Strong\nCavity-Optomechanical Transduction of Nanopillar\nMotion

Nanomechanical resonators\ncan serve as ultrasensitive, miniaturized\nforce probes. While vertical structures such as nanopillars are ideal\nfor this purpose, transducing their motion is challenging. Pillar-based\nphotonic crystals (PhCs) offer a potential solution by integrating\noptical transduction within the pillars. However, achieving high-quality\nPhCs is hindered by inefficient vertical light confinement. Here,\nwe present a full-silicon photonic crystal cavity based on nanopillars\nas a platform for applications in force sensing and biosensing areas.\nIts unit cell consists of a silicon pillar with a larger diameter\nat its top portion than at the bottom, which allows vertical light\nconfinement and an energy band gap in the near-infrared range for\ntransverse-magnetic polarization. We experimentally demonstrate optical\ncavities with <i>Q</i> factors exceeding 10<sup>3</sup>,\nconstructed by inserting a defect within a periodic arrangement of\nthis type of pillars. Each nanopillar naturally behaves as a nanomechanical\ncantilever, making the fabricated geometries excellent optomechanical\n(OM) photonic crystal cavities in which the mechanical motion of each\nnanopillar composing the cavity can be optically transduced. These\ngeometries display enhanced mechanical properties, cost-effectiveness,\nintegration possibilities, and scalability. They also present an alternative\nin front of the widely used suspended Si beam OM cavities made on\nsilicon-on-insulator substrates.