Cédric Blanchard

Confinement of photons and control of their emission using surface addressable photonic crystal membrane

High index contrast periodic structures can be exploited to perform an arbitrarily adjustable spatio-temporal molding of light at the wavelength scale. This tight control of photons is obtained through a shaping of resonant modes and a suitable adjustment of their coupling with propagative modes. In this talk, surface addressable (or above the light line) Bloch modes in photonic crystal membranes (PCMs) will be investigated. The concepts governing the properties of these modes will be first presented. It will be demonstrated that simple models can be considered to understand their behavior and, more specifically, their ability to capture photons during the desired lifetime. Bloch modes with a very large band width or a very high Q factor can be easily designed this way. The wide application range of these PCMs will be illustrated by different devices. Low Q Bloch modes will be first used as efficient and broadband reflectors and exploited to realize compact and efficient vertical cavity lasers with unprecedented functionalities. In addition, it will be shown that this kind of mirrors can be bent in order to confine photons in the 3 directions even in low index materials, opening the way to a new class of emitters and sensors. Finally, the exploitation of high Q Bloch modes to design highly directional thermal emitters with wavelength selectivity will be presented.

Automatic evaluation of the sinus of Valsalva from cine-MRI in patients with dilated aortic root

Methods Cine-MR images were acquired using a breath-hold ECG-gated steady-state free-precession sequence (TR = 1.54 ms, TE = 1.49 ms, 17 lines per segment, a = 65°, slice thickness = 5 mm, temporal resolution = 27 msec/ images, spatial resolution varied from 0.7 mm to 1.6 mm per pixel, according to the patient examination). The acquisition plane was oriented in aortic valve crosssection. Manual processing on the whole images remains a reliable but time-consuming solution. Then, an automatic method based on mathematical morphology, combining numerical geodesic reconstruction with RANSAC method to estimate area was elaborated in order to segment the aortic root. Relevant points, such as the commissures, the cusps and the centre of the SV are also automatically detected by using a distance transform for centre estimation and a radial study to find extremum radii points. Our method was tested on 13 examinations of patients with SV dilatation (2 women and 11 men, age: 54±11 years, body surface area: 1.97±0.19 m). Considering all images, the maximum distance between two cusps determines the maximum radius. Manual measurement of this parameter was made by an experienced observer. Results There is an excellent correlation between manual and automatic measurements (r= 0.93; y = 0.93 x + 4.0; p<10). The corresponding Bland-Altman study shows an excellent concordance between the two approaches (mean of the differences = 0.5 mm and standard deviation of the differences = 2.3 mm). Figure 1.

Automatic measurement of the sinus of Valsalva by image analysis

BACKGROUND AND OBJECTIVES Despite the importance of the morphology of the sinus of Valsalva in the behavior of heart valves and the proper irrigation of coronary arteries, the study of these sinuses from medical imaging is still limited to manual radii measurements. This paper aims to present an automatic method to measure the sinuses of Valsalva on medical images, more specifically on cine MRI and Xray CT. METHODS This paper introduces an enhanced method to automatically localize and extract each sinus of Valsalva edge and its relevant points. Compared to classical active contours, this new image approach enhances the edge extraction of the Sinus of Valsalva. Our process not only allows image segmentation but also a complex study of the considered region including morphological classification, metrological characterization, valve tracking and 2D modeling. RESULTS The method was successfully used on single or multiplane cine MRI and aortic CT angiographies. The localization is robust and the proposed edge extractor is more efficient than the state-of-the-art methods (average success rate for MRI examinations=84% ± 24%, average success rate for CT examinations=89% ± 11%). Moreover, deduced measurements are close to manual ones. CONCLUSIONS The software produces accurate measurements of the sinuses of Valsalva. The robustness and the reproducibility of results will help for a better understanding of sinus of Valsalva pathologies and constitutes a first step to the design of complex prostheses adapted to each patient.

Tight control of light trapping in surface addressable photonic crystal membranes: application to spectrally and spatially selective optical devices(Conference Presentation)

Surface addressable Photonic Crystal Membranes (PCM) are 1D or 2D photonic crystals formed in a slab waveguides where Bloch modes located above the light line are exploited. These modes are responsible for resonances in the reflection spectrum whose bandwidth can be adjusted at will. These resonances result from the coupling between a guided mode of the membrane and a free-space mode through the pattern of the photonic crystal. If broadband, these structures represent an ideal mirror to form compact vertical microcavity with 3D confinement of photons and polarization selectivity. Among numerous devices, low threshold VCSELs with remarkable and tunable modal properties have been demonstrated. Narrow band PCMs (or high Q resonators) have also been extensively used for surface addressable optoelectronic devices where an active material is embedded into the membrane, leading to the demonstration of low threshold surface emitting lasers, nonlinear bistables, optical traps... In this presentation, we will describe the main physical rules which govern the lifetime of photons in these resonant modes. More specifically, it will be emphasized that the Q factor of the PCM is determined, to the first order, by the integral overlap between the electromagnetic field distributions of the guided and free space modes and of the dielectric periodic perturbation which is applied to the homogeneous membrane to get the photonic crystal. It turns out that the symmetries of these distributions are of prime importance for the strength of the resonance. It will be shown that, by molding in-plane or vertical symmetries of Bloch modes, spectrally and spatially selective light absorbers or emitters can be designed. First proof of concept devices will be also presented.

Mid-infrared integrated photonics on a SiGe platform

The mid-infrared is of great interest for a huge range of applications such as medical and environment sensors, security, defense and astronomy. I will give a broad overview of the different activities recently launched in INL Lyon, in close collaboration with several French and Australian institutions, under the umbrella of “Mid-IR integrated photonics” with a particular focus on novel integrated sources for the Mid-IR exploiting a nonlinear SiGe platform.

Perturbation model for the control of the spectral properties of high contrast gratings

The comprehension and manipulation of the spectral characteristics of photonic structures is of great interest for a vast bunch of applications, in particular for energy efficiency. In this paper we focus on a perturbation model capable of providing insight and control on the resonances that are supported by high index contrast gratings.

Photonic crystal mirror based optical microsources for silicon photonics

Surface-addressable photonic crystal membrane resonators are shown to constitute generic enablers for 3D harnessing of light. Conceptual approaches used to analyse their optical properties are briefly presented and leads to simple design rules. Application to VCSELS is emphasized

A new morphological tool to extract blood vessels in cross sectional MRI

In this paper, we propose a new method of mathematical morphology called Aurora transform. This is a geodesic reconstruction that only spreads in radial orientations from a center. Thanks to this method, star domains such as blood vessels in cross sectional planes are extracted even if these regions are often inhomogeneous or some parts of their edges are not drawn very well. This method has been successfully applied to extract the edges of the aortic root, the ascending and the descending aorta in cross sectional cine-MRI. It has been then compared to the use of some active contours.