Serge Caron

Distributed fibre optics polarimetric chemical sensor

A new distributed fibre optic chemical sensor based on evanescent wave polarimetric interferometry is proposed with the underlying objective to apply the technology to gas chromatography. It allows real-time monitoring of the displacement of a chemical substance along a capillary. Theoretical analysis, modelling and fabrication of a special fibre containing an off-axis capillary is presented. Proof of the principle is experimentally demonstrated with liquid droplets.

Photodarkening and partial photobleaching: application to dichromated gelatin.

Photodarkening or partial photobleaching of photochromic solid media is described by means of an approximated analytical equation. The equation shows that the effective rate of the photochemical reaction is proportional to the square root of the final transmittance of the illuminated layer. The model is applied to describe the photodarkening of dichromated gelatin at 488 nm.

Vapor zone velocities measurement using a capillary optical fiber sensor with an application to gas chromatography

A fiber optic sensor has been used for real-time measurement of the migration rates of all the compounds in a mixture separated by gas chromatography. The sensor makes use of a coated capillary optical fiber as the column. This new type of waveguide consists in a polarization-maintaining optical core positioned close to the capillary edge along the entire fiber length. The optical detection is performed through the coupling of the two polarization modes of the waveguide and this coupling is detected by a polarimetric interferometry technique. Through some signal processing, the resulting interferogram provides the migration rates of the various compounds of a gas mixture flowing in the capillary. One of the major benefits of this optical migration rate sensing is that the detection of each velocity peak appears as soon as the analyte enters the capillary fiber and the peaks are constantly measured during the whole separation process. Carrier gas acceleration occurring in the column is plainly demonstrated. This paper presents a proof-of-concept on a qualitative basis. The experiments were done at 29 degrees C because the current opto-fluidic set-up cannot withstand a higher temperature.

Ethanol concentration measurement by Raman spectroscopy in liquid-core microstructured optical fiber

A liquid-core air-clad microstructured fiber has been developed for determination of ethanol concentration in aqueous solutions by Raman spectroscopy. The sensor shows a linear response and a low ethanol concentration solution has been characterized using the calibrated sensor. The configuration used for light and liquid injection is stable and robust, making the sensor useful for on-line measurements.

Photobleaching of a solid photochromic medium by a Gaussian laser beam

Equations that describe the photobleaching of photochromic layers illuminated by Gaussian laser beams are given. The photochromic samples are made of thionine, triethanolamine, and polyvinyl alcohol and follow simple kinetics law. Spatial absorbance and time-dependent power transmittance are well described by the developed equations. The model is used to calculate the Gaussian dimension of helium-neon laser beams from kinetics data.

Fiber optic volatile organic compounds sensor based on polymer coated FBG refractometer

Fiber Bragg Grating (FBG) refractometer for liquid refractive index monitoring and its applications have been widely studied in the past few decades. This paper proposes a novel fiber optic volatile organic compounds (VOCs) sensor, achieved by means of polymer film coated high performance FBG refractometer, i.e. cladding removed FBG or even core thinned FBG. Polymer film coated sensor has partial selectivity, which makes this kind of sensors suitable for optical nose systems. While being exposed to VOCs, the sensing layer swells and its refractive index changes at the same time. Transduction part of this sensor, the thinned FBG, works as both strain transducer and refractometer. The mathematical model of the FBG VOCs sensor is introduced and experimentally evaluated with OV-1 coated FBG refractometer, which shows partial selectivity to different vapors and about 100 ppm detection limit to toluene.

Selecting the appropriate splitter for a reflective optical fiber dosimeter probe

Based on an innovative in-vivo optical dosimeter platform developed by scientists at University Health Network, we miniaturized the optical dosimeter in a tiny probe that fits the tip of an optical fiber. The approach consists in a measure of the absorbance change of a sensitive radiochromic material. The increase in absorbance is measured at a single wavelength and the linearly depends on the ionizing radiation dose. For compactness and design reasons, the proposed probe works in a reflective mode. A significant drawback when working with a reflective configuration is that reflections coming from splitter interfaces add to the signal and cause an apparent deviation from linearity. We studied the back reflections coming from a standard splitter and two custom made bifurcated optical fibers assemblies; 1) 7 fibers and 19 fibers. The 7 fibers connected to a 500 μm plastic optical fiber had the lowest reflection of 0.016% which was 3 times less than the 19 fibers and 100 times less than the standard splitter. An appropriate choice of the splitter was then imperative otherwise an under evaluation of the relative absorbance of −30% will happen.

Real-time optical fiber dosimeter probe

There is a pressing need for a passive optical fiber dosimeter probe for use in real-time monitoring of radiation dose delivered to clinical radiation therapy patients. An optical fiber probe using radiochromic material has been designed and fabricated based on a thin film of the radiochromic material on a dielectric mirror. Measurements of the net optical density vs. time before, during, and after irradiation at a rate of 500cGy/minute to a total dose of 5 Gy were performed. Net optical densities increased from 0.2 to 2.0 for radiochromic thin film thicknesses of 2 to 20 μm, respectively.

Fabrication and Characterization of a Real-Time Optical Fiber Dosimeter Probe

There is a pressing need for a low cost, passive optical fiber dosimeter probe for use in real-time monitoring of radiation dose delivered to clinical radiation therapy patients. An optical fiber probe using radiochromic material has been designed and fabricated based on the deposition of a radiochromic thin film on a dielectric mirror. Measurements of the net optical density vs. time before, during, and after irradiation at a rate of 500 cGy/minute to a total dose of 5 Gy were performed. Net optical densities increased from 0.2 to 2.0 for radiochromic thin film thicknesses of 2 to 20 μm, respectively. An improved optical fiber probe fabrication method is presented.

Dynamic and polychromatic SPR-leaky mode spectroscopy with Teflon AF films on silver for chemo-sensing

The reflectivity of a polymer film on top of a thin metal layer is usually recorded for a fixed wavelength and the TM polarization as a function of the angle of incidence. This angular spectrum contains the surface plasmon resonance due to the metal layer and the leaky modes caused by the waveguide resonances of the polymer film. Here we investigated the reflectivity spectrum of such a multilayer for a white light source as a function of the wavelength at a constant angle of incidence. The leaky mode resonances on the wavelength scale have been detected. Dynamic measurements of the reflectivity of such a multilayer at constant angle and constant wavelength have been demonstrated for vapors of Toluene as an example. The realization of compact and simple devices using this technique is possible.