The optical and mechanical properties of silicon and silica glass make the silicon-on-insulator material system a platform natural for photonics and challenging for phononics. High index-contrast enables index-guiding in silicon waveguides on glass, but silicon's relative stiffness and high sound velocity hampers analogous efforts to ``index-guide'' acoustic waves. Waveguide geometry plays fundamentally different roles in the dispersion of mechanical and optical waves, enabling radiation-free waveguiding in high aspect-ratio cantilevers defined in silicon. We fabricate silicon fins, here 80 nm wide in 340 nm SOI, that exhibit low-loss mechanical resonances at 600-700 MHz.
We present designs, numerical studies, and the first measurements of release-free optomechanical “fin cavities” in 340 nm SOI. The dispersion of flexural fin mechanical modes is readily engineered by variation of the fin's width. TE and TM optical cavities at telecom frequencies are made with an adjoined nanobeam. Nanobeam geometry independently influences the optics decoupling optical and mechanical design problems. Optical and mechanical modes can be colocalized with a simple cavity where a parabolically curved fin is placed near a photonic crystal waveguide. We simulate and measure optical and mechanical spectra of these devices. Optomechanical interaction rates ranging from low kHz to 500 kHz for the fin cavities are demonstrated. Furthermore, by analyzing the interaction rates we identify the different optical modes of these structures. The demonstrated SOI fin cavities create new opportunities for quantum optomechanical sensing in a truly CMOS-compatible setting.
Christopher J. Sarabalis, Jeff T. Hill, and Amir H. Safavi-Naeini, "Cavity optomechanics in silicon-on-insulator (Conference Presentation)," Proc. SPIE 10112, Photonic and Phononic Properties of Engineered Nanostructures VII, 101121Y (Presented at SPIE OPTO: February 03, 2017; Published: 28 April 2017); https://doi.org/10.1117/12.2253180.5395679929001.
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