Fiber Construction


Optical fiber for telecommunications consists of three components: core, cladding and coating. The core is the central region of an optical fiber through which light is transmitted.

Inngeneral, the telecommunications industry uses sizes from 8.3nmicrometers (µm) to 62.5 micrometers. The standard telecommunicationsncore sizes in use today are 8.3 µm (single-mode), 50 µm (multimode), andn62.5 µm (multimode). (Single-mode and multimode will be discussednshortly.)

The cladding is a glass sheath that surrounds the core,nwhich acts like a mirror, reflecting light back into the core. Thencladding itself is covered with a plastic coating and strength materialnwhen appropriate. The diameter of the cladding surrounding each of thencores is typically 125 µm.

Light in the core travels slightlynslower than light in the cladding and this property tends to keep anynlight sent into the core from one end of the fiber from leaking out,nuntil it reaches the far end. The core and cladding arenmanufactured together as a single piece of silica glass with slightlyndifferent compositions, and cannot be separated from one another. Thenglass does not have a hole in the core, but is completely solidnthroughout.

The third section of an optical fiber is thenouter protective coating. This coating is typically an ultraviolet (UV)nlight-cured acrylate applied during the manufacturing process to providenphysical and environmental protection for the fiber. During theninstallation process, this coating is stripped away from the cladding tonallow proper termination to an optical transmission system.

How is the fiber made?

  • Create the pre-form
  • Take glass tube
  • Inject germanium and silicon dioxide
  • Fuse internal gasses into a glass
  • Draw optical fiber from the pre-form
  • Attach coating layer while drawing
  • Roll drawn fiber off onto rolls
  • Test fiber