Danaë Delbeke

High-efficiency semiconductor resonant-cavity light-emitting diodes: a review

An overview of highly efficient resonant-cavity light-emitting diodes is presented. First, the basics of dipole emission in planar cavities are reviewed. From these, a number of design rules are derived. We point out some guidelines for comparison of high-efficiency light-emitting diodes, and use these to review the state-of-the-art devices in different material systems and at different wavelengths. We also discuss some advanced techniques based on gratings or photonic crystals to improve the efficiency of these devices.

Rigorous electromagnetic analysis of dipole emission in periodically corrugated layers: the grating-assisted resonant-cavity light-emitting diode

We study the grating-assisted light-emitting diode, an LED design for high brightness based on a resonant cavity containing one- or two-dimensionally periodically corrugated layers (grating). We give in detail a generally applicable electromagnetic analysis based on the rigorous coupled-wave theory to calculate the extraction efficiency of spontaneous emission in a periodically corrugated layer structure. This general model is then specified on the grating-assisted resonant-cavity LED, showing simulated efficiencies of more than 40%.

Intracavity generation of radially polarized CO2 laser beams based on a simple binary dielectric diffraction grating

We present experimental results on the intracavity generation of radially polarized light by incorporation of a polarization-selective mirror in a CO(2)-laser resonator. The selectivity is achieved with a simple binary dielectric diffraction grating etched in the backsurface of the mirror substrate. Very high polarization selectivity was achieved, and good agreement of simulation and experimental results is shown. The overall radial polarization purity of the generated laser beam was found to be higher than 90%.

Polarization-selective beam splitter based on a highly efficient simple binary diffraction grating

A polarization beam splitter (PBS) based on a giant-reflection to zero-order (GIRO) grating is presented. The GIRO grating is a simple binary diffraction grating with parameters chosen such that the excited optical modes in the grating interfere constructively and destructively at the respective interfaces. This interference results in high-zero-order reflection (>99%) with a high polarization-selective extinction ratio (+/-30 dB). The grating shows a low aspect ratio. The GIRO PBS is theoretically and experimentally shown to be an adequate PBS for use as an optical isolator in combination with a quarter-wave plate in a CO2-laser system.

A Noncontact Approach for the Evaluation of Large Artery Stiffness: A Preliminary Study

BACKGROUND The time from carotid to femoral pulse wave propagation (pulse transit time (PTT)) is required to estimate the carotid-femoral pulse wave velocity (PWV), a reliable index for evaluating large artery stiffness. METHODS In this work, we propose a novel, noncontact laser-based technique, named optical vibrocardiography (VCG), for evaluating PTT from synchronous recordings of the motion of the skin on the neck and the groin. These measurements, which have been demonstrated to be related to the radial displacement of the underlying blood vessels, were performed on 14 healthy subjects. As validation, applanation tonometry was performed to determine PTT between the carotid and the femoral artery. RESULTS PTT evaluated by VCG was not different from applanation tonometry (74.86 +/- 8.63 ms vs. 75.85 +/- 8.61 ms, P = 0.377). CONCLUSIONS Our preliminary results demonstrate that laser-based noncontact measurement in young healthy volunteers is feasible, and yields PTTs that are equivalent to those measured using arterial applanation tonometry. Its clinical application can overcome limitations inherent to a contact method like arterial tonometry.

Resonant-cavity light-emitting diodes: a review

An overview of planar resonant-cavity light-emitting diodes is presented. Letting spontaneous emission happen in a planar cavity will in the first place affect the extraction efficiency. The internal intensity distribution is not longer isotropic due to interference effects (or density of states effects). The basics of dipole emission in planar cavities will be shortly reviewed using a classical approach valid in the so called weak-coupling regime. The total emission enhancement or Purcell factor, although small in planar cavities, will be explained. The design of a GaAs/AlGaAs RCLED is discussed. We review the state-of-the-art devices in different semiconductor material systems and at different wavelengths. Some advanced techniques based on gratings or photonic crystals to improve the efficiency of these devices are discussed. RCLEDs are not the only candidates that can be used as high-efficiency light sources in communication and non-communication applications. They compete with other high-efficiency LEDs and with VCSELs. The future prospects of RCLEDs are discussed in view of this competition.

Transfer-printing-based integration of single-mode waveguide-coupled III-V-on-silicon broadband light emitters

We present the first III-V opto-electronic components transfer printed on and coupled to a silicon photonic integrated circuit. Thin InP-based membranes are transferred to an SOI waveguide circuit, after which a single-spatial-mode broadband light source is fabricated. The process flow to create transfer print-ready coupons is discussed. Aqueous FeCl3 at 5°C was found to be the best release agent in combination with the photoresist anchoring structures that were used. A thin DVS-BCB layer provides a strong bond, accommodating the post-processing of the membranes. The resulting optically pumped LED has a 3 dB bandwidth of 130 nm, comparable to devices realized using a traditional die-to-wafer bonding method.

Simultaneous Interrogation of Multiple Fiber Bragg Grating Sensors Using an Arrayed Waveguide Grating Filter Fabricated in SOI Platform

A novel fiber Bragg grating (FBG) interrogator is demonstrated based on an optimized arrayed waveguide grating (AWG) filter. The AWG response is optimized to achieve large crosstalk between the output channels, which allows simultaneous detection of multiple FBG peaks, using centroid signal processing techniques, without constraints on the minimum FBG peak spectral width. The measured interrogator resolution is 2.5 pm, and the total measurement range is 50 nm. The device is fabricated in a silicon-on-insulator platform and has a footprint of only 2.2 × 1.5 mm. A novel approach to minimize the polarization dependence of the device is proposed and experimentally demonstrated.

ESSenTIAL: EPIXfab services specifically targeting (SME) industrial takeup of advanced silicon photonics

ePIXfab brings silicon photonics within reach of European small and medium sized enterprises, thereby building on its track record and its integration into Europractice. To this end, ePIXfab offers affordable access to standardized active and passive silicon photonic IC and packaging technology, a path from design to manufacturing and hands-on training. Based on a consortium of major research institutes with silicon photonics expertise, ePIXfab reaches out to European industry and supports them to evaluate silicon photonics in the context of concrete applications and markets. In order to ensure low-cost, quick access and scalability to manufacturing, the maturity of silicon photonic IC technology is enhanced by setting up a library of generic devices, a level of process and device benchmarking and a well maintained design flow. For the first time, devices in a standard package are offered to facilitate measurements. Training programs on the IC and packaging services are also offered, including hands-on training in making designs. Maturity, standardization and sustainability are driven by a steadily growing worldwide user base.

Electrically pumped grating-assisted resonant-cavity Light-Emitting Diodes

The Grating -Assisted Light-Emitting Diode, an LED design for high brightness based on a resonant cavity containing 1D or 2D periodically corrugated layers (grating), is subject of this presentation. The diffractive properties of the wavelength scaled periodic grating integrated in one or both of the interfaces of the resonant-cavity, can redirect the laterally propagating resonant guided mode to an extractable direction. Because of the high power fraction in these guided modes, the use of such gratings can result in a higher extraction efficiency than a homogeneously layered RCLED, in which the trapped guided mode is a loss of power. In this scope, a generally applicable rigorous electromagnetic analysis based on the Coupled Wave Theory for diffractive gratings, has been developed to calculate the extraction efficiency of spontaneous emission in a periodically corrugated layer structure. This general model has been applied to a GA-RCLED emitting at 980 nm. The structure consisting of a hybrid bottom-emitting cavity with metallic grating and bottom DBR mirror, shows simulated efficiencies of over 40%. Electrically pumped devices have been processed. Experimental data and simulation results, such as polarization selective emission, spectral behavior and efficiency are compared and discussed.