相移光纤光栅退火前后的光谱分析

Spectral Analysis of Phase-Shifted Fiber Grating before and after Annealing

将相移光纤光栅等效为法布里珀罗腔，进行理论分析与仿真，研究了折射率调制深度和光纤有效折射率对相移光纤光栅光谱的影响。在此基础上，分析和研究了相移光纤光栅退火前后光谱的变化规律。结果显示，载氢光纤退火后，由于色芯结构的变化，会导致调制深度和有效折射率分别降低了10-5和10-4数量级。等效腔长增加5%左右，从而使得相移光纤光栅整个光谱和透射窗口往短波方向移动。通过对实验室刻写的相移光纤光栅退火前后的光谱进行拟合，发现实验结果与理论分析基本一致，这对相移光纤光栅的刻写和分布反馈激光器（DFB）的制作有一定的指导意义。

The basic characteristics of the phase-shifted grating are theoretically analyzed and simulated based on the Fabry-Perot （F-P） model, and the transmission spectra impacted by the effective refractive index of the fiber core and the index modulation depth are investigated. On this basis, the variation of the transmission spectra before and after annealing is also reported in detail. The results show that, due to the change of the color center structure, the effective refractive index and the modulation depth decrease at the order of 10-5 and 10-4 separately after annealing. The equivalent cavity length increases about 5%, which makes the whole spectra and the transmission window drift towards shorter wavelength. The data fitting results of the spectra of the fabricated phase-shifted grating before and after annealing are in agreement with the theoretical calculation, which can be significant for the fabrication of the phase-shifted grating and distributed-feedback （DFB） fiber laser.