What is the "Fiber Coating"?

International Zone (English) OFSCN Knowledge Base (Public)
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What are those colored filaments visible once you strip away the outer jacket? What kind of protection do they provide?

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In optical fiber technology, the colored filaments you see after removing the outer jacket are known as the Fiber Coating (or Primary Coating). These are critical structural components of the optical fiber itself.

1. What is Fiber Coating?

The fiber coating is the first layer applied directly over the glass cladding during the fiber drawing process. While the glass core and cladding (typically 125 microns in diameter) handle light transmission, they are extremely fragile and susceptible to environmental damage. The coating increases the outer diameter—typically to 240µm or 250µm—to provide mechanical and chemical protection.

2. What Protection Does It Provide?

  • Mechanical Protection: It protects the glass surface from scratches and micro-abrasions. Even a microscopic nick on the glass surface can cause the fiber to snap under tension.
  • Micro-bend Resistance: It cushions the fiber against localized stresses (micro-bending) that could otherwise cause significant signal loss (attenuation).
  • Environmental Barrier: It prevents moisture and chemicals from reaching the glass surface, which helps prevent “stress corrosion” and ensures long-term reliability.
  • Identification: The “colored” aspect you mentioned is achieved by adding dye to the coating (or a thin layer of ink over it), allowing technicians to identify specific fibers within a high-count cable.

3. Common Coating Materials at OFSCN®

In professional sensing and telecommunications, different environments require different coating materials. Based on our technical standards at Beijing Dacheng Yongsheng Technology (OFSCN), common materials include:

  • Acrylate: The standard for indoor/outdoor telecom cables. It is easy to strip but generally limited to temperatures below 85°C.
  • Polyimide: Used for high-temperature applications (up to 300°C or even 400°C). It is much thinner than acrylate and often requires chemical or thermal stripping.
  • Metal Coatings (Gold/Copper): Used for extreme environments where even polymers fail.

4. Visual Reference

Below is a standard representation of the fiber structure, showing the relationship between the core, cladding, and the coating/buffer layers:

For more technical details on how these coatings affect the performance of Fiber Bragg Grating (FBG) sensors, you can explore our resources here:
OFSCN® Fiber Bragg Grating (FBG) Sensors