High speed modulation of diode lasers

Conventional laser sources have their bit rates limited to around 10 GHz to 20 GHz by the internal photon-electron resonance of the laser combined with carrier transport effects and the package parasitics. The spread in the modulated spectrum is typically 5 to 10 times the ideal Fourier transform limit. This `chirp´ in the laser leads to dispersion of the optical pulse in the optical fibre and leads to unacceptable penalties in the system. Further, the functionality of conventional laser sources is limited. One would like to pre-chirp the optical signal prior to launch to compensate for fibre dispersion; or to recover the clock by an all optical recovery system; or to generate optical clocks at multi-gigabit rates for use in opto-electronic signal processing, clock distribution soliton pulse generation etc. This paper gives three examples of design techniques of future laser sources through using large signal dynamic modelling. This modelling escapes from the conventional “lumped” rate equation approach and looks at the complex motion of photonic wave-packets inside the laser. The techniques provide both new insights and new designs