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.
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.
Theoretical and experimental work is reported on a distributed polarimetric fibre optic sensor designed for application in
capillary gas chromatography. Emphasis is on the improvement of the modeling of the polarization mode coupling
mechanism so as to get not only qualitative (vapor identification), but also quantitative (vapor concentration)
information from the analysis of a time-modulated signal transmitted through a polarizer at the end of a custom capillary
fibre.
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.
An analysis of the optical signal transmitted by a polarimetric sensor developed for the measurement of velocities of fluids in a capillary optical fiber is presented. It allows one to determine whether a fluid is moving in the vapor or the liquid phase.
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.
Multimode PMMA optical fibres with a cladding made from ion-selective membrane were designed, prepared, and
investigated. Some were prepared by direct drawing of membrane-coated preforms and others were overcoated. Results
obtained indicate loss of membrane sensitivity that is attributed to decrease of its ionic permeability. Absorbance of the
fibre follows a modified Beer law as confirmed by rank analysis of series of spectra and explained by significant mode
coupling within the fibre.
A quasi-distributed fibre optics polarimetric sensor has been studied both theoretically and experimentally. Theoretical results demonstrate the feasibility of such a sensor when a polarization-maintaining optical fibre has been properly designed. Two designs are proposed. Distributed detection of water has been demonstrated with a standard polarization-maintaining fibre whose cladding was locally removed by chemical etching.
Other than from its sensing and processing capabilities, a mobile robotic platform can be limited in its use by its ability to move in the environment. A wheeled robot works well on flat surfaces. Tracks are useful over rough terrains, while legs allow a robot to move over obstacles. In this paper we present a new concept of mobile robot with the objective of combining different locomotion mechanisms on the same platform to increase its locomotion capabilities. After presenting a review of multi-modal robotic platforms, we describe the design of our robot called AZIMUT. AZIMUT combines wheels, legs and tracks to move in three-dimensional environments. The robot is symmetrical and is made of four independent leg-track-wheel articulations. It can move with its articulations up, down or straight, or move sideways without changing the robot's orientation. The robot could be used in surveillance and rescue missions, exploration or operation in hazardous environments.
Many devices using the electro-optic effect, in which the index of refraction changes upon application of an external electrical field, have been proposed to control the propagation of light in planar waveguides. Some electro-optic waveguides are made from polymers materials. However, none of them has the circular symmetry of optical fibers. Therefore the connection between optical fibers and planar waveguides is a difficult and costly task. A solution to this problem is to insert electro-optic polymers in a porous optical fiber. Such porous fibers are made of a plurality of interconnected micro-pores in a skeleton of silica glass and can be obtained from phase separation of alkali-borosilicate optical fibers. In this work, we describe porous optical fibers filled with a DR1-polyacrylate electro-optic polymer.
Reconstructed silica made from porous glass is used to fabricate doped multimode optical fibres. This process constitutes an alternative to the more classical Modified Chemical Vapour Deposition (MCVD) process when used in conjunction with solution doping. Comparison between porous glass and porous silica soot obtained from MCVD allows to highlight the advantages and disadvantages of both methods. The reconstructed glass process has been used to develop a multimode high attenuation optical fibre (HAF) working at 850nm.
We report on our irradiation experiments on different types of fiber-optic sensors, including three types of commercially available temperature sensors, a multimode extrinsic Fabry-Perot cavity strain sensor and fiber Bragg- gratings. For the temperature sensors, results show that gamma radiation does not interfere with the basic sensing mechanism and that the most critical component turns out to be the optical fiber itself. Semiconductor absorption temperature sensor showed no degradation up to total doses of 250 kGy, whereas the specifications of Fabry-Perot type sensor and fluorescence temperature sensors were already dramatically influenced below the kGy-level. Replacing the optical fiber by a more radiation resistant version allowed to increase the radiation hardness of the fluorescence sensors system by orders of magnitude. The use of fiber- optic sensors in the presence of neutron radiation remains compromised. Similar conclusions are valid for the Fabry- Perot type fiber-optic strain sensors. We finally show that the Bragg-grating resonance wavelength can shift with radiation dose, but that the temperature sensitivity remains unaltered.
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.
Navigation in polar waters presents a formidable challenge to ships' propulsion systems as large ice pieces impinging on their propeller blades sometimes result in stresses exceeding the yield strength of the blade material. Damage to propellers is costly and can also spell disaster if a ship becomes disabled in a remote area. To prevent such situations, design practice must be improved and theoretical models of propeller/ice interaction must be validated against experimental data. The blade shape requires that the load be monitored at many locations in order to obtain an accurate picture of the stress and load distribution. Fiber optic sensors are ideally suited for such an application, owing to their small size, stability over time, immunity to electro-magnetic interference, resistance to corrosion and chemical attack by sea water and hydraulic oil. We report the full-scale instrumentation of an icebreaker propeller blade with 54 Fabry-Perot based fiber optic strain gauges and shaft-mounted electronics. The instrumentation design and installation procedures are described. Additional data gathered from the propulsion control system and the ship's navigation equipment is presented and the data fusion performed with underwater video imagery of the instrumented blade is also discussed. An overview of the noise-free data obtained during the Antarctic trials is given. We finally discuss the sensors behavior and long term response, presenting their applicability to smart structures.
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