Fiber Optic Interferometry for Nanomechanical Displacement Detection

Nanoelectromechanical (NEMS) resonators, with their small masses, high frequencies, and low energy dissipation, show potential for sensitive and precise applications in detecting mass, force, and other physical quantities. Optical interferometry is an important tool for NEMS. Most NEMS instruments utilize costly and hard-to-tune free-space design, whereas fiber optic methods have the potential to be more stable, compact, and cost-effective. We present an interferometer and an imaging system based on a fiber-optic circulator and a 635 nm laser. Having passed through the fiber, light is reflected from the NEMS surface and from the tip of the fiber. The circulator directs reflected light to the detector, where interference of the two reflected beams occurs. For alignment purposes, we developed an imaging system that utilizes the nature of this interference by taking the relative magnitude of the returning signal at each point in a raster scan of an area as large as 40 x 40 µm on the sample. This data is compiled with each data point being a pixel that's brightness corresponds to the relative signal intensity. Excited using an ultrasound transducer, NEMS oscillations cause oscillations of the interference signal that are recorded with a spectrum analyzer. The results of this system are presented. The authors are thankful to Atakan B. Ari and M. Selim Hanay for providing our sample and Kamil Ekinci for continuous help.