Magnet-Free Non-Reciprocal Photonic Platform Based on Time-Modulated Graphene

We propose a novel paradigm to achieve giant photonic non-reciprocity based on time-modulated graphene capacitors coupled to photonic waveguides, without reliance on any magneto-optic effects. The resulting hybrid graphene-dielectric platform is low-loss, silicon-compatible, robust against graphene's imperfections, scalable from terahertz to near infrared frequencies, and it exhibits very large nonreciprocal responses using realistic biasing schemes. Analytical frameworks based on solving the eigenstates of the modulated structure and on spatial coupled mode theory have been developed to unveil the underlying physics that dominate the proposed platform and to quickly design and analyze various isolators. Results, validated through harmonic balance full-wave simulations, confirm the flexibility of our low-loss (<3dB) platform to engineer a wide variety of responses and even to extend the isolation bandwidth. We envision that this technology will pave the wave to magnetic-free, fully-integrated, and CMOS-compatible nonreciprocal components with wide applications in sensing, communication systems, and optical networks.