Preamplifier ASK system performance with incomplete ASK modulation: influence of ASE and laser phase noise

Present extensions of the rigorous model of Jacobsen and Garrett and of the Gaussian approximation of Tonguz and Kazovsky for the performance of optically amplified direct detection ASK receivers. These new models take into account incomplete ASK modulation, nonzero laser linewidth, and spontaneous emission noise from the optical amplifier in both polarization control (PC) and polarization diversity (PD) receiver configurations. The penalty associated with the polarization diversity configuration is shown to be consistently under 1 dB for a wide range of ASK modulation depths. The penalty due to the noise in the orthogonal polarization decreases with ASK modulation depth. We find optimum optical filter bandwidths and linewidth-induced performance penalties as a function of ASK modulation depth and linewidth. We provide detailed tables of optimum filter bandwidths for bath PC and PD receivers using both the rigorous method and the Gaussian approximation; the Gaussian approximation frequently underestimates the optimum bandwidth values. A linewidth-induced floor in the minimum usable ASK modulation depth is found for nonzero linewidth and a fixed optical filter bandwidth. Though the Gaussian approximation is found to be accurate within 1.5 dB in all computed cases for optimum optical filter bandwidths, it does not predict the floor accurately in the case of a nonoptimum filter bandwidth.<
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