Distance-adaptive modulation is effective at enhancing network capacity as it allows the maximum possible modulation order to be selected for each optical path. However, present single-carrier systems can only select just one modulation order for each optical path and hence the adaptability to transmission characteristics is strictly limited. In contrast, digital subcarrier multiplexing systems can select a combination of modulation orders for multiple subcarriers on each optical path and can flexibly adapt to various transmission characteristics. This paper numerically evaluates the transmission characteristics of digital subcarrier multiplexing systems. The interaction between laser phase noise and chromatic dispersion is well examined by extensive simulations, and two-phase estimation methods are compared. The results show that digital subcarrier multiplexing systems with the appropriate phase estimation method enable longer transmission distances.
The popularity of high-capacity communication services such as video streaming and cloud computing has accelerated the growth in IP traffic. In order to effectively manage and maintain networking systems, various intelligent technologies based on software-defined networking (SDN) have been widely studied. An SDN system that offers flexible optical path management exploiting optical performance monitoring, digital signal processing, and resource allocation is expected to realize higher capacity networks by lowering margins needed to offset system uncertainty. In this paper, we provide a comprehensive survey of optical path management schemes based on machine learning.
We propose a cost-effective metro network architecture with fiber-granular routing and path-granular add/drop operations together with its ILP-based design algorithm. The proposal alleviates the impact of filtering impairment while using already deployed OXC/ROADM nodes. Numerical simulations on several real-world metro topologies verify that it increases the spectral efficiency compared to the ideal method for DWDM networks.
Optical-path networks based on wavelength-selective switches (WSSs) can cost-effectively process wavelength-divisionmultiplexed (WDM) signals. To deal with the continuously increasing network traffic, the spectral efficiency must be improved by minimizing guardband bandwidths. Quasi-Nyquist WDM systems are seen as offering the highest spectral efficiency. However, such highly dense WDM systems suffer from signal-spectrum narrowing induced by the nonrectangular passbands of WSSs. Furthermore, widely deployed WSSs cannot process quasi-Nyquist WDM signals since the signal-alignment granularity does not match the passband resolution of the WSSs. In this paper, we propose a network architecture that enables quasi-Nyquist WDM networking. First, multiple channels are bundled so that the total channel bandwidth matches the WSS-passband resolution. Second, the number of spectrum-narrowing events of each path is limited by our restriction-aware algorithm. These proposals allow a 100-GHz bandwidth to accommodate three 100-Gbps DP-QPSK signals aligned with 33.3-GHz spacing and a 200-GHz bandwidth to accommodate three 400-Gbps dual-carrier DP-16QAM signals aligned with 66.6-GHz spacing. Intensive network analyses confirm that the spectral efficiency is improved by up to 46.4%. Feasibility is verified by transmission experiments using 69-channel 400-Gbps dual-carrier DP-16QAM signals aligned with 66.6-GHz spacing in the extended C-band. The fiber capacity of 27.6 Tbps and the transmission distance of 800 km are attained by our proposed quasi-Nyquist WDM networking.
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