We carry out a very early theoretical study on surface waveguide modes excited in a long-period fiber grating (LPFG) coated with gold–silicon thin films for refractive index sensing. The surface waveguide modes originate from the intermode transition of EH cladding modes and present a very strong evanescent field penetrating into the surrounding medium, which makes them ultrasensitive to external changes. By tracking the dual resonances of surface waveguide modes, ultrahigh sensitivity up to $7267.7 {\rm{nm}}/{\rm{RIU}}$ around 1.315 is obtained, which is 76-/4-fold higher than the case of bare LPFG/LPFG-assisted surface plasmon resonance, together with the capability of self-referenced measurement. This new, to the best of our knowledge, concept is expected to find wide applications based on refractive index sensing.

中文翻译：

---

金硅纳米涂层在长周期光纤光栅中激发的表面波导模式的传感性能

我们对表面波导模式进行了非常早期的理论研究，该表面波导模式是在长周期光纤光栅（LPFG）中激发的，该光栅镀有金硅薄膜以用于折射率传感。表面波导模式源自EH包层模式的模间转换，并呈现出一个非常强的渐逝场穿透到周围介质中，这使它们对外部变化非常敏感。通过跟踪表面波导模式的双共振，超高灵敏度高达$ 7267.7 {\ rm {nm}} / {\ rm {RIU}} $可获得约1.315的信号，比裸LPFG / LPFG辅助的表面等离子体激元共振的情况高76 // 4倍，并具有自参考测量的能力。据我们所知，这种新概念有望在折射率感应的基础上找到广泛的应用。