A laser located within a casing of an optoelectronic module is operated by heating the laser to an operating temperature at or above the maximum specified, operating temperature of the module casing using a heater device within the module, the laser having operating characteristics at its operating temperature that are sufficient for its required function. The heater device can be separated from the module casing by an insulating layer or by a thermal switch. The thermal switch can include a droplet of thermally conductive fluid displaceable between a first position where it provides a low thermal impedance path between the heater device and the module casing and a second position wherein a high thermal impedance path is provided between the heater device and the module casing.