Optical fibers form one of the most mature and indispensable platforms in modern photonics. They underpin global telecommunications networks, enable high-power laser delivery and serve as the backbone of distributed sensing technologies. At the same time, the past decade has witnessed the rapid emergence of topological photonics [
1], where concepts originating from condensed-matter physics-such as topological invariants, band inversion and defect-bound states-are used to engineer optical modes with intrinsic robustness. These ideas have led to striking demonstrations of topological photonics in platforms including photonic crystals, waveguide arrays, and microcavities.
Bringing such topological concepts into optical fibers, however, has proven challenging. Unlike planar photonic systems, fiber systems operate over macroscopic propagation lengths and must remain compatible with scalable fabrication technologies for practical applications. As a result, implementing sophisticated topological band-structure designs within realistic fiber architectures has remained a long-standing challenge.
A recent experimental demonstration of the realization of a Dirac-vortex topological photonic crystal fiber represents an important step toward addressing this challenge [
2]. While the concept of Dirac-vortex fibers had previously been proposed theoretically [
3], the work shows that the complex topological design can be implemented within a practical fiber geometry fabricated using the conventional stack-and-draw process. The result establishes a direct link between topological band engineering and the fiber platform, opening new possibilities for robust fiber-based photonics.
1 A topological approach to broadband single-mode guidance
One of the most intriguing features of the Dirac-vortex fiber lies in the mechanism by which it achieves single-polarization single-mode guidance. In conventional fiber designs, single-mode operation typically relies on carefully tuning of the core size, refractive-index contrast or structural asymmetry to suppress higher-order modes. Such approaches often involve trade-offs between bandwidth, confinement and fabrication tolerances.
The Dirac-vortex fiber provides an alternative strategy rooted in topology. Instead of relying solely on geometric confinement, the guided mode arises from a topological mid-gap defect state embedded within the photonic band structure of the fiber lattice [
3–
5]. Because its existence is characterised by the Dirac-mass winding number, the topological invariant of the structure, the mode resides within the bandgap and is spectrally isolated from the bulk states.
2 From theoretical concept to manufacturable structure
Building on these theoretical predictions, a Dirac-vortex photonic crystal fiber has recently been realized experimentally on a silica fiber platform [
2]. In this design, a Kekulé distortion applied to a triangular photonic crystal lattice lifts the Dirac degeneracy and opens a bandgap. When the modulation phase winds azimuthally around the fiber core to form a vortex, a topological mid-gap mode emerges at the vortex center. This state constitutes the photonic realization of the Dirac-vortex zero mode predicted by the Jackiw-Rossi model-a concept that has attracted broad interest across topological physics. The resulting mode is tightly confined to the fiber core and propagates along the fiber axis within the bandgap.
Translating this elegant theoretical concept into an optical fiber, however, poses considerable challenges. The fiber cross-section must reproduce a spatially varying modulation of the photonic lattice with sufficient precision, while remaining compatible with scalable fabrication techniques. The reported realization achieved this by implementing the design using the standard stack-and-draw method, assembling silica capillaries with carefully tailored inner diameters to emulate the required Kekulé modulation.
This approach demonstrates that even relatively intricate topological structures can be engineered within the constraints of established fiber manufacturing processes. More broadly, it suggests that topological photonics is beginning to move beyond proof-of-principle demonstrations in planar nanophotonic systems toward practical or scalable optical platforms.
Experimentally, the fiber supports single-polarization single-mode propagation across the entire telecommunications window, spanning more than 400 nm. Such broadband behavior is particularly attractive for applications in optical communications, high-power fiber lasers and structured-light transmission. Beyond the immediate performance metrics, the work illustrates a broader design principle: topology can serve as an effective tool for mode selection and control in fiber systems, offering new possibilities for engineering optical modes beyond conventional refractive-index-based strategies.
3 Challenges for Dirac-vortex fibers in future photonics
The development of Dirac-vortex topological photonic crystal fibers represents an important convergence between topological photonics and advanced fiber optics. By exploiting topological protection, these fibers enable remarkable properties such as broadband single-polarization single-mode guidance, controllable mode degeneracy and resilience to structural disorde across the telecommunication window.
Despite these promising advances, several challenges remain for future applications. First, accurate theoretical modeling is difficult because topological band theory must be integrated with classical fiber waveguide analysis while accounting for realistic fabrication constraints. Second, achieving the required micro- and nano-scale structural precision over long lengths during high-temperature fiber drawing remains technically demanding. Third, extending Dirac-vortex designs beyond the near-infrared region to the visible or mid-infrared range requires new material platforms with suitable optical and thermal properties. Finally, environmental perturbations such as temperature, strain and high optical power may influence the stability of topological states.
At the same time, these challenges also reveal opportunities. AI-assisted design, advanced fiber fabrication techniques and integration with nonlinear or gain materials could enable novel topological fiber devices, including robust fiber lasers, quantum light sources and high-precision sensors. With continued progress, Dirac-vortex topological photonic crystal fibers may open new possibilities for robust optical transmission and advanced fiber-based photonic technologies.
4 Expanding the perspective on topological fibers
The realization of Dirac-vortex photonic crystal fibers [
2], together with several recent advances [
6–
10], marks an important milestone in the development of topological fibers. It demonstrates that sophisticated topological band-structure concepts can be translated into the mature and scalable platform of optical fibers.
More broadly, these works signal a shift in the role of optical fibers within topological photonics. Rather than acting merely as passive transmission channels, fibers may become active platforms for topological band and structure engineering, capable of supporting novel defect modes and unconventional light-matter interactions. In particular, their hybrid integration with emerging material platforms (Fig. 1), such as two-dimensional materials and their heterostructures [
11–
15], could open new opportunities for tunable nonlinear optics, active topological functionalities (e.g. lasers, interferometers, mode-converters), and hybrid photonic devices.
As research in this direction continues, the central question will no longer be whether topological modes can exist in optical fibers, but how such topological design principles can be harnessed to deliver tangible advantages for next-generation fiber technologies. The emergence of Dirac-vortex fibers therefore marks not just the realization of a particular design, but the beginning of a broader exploration of topological physics in fiber-based photonic systems, with potential impact on nonlinear optics, sensing, communication, computing, imaging and beyond (Fig. 1).
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