A combined high‐speed analog to digital converter, and optical transmitter, based on the frequency tuning capability of cleaved‐coupled‐cavity semiconductor lasers is proposed and demonstrated. The device, which acts as a level discriminator with optical outputs can either continuously sample the analog input or be strobed at rates up to ∼ 1 Gsamples/s. A four‐level conversion of a 100‐MHz sinusoidal input is shown.