Bricks-on-pedestals silicon optomechanical cavity: a mass sensor for nanoparticles detection

Optomechanical cavities can be used as highly sensitive mass sensors actuated by an optical field. In this work, we introduce and numerically demonstrate a new design for an optomechanical cavity consisting of a series of asymmetrically distributed rectangular silicon nanobricks, with each brick acting as an independent mechanical resonator but all coupled to the same optical field. Each silicon brick is placed on top of a thin silica pillar that ensures mechanical support whilst providing enough acoustic isolation between the individual mechanical resonances - at GHz frequencies - of each brick. The mass sensing capabilities of this cavity are studied through numerical simulations, proving that a point mass approximation can be used for silica nanoparticles with a radius smaller than 100 nm and that different nanoparticles can be measured independently but simultaneously and in real-time.