膜层厚度对长周期光纤光栅谐振波长的影响

基于三包层长周期光纤光栅的模型及其色散方程,研究了镀膜长周期光纤光栅的膜层厚度对长周期光纤光栅谐振波长的影响。研究发现,当膜层厚度达到一定值后,包层模式中有效折射率最大(也即包层模式最低的模式)的模式将会消失,这些模式的消失将会导致其后的模式往前移位,从而引起模式重组并导致相应的有效折射率发生跳跃。与有效折射率的变化相对应,随着膜层厚度的增加,包层模式的谐振波长的漂移特性可以分为3个区域,在区域一和区域三,膜层厚度的变化引起的谐振波长的变化较小,而在区域二,谐振波长对膜层厚度极为敏感,厚度的小小变化既可引起谐振波长的较大漂移,在这个区域存在一个最优厚度(opti-mum overlay thickness,OOT),当膜层厚度等于最优厚度时,谐振波长对厚度的变化极度敏感。

Influence of overlay thickness on the resonant wavelength of LPG

Based on the model of triple-clad long-period fiber grating and dispersion equation,the influence of overlay thickness on the resonant wavelength of LPG is studied.It comes to the conclusion that,when the overlay thickness reaches a certain value,the modes with peak effective index in the cladding modes(those with lowest cladding modes)will gradually disappear.The disappearance of these modes will result in the moving forward of subsequent modes,which will cause a leap of the effective index.In correspondence with the changes of the effective index,the shift characteristics of resonant wavelength of cladding modes may fall into three areas with the increase of the overlay thickness.In the first and third areas,the change of the overlay thickness has few effects on the change of the resonant wavelength,but in the second area,the resonant wavelength is quite sensitive to the overlay thickness-a small change can cause large shift of resonant wavelength.An optimum overlay thickness(OOT)exists in this area,and once the overlay thickness equals OOT,the resonant wavelength of LPG would be remarkably subtle to the changes of overlay thickness.