Magnet-Free Quasi-Electrostatic Circulators and Topological Insulators Based on Temporal Modulation​

Devices with non-reciprocal functionalities are crucial for wireless communications, radar/imaging systems and for the growing field of quantum computing. 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. Several approaches to achieve magnet-free non-reciprocity have been explored in the past few years, including the use of active voltage-/current- biased transistors and nonlinearities. However, these approaches have found limited application due to their poor noise and linearity performance, limitations on the range of signal power for which nonreciprocity can be achieved, and signal distortions. 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. In Phase I of this project we have set the basis to successfully implement ultrabroadband, ultracompact circulator, and arrays of them, applying this quasi-electrostatic slow-wave response to enable integrated circulators and topological insulators that overcome all the challenges that have hindered their broad commercialization to date. The goal of Phase II will be to translate this initial success into a practical device, operating at higher frequencies, aiming at mm-wave frequencies, and demonstrating ultra-compact, ultra-broadband circulators with low insertion loss that do not rely on resonant mechanisms, but instead operate essentially independent of frequency. We have also explored arrays of such elements to demonstrate the analogue of Floquet topological insulators. In Phase 1 of this project we have realized a first prototype of such a device, and have also realized its exciting opportunities for broadband slow-waves, enabling to overcome in a uniquely robust way the delay-bandwidth limit for practical technologies. Overall, our efforts in Phase II will address the residual challenges hindering the commercialization of magnet-free nonreciprocal and true-time-delay technology, by extending the bandwidth by orders of magnitude compared to current state-of-the-art, reducing their footprint and adding robustness and real-time reconfigurability.