Microwave Photonic Filter With Complex Coefficient Based on Optical Carrier Phase Shift Utilizing Two Stimulated Brillouin Scattering Pumps

A microwave photonic filter (MPF) with complex coefficient based on the frequency transparent magnitude response by independent control of the frequency and power of two stimulated Brillouin scattering (SBS) pumps is proposed and experimentally demonstrated. The motivation of this paper lies in the fact that the operation bandwidth of the previous SBS-based complex coefficient MPFs is unavoidably limited by the Brillouin frequency shift. In our scheme, the complex coefficients are obtained by a broadband microwave photonic phase shifter based on the two SBS pumps. The two SBS pump signals are located at the same side of the optical carrier. In principle, the working bandwidth of the proposed MPF is infinite. One pump is used to introduce a controllable phase shift on the optical carrier, whereas the other pump is used to retain the power of the optical carrier invariant. By simply changing the phase shift of a complex coefficient, the frequency response of the two-tap complex coefficient MPF is continuously tuned over the full free spectral range (FSR), keeping shape and FSR invariant.