UV laser aids silica microwire self-assembly

Silica optical microwires—smaller than ordinary optical fibers and with potential applications in sensing, as single-photon sources, and for use in optical interconnects—are difficult to uniformly manufacture using bottom-up fabrication processes such as tapering down larger-diameter optical fibers. Fortunately, researchers at the University of Sydney (Sydney, Australia) and Université Paris Sud (Orsay, France) have recently accomplished self-assembly of silica microwire waveguides on hydrophilic glass slides using convective flow within an evaporating drop containing silica nanoparticles, all at room temperature. The development opens up the possibility of integrating any material into silica for the first time.

The researchers improved the self-assembly uniformity by demonstrating that alteration of the contact angle distribution around a solution droplet on a glass slide improves the uniformity of the microwires as the droplet is evaporated. To accomplish this reduced angle and create a more elliptical-vs.-spherical water droplet, application of an ultraviolet (UV) laser beam at 193 nm fine-tunes the interfacial solid-liquid interface around the droplet and alters its effective geometry. That is, the laser treatment transforms (in the small-drop-domain limit) a spherical caplet formed on a hydrophilic surface into a more ellipsoidal-like (angle on one side is different than the opposite side) form, which improves convective self-assembly of silica nanoparticles into microwires within the drop. Uniform microwires with diameters of tens of micrometers were demonstrated using the technique. Contact John Canning at [email protected].