Sensing performance of surface waveguide modes excited in long-period fiber grating with gold–silicon nanocoatings

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 n m / R I U 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.