Fiber Optic Cable

Properties of Fiber-Optic Cabling

Fiber optic cable can transmit data over long distances with higher bandwidths than any other networking media. Optic fiber cable can transmit signals with less attenuation and is totally protected to EMI and RFI. OFC is generally used to connect network devices.

Fiber optic cable is a flexible, but very thin; a transparent strand of very pure glass, not much bigger than a human hair. Bits are encoded on the fiber as light impulses. The fiber-optic cable acts as a waveguide; or “light pipe,” to transmit light between the two ends with the minimal loss of signal.

As an analogy, consider an empty paper towel roll with the inside coated like a mirror. It is a thousand meters in length, and a small laser pointer is used to send Morse code signals at the speed of light. Essentially that is how a fiber-optic cable operates; except that it is smaller in diameter and uses sophisticated light technologies.

Fiber-optic cabling is now being used in four types:

• Enterprise Networks: Used for backbone cabling and interconnecting infrastructure devices.


• Fiber-to-the-Home: Used to provide always-on broadband services to homes and small businesses.


• Long-Haul Networks: This type is used by service providers to connect countries and cities.


• Submarine Networks: Used to provide reliable high-speed; high-capacity solutions capable of surviving in harsh undersea environments up to transoceanic distances.

Fiber Optic Cable structure

The optical fiber is composed of two kinds of glass (core and cladding) and a protective outer shield (jacket) as shown in figure 3-8. 

Core

The core is actually the light transmission element at the center of the optical fiber. This core is typically silica or glass. Light pulses travel through the fiber core.

Cladding

Made from little different chemicals than those used to make the core. It tends to perform like a mirror by reflecting light back into the core of the fiber. This keeps the light in the core as it travels down the fiber.

Buffer

Used to help shield the core and cladding from damage.

Strengthening Member

 Surrounds the buffer, prevents the fiber cable from being stretched out when it is being pulled. The material used is often the same material used to manufacture bulletproof vests.

Jacket

Typically a PVC jacket that protects the fiber against abrasion; moisture, and other contaminants. This outer jacket composition can vary depending on the cable usage.

Types of Fiber Media

Light pulses in lieu of the transmitted data as bits on the media are generated by either:

• Lasers


• Light emitting diodes (LEDs)

Electronic semiconductor devices called photodiodes detect the light pulses and convert them to voltages. The laser light transmitted over fiber-optic cabling can damage the human eye. Care must be taken to avoid looking into the end of an active optical fiber.

Fiber-optic cables are mostly classified into two types:

• Single-mode fiber (SMF): its core is very small and this type of fiber uses very expensive laser technology to send a single ray of light; as shown in Figure 3-9 Popular in long-distance situations spanning hundreds of kilometers; such as those required in long haul telephony and cable TV applications. Following is single mode cable characteristics.
  
  
  
  
  • Small core
  
  
  • Less dispersion
  
  
  • Use laser as the light source
  
  
  • Suited for long distance application
  
  
  • Commonly used with campus backbone for a distance of several thousand meters.
  
  
  
  

• Multimode fiber (MMF): Its core is very large and this type of cable uses LED emitters to send light pulses. Specifically, light from a LED enters the multimode fiber at different angles; as shown in Figure 3-10. Popular in LANs because they can be powered by low-cost LEDs. It provides bandwidth up to 10 Gb/s over link lengths of up to 550 meters. Following is single mode cable characteristics.


• Larger core than single mode cable


• Uses LEDs as the light source


• Allows greater dispersion and therefore, loss of signal


• Suited for long distance application; but shorter than single mode


• Commonly used with LANs or distances of a couple hundred meters within a campus network.