An auxiliary component such as a bias inductance (6) associated with a laser source (2) is mounted generally "upright", that is with its major dimension substantially orthogonal to the general plane of the submount (S) supporting both the laser (2) and the auxiliary component (6). The inductor (6) is preferably mounted at a location displaced laterally with respect to the lasing direction (X) of the laser source. The arrangement preferably includes a submount (S) with a recess (13) and at least part of the laser driver is arranged in the recess so that the driver (3) has an end surface extending from the recess substantially flush with the pad (12) for mounting the laser source. The arrangement minimises surface occupation as well as RF and EMI parasitic effects related to wirebonding.