Multilevel Edge-Disjoint Fiber-Tree Planning and Spectrum Assignment for Filterless Optical Networks with Hybrid Spectrum–Cost Objectives

We study multilevel edge-disjoint fiber-tree planning for backbone filterless optical networks (FONs) under a tree-diameter bound of 1,500-km. Each level consists of pairwise edge-disjoint fiber trees. Different levels may reuse the same physical links and are allocated to spectrally disjoint slices.Given bidirectional traffic demands, we jointly construct per-level tree sets. We map each demand to exactly one tree across levels and perform spectrum assignment with continuity/contiguity and guard-band constraints under the FON tree-wide reservation rule.To reflect provisioning trade-offs, we incorporate an equipment-cost model for transceivers and passive splitters/combiners and optimize a hybrid objective $C_{\mathrm{hyb}}=\alpha F+\beta C_{\mathrm{equip}}$, where $F$ is the total spectrum width across levels.We develop a deterministic bottleneck-driven heuristic algorithm (HA) with global reassignment and backtracking refinement, as well as a multiple-initial-state simulated annealing (MISSA) framework with feasibility-preserving neighborhoods. Simulations on multiple topologies and traffic settings demonstrate that multilevel designs reduce the required spectrum and equipment costs compared to single-level baselines, and that SA-guided tree construction further improves spectrum efficiency over heuristic-seeded solutions for spectrum-dominated or hybrid objectives.