中文摘要：

提出了一种光纤横截面折射率变化呈旋转非对称变化的长周期光纤光栅（R-LPFG）结构,并利用多层圆波导理论和横截面折射率离散分析方法,结合模式耦合方程组和数值求解方法理论分析了这种光栅的模式耦合特征.理论分析表明R-LPFG纤芯基模主要与一阶非对称包层模发生耦合,当光栅旋转度逐渐变大时,R-LPFG基模会与一阶非对称包层模的奇模和偶模同时发生耦合,这就会使原来单一的谐振峰逐渐分裂成双峰,这是常规光栅类型所不具有的透射谱特征.由于R-LPFG的双峰来自同一对耦合模式,它们对温度的响应很相似,因此可利用双峰间距来进行无需温度补偿的扭曲、应变等物理量的测量.最后利用高频CO2激光脉冲写入法制作了这种光栅,并实验研究了这类光栅的传输谱演变特征,实验结果和理论分析一致.可以预见,这类光栅在光纤传感或通信中将具有较大的潜在应用价值.

英文摘要：

The structure of asymmetric LPFG with rotary refractive index modulation （R-LPFG） along the fiber axis is proposed and fabricated by using high frequency CO2 laser pulses. The transverse refractive index distribution of LPFG with asymmetric refractive index modulation in the cross-section is divided into multilayer circular waveguides, which are then discretized according to the magnitude of index. The mode coupling characteristics of this asymmetric LPFG is discussed by adopting coupled-mode equation sets and the revised Bragg condition. It＇s observed that the transmission spectrum has different features depending on the rotation angle. For small angles, resonance peak is unique, however, when the angle becomes greater, the resonance peak will be split into two, which is different from the transmission spectrum of previous LPFGs. Moreover, the two split peaks have almost the same temperature sensitivity because they originated from the same two coupling modes. The high sensitivity torsion meter and strain meter without temperature compensation can be designed by adopting the wavelength spacing between the two split peaks.