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Know a little on the Fiber optic - (Material of training
of Fujihara Telecomunicações)
The History of the Optical Communication
There are five million years primitive men began the optical communications
with signs and visual gestures.
Century VI B.C. - Ésquilos informed Argos of the fall of
Tróia through a chain of fire signs.
Century II B.C. - Polybius proposed a system of transmission of
the Greek alphabet through fire signs (two digits and five levels
(52=25 codes)).
200 - Heron of Alexandria studied the reflection. The first glasses
(babilônios, Egyptian and Phoenician) they were not transparent.
They were simply made melting the sand of the sea. The transparent
glasses appeared in the medium age. (100 B.C.) Glasses of optical
quality only appeared after the appearance of the famous Venetian
crystals, in Renaissance. The beginnings of the fiber optic are
known from the antiquity and they were used in prisms and illuminated
sources.
1621 - Willebrod Snell discovered that when the light crosses two
means, his/her mute direction (refraction).
1678 - Christian Huygens models the light as wave.
1792 - Claude Chappe invented a system of mechanical transmission
for long distances (B <1 bps).
1800 - Sir William Herchel discovered the infrared part of the spectrum.
1801 - Ritler discovers the ultraviolet part of the spectrum.
1830 - telegraph with code Morse (digital) and repeaters arrived
to 1000km (B=10 bps).
1866 - first transatlantic transmission of telegraph.
1870 - John Tyndall showed to Royal Society that the light bends
to accompany a squirt of water.
1876 - invention of the analogical telephone for Graham Bell that
exists until today (the telephone).
1880 - Photophone of Graham Bell.
Century XX: The world gets entangled of analogical phone nets.
1926 - John Logie Bird patents a TV to you blush primitive that
it used glass sticks to transport light.
1930-40 - some light guides were developed of Perplex to illuminate
surgeries.
1940 - 1o coax cable transports until 300 phone calls or a channel
of TV with a bearer of 3MHz.
1948 - the coax cables present big losses for f>10MHz. it appeared
Like this to 1a transmission for microwave with bearer of 4GHz.
1950 - researchers begin to suggest the use of a peel in turn of
the fiber to guide the light. The first "fiberscopes"
were developed, but the cost is still prohibitive.
1964 - Kao speculated that, if the loss of the fiber only goes 20dB/km,
it would be possible, at least theoretically, to transmit signs
at the long distance with repeaters. 20dB/km: only 1% of the light
remain after 1km of trip.
1968 - the fibers of the time had a loss of 1000dB/km. The Post
Office sponsors projects to obtain glasses of smaller loss.
1970 - Corning Glass produced some meters of fiber optic with losses
of 20dB/km.
1973 - a phone link of fiber optic was installed in EEUU.
1976 - Bell Laboratories installed a phone link in Atlanta 1km and
it proved to be practically possible the fiber optic for telephony,
mixing with conventional techniques of transmission. The first link
of cable TV with fiber optic was installed in Hastings (UK). Rank
Optics in Leeds (UK) it manufactures fibers of 110mm for illumination
and decoration.
1978 - it begins in several points of the world the production of
fiber optic with smaller losses than 1,5dB/km for the most several
applications.
Advantages of the fiber optic
1. immunity to Interferences:
The light bunch transmitted by the fiber optic doesn't suffer interference
of external electromagnetic systems.
2. secrecy:
Due to the difficulties of extraction of the transmitted sign, it
is obtained secrecy in the communications.
3. Small size:
A cable of 3/8 of inch (9,18mm) with 12 equal of fiber, operating
to 140 MBPS it can carry as many voice channels as one of 3 inches
(73mm) of copper with 900 equal plans. Such minor means better use
of internal dutos.
4. Null Electric conductivity
The fiber optic doesn't need to be protected of electric discharges,
not even he/she needs to be covered with earth, could support high
potential differences.
5. lightness
The cable of pairs plans weighs 7.250Kg/km. This makes possible
larger puxamento throws for the fiber optic cable.
6. width of Band
Fiber optic were tested up to the 350 billion bits a second in a
distance of 100km. Theoretical taxes of 200-500 trillion bits a
second they are reachable.
7. low Loss
The fibers current monomodo possess losses as low as 0,2dB/km (in
1550nm).
8. immunity to Noises
Different from the metallic systems, that you/they request screening
to avoid radiation and electromagnetic reception, the optical cable
is a dielétrico and it is not affected by interferences of
radio frequency or electromagnetic. The potential for low mistake
taxes elevates the efficiency of the circuit. The fiber optic are
the only middle that can transmit through atmospheres under severe
radiation.
9. high Strip of Temperature
Fibers and cables can be manufactured to operate in temperatures
of -40 C up to 93 C. there are resistance registrations the temperature
of -73 C up to 535 C.
10. Without Risk of Fire or Centelhamento
The fiber optic offer a middle for data without circulation of electric
current. For applications in atmospheres dangerous or explosive,
they are a form of safe transmission.
What is a fiber optic
A fiber optic is a thread of dimension capillary, flexible and formed
by crystalline and homogeneous materials, enough to guide a light
bunch (visible or infrared) through any itinerary. The basic structure
of those capillary ones is formed by concentric cylinders with certain
thickness and with refraction indexes such a that allow the phenomenon
of the reflection intern total. The center (inside) of the fiber
it is called of nucleus and the area expresses is called of peel.
The basic idea is the transmission of an optical sign of a point
for other, with a minimum of distortion of the light.
A variety of fiber optic exists, each one returned to a specific
application. The types can vary in agreement with the materials,
dimensions and the processes of production of the same ones.
The basic types of fiber optic are:
" Fiber Multimodo Índice Degrau;
" Fiber Multimodo Gradual Index;
" Fiber Monomodo Índice Degrau;
Types of Fiber optic
Characteristic
- Band width in the order of 1500Mhz - km.
- Losses from 1 to 6dB/Km.
- Nuclei of 50 / 62.5 / 85 / 100 m.
- External diameter of the peel from 125 to 140 m.
- It is effective with leisure sources and LED.
- Components, test equipments and transmitters / receivers of low
cost.
- Used mainly in nets of computers.
- It transmits many manners (500) or light roads, it admits many
propagation manners.
- It possesses limitation due to the high losses and modal dispersion.
- It transmits to the 820-850 and 1300 m.
- Manufactured in lengths of up to 2,2km.
Characteristic
- Applications for great band width (350Ghz).
- Low losses: Typically 0,3dB/km even 0,5dB/Km (1300 m), and 0,2
dB/km (1550 m).
- Nucleus of 8 á 10 m.
- External diameter of the peel 125 m.
- Superior costs for connectors, amendments, test equipments and
transmitters / receiving.
- It transmits a way or light road.
- It transmits in wavelength of 1300 and 1550 m.
- Manufactured in length of up to 25km.
- Sensitive to curvatures.
As the Fiber is Manufactured
The basic materials used in the production of fiber optic are pure
sílica or doped, composed glass and plastic. The fiber optic
of pure sílica or doped are the ones that present the characteristic
best of transmission and they are them used in systems of telecommunications.
All of the production processes are complex and expensive. The fiber
optic manufactured with composed glass and plastic don't have good
transmission characteristics (they possess high reduction and low
width of band passer-by) and they are used in systems of telecommunications
of low capacity and small distances and illumination systems. The
processes of production of those fibers are simple and cheap if
compared with the fibers of pure sílica or doped.
Production of the fiber:
Once obtained her preforms, this is taken to a structure vertical
call puxamento tower and it is fastened in a feeder that introduces
her/it in an oven (usually of lead, that uses special blowpipes
or lasers of high potency) with temperature of approximately 2000
C, that you/they will make the drainage of the material forming
a capillary of glass, the fiber optic. The diameter of the fiber
depends on the feeding speed of the it preforms in the oven and
of the speed of bobinamento of the fiber, both controlled by computer.
The control of that process is made through an optical meter of
diameter (that works to laser).
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