A 25.78125Gbps Bi-directional Transceiver with Framed-Pulsewidth Modulation (FPWM) for Extended Reach Optical Links in 28nm CMOS

We report 25.78125Gb/s time-based modulation scheme referred to as FPWM that extends the reach of C-band optical links by more than 20km as compared to NRZ. The FPWM is insensitive to component nonlinearity since only two signal levels are used unlike PAM4. Measurements show that FPWM achieves 6dB SNR gain over PAM4 in back-to-back and 8dB gain over NRZ at 15km.