Lee B H, Nishii J
Opt Lett. 1998 Oct 15;23(20):1624-6. doi: 10.1364/ol.23.001624.
The interference fringes formed in a long-period fiber grating pair are sensitive to the loss in the cladding mode, which can be induced by bending or by coating on the fiber. Assuming that there is no loss and that both gratings are identical, the interference fringes are shown to have 100% contrast when each grating has 50% transmissivity. By contrast, if the cladding mode is absorbed or scattered the fringe contrast is shown to be degraded. The spectral behaviors of a long-period fiber grating pair with loss is analyzed by the coupled-mode theory and is compared with experimental results.
在长周期光纤光栅对中形成的干涉条纹对包层模中的损耗敏感，这种损耗可由光纤弯曲或涂覆引起。假设不存在损耗且两个光栅相同，当每个光栅的透射率为50%时，干涉条纹的对比度显示为100%。相比之下，如果包层模被吸收或散射，条纹对比度会降低。利用耦合模理论分析了存在损耗的长周期光纤光栅对的光谱特性，并与实验结果进行了比较。
