We achieved a low coupling loss of 0.5 dB/point between 1.5-Δ silica-based waveguides and a single-mode fiber by employing a simple laterally tapered waveguide with a narrow core width. By applying this structure to an Arrayed Waveguide Grating (AWG), we decreased the insertion loss from 4.9 to 2.6 dB. The spotsize converter enabled us to realize a compact and a low-loss practical optical device.
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