400 Gbps PAM4 and 280 Gbps NRZ Silicon Photonic Transmissions With Fabrication-Tolerant Silicon Nitride CWDM4 Filters

We demonstrate an integrated transmitter with a robust silicon nitride coarse wavelength division multiplexing 4 lane (CWDM4) filter and 4 high-speed Mach-Zehnder modulators (MZM). The fabrication-tolerant CWDM4 filter comprises two-stage cascaded asymmetric Mach-Zehnder interferometers (AMZI) utilizing multi-sectional phase shifters. This design eliminates the spectral shifts induced by manufacturing linewidth variabilities. Experimental results show a good match of the operating wavelengths with predefined values. The insertion loss is <-0.72 dB, and crosstalk is <-13.17 dB over four operating wavelengths. The temperature dependence is 16.3 pm/degrees C. The 3 mm long silicon photonic MZM exhibits electro-optical bandwidths of 32.88 GHz at -3 V and 36.68 GHz at -7 V. The half wave voltage is measured to be 4.97 V. Transmissions of 4 x 100 Gbps pulse amplitude modulation-4 (PAM4) signals, and 4 x 70 Gbps non return to zero-on-off keying (NRZ-OOK) signals were successfully carried out. The proposed transmitter with the robust CWDM4 design offers a practical solution for Ethernet networks in data centers and has the potential for future optical communications in high-performance computing systems.