17-04-2012, 01:52 PM
industrial uses of optical fiber
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fiber optic (or "optical fiber")
refers to the medium and the
technology associated with the
transmission of information as light
impulses along a glass or plastic wire
or fiber. Fiber optic wire carries much
more information than conventional
copper wire and is far less subject to
electromagnetic interference. This
technology is based on the concept of
light reflection. In the case of fiber
optics technology, light carrying digital
signals is reflected inside the optical cable to transfer information. Total internal reflection is the
principle behind the success of this technology.
Fiber optic technology experienced a phenomenal rate of progress in the second half of the
twentieth century. Early success came during the 1950's with the development of the
fiberscope. This image-transmitting device, which used the first practical all-glass fiber, was
concurrently devised by Brian O'Brien at the American Optical Company and Narinder Kapany
(who first coined the term 'fiber optics' in 1956) and colleagues at the Imperial College of
Science and Technology in London. Early all-glass fibers experienced excessive optical loss,
the loss of the light signal as it traveled the fiber, limiting transmission distances.
This concept is explained by Snell's Law which states that the angle at which light is reflected is
dependent on the refractive indices of the two materials, the core and the cladding. The lower
refractive index of the cladding (with respect to the core) causes the light to be angled back into
the core as illustrated in Figure 1.
The early work on fiber optic light source and detector was slow and often had to borrow
technology developed for other reasons. For
example, the first fiber optic light sources
were derived from visible indicator LEDs. As
demand grew, light sources were developed
for fiber optics that offered higher switching
speed, more appropriate wavelengths, and
higher output power.
Multimode Fiber
Multimode fiber is best designed for short transmission distances, and is suited for use in LAN
systems and video surveillance.
Multimode fiber, the first to be manufactured and commercialized, simply refers to the fact that
numerous modes or light rays are carried simultaneously through the waveguide. This fiber type
has a much larger core diameter, compared to single-mode fiber, allowing for the larger number
of modes, and multimode fiber is easier to couple than single-mode optical fiber. Multimode fiber
may be categorized as step-index, in which the principle of total internal reflection applies to
multimode step-index fiber or graded-index fiber which refers to the fact that the refractive index
of the core gradually decreases farther from the center of the core.
Single-mode Fiber
Single-mode fiber is best designed for longer transmission distances, making it suitable for longdistance
telephony and multichannel television broadcast systems. Single-mode fiber allows for
a higher capacity to transmit information because it can retain the fidelity of each light pulse
over longer distances, and it exhibits no dispersion caused by multiple modes. Single-mode
fiber also enjoys lower fiber attenuation than multimode fiber. Thus, more information can be
transmitted per unit of time.
Designing Fiber Optic Systems
The first step in any fiber optic system design requires making careful decisions based on
operating parameters that apply for each component of a fiber optic transmission system. The
main questions, given in the table below, involve data rates and bit error rates in digital systems,
bandwidth, linearity, and signal-to-noise ratios in analog systems, and in all systems,
transmission distances.
Parts of A Fiber Optic Link
Fiber optic transmission uses the same basic elements as copper-based transmission systems:
A transmitter, a receiver, and a medium by which the signal is passed from one to the other, in
this case, optical fiber. Figure 5 illustrates these elements. The transmitter uses an electrical
interface to encode the use information through AM, FM or digital modulation. A laser diode or
an LED do the encoding to allow an optical output of 850 nm,1310 nm, or 1550 nm (typically).
Fiber Optic Connectors
Fiber optic connectors have traditionally been the biggest concern in using fiber optic systems.
While connectors were once unwieldy and difficult to use, connector manufacturers have
standardized and simplified connectors greatly. This increasing user-friendliness has
contributed to the increase in the use of fiber optic systems; it has also taken the emphasis off
the proper care and handling of optical connectors. Figure 7 illustrates the different parts of the
Fiber Optic Connector.
Care and Handling of Fiber Optic Connectors
A number of events can damage fiber optic connectors. Unprotected connector ends can
experience damage by impact, airborne dust particles, or excess humidity or moisture. The
increased optical output powers of modern lasers also have the potential to damage a
connector, an often overlooked factor in discussions about handling and caring for optical fibers
and connectors. Most designers tend to think of the power levels in optical fibers as relatively
insignificant. However, a few milliwatts at 850 nm will do permanent damage to a retina.
Applications and advantages of Optical Fiber
The technology and applications of optical fibers have progressed very rapidly in recent years.
Optical fiber, being a physical medium, is subjected to perturbation of one kind or the other at all
times. There are enormous advantages of fiber optics; in the real sense fiber optics is the
backbone of the future applications.
Benefits
Performance
· Unmatched stable optical performance
· Extreme temperature, shock, and vibration performance
· Crush and tensile load resistance assemblies