AI summaryⓘ
The authors explain challenges when mixing hollow-core fibers (HCF) with traditional single-mode fibers (SMF) in network protection setups. They compare two methods for backup paths—1+1 dedicated and shared backup path protection (SBPP)—showing how signal quality and speed can be affected when switching between fiber types. Their simulations reveal that switching from HCF to SMF causes more signal loss and distortion than the opposite direction, and that 1+1 protection generally performs better than SBPP in hybrid networks. They also suggest ways to reduce these problems, such as using advanced signal processing and better network planning. Overall, their results help guide upgrades as network operators move toward using more HCF.
Hollow-core fiberSingle-mode fiberProtection switching1+1 dedicated protectionShared backup path protectionChromatic dispersionGeneralized signal-to-noise ratioModulation formatMonte Carlo simulationNetwork topology
Abstract
Hollow-core fibers (HCF) are transitioning from laboratory curiosities to production-deployed infrastructure, with cloud providers operating thousands of kilometers of hollow-core links. As operators upgrade their networks, working and protection paths will inevitably traverse different fiber types, creating a class of protection switching challenges absent in homogeneous single-mode fiber networks. This article provides a comprehensive overview of these challenges and presents a comparative analysis of protection switching under two architectures - 1+1 dedicated and shared backup path protection (SBPP) - in hybrid hollow-core and single-mode fiber networks. Using Monte Carlo simulation with random per-link fiber assignment across six reference topologies (1,602 node pairs), we quantify chromatic dispersion (CD) steps, generalized signal-to-noise ratio (GSNR) penalties, and modulation-format degradation for both architectures. At 50% HCF deployment mean CD steps range from 4,000 to 22,000 ps/nm, with GSNR penalties of 1.6-3.1 dB and 38-59% of node pairs requiring modulation downgrade under 1+1 protection. A complementary cross-fiber extreme analysis reveals that the two switching directions are fundamentally asymmetric: HCF-to-SMF switching doubles the CD step and inflicts about a 10 dB GSNR penalty while SMF-to-HCF switching delivers a negative GSNR penalty (the protection path is higher quality than the working path). SBPP shows up to 7% higher CD steps and 4 percentage points more downgrade in sparsely connected topologies due to its greedy shortest-first path selection. Capacity retention improves with HCF penetration for both architectures, reaching 85-99% at full HCF deployment. We present mitigation strategies including DSP pre-loading, spectral pre-equalization, and network planning guidelines, concluding that 1+1 dedicated protection is preferable to SBPP for hybrid deployments.