Distribution of Double-Sideband OFDM-UWB Radio Signals in Dispersion Compensated Long-Reach PONs

The performance of orthogonal frequency division multiplexing ultra wideband radio signals distribution in dispersion compensated (DC) long-reach passive optical networks (LR-PONs) is assessed numerically for conventional chirpless Mach-Zehnder (MZ) and chirped linearized (L) electro-optic modulators (EOMs). The optimum modulation index and the minimum required optical signal-to-noise ratio are evaluated for optical network units (ONUs) at different distances from the optical line termination (OLT). The degradation due to first-order polarization mode dispersion (PMD), fiber nonlinearity, phase noise due to the Kerr effect, and the phase noise due to finite laser linewidth is assessed as well. It is shown that the use of dispersion compensation in LR-PONs employing the MZ-EOM is a powerful solution to mitigate the dispersion-induced power fading. It is also shown that, contrarily to the L-EOM case, the same optimum voltage level at the EOM input is required by DC LR-PONs employing the MZ modulator, independently of the ONUs distances. In addition, an optical signal-to-noise ratio penalty not exceeding 0.5 dB due to first order PMD effect is obtained for a PMD parameter below 0.5 ps·km^-1/2 and for a fiber nonlinearity corresponding to a nonlinear phase shift not exceeding 11 mrad. This conclusion holds for pre (at the OLT) and post (at the remote node) compensation schemes. The performance degradation induced by the laser phase noise is also negligible in DC LR-PONs for typical laser linewidths due to the reduced phase-to-intensity noise conversion.