The invention is directed to an OSA having a TO-can-type configuration that is relatively low-cost to manufacture and that has functionality for monitoring and controlling the temperature of the laser diode without the need for additional pins or an increase in the size of the OSA. Thus, the OSA typically includes four or five pins at most. These features of the invention are achieved by providing a thermal control circuit, a temperature sensor and a heater that are integrated along with a laser output power monitor photodiode into the submount assembly substrate.