Recent Progress in Development of Hollow-Core Fibers for Telecommunications and Data Transmission

This is a follow-on review of progress in development and applications of hollow core optical fibers (HCFs) after publication of earlier review in 2023 [1], to be read together with it. Progress after 2023 in several fields is significant. Loss of best HCFs was reduced down to 0.05–0.10 dB/km at 1550 nm [2–6], while lowest loss achieved in single mode fiber with pure silica core is 0.14 dB/km [7]. Polarization mode dispersion (PMD) has been reduced to a level typical for SMFs by means of fiber spinning [8]. In November 2024, Microsoft announced a 2-year plan to install 15,000 km of HCF cables between data centers providing data processing for Microsoft Azure cloud services, and inside these facilities [9,10]. Besides UK-based Microsoft Azure Fiber and two Microsoft subcontractors: Corning Inc. and Heraeus Covantics, two major HFC manufacturers: YOFC and Linfiber emerged in China. Unfortunately, progress in standardization and elimination of loss introduced by contaminants in the fiber was absent. Standardization is blocked by multiple fiber designs being tried, with no clear winner yet. Despite this, hollow core fibers have successfully made large-scale commercial debut in Microsoft Azure data centers.