TUD successfully applied their ADDAPT TX for an error-free link measurement at 40 Gb/s NRZ with BER < 10 -12. As RX a TUD design in 28 nm bulk-CMOS technology from another project has been used. The total link energy efficiency is 3.4 pJ/bit at 40 Gb/s. At lower data rates, the bandwidths of the circuits can be decreased adaptively to save power. This results in 2.7 pJ/bit at 20 Gb/s. A sensitivity of -1.9 dBm optical modulation amplitude could be measured at the RX for 40 Gb/s.These results were published in IEEE Photonics Technology Letters. At the time of publication, this was the fastest 850-nm VCSEL-based single-lane non-return-to-zero optical link with all the analog front-end components fabricated in CMOS.