Biomedical Engineering Reference
In-Depth Information
NLO effects in the thin films. Hyperbranched polymers should be ideal ma-
trix materials as they offer three-dimensional spatial separation of the NLO
chromophores in the spherical architecture, and their void-rich topological
structure should help minimize optical loss in the NLO process.
The
hb
-PAEs of
hb
-P
13
and
hb
-P
15
contain NLO-active azo-functionalities,
which are soluble, film-forming, and morphologically stable (
T
g
>
180
◦
C).
Their poled films exhibited high SHG coefficients (
d
33
up to 177 pm
V),
thanks to the chromophore-separation and site-isolation effects of the hy-
perbranched structures of the polymers in the three-dimensional space
(Table 5) [28]. The optical nonlinearities of the poled films of the polymers
are thermally stable with no drop in
d
33
observable when heated to 152
◦
C
(Fig. 8), due to the facile cross-linking of the multiple acetylenic triple bonds
in the
hb
-PAEs at moderate temperatures (e.g., 88
◦
C).
Advanced photonic devices are often composed of working units with high
RI contrasts. The RI values of existing polymers, however, vary in a small
range (
n
= 1.338-1.710) [130, 131], which limits the scope of their photonic
applications. Theory predicts that molecules consisting of groups with high
/
Table 5
NLO properties of
hb
-PAEs
m)
a
V)
b
hb
-PAE
l
f
(
µ
d
33
(pm
/
hb
-P
13
0.14
177
hb
-P
15
0.42
55
a
Thickness of solid film
b
SHG coefficient.
Fig. 8
Decays of SHG coefficients of
hb
-PAEsasafunctionoftemperature
