Radiation-Resistant Optical Fibers And Applications

Radiation-Resistant Optical Fibers

In today's world, where optical communication and sensing technologies permeate every aspect of life, optical fibers are regarded as the "blood vessels" of the information society. However, in extremely harsh environments, these ordinary "blood vessels" become unusually fragile-especially in high-radiation scenarios such as space, nuclear reactors, particle accelerators, and high-energy medical treatment facilities. In such environments, conventional optical fibers degrade rapidly. At this critical juncture, radiation-resistant optical fibers-like warriors clad in specialized armor-play a vital role in ensuring reliable information transmission under intense radiation conditions.

1. Effects of Radiation on Optical Fibers

The core function of an optical fiber relies on total internal reflection, which confines optical signals within the fiber core. The core is typically made of high-purity silica (SiO₂) doped with germanium dioxide (GeO₂). However, when exposed to ionizing radiation (such as gamma rays, X-rays, and high-energy charged particles), this glass structure faces significant challenges.

1.1 Radiation-Induced Darkening: "Blindness" of Optical Fibers

When high-energy particles or radiation pass through the fiber's glass structure, they transfer energy to atoms within the material. This energy can break silicon–oxygen (Si–O) bonds or other atomic bonds, creating structural defects in the glass network.

These defects act as microscopic "traps" that absorb transmitted optical signals. At the same time, additional scattering occurs at these defect sites. The combined effects significantly increase fiber attenuation, weakening the received signal or even rendering it undetectable. This phenomenon, known as radiation-induced darkening (RID), can cause conventional fibers to fail within minutes-or even seconds-in high-radiation environments.

1.2 Radiation-Induced Embrittlement: "Fracture" of Optical Fibers

Radiation-induced structural defects can also alter the physical properties of the glass. These changes may lead to fiber crystallization or the formation of microscale stress regions. Macroscopically, this manifests as increased brittleness and a higher risk of fracture.

Furthermore, prolonged radiation exposure accelerates the aging of fiber coating materials, reducing their protective capability and significantly shortening service life. This is particularly critical for long-term missions such as satellites and space stations.

1.3 Radiation-Induced Luminescence: Source of Sensing Noise

Under radiation exposure, certain impurities or defects within the fiber can become excited and emit light at specific wavelengths. This radiation-induced luminescence introduces background noise that interferes with optical sensing signals, thereby reducing measurement accuracy.

2. Core Manufacturing Technologies of Radiation-Resistant Optical Fibers

After understanding the mechanisms of radiation damage, targeted "radiation-resistant armor" can be designed. Essentially, radiation-resistant fibers minimize radiation-induced defect formation and repair existing defects through material optimization, structural design, and advanced manufacturing processes.

2.1 Material Selection and Optimization

In traditional silica fibers, two major radiation-sensitive components are hydroxyl groups (OH⁻) and germanium dioxide (GeO₂).

Hydroxyl groups exist as Si–OH bonds within the silica network. Under radiation, these bonds are easily broken, generating defects. Germanium atoms, which replace silicon atoms to increase refractive index, are more chemically reactive and prone to forming oxygen-deficient centers. These centers contain dangling bonds that can trap electrons or holes under radiation, contributing to darkening.

To improve radiation resistance, it is therefore essential to minimize the content of these sensitive components.

Reduction of Hydroxyl Content

By using ultra-high-purity raw materials, controlling humidity during preform and fiber fabrication, and avoiding oxyhydrogen flame processing, hydroxyl content can be reduced below 1 ppm-or even to the ppb level-significantly enhancing radiation resistance.

Pure Silica Core Design

Traditional fibers use GeO₂ doping in the core to raise the refractive index. In contrast, radiation-resistant fibers adopt a pure silica core while doping fluorine (F) into the cladding to reduce its refractive index. This maintains the required refractive index difference for total internal reflection while significantly lowering the probability of radiation-induced defect formation.

2.2 Functional Dopants for Defect Suppression

Even with optimized materials, some defects inevitably form during manufacturing. Specific dopants can be introduced to suppress or repair radiation-induced defects.

Cerium (Ce) Doping

Cerium doping is one of the most widely used radiation-resistant technologies. Trivalent cerium ions (Ce³⁺) possess a unique energy-level structure that allows them to capture radiation-generated electrons or holes. They transition between energy states and harmlessly dissipate energy, effectively passivating defects responsible for darkening.

Fluorine (F) Doping

In addition to reducing cladding refractive index, fluorine helps stabilize the silica network and reduces radiation-induced bond breakage.

Hydrogen (H) Loading

Hydrogen molecules can be diffused into fibers after drawing. Hydrogen can pre-react with potential defect sites or directly repair radiation-induced defects. However, since hydrogen gradually diffuses out, its effectiveness is temporary unless special sealing or packaging methods are applied.

2.3 Structural and Process Optimization

Precise control of temperature, drawing speed, and cooling rate during fiber fabrication ensures a uniform glass structure with minimal internal stress, as stress concentration points are susceptible to radiation damage.

Additionally, applying specialized coatings-such as polyimide, carbon, or metal-improves mechanical strength and enhances resistance to radiation-induced aging, preventing coating degradation in harsh environments.

A particularly effective technique is radiation preconditioning (also known as "radiation domestication"), in which fibers are pre-irradiated under controlled conditions to stabilize defect states before deployment.

3. Applications of Radiation-Resistant Optical Fibers

With their customized "armor," radiation-resistant optical fibers play indispensable roles in extreme environments.

3.1 "Lifeline" for Space Exploration

Radiation-resistant fibers function as the neural network of satellites, space stations, and deep-space probes. Their lightweight structure and immunity to electromagnetic interference enable reliable transmission of telemetry data, scientific measurements, and communication signals in high-radiation space environments. They are also used in spacecraft attitude control and structural health monitoring systems.

3.2 "Sharp Eyes" in Nuclear Energy

Inside nuclear reactors and nuclear waste storage facilities, radiation-resistant fibers can directly enter high-radiation zones. Combined with sensors, they enable real-time monitoring of neutron flux, temperature, pressure, and other critical parameters, ensuring safe operation.

3.3 "Neural Vessels" in High-Energy Physics

In particle accelerators and colliders, radiation-resistant fibers withstand intense transient radiation while transmitting beam diagnostics and detector signals, serving as reliable bridges between radiation zones and backend processing systems.

3.4 "Precision Ruler" in Advanced Medicine

In proton and heavy-ion radiotherapy, radiation-resistant fibers can operate directly within radiation beams to monitor beam position and dose in real time, ensuring accurate tumor targeting.

3.5 Other Frontier Fields

They are also widely used in military systems, aerospace propulsion testing, fusion research, and other extreme scientific environments.

4. Challenges and Future Outlook

Despite substantial progress, radiation-resistant fiber technology continues to evolve. Key development directions include:

Extreme Radiation Resistance

Future applications such as nuclear fusion reactors require fibers capable of maintaining ultra-low attenuation under GGy-level radiation doses. This demands new materials and deeper understanding of radiation damage mechanisms.

Enhanced High-Temperature Stability

Many radiation environments involve elevated temperatures. Long-term stability at temperatures ranging from several hundred to over one thousand degrees Celsius requires advanced high-temperature-resistant coatings.

Multifunctional Integration

Future fibers will integrate sensing and transmission functions. For example, embedding radiation-resistant fiber Bragg gratings (FBGs) will allow simultaneous monitoring of temperature, strain, and radiation.

Cost Reduction and Scalability

High-performance radiation-resistant fibers remain costly. Simplifying production processes and reducing costs are essential for broader adoption.

Advanced Materials Exploration

Research is ongoing into nanostructured fibers, non-silica glass systems, and AI-assisted material design to accelerate innovation.

5. R&D Progress of Radiation-Resistant Optical Fibers at YOEC

In 2025, YOEC's Special Optical Fiber Division completed Phase I of its capacity expansion project, introducing a Modified Plasma Deposition System (MPDS) and a T4 high-temperature-resistant fiber drawing tower.

The division has mastered:

Pure silica core single-mode preform manufacturing

Fluorine-graded pure silica core multimode preform technology

Polyimide (PI) thermal-curing coating technology

These advancements enable the production of radiation-resistant and high-temperature-resistant optical fibers capable of operating at 300–400°C.

Based on MPDS technology, trial production of pure silica core single-mode fibers and fluorine-graded pure silica core multimode fibers has been completed.

Performance Results

Pure Silica Core Single-Mode Fiber

Attenuation at 1310 nm: 0.487 dB/km

Attenuation at 1550 nm: 0.346 dB/km

After 500 krad irradiation:

Increased to 2.325 dB/km (1310 nm)

Increased to 3.022 dB/km (1550 nm)

After 6 days of stabilization:

1.890 dB/km (1310 nm)

2.476 dB/km (1550 nm)

The optical and radiation-resistance performance has reached a leading domestic level.

Fluorine-Graded Pure Silica Core Multimode Fiber

Attenuation at 850 nm: 2.086 dB/km

Overfilled launch bandwidth (850 nm): 1537 MHz·km

Effective modal bandwidth (EMB, 850 nm): 1588 MHz·km

Optical performance is close to the OM3 standard.

6. Future Development Plan

In 2026, YOEC's Special Optical Fiber Division will:

Continue in-depth R&D on radiation-resistant single-mode and multimode fibers

Optimize preform design and process control

Systematically verify long-term reliability under high-intensity radiation

Upgrade the T4 drawing tower with metal coating capabilities

The goal is to establish a versatile drawing platform dedicated to specialty fibers for extreme environments and further strengthen YOEC's competitiveness in radiation-resistant specialty optical fibers.

Conclusion
Radiation-resistant optical fibers originate from humanity's pursuit of deep-space exploration, controllable clean energy, and advanced medical treatment. While conventional fibers fail in high-radiation "forbidden zones," radiation-resistant fibers rise to the challenge, serving as bridges between the unknown and the known.

They represent not only a technological breakthrough but also a guarantee that humanity can continue to "see" and "hear" even in the most extreme environments