CLADDING-MODE RESONANCES IN SHORT-PERIOD AND LONG-PERIOD FIBER GRATING FILTERS

The transmission of a mode guided by the core of an optical fiber thro ugh an ultraviolet-induced fiber grating when substantial coupling to cladding modes occurs is analyzed both experimentally and theoreticall y. A straightforward theory is presented that is based on the calculat ion of the modes of a three-layer step-index fiber geometry and on mul timode coupled-mode theory that accurately models the measured transmi ssion in gratings that support both counterpropagating (short-period) and co-propagating (long-period) interactions. These cladding-mode res onance filters promise unique applications for spectral filtering and sensing. (C) 1997 Optical Society of America.