using fiber optics and scattering methods rayleigh,brillouin and raman scattering

1. Crack Detection In
Railway Track
Ankit Advisor
M.Sc.Physics Rajan Jha
16PH05016
School of Basic Sciences

2. Out lines
Introduction
Optical fiber
Scattering of light inside the optical fiber
Optical time domain reflectometry(OTDR)
Applications
Strain sensors

3. Introduction
First reference of Optic sensors relates to flexible
endoscope developed in 1950.
After that in 1982 magnetic, acoustic,pressure,
temperature, acceleration,displacement,
fluid level, torque, photo acoustic, current,and
strain sensors were among the fiber optic
sensors already developed and being
researched.

4. Overview of fiber optics sensor

5. Optical fiber
An optical fiber is a cylindrical symmetric structure that
is
composed by a central core with a diameter between 4
and 600 micrometer.It then enclosed by a cladding with
a relative lower refractive index trapping the light-wave
being carried in the core by the reflection at the interface
between core and cladding.

6. Scattering of light inside the optical
fiber
The propagation of light through the core of an optical fiber is
based on total internal reflection of the light wave.
Rough and irregular surfaces, even at the molecular level, can
cause light rays to be reflected in random directions.
This is called diffuse reflection or scattering, and it is typically
characterized by wide variety of reflection angles.
Three different scattering processes namely: Raman, Brillouin
and Rayleigh scattering.
Using this scattering process we can make distributed sensor.

8. Why Distributed sensors
Distributed sensing replaces complex integration of thousands
of sensor with one optical fiber system.
The inherent distributed sensing nature of fiber optic sensors
can be used to create unique forms of sensors for which, in
general, there may be no counterpart based on conventional
sensor technologies.
Optical fiber is cheap, light, pliable, and immune to
electromagnetic interference (EMI), which makes it a cost-
effective, flexible and an inert sensor medium.
Distributed fiber optic sensors can be depend on different
techniques and principles.

9. Optical Time Domain Reflectometry
(OTDR)
An optical time domain reflectometary ia an
optoelectronic instrument that used to charaterize an
optical fiber.
The spatial resolution of an OTDR instrument is the
smallest distance between two scatters that can be
resolved.We can see from this formula,
n2
c
Zmin
τ
=∆

10. Principle OTDR based on R.B.

11. BOTDR
Brillouin scattering occurs from acoustic
vibration stimulated in the optical fiber.
These vibrations produce a counterpropagating
wave, called Brillouin scattering wave.
Which weakens the forward-moving input
pulse.

12. BOTDR Setup

13. Performance of distributed and quasi-
distributed sensing techniques
Sensing
Technology
Transducer Type Sensing Range Spatial
Resolution
Main
Measurands
Raman OTDR Distributed 1 km -37km 1cm-17m Temperature
BOTDR Distributed 20–50 km 1m Temperature and
Strain
BOTDA Distributed 150–200 km 2 cm (2 km)
2 m (150 km)
Temperature and
Strain
Rayleigh
OFDR/OBR
Distributed 50–70 m 1mm Temperature and
Strain
FBG Quasi-distributed
100 channels
2 mm (Bragg
length)
Temperature ,
Strain and
displacement
≈
≈
≈

14. Strain Sensor result

15. References
 Cheng, J.-X.; Xie, X.S. Coherent Anti-Stokes Raman
Scattering: Instrumentation, Theory, and Applications. J. Phys.
Chem. B 2004, 108, 827–840. [CrossRef]
 Bao, X.; Dhliwayo, J.; Heron, N.; Webb, D.J.; Jackson, D.A.
Experimental and theoretical studies on a distributed temperature
sensor based on Brillouin scattering. J. Lightwave Technol. 1995,
13, 1340–1348. [CrossRef]

16. THANK YOUTHANK YOU