基于光折变光栅的可调谐滤波方案及特性分析

Tunable Filtering Scheme and Characteristics Analysis Based on Photorefractive Gratings

在LiNbO3单模波导上利用双光束干涉可形成光折变波导光栅,针对粗波分复用系统提出了通过实时改变双光束之间的夹角进而改变光栅间距,实现可调谐滤波的方案。利用光折变动力学理论,得到光栅调谐时间在毫秒数量级。研究发现,适当提高光强和增加杂质掺杂浓度可提高衍射效率、减少光栅初次建立时间。基于耦合波理论的数值模拟结果表明,增大光栅长度能使衍射效率提高且带宽变小,而增加折射率调制度使衍射效率提高但同时带宽变宽。在折射率调制度为8×10-5,光栅长度大于12mm时,可获得91%以上的衍射效率和小于0.08nm的带宽。

Photorefractive waveguide grating can be formed using two-beam interference method in lithium niobate with the single-mode waveguide.A scheme for Coarse Wavelength Division Multiplexing（CWDM） is proposed to realize tunable filter by changing the angle between the two recording beams which changes the grating pitch.With photorefractive dynamics,tuning time of several milliseconds is obtained.It is found that diffraction efficiency can be increased and the building time decreased by suitable intensity and dopant.The results based on coupled wave theory show that diffraction efficiency can be increased and bandwidths narrowed when the grating length is increased,and diffraction efficiency can be increased but bandwidths widened with the increasing refractive index modulation.When refractive index modulation is 8×10^-5 and the grating length is longer than 12 mm,diffraction efficiency more than 91% and bandwidth narrower than 0.08nm can be obtained.