Bandwidth Limits of Connector Wipe Stub for Reliable 224 Gbps Signaling

The λ/4 resonance due to unwanted stub effect along the signal path can play a significant role for the Chip-to-Module interface running at 224 Gbps in PAM4 which involves a typical optical module connector. A OSFP connector example is considered in this paper and the impact of the residual stub given by the spring wipe is analyzed. The stub resonance is predicted analytically with acceptable error, and the stub notch resonance is extracted from full-wave simulations for several cases of wipe length. A length limit is derived in order to keep the notch frequency of the resonating stub outside the usable bandwidth practically set at 0.75 times the baud rate for the PAM 4 type of modulation.