Image Processing Reference
In-Depth Information
86
Chapter 8
Figure 8.1
Schematic layout of a twisted nematic LC cell with the main components.
Figure 8.2
Simplified illustration of how a twisted nematic cell acts upon polarized
light. When the cell is off (left), the polarized light is orthogonal to the exit polarizer
(analyzer). When the cell is on, the state of polarization is rotated and thus the light
can go through the analyzer (right).
the surface. This last issue is not a problem for display but may generate diffraction
in a high-quality adaptive optical component. As shown in Fig.8.2, the way an LC
device can modulate phase is related to the fact that the applied voltage rotates the
molecules, which are rod-shaped dipoles (in first approximation), to align with the
field created within the cell.
If one defines
n
||
and
n
⊥
as the ordinary and extraordinary components of the re-
fractive index, then the phase modulation induced in one of the polarization com-
ponents of the light going through the cell is
