Del Villar Ignacio, Matias Ignacio R, Arregui Francisco J
Departamento de Ingeniería Eléctrica y Electrónica, Universidad Pública de Navarra, Pamplona, Spain.
J Opt Soc Am A Opt Image Sci Vis. 2006 Mar;23(3):651-8. doi: 10.1364/josaa.23.000651.
A thin overlay of higher refractive index than that of the cladding of a long-period fiber grating induces in cladding modes strong variations in effective index, mode profile, cross-coupling coefficient with the core mode, and self-coupling coefficient. Some conditions must be met in order to obtain the highest inducement. The key parameters are the thickness and the refractive index of the overlay, and the ambient refractive index. Under optimum conditions, the sensitivity of the device to variations in any of the critical parameters is improved in a great manner. The result is large shifts of the attenuation bands in the transmission spectrum. If the refractive index of the overlay is complex, there is an additional phenomenon of vanishing of the attenuation bands in the transmission spectrum. This occurs for specific thickness values of the overlay. The problem is solved in two steps: a vectorial analysis of the modes and the application of coupled-mode theory.
与长周期光纤光栅包层相比具有更高折射率的薄覆盖层会在包层模式中引起有效折射率、模式分布、与纤芯模式的交叉耦合系数以及自耦合系数的强烈变化。为了获得最大的诱导效果，必须满足一些条件。关键参数是覆盖层的厚度和折射率以及环境折射率。在最佳条件下，该器件对任何关键参数变化的灵敏度会大幅提高。结果是传输光谱中的衰减带发生大幅偏移。如果覆盖层的折射率是复数，传输光谱中会出现衰减带消失的额外现象。这在覆盖层的特定厚度值时会发生。这个问题分两步解决：模式的矢量分析和耦合模理论的应用。
