FABRICATION OF HIGH-REJECTION-LOW-LOSS SINGLE-PASSBAND FILTERS IN CLADDING DEPRESSED FIBER BY THE CHIRPED-GRATING CONCATENATION METHOD

High-rejection-low-loss single-passband filters have been successfully fabricated by the chirped-grating concatenation method in a cladding depressed fiber. The enhanced photosensitivity, the enlarged bandgap b etween the Bragg resonance and the cladding modes, and the effective s uppression of the cladding-mode outcoupling of the cladding depressed fiber permitted what is to our knowledge the first achievement of an s imilar to 1-dB loss in the passband and 50-dB rejection for a 50-nm-wi de stop band covering the entire amplified spontaneous emission spectr al range of an Er-doped fiber amplifier. (C) 1998 Optical Society of A merica.