Stimulated Brillouin scattering-based ultra-narrow passband microwave photonic filter with high out-of-band rejection

A novel ultra-narrow Microwave Photonic Filter (MPF) utilizes Stimulated Brillouin Scattering (SBS) to achieve a passband as narrow as 3 MHz as well as an impressive out-of-band (OOB) rejection ratio with regard to approximately 41 dB. As the demand for high-performance communication systems escalates, traditional microwave filters encounter limitations that this advanced MPF seeks to address. The filter operates by converting Radio Frequency (RF) signals into the optical domain, leveraging a specially designed SBS medium and an SBS pump with multiple lines configuration to narrow the passband effectively. The operational principles include polarization modulation techniques that enhance filtering efficiency. The Bandwidth (BW) of the MPF is effectively reduced by employing Composite SBS (CSBS) technology, which superimposes a pair of Brillouin loss spectra onto a central Brillouin gain. Nevertheless, this superposition results in a reduction in SBS gain, which in turn reduces the MPF's OOB rejection capabilities. In order to resolve this issue, Vector SBS (VSBS) technology is implemented, which improves OOB rejection by compensating for SBS gain and suppressing unamplified spectral components by manipulating polarization states. It comprises simulation experiments carried out through OptiSystem software and a mathematical model developed based on basic equations. This work highlights the filter's potential to improve BW utilization and significantly reduce size and power consumption, making it particularly relevant for future applications in advanced wireless communication technologies. Overall, the findings underscore the significant contributions of this MPF design in the evolving landscape of Microwave Photonics (MWPs).