# What is hydrogen-induced attenuation in optical fibers?

**URL:** <https://forum.ofscn.net/t/what-is-hydrogen-induced-attenuation-in-optical-fibers/2643>\
**Category:** OFSCN Technical Knowledge Base\
**Tags:** fbg-technology\
**Created:** [August 26, 2026, 3:05am UTC](https://forum.ofscn.net/t/what-is-hydrogen-induced-attenuation-in-optical-fibers/2643 "2026-08-26T03:05:31Z")\
**Posts on this page:** 2\
**Page:** 1

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**Author:** ![VoidWalker](https://forum.ofscn.net/letter_avatar_proxy/v4/letter/v/848f3c/32.png) [@VoidWalker](https://forum.ofscn.net/u/VoidWalker)\
**Post date:** [August 26, 2026, 3:05am UTC](https://forum.ofscn.net/t/what-is-hydrogen-induced-attenuation-in-optical-fibers/2643/1 "2026-08-26T03:05:31Z")

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How does hydrogen get into solid glass? Does it discolor or embrittle optical fibers?

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**Author:** ![OFSCN\_Tech\_Expert](https://forum.ofscn.net/user_avatar/forum.ofscn.net/ofscn_tech_expert/32/199_2.png) [@OFSCN\_Tech\_Expert](https://forum.ofscn.net/u/OFSCN_Tech_Expert)\
**Post date:** [August 26, 2026, 3:07am UTC](https://forum.ofscn.net/t/what-is-hydrogen-induced-attenuation-in-optical-fibers/2643/2 "2026-08-26T03:07:54Z")

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The “Hydrogen-induced Attenuation” of optical fibers is a critical physical-chemical aging phenomenon in fiber optics and fiber sensing. Addressing your questions on “how hydrogen enters solid glass” and “whether it causes discoloration or embrittlement,” the physical mechanisms and microscopic manifestations are as follows:

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### I. How Does Hydrogen Diffuse into Solid Fused Silica Glass?

Although macroscopically, the core material of optical fibers – high-purity fused silica glass (Silicon Dioxide, \text{SiO}\_2) – appears as a dense solid, at a microscopic level, it is an **amorphous silica network**.

1. **Network Interstices:**  
The topological network of amorphous silica’s silicon-oxygen tetrahedra is not absolutely tightly packed. It contains numerous atomic/molecular-scale voids. The effective average size of these micropores is approximately 0.3\ \text{nm}.
2. **Molecular Diffusion:**  
Hydrogen molecules (\text{H}\_2) are extremely small and lightweight molecules. Their effective kinetic diameter is only about 0.289\ \text{nm}. Driven by thermal motion, external hydrogen molecules can easily penetrate the fiber’s protective outer layers and shuttle through the microscopic interstices of the silica network, diffusing towards the core (Physical Diffusion).

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### II. Does Hydrogen Cause Optical Fibers to “Discolor” or “Become Brittle”?

#### 1. Does it Discolor? – No (No Significant Absorption Changes in the Visible Spectrum)

- **Physical Fact:** The ingress and subsequent reactions of hydrogen molecules do not cause electronic transitions that absorb light in the visible spectrum (380\ \text{nm} \sim 750\ \text{nm}). Therefore, visually, the transparency and color of the fiber do not change noticeably.
- **Attenuation Occurs in the Near-Infrared Region:** The “dimming” caused by hydrogen refers to a severe decrease in the transmission of light in the **near-infrared wavelengths** used for communication and sensing (e.g., 1310\ \text{nm} and 1550\ \text{nm}), resulting in significant transmission loss.

#### 2. Does it Become Brittle? – No Significant Change in Macro-Mechanical Strength

- **Physical Fact:** The physical dissolution of molecular hydrogen in the glass voids does not break the main covalent bonds of the silica network. It does not lead to macroscopic embrittlement, cracking, or a sharp decrease in tensile strength of the fused silica glass.
- **Additional Note:** The primary physical-chemical mechanism that causes a significant reduction in fiber mechanical strength and leads to brittle fracture is **stress corrosion** induced by **water molecules** (hydrolytic stress cracking), not the diffusion of pure hydrogen molecules.

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### III. The True Destructive Force of “Hydrogen Loss”: Optical Attenuation

Once hydrogen invades the fiber core, it causes signal attenuation primarily through two mechanisms:

1. **Physical Hydrogen Loss (Molecular Free Absorption, Reversible):**

2. **Chemical Hydrogen Loss (Defect Reaction Forming Hydroxyl Groups, Irreversible):**

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### IV. Engineering Solutions to Suppress Hydrogen Loss

In harsh environments such as downhole oil and gas wells, geothermal monitoring, hydrogen energy industry, and high-radiation applications, standard doped silica fibers are highly susceptible to failure due to hydrogen loss. For high-hydrogen or high-temperature environments, fiber engineering typically employs **pure silica core** technology or specialized coatings like polyimide to reduce defect activity and diffusion rates.

Beijing Dacheng Yongsheng Technology Co., Ltd.'s (OFSCN®) [OFSCN® 300℃ SM Polyimide Optical Fiber](https://www.ofscn.org/optical-fibers/polyimide-coated-sm-300.html) utilizes high-temperature resistant polyimide material coating and supports customized pure silica core structures, which can effectively reduce the risk of hydrogen-induced attenuation in high-temperature and special environments:

 ![OFSCN® 300℃ SM Polyimide Optical Fiber](https://forum.ofscn.net/uploads/default/original/1X/ce90be3e4b9bb517d521f23c595dfb4d1985b218.jpeg)