D. Labilloy

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.

Confined Electrons and Photons

The scientific fields of confined electrons and photons have become areas of major efforts worldwide. Their appeal originates in the many facets they offer in fundamental and applied science, in technology and device development, and to high technology, large-scale industries.

Use of guided spontaneous emission of a semiconductor to probe the optical properties of two-dimensional photonic crystals

We describe an experimental setup, which allows assessing the optical properties of two-dimensional photonic crystals combined with a waveguide geometry, and etched into a light-emitting (GaAs/InGaAs) semiconductor. By means of a guiding layer, the spontaneous emission of the material is used as a built-in source to probe the properties of the etched microstructure, conveniently compared to the usual measurement schemes. We show polarized transmission and coefficients largely depending on the photonic crystal orientation.

High-finesse disk microcavity based on a circular Bragg reflector

We made disk-shaped microcavities of approximately 10 μm2 in area in a GaAs/AlGaAs waveguide structure by etching deep vertical concentric trenches. The trenches form a circular Bragg-like reflector that confines light in the remaining two lateral dimensions. We demonstrate from photoluminescence excited in the waveguide the confinement of discrete disk modes whose wave vector is mainly radial, in contrast with whispering gallery modes. Their quality factors up to Q=650 indicate in-plane reflectivities approaching 90%. In the near infrared, this represents a demonstration of wavelength-scale light confinement based on photonic crystal effects in two dimensions.

Lasing properties of disk microcavity based on a circular Bragg reflector

The lasing properties of quantum well structures, where the cavity is defined in the plane of the wells by circular Bragg reflectors are investigated. Diffraction of the in-plane lasing modes into the vertical direction by the circular distributed Bragg reflector (DBR) allows the simultaneous measurement of near-field emission patterns and emission spectra, allowing unambiguous assignment of azimuthal quantum numbers to the lasing modes. The radial quantum number is determined by fitting the lasing spectrum to theory. Lasing is shown to occur in modes whose wave vector is mainly radial, confined by the circular DBR structure, rather than in whispering gallery type modes which are mainly azimuthal.

Photonic crystals in two-dimensions based on semiconductors : fabrication, physics and technology

Wavelength-scale periodically structured dielectrics in two or three dimensions, the so-called photonic crystals (PCs), may acquire outstanding electromagnetic properties, due to the appearance of a photonic gap and of the peculiar photon dispersion relations around such gaps. One may take advantage of these properties to elaborate novel devices based on microresonators, integrated mirrors, etc. In this paper, we start with a brief introduction to two-dimensional (2D) crystals and to defects in these crystals. We next discuss the physical and technological issues raised by some recent realisations. The incorporation of PCs into various devices is then examined, restricting ourselves to applications to light-emitters and integrated optics, a case for which radiation losses of PCs, are discussed.

Photonic Crystals for Light-Emitting Devices

Photonic crystals or photonic bandgap (PBG) structures promise to revolutionize optoelectronics by making anew class of highly efficient, low noise light emitters possible. We present data to show that their properties, in particular 2D systems, have now been fully characterized in the relevant semiconductor material system and at near-IR wavelengths, so effort can be redirected towards making active light emitters. As a first example, we present a semiconductor laser with one output mirror designed according to PBG principles. From threshold and efficiency data, we derive a reflectivity of 95 +/- 10 percent for this mirror, which underlines the viability of the PBG approach for practical devices. In order to realize the full potential of photonic crystal light emitters, however, important material issues need to be considered. Non- radiative recombination, for example, is a big problem when the photonic crystal is an integral part of the active region because of the relatively large areas of exposed surface. Several possible solutions to this problem are presented.

Directional effects in photonic bandgap cavities

We present here measurements on hexagonal cavities that have areas between 2.0 and 8.6 /spl mu/m/sup 2/. The 2D triangular lattice PBG mirrors are etched into a GaAs/AlGaAs waveguide heterostructure with 3 layers of InAs quantum dots at the centre of a 240 nm thick GaAs core. The photoluminescence of the InAs dots internally probes the cavity resonances and the small fraction of light that is scattered into air is collected and fed to an optical multichannel analyser. The hexagonal cavities defined by 2D photonic bandgap mirrors offer good in-plane confinement (R>90%; Q/spl sim/1000). Perturbations to the mirrors along specific directions probe the varying degree of confinement offered by the resonators and highlight the directional dependence of the mirrors. Calculations show that these directional effects can be used to integrate the microcavities with other photonic bandgap structures.