A method for tuning a tunable optical transmitter of a given type out of a plurality of optical transmitters that are connected to a first end of an optical WDM transmission link to a predetermined target wavelength, especially during a power-on procedure of the tunable optical transmitter, (a) wherein the tunable optical transmitter is controllable to create an optical signal having a predetermined wavelength according to a tuning information which is supplied to the tunable optical transmitter through at least one tuning signal (S tune), wherein the tuning information comprises at least one parameter of the at least one tuning signal (S tune), the method comprising the steps of: (b) controlling the tunable optical transmitter to create an optical calibration signal (S cal) according to a nominal tuning information in such a way that the optical calibration signal (S cal) has a wavelength lying within a secure wavelength range, (i) the nominal tuning information being determined by using a known nominal wavelength dependency characterizing the wavelength dependency of the given type of tunable optical transmitters on the at least one parameter of the at least one tuning signal (S tune), and (ii) the secure wavelength range being defined in such a way that it does not comprise any optical channel wavelength range predefined for transmitting an optical channel signal in the direction of the optical calibration signal (S cal) over the WDM transmission link and that it is broad enough to ensure that the wavelength of the optical calibration signal (S cal) lies within the secure wavelength range, (c) determining a calibration information for the optical tunable transmitter by directly or indirectly measuring, within the secure wavelength range, a deviation between an actual wavelength dependency of the tunable optical transmitter and the nominal wavelength dependency, and (d) controlling the tunable optical transmitter to create an optical channel signal according to a target tuning information in such a way that the optical signal has a wavelength being equal or lying, within predetermined acceptable tolerances, close to the target wavelength, (e) wherein the target tuning information is determined by using a corrected nominal wavelength dependency, the correction being effected by using the calibration information. (a) wherein the tunable optical transmitter is controllable to create an optical signal having a predetermined wavelength according to a tuning information which is supplied to the tunable optical transmitter through at least one tuning signal (S tune), wherein the tuning information comprises at least one parameter of the at least one tuning signal (S tune), (b) controlling the tunable optical transmitter to create an optical calibration signal (S cal) according to a nominal tuning information in such a way that the optical calibration signal (S cal) has a wavelength lying within a secure wavelength range, (i) the nominal tuning information being determined by using a known nominal wavelength dependency characterizing the wavelength dependency of the given type of tunable optical transmitters on the at least one parameter of the at least one tuning signal (S tune), and (ii) the secure wavelength range being defined in such a way that it does not comprise any optical channel wavelength range predefined for transmitting an optical channel signal in the direction of the optical calibration signal (S cal) over the WDM transmission link and that it is broad enough to ensure that the wavelength of the optical calibration signal (S cal) lies within the secure wavelength range, (i) the nominal tuning information being determined by using a known nominal wavelength dependency characterizing the wavelength dependency of the given type of tunable optical transmitters on the at least one parameter of the at least one tuning signal (S tune), and (ii) the secure wavelength range being defined in such a way that it does not comprise any optical channel wavelength range predefined for transmitting an optical channel signal in the direction of the optical calibration signal (S cal) over the WDM transmission link and that it is broad enough to ensure that the wavelength of the optical calibration signal (S cal) lies within the secure wavelength range, (c) determining a calibration information for the optical tunable transmitter by directly or indirectly measuring, within the secure wavelength range, a deviation between an actual wavelength dependency of the tunable optical transmitter and the nominal wavelength dependency, and (d) controlling the tunable optical transmitter to create an optical channel signal according to a target tuning information in such a way that the optical signal has a wavelength being equal or lying, within predetermined acceptable tolerances, close to the target wavelength, (e) wherein the target tuning information is determined by using a corrected nominal wavelength dependency, the correction being effected by using the calibration information.