# Fiber Optic Cable ## What is Fiber Optic Cable Fiber optic cable transmits data as pulses of light through strands of glass or plastic fiber rather than as electrical signals through copper wire. Each fiber strand is thinner than a human hair, yet it can carry enormous amounts of data at speeds approaching the speed of light. Fiber optic cable is immune to electromagnetic interference because it uses light rather than electricity, making it ideal for environments with high levels of electrical noise. It is also much more secure than copper cable because it does not emit electromagnetic signals that could be intercepted without physically cutting the cable. ## How Fiber Optic Works Light enters one end of the fiber from a laser diode or LED light source. The fiber is constructed so that light traveling through it undergoes total internal reflection whenever it tries to escape through the sides of the fiber. Total internal reflection occurs because the core of the fiber has a higher refractive index than the surrounding cladding layer, causing light to bounce back into the core at the interface rather than passing through. This allows light to travel through curves and bends in the fiber while remaining trapped inside. At the receiving end, a photodetector converts the light pulses back into electrical signals. ## Types of Fiber Optic Cable Single-mode fiber has a very narrow core, typically about 9 micrometers in diameter. This narrow core allows only a single path or mode of light to propagate through the fiber. Single-mode fiber supports transmission over very long distances, potentially hundreds of kilometers, and supports very high bandwidths. It is used for long-distance telecommunications and in internet backbone connections. Single-mode fiber requires laser light sources, making it more expensive. Multi-mode fiber has a larger core diameter, typically 50 or 62.5 micrometers. The larger core allows multiple paths of light to travel through simultaneously. Multi-mode fiber is less expensive than single-mode and is used for shorter distances within buildings and campuses. However, at higher speeds, multiple modes cause signal degradation over longer distances. ## Advantages of Fiber Optic Fiber optic cable supports much higher bandwidths than copper cable. A single fiber strand can carry terabits per second of data. It supports transmission over much longer distances than copper cable without needing repeaters, making it essential for long-distance telecommunications. It is completely immune to electromagnetic interference because it uses light rather than electricity. It provides superior security because it is very difficult to tap without detection. ## Disadvantages of Fiber Optic Fiber optic cable is significantly more expensive than copper cable. The installation requires specialized equipment and trained technicians. Fiber cables are more fragile than copper cables and can break if bent too sharply. The connectors and splicing equipment used with fiber are more expensive and require more skill to use than the connectors used with copper cable. ## Applications Fiber optic cable is used for internet backbone connections between cities and countries, for connections between buildings on large campuses, in data centers where high-speed connections between servers and switches are needed, for high-speed internet access to homes and businesses through fiber to the home services, and in many industrial and telecommunications applications.