SUPPRESSION OF THE CLADDING MODE INTERFERENCE IN CASCADED LONG PERIOD FIBER GRATINGS WITH LIQUID CRYSTAL CLADDINGS

摘要

We propose a cascaded structure of long period fiber gratings (LPFGs) with a liquid crystal (LC) as a surrounding medium. In this structure, the electro-optic tuning properties of each LPFG and the interferences between the spectra of LPFGs are studied. Since the electrically tunable cladding modes are radiation modes which are partially guided by Fresnel reflection, the modal interferences among the cascaded LPFGs are eliminated. The cascaded structure of LPFGs with LC claddings is suitable for arbitrary loss filters that compensate for nonuniform optical gain in an erbium doped fiber.