GLOBAL COLLEGE OF ENGINEERING &TECHNOLOGY: YSR DIST.
Unit -VII Fiber Optics Engineering Physics
Introduction
Fiber optics deals with the light
optics plays an important role in the field propagation through thin glass fibers. Fiber
of communication to transmit voice, television
and digital data signals fro one place to another. The
transmission of light along the thin
cylindrical glass fiber by total internal reflection was first
in 1870 and the application of this phenomenon in the field demonstrated by John Tyndal
of
only from 1927. Today the applications of fiber optics are alsocommunication is tried
field in the form of endoscopes and to instrumentation extended to medical
sensors. engineering in the form of optical
1. The Basic principie of opticai fiber
Or
principle of total internal reflection
Principle:
The basic principle of optical fiber in the transmission of optical signal is
reflection. total internal
Total interna! reflection:
When the light ray travels from denser medium to rarer medium the refracted ray
bends away from the normal. When the angle of incidence is greater than the critical
angle, the refracted ray again reflects into the same medium. This phenomenon is
called total internal reflection.
The refracted ray bends towards the normal as the ray travels from rarer medium
to denser medium. The refracted ray bends away from the normal as it travels from
denser medium to rarer medium.
Normal
Normal
i= 9.|
Denser medium
Denser medium
r=90°
Rarer medium
Rarer medium
Let, a ight ray traveling from denser medium (refracive index n,) to rarer medium
(refractive index n,) with an angle of incidence i, then the angie of refraction r can be
obtained by Snell's law.
n, Sin i=n, Sin r
When the angle of incidence is increased angle of reflection also increases and for a
particular angle of incidence(i= )the refracted ray
travels along the interface of two mediums. This Normal
angle of incidence is known as critical angle (O.).
n, Sin Oc =n, Sin 90 Denser mediun
n, Sin o =n, ’ Sin Oç=
Rarer medium
O = Sin
P.Sreenivasula Reddy MSc. (PHD) Website: www.engineeringphysics.weebly.com Page I
, GLOBAL COLLEGE OF ENGINEERING &TECHNOLOGY: YSR DIST.
Unit -VII Fiber Optics Engineering Physics
When the angle of incidence is greater than the critical angle(i >9), the refracted
total internal
ray again reflects into the same medium. This phenomenon is called
reflection
> When (i<), then the ray refracts into the secondary medium
> When (i=9.), then the ray travels along the interface
When (i> 0), then the ray totally reflects back into the same medium
2. Construction of optical fiber:
The opticai fiber mainiy consists the following six parts as shown in figure
Coré
Silicon Buffer Strength Outer
Cladding Jacket
Coating Jacket Menber
Core:
diameter is
Atypical glass fiber consists of a central core material. Generally Gore
refractive is always
50 um. The core is surrounded by cladding. The core medium
greater than the cladding refractive index.
Cladding
index. The over all
Cladding refractive index is lesser than the cores refractive
diameter of cladding is 125 um to 200 um.
Silicon Coating
It improves the
Silicon coating is provided between buffer jacket and cladding.
quality of transmission of light.
Buffer.Jacket
is made of plastic and
Silicon coating is surrounded by buffer jacket. Buffer jacket
protects the fiber cable from moisture.
Strength Member
strength to the fiber
Buffer jacket is surrounded by strength member. It provides
cable.
Outer Jacket
jacket. Because of this
Finally the fiber cable is covered by polyurethane outer
stretching
arrangement fiber cable will not be damaged during pulling, bending,
and rolling through the fiber cabie is made up of glasses.
www.engineeringphysics.weebly.com Page 2
P.SreenivasulaReddy MSc (PhD) Website:
, GLOBAL COLLEGE OF ENGINEERING &TECHNOLOGY: YSR DIST.
Unit-VII Fiber Optics Engineering Physics
3. Classification of fibers:
Based on the refractive index of core medium, optical fibers are classified into two
categories.
i Step index fiber
Graded index fiber
Based on the number of modes of transmission, optical fibers are classified into two
categories
i. Single mode fiber
ii. Multi mode fiber
Based on the material used, optical fibers are may broadly classified into four categories
Allglass fibers
All plastic fibers
Glass core with plastic cladding fibers
ÎV. Polymer clad silica fibers.
Step index fiber:
In step index fibers the refractive index of the core medium is uniform and
undergoes an abrupt change at the interface of core and cladding as shown in figure.
The diameter of core is about 10micrometers in case of single mode fiber and 50 to 200
mícrometers in multi mode fiber.
Core
ni
n2
Cladding
Step index single mode Step index multi mode
Attenuation is more for step index multi mode fibers but less in step index single mode
fibers
Numerical aperture is more for step index multi mode fibers but it is less in step index
single mode fibers
P.SreenivasulaReddy MSc (PHO) Website: www.engineeringphysics.weebly.com Page 3
Unit -VII Fiber Optics Engineering Physics
Introduction
Fiber optics deals with the light
optics plays an important role in the field propagation through thin glass fibers. Fiber
of communication to transmit voice, television
and digital data signals fro one place to another. The
transmission of light along the thin
cylindrical glass fiber by total internal reflection was first
in 1870 and the application of this phenomenon in the field demonstrated by John Tyndal
of
only from 1927. Today the applications of fiber optics are alsocommunication is tried
field in the form of endoscopes and to instrumentation extended to medical
sensors. engineering in the form of optical
1. The Basic principie of opticai fiber
Or
principle of total internal reflection
Principle:
The basic principle of optical fiber in the transmission of optical signal is
reflection. total internal
Total interna! reflection:
When the light ray travels from denser medium to rarer medium the refracted ray
bends away from the normal. When the angle of incidence is greater than the critical
angle, the refracted ray again reflects into the same medium. This phenomenon is
called total internal reflection.
The refracted ray bends towards the normal as the ray travels from rarer medium
to denser medium. The refracted ray bends away from the normal as it travels from
denser medium to rarer medium.
Normal
Normal
i= 9.|
Denser medium
Denser medium
r=90°
Rarer medium
Rarer medium
Let, a ight ray traveling from denser medium (refracive index n,) to rarer medium
(refractive index n,) with an angle of incidence i, then the angie of refraction r can be
obtained by Snell's law.
n, Sin i=n, Sin r
When the angle of incidence is increased angle of reflection also increases and for a
particular angle of incidence(i= )the refracted ray
travels along the interface of two mediums. This Normal
angle of incidence is known as critical angle (O.).
n, Sin Oc =n, Sin 90 Denser mediun
n, Sin o =n, ’ Sin Oç=
Rarer medium
O = Sin
P.Sreenivasula Reddy MSc. (PHD) Website: www.engineeringphysics.weebly.com Page I
, GLOBAL COLLEGE OF ENGINEERING &TECHNOLOGY: YSR DIST.
Unit -VII Fiber Optics Engineering Physics
When the angle of incidence is greater than the critical angle(i >9), the refracted
total internal
ray again reflects into the same medium. This phenomenon is called
reflection
> When (i<), then the ray refracts into the secondary medium
> When (i=9.), then the ray travels along the interface
When (i> 0), then the ray totally reflects back into the same medium
2. Construction of optical fiber:
The opticai fiber mainiy consists the following six parts as shown in figure
Coré
Silicon Buffer Strength Outer
Cladding Jacket
Coating Jacket Menber
Core:
diameter is
Atypical glass fiber consists of a central core material. Generally Gore
refractive is always
50 um. The core is surrounded by cladding. The core medium
greater than the cladding refractive index.
Cladding
index. The over all
Cladding refractive index is lesser than the cores refractive
diameter of cladding is 125 um to 200 um.
Silicon Coating
It improves the
Silicon coating is provided between buffer jacket and cladding.
quality of transmission of light.
Buffer.Jacket
is made of plastic and
Silicon coating is surrounded by buffer jacket. Buffer jacket
protects the fiber cable from moisture.
Strength Member
strength to the fiber
Buffer jacket is surrounded by strength member. It provides
cable.
Outer Jacket
jacket. Because of this
Finally the fiber cable is covered by polyurethane outer
stretching
arrangement fiber cable will not be damaged during pulling, bending,
and rolling through the fiber cabie is made up of glasses.
www.engineeringphysics.weebly.com Page 2
P.SreenivasulaReddy MSc (PhD) Website:
, GLOBAL COLLEGE OF ENGINEERING &TECHNOLOGY: YSR DIST.
Unit-VII Fiber Optics Engineering Physics
3. Classification of fibers:
Based on the refractive index of core medium, optical fibers are classified into two
categories.
i Step index fiber
Graded index fiber
Based on the number of modes of transmission, optical fibers are classified into two
categories
i. Single mode fiber
ii. Multi mode fiber
Based on the material used, optical fibers are may broadly classified into four categories
Allglass fibers
All plastic fibers
Glass core with plastic cladding fibers
ÎV. Polymer clad silica fibers.
Step index fiber:
In step index fibers the refractive index of the core medium is uniform and
undergoes an abrupt change at the interface of core and cladding as shown in figure.
The diameter of core is about 10micrometers in case of single mode fiber and 50 to 200
mícrometers in multi mode fiber.
Core
ni
n2
Cladding
Step index single mode Step index multi mode
Attenuation is more for step index multi mode fibers but less in step index single mode
fibers
Numerical aperture is more for step index multi mode fibers but it is less in step index
single mode fibers
P.SreenivasulaReddy MSc (PHO) Website: www.engineeringphysics.weebly.com Page 3
