Development Of Hollow-Core Optical Fiber Technology For Communications And Challenges In Engineering Applications

Hollow-core fiber (HCF) utilizes a specialized cladding structure to confine light to an air core for transmission. This fundamentally changes the way light is transmitted, avoiding the inherent limitations of traditional silica glass fibers and achieving lower attenuation. Because light propagates through the hollow core of a hollow-core fiber, the transmission delay of optical signals is reduced by approximately one-third compared to traditional silica-core fibers. Regarding nonlinear effects, the low nonlinear refractive index of air gives hollow-core fibers ultra-low nonlinearity. Furthermore, hollow-core fibers exhibit excellent dispersion and other characteristics. These properties hold great potential for applications in optical communications, high-power laser transmission, and light-matter interactions.

However, practical applications of hollow-core optical fibers still face numerous challenges, including fusion splicing and ensuring the integrity of the supply chain. Due to its inherent mechanical properties, the air hole transmission in hollow-core optical fibers results in extremely low Rayleigh scattering, making traditional optical time-domain reflectometry (OTDR) technology ineffective. This makes it difficult to accurately measure length using existing technologies, posing process challenges during precise cabling and wiring construction. Because hollow-core optical fibers rely heavily on the morphology and structure of the air holes, the thin quartz walls that comprise the air holes are susceptible to accelerated breakage or deformation due to environmental influences, leading to operational lifespan limitations. Furthermore, maintaining stable transmission performance in complex field environments, such as high and low temperatures, poses challenges for engineering applications. Further research is needed to advance its application in specific scenarios.

Overview of Hollow-Core Fiber Technology

Structure and Principle of Hollow-Core Fiber

Traditional optical fibers typically use a solid core made of materials such as quartz glass. In contrast, hollow-core fibers have a hollow region at their center composed of air or other gases, where light primarily propagates. The optical transmission principle of hollow-core fibers is primarily based on two effects: the photonic bandgap effect and the antiresonance effect. Consequently, hollow-core fibers can be categorized as hollow-core photonic bandgap fibers (HC-PBF) and hollow-core antiresonant fibers (HC-ARF).

The light guidance principle of hollow-core photonic bandgap fibers is based on the photonic bandgap effect. As shown in Figure 1, the periodic microstructure of the cladding in a hollow-core photonic bandgap fiber forms a photonic crystal. When a light signal enters the air core of the fiber, the photonic bandgap effect of the cladding's photonic crystal structure prevents light of a specific frequency from propagating through the cladding, confining it to the air core. This type of optical fiber can achieve single-mode transmission and can precisely control the range and characteristics of the photonic band gap by adjusting the microstructure parameters of the cladding, such as the size, spacing and arrangement of the air holes, thereby achieving effective transmission of light of different wavelengths.

Figure 1 - Hollow-core Photonic Bandgap Fiber

Figure 2 - Hollow-core Antiresonant Fiber

Hollow-core antiresonant optical fibers utilize the antiresonance effect to transmit light. As shown in Figure 2, their cladding typically consists of multiple concentric quartz rings nested together. By adjusting the ring wall thickness, light propagation in the cladding is strongly suppressed at specific wavelengths, confining it to the central air core. Specifically, when the wavelength of light meets the antiresonance condition, the reflectivity at the cladding interface is extremely high, making it virtually impossible for light to enter the cladding and instead propagating through the air core.

Development of Hollow-Core Fibers

In 2002, Professor Russell and Professor F. Benabid of the University of Bath in the UK proposed a hollow-core fiber technology, also known as photonic bandgap hollow-core fiber. Due to the significant surface scattering losses within the core of photonic bandgap hollow-core fibers, their attenuation was difficult to reduce to below 1 dB/km. Subsequently, a new type of bandgap hollow-core fiber with irregularly arranged air holes was developed. Because its end-face structure resembles the traditional Japanese kagome weave pattern, it is also called kagome fiber. However, whether the light guidance mechanism of this hollow-core fiber can be explained by bandgap theory has been controversial.

In 2008, G. J. Pearce et al. of the Max Planck Institute used the antiresonant reflection waveguide (ARROW) model to construct a new light guidance principle and characteristic model for hollow-core fibers, using the antiresonant reflection mechanism. This model provided a new interpretation of thetransmission mechanism of kagome fibers. Based on this new light guidance mechanism, this type of fiber was named hollow-core antiresonant fiber. From then on, the development of hollow-core fibers entered a new trajectory.

In 2013, researchers discovered that negative-curvature core structures can achieve lower losses than positive-curvature core structures. Research revealed that the contact points between the cladding tubes are a significant contributor to the increased loss in HC-ARF (High-Cell Array Frequency Reduction) (HC-ARF), leading to the proposal of a single-layer circular tube nodeless HC-ARF. Building on this foundation, from 2017 to 2024, researchers at Beijing University of Technology, the University of Southampton, and other institutions conducted extensive research on hollow-core antiresonant fibers. As shown in Figure 2, by 2024, the attenuation of hollow-core antiresonant fibers in the 1550 nm band was reduced from over 1 dB/km to 0.1 dB/km. Recent research on hollow-core fibers with attenuation below 0.1 dB/km was reported at the 2025 OFC. However, in current long-distance testing, the CO2 absorption peak has become a factor affecting transmission in the C+L band, increasing the maximum absorption loss to nearly 0.4 dB/km.

Figure 3 - Typical Structure of Hollow-core Antiresonant Fibe

Key Features of Hollow-Core Fiber

One of the most notable features of hollow-core fiber is its ultra-low loss. While traditional quartz fiber has achieved tremendous success in communications, its loss is approaching the intrinsic material limit. However, hollow-core fiber, because light propagates through the air core, avoids absorption and scattering losses caused by the material. In recent years, continuous technological breakthroughs have significantly reduced the loss of hollow-core fiber. For example, the loss of multi-layer nested hollow-core antiresonant fiber has been reduced to less than 0.08 dB/km at 1550 nm, surpassing the loss limit of 0.14 dB/km at 1550 nm for traditional quartz glass fiber. This ultra-low loss allows optical signals to be transmitted over longer distances in hollow-core fiber, reducing the number of signal relay stations.

Hollow-core fiber exhibits ultra-low nonlinearity. In traditional quartz fiber, due to the strong interaction between light and the quartz material, high optical power can easily produce nonlinear effects such as the Kerr effect and stimulated Raman scattering. These nonlinear effects can cause optical signal distortion and crosstalk, limiting the transmission capacity and distance of optical communication systems. In hollow-core fiber, light primarily propagates in the air core. Air has a much lower nonlinear refractive index than quartz, resulting in nonlinear effects three to four orders of magnitude lower than those in conventional fiber. This meanshigher-power optical signals can be transmitted through hollow-core fiber without significant nonlinear distortion. For example, with 128-degree quadrature amplitude modulation (QAM) and high-power amplifier technology, the ultra-low nonlinearity of hollow-core fiber allows for a significant increase in input optical power, expected to at least double system capacity and transmission distance. In the field of high-power laser transmission, this ultra-low nonlinearity also enables hollow-core fiber to more efficiently transmit high-power lasers, avoiding laser energy loss and beam quality degradation caused by nonlinear effects.

Hollow-core fiber also exhibits ultra-low latency. According to the principle of light propagation, the speed of light in a medium, v, is inversely proportional to the medium's refractive index, n: that is, v = c/n, where c is the speed of light in a vacuum. The refractive index of air is approximately 1, while the refractive index of a quartz fiber core is typically between 1.45 and 1.50. This reduces the transmission latency of light in hollow-core fiber from approximately 5 μs/km to 3.46 μs/km compared to traditional quartz fiber. In data center interconnects, low latency improves data transmission efficiency, accelerates data processing, and enhances overall data center performance.

The flexible structural design of hollow-core fiber can broaden its transmission bandwidth, accelerating its application in the communications field. By controlling the nested ring wall thickness t to approximately 0.5 μm, the antiresonant transmission band of the hollow-core fiber can be positioned within the first resonant band, enabling transmission across multiple optical bands, such as the O, S, E, C, L, and U bands. This broadband transmission characteristic gives hollow-core fiber significant advantages in wavelength division multiplexing (WDM) communication systems, enabling higher-capacity communication transmission.

Progress in Hollow-Core Fiber Communication Applications

In 2020, Lumenisity, the industrialization spinoff of the University of Southampton, launched a fiber optic patch cord based on hollow-core antiresonant fiber. Its specially designed encapsulated connectors enable convenient, low-loss, and highly reliable splicing. British Telecom piloted Lumenisity's technology in 2021 for mobile network deployment and explored quantum key distribution on hollow-core fiber.

Microsoft acquired Lumenisity in 2022 and, in November 2024, announced plans to deploy 15,000 kilometers of hollow-core fiber within 24 months. In February 2024, Spanish telecom operator Lyntia Networks, in collaboration with Nokia, OFS, and Interxion, conducted a real-world field trial of hollow-core fiber near its headquarters in Madrid. Round-trip latency was reduced by 4.287 μs over a 1,386-kilometer link.

Domestic operators are actively conducting pilot projects for hollow-core fiber communication system technology. In May 2024, FiberHome Communications, in collaboration with Pengcheng Laboratory, China Mobile, the National Key Laboratory of Optical Communication Technology and Networks, and others, developed an ultra-large capacity real-time transmission system based on hollow-core optical fiber, achieving 19.65 Thz ultra-wideband S+C+L band real-time transmission, and a single-fiber bidirectional same-wavelength transmission with a maximum transmission capacity of over 270 Tbit/s. The low loss, ultra-low nonlinearity, and ultra-low backscattering characteristics of hollow-core optical fiber were verified. The system construction is shown in Figure 4.

Figure 4 - Hollow-core Fiber Multi-band Real-time Transmission System

On December 4, 2024, China Mobile Research Institute held the "China Mobile Hollow-Core Fiber Technology Achievement Release and Seminar," unveiling a new hollow-core antiresonant fiber with a four-unit truncated double-layer nested structure. The fiber exhibits ultra-low loss of 0.10 dB/km at 1550 nm and a high-order mode suppression ratio of 26,000. A 160-wavelength × 800G transmission system technology trial was completed between Longgang, Shenzhen, and Fenggang, Dongguan, using hollow-core fiber. In the laboratory, a single-fiber bidirectional 377.6 Tb/s transmission over 100 kilometers using ultra-wideband S+C+L transmission on the same wavelength was achieved using hollow-core fiber, increasing the existing single-fiber capacity record by more than 1.5 times.

In 2024, China Telecom's procurement website released the "China Telecom Zhejiang Company 2024 Hollow-Core Fiber Cable Field Trial Project Prequalification Announcement," procuring 95 pico-kilometers of hollow-core fiber for the first time. This will launch the world's first live network demonstration project for a hollow-core fiber cable transmission system, boasting a single-wavelength transmission capacity of 1.2 Tbit/s, one-way transmission exceeding 100 Tbit/s, and a transmission distance of 20 km. China Unicom, in collaboration with Yangtze Fiber and Leading Technology, achieved a 32x1.2 Tbit/s transmission capacity over 10.2 km of hollow-core fiber.

In terms of application expansion, in 2024, teams from the State Key Laboratory of High-Field Laser Physics at the Shanghai Institute of Optics and Precision Mechanics, Chinese Academy of Sciences, and the Russell Center for Advanced Lightwave Science made progress in research on blue-shifted solitons in hollow-core antiresonant fibers. Combining theory and experiment, they revealed that the spectral width of blue-shifted solitons follows the soliton area theory. By varying the gas pressure and incident pulse energy in a hollow-core antiresonant fiber, tunable ultrafast pulses were achieved, with a central wavelength tuning range of 900 nm to 650 nm and a bandwidth tuning range of 100 nm to 180 nm (at 700 nm).

The low loss and low dispersion properties of hollow-core fiber also make it a promising transmission medium for optical quantum signals in quantum communications. Transmitting single photons or entangled photon pairs through hollow-core fiber can enable quantum key distribution and quantum teleportation, potentially providing new technological avenues for the development of quantum communications.

Challenges Faced by Hollow-Core Fiber Technology

The Difficulty of Accurate Length Measurement

Common methods for measuring fiber attenuation include the shear method, backscattering, and insertion loss. A specialized OTDR (Operating Time Delay Detector) is available for the backscattering method, making it an essential instrument for production workshops and construction sites. The backscattering method is based on the principle of scattering in optical fibers. It not only measures the fiber attenuation coefficient, but also determines attenuation uniformity along the fiber, optical continuity, physical defects, connection loss, and fiber length.

Traditional optical fiber length measurement using an  OTDR is based on the backscattering phenomenon in optical fibers. When a light signal is injected into an optical fiber, some of the light is backscattered. The OTDR measures the time delay and intensity variation of this backscattered light to calculate the fiber's length and loss distribution. In hollow-core fiber, light primarily propagates through the air core, where the backscattering coefficient is much lower than that of the quartz material used in traditional optical fibers. This makes the backscattered light signal received by the OTDR extremely weak, significantly impacting measurement accuracy and reliability.

According to the OTDR's measurement principle, its accuracy is closely related to the intensity of backscattered light. When the backscattered light intensity is too low, the measurement results are easily affected by noise, resulting in increased measurement errors. When the backscattered light intensity falls below the OTDR's detection threshold, the backscattered signal may not be accurately detected, making it impossible to effectively measure the hollow-core fiber length. Furthermore, the unique structure of hollow-core fiber can cause changes in the mode coupling and scattering characteristics of light during transmission, further complicating measurements based on traditional OTDR principles.

Figure 5 - Transmission Modes in Hollow-core Antiresonant Fiber

According to ARROW theory and confined coupling theory, as shown in Figure 6, three modes exist in antiresonant hollow-core fibers: core mode, cladding mode, and interface scattering mode. This makes it difficult to accurately calculate fiber length by measuring delay. Due to the presence of multiple modes, light transmitted through hollow-core antiresonant fibers still exhibits a dispersion of approximately 3 ps/nm/km at 1550 nm. Furthermore, when the external environment affects the fiber state and causes mode fluctuations, thisdispersion can undergo subtle changes. This makes the length of currently available hollow-core antiresonant fibers more dependent on the winding meter used by fiber drawing towers and screening and rewinding machines. Subsequent attenuation measurements of antiresonant hollow-core fibers using spectrometers or optical power meters require precise manual measurement of the cut fiber length to more accurately calculate the fiber attenuation.

Industry research has also explored injecting gas into hollow-core fibers to enhance Rayleigh scattering, enabling kilometer-level length measurements. In the actual system construction, we also adopted the method of fusing single-mode optical fibers at both ends to achieve the attenuation and length measurement of hollow-core optical fibers through OTDR. The OTDR test curve is shown in Figure 6.

Figure 6 - OTDR Test Curve after Splicing Hollow-core Fiber to Single-mode Fiber

Environmental Factors

The length measurement accuracy of hollow-core fibers is significantly affected by environmental factors. Temperature fluctuations cause minute thermal expansion and contraction of the hollow-core fiber's material and structure, altering the fiber's length and refractive index profile. For some high-precision fiber sensing and communication applications, this temperature-induced length change can result in measurement errors exceeding acceptable limits. According to the principle of thermal expansion and contraction, there is a linear relationship between the length change of the fiber material and temperature, with the thermal expansion coefficient determining the extent of the length change. Different types of hollow-core fibers have different thermal expansion coefficients due to differences in material and structure, making it difficult to accurately predict and compensate for the length change characteristics of hollow-core fibers under different temperature environments.

Changes in air pressure also affect hollow-core fiber length measurement. There is a pressure difference between the air core of a hollow-core fiber and the surrounding environment. When the external air pressure changes, especially during long-term hollow-core fiber drawing, the air pressure in the air core also changes, causing changes in the air's refractive index.

Experiments have shown that when the air pressure drops from the standard atmospheric pressure of 1013 hPa to approximately 500 hPa at high altitude, the group refractive index of a hollow-core fiber changes by Δng≈1×10-6. This can result in a time delay error of up to 3.3 ps over 1 km of fiber, corresponding to a length measurement error of approximately 0.5 mm over 1 km. The long-term operating life of hollow-core fiber is significantly affected by its material and structure. Due to its brittle nature, quartz fiber inevitably harbors tiny cracks, known as Griffith cracks. These cracks can amplify local stresses to 10 or even more than 100 times the total applied stress, resulting in actual strength being 1 to 3 orders of magnitude lower than theoretically predicted. For an atomic spacing d = 2×10-10 m, a crack with a length of L = 0.5 μm can reduce the fracture strength to 0.5% of the theoretical strength.

Figure 7 - Relationship Between Theoretical Fracture Strength and Crack Size

Traditional quartz optical fibers with a diameter of 125 microns are typically required to have a lifespan of around 30 years. Current extreme tests have estimated a lifespan of approximately 60 years for high-reliability optical fibers.

To achieve comparable strength to traditional quartz optical fibers, the quartz cladding wall thickness of current antiresonant hollow-core fibers is typically at least 60 μm. However, the multi-nested tube structure of hollow-core fibers also complicates long-term operation. According to antiresonance theory, even if the quartz cladding of an antiresonant hollow-core fiber remains intact, if the nested ring wall fractures, the antiresonance effect will be severely impacted, resulting in increased attenuation and even inability to transmit optical signals. Currently, the nested ring wall thicknesses of antiresonant hollow-core fibers used in the communications band typically come in three types: 0.5 μm, 1.0 μm, and 2.0 μm. According to Equations 3 and 4, the theoretical fracture stress σ of quartz material is positively correlated with the surface energy per unit area r, which in turn is positively correlated with the corresponding quartz material thickness.
Therefore, for an antiresonant hollow-core fiber with a quartz ring wall thickness of approximately 1.0 μm, its theoretical fracture stress, σ, is at least 10 times smaller than that of conventional quartz fiber. Consequently, when subjected to the same stress, the fracture time of an antiresonant hollow-core fiber is significantly reduced compared to that of a conventional quartz fiber. Because microcrack growth is a slow-to-accelerate process, this means that after a certain period of operation, the subsequent failure of the hollow-core fiber may occur rapidly at an unpredictable time. This poses a significant challenge to its engineering applications.

Challenges of Highly Stable Operation in Field Environments

Hollow-core optical fibers face the risk of environmental corrosion in practical applications, posing a serious threat to their long operating life. Moisture vapor is a key environmental factor affecting the performance of hollow-core optical fibers. The air core of a hollow-core optical fiber maintains a certain degree of connectivity with the external environment, allowing moisture vapor to easily enter the fiber. Once this moisture enters the hollow-core optical fiber, it forms a water film inside the fiber. Water strongly absorbs light, increasing optical signal attenuation and thus reducing the fiber's transmission performance. Moisture vapor can also hydrolyze the fiber's material, causing microcracks and impacting its structure and performance. High temperature and high humidity accelerate this hydrolysis reaction, rapidly increasing fiber loss and severely impacting its long operating life.

Figure 8 - Silica Glass Molecular Structure and Damage to SiO2 Molecules by OH Ions

Since the length of antiresonant hollow-core optical fiber is difficult to measure accurately, it is difficult to accurately control the excess length during cabling. This will make it challenging to operate stably in the field environment. Since the nested tube wall of the hollow-core optical fiber is relatively thin, usually a few microns or even thinner, it is more susceptible to external stress and extrusion deformation. During the actual laying and use process, the optical fiber may be subjected to external forces such as stretching, bending and extrusion. Due to mechanical limitations, the bending radius of the antiresonant hollow-core optical fiber cannot be too small in the case of bending, otherwise it will cause leakage of the optical signal and a decrease in transmission performance. Traditional quartz optical fiber can still maintain good transmission performance when the bending radius is a few millimeters, while the minimum bending radius of hollow-core optical fiber usually needs to be more than tens of millimeters. This places higher requirements on the actual laying and installation of the project, and also places higher requirements on the control of the excess length of the antiresonant hollow-core optical cable.

Further Development Directions for Antiresonant Hollow-Core Fiber Technology

Development of New Measurement Technologies

To address the challenges of accurately measuring hollow-core fiber lengths, actively exploring new measurement technologies is crucial.

Improvements based on optical frequency domain reflectometry (OFDR) are a key approach. Although OFDR is also based on Rayleigh scattering, it offers high spatial resolution, a wide dynamic range, and high test sensitivity. Currently, OFDR can improve measurement accuracy to centimeters or even higher for shorter hollow-core fibers by optimizing the light source's frequency sweep range and coherent detection algorithm. However, when hollow-core fiber lengths reach hundreds of meters or even kilometers, current OFDR technology still struggles to effectively avoid the problem of low signal-to-noise ratio, and further development is needed.

Brillouin optical time-domain analysis (BOTDA) is another approach. By leveraging the dependence of Brillouin scattering frequency shifts on temperature and strain, fiber length can be inferred through distributed sensing, enabling kilometer-level length measurements. The Brillouin gain spectrum of hollow-core fibers differs significantly from that of conventional fibers, necessitating the development of high-power pump light sources and cost reductions. Leveraging the coherence of a femtosecond laser frequency comb, precise measurement of optical path difference (OPD) through phase demodulation of interference fringes enables high-precision measurements at the micron level, making it suitable for specific applications involving short-distance hollow-core fibers.

Time-of-flight (ToF) is also a viable approach in short-distance laboratory environments. By directly measuring the round-trip time of the optical pulse, it can achieve ±1 mm measurement accuracy for hollow-core fibers within 1 km. Other studies have combined ToF with atmospheric pressure changes, demonstrating that a 10% change in atmospheric pressure in a 1 km hollow-core fiber results in a length error of approximately 2 mm.

Combinations of these methods, such as OFDR, time-of-flight measurement, and spectral interferometry, have also been employed to measure the length and dispersion of hollow-core fibers. By utilizing high-power, narrow-linewidth, single-frequency lasers, precise length and dispersion measurements of hollow-core fibers over 11 km have been achieved.

However, these methods still lag significantly behind existing solid-core fiber engineering technologies in practicality, and further research is needed.

Table 1 - Comparison of Several Fiber Length Measurement Methods

Standard Development and Improvement

Developing unified standards for hollow-core fiber products, test methods, and application requirements is crucial to promoting the development and application of hollow-core fiber technology. Currently, hollow-core fiber technology is still in its developmental stages, and hollow-core fibers produced by different manufacturers vary in structure and performance, lacking unified standards and specifications. This not only complicates the production and manufacturing of hollow-core fibers but also hinders their compatibility and interchangeability in practical applications. The development of unified product standards that clarify the structural parameters, performance indicators, and other requirements for hollow-core fibers will help regulate the market, improve product quality, and promote the healthy development of the industry.

Regarding test method standards, due to the unique structure and transmission characteristics of hollow-core fibers, traditional fiber testing methods are unable to meet their testing requirements. Therefore, specialized test method standards are needed. For example, standard methods for accurately measuring hollow-core fiber length will address issues with traditional measurement methods like OTDRs. Testing standards for hollow-core fiber performance indicators such as loss, nonlinearity, and latency will also be developed to ensure the accuracy and comparability of test results.

Developing application standards is also essential. Different application scenarios have different performance requirements for hollow-core optical fibers. For example, in high-speed optical communications, consideration should be given to developing interface standards and transmission protocol standards for hollow-core optical fibers and existing communication equipment under higher power transmission to ensure that hollow-core optical fibers can seamlessly connect with existing communication networks.

Expanding and Optimizing Application Scenarios

In short-haul interconnection scenarios like data centers, hollow-core fiber can effectively leverage its unique characteristics and reduce its application risks. Its ultra-low latency significantly improves data transmission speeds within and between data centers. Compared to traditional quartz fiber, hollow-core fiber reduces transmission latency from approximately 5 μs/km to 3.46 μs/km, a reduction of approximately one-third. This enables faster data transmission between servers, reduces data processing delays, and improves service responsiveness.

The low loss of hollow-core fiber reduces signal distortion and bit error rates, improving overall data center performance. In high-frequency trading scenarios, every millisecond of delay can result in significant financial losses. The low latency of hollow-core fiber meets the stringent timing accuracy requirements of high-frequency trading, providing financial institutions with faster and more accurate trading services.

To fully leverage the advantages of hollow-core fiber for short-haul data center interconnection, several key issues need to be addressed. For example, multimode optical modules and multimode optical fibers are commonly used in current data centers. Optimizing the leaky waveguide modes of hollow-core fibers to reduce their impact on valid signals requires developing anti-resonant hollow-core fibers covering the multimode band with an attenuation of up to 0.33 dB/km at 850 nm. Traditional quartz fibers are currently widely used in data center interconnects over long distances. To implement hollow-core fibers, new connectors and adapters are needed to seamlessly integrate them with existing equipment. Furthermore, optimizing hollow-core fiber splicing technology is necessary to improve splice quality and stability and reduce splice loss. By adopting advanced splicing processes and equipment, such as automated splicers and high-precision splice control technology, hollow-core fiber splice loss can be reduced to below 0.1 dB, meeting the requirements of real-world data center applications.

In conjunction with actual maintenance, performance monitoring and maintenance of hollow-core fibers in environments such as data centers also need to be strengthened. Distributed fiber optic sensing technology can be used, combined with the simultaneous laying of single-mode optical fiber and hollow-core optical fiber in the same tube, to conduct real-time monitoring of the external stress on the hollow-core optical fiber. Once an abnormality is found, timely measures can be taken to deal with it.

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