In the present paper coherent optical transmission systems (ASK and PSK) with homodyne detection will be optimized in regard to a minimum bit-error-rate (BER). By calculating the BER the laser phase noise, the additive Gaussian noise, the influence of the baseband filter on both noise terms and the intersymbol interferences are accounted for. The optimizable system parameters are identified as the PLL bandwidth, the bandwidth of the baseband filter and the decision threshold. It will be shown that the optimal filter bandwidth and the optimal threshold in ASK systems, in contrast to PSK systems, are dependent on the laser phase noise. The calculation of the optimal system parameters will be done exactly and by useful approximations.

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