长周期光纤光栅作为透射型光无源器件，以其在通信和传感领域具有广阔应用前景而引起人们的关注。要得到满足性能要求的光纤光栅，对其透射谱的分析是基础。通过耦合模方程确定了基模和一阶各次包层模之间的耦合常数。在设定的光纤光栅参数条件下，通过Matlab进行模拟得到了最终需要的长周期光纤光栅透射谱，并由此得出：长周期光纤光栅谐振波长出现的位置主要由光栅的周期决定，损耗大小可以通过调节光栅长度和折射率来实现。

As a transmissive and passive fiber-optic device, the long-period fiber grating is interested extensively due to its applications in fiber telecommunication and sensing technology. The transmission spectrum was analyzed to acquire the satisfactory fiber grating. The coupling constants between the fundamental mode and the first-order cladding modes were determined by a mode-coupling equation. With given parameters of the fiber grating, the transmission spectrum of the long-period fiber grating was obtained by simulation with Matlab. As a result, the position of the resonant wavelength of the long-period fiber grating is decided by the grating′s period. The attenuation changes with the length and refractive index of the grating.