A $4\times25$ Gb/s Optical Transmitter Using Low-Cost 10 Gb/s VCSELs in 40-nm CMOS

This letter presents a
$4\times 25$
Gb/s optical transmitter in 40-nm CMOS. Low-cost vertical cavity surface-emitting lasers (VCSELs) with 10-GHz bandwidth (BW) are employed, which are then overdriven to 25 Gb/s by the proposed pre-emphasized quad-channel driver. Digitally assisted asymmetric-pulsed equalization technique is proposed to overcome the VCSEL modulation non-linearity and maximize the eye-diagram margin against the 100-GbE standard mask. The measurement results show >30% eye-mask margin and error-free (BER
$< 10^{-12}$
) optical transmission for each 25-Gb/s channel, resulting in 280-mW power dissipation per channel under 1.2–/3.3-V dual supply.