C. Weisbuch

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.

Low-loss channel waveguides with two-dimensional photonic crystal boundaries

We have used transmission measurements to estimate the propagation loss of submicron channels defined in two-dimensional photonic crystals patterned into a Ga(Al)As waveguide. The measured propagation loss of the fundamental mode is indistinguishable from the material absorption, setting an upper limit of 50 cm−1 (2 dB per 100 μm). We also find that, provided the etching is deep enough, propagation losses of these photonic crystal waveguides are lower than those of ridge waveguides etched in the same run.

Miniband transmission in a photonic-crystal coupled-resonator optical waveguide

We demonstrate in the near infrared the coupled-resonator optical waveguide (CROW) concept that was recently proposed by Yariv et al. [Opt. Lett.24, 711 (1999)]. Two-dimensional photonic crystals have been used to define, in a GaAs-based waveguiding heterostructure, an array of micrometer-sized hexagonal cavities coupled through thin walls. With the photoexcitation of InAs quantum dots as an internal source, the transmission spectra of the coupled resonators show marked minibands and minigaps, in agreement with theoretical predictions.

Impact of planar microcavity effects on light extraction-Part II: selected exact simulations and role of photon recycling

In this paper we use an exact calculation of dipole emission modifications in an arbitrary multilayer structure to obtain the extraction efficiency from realistic planar microcavities, additional insights gained through this exact approach compared to the simplified one of Part I of this paper [see ibid., p. 1612, 1998] are first discussed in the case of a dielectric slab. We next optimize for the extraction purpose asymmetric cavities bounded by metal on one side and dielectric mirrors on the output side for any pair of material indices in a broad range (n=1.4-4). The decrease of extraction when taking into account relative linewidths of the source of a few percent is shown to be moderate, allowing the large enhancements of monochromatic light to be maintained in many useful cases. The fractions of power emitted into guided modes, leaky modes, etc., are detailed. The beneficial role of possible photon recycling (reabsorption of emitted photons by the active layer) on extraction efficiency is evaluated using the fractions of power in guided and leaky modes. Extraction efficiencies in the 50% range are predicted for optimized, hybrid, planar metal-semiconductor structures for a wide range of active materials and wavelengths. We show that exact calculations justify the simple model used in Part I evaluating the extraction efficiency of a microcavity-based light-emitting diode as 1/m/sub c/ where m/sub c/ is the effective cavity order.

Coupled semiconductor microcavities

The coupled semiconductor microcavity is a system in which there are three oscillators, two photonic and one electronic (quantum well excitons). It develops three strongly coupled modes which allow a wide design range for a variety of optoelectronic applications. The MBE grown structure is comprised of two λ sized GaAs cavities containing InxGa1−xAs quantum wells, separated by a common mirror. Reflectivity measurements show both two coupled photon mode behavior and three coupled mode behavior, i.e., two photon and one exciton, depending on the relative position of the exciton resonance.

Omnidirectional and compact guided light extraction from Archimedean photonic lattices

We address the issue of extracting light from a waveguide towards air in a compact way for randomly oriented guided waves. The goal is to enhance the extraction efficiency of light-emitting diodes while retaining planar processing. For incidence-angle-independent extraction, preferred lattice designs appear to possess a ring-shaped Fourier transform. We demonstrate this property for an Archimedean lattice. This system is the outer part of a resonant-cavity light-emitting diode. Data suggest that ∼40% extraction efficiency is at hand in a planar top-emitting device retaining its substrate.

DUAL-WAVELENGTH LASER EMISSION FROM A COUPLED SEMICONDUCTOR MICROCAVITY

We report photopumped operation of a monolithic coupled semiconductor microcavity laser. The structure consists of two λ-sized GaAs vertical cavities, one on top of the other, coupled together through a common mirror. Due to a wedge induced into each cavity, the detuning between the cavities can be continuously varied when moving across the sample. Depending on the detuning, laser action is simultaneously achieved at two different wavelengths or occurs only at one wavelength. At resonance, we observe coupled dual-wavelength laser emission at two widely spaced wavelengths (13 nm) with the same threshold and same dependence on pump power.We report photopumped operation of a monolithic coupled semiconductor microcavity laser. The structure consists of two λ-sized GaAs vertical cavities, one on top of the other, coupled together through a common mirror. Due to a wedge induced into each cavity, the detuning between the cavities can be continuously varied when moving across the sample. Depending on the detuning, laser action is simultaneously achieved at two different wavelengths or occurs only at one wavelength. At resonance, we observe coupled dual-wavelength laser emission at two widely spaced wavelengths (13 nm) with the same threshold and same dependence on pump power.

Coupled guide and cavity in a two-dimensional photonic crystal

We demonstrate, in a planar two-dimensional (2D) configuration, in the optical regime a clear association of two photonic crystal elements and the ability to produce a low-loss coupled system. A channel waveguide is brought to between two and five crystal rows (450 to 1126 nm) from a 2D microcavity fabricated in a GaAs/AlGaAs waveguide. We probe these two elements individually and explore their interaction.

Overview of fundamentals and applications of electrons, excitons and photons in confined structures

Abstract The advent of electron- and photon-confined structures has led to a wealth of novel physical phenomena and device applications. While the 1980s were devoted to 2D electronic quantum wells (QWs), the past decade has seen a flourish of 1D quantum wire (QWR) and 0D quantum dot (QD) studies. While remarkably sharp features were observed at the single QD level, fabrication of fluctuation-free ensembles of QDs remains a stumbling block for applications. On the other hand, more recently emerged photon-confined structures in the form of planar cavities, micropillars, photonic crystals have seen many achievements such as the Purcell effect, modification of light extraction efficiency, strong light–matter coupling. Advanced effects such as thresholdless lasers, squeezed photon generation, quantum condensation remain to be demonstrated. Although it might appear as a side effect, the interplay of electronic and photonic dimensionalities yields a profound insight on light–matter interaction.