When the attenuation coefficient of hollow-core fiber (HCF) broke through 0.1dB/km, surpassing the
theoretical limit of traditional solid-core fiber, the entire industry was excited. However, this glorious
milestone is not the end, but the starting point of the next, even more arduous climb. From reaching
a performance "singularity" to large-scale commercialization, what technical barriers must hollow-core
fiber overcome? Following the successful IFOC 2025 Hollow-Core Fiber Forum, ICC continued to gather
input from experts across industry, academia, research, and application to create a clear roadmap for
action.
1. Material Foundation: The "Pure" Revolution of Glass Tubes
Technological breakthroughs begin at the source. An expert from a university and research institute pointedly
pointed out, "In the future, the key focus will be on the quality and stability control of the raw materials
for the glass tubes." This seemingly fundamental aspect is precisely the key to the performance consistency
and yield of hollow-core fiber. Whether it's the photonic band gap or the antiresonant structure, their precise
optical properties are built on the microscopic glass material and glass tube. Any tiny compositional defects
or dimensional inconsistencies will be amplified during the high-speed drawing process, ultimately affecting
the fiber's performance. The ultimate pursuit of material purity and consistency is the first hurdle for hollow-core
fiber to move beyond the laboratory prototype stage and achieve stable, mass production.
II. Performance Optimization: Addressing the Three "Internal Frictions" of Gas Absorption, Loss Spectrum,
and Mode-Field Interference
A representative from an operator application provider presented more specific challenges from a user
perspective: "Currently, there are three key technical issues that urgently need to be addressed: gas
absorption, loss spectrum flatness, and inter-mode interference."
Gas Absorption: Trace amounts of gas molecules such as water vapor/hydroxyl (H2O) and carbon dioxide (CO2)
remaining in the hollow-core channel can form absorption peaks at specific wavelengths, eroding the
fiber's ultra-low loss advantage.
Loss Spectrum Flatness: Achieving uniform and extremely low loss across the entire communication window
(e.g., from the O-band to the C/L-band), rather than simply excelling in a single isolated wavelength band,
is crucial for wavelength division multiplexing (WDM) systems.
Mode Field Interference: Ensuring stable optical signal transmission within hollow-core fiber and
suppressing mode coupling and crosstalk are fundamental to ensuring reliable high-capacity,
long-distance transmission.
Addressing these three "internal frictions" requires collaborative innovation across the entire chain,
from mechanism research, structural design, fabrication processes, to packaging and testing.
III. Engineering Empowerment: Testing and Splicing Adapters Urgently Need Improvement
Technology maturity relies on supporting tools. Experts in testing and splicing highlight the practical
challenges facing engineering implementation.
Testing Challenges: Fortunately, most existing instruments are reusable, according to testing experts.
However, the lack of single-ended OTDRs (Optical Time Domain Reflectometers) is a major pain
point in current engineering maintenance. Due to the extremely weak air scattering, traditional OTDRs
struggle to accurately locate faults. The development of high-performance single-ended OTDRs will
become essential for the efficient deployment and maintenance of hollow-core fiber optic cable lines.
Fusion splicing process: Fusion splicing experts emphasize the need to improve fiber consistency
through standardization and optimize splicer performance and environment to minimize the entry
of contaminants such as moisture into the hollow core during the splicing process. This is a critical
step in ensuring end-to-end system performance.
The technical challenges of hollow-core fiber have entered a "deep waters" phase, delving from
macroscopic structural design to microscopic materials science, gas dynamics, and process control.
As industry experts have noted, this requires the collaborative efforts of fiber manufacturers,
equipment vendors, and operators. Every small step forward paves the way for the future large-scale
development of hollow-core fiber. Academic research institutions must also play a crucial role in
providing the finishing touch, delving into fundamental research to answer underlying questions and
exploring innovative applications of new methods in the field of hollow-core fiber.
