Simulations of statistical parameter distributions in distributed-feedback lasers using a transmission-line laser model

Abstract

A transmission-line laser model has been used for simulating distributed-feedback (DFB) lasers. Statistical distributions of laser parameters like threshold current, slope efficiency, front-to-back power ratio, or side-mode-suppression ratio (SMSR) are generated by varying randomly lasers’ facet phases. Model parameters were adjusted by comparing simulated and experimental distributions for a continuous wave (CW) index-coupled and a 2.5 Gbit/s gain-coupled directly-modulated (DM) DFB lasers. For the index-coupled DFB laser, agreement with experimental data is excellent except for the front-to-back power ratio, which has a larger spread than measured experimentally. For the gain-coupled DFB laser, distributions are in excellent agreement with experimental data, but the SMSR is calculated to have a median about 6 dB larger than measurement. Distributions of small-signal parameters and dispersion penalties after propagating in an optical fibre are also generated for various drive conditions and design parameters. It is shown that a grating with an index coupling larger than 4.0 and a gain coupling of around 0.05 gives the highest 2 dB dispersion penalty yields for a reach of 450 km. There is nevertheless a compromise between high dispersion penalty yields and CW single-mode yields when using large index coupling coefficients with only a small amount of gain coupling.