Optical Networks Lecture #1
T. Moneerah Aleidi
Overview :
• Light Characteristics
• Light Properties
• Reflection and Refraction
Light Characteristics
• Particle Characteristics
– Light has energy
– Photons are the smallest quantity of monochromatic light
• That is light with single frequency
– The energy of a photon is described by: E= hf
• (h=6.6260755E-34 joule- sec) and f is the frequency of
light
– Energy of light depends on its speed: E=mc^2 (Einstein’s
Eqn.)
– The relationship between frequency and speed: v=c/λ
• Speed of light changes as it enters denser materials
• Wave Characteristics
– Described by a series of equations
Example #1
A light wave with λ= 1 µm c = 3
×10^8m/sec. v =?
λ= 1 µm
c = 3x10^8
v = c/λ
v = 3x10^8 / 1x10^-6
=> 3x10^14 m/s
Example #2
Find the energy of a photon
travelling with 200 THz frequency.
Given that h is Planck’s constant =
6.6256 x10^-34.
E= hf
E =(6.6256x10^-34)*(200x10^12)
=> 1.32512x10^-19 Joule
Light Properties
• Light is electromagnetic radiation –
Impacted by many parameters:
reflection, refraction, loss, polarization,
scattering, etc.
• Light of a single frequency is termed
monochromatic
• Any electromagnetic wave is governed
by a series of equations
Wave Velocity Equation: Phase Velocity
• The wave moves a distance of one wavelength λ in one period T
• From this, we can calculate the phase velocity denoted vp.
- (It is how fast the peaks and valleys move.)
Vp = λƒ
= λ/T
Reminder:
ƒ= 1/T
Wave equations: Group Velocity
- The velocity of little oscillations governed by the first factor
- Leads to the same formula as before for phase velocity:
- The velocity of big oscillations governed by the second factor
- Leads to a formula for group velocity:
Example #3
What is the phase and group velocity for this wave?
Vp = λƒ
λ*1/T
λ/T
λ= 30 m
t= 30 s
1] vp = 30/30 = 1 ms
2] vg = 60/30 = 2 ms
Reflection and Refraction
• When light finds a surface separating two media
(air and water, for example), a beam gets reflected
and another gets refracted (transmitted).
-Law of reflection: the angle of incidence θ1 = θ2
the angle of reflection .
-Law of refraction: n2 sinθ2 = n1 sinθ1 (Snell’s law.)
n is the index of refraction of the medium.
In vacuum, n=1. In air, n~1. In all other media, n>1.
Example #4
Water has n=1.33. How much does a
beam incident at 45 refracts?
n2 sinθ2 = n1 sinθ1
sinθ2 = n1/n2 sinθ1
1/1.33 sin 45
.53165
Sin^-1 (.53165) = 32