Optical long-haul communication technology has kept up with the explosive growth of bandwidth by employing the wavelength-division-multiplexing (WDM) technology. The WDM technology will also dramatically improve the capabilities of metropolitan access networks. Since the metropolitan access market is extremely cost-sensitive, the metro-WDM networks must be economical. In this dissertation, we propose and demonstrate low cost modulation method and two cost-effective bidirectional WDM self-healing ring networks applied to metropolitan access networks.
Firstly, a spectral filtering method in directly modulated metro-WDM transmission system is proposed. The spectral filter reduces the chirp-induced dispersion penalty and the extinction ratio penalty. There exists optimum filter bandwidth to maximize spectral filtering effect. For wide band filters, we can enhance the spectral filtering effect by detuning the filter transmission wavelength from the transmission wavelength. The maximum improvement of bit error rate (BER) power penalty after 240 km is 3 dB when the bandwidth of spectral filter is 8 GHz. The pre-filtering method suppresses nonlinear effects and gives better performance improvement than the post-filtering. We also observed the improvement of power penalty in bi-directional ring networks.
Secondly, we demonstrate a bidirectional WDM self-healing ring network connecting a central office and N remote nodes with the add fiber and drop fiber. Each remote node consists of an add multiplexer connected to the add fiber and a drop demultiplexer connected to the drop fiber. In this way, we can relax the device requirement for the relative intensity noise (RIN) generated in the bidirectional ring network. In the normal state, we can double the transmission capacity. The proposed ring provides self-healing function within 10 ms. The scalability of the proposed ring network is limited by power budget and RIN. The 2.5 Gb/s-based ring network could accommodate 8 nodes without optical amplifiers when the node spacing is 15 km. One bidirectional optical amplifier of 19.6-dB gain could improve the network size by 4 nodes.
Finally, another bidirectional WDM add/drop self-healing ring network is demonstrated. The proposed ring network connects a central office and N remote nodes with a single strand of fiber, which maximizes the fiber efficiency. Each remote node consists of a bidirectional add/drop multiplexer. The transmission capacity can be doubled in the operating state. In this network, self-healing can be achieved within 8 ms. Considering the RIN and the receiver sensitivity, the ring network based on 2.5 Gb/s signals could accommodate 6 nodes without optical amplifiers when the node spacing is 15 km. One bidirectional optical amplifier of 11.8-dB gain could increase the number of nodes by 2.