wave definition stuff and theiry

Question 1

Define a progressive wave.

Answer 1

A progressive wave transfers energy without transferring material and is made up of particles of a medium (or field) oscillating e.g. water waves are made of water particles moving up and down

Question 2

Define phase difference.

Answer 2

How much a particle/wave lags behind another particle/wave, (units are radians, degrees or fractions of a cycle)

Question 3

What is a coherent light source?

Answer 3

A coherent light source has the same frequency and wavelength and a fixed phase difference .

Question 4

What are the two types of signal degradation?

Answer 4

Absorption - some of the signals energy is absorbed by the fibre.
Dispersion - pulse broadening with may cause overlap and loss of information.

Question 5

What is modal dispersion and how can it be reduced?

Answer 5

Caused by light rays entering the fibre at different angles, therefore they take different paths along the fibre, (for example some may travel down the middle of the fibre, while others are reflected repeatedly,) this leads to the rays taking a different amount of time to travel along the fibre, causing pulse broadening.
This can be reduced by making the core very narrow, therefore making the
possible difference in path lengths smaller.

Question 6

What is material dispersion and how can it be reduced?

Answer 6

Caused by using light consisting of different wavelengths, meaning light rays will travel at different speeds along the fibre, which leads to pulse broadening
This can be prevented by using monochromatic light .