C. Jouanin

Optical and confinement properties of two-dimensional photonic crystals

We describe experiments on a quasi-two dimensional (2-D) optical system consisting of a triangular array of air cylinders etched through a laser-like Ga(Al)As waveguiding heterostructure. Such a configuration is shown to yield results very well approximated by the infinite 2-D photonic crystal (PC). We first present a set of measurements of the optical properties (transmission, reflection, and diffraction) of slabs of these photonic crystals, including the case of in-plane Fabry-Perot cavities formed between two such crystals. The measurement method makes use of the guided photoluminescence of embedded quantum wells or InAs quantum dots to generate an internal probe beam. Out-of-plant, scattering losses are evaluated by various means. In a second part, in-plane micrometer-sized photonic boxes bounded by circular trenches or by two-dimensional photonic crystal are probed by exciting spontaneous emission inside them. The high quality factors observed in such photon boxes demonstrate the excellent photon confinement attainable in these systems and allow to access the detail of the modal structure. Last, some perspectives for applications are offered.

Radiation losses of waveguide-based two-dimensional photonic crystals: Positive role of the substrate

Radiation losses occurring in photonic crystals etched into planar waveguides are analyzed using a first-order perturbation approximation. Assuming the incoherent scattering limit, the model indicates that losses diminish as the cladding index approaches the core index. A simple scheme is devised to include these losses into purely two-dimensional calculations by using an imaginary index. Such calculations are shown to agree with corresponding experimental transmission through near-infrared photonic crystals, reproducing the contrasting behavior of the “dielectric” and “air” band edges.

Group velocity and propagation losses measurement in a single-line photonic-crystal waveguide on InP membranes

Single-line photonic-crystal waveguides are investigated. Photoluminescence experiments and three-dimensional calculation are performed and allow a clear identification of the guided modes. The propagation properties of the latter (group velocity, losses) are extracted from photoluminescence spectra obtained on closed waveguides which act as linear cavities.

Triangular and hexagonal high Q-factor 2-D photonic bandgap cavities on III-V suspended membranes

We demonstrate InP-based triangular and hexagonal two-dimensional (2-D) planar photonic bandgap (PGB) crystal-based microcavities, positioned on a suspended membrane. Photoluminescence spectra of the structure clearly show well-resolved cavity modes, whose structure depends on the cavity shape. Q factors from 200 up to at least 900 are derived.

Experimental demonstration of complete photonic band gap in graphite structure

We experimentally demonstrate the existence of complete photonic band gap in graphite-type photonic crystals, thereby confirming theoretical predictions reported in previous studies. Experiments are performed at microwave frequencies from 27 to 75 GHz using hexagonal lattices of alumina rods. Transmission spectra measured for E (TM) and H (TE) polarizations and for different orientations of the two-dimensional lattice are found to be in excellent agreement with numerical calculations. The complete photonic band gap results from the overlap of E7 and H5 forbidden bands. Attenuations larger than 30 dB are measured for structures comprised of only four rows of alumina rods.

Existence of two-dimensional absolute photonic band gaps in the visible

Using the plane wave method, we study two two-dimensional structures that possess absolute photonic band gaps: the triangular and the graphite photonic crystals. We compare their convenience in achieving photonic crystals which inhibit the propagation of visible electromagnetic waves. We show that this is very difficult to obtain with a triangular structure because its gap is too narrow and its dimensions are too small to be fabricated. On the contrary, wider gaps and larger dimensions that can easily be etched makes graphite a much more appropriate structure.

Optical properties of two-dimensional photonic crystals with graphite structure

We present a study of the transmission coefficients of two-dimensional photonic band gap materials consisting of dielectric cylinders in graphite arrangement. By the study of the attenuation versus slab thickness, we determine the most efficient graphite configuration. We show how uncoupled modes create opaque regions for plane waves propagating along the Γ-P direction and widen the gap originating from the existence of forbidden photonic bands. Our results demonstrate that graphite structure is a promising geometry yielding an attenuation as strong as triangular structure with greater convenience in the fabrication at the submicronic scale.

Photonic crystal modelling using a tight-binding Wannier function method

Using the concept of generalized Wannier functions, adapted from the electronic theory of solids, we demonstrate for two-dimensional photonic crystals the existence of a localized state basis and we establish an efficient computational method allowing a tight-binding-like parameter free modelization of any dielectric structure deviating from periodicity. Examples of numerical simulations using this formalism, including modal analysis of microcavities and waveguides are presented to prove the ability of this approach to deal accurately with large scale systems and complex structures. A tight-binding version of the transfer matrix method is proposed to describe the transmission and reflection properties of finite samples of photonic crystals.

First Observations of 2D Photonic Crystal Band Structure in GaN–Sapphire Epitaxial Material

We report on the first characterisation of the band structure of two-dimensional triangular photonic crystals of air holes in an epitaxial group III nitride film. The structures were fabricated by electron beam lithography and reactive ion-etching.

Modelling of 3D photonic crystals based on opals

The construction of 3D photonic crystals with gaps in the visible or the near-infrared frequency range requires engineering of complex microstructures which are very difficult to realize by etching and micro-fabrication. Consequently, self-ordered systems such as synthetic opals are very promising. Synthetic bare opals are constituted by SiO2 spheres that organize themselves by a sedimentation process in a face centered cubic (fcc) arrangement. Using the plane wave method, we examine the photonic band structures of close-packed opal-based photonic crystals with an SiO2 (n = 1.5) matrix. The incomplete photonic band gaps at the X- and L-points have been studied which correspond to normally incident plane waves onto the (100) and (111) crystal planes. With the transfer matrix method, we model the transmission properties. We find that the incomplete gap at the L-point fully inhibits the transmission of waves propagating in the [111] direction for opal sample thicknesses that are easily obtainable. This property shows that bare opals could be good candidates for complete inhibition of transmission in the near-infrared and visible frequency range for given orientations.