶体可能具有全方位的三维禁带结构,一维光子晶体材料可能制备出由二、三维光子晶体材料制作的器件,即一维光子晶体较二维、三维光子晶体在结构上更为简单,并且易于引入缺陷。因此,本文主要研究的是以向列相液晶为缺陷的一维光子晶体滤波器的滤波特性。在理论方面,运用传输矩阵法给出了液晶光子晶体滤波器的透过率公式,并通过Matlab软件数值模拟了液晶光子晶体滤波器的滤波特性并对其进行分析：当液晶缺陷层的厚度逐渐增加时,透射峰的位置随着缺陷层厚度呈线性增加；随着液晶缺陷层电压的增加,透射峰的波长发生蓝移。在实验方面,制备了液晶光子晶体滤波器,其有效面积为5mm×5mm,并分别用分光光度计和综合测试仪对其透射谱和响应时间进行测试,得到了液晶缺陷层在不同电压下的透射谱和液晶的响应时间。当该滤波器的电压范围在0V～10V内时,透射峰的相对透过率变化在37%-55%之间,禁带宽度近400nm,调谐范围约50nm,透射峰的半高宽为18nm。器件的上升时间为1.5ms,下降时间为6.5ms。除此之外,由于液晶分子具有双折射特性,所以传统液晶光子晶体滤波器的使用不可避免的伴随着偏振片的使用,即偏振片配合液晶的取向方向使用。在一些非偏振光的应用中,偏振片的使用会使得光能量减少。本文给出了非偏振光下的透射谱,详细分析了器件的偏振敏感特性,提出并设计了一种偏振非敏感型液晶光子晶体。双液晶缺陷层的设计起到了对偏振光相互补偿的作用,使得禁带中原本两个透射峰并为了一个透射峰,加强了光强度,增强了滤波性能。更多还原

【Abstract】 With the development of optical fiber communication, Dense Wavelength Division Multiplex (DWDM) has gradually become a key technology in optical transmission system. In order to adapt to the overall development of DWDM and cut down the photoelectric devices in communication system, now researchers are researching the practical application of all-optical communication networks and the tunable optical filter is indispensable. Therefore, higher requirements are expected in tunable filter-some characteristics such as stable and precise wavelength, small bulk, easily integrated and low power and so on.Photonic crystal has the advantages of simple structure, high reliability and control, easy integration. When the original periodicity of photonic crystal is damaged, a defect state can be introduced to the band gap, and the photons which are corresponding to the frequency of defect state will be localized in the defect location. This provides a technical foundation for making tunable optical filters. At present, introducing defects into photonic crystals to achieve light signals filtering technique attracts more and more attention. Liquid crystal(LC) is a kind of anisotropic optical material, whose electric-control birefringence makes the birefringence of liquid crystal be very sensitive to the changes of external parameters(electromagnetic field, temperature and pressure), based on these characteristics, the photonic crystal tunable filter infilled with liquid crystal as defects has the advantages of low cost, low power, wide tunable range, high tunable precision, high repeatability and real-time control and so on. Thus, it has important significance to study on the photonic crystal filter infilled with liquid crystal.Compared with cholesteric liquid crystal and smectic liquid crystal, nematic liquid crystal is easier to be obtained and its application is relatively mature. It has a larger dielectric anisotropy and refractive index, and is easier influenced by external electric field, magnetic field and temperature, therefore, it is a very good tunable material for filter. Fink has been proposed both in theoretical and experimental that one-dimension photonic crystal has omnidirectional three-dimensional band gap structure, and 1D photonic crystal material is possible to prepare the device which is prepared by 2D and 3D photonic crystal, it is that 1D photonic crystal is more simply in structure and easier to introduce defects than 2D and 3D photonic crystal. Thus, this paper is mainly about the filtering properties of 1D photonic crystal filter which is infiltrated with nematic liquid crystal as defect.In theory, we give out the transmittance formula of liquid crystal photonic crystal filter by transfer matrix method,and simulate the filtering characteristics of the filter with Matlab software and carries out an analysis of the characteristics: The location of transmission peaks increase as the liquid crystal defect layer thickness increases linearly; The wavelength of transmission peaks show blue shift as the voltage of LC defect layer increases.In experiment, we prepared liquid crystal photonic crystal filter whose effective area is 5mmx5mm, we also tested its transmission spectrum and response time by spectrophotometer and integrated testing instrument. When the voltage of the filter is between OV to 10V, the change of relative transmission of transmission peaks is between 37% to 55%, the band gap is nearly 400nm, the tuning range is about 50nm, FWHM(full width at half maximum) of the transmission peak is 18nm.The rising time of the device is 1.5ms,and dropping time is 6.5ms.In addition, as LC molecule has birefringent characteristics, the application of traditional LC devices inevitably combines with the polarizer, which accompanies with the orientation of LC. Polarizer will lead to light energy reduce in some application of non-polarized light, even in the system of polarized light. In this paper we also give out the transmission spectrum under non-polarized light, analyze the polarized sensitive characteristics of the device detailedly, propose and design a polarized non-sensitive liquid crystal photonic crystal filter. The design of double liquid crystal defect layers compensates the polarized light reciprocally, makes the original two transmission peaks in the band gap incorporate to one transmission peak, which enhances the light intensity and filter performance.更多还原