Leaky mode transition and enhanced resonance in tilted fiber Bragg grating

Abstract

Leaky mode resonance in tilted fiber Bragg grating (TFBG) has been widely underestimated and ignored. Herein, we theoretically demonstrate that the leaky mode resonance can be greatly enhanced, and it presents a highly sensitive property by virtue of its mode transition. The leaky mode transition consists of five stages from the cladding guided mode to radiationlike and guidedlike leaky modes for both p- and s-polarized modes of bare TFBG. However, the graphene induces only one transition for the s-polarized guidedlike leaky mode, which, in turn, leads to an insensitive wavelength shift. The resonance amplitude depends on the imaginary part of the effective refractive index. Consequently, the enhanced leaky mode resonance (eLMR) in the s-polarized state is obtained and presents higher sensitivity than the widespread surface plasmon resonance (SPR). Furthermore, a general empirical rule associated with the refractive index of nanometer materials for exciting the eLMR in TFBG is obtained (the SPR is also discussed for comparison). The results obtained in this work have shed contemporary light on the undervalued leaky mode resonance, which is of great interest and importance to the development of novel multimodal and multifunctional eLMR-based TFBG devices, such as tunable lasers, optical modulators, and sensors.