All-optical tunable microwave filters with negative multitaps based on uniform fiber Bragg gratings

This paper demonstrates a novel transversal filter with negative coefficients under incoherent operation. It is based on filtering a broadband optical source with fibre Bragg gratings (FBG's) to generate the taps with negative coefficients, while laser array generates the positive taps. This scheme used passive component; i.e., FBG's, and, in addition, the negative taps are fully independent on the positive taps and it is an all-optical and passive configuration, which exhibited a good performance and higher tunability and lower cost and was focused on reducing the frequency to hundreds of kHz without increasing the noise to signal ratio.