Water-walled microfluidics for high-optical finesse cavities

• Published in: Nature communications Vol. 7; no. 1; p. 10435
• Main Authors: Maayani, Shai, Martin, Leopoldo L., Carmon, Tal
• Format: Journal Article
• Language: English
• Published: London Nature Publishing Group UK 22.01.2016; Nature Publishing Group; Nature Portfolio
• Subjects: 639/766/400; Humanities and Social Sciences; multidisciplinary; Science; Science (multidisciplinary)
• ISSN: 2041-1723; 2041-1723
• DOI: 10.1038/ncomms10435

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. Micrometre-sized spheres of water can trap light, but they quickly evaporate and the light is lost. Here, the authors create water-droplet microcavities that can contain light for one million circulations by replenishing the evaporating fluid from a reservoir.