Microwave Photonic Notch Filter Helps Ensure Critical Mission Success

Interference mitigation is crucial in modern radio frequency (RF) communications systems with dynamically changing operating frequencies, such as cognitive radios, modern military radar, and electronic warfare (EW) systems. To protect sensitive RF receivers in these systems, frequency agile RF filters that can remove interferers or jammers with large variations in frequency, power, and bandwidth are critically sought. Unfortunately, an RF bandstop or notch filter that can simultaneously provide high resolution, high peak attenuation, large frequency tuning, and bandwidth reconfigurability does not presently exist. Microwave photonic (MWP) filters are capable of tens of gigahertz tuning and have advanced in terms of performance, but most are limited in stopband rejection due to the challenge in creating a high-quality-factor optical resonance used as the optical filter. To achieve MWP filters with similar performance to state-of-the-art RF filters in terms of isolation bandwidth and rejection is still very challenging, especially in compact integrated photonic chip footprint.

Microwave photonic filters based on stimulated Brillouin scattering (SBS) have shown excellent properties in terms of high resolution and extinction. Although efficiently generated in soft glasses such as chalcogenides, there is a strong demand to harness SBS in silicon, a material platform that supports large-scale integration between photonics and electronics. For the CMOS-compatible silicon-on-insulator (SOI) platform, SBS has been elusive. The low elastic mismatch between the silicon core and the silicon dioxide substrate results in weak acoustic confinement, preventing buildup of the SBS process.