High-speed transient sensing using dielectric micro-resonators

Abstract

In this paper, we demonstrate the use of whispering gallery mode (WGM) resonators for high-speed transient sensing. In the typical WGM sensor, the micro-resonator modes are interrogated by coupling light from a tunable laser through a single mode optical fiber. The laser is tuned over a narrow range by thermo-optic effect, and mode shifts in the transmission spectrum through the fiber are observed. For high-speed applications, thermal inertia of the optical system impedes the proper tuning of the laser, limiting the WGM sensor applications to slow varying phenomena. In order to use the sensors for high-speed transient applications, we tune the DFB laser using a harmonic rather than a ramp waveform and calibrate the laser response at various input frequencies and amplitudes using a Fabry-Perot interferometer. WGM shifts are tracked using a fast cross-correlation algorithm on the transmission spectra. We demonstrate dynamic force measurements up to 10 kHz using this approach. We also present a simple lumped-heat capacity thermal model to predict the laser response.