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.

Ab initio computational analysis of spectral properties of dielectric spheroidal resonators interacting with a subwavelength nanoparticle

“…dependence on e saturates so that when the ellipticity exceeds some crossover value cr e , the splitting remains virtually independent of e. The crossover value relatively small that all realistic nominally spherical solid resonators are characterized by ellipticity parameters cr e e > . The regime cr e e < can be in principle achieved in liquid droplets actuated as resonators, which recently started attracting significant attention [91][92][93][94][95]. Experiments with liquid droplets controlled by optical tweezers might provide the experimental verification of the effects presented in Figure 4.…”

Cavity optocapillaries

“…Continuous research in droplet optical resonators [16][17][18][19][20] has led to the recent demonstration of water droplets with ultrahigh-finesse [21]. In this demonstration, photons are confined in a tight, 180 nm region, adjacent to the droplet interface ( Fig.…”

“…For this reason, it is natural to ask if droplets with high optical-finesse can provide resonantly-enhanced access to thermal capillaries. Ideally, a 10 6 -finesse droplet, as reported in [21], can improve displacement resolution by a factor of a million. Yet being modest here, we investigate a 520-finesse system, where a 1% change in optical transmission represents a 0.026 Å droplet deformation.…”

“…This transmission can be easily measured with a photodetector. Relying on this principle, we use the optical mode [16][17][18][19][20][21] as a probe that optically interrogate the drop's thermal capillary oscillations [22,23]. As one can see in Fig.…”

“…Substituting typical values, the thermal capillary motion of an r=10 m droplet, at room temperature, is Δr = 1.8 Å. We fabricate our water-droplet resonator by dipping one side of a silica stem in a practically unlimited water reservoir [21]. As silica is hydrophilic, water creeps up the stem forming a droplet at its end ( Fig.…”