High-resolution Fabry-Perot interferometry is being developed and employed for demanding applications in mechanical displacement metrology.
Fabry-Perot interferometry has the highest resolution of any displacement sensor, below one picometer, and yet may be used to measure displacements of many centimeters. Equally important, it enables a natural and direct link to the SI unit of length, defined in terms of the speed of light. We are adapting this measurement technique to various challenges. One project underway is a new "calculable capacitor," which realizes the electrical unit of capacitance, the Farad, in terms of the mechanical displacement of an electrode over 5 – 10 cm. Ultimately the displacement will be linked to an atomic time standard via a femtosecond-laser frequency comb. Another project involves various types of MEMS accelerometers, in which the motion of a micromechanical resonator is probed with high bandwidth to realize an acceleration measurement that is directly traceable to SI units. The details of the measurements drive the use of various cutting-edge technologies, including frequency combs, narrow-linewidth tunable lasers, and a variety of optical modulation techniques.