Anti-Resonant Hollow-Core Fibers

Updated 29 October 2025

AR-HCFs are microstructured optical fibers that guide light in an air core using anti-resonant reflection, yielding low-loss and broadband performance.
Their performance is dictated by precise geometric design of thin-walled glass capillaries, controlling dispersion, modal properties, and attenuation.
Advanced fabrication enables applications in ultrafast optics, high-power delivery, and quantum communication by optimizing structure and material properties.

Anti-Resonant Hollow-Core Fibers (AR-HCFs) are a class of microstructured optical fibers in which light is guided within a hollow core by anti-resonant reflection from thin glass membranes. Unlike photonic bandgap or conventional total-internal-reflection fibers, AR-HCFs exploit the anti-resonance condition in the cladding to achieve broadband guidance with low optical loss, low nonlinearity, and propagation characteristics determined predominantly by the geometry and arrangement of the anti-resonant glass elements. This structural paradigm enables unique advantages for low-latency communication, high-power delivery, ultrafast nonlinear optics, and precision metrology.

1. Geometric Principle and Guiding Mechanism

AR-HCFs embed a hollow core—frequently air-filled—surrounded by a microstructured ring of thin-walled glass capillaries that do not necessarily touch each other ("nodeless," "free boundary"), or complex nested structures for advanced designs. The primary guiding mechanism is anti-resonant reflection at specific glass wall thicknesses. At non-resonant (anti-resonant) wavelengths, these membranes act as highly reflective barriers, confining most of the modal field inside the low-index central void.

The anti-resonance condition for a cylindrical membrane of thickness $t$ and material refractive index $n$ is

$\lambda_m = \frac{2t}{m}\sqrt{n^2 - n^2_{\text{core}}}$

where $m$ is an integer resonance order; at these $\lambda_m$ (resonances), the glass transmits energy efficiently, resulting in loss peaks. Between these, reflection is maximized (antiresonance), yielding minima in propagation loss and broad transmission bands. Broadband, low-loss operation is achieved by operating in the first anti-resonant window with thin wall thickness relative to the guided wavelength.

Advanced AR-HCF geometries include multiple nested rings, truncated tube designs, and multi-core assemblies—each leveraging antiresonant waveguiding but tailored for mode control, bandwidth, or channel multiplexing.

2. Structural and Material Design Considerations

Wall Thickness and Dispersion

Wall thickness $t$ is the dominant parameter controlling the spectral position and width of anti-resonant bands, minimum fiber loss, group velocity dispersion (GVD), and the onset of loss resonances. Empirical and analytical models, such as those by Marcatili-Schmeltzer, bouncing-ray, and impedance-perturbation formalisms, extend classic capillary theory to include the resonant/anti-resonant physics, accurately reproducing dispersion and loss characteristics otherwise accessible only by full finite-element modeling (Bache et al., 2018, Hasan et al., 2017). These models incorporate corrections for nested features, perimeter gaps, and capillary arrangement to yield predictive capacity for the effective index,

$n_{\text{eff}} \approx 1 - \frac{1}{8} \left( \frac{u_{01}\lambda}{\pi R_{\text{eff}}} \right)^2$

with $R_\text{eff}$ a function of the geometric core size, web thickness, and empirical factors capturing the multi-parametric structure (Hasan et al., 2017).

The number of capillaries, their spatial separation, capillary-to-core diameter ratio ( $d/D$ ), and the presence of truncations or multiple nesting dramatically influence the modal landscape, single- or multi-mode operation, and suppression of higher-order modes (HOMs). For robustly single-mode transmission, $d/D \approx 0.68$ is optimal; this exploits phase-matching between HOMs (e.g., LP $_{11}$ ) and leaky cladding states, causing their rapid attenuation while maintaining low loss for the fundamental mode (Chang et al., 1 Feb 2025, Gao et al., 20 Sep 2024).

Recent innovations, such as the four-fold truncated double-nested design (4T-DNANF), combine ultralow loss (down to 0.1 dB/km) and extreme HOM extinction ( $>10^4$ suppression), achieved by selective phase matching of HOMs to cladding air modes while detuning the fundamental, producing state-of-the-art mode purity and transmission (Gao et al., 20 Sep 2024).

Fabrication Tolerances and Coating Effects

Stack-and-draw fabrication, with precise gas pressure management and careful preform design, allows realization of ultrathin wall fibers (as low as 90 nm) directly without post-processing, yielding resonance-free transmission from deep-UV to NIR (Sabbah et al., 13 Dec 2024). Coating type and structural uniformity impact temperature sensitivity and mechanical robustness; single vs. double coatings modulate the temperature coefficient of delay (TCD), crucial for timing-sensitive applications—single-coat AR-HCFs exhibit TCD as low as 0.55 ppm/K, an order-of-magnitude better than standard single-mode fibers (Azendorf et al., 2022).

3. Optical Performance Metrics

Property	Typical AR-HCF Performance	Reference
Loss (NIR/telecom)	0.1–0.17 dB/km (FM), >400 dB/km (HOMs)	(Shi et al., 3 May 2025, Gao et al., 20 Sep 2024)
Bandwidth	0.25–2.5 μm, tailored by wall $t$	(Belardi, 2015)
Bending loss	0.25 dB/m (r = 5 cm, 1550 nm), single-ring	(Gao et al., 2016)
Temperature sensitivity	TCD: 0.55–1.5 ppm/K	(Azendorf et al., 2022)
Single-mode cutoff	$d/D \approx 0.68$	(Chang et al., 1 Feb 2025)
Polarization extinction	Birefringence $> 10^{-5}$ , 0.46 dB/m (PM fiber)	(Yerolatsitis et al., 2019)
UV transmission loss	0.13 dB/m (320 nm, single-mode)	(Dorer et al., 2023)

Achievable performance is contingent on precision fiber design, fabrication control, and coating material properties. For multi-core variants, losses of $0.03$ dB/m at 620 nm and negligible inter-core crosstalk (>$40$ dB isolation) are achievable, supporting spatial-division multiplexing (Mears et al., 22 Sep 2024).

4. Nonlinear Dynamics and Ultrafast Applications

Gas-filled AR-HCFs constitute a premier platform for high-peak-power nonlinear optics, ultrafast pulse compression, and tailored supercontinuum or dispersive-wave generation. The large, gas-filled core allows propagation of μJ-level, sub-200-fs pulses with negligible Kerr nonlinearity or Raman distortions at high energies (Yan et al., 2023), enabling:

Stable transmission for time/frequency metrology and large-scale laser facilities: Achievable path timing stability is below 6 fs RMS over 90 min in 10-m systems, with open-loop drift matching $<2 \times 10^{-7}$ relative variations (Yan et al., 2023).
Supercontinuum and deep-UV generation: Modulation instability (MI) and cross-phase modulation (XPM) in resonance-free, ultrathin-wall AR-HCFs (down to $t \sim 90$ nm) enable broadband, flat supercontinuum spanning 260–750 nm without spectral holes (Sabbah et al., 13 Dec 2024).
Tailored nonlinear phase-matching: Tapered AR-HCFs allow multi-stage dispersive wave up-conversion into the extreme-UV (down to 92 nm) at efficiencies of $\sim 2\%$ (190 nJ from 10 μJ input) using soliton—dispersive-wave re-collision engineered by the fiber geometry (Habib et al., 2017).
Pulse compression and MI control: Fiber wall thickness directly controls MI gain and onset. Thick-wall ( $T=820$ nm) AR-HCFs suppress MI, supporting high-peak-power, low-noise compressed pulse delivery, whereas thin-wall ( $T=300$ nm) AR-HCFs exhibit early MI onset, limiting energy scaling (Hemsworth et al., 27 Oct 2025).

5. Quantum and Telecommunication Applications

AR-HCFs are increasingly relevant for quantum communication and high-bit-rate telecom due to their unique combination of ultralow latency, low chromatic dispersion, high mode purity, and scalable fabrication:

Quantum entanglement distribution: Entangled photon pairs transmitted over 7.7 km AR-HCF demonstrated 34% lower latency and $\sim9\times$ lower chromatic dispersion than standard single-mode fiber, with concurrence $C \geq 0.90$ and preserved Bell-inequality violation down to 140 ps time-bin spacing (Antesberger et al., 2023). These virtues translate to higher secure key rates for time-bin encoded quantum key distribution and increased network synchronization.
Spatial-division multiplexing: Multi-core AR-HCFs with negligible inter-core crosstalk ( $\leq -40$ dB over 47.7 m, even under strong bending) enable high-channel-count, parallel transmission without modal mixing, suitable for advanced parallelized communication and distributed sensing architectures (Mears et al., 22 Sep 2024).
High-power, long-distance laser delivery: AR-HCFs have achieved all-fiber delivery of 2 kW over 2.45 km, with 85.3% transmission efficiency, M $^2$ near 1.3, and SRS suppression via source-side filtering and optimized fusion splicing, representing a nearly 500-fold increase in power-distance product over prior fiber-based systems (Shi et al., 3 May 2025).

6. Practical Engineering, Modeling, and Optimization

The rapid design iteration and theoretical analysis of AR-HCFs are facilitated by a suite of empirical and semi-analytical models:

Model Type	Purpose	Accuracy/Notes	Reference
Empirical formulae (Hasan et al., 2017)	Dispersion, mode area	Good for wideband/small deviations; core, gap, tube no.	(Hasan et al., 2017)
Poor-man’s analytical (Bache et al., 2018)	Resonance/loss/dispersion	Models antiresonances/loss profiles with a single fit parameter	(Bache et al., 2018)
Transfer matrix (Zinin et al., 2012)	ARR + Bragg fiber analysis	Single/multi-mode regime prediction via oscillatory loss mapping	(Zinin et al., 2012)

System-level metrology leverages correlation-OTDR (C-OTDR) for sub-picosecond group delay measurements, enabling fine assessment of temperature sensitivity, hysteresis, and coating effects (Azendorf et al., 2022).

Optimization

Mode purity, loss, and fabrication margin are jointly optimized by adjusting AR structure (e.g., truncations, nesting, gap size), wall thickness, and coating composition.
Thermal, modal, and nonlinear performance can be engineered for specific applications—including high-fidelity quantum links, industrial laser delivery, and low-drift metrology—by exploiting material and geometric degrees of freedom.

7. Research Impact and Future Directions

Continued advances in AR-HCF design, fabrication, and modeling are expanding the achievable application space across metrology, quantum networks, ultrafast optics, high-power laser delivery, and next-generation optical communication. Key ongoing trends include:

Further reduction of attenuation: Progress toward sub-0.1 dB/km losses across telecom bands, targeting the Rayleigh limit and potentially surpassing solid-core silica performance (Gao et al., 20 Sep 2024).
Integration with all-fiber systems: Achieving robust splicing, compact form factors, and environmental insensitivity for demanding, practical deployments (Shi et al., 3 May 2025).
Ultra-broadband guidance: Resonance-free deep-UV to NIR windows via direct-drawn sub-100 nm wall thicknesses and fine dispersion engineering (Sabbah et al., 13 Dec 2024).
Controlling nonlinear dynamics: Modal landscape, MI suppression, and soliton management for tailored ultrafast pulse applications (Hemsworth et al., 27 Oct 2025).
Scalable quantum and multiplexed systems: Multi-core and high-mode-count AR-HCFs with negligible crosstalk and low loss for future SDM/quantum information platforms (Mears et al., 22 Sep 2024, Mears et al., 22 Jan 2025).

A plausible implication is that AR-HCFs, with continued improvements in structure, coatings, and integration, are positioned to become the backbone technology for high-capacity, low-latency, and high-fidelity photonic systems in both classical and quantum domains.