Hernan Miguez

Opal Circuits of Light—Planarized Microphotonic Crystal Chips

We present a novel technique coined directed evaporation-induced self-assembly (DEISA) that enables the formation of planarized opal-based microphotonic crystal chips in which opal crystal shape, size, and orientation are under synthetic control. We provide detailed synthetic protocols that underpin the DEISA process and formulate directed self-assembly strategies that are suited for the fabrication of opal architectures with complex form and designed optical functionality. These developments bode well for the utilization of opal-based photonic crystals in microphotonic crystal devices and chips.

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.

Towards the synthetic all-optical computer: science fiction or reality?

The global race for the optically integrated photonic chip is driven by the prospective that miniaturization of optical devices and enhanced chip functionality may revolutionize the manufacture of optical circuits, and the futuristic dream of the all-optical computer may come true. The aim of this article is to take a brief yet critical look at some developments in microsphere self-assembly of colloidal photonic crystals and their technological potential from the perspective of research results that have recently emerged from our materials chemistry group. The focus of the discussion centers on the provocative vision of the “colloidal photonic crystal micropolis”, Fig. 1, which depicts the direction in which the colloidal photonic crystal research of our materials chemistry group is heading. It is intended to bring to the forefront the pointed question of whether the most recent versions of colloidal photonic crystals and their integration on chips, developed in our laboratory, can rise to the stringent specifications of structural perfection and optical quality, functionality and complexity that will be demanded for photonic crystal optical devices and optical circuits touted for next generation all-optical chip and telecommunication technologies.

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 properties of a three-dimensional silicon square spiral photonic crystal

Abstract We report the fabrication and optical characterization of a tetragonal square spiral photonic crystal with a three-dimensional relative band gap of approximately 10% using the glancing angle deposition (GLAD) technique. This thin film structure is produced in a one-step process that is highly versatile as a wide range of crystal structures can be created simply through the variation of deposition parameters. Measurements indicate upper and lower frequency band edges at vacuum wavelengths of 2.50 and 2.75xa0μm, in the infrared region of the spectrum.

Barium Titanate Inverted Opals—Synthesis, Characterization, and Optical Properties

Barium titanate inverted opals with powder and film morphologies were synthesized from barium ethoxide and titanium isopropoxide in the interstitial spaces of a polystyrene opal. This procedure involves infiltration of precursors into the interstices of the polystyrene opal template followed by hydrolytic polycondensation of the precursors to amorphous barium titanate and removal of the polystyrene opal by solvent extraction or calcination. In-situ variable temperature powder X-ray diffraction and micro-Raman spectroscopy allow one to observe the thermally induced transformation of the as-synthesized amorphous barium titanate inverted opal to the nanocrystalline form. In this way, a nanocrystalline barium titanate inverted opal can be engineered as either the cubic or tetragonal polymorph. Control of this process is key to the practical realization of a room-temperature stable ferroelectric barium titanate inverted opal that can be thermally tuned through the ferroelectric–paraelectric transition around the Curie temperature. Optical characterization demonstrated photonic crystal behavior of the inverted barium titanate opals and results were in good agreement with photonic band structure calculations. The synthesis of optical quality ferroelectric barium titanate inverted opals provides an opportunity to electrically and optically engineer the photonic band structure and the possibility of developing tunable three-dimensional photonic crystal devices.

Band spectroscopy of colloidal photonic crystal films

Here we report on the optical properties associated with photonic bands of three-dimensional photonic colloidal crystals. Optical spectroscopy analysis shows fluctuations of the transmitted and reflected light intensity in photon frequency regions where no stop bands open up. The different optical features observed at low and high photon energy ranges are analyzed in terms of the band structure of the crystal. A relationship is found between dispersion of the bands and the features observed experimentally. On these premises, we show it is possible to map the higher-energy band region along nonprincipal directions of the first Brillouin zone by transmission spectroscopy.

Vapor swellable colloidal photonic crystals with pressure tunability

Polyferrocenylsilane gel photonic crystals have been reversibly swollen using solvent vapors, and exhibit precise pressure tunability over a wavelength range of greater than 100 nm.

Replicating the Structure of a Crosslinked Polyferrocenylsilane Inverse Opal in the Form of a Magnetic Ceramic

Crosslinked polyferrocenylsilane inverse opals have been prepared by the thermal ring-opening polymerization of spirocyclic [1]silaferrocenophanes confined within the interstitial void spaces of silica crystal colloidal templates. These organometallic polymer inverse opals were converted to magnetic ceramic replicas through pyrolysis at 900u2009°C in high yields.

Photonic crystals for laser action

In this study we inspect the possibilities of using photonic crystals and, in particular, opal structures as hosts for active materials with the view to achieve laser action in solid state devices. We then show our recent work in the characterization of both the opal structure as a host and an active material. Our characterization of the opal is done by both optical and microscopy techniques and results in the evidence of their fcc structure which is appropriate for the purpose. Inhibition of the spontaneous luminescence is demonstrated with a dye embedded in the structure.