Noncontact Characterization Of Microstructured Optical Fibers Coating In Real Time

Functional nanocoatings have allowed hollow-core microstructured optical fibers (HC-MOFs) to be introduced into biosensing and photochemistry applications. However, common film characterization tools cannot evaluate the coating performance in situ. Here we report the all-optical noncontact characterization of the HC-MOF coating in real time. Self-assembled multilayers consisting of inversely charged polyelectrolytes (PEs) are deposited on the HC-MOF core capillary, and a linear spectral shift in the position of the fiber transmission minima with increasing the film thickness is observed as small as similar to 1.5 - 6 nm per single PE bilayer. We exemplify the practical performance of our approach by registering an increase in the coating thickness from 6 +/- 1 to 11 +/- 1 nm per PE bilayer with increasing ionic strength in the PE solutions from 0.15 to 0.5MNaCl. Additionally, we show real-time monitoring of pH-induced coating dissolving. Simplicity and high sensitivity make our approach a promising tool allowing noncontact analysis of the HC-MOF coating which is still challenging for other methods. (C) 2021 Optical Society of America.