Tunable optical beam focusing using static water droplets on an electrospun polymer fiber

• Static water microdroplets on a microfiber were used to vary the width of an optical beam. • The presence of PVC fibers improves the hydrophobicity of the glass and sustains the droplet shape. • Water with varying volume (3–60 µL) produces variable droplet radius and curvature, acting like plano-convex lenses. • Beam maintained its Gaussian profile even with the presence of microfibers in the surface. • The water droplets may cause controlled in-plane beam dispersion when the traversing the side of the droplets. This work explores the use of static water microdroplets on a microfiber to vary the width of an optical beam. Varying the water droplet volume changes the beam width without replacing any optical components. A surface derived from glass deposited with polyvinyl chloride (PVC) microfibers via electrospinning was used to sustain the droplet shape on the surface. Scanning electron microscopy revealed the presence of randomly intertwined microfibers with diameters of less than 3 µm which afforded the surface a hydrophobic property. A decrease in the optical transmittance of the films and an increase in the water contact angle were also observed as fiber density increases. Results revealed an increase in the beam size with increasing droplet volume manifesting a defocusing or magnifying effect as the beam passed through the droplets. The beam maintained its Gaussian profile, confirming that the presence of the deposited fibers did not significantly alter the beam type. By using droplets with different liquid volumes (5–60 µL), we replicate the action of a convex lens with varying focal length.