Time-reversal symmetry breaking with acoustic pumping of nanophotonic circuits


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 has demonstrated bandwidth exceeding that of the mechanical system, and all of them require optical power; these are both fundamental and practical issues. Here, we resolve both challenges by breaking time-reversal symmetry using a two-dimensional acoustic pump that simultaneously provides a non-zero overlap integral for light–sound interaction and also satisfies the necessary phase-matching. We use this technique to produce a non-reciprocal modulator (a frequency shifting isolator) by means of indirect interband scattering. We demonstrate mode conversion asymmetry up to 15 dB and efficiency as high as 17% over a bandwidth exceeding 1 GHz.

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Fig. 1: Conceptual schematic of acoustically pumped non-reciprocal nanophotonic modulator.
Fig. 2: Non-reciprocal nanophotonic modulator.
Fig. 3: Experimental set-up and characterization.
Fig. 4: Experimental demonstration of non-reciprocal optomechanical modulation.
Fig. 5: Modulation efficiency measured as a function of RF drive power.


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This material is based on research sponsored by the US Air Force Research Laboratory (AFRL) under agreement no. FA9453-16-1-0025 and by the US Air Force Office of Scientific Research (Young Investigator grant FA9550-15-1-0234). The US Government is authorized to reproduce and distribute reprints for Governmental purposes notwithstanding any copyright notation thereon. The views and conclusions contained herein are those of the authors and should not be interpreted as necessarily representing the official policies or endorsements, either expressed or implied, of AFRL and the Defense Advanced Research Projects Agency (DARPA) or the US Government. D.B.S. would also like to acknowledge support from a US National Science Foundation Graduate Research Fellowship.

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D.B.S. and G.B. conceived the idea and, with S.K., developed the theory. D.B.S. fabricated the device, conducted the experiment and analysed the data. All authors contributed to writing the paper. G.B. supervised all aspects of this project.

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Correspondence to Gaurav Bahl.

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Supplementary Information

Supplementary theory and results; Supplementary Table 1; Supplementary Figures 1–7; Supplementary references.

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Sohn, D.B., Kim, S. & Bahl, G. Time-reversal symmetry breaking with acoustic pumping of nanophotonic circuits. Nature Photon 12, 91–97 (2018). https://doi.org/10.1038/s41566-017-0075-2

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