Fiber Optic Cable

The reasons for fiber optic cable as a transmission medium providing a high degree of immunization to noise (EMI) as opposed to other transmission media all stem from the use of light to convey the information (signals) and the construction of the medium (the fiber optic cable).

Fiber Optic Lines

A fiber optic cable is comprised of varying numbers of bundled fiber optic lines (see Figure 1). Each fiber optic line has a core made of an incredibly thin long strand of optically pure glass or plastic capable of carrying digital information over very long distances through the propagation of light carrying signals. The key components of a fiber optic line include:

• Inner Core – The inner core is usually made of very long strands of optically pure glass or plastic. This is where the light travels
• Outer Insulating Jacket – Usually made of Teflon or PVC and helps to protect the other layers from mechanical damage and moisture
• Kevlar Fibers – Helps to strengthen the cable and prevent breakage
• Plastic Coating – Cushions the fiber core against shock damage as well as adding waterproofing functionality
• Optical Cladding Layer – Surrounds each individual glass or plastic strand. Without this cladding the propagation of the light signals down the length of the fiber cannot occur. This is the solid blue/gray layer in Figure 1 and that to which the arrow labeled “Cladding” is pointing at in Figure 2.

Fiber Optic Cables

Hundreds and sometimes even thousands of these individual fiber optic lines are bundled together to form a fiber optic cable. A protective jacket then encases (an additional outer covering) the bundles of fiber optic lines to form what we know as a fiber optic cable. The jacket also serves to keep all of the constituent fiber optic lines together in a neater more easily managed package.

Types of Optic Fibers

Optic fibers commonly come in one of two forms:

1. Single-Mode Fibers – These fibers have small cores that are about 9 microns in diameter and transmit infrared laser light (wavelength = 1,300 to 1,550 nanometers). Communications links greater than 200m are one of the major uses of single-mode optic fiber cables. 
2. Multi-Mode Fibers – Multi-Mode fibers have larger cores than single-mode fibers that are about 62.5 microns in diameter and transmit infrared light (wavelength = 850 to 1,300 nm) from Light-Emitting Diodes (LED). They also support multiple transmission paths hence their name multi-mode fibers. Their main applications are for communications over short distances or for applications requiring high power transmissions.

Fiber Optic Cable Connectors

While there are a number (20+) of different types of fiber optic connectors on the market, the majority of connections have predominantly used either one of two types.