Explore Maximal Potential Capacity of WDM Optical Networks Using Time Domain Hybrid Modulation Technique

The recent emerging time domain hybrid modulation (TDHM) technique is considered promising because it can realize continuous adaptation between spectral efficiency and transparent reach through appropriately allocating the time slot occupancy ratios of different modulation formats in a time-division multiplexing (TDM) frame. This technique is expected to achieve more efficient spectrum utilization or higher transmission capacity than the traditional transmission technique based on discrete modulation formats. For the point-to-point transmission system, the benefit of the TDHM technique has been experimentally verified. However, its benefit from the whole network perspective has not been explored yet. In this paper, we apply the TDHM technique to the optical network to maximize its transmission capacity. To evaluate the benefit of this technique, we consider the routing and wavelength assignment problem for the TDHM-based WDM network, for which we develop an integer linear programming model and a waveplane-based heuristic algorithm to maximize the total network transmission capacity for the cases with and without network protection. For the protection case, the shared backup path protection technique is employed owing to its efficiency of spare capacity sharing and simplicity in network operation. The simulation study shows that compared to the design with discrete modulation formats, the TDHM-based approach can significantly increase the network transmission capacity.