Propagation of light

Question 1

What is a wavelength?

Answer 1

The distance between 2 consecutive peaks in a wave

Question 2

What is Freq?

Answer 2

Time between 2 consecutive peaks in a wave.

Question 3

Name 4 Wavelengths windows of operation used by fibre?

Answer 3

# 850nm Multimode (Cheap LED's - short distances)
# 1300nm Multimode  (More exspensive LED's and LASERS - Standard datacoms and telcoms)
# 1310nm Singlemode (More exspensive LED's and LASERS - Standard datacoms and telcoms)
# 1550nm Singlemode (Expensive sophisticated lasers and detector systems - long distances without repeaters)

Question 4

Define Optical Communication?

Answer 4

A modulated beam of light is used for information Transmision

Question 5

Define Optical fibre?

Answer 5

A flexible filament is used to guide the light to the receiver

Question 6

What are the 2 main processes that occur when light passes boundries from media to another?

Answer 6

Refraction

Reflection

Question 7

What does RI and I.O.R stand for?

Answer 7

RI - refractive index

I.O.R - index of refraction

Question 8

How do you calculate the RI of silica?

Answer 8

(n) =
speed of light in a vacuum (c vac)
———————————————
speed of light in the material (c mat)

Question 9

Explain Reflection?

Answer 9

Angles greater than the critical angle the ray of lightwould be reflected back into material it originated from.

Question 10

Explain refraction?

Answer 10

Links the bending of lightwith the refractive index change of the materials at that point.

Question 11

What does TIR stand for?

Answer 11

Total Internal Reflection

Question 12

To achieve TIR what 2 things must happen?

Answer 12

Core must be denser than the cladding

Angle of incedence must be greater than critical angle

Question 13

What does NA stand for?

Answer 13

Numerical Aperture