Optical coupling between a long-period fiber grating and a parallel tilted fiber Bragg grating.

We experimentally demonstrate the contradirectional optical coupling between two parallel fibers that contain a long-period fiber grating and a tilted fiber Bragg grating, respectively. Strong coupling occurs between the cladding modes of the same order over the overlapped resonance bands of the two gratings. By optimizing the coupling conditions, we achieve a peak coupling efficiency of approximately 80% at approximately 1,534 nm with a 3 dB bandwidth of approximately 0.12 nm and a side-mode suppression ratio of approximately 16 dB, regardless of which fiber light is launched into. This coupler configuration can be explored for the development of narrow-band all-fiber optical components.