Dual-Carrier Floquet Circulator with Time-Modulated Optical Resonators

Spatiotemporal modulation has shown great promise as a strong time-reversal symmetry breaking mechanism that enables integrated nonreciprocal devices and topological materials at optical frequencies. However, ideal circulator and isolator performance has relied on spatial symmetry or momentum matching between modulation and optical modes. The resulting systems have been challenging to experimentally realize, due to the prohibitively complex and lossy biasing networks and tight fabrication tolerances that maintain the desired rotational and mirror symmetries. In this work, we propose a microresonator Floquet circulator that leverages the previously untapped degrees of freedom of the modulation, through waveforms with strong harmonic components. The Floquet circulator response exhibits ideal on-resonance isolation and supports broadband forward transmission with no trade-off in insertion loss. We present a numerical demonstration in an on-chip photonic crystal platform with just two modulated resonators requiring no rotational symmetry. Moreover, this approach is general and can leverage a variety of modulation mechanisms while not being limited by pump depletion and signal distortion associated with parametric nonlinear systems.