3D printed mounts for microdroplet resonators

Abstract

Liquid microdroplet resonators provide an excellent tool for optical studies due to their innate smoothness and high quality factors, but precise control over their geometries can be difficult. In contrast, three dimensional (3D) printed components are highly customizable but suffer from roughness and pixelation. We present 3D printed structures which leverage the versatility of 3D printing with the smoothness of microdroplets. Our devices enable the reliable creation of microdroplet resonators of varying shapes and sizes in an ambient environment, and our coupling scheme allows for high control over droplet position.

Fig. 1.

(a) SEM image of the water recirculation device, which highlights the surface roughness of 3D printed devices. (b) The water recirculation device coated with a thin film of water. (c) The fundamental R Polarized mode of the thin film device with a film thickness of 5 $\mu$ m. The 3D printed device is shown in tan, the water in light blue, and air in white. (d) Comparison of optical power inside and outside the 3D printed material as a function of water film thickness.

Fig. 2.

(a) Example of hydrophobic and hydrophilic innate contact angles $\theta$ *. (b) Devices showing the effects of corner pinning. The liquid in (i) does not exhibit corner pinning, and thus the contact angle is $\theta$ *. In (ii) the liquid is pinned at the bottom corner, and the angle formed is ${\theta }_p$ such that ${\theta }^{\ast }<{\theta }^p<{\theta }^c$ . (c) Our devices are sometimes treated by exposing them to oxygen plasma, which reduces the contact angle.

Fig. 3.

(a) 3D printed device for supporting microdroplet resonators. (b) Paraffin oil droplet supported by the 3D printed device. (c) Fundamental Z Polarized mode of the droplet. Oil is shown in light blue, and air is shown in white. (d) Visualization of the experimental setup. After an optical fiber is tapered, a 3D printed device supporting a microdroplet is brought close enough to the fiber to enable evanescent coupling. The throughput is monitored to determine resonance qualities.

Fig. 4.

(a) Profile view of a water/glycerol microdroplet of radius 257.9 $\mu$ m supported by a 3D printed device. (b) Z polarized resonant peak of water/glycerol droplet, fitted with a Lorentzian.

Fig. 5.

Resonance of a paraffin oil droplet fitted to a Lorentzian at both Z and R polarizations.

Fig. 6.

Comparison of coupling distance and coupling efficiency using Z polarized light for a paraffin oil microdroplet resonator supported by a 3D printed base.