UC Santa Barbara

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.