Ch5 Optics Flashcards
Define coherence
Fixed phase difference
Same frequency and wavelength
How do you increase diffraction?
What about fringe width?
Increase wavelength, decrease slit width
Same!
When light enters a more optically dense medium which way does it bend?
Towards normal
When does total internal reflection occur?
When light is at a boundary to a less optically dense medium
The angle of incidence is greater than the critical angle.
What is the purpose of cladding in optical fibre?
Prevents core from scratches which allow light to escape and degrade signal
Allows TIR as it has a lower refractive index than core
How does modal dispersion cause pulse broadening?
How can you reduce it?
Light enters at a different angle, path difference, different times so pulse broadening
Use very narrow fibre so path difference smaller
What is material dispersion?
How can you reduce it?
Light with different wavelengths so some slow down more than others, arrive at different times causing pulse broadening
Use monochromatic light
How can absorption and dispersion be reduced?
Use an optical fibre repeater to regenerate signal.
What are the advantages of optical fibres over copper wires?
Signal more info as higher freq
No energy lost as heat
No electrical interference
Cheaper
Very fast
How can you find critical angle?
Sin critical = n2 / n1
Where n1 greater than n2
How do you work out the refractive index n of a material?
n=c/v
C=speed of light in vacuum
V=speed of light in material
What formula is associated with Young’s double slit experiment?
W = (Wavelength×D) / s
W=fringe spacing
S= slit separation
