Localization of light in an optical microcapillary introduced by a droplet

Tabassom Hamidfar, Kirill V. Tokmakov, Brian J. Mangan, Robert S. Windeler, Artemiy V. Dmitriev, Dashiell L.P. Vitullo, Pablo Bianucci, Misha Sumetsky

Research output: Contribution to journalArticlepeer-review


Sensing with optical whispering gallery modes (WGMs) is a rapidly developing detection method in modern microfluidics research. This method explores the perturbations of spectra of WGMs propagating along the wall of an optical microcapillary to characterize the liquid medium inside it. Here we show that WGMs in a silica microcapillary can be fully localized (rather than perturbed) by evanescent coupling to a water droplet and, thus, form a high-quality-factor microresonator. The spectra of this resonator, measured with a microfiber translated along the capillary, present a hierarchy of resonances that allow us to determine the size of the droplet and variation of its length due to the evaporation. The resolution of our measurements of this variation equal to 4.5 nm is only limited by the resolution of the optical spectrum analyzer used. The discovered phenomenon of complete localization of light in liquid-filled optical microcapillaries suggests a new type of microfluidic photonic device as well as an ultraprecise method for microfluidic characterization.

Original languageEnglish
Pages (from-to)382-388
Number of pages7
Issue number4
Publication statusPublished - 29 Mar 2018

Bibliographical note

© 2018 OSA. Published by The Optical Society under the terms of the Creative Commons Attribution 4.0 License. Further distribution of this work must
maintain attribution to the author(s) and the published article’s title, journal citation, and DOI.

Funding: Horizon 2020 Framework Programme (H2020) (H2020‐EU.1.3.3, 691011), Engineering and Physical Sciences Research Council (EPSRC) (EP/P006183/1).


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