RF-Photonic Filters via On-Chip Photonic–Phononic Emit–Receive Operations

The creation of high-performance narrow-band filters is of great interest for many radio frequency (RF) signal processing applications. To this end, numerous schemes for electronic, microelectromechanical systems-based, and microwave photonic filters have been demonstrated. Filtering schemes based on microwave photonic systems offer superior flexibility and tunability to traditional RF filters. However, these optical-based filters are typically limited to gigahertz (GHz) widths and often have large RF insertion losses, posing challenges for integration into high-fidelity RF circuits. In this paper, we demonstrate a novel type of microwave filter that combines the attractive features of microwave photonic filters with high-Q phononic signal processing using a photonic-phononic emit-receive process. Through this process, an RF signal, which is encoded on a guided optical wave, is converted into a GHz-frequency acoustic wave, where it is filtered through shaping of acoustic transfer functions before being converted back to the optical domain. In contrast to prior phononic filters that utilize gain or loss based on stimulated Brillouin scattering, optical amplification is not used to mediate signal processing. This emit-receive functionality, realized in an integrated silicon waveguide, produces megahertz-bandwidth bandpass filtering while supporting low RF insertion losses necessary for high dynamic range in a microwave photonic link. We also demonstrate record-high internal efficiency for emit-receive operations of this type, and show that the emit-receive operation is uniquely suitable for the creation of serial filter banks with minimal loss of fidelity. This photonic-phononic emitter-receiver represents a new method for low-distortion signal processing in an integrated all-silicon device.