Topic 2

• Amplitude

  A wave’s maximum displacement from its equilibrium position.
• Antinode

  Position of maximum displacement in a stationary wave.
• Cladding

  A protective layer on an optical fibre

  • Improves tensile strength of fibre
  • Prevents scratching
  • Prevents signal transfer between adjacent fibres
• Coherence

  1. Same wavelength
  2. Same frequency
  3. Similar amplitudes
  4. Constant/fixed phase difference
• Diffraction

  Spreading of waves as they pass through a gap of similar magnitude to their wavelength.
• Frequency

  Number of waves that pass a point in a unit time period.
• Interference

  The superposition of waves that occurs when two waves meet.
• Longitudinal wave

  Particle oscillations are parallel to the direction of energy propagation.
• Pulse Broadening Reasoning

  Waves reach the end of the fibre at different times

  • Material Dispersion; wavelength of waves affect their speed.
  • Modal Disperion; Waves enter optical fibre at slightly different angles. (Different distance travelled)
• Node

  Position of minimum displacement in a stationary wave.
• Path Difference

  Measure of how far ahead a wave Is compared to another wave
• Phase difference

  Difference in phase between two points on a wave.
• Phase

  Measure of how far through the wave’s cycle a given point on the wave is.
• Polarisation

  The restriction of a wave so it can only oscillate in a single plane
• Pulse Broadening Definition

  Elongation of a signal passed down an optical fibre.
• Refractive Index

  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.
• Stationary Wave

  A wave that stores, but does not transfer, energy,
• Total Internal Reflection

  Effect that occurs in optical fibres where full reflection occurs at the inside boundary of the fibre

  • No radiation passes out
• Transverse Wave

  Particles oscillate perpendicular to the direction of energy propagation.
• Wavelength

  Distance between two identical positions on two adjacent waves.
• Progressive Waves

  Waves whose oscillations travel and transfer energy
• Reflective surfaces partially polarise light
• Law of superposition or smth

  Total displacement at a point is equal to the sum of the individual displacements at that point.
• Superposition

  The point where waves meet

  • Constructively interferes - in phase
  • Destructively interferes - out of phase
• Stationary wave formation

  1. A wave is generated at one end of the string and travels down it
  2. Wave is reflected at the other end and travels back the opposite direction
  3. Frequency of wave generation and length of the string are such that the next wave generated meets the reflected wave and undergoes superposition.
  4. In phase - constructive interference; maximum point (antinode)
  5. Out of phase - destructive interference; minimum point (node)
• Double Slit Interference

  Two illuminated slits act as coherent wave sources
• Diffraction depends on the gap width and the wave’s wavelength


  Unnoticeable - Most noticeable

  • Bigger -> Same size as wavelength

  Reflected when gap is smaller than the wavelength
• Intensity is a measure of power delivered per unit area


  Slit width

  • Increases; intense, narrow central maximum
  • Decreases; wider, less intense central maximum
• Refraction

  When a wave changes speed in a new medium

  • More optically dense; slows & bends towards the normal
  • Less optically dense; speeds up & bends away from the normal.
• Young’s Double Slit experiment

  Use of two coherent sources/single source with double slits to produce an interference pattern.
• Absolute refractive index

  Measures how much it slows down as a ratio

  • Of a material
• Relative Refractive Index

  Ratio of the speed of light in the two materials

  • At boundary between two materials
• Conditions for TIR

  1. Light must travel from a more to less optically dense medium.
  2. Angle of incidence of light must exceed its critical angle of the interface.
• Optical Fibres

  Makes use of total internal reflection to transfer signals.

  • high-speed internet cables
  • medical imaging as endoscopes
  • engineering inspections to view hard to reach areas
• Step-index optical fibres

  Made of two parts

  1. High refractive index core
  2. Low refractive index cladding
• Double Slit Explaination

  1. Diffraction at slits
  2. Overlapping of waves at two slits
  3. Superposition of waves
  4. Waves interfere.