D. P. Gaillot

Photonic band tuning in two-dimensional photonic crystal slab waveguides by atomic layer deposition

The photonic bands of two-dimensional (2D) triangular lattice photonic crystal Si slab waveguides were statically tuned using low temperature atomic layer deposition (ALD) of TiO2. Angular dependent reflectance measurements of bare and coated devices were well fitted by three-dimensional finite-difference time-domain calculations. The technique not only allows the physics of photonic band effects in 2D photonic crystals to be systematically studied but also demonstrates large static tuning and precise fine-scale control over band frequency and dispersion, with a frequency tuning range of 12% and precision of 0.005% per ALD cycle. Band tuning to achieve zero group velocity is demonstrated.

Design of annular photonic crystal slabs

We present the design of realistic annular photonic-crystal (APC) structures of finite thickness aiming to obtain a complete photonic bandgap (PBG). The APC is composed of dielectric rods and circular air holes in a triangular lattice such that each rod is centered within each hole. The optical and geometrical values of the structure are studied, and the interplay between various design parameters is highlighted. The coupled role of the inner-dielectric-rod radius, material types, and slab thickness is investigated. It is shown that the slab thickness is vital to obtain a complete photonic bandgap below the light line, and the specific value of the inner-dielectric-rod radius to sustain the maximum PBG if the hole radius is fixed at proper value is found.

Dispersion control in two-dimensional superlattice photonic crystal slab waveguides by atomic layer deposition

The frequency and dispersion of photonic bands in two-dimensional triangular-based superlattice photonic crystal Si slab waveguides were manipulated using atomic layer deposition. The samples were conformally coated with increasing thicknesses of TiO2 and characterized by polarized angular-dependent reflectance measurements, which revealed shifts in the photonic band frequencies of 16% as well as continuous changes in band dispersion. The ability to tune toward zero group velocity by tuning band repulsion between same-polarization bands is demonstrated. Finite-difference time-domain calculations, combined with a dielectric weighting model, were used to assess the observed band and dispersion tuning.

Photonic band gaps in non-close-packed inverse opals

An advanced dielectric function has been designed to compute the photonic band structures of non-close-packed inverse opals fabricated using conformal infiltration and by a recently described sacrificial-layer technique. A model is proposed to correctly simulate complex dielectric structures resulting from conformal backfilled infiltrations. While large photonic band gaps (PBGs) and a reduced refractive index requirement (RIR) are predicted to occur in these inverse structures, the results also indicate a high degree of sensitivity to the dielectric/air network topology enabling fine PBG tailoring. Optimized structurally modified non-close-packed inverse opals with lower refractive indices offer enhanced optical properties compared to narrow PBGs observed in conventional inverse shell opals using high index materials such as silicon or germanium. Three-dimensional finite-difference time-domain computations predict that many experimentally achievable non-close-packed inverse structures exhibit significantl...

Tunable Bragg peak response in liquid-crystal-infiltrated photonic crystals

We report the dependence of the first-order Bragg peak position and width on the liquid-crystal and backbone refractive indices for liquid-crystal-infiltrated large-pore inverse shell opals, which offer increased volume for electro-optic infiltration. We also present the dependence of the photonic response on the template architecture or liquid-crystal volume fraction, which can be manipulated with a multilayer atomic layer deposition process. It is demonstrated from a three-dimensional finite-difference time-domain band structure and transmission-reflection coefficients computations that certain large-pore architectures exhibit an unusual optical response that cannot be explained by a classical Bragg peak theory. These structures potentially offer a pathway for all-optical photonic switching devices.

Low-loss left-handed metamaterials at millimeter waves

An omega-type multilayered metamaterial aimed at operating at millimeter wavelengths was characterized between 75 and 110 GHz (W-band). The fabrication involves a monolithic integration of planar arrays of broad-side coupled microresonators with a benzocyclobutene spacing layer printed onto quartz substrates. The frequency dependence of the transmittance shows a well-resolved transmission window centered around 80 GHz with a 10% fractional bandwidth and another one starting from 100 GHz, both displaying comparable high transmission levels. The left- or right-handed behavior is assessed by the comparison of the phase delay between two devices of different lengths and by tilted-incidence transmission experiments.

INVESTIGATIONS AND MIMICRY OF THE OPTICAL PROPERTIES OF BUTTERFLY WINGS

Structural color in Nature has been observed in plants, insects and birds, and has led to a strong interest in these phenomena and a desire to understand the mechanisms responsible. Of particular interest are the optical properties of butterflies. In this paper, we review three investigations inspired by the unique optical properties exhibited in a variety of butterfly wings. In the first investigation, conformal atomic layer depositions (ALDs) were used to exploit biologically defined 2D photonic crystal (PC) templates of Papilio blumei with the purpose of increasing the understanding of the optical effects of naturally formed dielectric architectures, and of exploring any novel optical effects. In the second study, it was demonstrated that faithful mimicry of Papilio palinurus can be achieved by physical fabrication methods through using breath figures to provide templates and ALD routines to enable optical properties. Finally, knowledge of the optical structure properties of the Princeps nireus butterfly has resulted in bioinspired designs to enhanced scintillator designs for radiation detection.

TUNING OF PHOTONIC CRYSTAL BAND PROPERTIES BY ATOMIC LAYER DEPOSITION

We report the application of atomic layer deposition to manipulate the dielectric architecture of conventional and superlattice two-dimensional photonic crystal waveguides fabricated in silicon. Conformal deposition of a second dielectric layer is shown to have a dramatic influence on the photonic band structure and produces unique effects that cannot be emulated in a single dielectric slab photonic crystal material. With additional dielectric coatings, a strong decrease in photonic band frequencies and change in band slope are observed, which for the lowest photonic states produces strong degeneracies. The capability, in principle, to tune the position of bands to within 0.005% accuracy, is demonstrated. Additionally, new features are observed when differential band shifts result in band-crossing and for which like polarizations activate perturbation mechanisms that result in local and strong band curvatures. The extremely strong band bending resulting from band-band interactions could have applications, in slow light devices, and provide a way to introduce non-linear effects into tunable photonic crystal structures.

LUMINESCENT AND TUNABLE 3D PHOTONIC CRYSTAL STRUCTURES

We report an investigation of luminescent and tunable photonic crystal structures formed by the infiltration and inversion of opal templates with high index and luminescent materials. Protocols are reported for the deposition of these materials and the properties of the resulting structures investigated by conventional structural and optical measurements. The properties of multi-layered and backfilled structures are reported and demonstrate the potential to modulate and statically tune the luminescence from photonic crystals.

Split Ring Resonator Arrays: from Microwave to Optics

We numerically and experimentally investigated the electromagnetic properties of split ring resonator arrays excited under normal and oblique incidence angles and aimed at operating from the microwave to the infrared spectral region. Through fullwave EM analysis, the electromagnetic response is demonstrated in the metamaterial regime (inclusion rather than periodicity effect) responsible for high rejection in the TE and TM modes transmission spectra which are measured via Vectorial Network Analysis (VNA) at microwave and by Fourier transform spectroscopy (FTIR) in optics.