Development of Mach-Zehnder optical waveguide embedded in PDMS thin films by proton beam writing

加田 渉*; 三浦 健太*; 猿谷 良太*; 加藤 聖*; 久保田 篤志*; 佐藤 隆博; 江夏 昌志; 石井 保行; 神谷 富裕; 西川 宏之*; et al.

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An optical switch with a Mach-Zehnder (MZ) structure was previously fabricated in a Poly-methyl-methacrylate (PMMA) thin film by proton beam writing (PBW). The extinction ratio of the switch, however, needs to be enhanced by higher optical permeability for industrial use. In this study, the MZ optical waveguides have been fabricated in poly-dimethyl-siloxane (PDMS) thin films, which have higher optical permeability than PMMA. A PDMS film of a thickness of approximately 30 m was spin-coated on a silicon wafer (40 20 0.5 mm). The MZ waveguides of 8 m in width and total length of 30 mm were drawn in the film by a 750 keV proton microbeam of 1m in diameter having the penetration depth of 18 m with fluence of 40-100 nC/mm. The drawing of the total length was carried out combining an electric scanner and a mechanical sample-stage. A clear spot of 1.55 m single-mode light was observed propagated through the MZ waveguides, which indicated that the enhanced optical transmittance by the use of PDMS leads to their waveguides with higher extinction ratio.