In-liquid durable sensing with fused microknot optical transmission resonators: Folded versus straight configuration on hydrophilic and hydrophobic substrates

On-fiber micro-structures are favorable platforms for sensing in aqueous environments. Durable in-liquid operation with NIR light transmitted through fused optical microknot fibers defined on adiabatic tapers is presented in straight versus folded configurations. We suggest and demonstrate two schemes for OMF deployment: folded configuration which is intended for remote sensing, and straight configuration on either hydrophilic or hydrophobic substrate, the latter of which is useful in packaged geometries. We study experimentally the OMF preparation methods in folded, straight on glass surface and straight on PDMS surfaces. The persistent detection of NIR light transmission resonances in the presence of volatile liquid capabilities are experimentally demonstrated in the various configurations.