  Nanomechanical resonators can serve as ultrasensitive, miniaturized force
probes. While vertical structures like nanopillars are ideal for this purpose,
transducing their motion is challenging. Pillar-based photonic crystals (PhCs)
offer a potential solution by integrating optical transduction within the
pillars. However, achieving high-quality PhCs is hindered by inefficient
vertical light confinement. Here, we present a full-silicon 1D photonic crystal
cavity based on nanopillars as a new platform with great potential for
applications in force sensing and biosensing areas. Its unit cell consists of a
silicon pillar with larger diameter at its top portion than at the bottom,
which allows vertical light confinement and an energy bandgap in the near
infrared range for transverse-magnetic (TM) polarization. We experimentally
demonstrate optical cavities with Q-factors exceeding 1e3 constructed by
inserting a defect within a periodic arrangement of this type of pillars. Given
the fact that that each nanopillar naturally behaves as a nanomechanical
cantilever, the fabricated geometries are excellent optomechanical (OM)
photonic crystal cavities in which the mechanical motion of each nanopillar
composing the cavity can be optically transduced. These novel geometries
display enhanced mechanical properties, cost-effectiveness, integration
possibilities, and scalability, and opens and new path in front of the widely
used suspended Si beam OM cavities made on silicon-on-insulator.
