A 20Gb/s NRZ/PAM-4 1V transmitter in 40nm CMOS driving a Si-photonic modulator in 0.13µm CMOS

The need for more bandwidth driven by streaming video and other data intensive applications has been steadily pushing the optical link speed to the 40G/100G domain. Compared to VCSEL and ring resonator, Mach-Zehnder Interferometer (MZI) is the best solution for long distance (>500m), high data rate (>28Gb/s) optical communications [1–3]. However, high power consumption, low link density and high cost seriously prevent traditional MZI from being the next generation of optical link technology. To fundamentally reduce the cost of MZI, it is highly desirable to make the process CMOS compatible with high efficiency, thus the modulation voltage, size, and power can be reduced to a level where advanced sub-1V CMOS circuits can be used as the driver. This paper presents two CMOS-MZI-based optical transmitters, NRZ or configurable PAM-N (N = 4,16), featuring 20Gb/s data rate and sub-pJ/bit modulation energy (PAM-4) using a 1V supply. The fully CMOS compatible photonic device is highly cost-effective in terms of integration, manufacturability and scalability.