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Filter concatenation in metropolitan optical networks utilizing directly modulated lasers

We studied the impact of different chirp characteristics of 2.5 Gb/s directly modulated lasers on the filter concatenation effects in transparent metropolitan area optical networks. For adiabatic chirp-dominated lasers, it is found that the filter concatenation results in performance improvement, if the overall detuning between the laser wavelength and the center wavelength of the overall transfer function of the filter cascade is positive, and in significant performance degradation if the detuning is negative. For a transient chirp-dominated laser, a small penalty was observed for both positive and negative detunings. The measured Q-factor penalties, due to filter concatenation, were compared with theoretical Q-factor calculations for the worst-case transmitter and the results are in excellent agreement.