Till recently, no two- and three-dimensional structures have been known to yield a practical complete photonic bandgap (CPBG) for refractive indices available below infrared wavelengths, mainly because of the simultaneous requirements on the dielectric contrast and the modulation (the total number and the length of periodicity steps).We show a promising new route to achieve a CPBG below the infrared wavelengths, using a periodic arrangements of scatterers of material with Drude-like behaviour of the dielectric function. In two-dimensions, for a simple square lattice several CPBG's open and a relative gap width $g_w$ (gap width to the midgap frequency ratio)can be as large as $34\%$ even if the host dielectric constant $\varepsilon_h=1$. In three-dimensions, despite of recent claims, simple face-centered-cubic (fcc) structures of spheres are shown to yield a tunable CPBG in the region from GHz down to optical wavelengths using currently available experimental techniques. Up to four CPBG's can open in the frequency region $0.6\omega_p \leq \omega \leq 1.1 \omega_p$, with $\omega_p$ being the plasma frequency, where the sphere material bulk absorption is assumed to be small (a nonabsorptive window). The relative gap width $g_w$ can be as large as $10\%$even if the host refractive index $n_h=1$. These properties are rather robust against coating of such spheres with a semiconductor or an insulator. Using different coatings and supporting liquids, the width and midgap frequency of a CPBG can be tuned considerably. These results open a door to fabrication of CPBG structures in the visible using colloidal crystals. In the latter case, CPBS's can be switched on and off by applying an electric field, since the latter allows to switch in ms from an fcc colloidal crystal to a body centered tetragonal (bct) crystal: a so-called martensitic transition.
(Work done in collaboration with Han van der Lem)
References:
A. Moroz, Three-dimensional complete photonic-bandgap structures in the
visible,
Phys. Rev. Lett. {\bf 83}, 5274-5277 (1999);
A. Moroz, Photonic crystals of coated metallic spheres, submitted to
Europhys. Lett.;
H. van der Lem and A. Moroz, On a silver route to two-dimensional
complete photonic band gap structures below infrared wavelengths,
submitted to J. Opt. A: Pure Appl. Opt.