Polarization
Polarization refers to the orientation of
Electric Field oscillations
The m-waves are linearly polarized
along the axis of the transmitter diode.
The detector receives only the
component of the incident m-wave
parallel to the axis of the detector
diode.
When a linear polarizer is used,
nearly all incident light is converted
to linearly polarized light.
Unfortunately, there is no way to
detect to what extent light is actually
polarized without a second polarizer
(analyzer).
We used the receiver for this.
Polarization
When the analyzer’s transmission
axis is aligned with that of the
polarizer, the maximum intensity
passes through.
When the analyzer is rotated 90° to
this, most of the light is absorbed
and the minimum intensity is
attained.
When the receiver and transmitter
are perpendicular, with a polarizer at
angle q between them, the resulting
intensity is detected as:
I = I0 cosq sinq
which is a max for q = 45 degrees
The percentage of polarized
light (V) is then given by:
I max  I min
V
I max  I min
INCIDENT
Polarization
A Mechanical Analogy…
 Force pushes down on block
 Plane changes incident force’s
direction by “absorbing” some of the
incident force
 Block moves parallel to plane’s
“transmission axis”
Receiver at 90
Degrees
To Transmitter
Polarizer at 45 Degrees
1
2
3
IGNORED
RECEIVED
INCIDENT
Initial Polarization
Of Transmitted
Wave
Polarization
Resulting Intensity of Polarized light is given by Malus’ Law:
Polarization and Malus' Law
Data
1
Graph
Malus’ Law:
0.8
Intensity (V)
Malus' Law
I(q) = I0cos2q
0.6
0.4
0.2
0
0
20
40
60
80
100
120
140
160
180
Angle between Transmitter axis and Receiver axis (deg)
The m-waves were found to be 98% polarized from the transmitter,
but the wire polarizers, when used, were only 76% effective.
Polarization
… via Rayleigh Scattering
 A wave packet incident on a small
particle (<l/15) causes electron
oscillations, creating a dipole.
 Light is re-emitted in a random
direction, polarized parallel to the
dipole oscillation axis.
 Incoming light undergoes the
maximum polarization at 90° from
the angle of incidence.
Polarization
… via Rayleigh Scattering
 Atoms and molecules in the upper
atmosphere are <1nm in size, so
they can scatter light in the visible
spectrum (~400nm<l<~700nm)
 The intensity of the scattered light
increases with with (1/l)4, so the
intensity of blue light scattered by
the atmosphere is much greater
than that of red light.
 Therefore, we have blue skies, red
sunsets, and polarized light 90° from
the sun.