Page 668 - Introduction to Information Optics

652 11. Information Display with Optics

AA A AA/ \ A A A
0
fi /\ \ ^1
* •: h A V
0
^ A
- .-. H
«1 J J J .
n U U J tj
J ) ^
U >J
U \J J
w Vv V \j Ifl
/vV \J / V w
Fig. 11.28. Molecular ordering of nematic phase of liquid crystal.

For LC molecules without alignment, such as when contained in a bottle,
their appearance is often milky as they scatter light due to the randomness of
LC clusters. For realizing useful electro-optic effects, liquid crystals have to be
aligned. The nematic liquid crystal cell is composed of two glass plates (or glass
substrates) containing a thin liquid crystal layer (about 5 to 10 ^rn thick)
inside, as shown in Fig. 11.29.
The two glass plates impose boundary conditions on the alignment of
nematic liquid crystal molecules contained between them. Each glass plate is

Glass plates

Alignment
direction

Alignment
direction

Alignment layers
Fig. 11.29. Molecular arrangement in a twisted nematic liquid crystal cell.