Hollow Core Nested Antiresonant Nodeless Fibre

Updated 6 August 2025

Hollow Core Nested Antiresonant Nodeless Fibre is a silica-based optical fiber that confines light in its air core using antiresonant reflection from nested, thin-walled capillaries.
This design yields ultra-low attenuation, broad spectral bandwidth from ultraviolet to mid-infrared, and robust single-mode guidance while resisting nonlinear effects and bending losses.
Advanced nested configurations effectively suppress higher-order modes, enabling applications in quantum communications, high-power laser delivery, and precision sensing.

A hollow core nested antiresonant nodeless fibre is a silica-based microstructured optical fibre that confines light within an air core through antiresonant reflection from carefully engineered thin-walled nested glass capillaries arranged with no nodal points at the core boundary. This technology provides extremely low attenuation, broad transmission bandwidth ranging from the ultraviolet to the mid-infrared, robust single-mode or high-mode-purity guidance, and immunity to nonlinear effects and environmental perturbations. These fibres are enabling applications from quantum communications to high-power laser delivery, nonlinear optics, and advanced high-capacity optical networks.

1. Structural Design Principles and Antiresonance Mechanism

The core optical property of the hollow core nested antiresonant nodeless fibre (often abbreviated as HC-NANF) arises from the antiresonant mechanism: light is confined in a low-index air core by reflecting off thin glass boundaries (“antiresonant membranes”) that surround the core (Belardi, 2015, Klimczak et al., 2019). The transmission windows are governed by the antiresonance condition for the wall thickness $t$ : $\lambda_k = \frac{4 t}{2k + 1}, \quad k = 0, 1, 2, \ldots$ or, when including the refractive index $n$ ,

$\lambda_k = \frac{4 t \sqrt{n^2-1}}{2k+1}$

where $k$ is the transmission window index. The design enables precise tuning of the transmission bands by varying $t$ .

A defining feature of “nested” fibres is the use of one or more rings of additional thin-walled capillaries (“nested tubes”) placed within, but not touching, the main cladding tubes. A free boundary (nodeless) arrangement—where capillaries do not touch at points (nodes)—provides robust guidance and suppresses deleterious Fano resonances (Gao et al., 2016).

Typical structural parameters include:

Core diameter $D$ (e.g., 43 μm to >60 μm) (Belardi, 2015, Klimczak et al., 2019)
Cladding tube diameters and wall thicknesses, often with a dual-thickness approach (e.g., $t_{\text{outer}} = 0.3$ μm, $t_{\text{inner}} = 0.45$ μm in one design) to align antiresonant windows for minimized leakage (Belardi, 2015)
Number of capillaries (usually 5–7), with nested tubes inserted inside each outer tube (Habib et al., 2020)
Ratios such as $d/D$ , the diameter ratio between inner (nested) and outer tubes, critically determining modal loss and single-modeness (Habib et al., 2020)

The dominant loss mechanism at target wavelengths is confinement/leakage, which is minimized by aligning the antiresonance windows of the nested structures with the desired signal band. The nested configuration increases the likelihood that stray energy cannot phase-match to a leaky cladding mode, thereby pushing loss minima to extremely low values.

2. Transmission Performance: Loss, Bandwidth, and Bending

Hollow core nested antiresonant nodeless fibres offer some of the lowest measured losses in hollow-core technology across a broad spectral range (Belardi, 2015, Zhang et al., 2022, Gao et al., 20 Sep 2024). Key performance metrics include:

Parameter	Typical Value / Achievement	Reference
Minimum loss at 480 nm (visible)	175 dB/km	(Belardi, 2015)
Loss in near-IR (1.06 μm)	6.45 × 10⁻⁶ dB/km (NEARF1)	(Zhang et al., 2022)
Bending loss at 5 cm (1.06 μm)	<3×10⁻² dB/km	(Zhang et al., 2022)
Loss in mid-IR (4000 nm)	<0.5 dB/m (bending radius 40 mm)	(Klimczak et al., 2019)
Loss in C-band (typ. 1.55 μm)	~0.85–0.98 dB/km (deployed fibre)	(Clark et al., 31 Jul 2025)

Ultra-low loss at visible wavelengths (as low as 175 dB/km at 480 nm) is achieved by matching the antiresonant order of the nested tubes to coincide with the operational wavelength (Belardi, 2015). In the near-IR, loss can be reduced even further by introducing nested elliptical tubes and optimizing the relative positions (e.g., NEARF1 design: $6.45 \times 10^{-6}$ dB/km at 1.06 μm) (Zhang et al., 2022).

Bending resilience is another defining attribute. The nodeless layout avoids node-induced Fano resonances, suppresses core–cladding coupling, and enables low bending losses—e.g., 0.25 dB/m at a 5 cm radius at 1550 nm (Gao et al., 2016); <0.5 dB/m in mid-IR at 40 mm bending radius (Klimczak et al., 2019). This is critical for deployment in practical environments requiring fibre routing.

While antiresonant fibres are inherently multimode, nested and nodeless designs enable ultrahigh suppression of higher-order modes (HOMs) with minimal impact on the fundamental mode (FM) loss. This is achieved through:

Optimized gap and $d/D$ parameter regimes yielding a “V-shape” in the parameter space where HOMs are strongly phase-matched to cladding modes and thus suppressed (Habib et al., 2020)
Anisotropic nested tubes (nested ellipses) to further increase negative curvature and suppress unwanted coupling (Zhang et al., 2022)

Recent innovations, such as the four-fold truncated double-nested anti-resonant hollow core fibre (4T-DNANF), achieve FM loss as low as 0.1 dB/km while generating HOM loss up to 6500 dB/km, yielding a HOM extinction ratio of ~50,000 (Gao et al., 20 Sep 2024). Such mode purity is critical for high-speed coherent communications, high-precision sensing (e.g., gyroscopes), and high energy beam delivery.

4. Dispersion, Polarization, and Environmental Robustness

Empirical formulae have been developed for rapid estimation of group velocity dispersion (GVD) and effective mode area using structural parameters, validated against detailed finite-element modeling (Hasan et al., 2017). The presence of nested tubes increases the wavelength-dependent parameter $f_2$ in the effective radius formula, typically increasing long-wavelength dispersion due to tighter confinement.

Polarization extinction ratios (PER) as high as –70 dB in the C-band and –50 dB at 2 μm have been measured for 1 km fibres, with ultra-low birefringence due to minimal stress and geometric symmetry (Afxenti et al., 5 May 2024). This polarization purity keeps quantum bit error rates (QBER) below security thresholds in quantum key distribution protocols.

Temperature sensitivity—quantified via the temperature coefficient of delay (TCD)—is substantially lower (0.55–1.5 ppm/K) than in standard single-mode fibres (7.5 ppm/K), translating to <3.5 ps/K over hundreds of meters, due to the air core and low material content (Azendorf et al., 2022). Fibre coatings further modulate the TCD. These stability features are important for synchronization in precise timing and future network infrastructures.

5. Applications in Quantum, Classical, and Nonlinear Optics

The combination of ultra-low loss, ultrahigh single-modeness, negligible material nonlinearity, and environmental robustness makes hollow core nested antiresonant nodeless fibres pivotal in multiple domains:

Quantum Communications and Quantum-Classical Coexistence

Demonstrated coexistence of dense classical channels (e.g., 1.6 Tbps over eight 16-QAM channels) and quantum discrete-variable QKD channels at high co-propagating powers (0 dBm, 40–250 times that tolerated in SMF), with negligible SKR or QBER degradation, is only possible by virtue of the fibre’s hollow core and ultra-low nonlinearity (Alia et al., 2021, Alia et al., 2022).
Maintaining entanglement-based quantum channels alongside 800 Gbps DWDM traffic in a four-node quantum network over 11.5 km with Bell state fidelity up to 90% and sustained SKR over 55 hours further demonstrates scalability (Clark et al., 31 Jul 2025).
For polarization-encoded QKD in the C-band and at 2 μm, polarization extinction remains high, yielding low QBER (down to 2.7%) and positive secret key rates for both prepare-and-measure and entanglement-based protocols (Afxenti et al., 5 May 2024).
The suppression of Raman and FWM induced noise allows quantum and classical channels to share the same fibre with minimal additional filtering and loss budget.

High-Power and Ultrafast Laser Delivery

All-fibre delivery of 2 kW at 1080 nm over 2.45 km with an efficiency of 85.3% and record-low transmission loss (0.175 dB/km) (Shi et al., 3 May 2025), enabled by optimal nested tube scaling, low overlap integral (~10⁻⁵) with silica, and robust coupling to standard solid-core fibres.
Ultrafast pulse delivery (e.g., 5 GW, 40 fs at 800 nm) over 10 m with high-quality, near-transform-limited output at 3 PW/cm² is accomplished by tuning fibre dispersion, controlling plasma effects, and managing the fluence at the core-wall interface to avoid glass damage (Lekosiotis et al., 2023).
Direct integration in nonlinear pulse compression and high-harmonic generation experiments is facilitated by pressure-tuneable gas filling, fast environmental access (via lateral cut technique), and broad spectral transparency (Belardi, 2015, Klimczak et al., 2019, Gebhardt et al., 2020).

Spectroscopy, Sensing, and Network Synchronization

The robust transmission window from deep-UV (down to 190 nm with 0.13 dB/m attenuation (Mears et al., 2023)), through visible and IR (to >4000 nm with low bending loss and wide gas access (Klimczak et al., 2019)), supports high-resolution spectroscopy and integrated gas-based sensors.
The lateral cut modification enables rapid gas access to the core with negligible excess loss (~0.01 dB/km), accelerating gas detection for trace analytes or environmental monitoring (Belardi, 2015).
Superior stability against temperature-induced delay variations and low bend sensitivity position these fibres for fibre-based synchronization systems and delay-critical telecommunications (Azendorf et al., 2022).

6. Fabrication Tolerances, Design Tradeoffs, and Recent Innovations

Performance is inherently sensitive to geometric tolerances:

Monte Carlo simulations show that random tube angle offsets (as opposed to wall thickness fluctuations) dominate the increase in propagation loss, especially for HOMs (loss increase +65% for HOMs vs. +5% for fundamental in five-tube designs at 1.55 μm) (Petry et al., 2022). Such fabrication-induced “single-modeness” may be advantageous for HOM suppression.
Bending further amplifies the impact of geometric imperfections, with loss increases up to +50% at a 4 cm radius (Petry et al., 2022).
Practical design must therefore optimize the $d/D$ ratio, gap separation, and introduce elliptical or anisotropic nesting for ultimate suppression of HOMs with low FM loss (Habib et al., 2020, Zhang et al., 2022).
State-of-the-art designs such as 4T-DNANF, utilizing geometric phase-matching between HOMs and dispersive air modes in the cladding, achieve mode extinction ratios exceeding 50,000, FM loss ≤0.13 dB/km and robust guiding across the C-band (Gao et al., 20 Sep 2024).

Controlled empirical formulae allow rapid estimation of GVD and mode area for new designs (Hasan et al., 2017). Multi-mode hollow core antiresonant designs supporting up to 50 modes have been realized (loss 0.1–0.2 dB/m), extending the operational regime for spatial multiplexing, wideband sensing, and specialized multi-mode laser delivery (Mears et al., 22 Jan 2025).

7. Outlook and Impact

Hollow core nested antiresonant nodeless fibres unify ultra-low loss, environmental robustness, wideband transparency, and tailored modal properties in a scalable silica platform. Their unique “free boundary” design, coupled with sophisticated nested and elliptical geometries, enables:

Robust quantum and classical channel coexistence at very high aggregate powers with negligible nonlinear impairment or QBER penalty, paving the way for integrated quantum–classical networks (Clark et al., 31 Jul 2025).
Ultrahigh power and femtosecond pulse delivery for advanced laser and nonlinear photonics experiments, with record transmission distances and efficiencies (Shi et al., 3 May 2025).
Next-generation, dispersion-engineered, polarization-maintaining fibres for high-fidelity quantum and metrological systems (Afxenti et al., 5 May 2024).
Flexible, low-loss, single- and multi-mode platforms for gas spectroscopy, fiber gyroscopes, multipass laser delivery, and precision sensing.

Research continues to extend these capabilities, with current efforts focusing on ultra-high mode extinction, improved fabrication tolerance, dynamic acousto-optic modulation, and further scaling of bandwidth and transmission distance. This positions hollow core nested antiresonant nodeless fibre as a cornerstone technology for future photonics infrastructure spanning quantum, classical, and nonlinear domains.