Notesale: Turn your study into money

Document Preview

Extracts from the notes are below, to see the PDF you'll receive please use the links above

---

Mansoura University
Faculty of Science
Physics Department

Research
Characterization of polymer fiber using two beam
interferometry

Prepared by

Mohamed Hasanin Farg
Premaster degree

Introduction
Optical fiber is based on the idea of total internal reflection (it is a
phenomenon happen when electromagnetic waves incident on the
boundary surface from medium with high refractive index to low
refractive index by angle larger than a particular critical angle with
respect to normal to the surface, all incident waves reflected) So they
have the ability to transfer the waves inside fibers without losing or very
small losing in its energy
...
There are
some type of fibers have two or multi layers Provided that they are the
highest in the internal layer refractive index
...
49 and 1
...
There
are many uses depend on optical fiber (communication,
illumination, sensors and fiber lasers ) for all these uses we will
investigate the characterization of optical fibers by two beam
interferometry microscope
...
(3)

Figure (1)
a-One layer
...
These rays are
different modes
...
(3)

Figure (2)

c-Some fibers have very small diameter core that they can carry only one
mode which travels as a straight line at the center of the core
...
(3)

Figure (3)
d-Multilayer step-index

Figure (4)

Graded index:

Figure (5)
Refractive index varies gradually as a function of radial distance from the
fiber center
...


Figure (6)
All patterns depend on path difference

Bright patterns: when two beams make constructive interference (zero
path difference)
𝜆

Dark patterns: when two beam make destructive interference (( ) path
2

difference, λ wavelength of wave)

Figure (7)
Path length difference can change if one of two beam inter to medium has
different in refractive index, this will affect on shape of interference
patterns, so we can make relation between path difference and shape of
pattern and refractive index of medium
...

𝑎
We can determine these optical properties by the complementary use of
scanning electron microscopy and interference microscopy
...


Figure (8)
2-interference microscope:
There are many microscopes were developed using the two beam
interference technique (the Mach-Zehnder interferometer , the Nomaraski
interferometer , Pluta polarizing interference microscope , the Interphako
interference microscope and Baker Dyson ,Leitz and Zeiss-Limmik
interference microscope
...

The accuracy of the determination of the fiber diameter is about 1µm
(Pluta 1972)
The result from Pluta microscope shown as interference pattern:

Figure (10)

Get a formula for measuring the mean birefringence for optical polymer
fiber:
𝑛 𝑙 Is the refractive index of liquid
𝑛″ The mean refractive indices of the fiber for the plane polarized light
𝑎
vibrating parallel
𝑛⊥ The mean refractive indices of the fiber for the plane polarized light
𝑎
vibrating perpendicular
...

We will integrate the equation of 𝑧 ″ in the region (s ≥d≥I )
𝑙

𝑙

𝛥𝑧
∫ 𝑧 ″ 𝑑𝑥 = (𝑛″𝑎 − 𝑛 𝑙 ) ∫ 𝑡 𝑑𝑥
𝜆
𝑠

𝑠

𝐹″ =

𝛥𝑧 ″
(𝑛 𝑎 − 𝑛 𝑙 )𝐴
𝜆

A is the mean cross sectional area of the fiber
...

𝐹 ″ For parallel
𝐹 ⊥ For perpendicular

𝑛″𝑎

𝐹″ 𝜆
= 𝑛𝑙 +
𝛥𝑧 𝐴

𝑛⊥
𝑎

𝐹⊥ 𝜆
= 𝑛𝑙 +
𝛥𝑧 𝐴

𝐹″ − 𝐹⊥ 𝜆
𝛥𝑛 𝑎 = (
)
𝛥𝑧
𝐴
From last equation, we can determine the mean birefringence for optical
polymer fiber by knows (wavelength, and shift in pattern and area of shift
in parallel and perpendicular and mean cross sectional area of fiber)

Reference
1- http://en
...
org/wiki/Plastic_optical_fiber
2-Figures (1, 4, 5, 9, 10, 11) from book (Interferometry of Fibrous
Materials) (N Barakat and A A Hamza )
3-http://www
...
com/Merchant2/optical-fiber

---