Amplitude
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 Grating
A grating with hundreds of slits per millimetre , that results in sharper interference patterns . They are used to calculate atomic spacing and to analyse elements .
Diffraction
The spreading of waves as they pass through a gap of a similar magnitude to their wavelength .
Electromagnetic Waves
Waves that consist of perpendicular electric and magnetic oscillations .
Frequency
The number of waves that pass a point in a unit time period . It is the inverse of the time period .
Fringe Spacing
The distance between two adjacent bright fringes or two adjacent dark fringes .
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 .
Laser
A light source that produces a collimated and coherent beam .
Longitudinal Wave
coherent beam . A wave with oscillations that are parallel to the direction of energy propagation . Sound waves are an example of a longitudinal wave .
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 .
Node
A position of minimum displacement in a stationary wave .
Optical Fibre
A thin glass fibre through which signals are passed through . Optical fibres usually have cladding surrounding them .
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 .
Phase
A measure of how far through the wave's cycle a given point on the wave is .
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 .
Speed
The product of a wave's frequency and wavelength .
Stationary Wave
A wave that stores , but does not transfer , energy
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 .
Transverse Wave
A wave with oscillations that are perpendicular to the direction of energy propagation . Electromagnetic waves are examples of transverse waves.
Wavelength
The distance between two identical positions on two adjacent waves . It is commonly measured from peak to peak or trough to trough .
Young's Double - Slit Experiment
An experiment that demonstrates the diffraction of light by passing monochromatic light across two narrow slits and observing the resulting pattern of bright and dark fringes .