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Reduction of cladding mode coupling losses in fiber Bragg gratings

We present a theoretical discussion of special fiber designs for the reduction of Bragg grating induced cladding mode losses. The model includes possible coupling to asymmetrical cladding modes occurring in the case of asymmetry in the UV-induced index grating. It is found for the considered fiber designs that a high numerical aperture fiber increases the spectral separation between the Bragg resonance and the onset of cladding mode losses. A depressed cladding fiber reduces the coupling strength to the lower order cladding modes, and the UV-sensitive cladding design reduces the cladding mode coupling loss.