This document discusses fiber optic communication and sensor systems. It begins with an introduction to fiber optics and covers topics like multichannel systems, optical switching and networks, all-optical time-division multiplexing technology, and optical fiber sensor technology. It then discusses key concepts in fiber optic communication like bandwidth, signal to noise ratio, transmission media alternatives to fiber optics, advantages of optical communication over satellite communication, wavelength-division multiplexing, numerical aperture, dispersion, and the tradeoff between high launching efficiency and reduced dispersion in optical fiber design.

1. FIBER OPTICS
COMMUNICATION AND SENSOR
SYSTEMS
1. INTRODUCTION TO FIBER
2. MULTICHANNEL SYSTEMS
3. SOLITON SYSTEM
4. OPTICAL SWITCHING AND NETWORKS
5. ALL-OPTICAL TIME-DIVISION
MULTIPLEXING TECHNOLOGY
6. OPTICAL FIBER SENSOR TECHNOLOGY
7. FIBER OPTICS APPLICATIONS

3. For good communication a system needs to have following things.
(1) Bandwidh (BW)
(2) Good signal to noise ratio (SNR) i.e. low loss
The BW at optical frequencies is expected to be 3 to 4 orders of
magnitude higher than that at the microwave frequencies (1GHz to
100GHz).

4. There are various wired and wireless media used for long and
short distance communication. Their broad characteristics are
summarized in the following
Transmission media Alternative
to the Optical Communication

5. Transmission media Alternative
to the Optical Communication

6. Comparison of Satellite and
Optical communication
• Satellite Fiber Optics
• Point to Multi-point Point to point
• BW ~ GHz BW ~ THz
• Maintenance free Needs Maintenance
• Short life ~7-8 Yr Long life
• No upgradeability Upgradeable
• Mobile, air, sea On ground only
• Satellite and Optical communication will co-exist due
their complementary nature

7. Advantages of Optical
Communication
• Ultra high bandwidth (THz)
• Low loss (0.2 dB/Km)
• Low EMI
• Security of transmission
• Low manufacturing cost
• Low weight, low volume
• Point to Point Communication

9. Frequency BW /wavelength BW
Where
is the velocity of light in vacuum,
is the refractive index of the medium,
is the central wavelength of the band, and
is the wavelength bandwidth (also called spectral width ).
For 1550nm window, ∆ λ =1550 and λ =100nm, n=1.5, ∆ f=?
So we have Approximately.
So , as a rule of thumb we can take for optical communication,

12. Characteristics of light
• Intensity (Power per unit solid angle)
• Wavelength (Color)
• Spectral width ( purity of color)
• Polarization
- Linear
- Circular
- Elliptical

14. Wave Function
• A : Amplitude of the wave
• ω : Angular frequency of the wave (rad/s)
• β: Phase constant (rad/m)
• χ: Distance
• t: Time

15. Some Basics
• Wavelength λ= ν / f
• Velocity ν = c / Refractive Index n
• Frequency f = Energy / Plank’s Constant

16. Refraction and reflection
Snell’s Law: n1 Sin Φ1 = n2 Sin Φ2
Critical Angle:
Sin Φc=n2/n1

17. Basic Fiber Structure

18. Ray Model
• For light to propagate inside the fiber
through total internal reflections at core-
cladding interface, the refractive index of
the core must be greater than the
refractive index of the cladding. n1 > n2

19. Skew Rays

20. Propagation of Meridional Rays

21. under what conditions the ray is
ultimately guided inside the
core due to total internal reflections at
the core cladding boundary?
• Now as we increase the launching angle ,
the angle also increases.
• Since
•The maximum launching angle
then corresponds to

22. • Let us apply Snell's law at the launching
point and at the core-cladding interface for
the maximum launching angle
(since )
now,
=Numerical Aperture

23. Numerical Aperture
• This parameter tells us that if we take an optical
fiber and put it in front of an optical source then
how much light is collected by the fiber from the
source.
• Smaller the value of N.A, smaller the value of
(maximum launching angle) and smaller is the
power accepted by the fiber.
• In other words, if the light is available from
various directions from the source, only a portion
of light is accepted by an optical fiber and the
remaining part of the light is rejected by it.

24. • If we want good light launching efficiency then
should be as large as possible.
• Reduce refractive index of the cladding
• n2=1(air) minimum possible value
• So cladding is an undesirable feature.
• It is only for mechanical support.

25. DISPERSION
• Important parameter is the data rate which
the fiber can handle.

26. Dispersion(2)
• The time difference between the axial ray
and the extreme ray then is:

27. Dispersion(3)
• The time difference ∆t essentially is the
measure of pulse broadening on the
optical fiber.
∀∆t per km α ( )
• For low dispersion ( ) should be
as small as possible .
• So for an optical fiber the refractive index
of core has to be made as close to the
refractive index of cladding as possible.

28. Contradictory Requirement
(a) For higher launching efficiency (higher
NA), should be as large as possible .
(b) For high data rate (bandwidth), should be
as small as possible .
• Since data transfer rate is rather more
important in communication, is made as
small as the fabrication technology permits.
• So for, all practical fibers,
• Refractive index of the cladding differs from
that of the core by only 0.1 to 1%.