Transition-Based Feedback-Equalizer for Error Mitigation in High-Speed Short-Reach Optical Communication System

VCSEL-based short-reach (<100 m) optical communication systems with intensity modulation and direct detection (IM-DD) have become a favorable choice for providing high-speed, low-cost, and low-power optical interconnects in data-center applications [1]. However, non-idealities of VCSELs, such as power nonlinearities, bandwidth variations dependent on bias current, and rise and fall times that change with DC and AC inputs, pose significant challenges in multilevel IM/DD communication systems. These issues manifest as nonlinear power output [2] and time-skew across multilevel amplitudes [3]. To address the nonlinear power output, the amplitude levels from the DAC can be adjusted to produce an electrical signal with nonlinearly spaced levels. When modulated through the VCSEL, this adjustment produces an optical signal with approximately linear spacing between levels. A typical de-skew filter to decrease the BER involves upsampling the detected signal and interpolating the upsampled detected signal with multiple filters [2], [3]. Meanwhile, the typical commercial DSP for short-reach applications operates only at 1 sample/symbol to maintain the lower power consumption.