Compact and low insertion loss (~1.0 dB) Mach-Zehnder interferometer-synchronized arrayed-waveguide grating multiplexer with flat-top frequency response

We have developed a compact Mach-Zehnder interferometer (MZI)-synchronized arrayed-waveguide grating (AWG) multiplexer with 40 100-GHz-spaced channels using 1.5-% Δ waveguides. This MZI-synchronized AWG has a chip size of only 35×28 mm2, and a low insertion loss of 1.0 - 1.2 dB with a flat-top frequency response. This low insertion loss is achieved by i) installing spot-size converters at the ends of optical input and output waveguides, and ii) employing a narrow gap in a directional coupler at the junction of the MZI and AWG. This device exhibited other excellent characteristics including a wide 0.5-dB passband of more than 45 GHz and a low adjacent crosstalk of less than -35 dB.