What is the layer of glass surrounding the core called? Is its primary purpose to prevent light from leaking out?
In the structure of an optical fiber, the layer of glass surrounding the core is called the Cladding.
1. Technical Principle
You are correct regarding its primary purpose. The cladding has a lower refractive index than the core. This difference in refractive index allows for Total Internal Reflection (TIR) to occur at the interface between the core and the cladding. This mechanism ensures that light signals remain confined within the core and travel along the fiber without leaking out, even when the fiber is bent.
2. Physical Dimensions
In standard telecommunications and sensing fibers, such as those used in DCYS (OFSCN) products, the cladding typically has a diameter of 125μm. This is a global industry standard for most single-mode and multi-mode fibers.
For example, our standard OFSCN® G.652D Optical Fiber and OFSCN® G.657 Optical Fiber both feature a 9μm core surrounded by a 125μm glass cladding.
3. Material Composition
The cladding is typically made of high-purity silica glass (SiO_2), often doped with materials like fluorine to precisely lower its refractive index relative to the core.
4. Product Mapping
In the field of Fiber Bragg Grating (FBG) sensing, the cladding plays a vital role. For instance, in our OFSCN® Polyacrylate Fiber Bragg Gratings, the FBG is inscribed directly into the core, while the 125μm cladding maintains the structural integrity and optical confinement of the sensor.
Here is a visual representation of a standard optical fiber structure (Core/Cladding/Coating):
If you have further questions about how the cladding interacts with different types of protective coatings (like Polyimide or Gold), feel free to ask.