Novel Electroactive Materials and Tunable Photonic Crystals

1
Penn State MRSEC Center for Molecular
Nanofabrication and Devices   Mallouk T.E.
DMR-0213623Novel Electroactive Materials and
Tunable Photonic Crystals
Photonic crystals with large tunability are
attractive for many important operations in optic
communications including programmable filters,
dynamic gain equalization and chromatic
dispersion compensation. Among various methods,
electric filed induced tuning offers many
advantages. One challenge in achieving large
tuning range by external fields in photonic
crystals is the small strain (lt0.1) or
refractive index change (lt0.1) in the currently
available electroactive materials. Recently,
based on first principles calculations, we
predicted that there is a large electro-optic
(E-O) effect in a P(VDF-TrFE) based polymer when
undergoing a conformational change between the
polar and nonpolar forms (refractive index change
10). Indeed, we show that in P(VDF-TrFE-CFE)
terpolymer in which a small amount of chlorinated
termonomer is copolymerized with P(VDF-TrFE) to
modify the phase stability between different
conformations and create nano-polar phases, a
large E-O effect can be realized. Furthermore,
the terpolymer also exhibits large
electrostrictive strain (Figure 1). Utilizing the
P(VDF-TrFE-CFE) terpolymer, a 1.5D photonic
crystal a long period fiber grating (LPFG) is
under investigation in which a refractive index
change in the cladding can result in a large
tuning. Photonic crystals with defects modes will
be investigated in which the large tuning
available can produce switching in the guided
modes.
Figure 1. (a) FT-IR data under different electric
field, showing large refractive index change (the
shift of the inference pattern with field) (b)
Electrostrictive strain (c) Long period fiber
grating and simulated tuning due to index change
(d) Defect mode tuning in 2-D photonic crystals.
D. Jeong, Q. Chen, Y. Wang, Q. M. Zhang, V.
Gopalan, S. Yin (PSU) G. Kavarnos (URI and NUWC)