1. FIBER OPTICS
Light propagation through thin glass fibers

2. FIBER OPTICS Advantages Low Attenuation (less signal degradation)
Very High Bandwidth over long distances
Small Size and Low Weight
No Electromagnetic Interference
Non-Conductive Cables
Easy installation
Eliminates Spark Hazards (non-flammable)
Data Security

3. PRINCIPLE OF FIBER OPTICS
Optical fibers are used as dielectric waveguides for guiding the electromagnetic waves at optical frequencies
Light is guided through transparent glass fibers by total internal reflection

4. TOTAL INTERNAL REFLECTION
Snell’s law
When the transmitted (refraction angle) reaches 90⁰, the incidence angle is called as the critical angle

5. TOTAL INTERNAL REFLECTION
Angle of incidence less than the critical angle
Angle of incidence equal to the critical angle
Angle of incidence greater than the critical angle
Total internal refection takes place only when the light travels from denser to rarer medium and angle of incidence should be greater than the critical angle of the denser medium

6. TOTAL INTERNAL REFLECTION

7. Structure Fiber Optic Cable
Glass fiber consists of a central core glass (≈ 50 μm) surrounded by a cladding
Refractive index of cladding is slightly lower than the refractive index of core
Core + Cladding ≈ 125 – 200 μm
Fiber is made of silica (SiO2) glass
Cladding is also made of silica but the outer layer is added with small amount of B, Ge or P to decrease the refractive index

8. Structure Fiber Optic Cable
Cladding provides
Proper light guidance (to retain the light wave within the core)
High mechanical strength
High safety to the core from the scratch
Buffer Jacket
Made of plastic and protects the fiber from moisture and abrasion

9. Structure 0f Fiber Optic Cable
Strength Members
Provides necessary toughness and tensile strength
Fiber optic cable withstands during hard pulling, bending, stretching or rolling without fracture even though the fiber is made from brittle glass
Black Polyurethane Outer Jacket
Avoids mechanical crushing

11. Propagation of Light through Optical Fibers
Consider the light propagation through a step index fiber
Fiber is placed in a medium of refractive index “no”
Let ɸmax is the incident angle at the entrance end of the fiber with respect to the axis of the fiber
Let θr be the corresponding angle of refraction

12. Propagation of Light through Optical Fibers
In the limit of total internal reflection
By Snell’s law

13. Propagation of Light through Optical Fibers
Since
Angle of incidence at the core-cladding interface
(or)

14. Propagation of Light through Optical Fibers

15. Propagation of Light through Optical Fibers
If the fiber is placed in air
(n0 = 1)

16. Acceptance Angle
Maximum value of the angle of incidence at the entrance end of the fiber, at which the angle of incidence at the core-cladding surface is equal to the critical angle of the core medium

17. Acceptance Angle
Acceptance angle of the fiber is the maximum angle of incidence up to which a light ray can enter into the fiber and still be totally internally reflected

18. Numerical Aperture
Numerical Aperture (N.A.) is the light collecting efficiency of the fiber and is the measure of amount of light rays that can be accepted by the fiber
If n1 ≈ n2,
then (n1+n2) = 2n1
Relative refractive index difference of the fiber (Δ)

19. Step Index Fiber
The refractive index of the core of the step index fiber is constant through out the core
Graded Index fiber
The refractive index of the core of the graded index fiber is maximum at the center of the core and then it decreases towards core-cladding interface