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 between the Bragg resonance and the cladding modes, and the effective suppression of the cladding-mode outcoupling of the cladding depressed fiber permitted what is to our knowledge the first achievement of an ∼1-dB loss in the passband and 50-dB rejection for a 50-nm-wide stop band covering the entire amplified spontaneous emission spectral range of an Er-doped fiber amplifier. © 1998 Optical Society of America.