Examples described herein relate to calibration of an optical communications link. Data signals received over the optical communications link are measured to obtain an eye scan. A height of an upper eye region and a height of a lower eye region are compared in the eye scan. A common mode calibration value is adjusted based on any difference in the heights. A common mode adjustment circuit is then controlled based on the common mode calibration value. The common mode adjustment circuit is configured to remove a direct current bias within a receiver for the optical communications link.