Refractive index fiber sensor based on cladding modes interference

We present the optical fiber sensor based on fused silica capillary as a sensing element spliced between the lead-in and lead-out singlemode (SM) fibers. In the region of the splice the cladding modes of capillary are excited from the fundamental mode of led-in SM fiber. The intermodal interference of the propagating cladding modes results in the formation of the resonant peaks in the transmission spectrum. With the variations of the external refractive index the shift of resonance wavelength of the peak can be observed. The sensitivity for the refractive index values around n=1.33 is observed and using the wet etching technique can be increased, what gives an assumption for its using in a biomedical sensing applications.