The Three C’s of an Optical Fiber
The basic elements of an optical fiber in terms of fiber testing are sometimes referred to as the “three C’s”:
Core: The center of the fiber cable, made of specially treated glass or plastic. This is the medium for light transmission throughout the span of the cable, so it must be as pure and clean as possible.
Cladding: An additional layer made of material similar to the core, but with a lower refractive index to facilitate continuous reflection of the light source back into the core.
Coating: The outer layer of the cable which wraps, protects, and insulates the core and cladding.
Types of Fiber
Fiber is classified into different types (multimode or single mode) based on the way in which the light travels through it. The fiber type is closely related to the diameter of the core and cladding. Multimode fiber has a larger core diameter that allows multiple modes of light to pass through it simultaneously.
The primary advantages of multimode fiber are the ease of coupling to light sources and to other fibers, lower cost light sources (transmitters), and simplified connectorization and splicing processes. However, its high attenuation (optic loss) and low bandwidth limit the transmission of light over multimode fiber to short distances.
The advantage of single-mode fiber is its higher performance with respect to bandwidth and attenuation.
The small core size of single-mode fiber requires more expensive transmitters and alignment systems to achieve efficient coupling. Nonetheless, for high performance systems or for systems that are more than a few kilometers in length, single-mode fiber remains the best option.
