Abstract: The present invention discloses an optical transmitter that enables to precisely control the temperature of the LD and to keep the emission wavelength constant. The controller installed within the transmitter includes a control signal generator, a differential amplifier and a current driver. The signal generator generates a control signal based on the current provided to the TEC and the outside temperature of the optical module. The differential amplifier differentiates the control signal from the inside temperature with in the module to generate a differential signal. The current driver, based on the differential signal, provides the current to the TEC.