对多相移光纤光栅滤波器的光谱进行了理论仿真。理论结果证明:通过精确设计多相移光纤光栅的相移点数目、相移位置分布、耦合系数、长度等参数,可以获得窄带平顶滤波响应的光谱;而实际制备中引入的误差会导致滤波器光谱性能恶化。随后采用紫外辐照后处理的方式,制备了多相移光纤光栅滤波器,并对其光谱进行了测试。结果表明:当多相移光纤光栅滤波器带宽较宽时,实测光谱与理想仿真结果较为吻合;增大耦合系数以减小带宽时,滤波器的性能对工艺误差更敏感。最后对误差项进行了深入的分析与讨论,结果证明,采用较长的多相移光纤光栅可以有效地增大相移点位置和相移差的容限,减弱光致损耗对其性能的影响。

First, the spectral characteristics of multi-phase-shifted fiber Bragg gratings (MPSFBGs) were studied theoretically. The results confirmed that we could acquire the spectra with narrowband flat-top filter response by accurately designing the key parameters of the MPSFBGs, such as the number and position distribution of phase shifts, the coupling coefficient and length of the gratings. However, the process errors introduced in the inscription process would worsen the filter spectra. To this end, MPSFBGs were inscribed by a post-ultraviolet-radiation technique and the relevant spectra were measured. The results demonstrate that the experimental spectra are in agreement with the ideal simulation results when the MPSFBGs have a large bandwidth, indicating that the control accuracy can meet the requirements of the gratings. However, the performance of the narrow-bandwidth filter with a larger coupling coefficient is more sensitive to the process errors. Furthermore, the process errors were analyzed and discussed. It turns out that increasing the length of MPSFBGs can effectively widen the tolerance of phase-shift position distribution, and phase-shift difference, and weaken the effect of UV-induced loss on the loss characteristic of the filters.