Wavelength division multiplexed passive optical networks

Abstract

Optical fiber transmission technology has been used widely and has been playing a more and more important role in today's telecommunication networks. As a transmission medium, optical fiber offers many advantages comparing with other alternatives, such as broad bandwidth and low attenuation. This enables large data capacity over an extremely long transmission distance. It has been the main medium of signal transmission for long haul networks and from the beginning of this century, significant amount of research work has also been carried out in using optical communication technology for optical access networks as the best solution for the "last-mile" connectivity. Wavelength division multiplexing passive optical network (WDM-PON) is a promising candidate for the next generation optical access networks. In this thesis, several interesting WDM-PON schemes are proposed and investigated to solve some research challenges in WDM-PON system, which are colorless ONU, Rayleigh backscattering, and dual independent service data transmission. Subcarrier multiplexed WDM-PON system is studied. The system uses subcarrier multiplexed single sideband (SSB) modulation for downlink data transmission and RSOA re-modulation of baseband data for uplink data transmission to realize a bidirectional PON system. The scheme reduces the effect of RB and since self-heterodyne coherent detection can be realized, high order modulation can be employed to further increase the data rate and dispersion equalization can be easily realized. The use of a high frequency subcarrier also allows direct detection to be employed for uplink data detection without the need for optical and electrical filtering at the OLT. Using the proposed system, a 2.5Gb/s bidirectional WDM PON system with RSOA re-modulation is demonstrated experimentally. OFDM-WDM-PON system is investigated. In this scheme, a WDM PON system using direct detected OFDM for downlink signal transmission is studied experimentally. Single sideband modulated OFDM signal with a guardband at the baseband is used to simplify direct detection of the OFDM signal at the ONU. The guardband portion of the downlink signal is used by an RSOA for baseband signal re-modulation. The use of OFDM for uplink signal transmission allows high data rate to be realized for limited RSOA bandwidth. Using the proposed system, 40Gb/s downlink signal transmission and 10Gb/s uplink transmission for a WDM PON system are demonstrated. Pol-MUX WDM-PON system is evaluated through simulation. The downlink is a Pol-MUX signal with two orthogonally single-sideband (SSB) signals with different local oscillator (LO). One upper-sideband (USB) is used as wired service, the other lower-sideband (LSB) is used as wireless service. This configuration can overcome the CD and RB effect and eliminate undesirable beat frequency of dual service signals to maximize RF spectrum utilization. It avoids the complex polarization de-multiplexing at the ONUs and enables a scalable receiver frontend without additional filters. By using the proposed system, 10Gbps downlink transmission with scalable ONUs for a dual service WDM-PON system is demonstrated through simulation.