D. Cassagne

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.

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.

Scattering method calculation of losses in two-dimensional photonic crystal slabs and waveguides

We describe a scattering matrix formalism used to model optical properties of two dimensional photonic crystals slabs. The determination of the scattering matrix poles allows us to simultaneously calculate the band structure and the corresponding losses of the electromagnetic modes, which contributes then to give a complete physical insight of the intrinsic properties of photonic crystal slabs. Using an in-plane supercell approach, a linear defect is also studied, leading to a complete evaluation of photonic crystal slab waveguides performances.

Characterization of photonic crystal cavities: investigation on the coupling between microresonators and waveguides

In this work, we report on properties of two-dimensional photonic crystal (2D PC) based microcavities fabricated on InP suspended membranes. Their characterization is based on the observation of diffracted photoluminescence (PL). Comparison is made with theoretical calculations obtained by a plane wave method. In section I, the samples fabrication and the characterization methods are described. In section II, we investigate the influence of the PC surfacic air filling factor (f) on the spectral properties of PC defect cavities. Section III is about the analysis of single line defect waveguides designed as a closed cavity. First results on the coupling between a cavity and a waveguide are lastly shown in section IV.

Optical Mirage in graded photonic crystals

We present the concept of graded photonic crystals (GPC) and show its ability to enhance the control of light propagation. It is shown that gradual modifications of photonic crystal parameters are able to curve the path of light. This light bending which depends on the wavelength and on the incident angle is examined through parametric studies of the iso-frequency curves. We demonstrate that photonic mirages originate from the same physical principles as the usual atmospheric mirages. Two optical components based on two-dimensional GPCs presenting a super bending effect and a large beam shifting are presented.

Enhancement of second harmonic in one-dimensional and two-dimensional epitaxial GaN-based photonic crystals

The second-harmonic field generated has been measured in reflection from the surface of one-dimensional and two-dimensional photonic crystals etched into a GaN layer. A very large second-harmonic enhancement is observed when simultaneously the incident beam at the fundamental frequency w excites a resonant Bloch mode and the second-harmonic field generated is coupled into a resonant Bloch mode at 2w. A smaller, but still substantially enhanced, second-harmonic generation level was also observed when the fundamental field was coupled into a resonant mode, while the second-harmonic field was not. By using calculated and experimental equifrequency surfaces, it is possible to identify the geometrical configurations that will allow quasi-phase matching to be satisfied - and observed experimentally in the available wavelength tuning range of the laser. The extended transparency window of III-nitride wide-bandgap semiconductors, coupled with large non linearities, is an appealing feature pointing towards the control and manipulation of light in photonic structures.

Second harmonic generation in GaN-based photonic crystals for single molecule investigations

III-Nitride semiconductors are promising nonlinear materials for optical wavelength conversion. However second harmonic generation in bulk GaN is weak because GaN is strongly dispersive. We show that appropriate photonic crystal patterning in GaN helps to overcome dispersion and provides quasi-phase matching conditions, resulting in substantially increased conversion efficiency obtained in a flexible manner. Enhancement factors of more than five orders of magnitude can be achieved. Use of photonic crystals makes it possible to reduce the effective observation volume, thereby opening new opportunities such as the study of single-molecule dynamics, even in high concentration solutions. We have demonstrated sharp enhancement of the fluorescence of single molecules immobilized on the surface of a GaN photonic crysta,l when the molecules are excited via the resonant second harmonic generation process.

Slow-light photonic crystal waveguides with ring-shaped holes on silicon-on-insulator

We discuss properties of line defect waveguides in planar photonic crystals with a triangular lattice of ring shaped holes (RPhCWs). We introduce slow-light RPhCWs with tailored dispersion properties and a compact and efficient coupler to efficiently inject light into such slow-light waveguide sandwiched between strip waveguides. We will also discuss the potential application of the RPhCW in biomedical applications and show experimental results on the RPhCW fabricated on the silicon-on-insulator substrate.

Designing waveguides and microcavities in hybrid architectures based on direct and inverse opals

In the past few years, self assembly colloidal structures based on opals have received large attention because they offer a cost-effective way of designing ultra-compact and efficient all-optical devices. In this study, we present various approaches to design waveguides and cavities in three-dimensional opal-based photonic crystals. Three practical designs with size suitable to telecommunication technologies at 1.55 μm are presented. First, we show that the creation of a hexagonal superlattice of defects in a direct monolayer of spheres yields the opening of a photonic band gap below the light line so that the inclusion of a linear defect in this structure enables the creation of a theoretically lossless waveguide. We also propose the design of a waveguide in a 2D-3D heterostructure, where a graphite lattice of rods is sandwiched between two inverse opal claddings. This structure enables single-mode waveguiding with a maximal bandwidth of 129 nm. Finally, we give the design of a linear cavity, whose quality factor is increased by a factor of 5 when surrounded by an inverse opal.

Linear waveguides in photonic crystals based on periodic arrangement of spheres

We demonstrate the possibility of waveguiding electromagnetic waves in a monolayer of dielectric spheres. While light is confined vertically by index guiding, a triangular superlattice monolayer of spheres was found to exhibit a photonic band gap below the light cone, thereby preventing light from propagating laterally. A gap map of this structure is presented. We propose a possible waveguide configuration that yields two non-degenerate defect modes lying within the photonic band gap. Such a structure may be particularly interesting for coupling light into self-assembled colloidal photonic crystals.