optical fiber cable v2
Post on 31-Jul-2015
187 Views
Preview:
TRANSCRIPT
WELCOMETO SEMINAR
ON
MADE BY - PRATYUSHEC – 42 (Roll No.-35)
OPTICAL FIBER CABLE
CONTENTS Brief Introduction History Optical fiber construction Critical angle & Total Internal Reflection Types of fibers/transmission modes Acceptance angle & acceptance cone Numerical Aperture V-Number Dispersion & its types Attenuation and Losses in Fiber Fiber optic communication Fiber Vs Copper Cable Fiber VS Co-axial Cable Disadvantages Applications References
BRIEF INTRODUCTION
Optical fiber is flexible, transparent fiber made of silica or plastic slightly thicker than a human hair
It is a form of guided or wired non conducting medium
Its working is based on principle of Total Internal Reflection
It permits transmission over longer distances and at higher bandwidths than other forms of communication
HISTORY
In 1870, Tyndall introduced concept of Total Internal Reflection with a demonstration.
In the same year, Alexander Graham Bell, developed a optic voice transmission, which he named the photo phone.
HISTORY (contd.)
Later around 1954, Brien, Hopkins & Kapany achieved low loss transmission through 75 cm bundle of thousand fibers
Jun-ichi Nishizawa, was the first to propose the use of optical fibers for communications in 1963
Kao and Hockham were first to reduce attenuation in optical fibers below 20 (dB/km), making it a practical communication medium which earned Kao the Nobel Prize in Physics in 2009.
OPTICAL FIBER CONSTRUCTION
CoreGlass or plastic with a higher index
of refraction than the claddingCarries the signal
CladdingGlass or plastic with a lower index of
refraction than the core Buffer
Protects the fiber from damage and moisture
JacketHolds one or more fibers in a cable
CRITICAL ANGLE & TOTAL INTERNAL REFLECTION
Critical angle is angle of incidence in denser medium for which angle of refraction in rarer medium is 90 degrees.
Total internal reflection-If angle of incidence in denser medium is increased beyond critical angle , then ray of light is reflected back completely into denser medium.
OPTICAL FIBER TRANSMISSION MODES/ TYPES OF FIBERS
TYPES OF FIBERS (contd.) Multimode step-index fiber
the reflective walls of fiber move light pulses to receiver
Multimode graded-index fiber acts to refract light toward center of fiber
by variations in density
Single mode fiber the light is guided down center of an
extremely narrow core
TYPES OF FIBERS (contd.)
SINGLE MODE FIBER
Advantages: Minimum dispersion: all rays take same path,
same time to travel down the cable. A pulse can be reproduced at the receiver very accurately.
Less attenuation, can run over longer distance without repeaters.
Larger bandwidth and higher information rate
Disadvantages: Difficult to couple light in and out of the tiny core Highly directive light source (laser) is required Interfacing modules are more expensive
MULTIMODE FIBER
Multimode step-index Fibers: inexpensive easy to couple light into Fiber result in higher signal distortion lower TX rate
Multimode graded-index Fiber: intermediate between the other two types
of Fibers
ACCEPTANCE ANGLE
Acceptance angle is maximum angle at which a light ray enters into core and propagate through it in zigzag path
Acceptance angle
ACCEPTANCE CONE
If all possible direction of acceptance angle are considered at same time we get a cone corresponding to surface known as acceptance cone
NUMERICAL APERTURE
It defines gathering capability of fiber mathematically expressed as sine of acceptance angle
High Numerical Aperture increases dispersion hence low Numerical Aperture is desirable
V- NUMBER
No. of modes supported by optical fiber is obtained by cut-off condition known as normalized frequency or V-Number
Number of modes (N) = ½ V² V- number can be reduced either by
reducing numerical aperture or by reducing diameter of fiber
DISPERSION & ITS TYPES
Dispersion is the spreading out of a light pulse as it travels through the fiber
It is of two main types: Intermodal or Modal Dispersion Intra modal or Chromatic
Dispersion
INTERMODAL OR MODAL DISPERSION
Spreading of a pulse because different modes (paths) through the fiber take different times
Only happens in multimode fiber
Reduced, but not eliminated, with graded-index fiber
INTRA MODAL OR CHROMATIC DISPESRSION
Different wavelengths travel at different speeds through the fiber
This spreads a pulse in an effect named chromatic dispersion
Chromatic dispersion occurs in both single mode and multimode fiber
It is of two types1) Material Dispersion which is wavelength based effect caused by glass of which fiber is made2) Waveguide Dispersion occurs due to change in speed of wave propagating through waveguide
ATTENUATION
Modern fiber material is very pure, but there is still some attenuation The wavelengths used are chosen to avoid absorption bands
-850 nm, 1300 nm, and 1550 nm-Plastic fiber uses 660 nm LEDs
LOSSES IN FIBER
Absorption Losses- due to material, impurities & atomic defects in glass fiber
Geometric Effects- due to manufacturing defects like irregular diameter of core
Rayleigh Scattering- Change in local refractive index due to
local microscopic variation density It is a scattering loss
FIBER OPTIC COMMUNICATION
InputSignal
Coder orConverter
LightSource
Source-to-FiberInterface
Fiber-to-lightInterface
LightDetector
Amplifier/ShaperDecoder
Output
Fiber-optic Cable
Receiver
TX, RX, and Fiber Link
Transmitter
FIBER OPTIC COMMUNICATION (contd.)
Light source: Amount of light emitted is proportional to the drive
current Two common types:
LED (Light Emitting Diode) ILD (Injection Laser Diode)
Source–to-fiber-coupler (similar to a lens): A mechanical interface to couple the light emitted
by the source into the optical fiber Light detector: PIN (p-type-intrinsic-n-type) APD (avalanche photo diode) Both convert light energy into current.Note- For long links,repeaters are used to
compensate for signal loss
FIBER VS COPPER CABLE
Smaller size & weight Greater capacity Faster communication Transmit over Longer distances Can be used for both analog & digital
transmission Broader Bandwidth – more data per
second
FIBER VS COPPER CABLE (CONTD.)
Immunity to Electromagnetic Interference Low attenuation/transmission loss over
long distances Electrical Insulator Lack of costly metal conductor Dielectric waveguide Signal Security
FIBER VS CO-AXIAL CABLE
More information carrying capacity with higher data rates and fidelity
Greater transmission speed Smaller in size and light in weight Easier to handle and install Immune towards environmental hazards &
electromagnetic interference Higher Bandwidth Economical Low signal loss
DISADVANTAGES Cumulative losses due to large size of
fiber couplers Hazardous emissions like glass shards &
optical radiation Requires technicians with special expertise
for installation & maintenance
APPLICATIONS
Used in Cable T.V. , HDTV, LANs & CCTV systems
Used in Optic Fiber Communication for transmission of analog & digital data
Used in Imaging Optics & Spectroscopy Used in illumination applications Used in various military applications Fiber optic sensors & couplers
REFERENCES
Govind P. Agrawal, “Fiber Optic Communication Systems”, John Wiley, 3rd Edition,2004.
R J Hoss and EA Lacy, Fiber optics 2nd edition (Prentice Hall, New Jersey, 1993)
John M. Senior, “Optical Fiber Communications”, PEARSON, 3rd Edition, 2010.
Gerd Keiser, “Optical Fiber Communications”, TMH, 4th Edition, 2008.
Joseph C. Plais, “Fiber Optic Communication”, Pearson Education, 4th Ed, 2004.
THANK YOU
top related