Over three decades ago, when optical communication was commercially adopted, it relied on two main technologies: wireless Free Space Optical (FSO) transmission and fiber optic technology, which used physical wires. Since the 1990s, optical fiber technology has seen significant advancements in distance, bandwidth, speed, reliability, and other improvements that have contributed to its widespread adoption.

Today, quantum technologies stand at the threshold of a revolutionary era with the potential to bring extraordinary new computational capabilities that could tackle intricate logical challenges, enhance medical innovations, and establish novel cryptographic protocols for communication security.

Despite these promising advancements, the current global information transmission infrastructure—especially the solid-core optical fibre networks—might not be sufficient to effectively support the requirements of quantum communication.

"The conventional optical fibres that are the workhorse of our telecommunications networks of today transmit light at wavelengths that are entirely governed by the losses of silica glass. However, these wavelengths are not compatible with the operational wavelengths of the single-photon sources, qubits, and active optical components, that are required for light-based quantum technologies." said Dr Kristina Rusimova from the Department of Physics at Bath. 

 

Hollow-Core Optical Fibers for Telecommunications and Data Transmission

HCFs with Kagome lattice: (a) “pure” Kagome; (b) with “negative curvature” surfaces towards core; (c) with hybrid lattice including “levitating” anti-resonant capillaries (right). Drawings show ideal structures without distortions introduced during consolidation of preform and drawing of fibre. (Reference: 'Hollow-Core Optical Fibres for Telecommunications and Data Transmission' by Krzysztof Borzyck and Tomasz Osuch, 26th September 2023)

Dr. Rusimova and her colleagues describe the state-of-the-art fibres developed at Bath, along with recent and upcoming advancements in the emerging field of quantum computing, in an academic paper published on the 29th of July 2024 in Applied Physics Letters Quantum.

Dr. Rusimova, the lead senior author of the paper, added that "the optical fibres we are developing with quantum computers in mind are laying the foundations for the data transmission needs of tomorrow."

 

Optical Fibre for Quantum Communications

Quantum computing, along with data security and the engineering sector, is poised for transformative leaps. However, quantum networks and computers need further advancements to fully realise their potential and become widespread.

For example, integrating optical fibre networks is crucial as they possess the high bandwidth and low-decoherence characteristics necessary to exploit quantum phenomena such as entanglement.

Quantum communication demands swift and loss-free data transfer, which traditional copper cables and radio waves cannot provide due to their inadequate precision. Fibre optic cables, the backbone of quantum communication infrastructure, enable light-speed data transmission and are resilient to interference.

Here we refer again to the work of Cameron McGarry, Kerrianne Harrington, Alex O. C. Davis, Peter J. Mosley, and Kristina R. Rusimova in their paper ‘Microstructured optical fibres for quantum applications: Perspective’ from the 29th of July, 2024. 

1. Secure Data Transmission

Quantum communication revolutionises security by enabling secure data transmission through quantum key distribution (QKD). Quantum communication is an emerging field that harnesses the principles of quantum mechanics to facilitate secure communication. Optical fibres play a pivotal role in enabling Quantum Key Distribution (QKD) over extended distances, including the photons utilised in quantum communication, with minimal loss. For working with these fibers, AusOptic relies on the FITEL S185-Series Fusion Splicers with models specifically designed for polarisation-maintaining fibers, HCF, and other specialty fiber types, achieving rapid splicing times and consistent results.

2. Low-Loss Transmission

Achieving seamless, low-loss, and alignment-free integration between quantum network components and optical fibres is crucial for quantum communication, as signal loss during qubit transport is paramount. However, current photon sources, quantum memories, optical switches, quantum processors, and detectors span a wide range of physical systems from near-UV to mid-IR, making it challenging to find a single wavelength that caters to all functionalities. Previous attempts have focused on integrating on-chip architectures and atomic ensembles with the evanescent field of tapered nano-fibres or through grating couplers, edge couplers, and trenches. Integrating these schemes with in-fibre cavities has been shown to enhance their performance, but the scalability of the free-space laser components remains a limitation.

3. Long-Distance Quantum Communication

Quantum communication networks are expanding, and reliable long-distance data transmission is crucial. Anti-resonant hollow core fibres (HCFs) show promise for various quantum technologies, beyond long-distance communications. For example, quantum information processing networks need to scale from on-chip designs to multiple remote computational nodes. A suitable transmission medium is crucial. Hollow core fibres are among the most suitable candidates for providing a scalable and robust solution for long-range quantum communication.

4. Low-Latency Hollow-Core Fibre Transmission

Hollow core fibres (HCFs) offer low latency, low nonlinearity, and low loss at wavelengths not achievable in solid silica-based fibres. This makes them ideal for quantum network components operating at diverse central wavelengths, particularly between 580 and 900 nm, where many quantum systems utilise optical transitions.

The key for a transmission medium in quantum applications is low loss across a broad spectrum to preserve information encoded in quantum states over extended transmission lengths.

Achieving lower attenuation in HCFs compared to solid-core optical fibres, especially at telecommunications wavelengths, has been a challenge, but innovative techniques pioneered by OFS and Furukawa are gradually overcoming this.

 

Challenges in Splicing Hollow Core Fibres:

To address the specific challenges associated with splicing these advanced structures, specialised heating methods and precise fibre fusion techniques are being developed by OFS, Lightera and Furukawa Electric with their FITEL S185-Series Fusion Splicers. The intricate nature of hollow core and multi-core fibres necessitates advanced splicing equipment and methodologies to preserve the integrity of their complex internal architectures.

The microstructure of hollow-core fibres (HCFs) and multi-core fibres (MCFs), designed for optical transmission efficiency with attenuation below 0.5 dB/km, requires specialised splicing equipment for sub-micron core alignment. (Reference: Overcoming Transmission Capacity Limitations: Multi-core Fibre)

For MCFs with 43μm core spacing, advanced fusion splicing employs free-space optical coupling to achieve insertion losses under 0.5 dB, crosstalk suppression over 45 dB, and return loss above 55 dB. You can read more about that in our blog post on the work of the team at the Future Photonic Network Open Lab at Keio University, Japan.

In the case of antiresonant hollow-core fibres, ultralow-loss fusion splicing can achieve connection losses below 0.3 dB and return loss under -28 dB through optimised parameters and controlled thermal gradients. These methods utilise calibrated fusion arc parameters, optimised heating profiles, and multi-axis alignment systems to maintain the integrity of complex internal architectures like photonic bandgap structures. (Reference: Ultralow-loss fusion splicing between antiresonant hollow-core)

Innovative techniques, such as reverse-tapering for negative curvature HCFs and specialised procedures for antireflection-coated fibre interfaces, have successfully overcome traditional splicing limitations.

The advanced splicing protocols demonstrate a deep understanding of modal field optimisation, thermal stress management, and geometrical conservation. Engineers can now create splices that ensure mode field diameter compatibility, minimise Fresnel reflections, and preserve waveguiding properties, enhancing signal integrity, reducing power budgets, and improving the reliability of optical communication systems approaching 100 Tbit/s.

 

FITEL S185-Series Fusion Splicers Featuring 3-Electrode ROF (Ring of Fire) Large Plasma Field

FITEL S185-Series Fusion Splicers Featuring 3-Electrode ROF (Ring of Fire) Large Plasma Field

Developed in collaboration with the expert team at 3SAE, the FITEL S185PMROF Fusion Splicer has been engineered to achieve optimal low-loss splicing results specifically tailored for hollow-core and multi-core fibers. This state-of-the-art device stands out in the field of fiber optic technology, thanks to its innovative features, which include:

  • Advanced Three-Electrode Configuration: The splicer utilizes a sophisticated three-electrode design that enhances the precision of the splicing process. This configuration allows for improved control over the arc discharge, leading to a more stable and consistent splice.
  • Enhanced Plasma Arc Generation: The FITEL S185PMROF boasts advanced plasma arc generation technology that produces a high-quality arc for fusion splicing. This feature is crucial for achieving low splice loss, particularly in complex fiber types, as it ensures a stronger bond between fibers.
  • Uniform Heat Distribution Across the Splice Point: One of the critical aspects of successful splicing is the uniform application of heat. This splicer ensures even heat distribution at the splice point, which is vital for preserving the integrity of the fibers' internal structures. This uniformity mitigates the risk of damage and enhances the overall reliability of the splice.

The combination of these advanced features is essential for maintaining the integrity of complex internal structures during the splicing process, making the FITEL S185PMROF an invaluable tool for professionals working with cutting-edge fiber optic technologies. For further insights into the latest research and advancements in multicore fiber splicing, read more in our blog post linked here.

Fibre Optic Solutions for Free Space Optical and Quantum Communication

The team at AusOptic work with with US-based OFS and Lightera, and Japanese partner Furukawa Electric, who manufacture the AccuCore HCF Optical Fibre Cable, the world’s first terrestrial hollow-core fibre (HCF) solution. Their hollow core allows light to travel 50% faster than conventional optical fibre with a solid silica core, arriving 1.54 microseconds sooner per kilometre, enhancing speed. The AccuCore HCF Optical Fibre Cable includes indoor and outdoor options, with terminations featuring standard connectors fused to patented photonic band gap hollow-core fibre. OFS also provides installation services and a range of components, both passive and active, to meet diverse customer needs. The AccuCore HCF optical fibre cable has effectively deployed live traffic across multiple networks.

Read the press releases:

Applications:

  • High-frequency trading
  • High-performance computing
  • 5G X-haul mobile networks
  • Intra-data center interconnection

These hollow core fibres have lower loss than solid core fibres and can integrate into existing systems. They are ideal for quantum communications, especially for quantum key distribution (QKD) and entanglement distribution. These fibres transmit co-propagating classical and quantum channels at different wavelengths, reducing nonlinear scattering between channels. Early experiments with Hollow Core Fibres (HCFs) achieved a record coexistence transmission rate of 1.6 Tbps over a 2 km classical channel. HCFs also show superior phase and thermal stability compared to other transmission media.

 

 

Looking Ahead

Optical communication technologies, particularly Free Space Optical (FSO) and quantum communications, are revolutionising data transmission. Advanced fibre optic technologies, such as microstructured optical fibres, anti-resonant hollow core fibres, and innovative splicing techniques, have significantly enhanced quantum communication network capabilities. These innovations meet the critical requirements for low-latency, high-capacity, and secure data transfer and pave the way for scalable quantum networks for future applications like quantum computing, high-frequency trading, and next-generation mobile networks. As global research and collaborative efforts continue, robust, long-distance quantum communication and the seamless integration of fibre optic solutions into various technological environments appear exceptionally promising.

As the landscape of optical communication rapidly evolves with groundbreaking innovations in Free Space Optical (FSO) and Quantum Communications, staying ahead means leveraging the latest advancements in fibre optic technology. At AusOptic, we are at the forefront, collaborating with leading global partners like OFS, Lightera, and Furukawa Electric to bring you cutting-edge solutions.

Whether you're exploring new fibre applications or enhancing existing systems, our team of experts is equipped with the knowledge and technology to support your ambitions. From secure data transmission with Quantum Key Distribution (QKD) to the deployment of the world's first terrestrial hollow-core fibre (HCF) solution, we provide tailored solutions that meet the demands of tomorrow’s technologies.

Looking to working with optical fibre for transmission applications?

Get in touch with the team at AusOptic, we’re happy to discuss your new and emerging fibre requirements and explore what new things can be achieved.