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Compact Eight-Channel Thermally Reconfigurable Optical Add/Drop Multiplexers on Silicon

A compact thermally reconfigurable optical add/ drop multiplexer (ROADM) is realized with 500 nm × 220 nm silicon-on-insulator (SOI) strip waveguides. The demonstrated ROADM has eight channels with a channel spacing of 400 GHz and consists of two identical arrayed-waveguide gratings integrated with eight thermo-optic switches on the same chip. These thermo-optic switches have a broad bandwidth with low loss (<;1 dB) as well as high extinction ratio (>20 dB) for covering all wavelength channels by utilizing point-symmetric Mach-Zehnder interferometers with bent directional couplers. The ROADM's footprint is about 770 μm × 880 μm only due to the ultra-strong confinement ability of SOI strip waveguides. The total on-chip loss of the fabricated ROADM is ~15 and ~7 dB for the transmitted signals and the added/dropped signals, respectively.