Microresonator-based mid-IR devices

Abstract

High optical quality (high-<i>Q</i>) whispering-gallery mode (WGM) microresonators are key enablers for numerous highperformance photonic devices, including ultrasensitive molecular detectors and advanced light sources such as narrowlinewidth lasers and comb generators. For sensing applications, the unique characteristics of such WGM devices appear to be particularly relevant in the mid-IR (MIR) spectral region because of the stronger molecular absorption bands in this spectral region. However, most current WGM-based passive and active devices function in the near-IR (NIR) spectral region. We propose the development of reproducible high-<i>Q</i> WGM microresonators for the MIR by using low phonon energy glasses (such as fluorides, chalcogenides, and tellurides) along with an elegant and reproducible microsphere fabrication technique based on the use of novel state-of-the-art microheaters. In this paper, we first review the current state-of-the-art of WGM MIR microresonators and related optoelectronic devices, and then present recent results of our work on fabrication and characterization of high-<i>Q</i> WGM optical microresonators with several fluoride (ZBLAN, InF₃ and AlF₃) glasses. Intrinsic quality factors in excess of ten million have been measured in the NIR regime in the fluoridebased microspheres fabricated in our lab with the proposed -- highly reliable and reproducible – microheater fabrication method, and similar or better performances are expected from similar microspheres at MIR wavelengths between 2 to 5 microns. We next discuss potential applications of these microresonators, notably for low-threshold and narrowlinewidth MIR lasers and MIR comb applications.