Determination of the Core Diameter and Refractive Index of the Fiber Bragg Gratings

提出一种通过布拉格光纤光栅传输谱线计算其纤芯直径和折射率的方法.实验中采用较短波长的相位掩模板及紫外光照射载氢的单模光纤来写布拉格光栅.通过测量LP01模与反向传输的LP01、LP02模耦合所对应的损耗峰,并将对应的两中心波长分别带入色散方程,来计算同时满足布拉格光栅相位匹配条件的解,即可求出该光纤光栅纤芯直径和折射率.这种方法为测量光纤光栅参数提供了一种新的途径.A new method to determine the core diameter and refractive index of the fiber Bragg gratings(FBG) is proposed by measuring its transmission spectrum, which is fabricated by writing a short wavelength grating in the step-index single mode fiber. In the experiment, the loss peaks of the transmission spectrum is measured, formed by the mode coupling between the forward propagation LP_(01) mode and backward propagation LP_(01) and LP_(02) modes, are measured. The measured central wavelengths of the transmission spectra are substituted into the corresponding dispersion equations and through the numerical calculation, the core diameter and refractive index of FBG can be obtained when they satisfy the phase-matching conditions. This method provides a new approach to obtain the equivalent step-index parameters of FBGs