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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.
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 reduce the power of 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.
Insertion Loss: The attenuation caused by the insertion of a device (such as a splice or connection point) to a cable.
Loss Budget: The maximum amount of power that is allowed to be lost per optical link.
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.
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.
Single mode: A type of fiber with a small core that allows only one mode of light to propagate.
Wavelength: A means of measuring light color. Expressed in nanometers (nm).


A Quick Lesson In Optical Transmission
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.

In today’s high speed networks, Graded Index Multimode fiber or Step Index Single mode fiber is used to improve light transmission over long distances. Multimode fiber has a larger core and is typically used in short runs within buildings. Single mode fiber has a smaller core and is used in long distance runs typically outside between buildings.

Fiber Core Sizes
Fiber specifications list the core and cladding diameters as a ratio. Multimode fiber is commonly 62.5/125 or 50/125 micron, single mode fiber is commonly 9/125 micron.
Fiber Core Sizes

Fiber Glass Types
Fiber Glass Types

How Do Fiber Optics Work?

Commonly Used Fiber Connectors
 
Connector
Type
Coupling
Type
Fiber Type
Polish
No.
of Fibers
Typical
Applications
Comment
ST
ST
Twist on
Single mode
/Multimode
PC, UPC
1
LANs
Keyed
FC
FC
Screw on
Single mode
/Multimode
PC, UPC, APC
1
Datacom,
Telecommuni-
cations
Keyed
SC
SC
Snap on
Single mode
/Multimode
PC, UPC, APC
1
CATV,
Test
Equipment
Keyed
LC
LC
Snap on
RJ45 style
Single mode
/Multimode
PC, UPC, APC
1
Gigabit
Ethernet,
Video
Multimedia
Small Form
Factor (SFF)
MU
MU
Push/Pull
Single mode
/Multimode
PC, UPC, APC
1
Medical,
Military
Small Form
Factor (SFF)


MT-RJ

MT-RJ
Snap on
RJ45 style
Single mode
/Multimode
N/A
2
Gigabit
Ethernet,
Asynchronous
Transmission
Mode (ATM)
One of
Mating
Connectors
must have
Alignment
Pins

MTP
MPO
(MTP)
Push/Pull
Single mode
/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
  
    
 
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