Following the Mechanisms of a Single Water Droplet Drying by Means of Photonic Resonant Structure

We have designed and fabricated integrated photonic micro-resonators (MRs) devices in polymer UV210 on a SiO2 substrate. UV210 is a positive resin that features an absorption band in the deep-UV domain. Such a property allows us to perform photolithography at lower wavelength than the traditional i-line photolithography so as to design smaller and more precise structures [1]. By using such MR as sensor [2,3], we have monitored the evaporation of a sessile water droplet by dynamically tracking its optical transduced signal. To do so, a broadband laser (λ = 790 nm, FWHM = 40 nm) is coupled to a set of MRs through the injection in a tapered access waveguide. The use of a broadband laser allows us to visualize several resonances on the same spectrum, which increases the precision of the data treatment. The water droplet is deposited on the MRs and the transduced signal is acquired during the whole drying process. The output optical signal is monitored by the mean of an optical spectrum analyser with a frequency of acquisition of about 1 Hz.