Browsing by Author "Staines, Stephen E."
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Item Open Access All-electronic frequency stabilization of a DFB laser diode(Optical Society of America, 2017-05-10) Asmari, A.; Hodgkinson, Jane; Chehura, Edmon; Staines, Stephen E.; Tatam, Ralph P.A laser diode’s junction voltage is a sensitive measure of its temperature and can be used in a thermal control feedback loop. To compensate for the temperature dependence of the laser’s internal resistance, we have measured the dynamic resistance, ∂V/∂I, by modulating the injection current and measuring the demodulated voltage. The junction voltage was thus controlled while operating at fixed DC injection current. Over an external temperature range of 15°C to 35°C, this stabilised the centre frequency (wavelength) of a 1651 nm DFB laser diode with a residual mean frequency shift of 60 MHz (0.5pm), less than the uncertainty on the centre frequency of 80 MHz (0.7 pm). Under the same conditions, conventional thermistor control gave a systematic wavelength shift of −8.4 GHz (−76 pm), and control of the uncompensated forward voltage gave a shift of 9.9 GHz (90 pm).Item Open Access Characterization of the response of fibre Bragg gratings fabricated in stress and geometrically induced high birefringence fibres to temperature and transverse load.(Institute of Physics, 2004-08-01T00:00:00Z) Chehura, Edmon; Ye, Chen-Chun; Staines, Stephen E.; James, Stephen W.; Tatam, Ralph P.The transverse load and temperature sensitivities of fibre Bragg gratings (FBGs) fabricated in a range of commercially available stress and geometrically induced high birefringent (HiBi) fibres have been experimentally investigated. The wavelength reflected by the FBG in each polarization eigenmode was measured independently and simultaneously using a custom designed interrogation system. The highest transverse load sensitivity, of 0.23 ± 0.02 nm/(N/mm), was obtained with HiBi FBGs fabricated in elliptically clad fibre. This was higher than for any other HiBi fibre, which, coupled with the small diameter of the fibre, makes it a good candidate for an embedded or surface mounted strain sensor. The highest temperature sensitivity of 16.5 ± 0.1 pm °C-1, approximately 27% greater than any other fibre type, was obtained with the HiBi FBG fabricated in Panda fibre. HiBi FBG sensors fabricated in D-clad fibre were the only ones to exhibit identical temperature sensitivities for the slow and fast axes (11.5 ± 0.1 pm °Item Open Access Development and application of optical fibre strain and pressure sensors for in-flight measurements(IOP Publishing, 2016-09-16) Lawson, Nicholas J.; Correia, Ricardo N.; James, Stephen W.; Partridge, Matthew; Staines, Stephen E.; Gautrey, James E.; Garry, Kevin; Holt, Jennifer C.; Tatam, Ralph P.Fibre optic based sensors are becoming increasingly viable as replacements for traditional flight test sensors. Here we present laboratory, wind tunnel and flight test results of fibre Bragg gratings (FBG) used to measure surface strain and an extrinsic fibre Fabry–Perot interferometric (EFFPI) sensor used to measure unsteady pressure. The calibrated full scale resolution and bandwidth of the FBG and EFFPI sensors were shown to be 0.29% at 2.5 kHz up to 600 με and 0.15% at up to 10 kHz respectively up to 400 Pa. The wind tunnel tests, completed on a 30% scale model, allowed the EFFPI sensor to be developed before incorporation with the FBG system into a Bulldog aerobatic light aircraft. The aircraft was modified and certified based on Certification Standards 23 (CS-23) and flight tested with steady and dynamic manoeuvres. Aerobatic dynamic manoeuvres were performed in flight including a spin over a g-range −1g to +4g and demonstrated both the FBG and the EFFPI instruments to have sufficient resolution to analyse the wing strain and fuselage unsteady pressure characteristics. The steady manoeuvres from the EFFPI sensor matched the wind tunnel data to within experimental error while comparisons of the flight test and wind tunnel EFFPI results with a Kulite pressure sensor showed significant discrepancies between the two sets of data, greater than experimental error. This issue is discussed further in the paper.Item Open Access Development of the Cranfield University Bulldog Flight Test Facility(Cambridge University Press, 2017) Lawson, Nicholas J.; Correia, Richardo N.; James, Stephen W.; Gautrey, James E.; Staines, Stephen E.; Partridge, Matthew; Tatam, Ralph P.Cranfield University’s National Flying Laboratory Centre (NFLC) has developed a Bulldog light aircraft into a flight test facility. The facility is being used to research advanced in-flight instrumentation including fibre optic pressure and strain sensors. During the development of the test bed, computational fluid dynamics (CFD) has been used to assist the flight test design process, including the sensor requirements. This paper describes the development of the Bulldog flight test facility, including an overview of the design and certification process, the in-flight data taken using the installed fibre optic sensor systems and lessons learned from the development programme, including potential further applications of the sensors.Item Open Access Dynamic fiber-optic shape sensing using fiber segment interferometry(IEEE, 2017-09-12) Kissinger, Thomas; Chehura, Edmond; Staines, Stephen E.; James, Stephen W.; Tatam, Ralph P.Dynamic fiber-optic shape sensing, often also referred to as curvature or bend sensing, is demonstrated using fiber segment interferometry, where chains of fiber segments, separated by broadband Bragg grating reflectors, are interrogated using range-resolved interferometry. In this work, the theory of interferometric curvature sensing using fiber segments is developed in detail, including techniques to infer lateral displacements from the measured differential strain data and methods for directional calibration of the sensor. A proof-of-concept experiment is performed, where four fiber strings, each containing four fiber segments of gauge length 20 cm each, are attached to the opposing sides of a flexible support structure and the resulting differential strain measurements are used to determine the lateral displacements of a 0.8 m cantilever test object in two dimensions. Dynamic tip displacement measurements at 40nm . HZ-0.5 noise levels over a 21 kHz bandwidth demonstrate the suitability of this approach for highly sensitive and cost-effective fiber-optic lateral displacement or vibration measurements.Item Open Access Fabrication of fiber optic long period gratings operating at the phase matching turning point using an ultraviolet laser(Optical Society of America, 2014-06-12) Wong, Rebecca Y. N; Chehura, Edmon; Staines, Stephen E.; James, Stephen W.; Tatam, Ralph P.It is known that optical fiber long period gratings (LPGs) exhibit their highest sensitivity to environmental perturbation when the period is such that the phase matching condition is satisfied at its turning point. The reproducible fabrication of LPGs with parameters satisfying this condition requires high resolution control over the properties of the grating. The performance of an LPG fabrication system based on the point-by-point UV exposure approach is analyzed in this paper, and the control of factors influencing reproducibility, including period, duty cycle, and the environment in which the device is fabricated, is explored.Item Open Access Fibre Bragg grating based effective soil pressure sensor for geotechnical applications(International Society for Optical Engineering; 1999, 2009-12-31T00:00:00Z) Correia, Ricardo N.; Li, Jin; Staines, Stephen E.; Chehura, Edmon; James, Stephen W.; Tatam, Ralph P.; Kutner, Joel; Dewhurst, Paul; Ferreira, PedroAn effective-soil-pressure sensor for geotechnical applications based on Fibre Bragg Gratings is presented. The sensor simultaneous measures total soil pressure and pore pressure, allowing the calculation of the effective stress of soil. Calibration of the sensor using pressurised air demonstrated a pressure sensitivity of 2.02x10 ± 2.84x10nm/kPa and 1.87x10 ± 6.88x10nm/kPa for the total and pore pressure respectively. This corresponds to a pressure resolution of 4.95x10 kPa and 5.46x10kPa for total and pore pressure using a 1pm interrogation system. Measurements undertaken in two types of soil demonstrated dependence of the total pressure sensitivity on soil density/stiffness. Pore pressure measurements agreed well with the preliminary calibratioItem Open Access A fibre Bragg grating based inclinometer system for ground movement measurement(International Society for Optical Engineering; 1999, 2010-12-31T00:00:00Z) Li, Jin; Correia, Ricardo N.; Chehura, Edmon; Staines, Stephen E.; James, Stephen W.; Tatam, Ralph P.The measurement of ground movement is an essential part of many geotechnical engineering operations. For decades, inclinometer systems have traditionally been used for this purpose to provide crucial information to engineers and researchers. However, conventional inclinometer systems have their limitations, such as high cost and poor durability. In this paper a fibre optic based inclinometer system is reported, which utilizes fibre Bragg grating sensors attached to the casing of a conventional inclinometer. The characterization of the sensor revealed good agreement with theory and conventional displacement measurements. For a casing of length 2.5 m, the minimum measureable deflection of the top of the casing was found to be 0.48 mm when the FBGs were interrogated with a 1 pm wavelength resolution system.Item Open Access Instrumentation for quantitative analysis of volatile compounds emission at elevated temperatures. Part 1: Design and implementation(Nature Publishing Group, 2020-05-26) Lourenço, Célia; Bergin, Sarah; Hodgkinson, Jane; Francis, Daniel; Staines, Stephen E.; Saffell, John R.; Walton, Christopher; Tatam, Ralph P.A novel suite of instrumentation for the characterisation of materials held inside an air-tight tube furnace operated up to 250 °C has been developed. Real-time detection of released gases (volatile organic compounds (VOCs), CO2, NO, NO2, SO2, CO and O2) was achieved combining commercial off-the-shelf (COTS) gas sensors and sorbent tubes for further qualitative and semi-quantitative analysis by gas chromatography-mass spectrometry coupled to thermal desorption (TD-GC-MS). The test system was designed to provide a controlled flow (1000 cm3 min−1) of hydrocarbon free air through the furnace. The furnace temperature ramp was set at a rate of 5 °C min−1 with 10 min dwell points at 70 °C, 150 °C, 200 °C and 250 °C to allow time for stabilisation and further headspace sampling onto sorbent tubes. Experimental design of the instrumentation is described here and an example data set upon exposure to a gas sample is presented.Item Open Access Monitoring techniques for the manufacture of tapered optical fibers(OSA Publishing, 2015-10-01) Mullaney, Kevin; Goncalves Correia, Ricardo; Staines, Stephen E.; James, Stephen W.; Tatam, Ralph P.The use of a range of optical techniques to monitor the process of fabricating optical fiber tapers is investigated. Thermal imaging was used to optimize the alignment of the optical system; the transmission spectrum of the fiber was monitored to confirm that the tapers had the required optical properties and the strain induced in the fiber during tapering was monitored using in-line optical fiber Bragg gratings. Tapers were fabricated with diameters down to 5 μm and with waist lengths of 20 mm using single-mode SMF-28 fiber.Item Open Access On-line monitoring of multi-component strain development in a tufting needle using optical fibre Bragg grating sensors(Institute of Physics, 2014-05-20T00:00:00Z) Chehura, Edmon; Dell'Anno, Giuseppe; Huet, Tristan; Staines, Stephen E.; James, Stephen W.; Partridge, Ivana K.; Tatam, Ralph P.Dynamic loadings induced on a tufting needle during the tufting of dry carbon fibre preform via a commercial robot-controlled tufting head were investigated in situ and in real-time using optical fibre Bragg grating (FBG) sensors bonded to the needle shaft. The sensors were configured such that the axial strain and bending moments experienced by the needle could be measured. A study of the influence of thread and thread type on the strain imparted to the needle revealed axial strain profiles which had equivalent trends but different magnitudes. The mean of the maximum axial compression strains measured during the tufting of a 4-ply quasi-isotropic carbon fibre dry preform were - 499 ± 79 με, - 463 ± 51 με and - 431 ± 59 με for a needle without thread, with metal wire and with Kevlar® thread, respectively. The needle similarly exhibited bending moments of different magnitude when the different needle feeding configurations were used.Item Open Access A polarisation maintaining fibre Bragg grating interrogation system for multi- axis strain sensing(International Society for Optical Engineering; 1999, 2002-12-31T00:00:00Z) Ye, Chen-Chun; Staines, Stephen E.; James, Stephen W.; Tatam, Ralph P.; Daniele, Inaudi; Eric, UddFibre Bragg gratings (FBGs) written into polarisation maintaining (PM) fibres have been employed for multi-axis strain and temperature sensing. In this paper we report the development of a FBG interrogation system that is capable of detecting independently the two orthogonally polarised signals reflected from a PM FBG. The interrogation system imposes no limitation on the measurable strain range. This relaxes the requirements on the bandwidth of the grating spectrum, allowing the use of a shorter PM FBG (larger bandwidth) for sensing applications where a higher spatial resolution is required. In particular, this system is useful in the cases where the spectra of the reflected polarised signals are broadened or split, resulting from strain-induced structural changes of the PM fibre, or caused by the application of a non-uniform strain on the FBG.Item Open Access Submicrometer fiber-optic Fabry-Perot interferometer formed by use of the Langmuir-Blodgett technique(Optical Society of America, 2001-12-01T00:00:00Z) Rees, N. D.; James, Stephen W.; Staines, Stephen E.; Tatam, Ralph P.; Ashwell, Geoffrey J.The fabrication of an optical cavity at the distal end of an optical fiber has been achieved by Langmuir-Blodgett (LB) deposition of tricosanoic acid. This technique allows nanometer-scale control over the cavity length to a total thickness of ~0.5 à µm. The cavity has been shown to act interferometrically and, thus, has potential sensing applications