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High-bandwidth density and energy-efficient readout interfaces connecting the superconductor electronic (SCE) integrated circuits (IC) with room-temperature environments are essential for emerging quantum and classical superconducting computing applications, which motivate the design of cryogenic optical links. This work addresses four challenges in this communication link. First, a comprehensive link model, which consists of superconductor and semiconductor electronic/photonic components, is built to analyze the performance and energy efficiency of the link. Then, a novel cryogenic optical link based on the monolithic silicon photonic process and laser-forwarded coherent architecture is proposed to balance power consumption at cryogenic and room-temperature environments and improve overall energy efficiency. Next, an accurate device model is necessary for circuit design nowadays, while little is known about the transistor's behavior at cryogenic temperatures. A detailed theoretic analysis and device characterization of transistors from monolithic silicon photonic processes is presented. Following that, a proof-of-concept single-chip CMOS electronic-photonic cryogenic transmitter is designed and implemented in the 45RFSOI process. The link experiment at cryogenic temperatures with the direct drive from superconductor IC demonstrates its function, performance, and energy efficiency. Compared to the existing solution, our work shows the best energy efficiency by eliminating the extra discrete cryogenic amplifier requirement. Finally, a new type of EOPLL, including a boundless phase shifter-based phase rotator and dLev comparator-based phase estimator, is proposed to solve the inevitable time-varying phase offset issue in the laser-forwarded coherent architecture. A proof-of-concept coherent receiver with proposed EOPLL is designed and implemented in the 45SPCLO process.

Data center traffic continues to experience considerable growth due to the vast amount of data generated by cloud computing, augmented reality, and the internet of things and Intra-data center traffic makes up to 77% of the total traffic, so improvements in spectral efficiency, bandwidth and power consumption of data center interconnections contribute to overall energy efficiency. Intra-data center traffic interconnects aim for data rates above 200 Gbps per wavelength while reducing power consumption. Coherent links leveraging orthogonal polarization and quadrature modulation schemes are an energy-efficient alternative approach to commonly used intensity modulation direct detection (IMDD). A component to this vision is the realization of low-power, broadband optical receivers for quadrature phase shift keying (QPSK) or higher-order coherent waveforms.Improvements in energy efficiency through increased data rate and reduction in power consumption is also significantly affected by electronic-photonic integration. Co-packaged optics have been proposed as one approach to fulfill this demand by minimizing the high-speed I/O power consumption. Nevertheless, parasitic resistance, inductance and capacitance between electronic and photonic circuits deteriorates the high-speed performance and requires power hungry equalization, thereby eliminating improvements in energy efficiency. Consequently, packaging approaches that enable either monolithic or 3D integration of heterogeneous ICs, i.e. silicon photonic and electronic ICs, are promising approaches to improve performance.The focus of this work is to develop energy-efficient optical fiber communication links through studying the system architecture trade-offs, as well as integrated opto-electrical circuit design for the link implementation. Performance degradation due to packaging effects is also studied and quantized. Several fiber optic communication links have been designed and measured. The first monolithically integrated CMOS-Photonic coherent optical receiver was implemented and achieved 80 Gbps with 1.2 pJ/bit energy efficiency. The O-band receiver was redesigned to further improve the performance and achieved above 100 Gbps and a record energy efficiency below 1 pJ/bit. These results show the possibility to implement O-band coherent optical links to support 200 Gbps per wavelength below 10 pJ/bit for next generation intra data center applications.