Laser optimisation for dispersion supported transmission systems

Ideal single-mode laser intrinsic parameters that optimise the performance of dispersion supported transmission (DST) systems are investigated. Laser parameter optimisation is performed to accomplish two goals: maximising the back-to-back sensitivity (BBS) and the total dispersion tolerance (TDT), with fixed laser bias and modulation currents, thus avoiding the usual DST laser current tailoring to the fibre length. Extensive numerical simulations reveal that significant improvement of DST system performance can be achieved by optimising simultaneous, independently and without restrictions, four laser intrinsic parameters; namely, linewidth enhancement factor (α), photon lifetime, gain parameter and gain compression factor (ε). The optimised laser shows good robustness of BBS and TDT to variations of those laser intrinsic parameters and a remarkable improvement in BBS and the TDT in comparison with the non-optimised DST system is achieved. It is shown that, to achieve the best DST performance at 20 Gbit/s using fixed laser currents, lasers with low α (α ≈ 0.8) and high ε (ε ≈ 10 × 10^-23 m³) are required. The physical feasibility of the optimal laser intrinsic parameters is discussed from the standpoint of current laser technology. It is shown that a suboptimal set of laser intrinsic parameters consistent with strained multi-quantum well laser technology gives improved system performance.