Ralph P. Tatam

Fibre-Optic Chemical Sensor Approaches Based on Nanoassembled Thin Films: A Challenge to Future Sensor Technology

Optical phenomena have been employed extensively by human civilization throughout the centuries for lighting, communication, calculations, observations, etc. and have played a crucial role in industrial development. The applications of the optics increased significantly after the first demonstration of the light guiding phenomenon based on total internal reflection in the 1840s, which was the precursor for the development of modern optical fibres. In modern life, optical fibres found their niche in telecommunications and, more recently, as sensors.

Optical Fibre Long-Period Gratings Functionalised with Nano-Assembled Thin Films: Approaches to Chemical Sensing

© 2013 Lee et al., licensee InTech. This is an open access chapter distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. Optical Fibre Long-Period Gratings Functionalised with Nano-Assembled Thin Films: Approaches to Chemical Sensing

Experimental determination of 2 nd order phase matching turning points in long period gratings

The fabrication of optical fibre long period gratings (LPGs) displaying 2nd order resonant bands operating at the phase matching turning point (PMTP) is explored. Previous reports that exploited 2nd order attenuation bands in sensing schemes did not access the highly sensitive PMTP region. To overcome this limitation, LPGs with periods between 167–177 μm were fabricated using UV irradiation. The spectra acquired were subsequently analyzed and the development of the 2nd order PMTP was identified utilizing peak tracking software. This work has provided the platform for LPG design focused on the prospect of sensitive multi-parameter discrimination.

In-situ pathlength calibration of integrating spheres used in measurement of absorbance

When used as samples cells for optical absorbance measurements, integrating spheres offer increased pathlengths compared to single pass cells combined with tolerance to misalignment. This makes them attractive during alignment of optical instruments and in challenging environments subject to vibration. However, integrating spheres can suffer problems when used in sensitive and / or accurate absorbance measurement. We present our work to date to address these issues in high resolution laser spectroscopy. Firstly, optical interference effects include both random laser speckle and structured interference fringes created by optical feedback to the laser. Secondly, the sphere’s optical pathlength is a combination of multiple paths that take an exponential pathlength distribution. At low values of absorbance, the measured signal is linear with concentration, but at higher absorbances signals follow a nonlinear but predictable function of absorbance. Thirdly, our most recent work concerns calibration of the optical pathlength, which is a sensitive function of its internal reflectivity. In-situ calibration is needed if the sphere is to be used in dirty environments or with condensing samples. Measurements from multiple independent sources and / or detectors are combined to provide compensation from fouling of the sphere walls and windows. Results are presented for an integrating sphere used in the measurement of methane. The emission from a tunable DFB laser at 1651nm was tuned across the gas absorption line to measure its concentration. Reduced sphere reflectivity was simulated by applying small areas of black tape on the inner surface. Finally, we give an example of one application where our results are being put into practice: use of an integrating sphere with a tunable laser at 3.3μm to measure atmospheric methane, installed on a two seater light aircraft.

Dual sensing-light-sheet OCT for microfluidic PTV

A novel dual beam Optical Coherence Tomography (OCT) system is presented for microfluidics applications. The dual sensing-light-sheet approach presented here achieves high velocity flow measurement because the rapid re-imaging by the second sensing-light-sheet allows for particle tracking between each image-frame of the pair. We have demonstrated measurements of microchannel flow using 10 μm particles in a 700 μm deep channel with peak velocities of approximately 0.28 metres-per-second (m/s), approximately two orders of magnitude higher than previously reported OCT systems operating at a few millimeters-per-second.

3D Fibre Optic Laser Doppler Velocimeter

In this paper the design and preliminary testing of a single headed 3D fibre optic laser Doppler velocimeter for implementation on turbomachinery rigs is described.