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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∊.
- Optical fiber sensors: a route from University of Kent to PortugalPublication . Santos, José L.; Lobo Ribeiro, Antonio B.In this work the authors first summarily describe the main topics that were the subject of their post-graduate activity in fiber sensing at the Applied Optics Group of University of Kent in the late 1980s and early 1990s. After their return to Porto, Portugal, the know-how acquired during their stay at Kent and the collaboration paths that followed between the University of Porto and University of Kent were instrumental in the start-up and progress of optical fiber sensing activity in Portugal. The main topics addressed in this field, the description of some of the relevant developments achieved in recent years, the present situation and the guidelines for the future research and development activity in Portugal in fiber sensing will be the core of this work.
- Algorithm for Excitation Optimization of Fabry–Pérot Filters Used in Swept SourcesPublication . Avanaki, Mohammad R. N.; Bradu, Adrian; Trifanov, Irina; Lobo Ribeiro, Antonio B.; Hojjatoleslami, Ali; Podoleanu, A. G.We investigate the improvement in the nonlinearity of a conventional wavelength swept laser source on the basis of a fiber Fabry-Pérot tunable filter using a well-established optimization method, simulated annealing (SA). The signal driving the filter is constructed from many short ramps of different slopes that are interconnected. The values of the slopes are optimized through the SA algorithm to achieve maximum amplitude for the Fourier transformed peaks of the photodetected interferometric signal.
- Suspended-core fibers for sensing applicationsPublication . Frazão, Orlando; Silva, Ricardo M.; Ferreira, Marta S.; Santos, José L.; Lobo Ribeiro, Antonio B.A brief review on suspended-core fibers for sensing applications is presented. A historical overview over the previous ten years about this special designed microstructure optical fiber is described. This fiber presents attractive optical properties for chemical/biological or gas measurement, but it can be further explored for alternative sensing solutions, namely, in-fiber interferometers based on the suspended-core or suspended-multi-core fiber, for physical parameter monitoring.
- A study of the optical properties of photopolymer Fabry-Perot microcavities by a dual-wavelength fibre optic architecturePublication . Heredero, Raquel L; Martin, Susana; Caleya, Ramón Fernández de; Lobo Ribeiro, Antonio B.; Araújo, Francisco M; Ferreira, Luís A; Santos, José Luís; Guerrero, HéctorWe present a novel method to study the behaviour of the optical properties of photopolymer materials with temperature. The photopolymer is deposited on the tip of optical fibres by dip coating to fabricate low-finesse Fabry–Perot microcavities. The signal processing technique utilized to interrogate the cavity is based on the generation of two quadrature phase-shifted interferometric signals using two Bragg fibre gratings. This technique enables the determination of the values of the thermo-optical coefficient and the linear coefficient of thermal expansion of the photopolymer. The effectiveness of the processing technique is also exploited in the study of the dependence of the temperature sensitivity on the cavity thickness.
- Progressive ladder network topology combining interferometric and intensity fiber-optic-based sensorsPublication . Lobo Ribeiro, Antonio B.; Caleya, R. F.; Santos, J. L.Progressive ladder topology is studied by consideration of its properties of power budget and coupler tailoring. Optimization criteria are addressed for lossless and real systems, and their basic characteristics are compared with other topologies. Numerical results are presented, and an experiment is described for the case in which the network supports interferometric and intensity (with referentiation) fiber-optic-based sensors.