Investigation of intra/inter-band cross-modulation in multiband radio-over-fiber systems

We theoretically and experimentally investigated the intra/inter-band cross-modulation (XM) induced by the nonlinearity of Mach-Zehnder modulator (MZM) in a multiband radio-over-fiber (RoF) system. A closed-form theoretical analysis was proposed to model and predict the nonlinear XM behaviors, for both single-band vector signals and multiband combination of scalar and vector signals. To verify the feasibility of the theoretical model, both simulation and experimental investigations were carried out, and according to the theoretical analysis, scalar signals only suffer from inter-band XM; whereas vector signals suffer from both intra- and inter-band XM. The signal quality degradation induced by MZM nonlinearity for a single-band 16QAM, QPSK, and two bands of OOK signals are investigated and characterized, and good agreement between theory and experiments was achieved. It was observed that QPSK shows superior performances compared with higher order QAM formats due to its intrinsic resistance to intra-band XM.