Large-range and high-sensitivity displacement sensing based on a SNAP microresonator by multimode encoding technique

Probe-type micro-displacement sensors with a large range and high sensitivity have important applications in both aerospace and nano-lithography. However, the state-of-the-art measurement range achieved using conventional methods such as charge coupled device imaging and fiber grating demodulation is limited to only tens of micrometers. In this study, we propose and demonstrate a displacement sensing mechanism with a large range and high sensitivity for measuring linear displacements. The mechanism is based on a multimode encoding technique implemented on a surface nanoscale axial photonics (SNAP) microcavity platform. By tracking the transmittance variations of multiple axial modes and employing encoding techniques, we can determine the rough absolute position as well as the axial mode with the highest sensitivity in each region. Moreover, the selected mode for each region is exploited to accurately measure the micro-displacement with a large range and high accuracy. As a proof-of-principle experiment, the results indicate a large sensing range about 346 mu m and a high sensitivity ranging up to 0.013 mu m(-1). Assuming that the transmittance can be resolved by 0.1%, the resolution of the measurement is about 0.1 mu m.