illustrating changes in the wavelength and output powerpower when we control the temperature of a tunable external cavity laser based on the temperature measured by a thermistor located on the side of a gain medium in according to an embodiment of the present invention temperature was controlled by measuring the temperature of a silicon block 710 with a thermistor 713 a gain medium 711 on is placed on the silicon block 710 a module of a tunable external cavity laser was seam sealed to exclude the effects by changes in humidity when the ambient temperature of a module is changed from 25 u00b0 c to 50 u00b0 c the wavelength changed by more than 0 4 nm and the output power by more than 1 5 db even though this temperature range is relatively narrower than a general operation range of optical module one can see that the changes of the wavelength and power are significantly large fig7 a and 7b is a view illustrating a configuration of a tunable external cavity laser 700 according to an embodiment of the present invention fig7 a is a plan view of a tunable external cavity laser 700 according to an embodiment of the present invention and fig7 b is a side view of a tunable external cavity laser 700 according to an embodiment of the present invention referring to fig7 a and 7b a tunable external cavity laser 700 according to an embodiment of the present invention includes a silicon block 710 silicon substrate 720 and thermoelectric.