Waves Flashcards
Amplitude
A wave’s maximum displacement from its equilibrium position.
Antinode
A position of maximum displacement in a stationary wave
Cladding
A protective layer on an optical fibre to improve the tensile strength of the fibre, prevent scratching and to prevent signal transfer between adjacent fibres.
Coherence
Waves are coherent if they have the same wavelength and
frequency, as well as there being a fixed phase difference between them.
Diffraction
The spreading of waves as they pass through a gap of a similar
magnitude to their wavelength.
Interference
The name given to the superposition of waves that occurs when two waves meet. If the waves are in phase they will constructively interfere, but if they are out of phase, they will destructively interfere.
Material Dispersion
Waves of different wavelengths travel at slightly different
speeds through an optical fibre and so reach the end of the fibre at slightly different times, causing pulse broadening. The use of monochromatic light fixes this.
Modal Dispersion
Waves enter an optical fibre at slightly different angles,
meaning the distance each beam has to travel is slightly different. This leads to the beams reaching the end at different times and so causes pulse broadening.
Path Difference
A measure of how far ahead a wave is compared to another
wave, usually expressed in terms of the wavelength.
Phase Difference
The difference in phase between two points on a wave. It is
usually expressed in radians.
Polarisation
The restriction of a wave so that it can only oscillate in a single
plane. This can only occur for transverse waves.
Pulse Broadening
The elongation of a signal passed down an optical fibre,
commonly due to modal or material dispersion.
Refractive Index
A material property that is equal to the ratio between the speed of light in a vacuum, and the speed of light in a given material.
Snell’s Law
A law linking a wave’s angle of incidence to its angle of refraction, with the use of the refractive indexes of the mediums involved.
n1 sin θ1 = n2 sin θ2
Total Internal Reflection
An effect that occurs in optical fibres, where full
reflection occurs at the inside boundary of the fibre, meaning no radiation passes out.
The light ray must move from a more dense medium to a less dense medium.
The angle of incidence must be greater than the critical angle
