Few-mode tilted long period fiber grating mode filter based on dual-peak resonance near phase-matching turning point

Abstract

This paper presents a novel few-mode tilted long period fiber grating (FM-TLPFG) mode filter based on the dual-peak resonance near phase-matching turning point (PMTP). On the basis of the coupled mode theory, the dual-peak resonance and the mode coupling in the FM-TLPFG are analyzed. The influences of grating period, tilt angle and grating length on the filter characteristics are analyzed. As the results show, the coupling characteristics between the core modes (LP01 and LP11) and the cladding modes will affect the bandwidth and the core mode loss of mode filters. As the efficiency of the resonant peak LP01-HE1,19 achieves ∼100%, the bandwidth can reach 70 nm. And the maximum coupling between the core mode LP01 and the cladding mode HE1,19 occurs in the tilt angle range of 80-82°, and the grating length range of 34–46 mm. Compared with the reported fiber mode filter, the performance of the FM-TLPFG mode filter is better. The bandwidth of FM-TLPFG mode filter is about 2.7 times than the reported filter, and the mode loss of LP01 is higher.