Storage Basics - Fibre Channel Cables and Connectors, Part 2 Page 2
Getting Physical with Fiber Optics
Despite the drawbacks of a fiber-optic solution, the performance gains achieved with fiber optics make it well worth the investment. To really understand why fiber offers such increased performance over copper-based media, it's necessary to take a look at the physical construction of fiber-optic cabling.
It is sometimes assumed that fiber-optic media, being glass, is quite fragile and must be handled delicately. While it is true that the fibers are made out of glass, optical fibers are a lot stronger than you might think and, once enclosed in a protective casing, can rival the strength of even copper-based media.
The strength of fiber cable is achieved using three separate layers. On the inside is the core, which is the central piece of glass tube used as a pathway for the light signals. Surrounding the core is the cladding, a type of sheath comprised of multiple layers of glass. This glass is used to reflect light signals back to the core, preventing light from leaking out. Both of these layers are encased in a buffer, a layer of hardened plastic that protects the core and the cladding. There are two types of buffers used in fiber optic cable, tight and loose buffers.
In a tight-buffered cable design, the buffering material is in direct contact with the fiber. Because the buffer layers are in direct contact with the fiber, any stress applied to the outside of the buffer is transferred to the fiber core. Tight-buffer configurations are generally used with indoor cables.
Loose-tube buffering systems separate the fiber from the buffer to minimize stress transfer. A gel layer between the fiber and buffer absorbs shock and high impact stresses. Cables incorporating loose-tube buffering system are much larger than those with tight-tube buffers and are often difficult to terminate. The construction of loose-fitting cables makes them well suited for outdoor application. Shown below is a comparison of tight and loose fitting fiber optic cables.
Tight-buffered Fiber Cable
Loose-buffered Fiber Cable