MONOLITHICALLY INTEGRATED TUNABLE SEMICONDUCTOR LASER

A monolithically integrated, tunable semiconductor laser with an optical waveguide, comprising a laser chip having epitaxial layers on a substrate and having first and second reflectors bounding an optical gain section and a passive section, wherein at least one of the reflectors is a distributed Bragg reflector section comprising a grating and configured to have a tunable reflection spectrum, wherein the laser is provided with a common earth electrode that is configured to be electrically grounded in use, wherein control electrodes are provided on the optical waveguide in at least the optical gain section and the at least one distributed Bragg reflector section, wherein the passive section is provided with a passive section electrode that electrically contacts the opposite side of the optical waveguide from the substrate, the passive section is configured not to be drivable by an electrical control signal, and no grating is present within the passive section, and wherein the passive section is a grounded passive section in which the passive section electrode is configured to be electrically grounded in use and electrically contacts the passive section, and wherein the passive section electrode and the common earth electrode electrically contact opposite sides of the optical waveguide.