Whispering Gallery Mode Microdroplet Resonators on 3D-Printed Mounts

Due to their mode stability and high quality (Q) factors; whispering gallery mode (WGM) resonators have a wide range of applications from biological sensing to lasing to quantum optical devices [1]. A variety of geometries and materials, including liquids, can be used to create WGM resonators [2]. There are several existing preparations for microdroplet resonators including suspending a drop on a glass stem [3,4] or suspending a droplet in another liquid [5,6]. These methods range in complexity, preparation time, and accessibility. The fabrication of 3D-prints is easy, quick, and accessible but their inherent surface roughness makes them less than ideal for optical applications. Due to this roughness, 3D-prints result in low-quality WGM resonators and can better serve as mounts for microdroplets. In this work a variety of different liquids, some with high dielectric constants (e.g., propylene carbonate), were characterized as WGM microdroplet resonators. Liquid-crystal WGM resonators with high dielectric constants have been shown to have a tunable geometry with an applied electric field [7]. This tunability of high dielectric materials could be advantageous for these microdroplet WGM resonators.<br/>[1] Vahala, K. J. Optical Microcavities. <i>Nature</i> <b>2003</b>, <i>424</i> (6950), 839–846.<br/>[2] Cai, L.; Pan, J.; Zhao, Y.; Wang, J.; Xiao, S. Whispering Gallery Mode Optical Microresonators: Structures and Sensing Applications. <i>physica status solidi (a)</i> <b>2020</b>, <i>217</i> (6), 1900825.<br/>[3] R. Dahan, L. L. Martin, and T. Carmon, “Droplet optomechanics,” Optica <b>3</b>(2), 175–178 (2016).<br/>[4] M. Gaira and C. Unnikrishnan, “Integrated table-top facility for the study of whispering gallery modes in dynamic liquid micro-cavities coupled to sub-micron tapered fibers,” arXiv preprint arXiv:1911.01187 (2019).<br/>[5] S. K. Tang, R. Derda, Q. Quan, M. Lončar, and G. M. Whitesides, “Continuously tunable microdroplet-laser in a microfluidic channel,” Opt. Express <b>19</b>(3), 2204–2215 (2011).<br/>[6] S. Maayani and T. Carmon, “Droplet raman laser coupled to a standard fiber,” Photonics Res. <b>7</b>(10), 1188–1192 (2019).<br/>[7] Humar, M.; Ravnik, M.; Pajk, S.; Muševič, I. Electrically Tunable Liquid Crystal Optical Microresonators. <i>Nature Photonics</i> <b>2009</b>, <i>3</i> (10), 595–600.