Narrowing the filter lineshape of microwave photonic device
Narrowing the filter lineshape of microwave photonic device lead image
Microwave-photonic signal processing can help utilize the wideband and low-loss properties of optical systems in the microwave domain. This hybrid form of signal processing promises to enable high speed, large bandwidth telecommunication and radar technologies of the future.
While it is possible to perform wideband signal processing in the optical domain, the sizable difference in frequencies between microwaves and light waves makes it difficult to achieve narrowband microwave filters. Gertler et al. present a narrowband, tunable filter in a silicon-based photonic-phononic emit-receive device. The device enhances the narrowband signal processing capabilities of photonic circuits by accessing acoustic phonons.
The authors coupled the optical and acoustic fields in the device through a Brillouin scattering process. The long-lived acoustic fields allowed the microwave signal to be filtered as it was transduced between the optical and acoustic domains. This resulted in narrower filter lineshapes than previously reported in silicon-based microwave phononics, which the authors said may enable new capabilities for signal processing.
A phononic crystal, which only let sound waves of specific wavelengths propagate in the device, suppressed frequencies outside the filtered region and resulted in a sharp, multi-pole filter lineshape. The filter can be tuned over a wide range of frequencies without degrading its lineshape.
“Some of the possibilities enabled by this work is to design filters with different frequency responses, taking advantage of the versatility of the photonic-phononic scheme,” said author Shai Gertler. “Furthermore, we can develop schemes that will enable a wider tunability range.”
The device’s demonstrated repeatability and stability of operation led the authors to believe this work could potentially enhance the performance of silicon-based microwave photonics.
Source: “Tunable microwave-photonic filtering with high out-of-band rejection in silicon,” by Shai Gertler, Eric A. Kittlaus, Nils Otterstrom, and Peter T. Rakich, APL Photonics (2020). The article can be accessed at https://doi.org/10.1063/5.0015174 .
