SILICON AUDIO RF CIRCULATOR LLC STTR Phase I Award, May 2022

Devices with non-reciprocal functionalities are common in wireless communications, quantum computing and radar/imaging systems. Traditionally, these functionalities are achieved using ferrite materials biased by an external magnetic field. Unfortunately, such materials face significant challenges: they are scarcely available, and they are not compatible with existing semiconductor manufacturing processes, leading to large size and high implementation costs. Our team has pioneered low-noise and linear magnet-free non-reciprocity through spatio-temporal modulation across several physical domains, including acoustics, microwave electronics and optics. Our approach has been based on the use of time modulation to induce a form of synthetic motion that mimics an angular momentum bias, taking inspiration from the fact that wave propagation in moving media is non-reciprocal. While promising, this approach has so far shown a fundamental trade-off between footprint, bandwidth and modulation speeds, since we relied on degenerate resonances to induce slow waves that facilitated strong wave-matter interactions – and hence nonreciprocity – through suitable temporal modulations. This limitation has hindered the broad applicability of these concepts and their commercialization. However, in a recent breakthrough our team has demonstrated that networks of switched capacitors can realize quasi-electrostatic wave propagation, slowing down the wave well beyond the delay-bandwidth limit, leading to ultra-wideband phase delays within very compact footprints. In this project, we will apply this quasi-electrostatic slow-wave response to enable integrated circulators that overcome all the challenges that have hindered their broad commercialization to date. We will demonstrate and commercialize ultra-compact, ultra-broadband circulators with low insertion loss that do not rely on resonant mechanisms, but instead operate essentially independent of frequency. We will also extend our efforts to arrays of these elements to realize the analogue of topological insulators for microwave radiation, adding intrinsic robustness of the response and real-time multiplexing to the benefits of the individual elements.