Performance Comparison of OFDM-UWB Radio Signals Distribution in Long-Reach PONs Using Mach-Zehnder and Linearized Modulators

The performance of orthogonal frequency division multiplexing ultra wideband (UWB) radio signals distribution in long-reach passive optical networks (LR-PONs) using conventional chirp-less Mach Zehnder (MZ) and linearized (L) Y-fed directional couplers electro-optic modulators (EOMs) is compared. Particularly, the optimum modulation index and the corresponding minimum optical signal-to-noise ratio (OSNR) required to achieve a bit error probability of 10(-12) are evaluated through numerical simulation for systems operating with single and three UWB sub-bands and different standard single-mode fiber (SSMF) distances indicated for LR-PONs. Both modulators are characterized experimentally and theoretical model parameters are adjusted to correctly describe the power and chirp characteristics of the electro-optic conversion in the simulation process. It is shown that the optimum modulation index and the tolerance to modulation index variations, considering either single or multi band UWB operation, is approximately two times higher for systems employing L-EOM than MZ-EOM. Additionally, with MZ-EOM, the required OSNR may increase considerably when the fiber length increases due to the power fading induced by fiber chromatic dispersion, achieving a penalty of almost 3 dB for systems with 100 km of SSMF and single UWB sub-band operation. Instead, with L-EOM, the required OSNR penalty (when compared with the back-to-back case) is lower for fiber lengths up to 100 km than it is for systems employing the MZ-EOM modulator due to the combined effect of the chirp generated by the modulator and the chromatic dispersion.