Refractive index sensor with acoustic grating in a low index contrast photonic bandgap fiber

We demonstrate and optimize a microfluidic refractive index sensor with ultra-high sensitivity based on an acoustic grating in a solid core photonic bandgap fiber. We optimized long period grating using an acoustic grating, and directly measure its sensitivity to refractive index. The sensitivity of the acoustic grating´s resonance is 17 900 nm/RIU which corresponds to smallest detectable changes in refractive index of 8.4×10⁻⁶.