Figure 1 Power spectral densities β½ and β½ of the second-2 3 and third-order distortion noise for an SCM hybrid AM-VSBrQAM Ε½ channeling 60 AM-VSB channels, m s 4%; 90 16-QAM AM -VSB channels, m s 0.6%; semiconductor laser emitted power s 2 QA M . mW, β r2 s 5 GHz . Typical values of semiconductor laser pa-R w x rameters have been drawn from 9 m s 4%; 90 16-QAM channels, m s 0.6%; semi-AM-VSB QAM
. conductor laser emitted power s 2 mW, β r2 s 5 GHz , R which is shown in the figure itself. Unlike other distortion phenomena, in this case, both spectral densities show similar behavior, substantially due to the same dependence on frequency. It is worth noting how this distortion noise affects the higher frequency interval of the available band to thus sensibly constrain the QAM channel performance. This effect can be found only by using a semiconductor laser with as high a relaxation oscillation frequency as possible.
The proposed model can therefore explain the overall distortion noise spectrum unlike other approaches that hold for particular portions of the spectrum.
IV. CONCLUSIONS
Nonlinear distortion effects in a semiconductor laser must be carefully analyzed in order to evaluate the performance of SCM-based optical access networks, in the case of operation in conjunction with wireless systems, for future personal Ε½ . communication systems PCS . The distortions that arise in the case of direct modulation of a semiconductor laser result from the interaction of photons and electrons, which is described by the rate equations. In this paper, closed expressions for the power spectral densities of the second-and third-order dynamic distortions are obtained, which can provide useful information about laser and system parameters that optimize network performance.