Performance Improvement of Radio-Over Fiber Links Using Mixed-Polarization Electro-Absorption Modulators

We analyze, in theory, simulation, and experiment the spurious-free dynamic range (SFDR) for a radio-over-fiber (RoF) system using a polarization-dependent electro-absorption modulator (EAM) that is linearized using mixed polarization. The mixed-polarization EAM makes use of a polarization-dependent EAM, where a linear polarizer is placed in front of and behind the optical modulator. It is found that improvements of more than 8.1 and 9.5 dB in SDFR for back to back and after 20 km of fiber transmission, respectively, are predicted in theory and simulation and verified experimentally. Suppression of second-order nonlinear distortion is also investigated by simulation and experiment. Moreover, closed forms of the adjacent channel power ratio and third-order intermodulation distortion to carrier power ratio of an orthogonal frequency division multiplexing (OFDM) ultra-wideband (UWB) signal are presented for an RoF link using mixed-polarization EAM. Finally, mixed-polarization EAM is verified for improving the error vector magnitude of the OFDM UWB signal over fiber by more than 3 dB.