镀含弱吸收膜两层膜系长周期光纤光栅谐振特性及其优化

采用严格的耦合模理论,建立了两层膜系长周期光纤光栅复特征方程,用微扰法对复特征方程进行求解,结果和D.V.Ignacio的结论相符.求得的谐振波长表明其随膜层厚度和膜层折射率变化明显,受消光系数影响很小.重点提出了两种途径来优化膜层参量组合,以获得较大的谐振波长偏移量,计算结果显示,参量组合取值为(h_3=122.76 nm,h_4=400 nm)和(n_3=1.572 2,h_4=400 nm)时,谐振波长偏移量分别为10.35 nm和11.74 nm,远高于只镀一层敏感膜LPFG的偏移量2.78 nm,从而证明敏感膜层厚度(h_4)较大的参量组合可提高传感器的灵敏度.

Resonant Characteristics and Optimization of Long Period Fiber Grating Coated with Weak Absorption Double-layer Films

Based on the coupled-mode theory,the complex characteristic equation of LPFG coated with weak absorption double-layer films is set up. By use of the perturbation method, the complex root is obtained.The result is coincident with the result of D. V. Ignacio. The film thickness and refractive index have a great influence on the resonant wavelength, but the extinction coefficient has a little influence on the resonant wavelength. And, the two methods of optimizing the film parameters are presented in order to obtain the larger shifts of the resonant wavelength. The results show that when the film parameter combinations are h_3=122.76 nm,h_4:400 nm and n_3 =1. 572 2,h_4 =400 nm,the wavelength shifts are 10.35 nm and 11.74 nm,respectively,which is much larger than the value of 2.78 nm obtained from the LPFG coated single film. It proves that the selection of the thicker film increase the sensitivity.