Nanoscale displacement measurement in a variable-air-gap optical waveguide

Instead of analyzing the fringe shift that was recently developed by us to detect slight displacement, an alternative approach by monitoring changes in the intensity of the light reflected from a variable-air-gap optical waveguide is presented in this work. Owing to the sensitive feature of the ultrahigh-order modes, a 1.7nm resolution of displacement measurement is demonstrated without any complicated optical interference system and servotechniques.