use of depletion edge translation as an in cavity phase modulation mechanism in lasers . aspects of the invention are especially relevant in transmitters for extended reach comprising an intra cavity phase and amplitude modulated laser for generation of a frequency modulated signal and a passive optical spectrum reshaper element , sometimes referred to as a chirp modulated laser . such techniques may be carried out as disclose herein by adopting predetermined doping profiles and applying predetermined voltage to the laser cavity , and more preferably to a phase section in or adjoining the laser cavity .