Fiber Optic Tutorial

What are Fiber Optic Cables?
Fiber optic cables consist of a glass core and cladding, buffer coating, Kevlar strength members and a protective outer jacket. Fiber optic cables use light pulses as opposed to electrical signals to send information.

How are Fiber Optic Cables used?
Fiber optic cables can be plugged into communications equipment and patch panels to provide a physical connection to a network or device.

Where are Fiber Optic Cables used?
Fiber optic cables are used by commercial business, governments, the military and many other industries for myriad applications involving the transmission of voice, video and data.

Fiber Optic Terms

Absorption: One cause of attenuation where light signal is absorbed into the glass during transmission.
Adapter: A device used to interconnect two different connector types.
Attenuation: Optical loss of power. Attenuation is measured in dB loss per length of cable. Attenuation is usually caused by absorption and scattering.
Attenuator: A device used to attenuate an optical signal.
Back Reflection: A measure of the light reflected off the polished end of a fiber connector. Measured in negative dB relative to incident power.
Bandwidth: The range of signal frequencies that a fiber optic cable will transmit.
Buffer: The protective coating over the fiber.
Coupler: A device used to connect two similar connector types.
Fusion Splice: A permanent splice where the two fiber ends are welded together.
Insertion Loss: The attenuation caused by the insertion of a device (such as a splice or connection point) to a cable.
Link: The entire span between two optical devices. Includes all cable, connections, and splices.
Loss Budget: The maximum amount of power that is allowed to be lost per optical link.
Jack: The female receptacle - usually found on equipment.
Mandrel: A fiber wrapping device used to cause attenuation within a fiber cable.
Mechanical Splice: A mechanical means of connecting two fibers.
Multimode: A type of fiber optic cable where the core diameter is much larger than the wavelength of light transmitted. Two common multimode fiber types are 50/125 and 62.5/125.
Plug: The male connector.
Return Loss: The ratio of the power launched into a cable and the power of the light returned down the fiber. This measurement is expressed in positive decibel units (dB). A higher number is better. Return Loss = 10 log (incident power / returned power).
Scattering: A second cause of attenuation. Scattering occurs when light collides with individual atoms in the glass.
Singlemode: A type of fiber with a small core that allows only one mode of light to propagate.
Termination: The process of mechanically installing a connector onto a fiber cable.
Wavelength: A means of measuring light color. Expressed in nanometers (nm).

How Do Fiber Optics Work? A Quick Lesson In Optical Transmission

www.L-com.com/videos/A15

Where copper cabling uses electricity to transmit signals from one end to another, fiber optics use light pulses to accomplish the same purpose. The fiber cable is made of a transparent glass core surrounded by a mirror like covering called cladding. Light passes through the cable, bouncing off the cladding until it reaches the other end of the fiber channel - this is called total internal reflection.

The diameter of the core corresponds directly with the angle of reflection. As this diameter increases, the light requires more reflections (and in turn a greater amount of time) to travel a given distance. Singlemode fiber optic cable has a smaller diameter core which lends itself to long distance, higher bandwidth runs. Multimode fiber has a larger diameter core and is more commonly used in shorter cable runs. Multimode cabling is more economical and easier to work with; it is the choice for most local area networks.

Fiber specifications list the core and cladding diameters as a ratio. The top example shows the ratio of core to cladding as 62.5/125 microns. Below, the ratio is 9/125 microns.

Multimode fiber is commonly 62.5/125 or 50/125 micron, singlemode fiber is commonly 9/125 micron.

Typical Fiber Optic Cabling (Exploded View)

Typical ST and SC Fiber Optic Connectors (Exploded Views)

Commonly Used Fiber Connectors

www.L-com.com/videos/A21

	Connector Type	Coupling Type	Fiber Type	Polish	Number of Fibers	Typical Applications	Comment
	ST	Twist on	Singlemode /Multimode	PC, UPC	1	LANs	Keyed
	FC	Screw on	Singlemode /Multimode	PC, UPC, APC	1	Datacom, Telecommuni- cations	Keyed
	SC	Snap on	Singlemode /Multimode	PC, UPC, APC	1	CATV, Test Equipment	Keyed
	LC	Snap on RJ45 style	Singlemode /Multimode	PC, UPC, APC	1	Gigabit Ethernet, Video Multimedia	Small Form Factor (SFF)
	MU	Push/Pull	Singlemode /Multimode	PC, UPC, APC	1	Medical, Military	Small Form Factor (SFF)
	MT-RJ	Snap on RJ45 style	Singlemode /Multimode	N/A	2	Gigabit Ethernet, Asynchronous Transmission Mode (ATM)	One of Mating Connectors must have Alignment Pins
	MPO (MTP)	Push/Pull	Singlemode /Multimode	N/A	4, 8, 12, 16, 24	Active Device Transceiver, Interconnec- tions for O/E Modules	One of Mating Connectors must have Alignment Pins

Selecting the right type of Fiber Optic Cable

The figure below illustrates some of the common conditions in a typical fiber cable installation and indicates the type of fiber cable normally utilized in each environment.

Bandwidth and Application Differences--Between Copper and Fiber Optic Cabling

Type:
Typical Bandwidth:	< 10 GHz	< 100 MHz (Cat 5E)	< 1 GHz (RG6)
Typical Use:	Data communications broadcast	Structured wiring in local area networks	Cable TV / Broadcast Test and instrumentation
Benefits:	Most bandwidth. Fastest transmission speeds. Immune to EMI/RFI.	Inexpensive, relatively easy to install and terminate	Inexpensive, relatively easy to install and terminate. Can span longer distances than UTP.
Limitations:	Difficult to terminate. Most expensive cost / foot.	Maximum distance of 100m. Can be affected by EMI/RFI.	Can be affected by EMI/RFI.