HISTORY,
DEVELOPMENT, FIBER OPTIC STRUCTURE
HISTORY OF
OPTICAL FIBER
The
use of light as a carrier of information has actually been widely used since
time immemorial, but just around the 1930s German scientists initiated the
experiment to transmit light through a material called fiber optics. This
experiment is also still quite primitive because the results achieved can not
be directly utilized, but must go through further development and refinement. A
further development was when British scientists in 1958 proposed a prototype of
fiber optics that is now used, consisting of glass core wrapped by another
glass. Around the beginning of the 1960s, fantastic changes took place in Asia,
when Japanese scientists managed to create a type of fiber optic that is able
to transmit images.
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| Fiber Optic Picture |
On
the other hand, scientists in addition to trying to guide light through glass
(optical fiber) also try to "tame" the light. The hard work was
successful when about 1959 laser was invented. The laser operates at a visible
frequency area of about 15 Hertz - 1014 Hertz or hundreds of thousands of times
the microwave frequency.
At
first, laser-generating equipment is still large and troublesome.Besides being
inefficient, it can only function at very low temperatures. The laser also has
not radiated straight. In very bright light conditions too, the jets easily
twist to follow the density of the atmosphere. At that time, a laser beam
within a distance of 1 km, can arrive at the final destination at many points
with a distance deviation up to a meter count.
Around
the 1960s, fiber optics were found to be very high purity, less than one part
in a million. In ordinary language it means that the very clear and not
electrically conductive fibers are so pure, so it is said that if the seawater
were as pure as optical fiber, with sufficient lighting we could watch the
inhabitants of the Pacific Ocean basin.
Like
lasers, fiber optics must go through the early stages of development. As the
light transmission medium, it is very inefficient. Until 1968 or two years
after the first optical fiber was forecast to be a light guide, the rate of
attenuation (loss) was still 20 dB / km. Through development in materials
technology, fiber optics undergoes purification, dehydran (drying), and others.
Slowly but surely the attenuation reaches a level below 1 dB / km. In the
1980s, the fiber optic industry race flag was really flying. The big names in
the world of fiber optic development are emerging. Charles K. Kao recognized
the world as one of the foremost pioneers. From Japan, appeared Yasuharu
Suematsu . Electronic giants like ITT and STL obviously have many roles in
deepening optical fiber research.
OPTICAL FIBER
DEVELOPMENT
Based
on its use, the fiber optic communication system (SKSO) is divided into 6
stages of generation, as described below.
1. First
Generation (starting 1975)
The
system is still simple and the basis for the next generation system, consisting
of an encoding tool that converts inputs (eg sound) into electrical signals,
transmitters that convert electrical signals into wavelength signals of LEDs
with wavelengths of 0.87 mm, silica fibers as conductor of wave signals , a
repeater as a weakened wave amplifier on the way, a receiver that converts a
wave signal into an electrical signal in the form of a photodetector, and a
decoding device that converts electrical signals into output (eg sound).
The
repeater works through several stages, at first it converts the already
weakened wave signal into an electrical signal, then amplified and converted
back into a wave signal. This first generation in 1978 reached a transmission
capacity of 10 Gb.km / s.
2. Second
Generation (starting 1981)
To
reduce the dispersion effect, the fiber core size is reduced to a single mode
type. The refractive index of the skin is made as close to the refractive index
of the terrace. By itself, the transmitter is also replaced by a laser diode
and the wavelength it emits is 1.3 mm. with this modification, the second
generation is able to achieve 100 Gb.km / s transmission capacity, 10 times
larger than the first generation.
3. Third
Generation (starting 1982)
There
has been a refinement of the manufacture of silica fibers and the manufacture
of 1.55 mm wavelength laser diode chip. the purity of the silica material is
increased so that transparency can be made for wavelengths of about 1.2 mm to
1.6 mm. This enhancement increases the transmission capacity to several hundred
Gb.km / s.
4. Fourth
Generation (starting 1984)
The
commencement of research and development of coherent system, the modulation
used is not the modulation of intensity, but the frequency modulation, so that
the already weak signal intensity can still be detected and the distance
traveled, as well as the transmission capacity is enlarged. In 1984, its
capacity was able to match the capacity of the direct detection system.
Unfortunately, this generation is hampered its development because the source
device technology and frequency modulation detection is still far behind.
However, it is undeniable that this coherent system has the potential to thrive
in the future.
5.Fifth
Generation (starting 1989)
In
this generation, developed an optical amplifier that replaces therepeater
function in previous generations. An optical amplifier consists of an InGaAsP
laser diode (wavelength 1.48 mm) and a number of optical fibers with erbium
doping (Er) on its terrace. When the fiber is irradiated with its laser diode,
the erbium atoms inside it will excite and create a population inversion, so
that when there is a weak signal entering the amplifier and passing through the
fiber, the atoms will simultaneously conduct a deoditation called stimulated
emission , Einstein. As a result, the already weakened signal will be reinforced
by this emission and forwarded out of the amplifier. The advantage of this
optical amplifier to the repeater is the absence of interference with the
traveling wave signal, the wave signal does not need to be converted into
electricity first and so on, as happens in therepeater . With this optical
amplifier, the transmission capacity is soaring. At the beginning of its
development only reached 400 Gb.km / s, but a year later, the transmission
capacity has penetrated the price of 50 thousand Gb.km / s.
6. Sixth
Generation (starting 1988)
In
1988, Linn F. Mollenauer pioneered the soliton communication system. Soliton is
a wave pulse consisting of many components of wavelength. The components have
different wavelengths only slightly and also vary in intensity. The length of
the soliton is only 10-12 seconds and can be divided into several adjacent
components, so that the soliton signals are information consisting of several
wavelength divisions ( wavelength division multiplexing ). Experiments show
that minimal solitons can carry five channels each carrying information at a
rate of 5 Gb.km / s. Channel blocks can be doubled if multiplexed polarization
is created because each channel has two different polarizations. The tested
transmission capacity reaches 35 thousand Gb.km / s.
The
working of this soliton system is the Kerr effect, ie, rays of the same
wavelength will propagate at different rates within a material if the intensity
exceeds a boundary price. This effect is then used to neutralize the dispersion
effect, so the soliton will not widen in time until it reaches thereceiver .
This is very advantageous because the level of error caused very small can even
be ignored. It appears that combining the features of several generations of
fiber optic technology will be able to produce an almost ideal communication
system, which has a maximum transmission capacity with the smallest error rate.
What is clear, in the future the world of communication, can not be avoided
anymore, will be dominated by fiber optic technology.
FIBER OPTICAL
BASIC THEORY
Optical
fiber is a light waveguide that contains a dielectric material with a specific
refractive index that can be used to propagate light energy.
An
optical fiber communication system has an important device, namely transmitter
, fiber optic cable, and receiver .
a.
Transmitter sends information in the form of electrical pulses of copper wires,
then translated into corresponding light pulses. To generate the light pulse,
LED or LD can be used. LEDs are generally used formultimode fiber optics and
LDs are commonly used for singlemode fiber optics.
b.
Fiber optic cable serves to propagate the optical signal from thetransmitter to
the receiver .
c.
The receiver receives an optical signal, then confirms it back to its original
electrical signal. The type of light detector that can be used is
aphotodetector .
Because
optical fiber transmission media always has a small attenuation, then at
certain times where transmitted information waves are already weakening close
to their thresholds, a reinforcement device is required to produce the same
reinforcement as the terminal output, the device is called a repeater . In a
repeater , there are amplifiers as amplifiers. At the moment there are two types
of repeaters used, namely as follows.
a.
Digital Repeater , which is an
electric level reinforcement. The way of reinforcement is by converting the
light waves to electrically then amplified and at the final stage converted
back from electric waves into light waves and then ready to be retransmitted to
optical fiber.
b.
Optical Repeater , ie reinforcement
at electrical level. The way of reinforcement is by mixing the weak waves of
light with new waves of light that are stronger than the light pump. After the
light waves are strong enough as the terminal output, the light waves are ready
to be fed back to the optical fiber.
The
repeater only amplifies the incoming light signal, so the noisethat comes is
also strongest. Therefore, for a considerable distance, such as SKKL (Marine
Cable Communications System), an optical regenerator is required to overcome
signal attenuation.
FIBER OPTICAL
BASIC STRUCTURES
Optical
fiber is a filament made of glass, a diameter the size of a human hair, which
is a light waveguide consisting of cores and claddingcapable of transmitting
information in the form of light, where the core diameter must be larger
compared to cladding diameter (core layer). This is so that if light is
reflected into the cladding, it can return to the core (not propagating to
cladding ).
In general, the
optical fiber parts are as follows.
a. Core (core)
The
transmitted light waves propagate and have a refractive index larger than the
second layer, and are made of glass. The core ( core ) has a diameter that
varies between 5 μm - 50 μm depending on the type of fiber optics.
Core
serves to determine the light propagates from an optical fiber tip to the other
end.
b. Cladding
(core layer)
This
section surrounds the core and has a smaller refractive index than the core,
and is made of glass. Cladding has a diameter that varies between 125μm (for
singlemode and multimode step index ) and 250 μm (formultimode grade index ).
The
cladding function is as follows.
1)
Reduce the light loss from the core to the surrounding air.
2)
Reduces scattering loss on core surfaces.
3)
Protects the fibers from surface absorption contamination.
4)
Adding mechanical strength.
c. Coating
(jacket)
This
section is a protective coating core and blanket made of elastic plastic
material (PVC). There are 3 types of coatings , namely: primary, secondary, and
protective wrap (PVC sheath ).