In this paper, we present a comprehensive model to address three-dimensional resource assignment (3D-RA) in space division multiplexing elastic optical networks using few-mode multi-core fibers (FM-MCFs). Accordingly, we present new 3D-RA algorithms in which the consequential resources include the spectrum, modes, and cores. We consider all spectral and spatial diversity types in FM-MCFs and introduce five 3D-RA scenarios including (i) single-mode and single-core (SMSC), (ii) single-mode and multi-core (SMMC), (iii) multi-mode and single-core (MMSC), (iv) multi-mode and multi-core (MMMC), and finally, (v) hybrid 3D-RA. In each scenario, the fractional joint (FrJ-) and independent (Ind-) switching (Sw) schemes are introduced and explored for the proposed scenarios. By using the FrJ- and Ind-Sw schemes, we performed the simulation process for the above-mentioned scenarios. The simulation results confirm the efficiency of the proposed 3D-RA algorithms. Furthermore, various 3D-RA scenarios are comprehensively compared using the obtained results in terms of vital metrics introduced in this work. It is also indicated that the SMSC and MMSC scenarios present superior performance for Ind-Sw and FrJ-Sw 3D-RA scenarios, respectively, in comparison to other proposed non-hybrid scenarios. The obtained results also reveal that the quad-hybrid 3D-RA scenario results in the lowest blocking probability in comparison with all other introduced scenarios in both switching schemes. These results recommend an efficient simulation system for compatible transceivers for Ind- and FrJ-Sw schemes.

In this paper, we study the quality of transmission (QoT) aware routing, modulation level, and resource assignment problem for transparent flexible optical networks over few-mode multi-core fibers. We consider two three-dimensional resource assignment (3DRA) algorithms, called liberal and conservative, that are compatible with fractional joint switching. The three resource dimensions are core, mode, and spectrum. Furthermore, we analyze two modulation-level selection (MLS) algorithms (one on-line and one off-line) and three path selection algorithms (favoring shortest path, best balanced load, or highest QoT). The results show that the liberal 3DRA algorithm has a similar blocking probability (BP) compared to conservative 3DRA. However, performance metrics such as computation time, optical signal-to-noise ratio (OSNR), and number of required lasers are all improved with conservative 3DRA. Moreover, the BP decreases and the average OSNR increases by applying the on-line MLS algorithm compared to the off-line algorithm. Finally, we use an on-line liberal algorithm with a path selection policy that favors load balancing to generate a solution with the lowest BP.

Both multi-band and space division multiplexing (SDM) independently represent cost-effective approaches for next-generation optical backbone networks, particularly as data exchange between core data centers reaches the petabit-per-second scale. This paper focuses on different strategies for implementing band and SDM elastic optical network (BSDM EON) technology and analyzes the total network capacity of three sizes of backbone metro-core networks: ultra-long-, long-, and medium-distance networks related to the United States, Japan, and Spain, respectively. Two BSDM strategies are considered, namely, multi-core fibers (MCFs) and BSDM based on standard single-mode fiber (SSMF) bundles of multi-fiber pairs (BuMFPs). For MCF-based BSDM, we evaluated the performance of four manufactured trench-assisted weakly coupled (TAWC) MCFs with 4, 7, 13, and 19 cores. Simulation results reveal that, in the regime of ultra-low (UL) loss and inter-core crosstalk (ICXT), MCF-based throughput can be up to 14% higher than SSMF BuMFP-based BSDM when the core pitch exceeds 43 µm and the loss coefficient is lower than that of standard single-mode fibers. However, increasing the number of cores with (non-)standard cladding diameters, UL loss, and ICXT coefficient is not beneficial. As core counts increase up to 13 for non-standard cladding diameters (<230µm), the core pitch and loss coefficient also increase, leading to degraded performance of MCF-based BSDM compared to SSMF BuMFP-based BSDM. The results indicate that, in scenarios with 19 MFPs, SSFM BuMFP-based BSDM outperforms 19-core MCF-based scenarios, increasing the throughput by 55% to 73%, from medium-backbone networks to ultra-long ones.

The relentless demand for high-bandwidth services and applications in the beyond-5G/6G era necessitates optical networks to provide ample spectral resources to accommodate the increasing traffic loads. This requirement is especially pronounced in metro and regional segments, where a projected traffic compound annual growth rate (CAGR) of over 40%, driven by content delivery network (CDN) traffic concentrated near the end users, threatens to push the fiber capacity to its limits on a number of heavily utilized links in the short to medium term. This limitation cannot be circumvented despite the utilization of spectrally efficient modulation formats designed for short-distance transmission. Thus, it is imperative to explore migration strategies to solutions that allow the expansion of spectral resources beyond the current usage of the extended C-band (4.8 THz). In this article, we present a comprehensive evaluation of multi-homed edge-to-core routing, modulation-level selection, and spectrum assignment simulations conducted over reference metropolitan area networks (MANs) by leveraging on a novel network planner called 6D-MAN, which we have developed to adapt to heterogeneous multi-layer networks based on multi-band and multi-fiber transmission. Our simulations consider coherent transmission with flexible modulation format transponders operating at capacities ranging from 100 to 400 Gbps on the 50 GHz grid and explore link-by-link migration strategies restricted to the C+L-band, ensuring optimal performance in terms of the generalized signal-to-noise ratio (GSNR). The obtained results demonstrate that deploying L-band equipment on a selected number of links effectively extends the lifespan of existing networks, enabling congestion-free operation with minimal intervention. In their entirety, our findings underscore the importance of contemplating alternative spectral resources beyond the conventional C-band. They unequivocally accentuate the potential of L-band equipment strategic deployment to tackle capacity constraints in MANs, resulting in a 60% reduction in fiber length and a remarkable 45% decrease in new fiber-pair link deployment needs. The profound implications of efficient fiber capacity utilization manifest themselves in substantial OPEX and optical total cost of ownership savings, amounting to approximately 71% and 17%–27%, respectively, over a 10-year period. This research provides valuable insights for MAN operators seeking sustainable strategies to support the growing demands of future beyond-5G/6G services.

In this letter, we propose to implement quantum key distribution (QKD) by using a multi-band strategy. We present a thorough noise analysis of quantum-classical coexistence while incorporating all relevant and precise noise parameters. Our research demonstrates that utilizing the entire extended C-band for quantum and transmitting classical channels (CChs) over the extended L-band with bandwidth of 75 GHz and power of 0 dBm yields no quantum communication beyond 13 km. To address the problem, we utilize the C+L-band to serve CChs and other bands (e.g., O, E, S) for quantum channels (QChs), while taking into account impairments over the quantum one. Results indicate that, while C+L-band is fully loaded, wavelengths of 1381 nm and below (1260-1381 nm) are appropriate for quantum signals, with 1381 nm offering the highest key rate (3.08 Mbit/sec) over a fiber length of 70 km. Finally, to explore an additional operational scenario when the network is not fully loaded, we focused on determining the optimal policy for assigning CChs. The results reveal the importance of prioritizing the maximization of the gap between the CChs and QChs. In addition, the channel assignment pattern of CChs affects the performance of QChs transmitted at other bands (O, E, and S).

Filterless optical networks (FONs) as an economical solution use passive couplers/splitters rather than expensive active filter devices. In this way, after intermediate and destination nodes, lightpaths are dropped and continued, which generates leakage signals in other links and wastes spectrum. Thus, designing efficient resource allocation in FONs by considering the leakage signals and their interfering effects is of utmost importance. On the other hand, a gradual transition from wavelength division multiplexing optical networks to elastic optical networks (EONs) is occurring due to their efficient utilization of spectrum. Furthermore, utilizing the L-band beside the conventional C-band for spectrum assignment offers a wide range of frequency resources. Therefore, in this paper, we propose an integer linear program (ILP) to solve quality of transmission (QoT)-aware tree selection, routing, modulation, and spectrum assignment problems in filterless EONs over the C+L-band. Furthermore, we provide heuristic algorithms to deal with complex large-scale networks. The performance gap of the proposed ILP and heuristic algorithms is evaluated over a small-scale (5-node) network. The results show that the ILP and heuristic algorithms have almost the same performance in terms of spectrum usage and assigned modulation format, and ILP has a slightly higher generalized signal-to-noise-ratio (GSNR) (0.23 dB or 0.8% at optimum launch power). Furthermore, the heuristic algorithms are also examined over a large-scale network (TID region A topology). The results reveal that the GSNR estimation method severely affects the performance in terms of spectrum usage, blocking, and outage. Furthermore, by using the proposed MX5 method, as long as there is a fill margin of approximately 2 dB, there is no outage or blocking over the C+L-band, up to a network throughput of 110 Tbps and conventional C-band transmission with lower throughput (i.e., 40 Tbps). Finally, our extensive numerical results provide a rule of thumb for balancing blocking, outage, spectrum usage, and the number of expensive L-band transponders by selecting the appropriate modulation assignment method.