  A tuning of the light transmission properties of 1D photonic structures
employing an external stimulus is very attracting and opens the way to the
fabrication of optical switches for colour manipulation in sensing, lighting,
and display technology. We present the electric field-induced tuning of the
light transmission in a photonic crystal device, made by alternating layers of
silver nanoparticles and titanium dioxide nanoparticles. We show a shift of
around 10 nm for an applied voltage of 10 V. We ascribe the shift to an
accumulation of charges at the silver/TiO2 interface due to electric field,
resulting in an increase of the number of charges contributing to the plasma
frequency in silver, giving rise to a blue shift of the silver plasmon band,
with concomitant blue shift of the photonic band gap. The employment of a
relatively low applied voltage gives the possibility to build a compact and
low-cost device. We also propose the fabrication of 1D photonic crystal and
microcavities employing a magneto-optical material as TGG (Tb3Ga5O12). With
these structures we can observe a shift of 22 nm with a magnetic field of 5 T,
at low temperature (8 K). The option to tune the colour of a photonic crystal
with magnetic field is interesting because of the possibility to realize
contactless optical switches. We also discuss the possibility to achieve the
tuning of the photonic band gap with UV light in photonic crystals made with
indium tin oxide (ITO).
