Transmission of Multiband OFDM-UWB Signals Along LR-PONs Employing a Mach–Zehnder Modulator Biased at the Quasi-Minimum Power Transmission Point

The influence of the Mach-Zehnder modulator (MZM) bias and driving voltages on the transmission performance of multiband orthogonal frequency division multiplexing ultrawideband radio signals is analyzed theoretically and experimentally. Particularly, the optical signal-to-noise ratio (OSNR) required to achieve a given bit error probability is evaluated for a bias voltage close to the minimum power transmission of the MZM characteristic. In addition, the required OSNR obtained for that bias voltage is compared with the OSNR required when the MZM is biased at the quadrature point. The analysis is performed for different fiber lengths indicated for long-reach passive optical networks (LR-PONs). It is shown that lower OSNR is required when the modulator is biased at the quasi-minimum point than when it is biased at the quadrature point, for all the fiber reaches analyzed. This is due to the compromise between additional distortion induced by the modulator and lower carrier-to-signal-power ratio when the quasi-minimum bias point is employed. In addition, it is also shown that, as for the quadrature bias point, similar optimum driving voltages are obtained for the different LR-PONs reaches analyzed, when the quasi-minimum bias point is employed.