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

In this paper, we report a frequency tunable, suppression depth tunable, narrow Microwave Photonic notch filter based on the State of Polarisation (SOP) control of Stimulated Brillouin Scat-tering (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 RF cancellation with a photodiode. We develop and present a math-ematical model explaining the polarisation dependent gain and the transfer function of the proposed filter. Experimental results demonstrate a tunable notch filter with a notch depth tuning range of 0-40dB with a frequency range of 2-26.5GHz. The -3dB width of the filter was recorded as 37MHz at its maximum depth, with a low 4MHz recorded in shallower notches. The notch depth is tuned by a polarisation controller that controls the SOP of the pump signal. This configuration has applications in dynamic notch filtering of signals such as Radio Frequency 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, telecom-munications and beyond communication technologies.