Core-cladding mode coupling and recoupling in photonic crystal fiber for enhanced overlap of evanescent field using long-period gratings

Abstract

Excitation of cladding modes has been achieved using long-period (LPGs) inscribed in an endlessly single-mode photonic crystal fiber (ESM PCF) by CO(2) laser irradiation. Core-cladding mode coupling and recoupling has resulted in marked 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 22% with a confinement loss of less than 1 dB/m in the cladding mode.