192-Channel Monolithically Integrated Reconfigurable Optical Add-Drop Multiplexer on Silicon for Ultrahigh-Capacity Hybrid WDM-PDM-MDM Systems

A monolithically integrated silicon photonic chip of 192-channel reconfigurable optical add-drop multiplexer (ROADM) for ultrahigh-capacity hybrid wavelength-division-multiplexing-polarization-division multiplexing-mode-division multiplexing (WDM-PDM-MDM) systems is proposed and demonstrated for the first time by involving 32 wavelengths, three guided modes, as well as dual polarizations. For the present silicon photonic chip, high-performance functional elements for the channel adding/dropping and the power equalization are included, such as crossbar wavelength-selective switches (WSSs) based on adiabatic elliptical-microrings (AEMs), ultralow-loss waveguide crossings, and variable optical attenuators (VOAs). In particular, the AEMs are designed with maximized free spectral ranges (FSRs) to cover the 32 wavelength-channels as desired for the improvement of the spectrum utilization. The fabricated 192-channel ROADM chip has more than 2000 elements integrated, including 192 AEMs, 1152 waveguide crossings, 384 grating couplers, 198 microheaters, 258 pads, 6 polarization-splitter-rotators (PSRs), 4 asymmetric adiabatic couplers (ADCs), showing on-chip excess losses of 5–15 dB, intermode crosstalk of <−10 dB, and interwavelength crosstalk of <−17 dB for any one of the 192 channels. With such a ROADM, one can arbitrarily add/drop the optical signals to/from any channels of the multimode bus waveguide by switching the corresponding AEM. The system experiments are demonstrated with a 28-GBaud 16 Quadrature Amplitude Modulation (16QAM) signal, showing that the optical signal-to-noise ratio (OSNR) power penalty due to the ROADM chip is less than 17 dB at the BER of 3.8 × 10–3. The proposed scheme can be extended to an even higher capacity by adopting more channels.