External vs. Integrated Light Sources for Intra-Data Center Co-Packaged Optical Interfaces

Co-packaging of optics and electronics for data center switches has been proposed to reduce system-level power consumption by minimizing power-hungry electrical interconnects. Co-packaging optical components near high-temperature electronics, however, can diminish their performance and reliability. Moreover, limitations of the switch environment, such as restricted footprint, power, and number of fiber attachments can limit practical co-packaging implementations. Here, we study four architectures for co-packaged optical interfaces using either single- or multi-wavelength light sources that can be either external to or integrated with the optical interfaces. We model the temperature- and current-dependent performance and reliability of the sources and calculate the link budget for switch bandwidths up to 102.4 Tb/s. We compare architectures based on coherent and direct detection and find that all coherent detection architectures support 102.4 Tb/s switching with over 13 dB link budget, while most direct detection architectures scale to 51.2 Tb/s or 102.4 Tb/s switching with link budgets less than 5 dB. In addition, we demonstrate that external-source architectures require wavelength-division multiplexing at lower switch bandwidths and consequently have link budgets 1-5 dB lower than integrated source architectures. Further, we demonstrate that higher-power lasers can scale external architectures to 102.4 Tb/s switching with over 4 dB link budgets. Finally, for 51.2 Tb/s switching, we show that a reduction in integrated source temperature improves link budgets by 2-4 dB and direct detection external-source architectures can achieve greater than 5 dB link budget with fewer than 300 fiber attachments.