Characterization of external refractive index sensitivity of a photonic crystal

Long-period gratings (LPGs) are fabricated in a photonic crystal fiber (PCF) using the symmetric pointby-point CO2 laser irradiation method to explore the sensitivity characterization of PCF–LPG. Numerical simulation is used to guide the investigation. It is found that the refractive index (RI) sensitivity of PCF–LPG depends on the coupled cladding modes as well as the coupled resonance wavelength (RW) of the LPG. Experimental studies show that the longer the RW, the higher the RI sensitivity fo