Achieving non-reciprocal light propagation via stimuli that break time-reversal symmetry, without magneto-optics, remains a major challenge for integrated nanophotonic devices. Recently, optomechanical microsystems in which light and vibrational modes are coupled through ponderomotive forces, have demonstrated strong non-reciprocal effects through a variety of techniques, but always using optical pumping. None of these approaches have demonstrated bandwidth exceeding that of the mechanical system, and all of them require optical power, which are both fundamental and practical issues. Here we resolve both of these challenges through breaking of time-reversal symmetry using an acoustic pump in an integrated nanophotonic circuit. GHz-bandwidth optomechanical non-reciprocity is demonstrated using the action of a 2-dimensional surface acoustic wave pump, that simultaneously provides non-zero overlap integral for light-sound interaction and also satisfies the necessary phase-matching. We use this technique to produce a simple frequency shifting isolator (i.e. a non-reciprocal modulator) by means of indirect interband scattering. We demonstrate mode conversion asymmetry up to 15 dB, efficiency as high as 17%, over bandwidth exceeding 1 GHz.Non-reciprocal devices, in which time reversal symmetry is broken for light propagation, provide critical functionalities for signal routing and source protection in photonic systems. The most commonly encountered nonreciprocal devices are isolators and circulators, which can be implemented using a variety of techniques encompassing magneto-optics [1, 2], parity-time symmetry breaking [3], spin-polarized atom-photon interactions [4,5], and optomechanical interactions [6][7][8][9][10][11][12]. On the other hand, recent developments 1 arXiv:1707.04276v2 [physics.optics] 25 Jul 2017 reveal a much broader and compelling vision of using time-reversal symmetry breaking for imparting protection against defects, through analogues of the quantum Hall effect [13] in both topological [14][15][16] and non-topological systems [17].The use of optomechanical coupling [18] for breaking time-reversal symmetry via momentum biasing [12,19] and synthetic magnetism [10,11] is particularly attractive since strong dispersive features can be readily produced, without needing materials with gain or magneto-optical activity. Additionally, the potential for complete isolation with ultralow loss [7] is a significant advantage over state-of-the-art in chip scale magneto-optics. All these systems feature dynamic reconfigurability through the pump laser fields and can potentially be implemented in foundries with minimal process modification. Unfortunately, all realizations of optomechanical nonreciprocal interactions to date only operate over kHz-MHz bandwidth. This fundamental constraint arises simply because the interaction is determined by the mechanical linewidth, which is traditionally 6-9 orders of magnitude lower than the optical system (potentially several THz). In this work we present a new appro...

Low-loss optical isolators and circulators are critical nonreciprocal components for signal routing and protection, but their chip-scale integration is not yet practical using standard photonics foundry processes. The significant challenges that confront integration of magneto-optic nonreciprocal systems on chip have made imperative the exploration of magnet free alternatives. However, none of these approaches have yet demonstrated linear optical isolation with ideal characteristics over a microscale footprint – simultaneously incorporating large contrast with ultralow forward loss – having fundamental compatibility with photonic integration in standard waveguide materials. Here we demonstrate that complete linear optical isolation can be obtained within any dielectric waveguide using only a whispering-gallery microresonator pumped by a single-frequency laser. The isolation originates from a nonreciprocal induced transparency based on a coherent light-sound interaction, with the coupling originating from the traveling-wave Brillouin scattering interaction, that breaks time-reversal symmetry within the waveguide-resonator system. Our result demonstrates that material-agnostic and wavelength-agnostic optical isolation is far more accessible for chip-scale photonics than previously thought.

The transport of sound and heat, in the form of phonons, can be limited by disorder-induced scattering. In electronic and optical settings the introduction of chiral transport, in which carrier propagation exhibits parity asymmetry, can remove elastic backscattering and provides robustness against disorder. However, suppression of disorder-induced scattering has never been demonstrated in non-topological phononic systems. Here we experimentally demonstrate a path for achieving robust phonon transport in the presence of material disorder, by explicitly inducing chirality through parity-selective optomechanical coupling. We show that asymmetric optical pumping of a symmetric resonator enables a dramatic chiral cooling of clockwise and counterclockwise phonons, while simultaneously suppressing the hidden action of disorder. Surprisingly, this passive mechanism is also accompanied by a chiral reduction in heat load leading to optical cooling of the mechanics without added damping, an effect that has no optical analog. This technique can potentially improve upon the fundamental thermal limits of resonant mechanical sensors, which cannot be attained through sideband cooling.

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