Highly Reconfigurable Microwave Photonic Bandstop Filters Using Ultra-Low Brillouin Gain

Microwave bandstop filters enable the rejection of unwanted signals in a particular frequency band, making it useful for radar, communications, and defence systems. Conventional electronic systems have a multitude of disadvantages including limited bandwidth and susceptibility to electromagnetic interference (EMI), thus prompting the shift to microwave photonic (MWP) systems. Stimulated Brillouin Scattering (SBS) is a third-order nonlinear optical processing technique which is relevant for MWP due to unique properties such as narrow linewidth (and hence high resolution), sharp phase response and optically tailorable responses [1]. Previous bandstop filters using SBS were achieved using signal cancellation but limited to notch responses [2]. To achieve wideband bandstop filters with a sharp filter response, multiple SBS pumps, generally using a frequency comb, had to be used [3]–[4], making the system very power-inefficient and complicated.