200 Gbit/s Optical PAM4 Modulation Based on Silicon Microring Modulator

We present an ultra-high speed silicon microring modulator with the $V_{\pi}\cdot L$ of 0.8 V\cdot cm$ and the 3-dB electro-optical bandwidth larger than 67 GHz. Using this high-performance and compact modulator, the modulations of 120 Gbit/s NRZ and 200 Gbit/s PAM4 are experimentally demonstrated with the bit error ratios of 1.5e-3 and 1.08e-3, respectively.