On-chip read-out of picomechanical motion under ambient conditions

Abstract

Monitoring the nanomechanical movement of suspended cantilever structures has found use in applications ranging from biological/chemical sensing to atomic force microscopy. Interrogating these sensors relies on the ability to accurately determine the sub-nanometre movements of the cantilever. Here we investigate a technique based on the combination of integrated silicon photonics and microelectromechanical systems (MEMS) to create an optically resonant microcavity and demonstrate its use for monitoring of the position of cantilevers on the picometer scale under ambient conditions with dynamic range extending over several microns. The technique is interferometric, and we show it to be sufficiently sensitive to measure both the first and second modes of cantilever Brownian motion. We anticipate that application of this technique will provide a physically robust, picometer precision, integrated cantilever movement read-out technology which can take cantilever sensors from laboratory controlled environments into real world conditions, allowing everyday applications.

Towards MEMS-based chem/bio sensing arrays with on-chip optical read-out

“…Destructive interference reduces output signal to minimum at this separation. Figure 2 (c) compares simulation and measurement results for suspended microcantilever as a function of the waveguidemicrocantilever gap [16,17]. The intensity of the light transmitted through the waveguide is amplitude modulated by movement of the MEMS microcantilever.…”

“…To test the experimental detection limits of the presented read-out system, and we attempted to detect movement of the cantilever due to room temperature stimulated thermal Brownian motion [17]. Measurements for the Brownian motion were conducted by connecting the signal from the optical output grating directly to an Agilent ESA-E Series model E4402B spectrum analyzer.…”

“…Predicted Brownian Motion: Ref [17] Measured Laser/Experimental Noise Measured Optical Transmission Fig. 3.…”

“…3. Measured optical power modulation of the read-out device compared to the predicted Brownian noise envelope for the cantilever [17]. Measurement of the noise of the laser when coupled through the chip without an overlying cantilever is also presented…”

“…Some of the light travelling through an underlying waveguide is allowed to diffract and reflect from the underside of the sensing cantilever back into the waveguide resulting in optical interference that is dependent on the waveguide-cantilever separation (c) The optical field distributions for propagated 1550nm light simulated using FDTD modeling in MEEP when the cantilever is at the height required to create (a) constructive and (b) destructive interference[16]. (c) Measured optical power transmitted through the device for two vibration cycles of a suspended cantilever (full circles) compared to 2D FDTD simulation results (dashed line) as a function of the waveguide-cantilever gap[17]…”