A 64 Gbaud/s Hybrid-Integrated Optical Transmitter Based on a 60 GHz Silicon Photonic Dual-Segment Microring Modulator and a CMOS Driver for High-Bandwidth DWDM Optical I/O

Silicon microring modulators (MRMs) are pivotal for enabling high-bandwidth, power-efficient dense wavelength division multiplexing (DWDM) optical I/O. This paper introduces a dual-segment MRM featuring four N-type and four P-type doping concentrations. By optimizing the doping profiles, the MRM achieves a 43% reduction in loss and a 10% reduction in capacitance, while maintaining comparable modulation efficiency to MRMs with three N-type and three P-type doping concentrations. This design achieves an electro-optic (EO) bandwidth exceeding 60 GHz, marking a 15% increase over its single-segment counterpart. An equivalent circuit model, which aligns excellently with experimental results, demonstrates the co-design capability of electronic and photonic integrated circuits (EPIC). The dual-segment MRM exhibits comparable modulation efficiency to the single-segment MRM, with a measurement of approximately 0.63 V$\cdot$ cm. Both modulators operate successfully at data rates of 106 Gb/s using PAM4. With the ample EO bandwidth, a data rate of 128 Gbaud/s using NRZ is also demonstrated for the dual-segment MRM. For the first time, a 64 Gbaud/s hybrid integrated dual-segment MRM transmitter (TX) is demonstrated, employing a segmented driver with a feed forward equalization (FFE) circuit. This TX is paired with a co-designed 28 nm complementary metal oxide semiconductor (CMOS) driver for DWDM optical I/O, showcasing high bandwidth density and power efficiency.