梯形折射率调制长周期光纤光栅的理论分析

Theoretical Analysis for the Long-period Fiber Gratings with a Trapezoid Index Modulation

提出一种新型光栅模型———梯形折射率调制类型长周期光纤光栅(LPG)。以耦合模理论为基础,研究了折射率调制梯形上、下底边宽度差对光栅传输光谱特性的影响。计算结果表明:随着梯形上、下底边差值的增大,传输谱谐振峰的位置将向长波方向漂移;与矩形折射率调制LPG相比,梯形折射率调制LPG可以有效地减小光栅的折变量;当梯形上、下底边宽度差值的1/2为30μm时,光栅的折变量仅为相同光栅参数下矩形折射率调制光栅的80.2%。

The long-period fiber grating（LPG） with trapezoid index modulation is presented as a novel grating. Based on the coupled-mode theory,the influences on the transmission charactreistics are analyzed, which include the difference between the top width and the bottom width （simplified to be “d” in the following text） of the trapezoid index modulation,Calculated results show that the resonance location displaces to the long wavelength when the d increases. Compared with the LPG with rectangle index modulation,the advantage of this novel grating is that it needs a smaller refractive index change. When d is 30 μm,the refractive index change is only 80.2% of that of the LPG with rectangle index modulation.