Francisco Meseguer

Large-scale synthesis of a silicon photonic crystal with a complete three-dimensional bandgap near 1.5 micrometres

Photonic technology, using light instead of electrons as the information carrier, is increasingly replacing electronics in communication and information management systems. Microscopic light manipulation, for this purpose, is achievable through photonic bandgap materials, a special class of photonic crystals in which three-dimensional, periodic dielectric constant variations controllably prohibit electromagnetic propagation throughout a specified frequency band. This can result in the localization of photons, thus providing a mechanism for controlling and inhibiting spontaneous light emission that can be exploited for photonic device fabrication. In fact, carefully engineered line defects could act as waveguides connecting photonic devices in all-optical microchips, and infiltration of the photonic material with suitable liquid crystals might produce photonic bandgap structures (and hence light-flow patterns) fully tunable by an externally applied voltage. However, the realization of this technology requires a strategy for the efficient synthesis of high-quality, large-scale photonic crystals with photonic bandgaps at micrometre and sub-micrometre wavelengths, and with rationally designed line and point defects for optical circuitry. Here we describe single crystals of silicon inverse opal with a complete three-dimensional photonic bandgap centred on 1.46 µm, produced by growing silicon inside the voids of an opal template of close-packed silica spheres that are connected by small ‘necks’ formed during sintering, followed by removal of the silica template. The synthesis method is simple and inexpensive, yielding photonic crystals of pure silicon that are easily integrated with existing silicon-based microelectronics.

Control of the Photonic Crystal Properties of fcc-Packed Submicrometer SiO2 Spheres by Sintering

We acknowledge M. Planes for his help during SEM characterization. This work was partially financed by the Spanish CICyT project No. MAT97-0698-C04 and the Fundacion Ramon Areces

Photonic crystal properties of packed submicrometric SiO2 spheres

In this letter, we investigate the optical properties of packed monodisperse silica submicron spheres by means of optical transmission measurements. The results are compatible with a three dimensional face centered cubic order in these solid structures. The lattice parameter of these structures, and therefore their optical properties, can be easily tuned through the sphere size (between 200 and 700 nm) thus covering the whole visible and near infrared spectrum.

CdS photoluminescence inhibition by a photonic structure

Here we present experimental evidence of the strong modification of the CdS photoluminescence when it is embedded in a SiO2 colloidal photonic crystal. When the emitted light matches a forbidden photonic band in the matrix, inhibition of the semiconductor photoluminescence is achieved. In this work we prove the effective control of this effect by means of the photonic lattice parameter of the host. CdS was grown by chemical bath deposition and its quality has been checked employing Raman spectroscopy and x-ray diffraction. Scanning electron microscopy is used to study the morphology of the composite.

Monodisperse silicon nanocavities and photonic crystals with magnetic response in the optical region

It is generally accepted that the magnetic component of light has a minor role in the light-matter interaction. The recent discovery of metamaterials has broken this traditional understanding, as both the electric and the magnetic field are key ingredients in metamaterials. The top-down technology used so far employs noble metals with large intrinsic losses. Here we report on a bottom-up approach for processing metamaterials based on suspensions of monodisperse full dielectric silicon nanocavities with a large magnetic response in the near-infrared region. Experimental results and theory show that silicon-colloid-based liquid suspensions and photonic crystals made of two-dimensional arrays of particles have strong magnetic response in the near-infrared region with small optical losses. Our findings might have important implications in the bottom-up processing of large-area low-loss metamaterials working in the near-infrared region.

A New Dielectric Metamaterial Building Block with a Strong Magnetic Response in the Sub-1.5-Micrometer Region: Silicon Colloid Nanocavities

A new dielectric metamaterial building block based on high refractive index silicon spherical nanocavities with Mie resonances appearing in the near infrared optical region is prepared and characterized. It is demonstrated both experimentally and theoretically that a single silicon nanocavity supports well-defined and robust magnetic resonances, even in a liquid medium environment, at wavelength values up to six times larger than the cavity radius.

Extraordinary Sound Screening in Perforated Plates

We report extraordinary effects in the transmission of sound through periodically perforated plates, supported by both measurements and theory. In agreement with recent observations in slit arrays, M. H. Lu et al. [Phys. Rev. Lett. 99, 174301 (2007)10.1103/PhysRevLett.99.174301], nearly full transmission is observed at certain resonant frequencies, pointing out similarities of the acoustic phenomena and their optical counterpart. However, acoustic screening well beyond that predicted by the mass law is achieved over a wide range of wavelengths in the vicinity of the period of the array, resulting in fundamentally unique behavior of the sound as compared to light.

Synthesis of inverse opals

Here we report different simple and inexpensive approaches to the fabrication of inverse opals originated from silica opal templates with sphere size in the range between 0.2 and 1.3 μm. The opal porous lattice is infiltrated with semiconductors (CdS, Ge, Si) as well as polymers by several methods such as chemical vapour deposition, chemical bath deposition, and hydrolysis. Afterwards the template is removed from the composite by a mild chemical etching method giving rise to an inverse opal. The periodicity of the template is chosen to guarantee that photonic gaps or pseudogaps are in the transparency region of the bulk-infiltrated material, which in the case of silicon and germanium can be easily integrated in the existing microelectronic technology.

Synthesis and photonic bandgap characterization of polymer inverse opals

Monodisperse silica colloids with diameters ranging from 200–500 nm aresynthesized following the Stober–Fink–Bohn method [47]. The as-synthesizedsilica sols are purified and redispersed in 200 proof ethanol by at least six centri-fugation/redispersion cycles. The methods described in our previous paper [36]are used to fabricate three-dimensionally ordered planar colloidal crystals withthickness ranging from one monolayer to 50 monolayers. In short, a glass slideis immersed vertically into ~15 mL purified silica sol (1% particle volume frac-tion) contained in a glass scintillation vial. After ethanol slowly evaporates, aniridescent film is formed on top of the glass slide. A large area (1 cm fl 3 cm)sample can be made over 3–5 days. After each single coating is deposited, thefilm is taken out of the silica sol and air-dried for 10 min and then dipped againinto another purified silica sol with differing particle size. This coating–drying–coating cycle can be repeated many times and each time the particle size can bearbitrary selected. The thickness of each crystalline sub-unit can be easily tunedby changing the concentration of the silica sol [36]. In this way, a layered struc-ture with an arbitrary pattern of sphere sizes can be assembled. Macroporouspolystyrene films are made by templating the colloidal crystal as describedbefore [18].SEM is carried out on a Philips XL30 ESEM. A CrC-100 sputtering systemhas been used to coat a thin layer of gold on the samples before SEM analysis.To reveal an edge appropriate for cross-sectional SEM analysis, the samples arescraped using a sharp razor blade and tilted 30–40˚. Transmission spectra areobtained by using an Ocean Optics ST2000 fiber optic UV–near-IR spectrome-ter. An Oriel model 6000 UV lamp with 68806 basic power supply is used topolymerize styrene.Received: October 5, 2000

Optical study of the full photonic band gap in silicon inverse opals

An optical study of the band structure of both silicon–silica composite and silicon inverse opals is presented. The study is aimed at demonstrating the development of a full photonic band gap for a system already revealed as paradigmatic. The characterization is based on the comparison between the band structure calculations and optical reflectance spectroscopy experiments. This study is carried out for various symmetry points in the Brillouin zone, some never explored before as K, (110) and W, (210). The results show that, in accordance with the band structure, there is a certain frequency range that produces a reflectance peak regardless of orientation and can be assigned to the band gap. Similarly all other reflectance peaks can be accounted for by other band structure features.