An optical transmitter (201) comprising: a laser diode (102) for transmitting an optical signal; a first temperature sensor (106) configured to measure a temperature at or proximate to the laser diode (102); a second temperature sensor (202) configured to measure a temperature of an environment in which the optical transmitter (201) is operating; a thermoelectric device (208) configured to apply heating or cooling to the laser diode (102); and a controller (212) configured to, using the temperature measurements taken by the first temperature sensor (106) and the second temperature sensor (202), control the thermoelectric device (208) to heat or cool the laser diode (102).