Three-dimensional photonic crystals: opals

Opals are three-dimensional (3D) photonic crystals consisting of dielectric spheres arranged in a fcc lattice. Artificial opals can be prepared by self-assembling of, e.g., silica or polystyrene spheres in a colloidal solution. These are the so-called direct opals, which possess a photonic band gap along the [111] or G-L direction and are interesting for the study of light propagation, diffraction, scattering, focusing etc in a 3D geometry. Inverse opals can be prepared by filling the silica template by a high refractive-index material (usually Si or TiO2) and removing the template, yielding a structure which in principle supports a complete photonic band gap.

Our research is concerned with experimental and theoretical studies of the optical properties of opals in the low energy region (close to the fundamental stop band) as well as in the high-energy region (close to the second-order stop band and above), where Bragg diffraction effects related to high-order crystalline planes come into play. Opals preparation and their infiltration by luminescent polymers is also pursued. On the experimental side, we studied optical properties by angle-resolved reflectance and related the presence of weak structures at large angles of incidence to the occurrence of Bragg diffraction effects. We determined the effective refractive index (real and imaginary parts) as a function of frequency by means of white-light interferometry and demonstrated the occurrence of slowing-down as well as superluminal propagation effects within the first- and second-order stop bands. Also, we demonstrated the presence of a three-fold (instead of a six-fold) symmetry axis in angle-resolved transmittance from micro-domains in thin opal films and related this macroscopic symmetry to the distinction between GLK and GLU orientations in the microscopic structure. On the theoretical side, we developed an accurate simulation method of the optical properties based on a Fourier-modal (scattering matrix) formalism in which the spheres are discretized into cylindrical slices.


L.C. Andreani, A. Balestreri, D. Comoretto, M. Galli, J.F. Galisteo-Lopez, M. Liscidini, F. Marabelli, M. Patrini


Department of Chemistry and Industrial Chemistry, University of Genova

Materials and Processes for Micro & Nano Technologies, Polytechnic of Torino

Instituto de Ciencia de Materiales de Madrid (ICMM), CSIC, Madrid

Instituto de Ciencia de Materiales de Sevilla (ICMS), CSIC, Sevilla


MIUR Cofin 2004 "Silicon-based photonic crystals for the control of light propagation and emission"

MIUR-FIRB 2003-2005 "Miniaturized systems for electronics and photonics"

MIUR Cofin 2002 "Silicon-based photonic crystals: technology, optical properties and theory"

PhD Theses:

A. Balestreri, "Optical properties of opal-based photonic crystals" (University of Pavia, 2007)

Key publications:

Optical response with three-fold symmetry axis on oriented microdomains of opal photonic crystals,

L. C. Andreani, A. Balestreri, J. F. Galisteo-López, M. Galli, M. Patrini, E. Descrovi, A. Chiodoni, F. Giorgis, L. Pallavidino, and F. Geobaldo,

Phys. Rev. B 78, 205304 (2008). PDF

Slow to superluminal light waves in thin 3D photonic crystals,

J. F. Galisteo-López, M. Galli, A. Balestreri, M. Patrini, L. C. Andreani, and C. López,

Opt. Express 15, 15342-15350 (2007). PDF

Optical properties and diffraction effects in opal photonic crystals,

A. Balestreri, L.C. Andreani, and M. Agio,

Phys. Rev. E 74, 036603 (2006). PDF

Effective refractive index and group-velocity determination of three-dimensional photonic crystals by means of white-light interferometry,

J.F. Galisteo-López, M. Galli, M. Patrini, A. Balestreri, L.C. Andreani, and C. López,

Phys. Rev. B 73, 125103 (2006). PDF

Band structure and optical properties of opal photonic crystals,

E. Pavarini, L.C. Andreani, C. Soci, M. Galli, F. Marabelli, and D. Comoretto,

Phys. Rev. B 72, 045102 (2005). PDF