【作者】 李文清；

【导师】 万助军；

【作者基本信息】 华中科技大学 ， 光学工程， 2016， 硕士

【摘要】 在基于波分复用(Wavelength Division Multiplexing,WDM)技术的智能光网络中,ROADM(Reconfigurable Optical Add/Drop Multiplexer,可重构光分插复用器)节点可以对光信号进行波长粒度的线路转换,而基于波长选择开关(Wavelength Selective Switch,WSS)的新一代ROADM技术可实现最好的波长交换灵活性。硅基液晶(Liquid Crystal on Silicon,LCOS)是实现WSS的主流技术方案之一,本论文研究基于LCOS的动态相位光栅的衍射特性,主要工作内容如下:回顾了WSS技术的应用背景和LCOS技术的发展历程,针对LCOS在WSS中的应用背景,建立了简化的2f光学系统模型,LCOS芯片和用作输入/输出端口的光纤准直器阵列分别放置在傅里叶透镜的前后焦平面上。建立了LCOS动态相位光栅模型,将其等效为一个由闪耀光栅和阶梯光栅构成的复合光栅;LCOS芯片上每个像素的相位调制量可通过电场独立控制,但相邻像素之间存在电场干扰,光栅模型中考虑了电场边缘效应的影响,在相位调制的回程区产生寄生光栅。基于上述光栅模型,以余弦函数拟合相邻像素的相位调制量之间的过渡区域,对LCOS相位光栅的衍射特性进行数值仿真。考虑在WSS中的应用背景,因电场边缘效应产生的寄生光栅,对WSS的插入损耗和串扰两项指标有较大影响。LCOS相位光栅对光束的衍射偏转角度越大,则电场边缘效应越显著,仿真拟合时设置的相位回程区越宽,才能与实验结果相吻合。基于上述仿真结果,设计实验系统的参数,搭建实验平台进行验证。将LCOS相位光栅设置为一定的周期,对应一定的衍射偏转角度,输入光纤准直器放置在傅里叶透镜后焦平面上的某个离轴位置,以另一个输出光纤准直器在后焦平面上的不同位置接收光信号,得到耦合效率与接收位置的关系曲线,对应目标输出端口位置的耦合效率即为插入损耗,对应其他端口位置的耦合效率即为串扰。测得不同偏转角度下的串扰水平,与仿真结果基本吻合,研究结果对LCOS型WSS的设计具有参考价值。更多还原

【Abstract】 In the agile optical network(AON) based on dense wavelength division multiplexing(DWDM) technology, reconfigurable optical add/drop multiplexing(ROADM) nodes can switch optical signal in wavelength granularity. The new generation of ROADM technology based on the wavelength selective switch(WSS) can realize the best wavelength switching flexibility. Liquid crystal on silicon(LCOS) is one of the main approaches for WSS module. This paper researches the diffraction characteristics of dynamic phase grating based on LCOS. The main work is as follow:The applications of WSS technologies and the development of LCOS technologies are reviewed. Based on application of LCOS in WSS module, a simple 2f optical model is built. In the model, the optical fiber collimator array employed as the input/output ports and the LCOS chip are placed on the front and rear focal planes of the Fourier lens, respectively. The model of LCOS dynamic phase grating is also built, which is equivalent as a composite grating composed of a blazed grating and an echelon grating. The phase modulation of each pixel in the LCOS chip is independently controlled by voltage, while electric field interference between the adjacent pixels exists. The influence of fringing-field effect is considered in the grating model, which generates a parasitic grating in the phase modulation return area.Based on above grating model, cosine function is employed to fit the transition region between the phase modulation of adjacent pixels, and the diffraction characteristics of LCOS phase grating are numerically simulated. Considering the application in WSS module, the parasitic grating resulting from the fringing field effect greatly affects the insertion loss and crosstalk of WSS. With the increment of the beam deflection angle diffracted by the LCOS phase grating, the fringing field effect is more remarkable, and a wider phase modulation return area should be set for simulation to match the experimental results.Based on above simulation results, the parameters of the experimental system are designed and an experimental platform is constructed to verify the simulation. The period of the LCOS phase grating is set according to a required diffraction angle. The input optical fiber collimator is placed at an off-axial position on the rear focal plane of the Fourier lens, and another output fiber collimator is employed to receive the optical signal at different positions on the rear focal plane. The curve relating the coupling efficient and the receiving position is obtained. The coupling efficient corresponding to the target port position is the insertion loss, and those corresponding to the other port positions are crosstalk. The measured crosstalk at different diffraction angle meets the simulation results generally. The research work could be reference for the design of a LCOS-based WSS module.更多还原