Application of coupled mode theory on modeling for circularly symmetric LPFG

Long period fiber grating (LPFG) is a fiber component different from the fiber Bragg grating. According to coupled mode theory, the forward propagating guided core mode is coupled to a number of co propagating cladding modes in an LPFG. The axial distribution for mode fields of the LPFG is analyzed and researched. Then the simplified model for the LPFG is deduced with ignoring longitudinal coupling of modes and coupling of cladding modes themselves, and also assuming the modulation of refractive index exists only in fiber core. Spectral characteristics of the circularly symmetric axial uniform LPFG is simulated. The accordant results between experiment and simulation show the simplified model deduced rational and appropriate.