An optical transmission system includes a laser module generating a modulated optical waveform, including both amplitude and frequency modulation, at center frequencies corresponding to different operating temperatures; and an optical shaping filter, with passbands corresponding to the different center frequencies, that converts at least part of the frequency modulation to additional amplitude modulation. The optical transmission system is tuned by: determining a range of temperatures at which the laser module center frequencies are within a passband of the optical shaping filter; setting the laser module to a temperature, within the range of temperatures, at which the modulated optical waveform is within the passband; measuring an average output power of the optical shaping filter; and adjusting the temperature of the laser module to a target temperature, within the range of temperatures, at which an output condition is achieved, based on the average output power and/or extinction ratio of the filtered waveform.