Multi-mode optomechanical systems have formed the basis of recent proposals and experiments, enabling optical frequency translation and hybridization of near-resonant mechanical modes. An important question is how to control the internal mechanical states of such systems using laser light. Such control enables engineering of effective nonlinearities for phonons, allowing phonon-phonon frequency translation, mechanical entanglement, and precision metrology. On-chip engineered nanostructures are particularly suitable for exploring multi-mode systems.
Here, we consider a silicon nanobeam optomechanical crystal with two mechanical modes coupled to a common optical mode. Simulations of the phonon-phonon scattering parameters of the system suggest that large conversion efficiency can be obtained at cryogenic temperatures. We show that remarkably, phonon-phonon conversion efficiency near unity is achievable, even when the loss rate of the intermediate optical mode dominates all other rates in the system by several orders of magnitude. This counter-intuitive phenomenon is the result of a long-lived mechanical dark state of the system that arises in the optical pumping scheme being used. We experimentally demonstrate two GHz frequency mechanical modes, separated by nearly 300 MHz, coupled to a first-order common optical TE mode with vacuum coupling rates of nearly 500 kHz. By optically driving the optomechanical crystal with two tones separated by the mechanical difference frequency we present evidence for optically induced phonon-phonon interactions at room temperature. We will present results of measurements in a cryogenic environment, operating at 4 Kelvin demonstrating improved large phonon-phonon conversion efficiency.
Rishi N. Patel, Wentao Jiang, Zhaoyou Wang, Jeff T. Hill, Christopher J. Sarabalis, and Amir H. Safavi-Naeini, "Laser-induced phonon-phonon interactions in an on-chip silicon optomechanical crystal (Conference Presentation)," Proc. SPIE 10112, Photonic and Phononic Properties of Engineered Nanostructures VII, 101121Z (Presented at SPIE OPTO: February 03, 2017; Published: 28 April 2017); https://doi.org/10.1117/12.2253031.5395679930001.
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