Silicon photonic interconnects hold great promise in meeting the high bandwidth and low energy demands of next-generation interconnects. System-level driven electronic-photonic co-design is the key to improving the bandwidth density and energy efficiency. In this study, a comprehensive co-optimization framework is developed for high-speed silicon photonic transmitters utilizing compact models and a detailed optical simulation framework. Given technology and link constraints, microring and Mach-Zehnder transmitter designs are optimized and compared based on a unified optical phase shifter model. Non-return-to-zero (NRZ) and pulse-amplitude-modulation-4 (PAM-4) modulation schemes are analyzed and compared for microring-based transmitters. Using the co-design approach, a monolithic 40Gb/s optical NRZ transmitter based on microring modulators is designed and demonstrated in zero-change 45nm CMOS SOI process. Electronic-photonic co-design with the high swing driver enables this transmitter to achieve total energy efficiency of 330fJ/b and the photonics and modulator driver area bandwidth density of 6.7 Tb/s/mm2. This dissertation also discusses the design and demonstration of the first full silicon photonic interconnect on a 3D integrated electronic-photonic platform. These results make the microring-based silicon photonic transceivers an attractive solution for the next-generation inter and intra-rack photonic interconnects. Finally, a short-reach laser-forwarding coherent link architecture is proposed to further improve the energy efficiency of silicon photonic interconnects. The key concepts of the proposed architecture are verified experimentally with microring-based silicon photonic transmitters. The architecture saves the laser power by 6-7.5x and could enable complex modulation schemes for the future short-reach optical links.