Cavity-Electro-Optomechanical Circuits with Broken Time-Reversal Symmetry

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Light generally travels in two-way streets - a forward propagating light is accompanied by a backward propagating light if it undergoes reflection. To eliminate the backward propagating cousin requires time-reversal symmetry breaking of light. This is challenging because photons - the quanta of light- do not carry charge and thus do not interact with magnetic fields which are the force behind time-reversal symmetry breaking of charged particles, such as electrons. Reflection-free light propagation is important to optical information communications, in particular for stabilizing laser frequencies and mitigating signal decay. In a miniaturized setting, today's integrated photonic microchips use low-power and broadband optical elements to perform information processing and communication unavailable with conventional electronic counterparts. Just like an optical network, the proper functioning of the photonic microchips also benefits from reflection-eliminating devices. The chip-scale realization of these devices, so called optical isolators, remains an outstanding challenge. It is known that time-reversal symmetry of light can be broken by inducing time-modulation of media's refractive index. An effective means of such time-modulation can be achieved by exciting acoustic waves in the optical media which perturb local electric polarization density. In this context, this program will explore time-reversal symmetry breaking induced by the interaction between light and mechanical motion, and study non-reciprocal light propagation and associated new physics in artificial optomechanical structures realized on microchips. The potential broader impact of this work lies primarily in the development of new devices and methodologies for integrated photonic technologies, in the education of students in this important field through hands-on research and new courses, and in the improvement of societal benefits with new generations of optoelectronic products.The proposed program aims at developing an innovative family of integrated photonic circuits with broken time-reversal symmetry, enabled by radiation pressure force in coupled electro-optomechanical resonators. Cavity-optomechanical systems, involving the coupling of light intensity to mechanical motion via radiation pressure at wavelength scale, create the requisite large optical nonlinearities for explicitly time-reversal symmetry breaking. The use of phase-correlated parametric optical pumps for controlling individual cavities highlights the approach of programmable synthetic fields, which leads to optical and acoustic nonreciprocity, and may even reveal topological wave interference in large-scale optomechanical structures. Piezoelectric driving of steady state mechanical motion, for inducing photonic transition in multimode optomechanical cavities as another means to break time-reversal symmetry, can be used to boost the bandwidth of cavity-electro-optomechanical circuits beyond the mechanical damping rate. Most prominent of this work will be studying nonreciprocal photon-phonon interactions in electro-optomechanical circuits, and realizing important photonic device applications including non-magnetic circulators and robust delay lines. New physics bearing topological properties in optomechanical crystals driven by mechanical motion will also be investigated. The intellectual merit of this proposal lies primarily in the development of a new paradigm of nanophotonic network architecture that will unlock new lines of research, from optical NEMS to topological optomechanics, and enable transformative technologies for microwave photonics, communications, and quantum information.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.