title: Water-walled microfluidics for high-optical finesse cavities.
abstract: In submerged microcavities there is a tradeoff between resonant enhancement for spatial water and light overlap. Why not transform the continuously resonating optical mode to be fully contained in a water microdroplet per se? Here we demonstrate a sustainable 30-μm-pure water device, bounded almost completely by free surfaces, enabling >1,000,000 re-circulations of light. The droplets survive for >16 h using a technique that is based on a nano-water bridge from the droplet to a distant reservoir to compensate for evaporation. More than enabling a nearly-perfect optical overlap with water, atomic-level surface smoothness that minimizes scattering loss, and ∼99% coupling efficiency from a standard fibre. Surface tension in our droplet is 8,000 times stronger than gravity, suggesting a new class of devices with water-made walls, for new fields of study including opto-capillaries.
authors.affiliation: Mechanical Engineering Department, Technion-Israel Institute of Technology, 32000 Haifa, Israel.
authors.forename: Shai
authors.initials: S
authors.lastname: Maayani
authors.affiliation: Mechanical Engineering Department, Technion-Israel Institute of Technology, 32000 Haifa, Israel.
authors.forename: Leopoldo L
authors.initials: LL
authors.lastname: Martin
authors.affiliation: Mechanical Engineering Department, Technion-Israel Institute of Technology, 32000 Haifa, Israel.
authors.forename: Tal
authors.initials: T
authors.lastname: Carmon