Isabelle Dicaire

Analytical modeling of the gas-filling dynamics in photonic crystal fibers

We present useful expressions predicting the filling time of gaseous species inside photonic crystal fibers. Based on the theory of diffusion, this gas-filling model can be applied to any given fiber geometry or length by calculating diffusion coefficients. This was experimentally validated by monitoring the filling process of acetylene gas in several fiber samples of various geometries and lengths. The measured filling times agree well, within +/-15%, with the predicted values for all fiber samples. In addition, the pressure dependence of the diffusion coefficient was experimentally verified by filling a given fiber sample with acetylene gas at various pressures. Finally, optimized conditions for gas-light interaction are determined by considering the gas flow dynamics in the design of microstructured fibers for gas detection and all-fiber gas cell applications.

Material Slow Light Does Not Enhance Beer-Lambert Absorption

We experimentally demonstrate that material slow light does not enhance Beer-Lambert absorption. A 26% group velocity reduction induced by stimulated Brillouin scattering in a gas-filled microstructured fiber caused no observable change in the measured absorption.

Probing molecular absorption under slow-light propagation using a photonic crystal waveguide

High-resolution infrared absorption spectroscopy of acetylene gas is demonstrated in a dispersion-engineered photonic crystal waveguide under slow-light propagation. Experimental enhancement factors of 0.31 and 1.00 are obtained for TE and TM polarization, respectively, for group indices ranging from 1.5 to 6.7. The dependence of molecular absorption on the evanescent electric-field distribution and on the group index under structural slow-light illumination is experimentally demonstrated and confirmed by time-domain simulations.

Spider silk : a novel optical fibre for biochemical sensing

Whilst being thoroughly used in the textile industry and biomedical sector, silk has not yet been exploited for fibre optics-based sensing although silk fibres directly obtained from spiders can guide light and have shown early promises to being sensitive to some solvents. In this communication, a pioneering optical fibre sensor based on spider silk is reported, demonstrating for the first time the use of spider silk as an optical fibre sensor to detect polar solvents such as water, ammonia and acetic acid.

Enhancing the light-matter interaction using slow light: towards the concept of dense light

A couple of experiments are here presented to clarify the impact of slow light on light-matter interaction. The experiments are designed, so that the process generating slow light and the probed light-matter interaction only present a marginal cross-effect. The impact of slow light on simple molecular absorption could be separately evaluated under either material or structural slow light propagation in the same medium and led to an entirely different response.

Structural slow light can enhance Beer-Lambert absorption

We experimentally demonstrate that structural slow light can enhance Beer-Lambert absorption. A 4-fold reduction of the group velocity induced by mere cavity effects has caused an increase of molecular absorption by 130%.

Optimized conditions for gas light interaction in photonic crystal fibres

This paper presents helpful expressions predicting the filling time of gaseous species inside photonic crystal fibres. Based on the theory of diffusion, our gas-filling model can be applied to any given fibre geometry or length by calculating diffusion coefficients. This was experimentally validated by monitoring the filling process of acetylene gas in several fibre samples of various geometries and lengths. The measured filling times agree well within ±15% with the predicted values for all fibre samples. In addition the pressure dependence of the diffusion coefficient was experimentally verified by filling a given fibre sample with acetylene gas at various pressures. Finally ideal conditions for gas light interaction are determined to ensure optimal efficiency of the sensor by considering the gas flow dynamics in the design of microstructured fibres for gas detection and all-fibre gas cell applications.

Suspended-core fibres as optical gas sensing cells: study and implementation

We have thoroughly studied and modelled many important aspects for the realization of gas-light interactions in suspended-core fibres. The fraction of the optical field propagating in holes could be calculated from the fibre geometry to predict the total absorption for a given molecular absorption line and fibre length. In addition, the gas diffusion into the fibre holes could be modelled to precisely anticipate the filling time for a given fibre geometry and length. This was experimentally validated by preparing several samples of suspended-core fibres showing various lengths. These samples were filled with acetylene at low pressure (< 50 mbar) and were hermetically and permanently sealed by fusion splicing each fibre end to a plain single-mode silica fibre. The adequacy between the modelling and the experimental results turned out to be excellent. Several physical parameters essential for the fibre characterization could be extracted from a set of measurements, sketching a specific metrological approach dedicated to this type of fibre. Finally, applications and advanced experiments that can be specifically carried out using these fibres are discussed.

Experimental verification of the effect of slow light on molecular absorption

The absorption of light by a gas molecule has been measured comparatively using light propagating in normal conditions and in a slow light regime. The experiment is designed to make the 2 measurements possible without modifying the interaction conditions, so that the sole effect of slow light is unambiguously observed. A 26% group velocity reduction induced by stimulated Brillouin scattering in a gas-filled microstructured fiber caused no observable change in the measured absorption, so that it is proved that material slow light does not enhance Beer-Lambert absorption and has a null impact on gas sensing or spectroscopic applications.

Exploring the Use of Native Spider Silk as an Optical Fiber for Chemical Sensing

A spider uses up to seven different types of silk, all having specific functions, as building material, weapon, and sensory organ to detect the presence of preys on its web. Recently, scientists have put under the limelight the extraordinary properties of this ancient material. Indeed, native silk, directly extracted from spiders, is a tough, biodegradable, and biocompatible thread used mainly for tissue engineering and textile applications. Blessed with outstanding optical properties, this protein strand can also be used as a bioresorbable optical fiber and is, moreover, intrinsically sensitive to chemical compounds. In this communication, the waveguiding properties of native dragline silk are assessed and a pioneering proof-of-concept experiment using pristine spider silk as an optical fiber to measure humidity content is demonstrated. The feasibility of using silk-based optical fiber chemical sensors is also discussed.