1. UNIT-7
 FIBER OPTICS.
 HOLOGRAPHY.
1

2. APPLIED PHYSICS
CODE : 07A1BS05
I B.TECH
CSE, IT, ECE & EEE
UNIT-7: CHAPTER 1.
NO. OF SLIDES :19
2

3. UNIT INDEX
S.No. Module Lecture PPT Slide No.
No.
1 Introduction. L -1 4-10
Acceptance angle.
Numerical
aperture
2 Types of optical L -2 11-17
fibres
3. Attenuation in optical L-3 18-19
fibres
3

4. Lecture-1
INTRODUCTION
Optical fibers are long, thin
strands of very pure glass about
the diameter of a human hair.
 They are arranged in bundles
called optical cables and used to
transmit light signals over long
distances. 4

5. Optical Fiber
There are 3 parts in optical fiber. They are
1.Core
2.Cladding.
3.Buffer coating.
5

6. OPTICALFIBER STRUCTURE
6

7. L
e
c
t
Core: u
r

- Thin glass center of the fiber where the
e
-
light travels
1
Cladding :
 Outer optical material surrounding the core
that reflects the light back into the core
Buffer coating:
Plastic coating that protects the fiber fom
damage and moisture.
7

8. Acceptance angle
8

9. “The maximum angle of incidence at
the core of the optical fiber for which
the rays undergo totall internal
reflections and travel along the
fiber” is called acceptance angle.
 The acceptance angle is given by
α m = Sin-1[(√n12-n22)/n0] 9

10. L
NUMERICAL APERTURE
e
c
t
u
 Numerical aperture of a fiber is a
r
e
measure of its light gathering
-
1
capacity.
 The numerical aperture (NA) is
defined as the sin of the acceptance
angle.
 (NA) = Sinα = (√n 2-n 2)/n
m 1 2 0
10

11. Lecture-2
Single-mode fibers:
 If the core diameter is small it
allows only one mode to travel
through it. Then the fiber is called
single mode or monomode fiber.
 The monomode fiber has very small
core diameter less than
10micrometers.
 They Transmit infrared laser light
(wavelength = 1,300 to 1,550
nanometers). 11

12. Multi-mode fibers
 If a fiber allows more number of
modes, then it is called multimode
fiber.
 It has larger core diameter than single
mode fiber.
12

13.  The relative refractive index
difference is also larger than single
mode fiber.
 It transmits infrared light
(wavelength = 850 to 1,300 nm) from
light-emitting diodes (LEDs).
13

14. Step index Fiber
 The refractive index of core is
constant through out the core.
 Different rays reach the exit end
at different times. Therefore, the
pulsed signal received at the exit
end gets broadened. This is called
‘intermodal dispersion’. 14

15. Graded Index Fiber
 If the core has a non-uniform refractive
index that gradually decreases from the
center towards the core-cladding
interface, the fiber is called graded index
fiber.
 The light travels at different speeds in
different directions.
15

16.  A ray is continuously bent and
travels a periodic path along the axis
in the form of helical or skew rays.
 There is no chance of intermodal
dispersion.
 Bandwidth is high.
16

17. Plasticfibers
Some optical fibers can be made
from plastic. These fibers have a
large core (0.04 inches or 1 mm
diameter)
transmit visible red light
(wavelength = 650 nm) from
LEDs
17

18. Lecture-3
L
e
ATTENUATION
c
t
uAttenuation is the loss of power
r
suffered by the optical signal as it
e
-
propagates through the fiber.
2
 It is also called fiber loss.
 Signal attenuation is defined as the
ratio of the input optical power Pi
into the fiber to the output received
optical power Po from the fiber. 18

19.  The attenuation coefficient of the
signal per unit length is given as
α =10/L log (Pi/Po) dB/km
 The mechanisms through which
attenuation takes place are
1.Absorption losses
2.Scattering losses 19

20. UNIT INDEX
S.No. Module Lectur PPT Slide
e No.
No.
1 Basic principles of L -4 3-6
Holography
2 Construction and L -5 7-18
reconstruction
Images
On hologram.
3. Applications of L-6 19-23
Holography.
20

21. Lecture-4
Holography
L
e
• Holographyis about the photographic
c
t
technique.
u
r
e
• The technic is called HOLOGRAPHY after
-
3
the greek words HOLOS, and GRAPHOS,
which mean ‘complete’, and ‘writing’
respectively.
• It is the science of producing holograms.
• It is a form of photography that allows an
image to be recorded in three dimensions. 21

22.  The technique of holography can also be used
to optically store, retrieve, and process
information.
 It is common to confuse volumetric displays
with holograms, particularly in science fiction
works such as Star Trek, Star Wars,
Red Dwarf, and Quantum Leap.
22

23. Technical description
 The difference between holography and
photography is best understood by considering
what a black and white photograph .It is a
point-to-point recording of the intensity of
light rays that make up an image. Each point
on the photograph records just one thing, the
intensity (i.e. the square of the amplitude of
the electric field) of the light wave that
illuminates that particular point.
23

24.  In the case of a colour photograph, slightly
more information is recorded (in effect the
image is recorded three times viewed through
three different colour filters), which allows a
limited reconstruction of the wavelength of the
light, and thus its colour.
 the holograms are recorded
monochromatically.
24

25. Holographic recording process
 To produce a recording of the phase of the
light wave at each point in an image,
holography uses a reference beam which is
combined with the light from the scene or
object (the object beam).
 If these two beams are coherent, optical
interference between the reference beam and
the object beam, due to the superposition of
the light waves, produces a series of intensity
fringes that can be recorded on standard
photographic film. 25

26.  These fringes form a type of
diffraction grating on the film, which is called
the hologram.
 The central goal of holography is that when
the recorded grating is later illuminated by a
substitute reference beam, the original object
beam is reconstructed, producing a 3D image.
26

27. Lecture-5

Construction process
27

28. Holographic reconstruction process
 When the processed holographic film is
illuminated once again with the reference
beam, diffraction from the fringe pattern on
the film reconstructs the original object beam
in both intensity and phase (except for rainbow
holograms where the depth information is
encoded entirely in the zoneplate angle).
28

29.  Because many viewpoints are stored, each of
the viewer's eyes sees the image from a
slightly different angle, so the image appears
three-dimensional. This is known as stereopsis
.
 The viewer can move his or her viewpoint and
see the image rotate
29

30. Reconstruction process
30

31.  HOLOGRAPHY-CONSTRUTION PROCESS
L
e
c
t
u
r
e
-
5
31

32.  HOLOGRAPHY-CONSTRUCTION PROCESS
32

33.  CONSTRUCTION PROCESS
33

34. Holograms as diffraction grating
 A diffraction grating is a transparent or
reflective sheet with thin slits, the distance
between them and their diameter being on the
order of the wavelength of the light. Light rays
travelling towards it are bent at an angle
determined by the distance between the slits
and the wavelength of the light.
34

35.  When holograms are constructed, the reference
beam and the object beam interfere with one
another and the dark and light fringes of the
interference pattern are recorded.
 When this photograph is developed, the light
parts become clear and the dark parts opaque.
35

36.  The clear, light parts become like the slits of a
diffraction grating, and the angle at which they
bend incoming light (the reconstruction beam)
is determined by the spacing between them,
which in turn was determined originally by the
object beam and reference beam, when the
hologram's interference pattern was made.
Thus the slits bend the reconstruction beam to
be the exact angles at each point that the object
beam was going at.
36

37. APPLICATIONS Lecture-6
 Holography can be applied to a variety of uses
other than recording images.
1 Holographic data storage is a technique that
can store information at high density inside
crystals or photopolymers.
 The ability to store large amounts of
information in some kind of media is of great
importance, as many electronic products
incorporate storage devices.
37

38.  As current storage techniques such as Blu-ray
reach the denser limit of possible data density
(due to the diffraction-limited size of the
writing beams), holographic storage has the
potential to become the next generation of
popular storage media.
 The advantage of this type of data storage is
that the volume of the recording media is used
instead of just the surface.
38

39. APPLICATIONS
2. Digital holography
 An alternate method to record holograms is to
use a digital device like a CCD camera instead
of a conventional photographic film. This
approach is often called digital holography.
 In this case, the reconstruction process can be
carried out by digital processing of the
recorded hologram by a standard computer.
 A 3D image of the object can later be
visualized on the computer screen or TV set.
39

40. APPLICATIONS
3.Use of holography in banknotes
 Holograms are used widely as a security device
in many currencies such as the Brazilian real 20
note, British pound 5/10/20 notes, Canadian
dollar 5/10/20/50/100 notes, Euro
5/10/20/50/100/200/500 notes, South Korean
won 5000/10000 notes, Japanese yen
5000/10000 notes, etc.
40

41. 4. Holography in art
 Early on artists saw the potential of
holography as a medium and gained access to
science laboratories to create their work.
Holographic art is often the result of
collaborations between scientists and artists,
although some holographers would regard
themselves as both an artist and scientist.
41