Power penalties due to in-band and out-of-band dispersion in FBG cascades

We measure the in-band dispersion penalty in a cascade of five 50-GHz low-dispersion linear-phase fiber Bragg gratings (FBGs) and compare the results with conventional apodised FBGs. At the 0.5-dB power penalty level, the usable bandwidth of a single linear-phase FBG (40 GHz) is twice as wide as that of a conventional apodised FBG (19 GHz). The bandwidth-utilization factor of a single linear-dispersion grating is 89%, while for the five-grating cascade, it is 76%. To our knowledge, these are the highest values reported to date for cascaded optical devices. The corresponding factors for the conventional gratings are 53% and 31%. We also measure the additional penalty on a dropped channel caused by a cascade of five adjacent-channel gratings. The bandwidth narrowing due to the adjacent-channel FBGs is 6 GHz both for linear-phase and conventional FBGs, giving a usable bandwidth of 34 GHz (linear-phase) and 13 GHz (conventional).