When people refer to “125 microns” and “250 microns,” which specific parts of the fiber are they measuring?
In optical fiber technology, these measurements refer to the concentric layers that make up the fiber. When people mention “125 microns” and “250 microns,” they are typically referring to the following parts:
1. 125 Microns: The Cladding Diameter
The 125 μm measurement refers to the Cladding. This is the glass layer surrounding the central core. 125 microns is the global industry standard for the outer diameter of the glass portion of most communication and sensing fibers (such as G.652D or G.657 fibers).
- Note on the Core: The innermost part, the Core (where light actually travels), is much smaller. For a standard single-mode fiber, the core diameter is typically around 9 μm.
2. 250 Microns: The Coating Diameter
The 250 μm measurement refers to the Coating (also called the primary buffer). This is a protective layer, usually made of polyacrylate, applied over the glass cladding to provide mechanical strength and protection against moisture and scratches.
Common Examples from OFSCN® Products:
- OFSCN® G.652D Optical Fiber: Core 9μm / Cladding 125μm / Coating 255μm (Standard polyacrylate).
- OFSCN® G.657 Optical Fiber: Core 9μm / Cladding 125μm / Coating 255μm (Bend-insensitive).
- OFSCN® 200℃ Polyimide Optical Fiber: Core 9μm / Cladding 125μm / Coating 155μm. (Note that specialty fibers like Polyimide use a much thinner coating than the standard 250μm to withstand high temperatures).
Standard Structure Visualization:
In summary: 125 microns is the size of the glass (cladding), and 250 microns is the size of the fiber once the first plastic protective layer (coating) is added.