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

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 randomly varying the lasers’ facet phases. Model parameters were adjusted by comparing simulated and experimental distributions for a continuous wave (CW) index-coupled laser and a 2.5Gb/s gain-coupled directly-modulated (DM) DFB laser. For the index-coupled DFB laser, agreement with experimental data is excellent but 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 5dB larger than measurement. Distributions of dispersion penalties after propagation in an optical fiber 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 2dB dispersion penalty yields for a reach of 450km. 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.