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We describe a silica-based arrayed-waveguide grating (AWG) with low channel-dependent loss variation achieved by using mode-field converters designed with the wavefront matching method. This mode-field converter converts the fundamental mode of the arrayed waveguide into the field distribution with a flat-top far field at the interface between the slab and output waveguides. We applied our mode-field converters to an AWG with a 100-GHz channel spacing and reduced the loss deviations experimentally from 2.4 to 0.7 dB over one free spectral range. Moreover, we confirmed that the introduction of our mode-field converters had no adverse effects on the AWG demultiplexing characteristics. It is notable that the loss uniformity was improved solely by replacing the conventional tapered waveguide between the arrayed waveguides and output slab waveguide with our mode-field converter without sacrificing the fabrication manageability or AWG design flexibility.