ACS Photon. https://doi.org/cvsj (2018)

On-chip optical sensors based on optomechanical resonances are potentially attractive for refractive index sensing for chemical, biological, medical and even environmental analysis, yet greater precision is still desired. Fei Pan and colleagues at Tsinghua University, Beijing, have now demonstrated an integrated optomechanical cavity based on a silicon nanobeam structure that they say exhibits a record (in an ambient environment) mechanical quality factor of 18,300. This mechanical quality factor is predicted to allow sensing with a sensitivity on the order of 10–7, which the authors say is an order of magnitude higher than that of conventional silicon-based approaches. The improvement is due to radiation-pressure antidamping; in particular, the linewidth of the mechanical resonance is effectively reduced by optical forces. The structure is a 556-nm-wide and 220-nm-tall Si beam with periodic hole-array mirrors containing a central defect. It should be noted that the authors have not yet conducted a sensing experiment and that the sensitivity was inferred.