High-speed imprinting on plastic optical fibers using cylindrical mold with hybrid microstructures

Abstract

• We developed a cylinder mold with hybrid-layered patterns. • A precise cutting was combined with 3-D photolithography using a flexible mask. • The imprint speed was improved by changing a press-force control method. • We succeeded in continuous imprinting on a POF at a feeding speed of 20 m/min. We are developing flexible and large-size e-textiles by weaving in a smart fiber. On the surface of the fiber, micro-electro-mechanical-systems (MEMS) structures, electronic circuit patterns, and guide structures for positioning during the weaving process are fabricated. In order to manufacture smart fibers in large quantities, we developed a cylindrical mold with hybrid-layered structures consisting of 260-μm-wide macro patterns and several 10-μm-wide patterns fabricated by precise cutting of substrate employing forming tools and 3-D photolithography, and using a micro-patterned flexible photomask. Initially, the polished surface of the cylinder is covered with an electroless-plated Ni–P alloy; and convex structures with rectangular cross-sections and arc shaped convex structures are cut. Next, the surface of the cylinder is coated with a positive-tone photoresist by a dipping process. Ultraviolet (UV) lights are then irradiated on the photoresist through a flexible micro-patterned photomask wrapped around the cylinder; and then the micro-patterns on the photomask are thus transferred onto the cylindrical surface. Next, following a Cu electroplating, hybrid-layered patterns are made that comprise 260-μm-wide macro and several 10-μm-wide microstructures. In the final step, the photoresist is then removed. And moreover, in order to realize high-speed imprinting, the mechanical stiffness of a reel-to-reel thermal imprint system is improved, and the press-force control method is changed. The imprint system is equipped with a completed cylindrical mold; and using the system, a plastic optical fiber (POF) comprising a 240-μm-diameter PMMA core with a 5-μm-thick fluoride clad is imprinted for a demonstration. The cylindrical mold heated up to 50 °C with an infrared lamp, is pushed into the surface of the POF to a depth of 4.5–6.7 μm. As a result, a continuous imprinting on the POF is achieved at an imprint speed of 20 m/min.