UWB-Over-Fiber Communications: Modulation and Transmission

The distribution of ultra-wideband (UWB) signals over optical fiber, or UWB over fiber (UWBoF), is proposed to extend the area of coverage and to offer the availability of undisrupted service across different networks. Various techniques have been reported recently for optical UWB pulse generation, but the study on the implementation of different modulation schemes based on these UWB pulses has just started. In addition, the influence of fiber dispersion on the power spectral density (PSD) of an UWB signal, and the bit-error-rate performance of an UWBoF system with different modulation schemes have not been systematically investigated. In this paper, we perform a comprehensive investigation of techniques to implement on-off keying (OOK), bi-phase modulation (BPM), pulse-amplitude modulation (PAM), pulse shape modulation (PSM), and pulse-position modulation (PPM) based on a phase modulator and an asymmetric Mach-Zehnder interferometer (AMZI). The AMZI is electrically reconfigurable by employing a polarization modulator (PolM). UWB signals with OOK, BPM, PAM, PSM, and PPM are realized by adjusting the polarization controllers in the AMZI and the amplitude of the electrical drive signal to the PolM. The UWB signals with OOK, BPM, PAM, and PSM are transmitted over a wired (single-mode fiber) and wireless link. Error-free operation is obtained for all the modulation schemes. The power penalties of transmission are less than 1.8 dB. The fiber dispersion on the PSD of the UWB signals is also theoretically studied and experimentally evaluated. An excellent agreement between the theoretical and the experimental results is achieved. The system is potentially integratable, which may provide a simple and cost-effective solution for UWBoF applications.