Signal Integrity Design Methodology for Package in Co-packaged Optics Based on Figure of Merit as Channel Operating Margin

Optical engines co-packaged with switching Application-Specific Integrated Circuit (ASIC) can offer a solution for advancement in bandwidth requirement and are potentially the ultimate direction for the long-touted "optical integration" era. This paper proposes a novel signal integrity (SI) design methodology for package of co-packaged optics (CPO) by using channel operating margin (COM) as a figure of merit (FOM) for the first time. The conventional design method of SI based on individual criteria, such as masks for loss, crosstalk, jitter, eye width/height, impedance, etc., are no longer able to be satisfied at the same time for current high-speed signals up to 50Gbps and even over 100Gbps. COM, combining most of the individual criteria into a single value of signal to noise ratio, provides the possibility to estimate the quality of the channel and achieve a balance between performance and design complexity in the early design stage. In this work, a design methodology in a format of a visible map using the most two significant factors, loss, and crosstalk, to satisfy the required COM is discussed in detail. With this novel methodology, one can predict the SI performance of a package in the early design stage when the real layout has not generated yet for full-wave simulation and can avoid the costly iteration in the conventional design concept.