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- All-fibre interrogation technique for fibre Bragg sensors using a biconical fibre filterPublication . Lobo Ribeiro, Antonio B.; Ferreira, L. A.; Tsvetkov, M.; Santos, J. L.A passive self-referencing all-fibre technique for Bragg wavelength shift detection using a biconical fibre filter is described. This filter, basically a tapered depressed-cladding fibre, exhibits a periodic spectral power dependence which permits direct tracking of wavelength shifts in a 20nm unambiguous range. Dynamic strain resolution of 1.5 μstrain/√Hz has been achieved.
- A simple, self-referenced, intensity-based optical fibre sensor for temperature measurementsPublication . Silva, Ricardo M.; Baptista, J.M.; Santos, J.L.; Lobo Ribeiro, Antonio B.; Araújo, F.M.; Ferreira, L.A.; Frazão, O.A sensing configuration based on an intensity optical fibre sensor for temperature measurement is reported. Two sensing heads, with identical geometrical configuration, connected in series are implemented. Each sensing head is placed between two fibre Bragg gratings (FBGs), being able to provide a self-referenced measurement, and thus eliminate errors that may arise from undesired intensity fluctuations in the configuration. The first FBG, placed before the aluminium tube, acts as the reference FBG, while the second FBG, placed after the aluminium tube, acts as the signal FBG. It is observed that the amplitude of the signal FBG decays when temperature increases, due to the increase of the ferrules' gap and as result of the material thermal expansion. The temperature response has a behaviour that corresponds to a polynomial fit of third order. The crosstalk between the two sensing heads in series is analysed. The temperature sensitivities obtained in the intervals regions of [36, 48.5] °C and [64, 85] °C are 2.67×10-3 °C-1 and 1.74×10-4 °C-1, respectively. Ten sensing heads with this configuration can be multiplexed in series network topology.
- Combined Neodymium–Ytterbium-Doped ASE Fiber-Optic Source for Optical Coherence Tomography ApplicationsPublication . Trifanov, I.; Caldas, P.; Neagu, L.; Romero, R.; Berendt, M. O.; Salcedo, J. A. R.; Podoleanu, A. Gh.; Lobo Ribeiro, Antonio B.Optical coherence tomography (OCT) imaging at the 1060-nm region proved to be a successful alternative in oph- thalmology not only for resolving intraretinal layers, but also for enabling sufficient penetration to monitor the subretinal vascu- lature in the choroid when compared to most commonly used OCT imaging systems at the 800-nm region. To encourage further clinical research at this particular wavelength, we have developed a compact fiber-optic source based on amplified spontaneous emission (ASE) centered at 1060 nm with 70-nm spectral bandwidth at full-width at half-maximum and output power 20 mW. Our approach is based on a combination of slightly shifted ASE emission spectra from a combination of Neodymium- and Ytterbium-doped fibers. Spectral shaping and power op- timization have been achieved using in-fiber filtering schemes. We have tested the performance of the source in an OCT system optimized for this wavelength.
- Characterization of a fibre optic swept laser source at 1 μm for optical coherence tomography imaging systemsPublication . Trifanov, Irina; Neagu, Liviu; Bradu, Adrian; Lobo Ribeiro, Antonio B.; Podoleanu, Adrian Gh.We report the development of a swept wavelength laser at 1 micron based on a linear cavity fibre configuration with an intra-cavity half symmetrical confocal Fabry-Perot tunable filter and a semiconductor optical amplifier as a gain medium. The performances of the source in terms of parameters like: sweep repetition rate (1-20 kHz), center wavelength (1065 nm), wavelength scanning range (max. 50nm), instantaneous line-width (<0.1nm) and a boosted output power of around 40 mW are demonstrated. The new source tested on an OCT system is exhibiting sufficient linearity in wave-number (k-space) at 1 kHz repetition rate; therefore no k-trigger, or wavelength rescaling process was needed.
- Simple multiplexing scheme for a fiber-optic grating sensor networkPublication . Jackson, D. A.; Reekie, L.; Archambault, J. L.; Lobo Ribeiro, Antonio B.A new approach for the interrogation of a large number of fiber-optic grating sensors is proposed and demonstrated for a small number of sensors in which signal recovery is achieved by matching a receiving grating to its corresponding sensor. This technique is demonstrated for both quasi-static and periodic measurands, and the resolution achieved for a single sensor–receiving grating pair for quasi-static strain is 4.12 μ∊.
- Simultaneous measurement of displacement and temperature using a low finesse cavity and a fiber Bragg gratingPublication . Ferreira, L.A.; Lobo Ribeiro, Antonio B.; Santos, J.L.; Farahi, F.An optical sensor capable of simultaneously measuring displacement and temperature is presented. It incorporates a fiber Bragg grating temperature sensor and a low-finesse extrinsic Fabry-Perot cavity. A white light tandem interferometric technique is used to recover signal from the low finesse cavity. Signals obtained from the interferometer and the Bragg grating provide required information to simultaneously determine temperature and displacement. Experimental results are presented which demonstrate the feasibility of this sensor topology in practical applications.
- Metal-coated fibre Bragg grating sensor for electric current meteringPublication . Cavaleiro, P.M.; Araújo, F.M.; Lobo Ribeiro, Antonio B.A hybrid fibre optic current sensor combining a metal-coated fibre Bragg grating with a standard current transformer is described. Measurements of the RMS current of power lines at 50 Hz with a resolution of 2 mA is demonstrated.
- Review of fiber-optic pressure sensors for biomedical and biomechanical applicationsPublication . Roriz, Paulo; Frazão, Orlando; Lobo Ribeiro, Antonio B.; Santos, José L.; Simões, José A.As optical fibers revolutionize the way data is carried in telecommunications, the same is happening in the world of sensing. Fiber-optic sensors (FOS) rely on the principle of changing the properties of light that propagate in the fiber due to the effect of a specific physical or chemical parameter. We demonstrate the potentialities of this sensing concept to assess pressure in biomedical and biomechanical applications. FOSs are introduced after an overview of conventional sensors that are being used in the field. Pointing out their limitations, particularly as minimally invasive sensors, is also the starting point to argue FOSs are an alternative or a substitution technology. Even so, this technology will be more or less effective depending on the efforts to present more affordable turnkey solutions and peer-reviewed papers reporting in vivo experiments and clinical trials.
- Experimental Method to Find the Optimum Excitation Waveform to Quench Mechanical Resonances of Fabry–Pérot Tunable Filters Used in Swept SourcesPublication . Trifanov, I.; Bradu, A.; Neagu, L.; Guerreiro, P.; Lobo Ribeiro, Antonio B.; Podoleanu, A. Gh.We report experimental evidence of improving the nonlinearity of conventional wavelength swept laser sources based on a fiber Fabry–Pérot tunable filter as a wavelength-selective element. Our solution is based on applying a nonsinusoidal, synthesized waveform to the tunable filter that can be identified experimentally. A significant improvement in the optical coher- ence tomography image quality has been obtained without any software recalibration method.
- Time-and-spatial-multiplexing tree topology for fiber-optic Bragg-grating sensors with interferometric wavelength-shift detectionPublication . Lobo Ribeiro, Antonio B.; Rao, Y. J.; Zhang, L.; Bennion, I.; Jackson, D. A.A combined time-and-spatial-division-multiplexed tree topology with eight fiber-optic Bragg-grating sensors operating at the 830-nm wavelength was constructed and tested for both quasistatic and periodic strain and temperature measurements. The system uses a interferometric wavelength-shift discriminator and incorporates a reference channel for thermal drift compensation in the output. Dynamic sensor sensitivity, as determined by primary noise sources, is evaluated, and numerical results are presented and compared with experimental results.