Fiber Optics strictly based on AKTU syllabus

1. Engineering Physics I Unit IV
Presentation By
Dr.A.K.Mishra
Professor
Jahangirabad Institute of Technology, Barabanki
Email: akmishra.phy@gmail.com
Arun.Kumar@jit.edu.in
6/24/2017
Dr A K Mishra, Academic Coordinator,
JIT Jahangirabad
1

2. Optical - Fiber
• At the end of this module successful students
will be able to:
• Understanding of dispersion and losses in optical.
• Understanding of optical sources including LED
and laser
• Understanding of optical receiver and
photodiodes.
• Understand digital transmission in optical fiber
systems.
6/24/2017
Dr A K Mishra, Academic Coordinator,
JIT Jahangirabad
2

3. Optical Fiber
• Fiber optics (optical fibers) are long, thin strands of very
pure glass about the size of a human hair. They are arranged
in bundles called optical cables and used to transmit signals
over long distances.
Fiber Optic Data Transmission Systems
6/24/2017
Dr A K Mishra, Academic Coordinator,
JIT Jahangirabad
3

4. Total internal Reflection and Critical Angle
1 ≤ c 1 = c 1 > c
n1 Denser n2 Rarer
• When light travel from denser medium to rarer it strike the
boundary at more than critical angle then it will reflect back
to the incident medium without penetrating second medium
is called total internal reflection.
6/24/2017
Dr A K Mishra, Academic Coordinator,
JIT Jahangirabad
4

5. Fiber Optics
• Dielectric waveguide of cylindrical geometry
with core and cladding of suitable material.
Refractive index of core > refractive index of
cladding
Main Motivation:
• To meet demand of increase in the
telecommunication data transmission.
6/24/2017
Dr A K Mishra, Academic Coordinator,
JIT Jahangirabad
5

6. Main Advantage
OPTICAL FIBER COMMUNICATION SYSTEM
• Higher bandwidth (extremely high data transfer
rate).
• Less signal degradation.
• Less costly per meter.
• Lighter and thinner then copper wire.
• Lower transmitter launching power.
• Less susceptible to electromagnetic interference.
• Flexible use in mechanical and medical imaging
systems
6/24/2017
Dr A K Mishra, Academic Coordinator,
JIT Jahangirabad
6

7. Main Applications
• Telecommunications.
• Sensors.
• Fiber Lasers.
• Bio-medical.
• Automotive and many other industries
6/24/2017
Dr A K Mishra, Academic Coordinator,
JIT Jahangirabad
7

8. Propagation of signals in optical Fiber
• If φi > φc is possible and light remains in the fiber but from
Snell’s law.
6/24/2017
Dr A K Mishra, Academic Coordinator,
JIT Jahangirabad
8
r
0
1
n
r
ci
0
1i
Sin
n
(1)eqfromBut
......(2)....................Cos
)-(90
180)90(
ABCfromThen
=whenoccursofuelowest valnow
)1...(....................
n
n







n
Sin
Sin
SinSin
Sin
Sin
i
r
r
r







9. 6/24/2017
Dr A K Mishra, Academic Coordinator,
JIT Jahangirabad
9
)4.........(..........
-
-1
Sin-1
n
90
Sin
Since
n
Sin
)3.....(..........Cos
n
,
(2)equation
n
nn
n
n
2
1
2
2
2
1
c
2
1
2
2
c
c
22
1
2c
1
2
c
c
0
1
m ax
m axic













Cos
Cos
Cos
nSinn
But
n
Sin
when
From
c

10. • Maximum external incident angle for which the light will
propagate in the fiber is known as the acceptance angle is
denoted by m.
• Maximum angle for that the light ray can have relate to axis of
fiber and propagate down the fiber.
• The light ray contained within the cone having a full angle
2m are accepted and transmitted along fiber. Is known as
acceptance cone
6/24/2017
Dr A K Mishra, Academic Coordinator,
JIT Jahangirabad
10
)5......(..........
-
Sin
-n
Sin
Cos
n
Sin
(3)in(4)fromvaluethe
0
2
2
2
1
m ax
1
2
2
2
1
0
1
m ax
c
0
1
m ax
nn
nn
n
nn
n
Putting







11. Numerical Aperture
• “ N.A is defined as the sine of Acceptance Angle”.
OR
• Light gathering capacity of fiber is known as Numerical Aperture. And is
expressed as
6/24/2017
Dr A K Mishra, Academic Coordinator,
JIT Jahangirabad
11
2n
small)verytodueneglectedis(-2n)-(1-1n
)
n
(-1n
(1)equationthen-1
n
n
n
n
-1
nnbecausevealwaysisIt
core)thetocladding&core
ofindexrefractivetheofdifferencetheof(Ratio
n
n-n
asdefinedisIndexRefractiveFractional
)1(....................-Sin
1
22
1
2
1
2
1
2
1
1
2
1
2
21
1
21
2
2
2
1m nn








NA
NA
n
NA
NA 

12. Classification of Optical Fiber
• Glass Fiber: It consist core and cladding of glass
refractive index of core> cladding
• To achieve Germanium, Boron, Phosphorus &
Fluorine impurity are added in glass for desired
refractive index.
• Plastic Clad Silica P.C.S Fiber: By replacing
cladding with plastic lower refractive index core.
Limitation:
• losses are more than glass fiber
• Refractive index varied with temperature.
• Fiber life is small, mainly in humid environment.
6/24/2017
Dr A K Mishra, Academic Coordinator,
JIT Jahangirabad
12

13. Classification of Optical Fiber
Plastic Fiber:
• Both core and cladding of plastic material. These fibers
are cheaper and have high losses and low bandwidth.
Refractive index varied with temperature. They are
used for short distance. e.g. computer application.
Classification depending on Modes:
Monomodes (Single Mode Fiber): only one ray can
enter the core and guided by TIR (we make the core of
order 2 μm to 8 μm for minimum dispersion Law and
hence highest transmission bandwidth only high
quality laser focused beam ……. )
6/24/2017
Dr A K Mishra, Academic Coordinator,
JIT Jahangirabad
13

14. Classification of Optical Fiber
• Certain difficulties to handle them.
• Splicing – union of Rope, (joint together the ends of
row by interweaving the stands)
• Coupling- connecting the parts of machine.
• Bending-
• Such fibers are used for long distance application.
• Multimode fiber: capable of transmitting more than
one mode.
• Core diameter of the order of 50 μm
• Accommodate many different rays of light each ray
enter the core at different angle dispersion loses are
more and band width length of the order of 1Ghz.- km
6/24/2017
Dr A K Mishra, Academic Coordinator,
JIT Jahangirabad
14

15. Classification of Optical Fiber
Certain benefits as compare to monomodes
• In coherent optical source can be used due to
large core diameter and large acceptance
angle.
• Easy or splicing or joining.
• Lower tolerance requirements on fiber
connectors.
6/24/2017
Dr A K Mishra, Academic Coordinator,
JIT Jahangirabad
15

16. Classification on index profile
• Multimode step index Fiber (MMSI)-
• Poorest of three type
• If refractive index is plotted against the radial distance from the core,
abruptly changed at the core cladding surface creating a step known as
step index.
6/24/2017
Dr A K Mishra, Academic Coordinator,
JIT Jahangirabad
16
021 nn n

17. Multimode Graded Index Fiber: (GRIN)
6/24/2017
Dr A K Mishra, Academic Coordinator,
JIT Jahangirabad
17

18. GRADED-INDEX FIBERS
• These are called graded-index fibers.
• The refractive index of these fibers changes
gradually from the core to cladding and at the
boundary between the core and cladding the
change is abrupt.
• The refractive index decreases gradually from the
center of the core to the edge of the cladding.
• Graded-index multi mode fibers collect light
better than small core single mode fibers and
have broader bandwidth than step-index multi
mode fibers.
6/24/2017
Dr A K Mishra, Academic Coordinator,
JIT Jahangirabad
18

19. GRADED-INDEX FIBERS
6/24/2017
Dr A K Mishra, Academic Coordinator,
JIT Jahangirabad
19

20. Single mode step index Fiber (SMSI)
• In this, the light propagates in a single or fundamental mode in the
core. Such fibers with only one mode are called single-mode fiber. It
allows a single light path, and typically used with LASER signaling.
The single mode fibers can allow greater bandwidth and cable runs
than that of multimode but it is more expansive. The single mode
fiber has the best characteristics of highest data rates and least
attenuation. The single mode fiber is of very small size. It has the
core of approximately 5 to 10 micro meter in diameters.
• Only one ray can enter the core and guided by T.I.R.
• Single mode transmission quality superior than other due to
absence of model dispersion.
• Exhibit greatest transmission band width.
• Lowest losses than other.
6/24/2017
Dr A K Mishra, Academic Coordinator,
JIT Jahangirabad
20

21. Classification depending on requirement
and uses
• Active Fiber: is one that emits light as well as
guides parts of it.
6/24/2017
Dr A K Mishra, Academic Coordinator,
JIT Jahangirabad
21

22. Classification depending on requirement and
uses
• Passive fiber: is one that guide light incident
on it from external source.
• Luminescent Fiber: is one emits luminescent
radiations. When excited by X- ray, ultraviolet
or any high energy particle.
6/24/2017
Dr A K Mishra, Academic Coordinator,
JIT Jahangirabad
22

23. Classification depending on requirement and uses
• Lasing Fiber: is one Laser takes place small
diameter capable of providing higher pumping
efficiency and better mode selection.
6/24/2017
Dr A K Mishra, Academic Coordinator,
JIT Jahangirabad
23

24. Classification depending on requirement and
uses
• Multiple Fiber: consist smaller diameter have
made possible availability of very small. Fibers
are capable of providing high resolution.
6/24/2017
Dr A K Mishra, Academic Coordinator,
JIT Jahangirabad
24

25. Classification depending on requirement and uses
• Conical Fiber: used for light condensing and
aligned assemblies for magnification and
demagnification purpose.
6/24/2017
Dr A K Mishra, Academic Coordinator,
JIT Jahangirabad
25

26. Normalized frequency and cut off wavelength of
a fiber
• The term normalized frequency or cut off parameter or V number is
characteristics
6/24/2017
Dr A K Mishra, Academic Coordinator,
JIT Jahangirabad
26
guide.wavethealongpropagatedmodesof
numberthedeterminesandpropagatedbeinglightof
gthon wavelenonlydependsfrequencyNormalized2n.
a2
small)verytodueneglectedis(2nAN
-2n)-(1-1nAN
)-1()-(AN
claddingofindexRefractiven
coreofindexRefractiven
lengthwave
rediuscorea
where)-(
2
1
2
1
2
1
2
1
2
1
2
1
2
22
1
2
2
2
1
2
1
2
2
2
1
n
nnn
nn
























n

27. Attenuation in Optical FIBER
Absorption:
• Intrinsic absorption
• Absorption due to impurities.
• Property of glass itself due to diff. mechanism
absorption losses
• Ultraviolet absorption due to electronic &
molecular transition band and it occurs due to
pure fused silica, valance electrons can be ionized
into conduction. By light and energy for
ionization.
6/24/2017
Dr A K Mishra, Academic Coordinator,
JIT Jahangirabad
27

28. Attenuation in Optical FIBER
• Infrared absorption due to variation of
chemical bond it takes place due to photon of
light energy are absorbed by atoms within the
glass molecules.
• Absorption due to impurities: metal ions and
OH- ions are main sources of absorption losses
presence of Iron, copper, chromium, cobalt,
nickel, magnize create losses. These impurities
must not exceed one part / billion to obtain
low losses.
6/24/2017
Dr A K Mishra, Academic Coordinator,
JIT Jahangirabad
28

29. Extrinsic Attenuation
Micro bending:
6/24/2017
Dr A K Mishra, Academic Coordinator,
JIT Jahangirabad
29

30. Macro bending:
6/24/2017
Dr A K Mishra, Academic Coordinator,
JIT Jahangirabad
30

31. 6/24/2017
Dr A K Mishra, Academic Coordinator,
JIT Jahangirabad
31
db/kminnattenuatioFiber
fiber.intocoupledpowerofAmountP
input.thefromLdistanceatPowerP
10PP
times1000inpowerinreduction30db
times100inpowerinreduction20db
times10inpowerinreductionmeans10db
wheredbinasexpressedisIt
fiberinpoweropticaloflossmeansnAttenuatio
db)
P
(log10nAttenuatio
in
o
10
L-
inO
O







where
Pin
Decibel is the unit of attenuation

32. Attenuation Loss
6/24/2017
Dr A K Mishra, Academic Coordinator,
JIT Jahangirabad
32
Po
Pin
log
L
10
log
L
10
-
10
L
-log
10loglog
10
01PinPo
10
L-
10
L-
10
L-












Pin
Po
Pin
Po
Pin
Po
Pin
Po
Since