High-Resolution, Large-Rejection and Tunable-Frequency Microwave Photonic Notch Filter Based on Brillouin Spectrum Shaping and Polarization Pulling

Nonlinear optical stimulated Brillouin scattering (SBS) interaction together with single sideband modulation is an effective approach to realize advanced microwave photonic notch filters (MPNFs). However, in this method, an inevitable trade-off exists between the filter resolution and its rejection, limiting the performances of MPNFs. To overcome this constraint, we propose and demonstrate an enhanced approach based on Brillouin spectrum shaping combined with polarization pulling. By introducing a three-line SBS pump wave, two groups of SBS gain spectra and one group of SBS loss spectrum are generated in a standard single-mode fiber. In further, the bandwidth of SBS loss spectrum can be narrowed by adjusting positions and amplitudes of two SBS gain spectra. Correspondingly, the resolution of the response filter is improved. Moreover, polarization pulling effect in the vector SBS process is considered and used to adjust the state of polarization (SOP) of the probe wave. In this way, the rejection of the filtering response is enhanced. The experimental results show that our proposed MPNF has a high resolution of 40 MHz and a large rejection of 65 dB. In addition, the center frequency is tunable among the range from 11 GHz to 29 GHz. As a paradigm demonstration oriented to practical scenarios, high-resolution radio frequency (RF) filtering aiming for interference rejection is performed. It is indicated that our proposed MPNF with enhanced performances might greatly advance the development of various microwave photonic applications.