Examples described herein relate to reducing a magnitude of a supply voltage for a circuit element of an optical transmitter device. In some such examples, the circuit element is a driving element that is to receive a first electrical data signal and to provide a second electrical data signal to an optical element that is to provide an optical data signal. A testing element is to compare the optical data signal to the first electrical data signal to determine whether the optical transmitter device meets a performance threshold. When the device meets the performance threshold, a regulating element is to reduce a magnitude of the supply voltage of the driving element.