Radiation-Pressure-Antidamping Enhanced Optomechanical Spring Sensing

On-chip refractive index sensing plays an important role in many fields, ranging from chemical, biomedical, and medical to environmental applications. Recently, optomechanical cavities have emerged as promising tools for precision sensing. In view of the sensors based on optomechanical cavities, the Q factor of mechanical modes is a key parameter for achieving high sensitivity and resolution. Here we demonstrated an integrated optomechanical cavity based on a silicon nanobeam structure. Our cavity supports a fundamental mechanical mode with a frequency of 4.36 GHz and a record-high mechanical Q of 18300 in the ambient environment, facilitated by the radiation-pressure antidamping. The distinctive nature of the optomechanical spring sensing approach combined with our high mechanical Q silicon cavity allows for a sensing resolution of (delta lambda/lambda(0) similar to 10(-7), which is at least 1 order of magnitude higher than that of conventional. silicon-based approaches and paves the way for on-chip sensors with unprecedented sensitivity.