3.3.2.3 - Refraction At A Plane Surface Flashcards
Refractive index of a material =
C / Cs (speed of light/speed of light in that material)
What is the refractive index of air?
1.
What is snell’s law?
n1 sin 01 = n2 sin 02
n = refractive index.
What causes light to be refracted along the boundary?
When light is reflected at the critical angle.
What causes light to be totally internally reflected?
When the angle is greater than the critical angle.
What values can sin take?
Smaller than 1.
Sin c =
1/ refractive index
n2 / n1
What are optical fibres used for?
To carry signals over long distances and round corners.
Why is cladding needed for optical fibres?
Optical fibres themselves have a high refractive index but are surrounded by cladding with a lower refractive index to allow total internal reflection. Moreover cladding protects the fibre from scratches which could let light escape.
Why is the fibre narrow?
So that light always hits the boundary between the fibre and cladding at an angle bigger than the critical angle.
What two things cause signal degradation?
Absorption and dispersion.
What does absorption cause?
Loss in amplitude.
How is absorption caused?
As signal travels, some of its energy is lost through absorption by the material the fibre is made from.
What does dispersion cause?
Pulse broadening.
What are the two types of dispersion?
Modal and material.