Silicon Photonic Micro-Ring Modulator-based 4 x 112 Gb/s O-band WDM Transmitter with Ring Photocurrent-based Thermal Control in 28nm CMOS

We present a 4λ×112 Gb/s/λ hybrid-integrated silicon photonic TX suitable for 400G Ethernet modules and co-packaged optics. The photonic IC (PIC) uses cascaded micro-ring modulators (MRMs) with integrated heaters for efficient wavelength division multiplexing (WDM). The 28nm CMOS electronic IC includes PAM4 MRM drivers with nonlinear FFE and control circuits to stabilize MRM performance against process and temperature variations. A thermal control scheme based on sensing MRM photocurrents is used to minimize monitoring hardware in the PIC. Measured results demonstrate 112 Gb/s PAM4 operation with <0.7 dB TDECQ from each of the 4 channels. To our best knowledge, this is the highest per-λ data rate reported for an O-band ring-based WDM transmitter.