理论分析和模拟计算了少模光纤布拉格光栅基模及高阶模的耦合与传输特性,得到在相同外部折射率变化情况下,少模光纤基模与高阶模耦合对应的布拉格波长变化,比正、反向基模之间耦合对应的布拉格波长变化显著增大。实验上制作了少模光纤布拉格光栅,测量了基模之间以及基模与高阶模之间对应的布拉格波长随外部折射率、温度变化的情况,得到与理论分析相符的结果。而对于温度变化对折射率测量结果干扰的问题,提出了通过计算布拉格波长差来克服温度影响的方法。这些结果为采用布拉格光纤光栅测量外部折射率变化提供了一种新的途径。

The coupling and propagation characteristics of fundamental modes and high-order modes in the few mode fiber Bragg grating was numerically analyzed and simulated. It is indicated that the shifts of the Bragg wavelength corresponding to the coupling between the fundamental mode and the backward high-order mode is obviously larger than the shift of the Bragg wavelength corresponding to the coupling between the forward and backward fundamental modes. The few mode fiber Bragg grating was fabricated, and the variations of Bragg wavelengths corresponding to fundamental modes coupling and fundamental-high-order modes coupling with external refractive index and temperature were measured. The experimental results agree with the theoretical analysis. Therefore by the means of Bragg wavelength difference calculation, the temperature induced fluctuation is overcome, which presents a new ray to measure the external refractive index change of fiber Bragg gratings.