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Fiber Optic Tutorial

(Information compiled from internal and external sources. Wikipedia.org, etc.)

Some Benefits of Fiber Optics vs. Copper

What is Fiber Optics?

Fiber-optics use light pulses to transmit information down fiber lines instead of using electronic pulses to transmit information down copper lines. Looking at the components in a fiber-optic chain will give a better understanding of how the system works in conjunction with wire based systems.

At one end of the system is a transmitter. This is the place of origin for information coming on to fiber-optic lines. The transmitter accepts coded electronic pulse information coming from copper wire. It then processes and translates that information into equivalently coded light pulses. A light-emitting diode (LED) or an injection-laser diode (ILD) can be used for generating the light pulses. Using a lens, the light pulses are funneled into the fiber-optic medium where they transmit themselves down the line.

Light pulses move easily down the fiber-optic line because of a principle known as total internal reflection. "This principle of total internal reflection states that when the angle of incidence exceeds a critical value, light cannot get out of the glass; instead, the light bounces back in. When this principle is applied to the construction of the fiber-optic strand, it is possible to transmit information down fiber lines in the form of light pulses.

Fiber Optic Diagram
Diagram showing how light is guided through an optical fibre

Incident rays which fall within the acceptance cone of the fiber are transmitted, whereas those which fall outside of the acceptance cone are lost in the cladding.

Types of Fiber Optics

There are three types of fiber optic cable commonly used: single mode, multimode and plastic optical fiber (POF).

The optical fiber can be used as a medium for telecommunication and networking because it is flexible and can be bundled as cables. Although fibers can be made out of either transparent plastic (POF = plastic optical fibers) or glass, the fibers used in long-distance telecommunications applications are always glass, because of the lower optical absorption. The light transmitted through the fiber is confined due to total internal reflection within the material. This is an important property that eliminates signal crosstalk between fibers within the cable and allows the routing of the cable with twists and turns. In telecommunications applications, the light used is typically infrared light, at wavelengths near to the minimum absorption wavelength of the fiber in use.

Fibers are generally used in pairs, with one fiber of the pair carrying a signal in each direction, however bidirectional communications is possible over one strand by using two different wavelengths (colors) and appropriate coupling/splitting devices.

Single Mode Fiber

Single Mode cable is a single stand of glass fiber with a diameter of 8.3 to 10 microns that has one mode of transmission. Single Mode Fiber with a relatively narrow diameter, through which only one mode will propagate typically 1310 or 1550nm. Carries higher bandwidth than multimode fiber, but requires a light source with a narrow spectral width. Synonyms mono-mode optical fiber, single-mode fiber, single-mode optical waveguide, uni-mode fiber.

Single-mode fiber gives you a higher transmission rate and up to 50 times more distance than multimode, but it also costs more. Single-mode fiber has a much smaller core than multimode. The small core and single light-wave virtually eliminate any distortion that could result from overlapping light pulses, providing the least signal attenuation and the highest transmission speeds of any fiber cable type.

Single-mode optical fiber is an optical fiber in which only the lowest order bound mode can propagate at the wavelength of interest typically 1300 to 1320nm.

Single Mode Fiber Diagram

Multimode Fiber

Multimode cable is made of of glass fibers, with a common diameters in the 50-to-100 micron range for the light carry component (the most common size is 62.5). POF is a newer plastic-based cable which promises performance similar to glass cable on very short runs, but at a lower cost.

Multimode fiber gives you high bandwidth at high speeds over medium distances. Light waves are dispersed into numerous paths, or modes, as they travel through the cable's core typically 850 or 1300nm. Typical multimode fiber core diameters are 50, 62.5, and 100 micrometers. However, in long cable runs (greater than 3000 feet [914.4 ml), multiple paths of light can cause signal distortion at the receiving end, resulting in an unclear and incomplete data transmission.

Multi Mode Fiber Diagram


Fiber Optic Cable Construction

Fiber Optic Connectors

ST Connector
ST - A slotted style bayonet type connector. This connector is one of the most popular styles.
SC Connector
SC - A push/pull type connector. This connector has emerged as one of the most popular styles.
FC Connector
FC - A slotted screw-on type connector. This connector is popular in single mode applications.
SMA Connector
SMA - A screw-on type connector. This connector is waning in popularity.
FDDI Connector
FDDI - A push/pull type dual connector. This connector is one the more popular styles.
MTRJ Connector
MTRJ - A new RJ style housing fiber connector with two fiber capability.
LC Connector
LC - A small form factor optic connector developed by Lucent Technologies.
SC Duplex
SC Duplex - Dual SC connectors.

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