Influence of cladding-mode coupling losses on the spectrum of multi-channel fiber Bragg grating (FBG) has been numerically investigated on the basis of the extended coupled-mode equations. It has been shown that there exists a reflection slope in the spectrum of both the intra- and inter-channels due to the existences of the cladding modes. This slope could be larger than 1 dB when the induced index change is about 3×10-3, which makes the channels considerably asymmetric. For comparison, a 39-channel linearly chirped FBG with a channel spacing of 0.8 nm and a chromatic dispersion of -850 ps/nm has been designed and fabricated. The experimental results show good agreement with the numerical ones. Finally, one method to pre-compensate the reflection slope within the intra-channels has been proposed and successfully demonstrated.
© 2005 Optical Society of America
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