Figure 10
Optomechanical data acquisition. a) Schematic of the mechanism by which "tuned-to-the-slope" cavity optomechanical detection is performed. We begin with an unperturbed optical cavity, with a resonance lineshape (solid, blue) centered at ω 0. The periodic displacement x of the mechanical resonator shifts this resonance by an amount Δω, producing a new trace (dashed, red) centered at ω(x). By tuning our laser to the observation frequency ω obs, the optical transmission (inset, green) oscillates in time at the mechanical device’s resonance frequency. This signal is maximized by choosing ω obs to be the value at which the optical resonance has maximum slope. Note that the schematic is exaggerated to better illustrate this effect. b) Plot of optomechanical data taken for a microcantilever side-coupled to an optical microdisk, as seen in Figure 9c. The solid blue trace is produced by scanning our laser frequency around an optical cavity resonance and monitoring DC transmission through the tapered fiber coupled to the device. While performing this scan, we simultaneously monitor the AC transmission signal through the fiber at the mechanical device’s resonance frequency, using a lock-in amplifier. By virtue of our optomechanical transduction scheme, this signal represents the peak value of the mechanical motion and is plotted in green. The dashed line is a numerical derivative of the optical trace normalized such that is has the same peak value as the green data, which indicates that mechanical signal is optimized at the points of highest slope in the optical resonance.