用于单频光纤激光器的光纤光栅双腔Fabry-Perot结构传输谱特性理论研究

分析了基于光纤光栅的全光纤型双腔Fabry-Perot(F-P)结构传输谱特性. 理论推出了两腔F-P结构传输率具体计算公式，给出在光栅中心波长处产生单谐振传输峰时，腔长与组成光栅反射率各需满足的条件. 基于理论分析结果，分两部分数值模拟了对称及非对称两腔F-P结构传输谱，讨论了计算结果并给出定性的解释，总结了腔长及光栅长度、折射率调制深度的设计原则. 结论表明，当单腔F-P结构腔长增大到阻带内出现多个谐振峰时，通过合理选取两腔结构的腔长及光栅参数，双腔F-P结构能够在整体长度不变条件下，抑制中心波长两侧的次谐振峰，而中心波长处的主谐振峰不受影响. 关键词： 光纤光栅 Fabry-Perot结构 光纤激光器

Theoretical investigation on the characteristics of transmission spectra of the two-cavity Fabry-Perot structure based on fiber gratings for single-frequency fiber laser

The characteristics of transmission spectra of the all-fiber two-cavity Fabry-Perot (F-P) configuration based on fiber Bragg gratings (FBG) are theoretically analyzed and modeled. The explicit expression of the transmission coefficient for two-cavity F-P structures is derived. When the single resonant transmission peak is produced at the central wavelength in FBG stop band, the general conditions for the lengths of two cavities and reflectivities of FBGs are presented. Based on the theoretical analysis, the transmission spectra of symmetric and asymmetric two-cavity F-P structures are simulated, and the simulation results are discussed and explained qualitatively. The design guidelines of the device, including the choices of cavity length, grating length and index modulation depth， are put forword. The results show that, when the increasing of the cavity length of a single-cavity F-P structure results in multiple resonant peaks in the stop band, the two-cavity F-P structures of the same length can suppress the secondary resonant peaks and keep the main peak unaffected without degrading the performance through appropriately designing the cavity lengths and FBGs.