基于叠加级联长周期光纤光栅的温度和应变传感的理论分析

设计了一种基于叠加型级联长周期光纤光栅的温度与应变双参量同时测量方案，该方案结构小巧、成本低、制作简单。方案在同一段光纤上重叠写入周期为的两个子栅，构成了叠加型级联长周期光纤光栅，这种叠栅的透射谱稳定可控，避免了串联式长周期光纤光栅透射谱谐振峰过于密集多峰、过于敏感不适合作为测量标的的缺陷。通过数值方法分析了不同周期、不同阶次谐振峰分别与温度及应变灵敏度的关系，仿真表明：在给定参数下，光栅的周期越大、两子光栅的周期差也越大时温度与应变灵敏度也越高，选用的两个谐振峰阶次越高、阶次的差异越大时温度与应变灵敏度也越高。利用仿真结果设计了增敏的传感解调矩阵，并对矩阵进行了摄动分析，结果表明得到的解调矩阵相对于其他方案的条件数更低，有效提高了传感器的抗扰性，减小了测量误差对测量精度的影响。

Simultaneous measurement of temperature and strain based on superimposed long period gratings

A dual-parameter simultaneous measurement scheme of temperature and strain based on superimposed long period gratings(SLPFG) is designed, which is compact in structure, low in cost and simple in fabrication.In the scheme, two sub-gratings with periods and are overlapped and written on the same fiber to form a superimposed long period grating(SLPFG). The transmission spectrum of this grating is stable and controllable, this avoids the disadvantages that the resonance peaks of the transmission spectrum of the tandem type cascaded long-period fiber grating(CLPFG) are too dense and multi-peaked, too sensitive, and not suitable as a measurement target.The relationship between different grating pitch, different order resonance peaks and temperature and strain sensitivity is analyzed by numerical method.The simulation shows that: under the premise of fixing certain parameters, the greater the absolute pitch of the grating and the greater the difference of the pitch between the two sub-gratings, the higher the temperature and strain sensitivity. The higher the order of the selected two resonance peaks and the greater the difference in order, the higher the temperature and strain sensitivity will be.Based on the simulation results, a sensor demodulation matrix with enhanced sensitivity is designed, and the perturbation analysis of the matrix is carried out. The results show that the obtained demodulation matrix has a lower condition number than other schemes, which effectively improves the immunity of the sensor,reducing the influence of measurement error on measurement accuracy.