Cryogenic 1/2-λ Cavity VCSEL With 5-μm Aperture Demonstrates Record Pout = 35 mW and 140 Gbps PAM-4 Optical Link at 2.9 K

High-power and high-speed cryogenic vertical-cavity surface-emitting lasers with a 1/2- $\lambda $ cavity and $5.0~\mu $ m oxide-aperture are designed and fabricated. By strategically etching down five top p-doped DBR pairs while preserving low threshold current (I ${}_{\mathrm {th}} =1.54$ mA), the device achieves an unprecedented output power of 35 mW and supreme linearity at 2.9 - 77 K for high-speed, power-efficient optical interconnects. The device also achieves sub-picosecond photon lifetime and bandwidth exceeding 50 GHz at 2.5 mA, enabling 140 Gb/s PAM-4 cryogenic optical interconnect.