The selective patterning of silver nanoparticles by a patent-pending process to act as a catalyst for metallization with electroless copper was explored on cotton, with a view towards application in the wearable technology sector. Whole area coverage or tracks serving as point-to-point connections were achieved by depositing the catalyst via spraying, or in a more controlled manner using a microdispenser, respectively.Optimization of the catalyst deposition is described, including substrate characterization via contact angle, FTIR and surface charge measurement. The effects of the copper plating bath temperature and dwell time in the plating bath are examined. With plating times as short as 10 minutes, samples of good conductivity (sheet resistance, R, = <10 Ω/sq) and consistency were produced. A higher or lower plating temperature (compared to supplier recommended conditions) increased or reduced the amount of copper deposited respectively. The technology was used to produce well-defined conductive tracks on cotton with widths between 1.5 and 4.0 mm.

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We present both a theoretical and an experimental study of a novel compact lensed fiber system utilizing a nanostructured GRIN lens. The lens can be integrated with an optical fiber, which ensures a unique and efficient focusing in any high index medium, such as a liquid. We use the effective medium approach to design lenses with arbitrary refractive index. To fabricate lenses, we utilize a discrete array of nano-sized rods made of two types of glasses, and apply a standard stack-and-draw fiber drawing technology. The fabricated nanostructured GRIN lenses have a parabolic refractive index profile with a diameter of a standard fiber, very short working distances (55 µm in the air) and a high numerical aperture (NA = 0.16). As a proof-of-concept of the new micro-lensed fiber system, we demonstrate an experiment on optical trapping of micrometer-sized glass beads. We also show that our method is compatible with optical fiber technology and allows for any shape of the refractive index distribution in 2D. Thanks to that a new functionality could be achieved by replacing the GRIN lens with an axicon lens, vortex type elements, micro-lenses arrays or diffraction elements.

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