single-mode tapered polymer optical waveguides are fabricated using the Mosquito method, which work as a spot-size converter (SSC). In this research, the axially taper shaped core is formed by accelerating the needle scanning velocity during the core dispense. For effective spot-size conversion, we demonstrate both theoretically and experimentally that the monomer diffusion between the core and cladding during the Mosquito method is a key. The fabricated 8-mm long tapered waveguide with perfect

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... circular core cross sections exhibits an effective MFD conversion from 4.1 µm to 7.5 µm, allowing an insertion loss as low as 1.89 dB at 1550-nm wavelength.