Sub-micron aperture VCSEL demonstrates ultralow ITH<b> = </b>0.05 mA and energy/bit<b> = </b>45.5 fJ/bit at 3 Kelvin

The 0.9 μm diameter oxide aperture vertical-cavity surface-emitting lasers (VCSELs) are developed for high-speed cryogenic operation. Ultralow threshold current of 0.05 mA was measured at 3 K by optimizing the gain–cavity resonance alignment and reducing the oxide aperture size to sub-micron. The VCSEL exhibits ultrahigh linearity with wide dynamic range of I/Ith &amp;gt; 100. The microcavity VCSELs deliver record energy/bit of 45.5 fJ/bit for 112 Gbps PAM-4 transmission operated at I = 1.8 mA with TDECQ = 3.21 dB. The sub-micron cryogenic VCSEL has proven to be energy-efficient optical transmitter for cryogenic optical interconnects.