Mode coupling in photonic crystal fiber using long-period gratings for enhanced overlap of evanescent field

An evanescent field sensing platform is being pursued through excitation of cladding modes using long-period (LPGs) inscribed in an endlessly single-mode photonic crystal fiber (ESM PCF) by CO2 laser irradiation. Core-cladding mode coupling and recoupling has resulted in significant improvement in the evanescent field overlap throughout the cladding air channels in the PCF-LPG, compared to the PCF alone. Our numerical simulation has shown that design optimization of the PCF-LPG configuration can lead to a field power overlap as high as 23% with a confinement loss of less than 1 dB/m in the cladding mode.