Evanescent-wave LPFG in D-fiber by periodically patterned overlay
G. Quero, A. Crescitelli, D. Paladino, M. Consales, University of Sannio (Italy); A. Buosciolo, M. Giordano, CNR-IMCB – National Research Council- Institute for composite and biomedical materials (Italy); A. Cusano, University of Sannio (Italy)
Long-period fiber gratings (LPFGs) represent an attractive fiber grating-based technological platform because of their selective spectral features together with the intrinsic sensitivity to surrounding refractive index (SRI). Unfortunately, their main limitation relies on the necessity to opportunely coat the glass substrate when sensitivity enhancement and/or specific functionalization are required. Here, we investigate the possibility to realize a self-functionalized and highsensitivity LPFG by evanescent-wave interaction of the propagating light with a periodically patterned overlay. In particular, a D-shaped optical fiber is considered because of its peculiar geometrical features. First chemical etching is used to allow the evanescent-wave interaction of the propagating light with the surroundings with the desired sensitivity. Successively a uniform atactic polystyrene overlay is deposited onto the flat surface of the structure by dip-coating technique. Finally the overlay is opportunely patterned by laser-micromachining techniques in order to create a LPFGlike structure. The reported results demonstrate the spectral features of the realized device and confirm the LPFG-like behavior with high SRI-sensitivity. The flexibility of the adopted fabrication method could allow the realization of innovative LPFGs to be adopted for a multitude of sensing applications, depending on the nature of the material deposited onto the flat surface of the etched D-fiber.
