Photonic crystal waveguides for coarse-selectivity devices

We discuss devices based on photonic crystal planar waveguides for use as wavelength-selective applications via the mini-stopband extraction mechanism. We present experimental data for the core of a compact demux system. We show that spatial and spectral behaviours are as intended from coupled-mode theory, as well as from the finite-difference time-domain approach. Finally, we propose architectures with large crosstalk and some inherent fabrication-related advantages achieved by duplicating the basic multimode waveguide and using it as a spectral filter.     

GaAs photonic crystal cavity with ultrahigh Q: microwatt nonlinearity at 1.55 microm

We haves realized and measured a GaAs nanocavity in a slab photonic crystal based on the design by Kuramochi et al. [Appl. Phys. Lett. 88, 041112 (2006)]. We measure a quality factor Q=700,000, which proves that ultrahigh Q nanocavities are also feasible in GaAs. We show that owing to larger two-photon absorption in GaAs nonlinearities appear at the microwatt level and will be more functional in gallium arsenide than in silicon nanocavities.     

Nanostructured silicon geometries for directly bonded hybrid III–V-silicon active devices

We discuss geometries with nanostructured cladding for active InP/silicon structures made by hetero-epitaxial bonding, which means that InP is directly bonded to silicon from a silicon-on-insulator without any intermediate layer. Such a cladding features low-index confinement and adds thermal sinking channels to those practised on the InP side. The first approach is a one-dimensional effective medium viewpoint, easily showing why grooves parallel to the waveguide are better. Then, two dimensional nanostructures are examined and found to perform better, given etching constraints. A more sophisticated geometry balancing thermal and optical confinement merits is then introduced thanks to a flip-flop algorithm.     

Integration of grating couplers with a compact photonic crystal demultiplexer on an InP membrane

We demonstrate the integration of a 30% efficient grating coupler with a compact photonic crystal wavelength demultiplexer (DeMUX). The DeMUX has seven output channels that are spaced 10 nm apart and is aimed at coarse WDM applications. The integrated devices are realized on a high-index-contrast InP membrane using a simple benzocyclobutene wafer bonding technique. Cross talks of -10 to -12 dB for four channels 20 nm apart are obtained without optimization.     

High extraction efficiency,laterally injected,light emitting diodes combining microcavities and photonic crystals

The use of photonic crystals (PCs) for realistic light emitting diodes (LEDs) is discussed, given the constraints of planar semiconductor technology. A viable route for the fabrication of high-efficiency high-brightness electrically injected LEDs is presented. The starting point is a top-emitting microcavity using a single Alox Bragg mirror. The active area is surrounded by two-dimensional PCs, namely arrays of air rods etched through the top layers; injection of the electrons is achieved through the crystals. Design rules for PCs as efficient out-couplers are detailed. The building blocks are assessed experimentally, and we show that promising results are at hand.     

Compact and fault-tolerant photonic crystal add-drop filter

We propose an add-drop filter consisting of two adjacent waveguides carved into a two-dimensional photonic crystal that is etched through a standard guiding structure. This filter is based on distributed energy transfer via the frequency-selective intermediate conversion of the fundamental guided mode to a high-order low-group-velocity mode. This geometry circumvents the fabrication sensitivity on the single-hole scale of previous cavity-based designs. Combining distributed energy transfer and reduced group velocity preserves compactness. The design is analytically optimized with a coupled-mode approach.     

Spontaneous emission enhancement at a photonic wire miniband edge

In a multimode photonic-crystal waveguide, we observe strong enhancement of the photoluminescence of embedded quantum dots at the edges of the so-called mini-stopband that were opened by Bragg diffraction between two guided modes. Taking into account light collection, we relate this observation to the singular photon density of states that is characteristic of a one-dimensional photon system. Furthermore, we quantify by how much the radiation losses smooth the divergence. For the first time to our knowledge, a clear account of the control of spontaneous emission in a one-dimensional system is thus demonstrated.     

Disorder-induced losses in planar photonic crystals

The phenomenological approach introduced by Benisty [Appl. Phys. Lett. 76, 532 (2000)] to model out-of-plane radiation losses in planar photonic crystals with a low vertical refractive index contrast is extended to the case of in-plane disorder. The model is experimentally validated by means of optical measurements on GaAs-based structures. For the present fabrication techniques the disorder-induced contribution is found to be negligible compared with the other loss mechanisms.     

Spontaneous emission enhancement of quantum dots in a photonic crystal wire

Photonic wires are the simplest extended low-dimensional systems. Photonic crystal confinement confers them a divergent density of states at zero-group-velocity points, which leads to enhancement of spontaneous emission rates [D. Kleppner, Phys. Rev. Lett. 47, 233 (1981)10.1103/Phys. Rev. Lett. 47.233]. We experimentally evidence, for the first time, the spectral signature of these Purcell factor singularities, using the out-of-plane emission of InAs quantum dots buried in GaAs/AlGaAs based photonic crystal based wire. Additionally, in-plane collection at the wire exit shows large enhancements of the signal at some of the density of states singularities.     

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.