Fiber Cabling Tutorial

Date:2010-12-27

Fiber Cabling Tutorial

Until around 1970 all cables used in telecommunications, cable television and data communications were copper. However, improvements in the clarity of the glass used in fiber optic cables allowed light to travel distances very similar to copper cables. Over time the speeds, capacity and distances associated with fiber surpassed those of copper, and this led to a great increase in fiber's popularity. In short, the growing popularity of fiber optic cable is primarily due to the following benefits:
Faster transmission speeds
Increased bandwidth capacity
Increased transmission distance
Immunity from electro-magnetic and radio-frequency interference
Decreased costs per cable capacity

How Fiber Optic Cable Works
Fiber optic cable transmits data in the form of light through the core of an extremely small strand of optical glass which is surrounded by a light-reflective layer (the cladding), a layer of protective plastic coating (the buffer), and other materials and jackets which protect the fiber strand from the environment in which they will be installed. The source of light at one end of a fiber optic transmission line usually consists of a light-emitting diode (LED) or a laser diode which shoots light into the cable. As the light travels toward a light-sensitive receiver at the other end of the cable the light strength decreases as the distance increases. This power loss is known as attenuation and is measured in decibels (dB) as in 3dB per kilometer (or 3dB/km). Below is a diagram of a typical fiber optical cable's construction:


 
Multimode vs Singlemode Fiber Optic Transmission
There are two basic modes of light dispersion into a fiber optic cable: multimode and singlemode. Multimode transmission uses a light-emitting diode (LED) as a light source. Because LEDs send light in several directions when entering a glass core, the light travels along multiple paths. Singlemode transmission uses a laser diode as a light source from which a single path of light travels. Typically the light sent through a fiber is transmitted at different wavelengths for multimode (850nm and 1300nm) and singlemode (1310nm and 1550nm). See the diagram below for details about LED and laser light sources.
Light is transmitted over fiber optic cable in various wavelengths (or colors) which are measured in nanometers (nm) as in 850nm. The wavelengths associated with fiber optic cable transmission are typically 850nm and 1300nm over multimode fiber and 1310nm and 1550nm over singlemode fiber. These transmission wavelengths fall into the infrared zone of color and are invisible to the human eye (which can only see colors ranging between violet at 400nm to deep red at 700nm).


Typically, the short distances and lower costs involved with LEDs and multimode fiber have led to its popularity in short distance trasmission at the local area network (LAN) level. The long distances and higher costs associated with lasers and singlemode fiber have made them more common at the metropolitan area network (MAN) level or wide area network (WAN) level. The size of the fibers involved are expressed in the following way: inner core diameter / outer cladding diameter. The most common multimode fiber sizes are 62.5/125 micron and 50/125 micron, and the most common singlemode fiber size is 9/125 micron. Below is a diagram of the distances associated with multimode fiber and singlemode fiber. For more details and loss calculation formulas, please see our Maximum Fiber Cable Distance article.

 

Until recently LEDs were usually associated with multimode fiber transmission and lasers were associated with singlemode fiber transmission. However, the introduction of the VCSEL (Vertical Cavity Surface Emitting Laser) allowed a laser light source to be transmitted through a multimode cable, and this has greatly increased the distance, speed and capacity over multimode fiber at the LAN level while greatly decreasing the associated costs. Although both types of multimode fiber (62.5/125 and 50/125) can transmit the light emitted by a VCSEL light source, 50/125 micron multimode fiber is able to carry VCSEL light signals over much longer distances. Another reason for the growing popularity of 50-micron fiber is the fact that most important standards organizations for fiber optics (IEEE, INCITS, InfiniBand, OIF, TIA, IEC and ITU-T) have specified high bandwidth laser-optimized 50-micron multimode fiber for new high-speed installations. 50-micron fiber has three times the bandwidth capacity of 62.5-micron fiber, and some of the new laser-based 50-micron fibers have 10 to 20 times the bandwidth of 62.5 micron fiber. For more detailed information about the benefits of 50/125 micron fiber compared to 62.5/125 micron fiber, please see our 50 Micron vs 62.5 Micron fiber article.

Trends and Fiber Optic Cable Migration
Fiber optic cable is the most popular form of cable used in telecommunications, cable television and data communications. It appears that over time both telecommunications and cable television may roll into data communications as phones, video and Internet connections merge. In data communications, fiber optic cable is often used to transmit data using the following network standards: Ethernet (including Fast Ethernet, Gigabit and 10-Gigabit Ethernet), ATM, FDDI, Fiber Channel, SONET, and ISDN. Ethernet is the most common transmission standard used at the local area network (LAN) level, and the other standards are often used in wide area networks (WANs). However, technological advances and cost reductions in Ethernet (known as Gigabit Ethernet at 1,000Mbps and 10-Gigabit Ethernet at 10,000Mbps) components have allowed LANs to expand their distances, speeds and banwidth capacity at an affordable price. To achieve longer distances using Gigabit and 10-Gigabit Ethernet usually requires 50/125-micron multimode fiber. Before installing new fiber optic cable in the LAN it is vitally important to research the latest trends in Ethernet (which include Fast Ethernet, Gigabit Ethernet and 10-Gigabit Ethernet) and in 50-micron multimode cable. For more detailed information about Ethernet or 50-micron fiber cable, please see our related articles.
 

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