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Thispaper presents novel continuous photolithography technology and system as well for fiber substrate. The newly-developed system mainly consists of spray coating and three-dimensional (3D) UV exposure units. Thin and uniform resist film is successfully prepared on fiber substrates and thus the photolithography results were improved much. It is noteworthy that thin resist film could be formed on 125 μm-in-diameter fiber even without rotation, suggesting that the spray coating technology has attractive prospects. With the 3D photolithography system, fine patterns of resist down to 20 μm line width are successfully formed on the 125 μm-in-diameter fiber.

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The authors have developed a novel thermal imprinting method to fabricate microstructures on the surface of plastic optical fibers (POFs) without causing any damage to them. In conventional thermal nanoimprinting using a planar mold, the shape of the molding material is in the form of a film spread on a planar substrate, or the molding material is used in its bulk form. In the case of any 3-dimensional shaped molding material such as in the case of a fiber, the shape becomes susceptible to a certain degree of damage caused by the planar mold. In order to address this problem, we have designed a thermal imprinting method using sliding planar molds. A fiber tightly stretched between two reel stations (for sending and winding of the fiber) is sandwiched between two planar molds facing each other. The fiber is then rolled against the pattern sides of the two planar molds while the rolling motion of the fiber remains synchronized with the sliding motion of the planar molds. The problem of twists in the fiber caused by the sliding planar molds was solved by dynamically rotating the two reel stations to match the rotation of the fiber. To demonstrate this technology, we employed a special electroformed-Ni mold with a mirror image of a string of characters forming the word “MACROBEANS” engraved in the form of a lattice, where the individual characters were composed of diffraction grating structures with 1 and 2 μm of linewidths. Using this mold, the cylindrical surface of a POF made of a 240-μm-diameter polymethyl methacrylate core with a coating of a 5-μm-thick fluoroplastic cladding was thermal-imprinted. From the observation of the imprinted patterns on the POFs, it was verified that the cylindrical surface was patterned without causing any damage to the POF. The height of the convex mold pattern was 1.1 μm, and the depth of the concave imprinted pattern was approximately 1.0 μm.