Investigation of Data-Dependent Channel Cross-Modulation in Multiband Radio-Over-Fiber Systems

Data-dependent channel cross-modulation (XM) in multiband radio-over-fiber (RoF) systems have been investigated and illustrated for the first time. Nonlinear XM behaviors induced by a Mach–Zehnder modulator (MZM), including the intra-band XM between in-phase (I) and quadrature (Q) components of vector signals, as well as the inter-band XM between multiple bands of scalar/vector signals, have been studied by a closed-form theoretical analysis, and validated by experimental measurements. Consistent results have been obtained by both theoretical and experimental investigations. It was demonstrated that scalar signals only suffer from inter-band XM; whereas vector signals suffer from both intra- and inter-band XMs. Intra-band XM induces constellation compression distortion to vector signals, while inter-band XM induces eye-diagram degradation to scalar signals, and constellation scaling distortion to vector signals. To mitigate the signal distortions induced by data-dependent XM, arcsine pre-distortion technique was implemented to compensate the nonlinear response of MZM. Effective cancellations of both intra- and inter-band XM were achieved.