A Tunable Depth Microwave Photonic Notch Filter Based on Polarization Control of Stimulated Brillouin Scattering

In this article, we report a frequency-tunable, suppression depth-tunable, narrow microwave photonic (MWP) notch filter based on the state of polarization (SOP) control of stimulated Brillouin scattering (SBS) in SMF. SBS gain is highly dependent on the SOPs of the pump-and-probe signals with a maximum gain when their SOPs are the same, and a minimum when they are orthogonal to one another. We exploit this phenomenon to create a tunable depth notch filter by adjusting the gain and loss of SBS for radio frequency (RF) cancellation with a photodiode. We develop and present a mathematical model explaining the polarization-dependent gain and the transfer function of the proposed filter. Experimental results demonstrate a tunable notch filter with a notch depth tuning range of 0–40 dB with a frequency range of 2–26.5 GHz. The -3 dB width of the filter was recorded as 37 MHz at its maximum depth, with a low 4 MHz recorded in shallower notches. The notch depth is tuned by a polarization controller that controls the SOP of the pump signal. This configuration has applications in dynamic notch filtering of signals such as RF interference (RFI) removal where control over the notch depth is of great importance. The proposed tunable depth notch filter would provide unique benefits for satellite, aerospace, telecommunications, and beyond communication technologies.