2. Brief flow of
presentation
1. What are Optical Fibers?
2. Introduction
3. Evolution of optical fiber
4. Structure of optical fiber
5. Workings principle of optical fiber
6. Classification of optical fiber
7. Optical fiber communication system
8. Advantages / Disadvantages of Optical fiber
9. Applications of Optical fiber
10. Conclusion
3. what is optical
fiBer? An optical fiber is a hair thin cylindrical fiber of glass or any
transparent dielectric medium.
The fiber which are used for optical communication are wave
guides made of transparent dielectrics.
Its function is to guide visible and infrared light over long
distances.
4. worKinG principle
Total Internal Reflection
When a ray of light travels from a denser to a rarer
medium such that the angle of incidence is greater
than the critical angle, the ray reflects back into
the same medium this phenomena is called total
internal reflection.
In the optical fiber the rays undergo repeated
total number of reflections until it emerges out of
the other end of the fiber, even if the fiber is bent.
5.
6. History
1880 Alexander Graham Bell
- Photo phone, transmit sound waves over beam of light
1930: TV image through uncoated fiber cables
1951: Flexible fiberscope: Medical applications
(endoscope).
camera
LIGHT
7. History Cont’d
1960: Laser invented
1967: New Communications medium: cladded fiber
1960s: Extremely lossy fiber:
More than 1000 dB /km
1970: Corning Glass Work NY, Fiber with loss of less
than 2 dB/km
70s & 80s : High quality sources and detectors
Late 80s : Loss as low as 0.16 dB/km
1990: Deployment of SONET systems
8. Optical Fiber: Advantages
Capacity: much wider bandwidth (10 GHz)
Long lyf of fibres compared to copper.
Unaffected by interference of
Lightening
Magnetic fields
Florescent light
Higher environment immunity
Weather, temperature, etc.
10. Optical Fiber: Advantages
• Attenuation is lower than coaxial cable or
twisted pair
• As it does not radiates energy any antenna or
detector cannot detects it hence provides signal
security
• There is no necessity of additional equipment
for protecting against grounding and voltage
problems.
12. Disadvantages
Higher initial cost in installation
Only point to point communication
Strength
Lower tensile strength
Remote electric power
More expensive to repair/maintain
Tools: Specialized and sophisticated
Staff : skilled and specialized
14. Optical Fiber Architecture –
Components
Light source
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
Input
Signal
Coder or
Converter
Light
Source
Source-to-Fiber
Interface
Fiber-to-light
Interface
Light
Detector
Amplifier/Shaper
Decoder
Output
Fiber-optic Cable
Receiver
Light detector:
PIN (p-type-intrinsic-n-type)
APD (avalanche photo diode)
Both convert light energy into
current
15. ILD versus LeD
Advantages:
more focused radiation pattern; smaller Fiber
much higher radiant power; longer span
faster ON, OFF time; higher bit rates possible
monochromatic light; reduces dispersion
Disadvantages:
much more expensive
higher temperature; shorter lifespan
16. OptIcaL FIber
cOnstructIOn
Core – thin glass center of the
fiber where light travels.
Cladding – outer optical material
surrounding the core(lower
R.index)
Buffer Coating – plastic coating
that protects the fiber.
17. FIber types
Plastic core and cladding
Glass core with plastic cladding PCS (Plastic-Clad
Silicon)
Glass core and glass cladding SCS: Silica-clad silica
Under research: non silicate: Zinc-chloride
1000 time as efficient as glass
18. Classification of optical fiber
• Optical fiber is classified into two
categories based on :-
1)The number of modes
A.SINGLE MODE
B.MULTIMODE
2) The refractive index
A.STEP INDEX
B.GRADED INDEX
19. types OF OptIcaL
FIber
Single-mode Fiber
step-index Fiber
graded-index Fiber
n1 core
n2 cladding
no air
n2 cladding
n1 core
Variable
n
no air
Light
ray
Index profile
20. 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
21. muLtI
mODe
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
22. Losses In optIcaL FIber
cabLes
The predominant losses in optic Fibers are:
absorption losses due to impurities in the Fiber
material
material or Rayleigh scattering losses due to
microscopic irregularities in the Fiber
chromatic or wavelength dispersion because of
the use of a non-monochromatic source
radiation losses caused by bends and kinks in the
Fiber
pulse spreading or modal dispersion due to rays
taking different paths down the Fiber (µs/km)
coupling losses caused by misalignment &
imperfect surface finishes
Single-mode fibers – in single mode fiber only one mode can propagate through the fiber. This type of fiber has small core diameter(5um) and high cladding diameter(70um) and the difference between the refractive index of core and cladding is very small. There is no dispersion i.e. no degradation of signal during travelling through the fiber.
The light is passed through the single mode fiber through laser diode.
Multi-mode fiber :-
Multi mode fiber allows a large number of modes for the light ray travelling through it.
The core diameter is (40um) and that of cladding is(70um)
The relative refractive index difference is also larger than single mode fiber.
There is signal degradation due to multimode dispersion.
They are not suitable for long distance communication due to large dispersion and attenuation of the signal.