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LECTURE
Single Mode Fiber
o Uses step index fiber and a highly focused source of light that limits beams to a small range of angles all close to the horizontal o Single Mode fiber is manufactured with a much smaller Diameter than Multimode o All of the beams arrive at the destination together and can be recombined without distortion to the signal
Fiber Sizes
o Optical Fibers are defined by the ratio of the diameter of their Core to the diameter of their Cladding o Both the diameters are expressed in Microns (Micrometers) Fiber type Core Cladding 62.5/125 62.5 125 50/125 50 125 100/140 100 140 8.3/125 8.3 125
Cable Composition
o A core is surrounded by cladding forming the Fiber. o In most cases, fiber is covered by a Buffer layer that protects it from moisture. o Finally the entire cable is encased in an outer jacket o Both core and cladding can be made of either glass or plastic but must be of different densities o In addition the inner core must be ultra pure and completely regular in size and shape o Chemical differences in material and even small variations in the size or shape of the core alter the angle of reflection and distort the signals
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o Some applications can handle a certain amount of distortion and their cables can be made cheaply but others depend on complete uniformity
have a purpose: –Plastic is lightweight and cheap but do not provide structural strength and
an be used in open air but it is expensive and
Light Sources o For tx to occur the sending device must have a light source and the receiving cell (Photodiode)
T l LED: light that strikes the boundaries of at uncontrollable angles
range allowing control over angle of
nce of Connectors ght, two cores can be compressed and angle of be altered
vice to be connected Advan e The ma r l cable are:
o The outer jacket can be made of several materials including Teflon, Plastic, Fibrous Plastic, metal tubing
Each of these materials
can emit fumes when burnt –Metal tubing provides strength but is costly –Teflon is lightweight and c does not increase cable strength
for Optical Cable
device with a photosensitive o Photodiode converts the light into current usable by the computer
he ight source can either be an LED or an ILD
–Cheaper but provide Unfocused channel –Limited to short distance use LASER: –Can be focused to a narrow incidence Fiber Optic Connectors o Importa o If connector is over ti reflection of the signal will o All of popular connectors are Barrel shaped that come in male and female versions o The cable has a male connector that fixes into a female connector attached to the de tag s of Optical Fiber jo advantages of Fiber over twisted pair and coaxia
Noise Resistance: –Because fib –External light the on
er uses light rather than electricity, noise is not a factor ly form of possible interference is blocked from the channel by the Outer jacket Less Signal Attenuation –Fiber optic Transmission distance is significantly greater than other
er Bandwidth
media –A signal can run miles w/o regeneration High –Can support higher BWs and higher data rates
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Types of Propagation :
Tropospheric ric
y considers the earth as surrounded by two layers here:
- Surface
- Ionosphe
- Line-of-Sight
- Space Radio Technolog of atmosp
TROPOSHERE o It is the portion of the atmosphere extending outwards approx. 30 miles surface
ariation and weather in general occur in the el
IO
from the earth’s o It contains what we call as AIR o Clouds, wind, Temp. v Troposhere as does jet plane trav
NOSPHERE o It is the layer of atmosphere above the troposhere but below space o It is beyond what we think of as atmosphere
Surface Propagation
o In surface propagation, radio waves travel through the lowest layer of the the earth
e of the planet
e signal
atmosphere, hugging o At the lowest frequencies signal emanate in all direction from the tx antenna and follow the curvatur
o Distance depends on the amount of power in th
Troposhpheric Propagation This can work in two ways:
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Line-of-Sight :
- A signal can be directed in a straight from Antenna to antenna
of the rom where it is reflected back to earth’s surface
o The e placed within line-of-sight distances and is limited by the curvature of the earth
Broadcast:
- Signal is broadcasted at an angle into the upper layers troposphere f
first method demands that both transmitter and receiver b
o The second method allows greater distances to be covered
Ionoshpheric Propagation
o Higher frequency radio waves are radiated towards the ionosphere where arth
nge direction bending back to earth
they are reflected back to the e o The difference in density between troposhphere and ionosphere causes each radio wave to speed up and cha o Allows greater distances to be covered by lower power output Line of Sight Propagation o Very high frequencies signals are transmitted in straight line from antenna
h to each other to avoid earth’s curvature
S
to antenna o Antennas must be directional facing each other or either tall enough or close enoug o Radio waves can reflect of the objects in the middle and can reach late to the receiver. These late signals distort signal
pace Propagation o A broadcast signal is received by the orbiting satellites which rebroadcasts nded receiver on the earth Summary Gui d cal Fiber Cable
cation dio Waves
Rea n
Networking” 4th Edition by Behrouz A.
the signal to the inte
de Media Opti Unguided Media Radio Frequency Allo Propagation of Ra
di g Sections Section 7.1,“Data Communications and Forouzan
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