This document discusses fiber Bragg gratings (FBG), which are periodic variations in the refractive index of an optical fiber that reflect specific wavelengths of light. It provides an introduction to FBG, the basic theory behind how they work, common fabrication methods, applications as optical filters and sensors, and their advantages and disadvantages. Key points covered include how the Bragg wavelength is determined by the refractive index and grating period, common types of grating structures, and how FBG can be used as sensors for strain, temperature, and acceleration.

1. A SEMINAR ON
FIBER BRAGG GRATING (FBG)
Presented By
Gouri patil
USN:3kb12ec012
Under The Guide Of
Prof. ZOHAR BEGUM
M.Tech
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2. CONTENTS
 INTRODUCTION
 BASIC THOERY OF FIBER BRAGG GRATING
 FBG FABRICATION METHODS
 GRATING STRUCTURE
 APPLICATIONS OF FIBER BRAGG GRATING
 FBG AS SENSOR
 ADVANTAGES AND DISADVANTAGES
 CONCLUSION
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3. INTRODUCTION
 A fibre Bragg grating (FBG) is a type of distributed
Bragg reflector constructed in a short segment of
fibre that reflects particular wavelengths of light and
transmits all others.
 This is achieved by adding a periodic variation to
the refractive index of the fibre core, which
generates a wavelength specific dielectric mirror.
 A fiber Bragg grating can be used as an inline
optical filter to block certain wavelengths.
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5. BASIC THOERY OF FIBER BRAGG
GRATING
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7.  The fundamental principle behind this operation is Fresnel
reflection.
 Bragg wavelength is , λB = 2nA
 were, n is effective refractive index of the grating
A grating period
 Where light travelling between media of different refractive indices
may both reflect and refract at the interface.
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8. FBG FABRICATION METHODS
 Interferometric Method
 Photo mask Method
 Point by point write method
 production 8

9. GRATING STRUCTURE
 Uniform
 Apodized gratings
 Chirped Fiber Bragg grating
 Tilted fiber Bragg gratings
 Long period fiber Bragg grating
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11. APPLICATIONS OF FIBER BRAGG
GRATING
 Communication
 Fiber Bragg grating sensors
 Fiber Bragg gratings used in fiber lasers
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12. APPLICATIONS IN OPTICAL
COMMUNICATION
 Fiber Lasers
 Fiber Amplifiers
 Fiber Filters
 Dispersion Compensators
 Optical Fiber Phase Conjugator
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13. FBG AS SENSOR
 FBG As strain sensor
 The shift in wavelength
 ΔλB=(1-Pe) λB ε 7.3
 Pe = (n2 /2 )[P12-μ(P11+P12)]
 were, μ is the poission ratio
of the optical fiber.
 ε is the applied strain.
 Pe is the photo elastic
coefficient term.
 FBG as temperature sensor
 It dependence on the Bragg wavelength on temperature
 It occurs due to two effect
1:Temperature dependence of the refractive index of the glass
2:Thermal expansion of the glass
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14.  Acceleration sensor
o The grating pitch will be
varying in accordance with
the acceleration.
o From this wavelength shift
We can measure the
Acceleration.
*ADVANTAGES * DISADVANTAGES
1.High resolution 1. Difficulty to demodulate the wavelength
2.Insensitive to the intensity shift
fluctuation 2.Expensive to build and maintain
3.Linear output as a function 3.Discrimination of their effect is
of the measurand difficult
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15. ADVANTAGES AND DISADVANTAGES
 ADVANTAGES
 Narrowband optic emission reflection
 Made of optical fiber
 Low optical loss
 Relatively simple and low-cost production
 Small size and easy integration into a wide variety of
systems
 Electrically immune, hence no conduction of electric
current
 DIADVANTAGES
 Thermal sensitivity
 Transverse strain sensitivity
 Lack of standards
 Limited supplies
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16. CONCLUSION
 Fiber Bragg grating is one of the key optical
components, which are gaining increasing attention
in different fields of optical technologies including
optical fiber communication and sensing
applications
 They rflect very narrow band of frequency, that can
be designed to have more complex responses.
 They can sense parameters which vary the
refractive index of grating.
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