Introduction

As we stand on the brink of the 6G era, the demand for higher data rates, lower latency, and more reliable connectivity is intensifying. Among the myriad of technologies being developed to meet these demands, air-core optical fibers (also known as hollow-core optical fibers) are emerging as a potential game-changer. This report explores the fundamentals of air-core optical fibers, their unique characteristics, and their potential to serve as a technical breakthrough in 6G networks.

Understanding Air-Core Optical Fibers

Definition and Structure

Air-core optical fibers are a type of optical fiber where the core is hollow, typically filled with air or another gas, surrounded by a microstructured glass cladding. Unlike traditional solid-core optical fibers where light propagates through a glass core, in air-core fibers, light travels through the hollow core and is confined by the photonic bandgap effect created by the microstructures in the cladding [42].

The typical design of air-core optical fibers features periodic or angularly uniform arrangements in their cross-section, such as honeycomb structures or single-layer capillary structures. These microstructures effectively create a “photonic bandgap” that guides light through the fiber while minimizing interaction with the glass material [42].

Working Principle

In traditional optical fibers, light propagation relies on total internal reflection at the interface between the core and cladding. In contrast, air-core optical fibers operate on different principles:

Photonic Bandgap Confinement: The microstructures in the cladding create a photonic bandgap that prevents certain frequencies of light from propagating through the cladding, effectively confining them to the hollow core.
Anti-Resonant Confinement: Some designs use anti-resonant effects where the light is confined because its wavelength does not match the resonant condition of the fiber’s structure.

Key Properties and Advantages

Low Attenuation and High Speed

One of the most significant advantages of air-core optical fibers is their ability to achieve extremely low signal attenuation. Since light propagates through air rather than glass, there is minimal absorption, allowing for longer transmission distances without the need for repeaters. This property makes them ideal for high-speed, long-distance communication links that will be essential for 6G networks.

Wide Bandwidth

Air-core optical fibers offer a wider usable bandwidth compared to traditional fibers. Their unique structure allows for a flatter dispersion profile, which is crucial for high-speed data transmission and supports the terabit-per-second data rates that 6G networks are expected to deliver [48].

Low Latency

Light travels faster in air than in glass, which inherently provides a latency advantage in air-core optical fibers. In 6G networks, where ultra-low latency is critical for applications like autonomous vehicles, augmented reality, and real-time industrial control systems, this advantage could be transformative.

Flexibility and Handling

Air-core optical fibers are generally more flexible than conventional solid-core fibers, making them easier to handle and deploy in various network infrastructures. This flexibility could be particularly beneficial in the complex deployments typical of 6G networks, which may involve integration with other technologies and infrastructure.

Sensing Capabilities

The hollow core design makes air-core optical fibers highly sensitive to external environmental conditions such as temperature, pressure, and refractive index changes. This sensitivity enables their use in various sensing applications, which could be integrated into 6G networks for monitoring network performance and environmental conditions [4].

Applications in 6G Networks

High-Speed Data Transmission

The exceptional bandwidth and low attenuation properties of air-core optical fibers make them ideal for the high-speed data transmission requirements of 6G networks. They could be used in backbone networks, data center interconnects, and other applications where terabit-per-second data rates are needed [10].

5G to 6G Evolution

As networks evolve from 5G to 6G, the infrastructure will need to support increasing data demands. Air-core optical fibers could play a crucial role in this evolution by providing the necessary bandwidth and performance improvements without requiring a complete overhaul of existing infrastructure.

Integration with Wireless Technologies

Air-core optical fibers can be integrated with various wireless technologies to create hybrid networks. For example, they can be used in radio-over-fiber (RoF) systems, where optical fibers are used to transport radio frequency signals to remote antennas, enabling the deployment of dense networks of small cells, which will be essential for 6G coverage and capacity [10].

Simultaneous Power and Data Transmission

A groundbreaking application demonstrated for potential 6G networks is the use of double-clad fibers for simultaneous power and data transmission (RPoF – radio and power over fiber). This technology allows for the transmission of both data and electrical power over the same fiber, which could be particularly useful in scenarios where powering remote equipment is challenging [10].

Non-Terrestrial Networks

6G networks are expected to include non-terrestrial components such as satellites, high-altitude platforms, and drones. Air-core optical fibers could provide the high-speed, low-latency connections needed for these components, enabling seamless integration between terrestrial and non-terrestrial networks [25].

Technical Challenges and Solutions

Manufacturing Complexity

One of the main challenges with air-core optical fibers is their complex manufacturing process, which involves creating precise microstructures in the cladding. However, advancements in manufacturing techniques, such as the stack-and-draw method, are making it possible to produce these fibers with increasing precision and at lower costs [12].

Loss and Dispersion Control

While air-core optical fibers offer many advantages, they also present challenges in terms of controlling losses and dispersion. Researchers are addressing these issues through innovative fiber designs, such as revolver hollow core optical fibers, which offer improved performance characteristics [47].

Compatibility with Existing Infrastructure

Integrating air-core optical fibers with existing network infrastructure is another challenge. However, their design allows for compatibility with standard optical communication systems, making them a viable upgrade path for network operators looking to enhance their networks for 6G [3].

Recent Developments and Breakthroughs

160-Wave x 800G Transmission System

In a significant breakthrough, researchers have achieved a 160-wave x 800G transmission system using air-core optical fibers, demonstrating the potential for ultra-high capacity transmission that will be essential for 6G networks [73].

SCL Super Wide Spectrum Single-Fiber Bidirectional Transmission

Another notable achievement is the demonstration of SCL (Super Channel Link) super wide spectrum single-fiber bidirectional transmission at 377.6 Tbit/s over 100 kilometers using air-core optical fibers. This represents a significant step toward the high-capacity optical networks needed for 6G [73].

Terabit-per-Second Transmission

Researchers have demonstrated terabit-per-second transmission using air-core optical fibers, showcasing their potential to meet the extreme bandwidth requirements of 6G networks [48].

Comparison with Traditional Optical Fibers

Performance Advantages

Air-core optical fibers offer several performance advantages over traditional solid-core fibers:

Lower attenuation: Due to the air core, there is less material absorption.
Wider bandwidth: The microstructured design allows for a broader usable spectrum.
Lower latency: Light travels faster in air than in glass.
Higher birefringence: Some designs offer high birefringence, which can be useful for certain applications [1].

Cost and Deployment Considerations

While air-core optical fibers offer significant performance advantages, they also present challenges in terms of cost and deployment. The complex manufacturing process and the need for specialized equipment and techniques can make them more expensive than traditional fibers. However, as manufacturing techniques improve and economies of scale are achieved, these costs are expected to decrease.

Future Prospects and Research Directions

Terahertz Communication

One promising area of research is the use of air-core optical fibers for terahertz communication, which is expected to be a key part of 6G networks. The unique properties of these fibers make them well-suited for handling the high frequencies and wide bandwidths required for terahertz communication [64].

Quantum Communication

Air-core optical fibers are also being explored for their potential in quantum communication, which could be an important part of 6G networks for secure data transmission. Their low loss and high purity make them suitable for carrying quantum information [69].

Multi-Core Designs

Researchers are developing multi-core air-core optical fibers, which could further increase the capacity of optical networks. These fibers contain multiple hollow cores, each capable of carrying independent data channels, potentially increasing the overall capacity of the fiber [68].

Conclusion

Air-core optical fibers represent a significant technological advancement in optical communication, offering unique properties that make them ideal for the high-speed, low-latency, and high-capacity requirements of 6G networks. Their ability to provide exceptional bandwidth, low attenuation, and low latency positions them as a key enabler for the next generation of wireless communication.

While there are still challenges to overcome in terms of manufacturing, cost, and integration, the rapid pace of innovation in this field suggests that these challenges will be addressed in the coming years. As 6G networks begin to take shape, air-core optical fibers are likely to play a crucial role in providing the optical infrastructure needed to support this new era of communication.

References

[1] Characteristics analysis of photonic crystal fiber with rhombus air-core. https://www.researchgate.net/publication/251490833_Characteristics_analysis_of_photonic_crystal_fiber_with_rhombus_air-core.

[3] 《Digital Low-Altitude Network Architecture, Coverage and Key Technology White Paper》Released. https://new.qq.com/rain/a/20250416A09ZIX00.

[4] HOLLOW-CORE OPTICAL FIBER SENSORS AND DEVICES. https://www.researchgate.net/publication/254737651_HOLLOW-CORE_OPTICAL_FIBER_SENSORS_AND_DEVICES.

[10] Power and data simultaneous transmission using double-clad fibers towards 6G. https://www.nature.com/articles/s41598-025-88383-9.

[12] The proposed split-PHY fronthaul architecture solution. https://www.researchgate.net/figure/The-proposed-split-PHY-fronthaul-architecture-solution_fig2_330423296.

[25] 6G SENTINEL. https://www.hhi.fraunhofer.de/en/departments/wn/projects/6g-sentinel.html.

[42] Vibration-insensitive polarimetric fiber optic current sensor based on orbital angular momentum modes in an air-core optical fiber. https://www.x-mol.com/paper/1772008287000518656.

[47] Revolver Hollow Core Optical Fibers. https://www.researchgate.net/publication/325649190_Revolver_Hollow_Core_Optical_Fibers.

[48] Power and data simultaneous transmission using double-clad fibers towards 6G. https://www.nature.com/articles/s41598-025-88383-9.

[64] Hollow-core fibers: state-of-the-art and prospects. https://www.researchgate.net/publication/377323671_Hollow-core_fibers_state-of-the-art_and_prospects.

[68] Polarization Sensitive Multi-Hollow-Core Antiresonant Fiber. https://www.researchgate.net/publication/380243478_Polarization_Sensitive_Multi-Hollow-Core_Antiresonant_Fiber.

[69] Hollow-core fiber for near-infrared quantum communication. https://www.researchgate.net/publication/367067615_Hollow-core_fiber_for_near-infrared_quantum_communication.

[73] China Mobile’s air-core optical fiber breakthrough: first realization of 160-wave x 800G transmission system and SCL super wide spectrum single-fiber bidirectional 377.6Tb/s 100km transmission. https://www.ithome.com/0/815/385.htm.

Knowledge

Air-Core Optical Fiber: Technical Breakthrough in 6G Networks