CAP

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This service develops its activity in the areas of optical sources, optical communications, fiber optic sensors and micro-manufacturing, having facilities for the design and development of electronic systems.

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Browsing CAP by Author "4061"
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    Acoustic Optical Fiber Sensor Based on Graphene Oxide Membrane
    ( 2021) Catarina Silva Monteiro ; Raposo,M ; Ribeiro,PA ; Susana Oliveira Silva ; Orlando Frazão ; 4061 ; 4678 ; 6568
    A Fabry–Pérot acoustic sensor based on a graphene oxide membrane was developed with the aim to achieve a faster and simpler fabrication procedure when compared to similar graphene-based acoustic sensors. In addition, the proposed sensor was fabricated using methods that reduce chemical hazards and environmental impacts. The developed sensor, with an optical cavity of around 246 µm, showed a constant reflected signal amplitude of 6.8 ± 0.1 dB for 100 nm wavelength range. The sensor attained a wideband operation range between 20 and 100 kHz, with a maximum signal-to-noise ratio (SNR) of 32.7 dB at 25 kHz. The stability and sensitivity to temperatures up to 90 °C was also studied. Moreover, the proposed sensor offers the possibility to be applied as a wideband microphone or to be applied in more complex systems for structural analysis or imaging.
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    Application of a Fiber Optic Refractometric Sensor to Measure the Concentration of Paracetamol in Crystallization Experiments
    ( 2021) Liliana Patrícia Soares ; Cruz,P ; Susana Novais ; Ferreira,A ; Orlando Frazão ; Susana Oliveira Silva ; 4061 ; 4678 ; 7662 ; 7725
    A refractometric sensor was applied to measure in real-time the concentration of Active Pharmaceutical Ingredients (APIs) in crystallization experiments. Paracetamol was used as a model system due to the extensive literature available for this API. The refractometric sensor was fabricated by a simple and inexpensive method that consisted in splicing a short section of a multimode fiber to a single mode fiber. The compact geometry of this sensor, with an external diameter of just $125\ \mu\mathrm{m}$, allowed it to measure the concentration of paracetamol, both in a stirred tank crystallizer operating in batch and in an oscillatory flow crystallizer operating continuously. The proposed technique shows the potential to monitor the concentration of APIs in crystallizers of different sizes and geometries as an alternative to more expensive and complex analysis equipment.
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    Bi-core optical fiber for sensing o temperature, strain and torsion
    ( 2019) Lobo Ribeiro,ABL ; Susana Oliveira Silva ; Orlando Frazão ; José Luís Santos ; 4678 ; 347 ; 4061
    Bi-core optical fiber structures are studied for applications in sensing. In this paper, an analysis is performed on the spectral characteristics of light propagating in these fibers with central launching core illumination from a standard single mode fiber. Reflective and transmissive configurations are addressed. The characteristics of a reflective bi-core fiber structure for measurement of strain, temperature and absolute value of torsion are investigated and highlights for further research are presented.
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    Cavity length dependence on strain sensitivity for Fabry-Perot sensors
    ( 2022) António Vaz Rodrigues ; Reis,J ; Martins,AJM ; Catarina Silva Monteiro ; Susana Oliveira Silva ; Caridade,CMR ; Tavares,SO ; Orlando Frazão ; 4061 ; 4678 ; 6514 ; 6568
    This study presents the dependence of strain sensitivity on cavity length in conventional Fabry-Perot (F-P) sensors. A high number of F-P sensors were required and to ensure their reproducibility, a manufacturing process was developed to obtain similar sensors but with different types of lengths. A hollow-core silica tube was used to fabricate several F-P cavities by fusion splicing it between two sections of SMF28 fiber. The fabricated F-P has a varying length ranging from 15 to 2500 mu m. The cavities were measured under a microscope and the reflected spectrum was acquired for each one. Strain measurements were performed for a maximum strain of 1000 mu epsilon. The strain sensitivity showed a highly linear correlation with increment lambda(FSR). Small length variations for short cavities heavily affect the FSR value. The smallest and longest cavities present sensitivities of 8.71 and 2.68 pm/mu epsilon, respectively. Thermal characterization for low- and high-temperature regimes was also performed and is constant for tested sensors.
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    Cleaved Silica Microsphere for Temperature Measurement
    ( 2018) André Delgado Gomes ; Beatriz Machado Silveira ; Dellith,J ; Becker,M ; Rothhard,M ; Bartelt,H ; Orlando Frazão ; 4061 ; 6406 ; 6684
    A sensing structure based on a cleaved silica microsphere is proposed for temperature sensing. The microsphere was cleaved using focused ion beam milling. The asymmetry in the structure introduced by the cut generates not only new cavities but also random interferometric reflections inside the microsphere. These two spectral components can be separated using low-pass and high-pass filters, respectively. The sensor response to temperature can be extracted from the cavities' component using a correlation method. The device achieved a temperature sensitivity of -10.8 +/- 0.2 pm/degrees C between 30 degrees C and 80 degrees C. The same effect is impossible to be obtained in a normal uncleaved microsphere. The random interferometric component did not provide any information on temperature using the same analysis. However, when changing the temperature, a new and completely distinct reflection spectrum with no apparent correlation with others at different temperatures was achieved.
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    Colossal enhancement of strain sensitivity using the push-pull deformation method
    ( 2021) Paulo Robalinho ; André Delgado Gomes ; Orlando Frazão ; 4061 ; 6406 ; 7405
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    Curvature detection in a medical needle using a Fabry-Perot cavity as an intensity sensor
    ( 2020) Susana Novais ; Susana Oliveira Silva ; Orlando Frazão ; 4061 ; 4678 ; 7725
    The use of optical sensors inside the needle can improve targeting precision and can bring real-time information about the location of the needle tip if necessary, since a needle bends through insertion into the tissue. Therefore, the precise location of the needle tip is so important in percutaneous treatments. In the current experiment, a fiber sensor based on a Fabry-Perot (FP) cavity is described to measure the needle curvature. The sensor is fabricated by producing an air bubble between two sections of multimode fiber. The needle with the sensor therein was attached at one end and deformed by the application of movements. The sensor presents a sensitivity of -0.152 dB/m-1 to the curvature measurements, with a resolution of 0.089 m-1. The sensory structure revealed to be stable, obtaining a cross-sensitivity to be 0.03 m-1/°C. © 2019 Elsevier Ltd
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    Curvature Sensor Based on a Long-Period Grating in a Fiber Ring Resonator Interrogated by an OTDR
    ( 2020) Magalhaes,R ; Susana Oliveira Silva ; Orlando Frazão ; 4061 ; 4678
    The proposed technique demonstrates a fiber ring resonator interrogated by an optical time domain reflectometer (OTDR), for intensity sensing. By using this methodology, a cavity round trip time of 2.85 µs was obtained. For a proof of concept, a long-period grating was inserted in the resonant cavity operating as a curvature sensing device. A novel signal processing approach was outlined, regarding to the logarithmic behavior of the OTDR. Through analyzing the experimental results, an increase in the measured sensitivities was obtained by increasing applied bending. With curvatures performed from 1.8 m-1 to 4.5 m-1, the sensitivity values ranged from 2.94 dB·km-1 to 5.15 dB·km-1. In its turn, the sensitivities obtained presented a linear behavior when studied as a function of the applied curvature, following a slope of 0.86×10-3 dB. The advantages of applying this technique were also discussed, demonstrating two similar fiber rings multiplexed in a series of configurations. © 2019, The Author(s).
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    Detection of the Crystallization Process of Paracetamol with a Multi-Mode Optical Fiber in a Reflective Configuration
    ( 2020) Soares,L ; Susana Novais ; Ferreira,A ; Orlando Frazão ; Susana Oliveira Silva ; 4061 ; 4678 ; 7725
    A configuration of a refractometer sensor is described with the aim of optically detecting the crystallization process of paracetamol. The developed sensing head is based on a conventional cleaved multi-mode fiber. The fiber tip sensor structure was submitted to contact with the liquid of interest (paracetamol fully dissolved in 40% v/v of ethanol/water) and the crystallization process of paracetamol, induced with continued exposure to air, was monitored in real time.
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    Discrimination of benign and malignant lesions in canine mammary tissue samples using Raman spectroscopy: A pilot study
    ( 2020) Dantas,D ; Soares,L ; Susana Novais ; Vilarinho,R ; Moreira,JA ; Susana Oliveira Silva ; Orlando Frazão ; Oliveira,T ; Leal,N ; Faisca,P ; Reis,J ; 4061 ; 4678 ; 7725
    Breast cancer is a health problem that affects individual life quality and the family system. It is the most frequent type of cancer in women, but men are also affected. As an integrative approach, comparative oncology offers an opportunity to learn more about natural cancers in different species. Methods based on Raman spectroscopy have shown significant potential in the study of the human breast through the fingerprinting of biological tissue, which provides valuable information that can be used to identify, characterize and discriminate structures in breast tissue, in both healthy and carcinogenic environments. One of the most important applications of Raman spectroscopy in medical diagnosis is the characterization of microcalcifications, which are highly important diagnostic indicators of breast tissue diseases. Raman spectroscopy has been used to analyze the chemical composition of microcalcifications. These occur in benign and malignant lesions in the human breast, and Raman helps to discriminate microcalcifications as type I and type II according to their composition. This paper demonstrates the recent progress in understanding how this vibrational technique can discriminate through the fingerprint regions of lesions in unstained histology sections from canine mammary glands. © 2020 by the authors. Licensee MDPI, Basel, Switzerland.
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    Environmental Sensitivity of Fabry-Perot Microcavities Induced by Layered Graphene-Dielectric Hybrid Coatings
    ( 2021) Peixoto,R ; Pires,JPS ; Catarina Silva Monteiro ; Raposo,M ; Ribeiro,PA ; Susana Oliveira Silva ; Orlando Frazão ; Lopes,JMVP ; 4061 ; 4678 ; 6568
    We propose a fiber-based environmental sensor that exploits the reflection-phase-shift tunability provided by the use of layered coatings composed of dielectric slabs spaced by conducting membranes. A transfer-matrix study is done in a simplified theoretical model, for which an enhanced sensitivity of the reflection interference pattern to the output medium is demonstrated, in the typical refractive index range of liquid media. An experimental configuration using a cascaded Fabry-Perot microcavity coated by a graphene oxide/polyethylenimine (GO/PEI) multilayered structure is demonstrated. Its cost-effective chemical production method makes graphene oxide-based hybrid coatings excellent candidates for future real-life sensing devices.
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    Femtosecond laser direct written off-axis fiber Bragg gratings for sensing applications
    ( 2020) Carlos Duarte Viveiros ; Vítor Oliveira Amorim ; João Miguel Maia ; Susana Oliveira Silva ; Orlando Frazão ; Pedro Jorge ; Fernandes,LA ; Paulo Vicente Marques ; 3565 ; 4061 ; 4287 ; 4678 ; 5872 ; 6407 ; 6596
    First order off-axis fiber Bragg gratings (FBGs) were fabricated in a standard single mode fiber (SMF-28e) through femtosecond laser direct writing. A minimum offset distance between the grating and core center of 2.5 µm was found to create a multimode section, which supports two separate fiber modes (LP0,1 and LP1,1), each split into two degenerate polarization modes. The resulting structure breaks the cylindrical symmetry of the fiber, introducing birefringence (˜10-4) resulting in a polarization dependent Bragg wavelength for each mode. Based on the modal and birefringence behavior, three off-axis FBGs were fabricated with 3.0, 4.5 and 6.0 µm offsets from the core center, and then characterized in strain, temperature, and curvature. The tested off-axis FBGs exhibited a similar strain sensitivity of ~1.14 pm/µ? and a temperature sensitivity of ~12 pm/C. The curvature and orientation angle were simultaneously monitored by analyzing the intensity fluctuation and the wavelength shift of the LP1,1 Bragg resonance. A maximum curvature sensitivity of 0.53 dB/m-1 was obtained for the off-axis FBG with a 3.0 µm offset. © 2020 Elsevier Ltd
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    Femtosecond laser direct written off-axis fiber Bragg gratings for sensing applications
    ( 2020) Carlos Duarte Viveiros ; Vítor Oliveira Amorim ; João Miguel Maia ; Susana Oliveira Silva ; Orlando Frazão ; Pedro Jorge ; Fernandes,LA ; Paulo Vicente Marques ; 3565 ; 4061 ; 4287 ; 4678 ; 5872 ; 6407 ; 6596
    First order off-axis fiber Bragg gratings (FBGs) were fabricated in a standard single mode fiber (SMF-28e) through femtosecond laser direct writing. A minimum offset distance between the grating and core center of 2.5 µm was found to create a multimode section, which supports two separate fiber modes (LP0,1 and LP1,1), each split into two degenerate polarization modes. The resulting structure breaks the cylindrical symmetry of the fiber, introducing birefringence (˜10-4) resulting in a polarization dependent Bragg wavelength for each mode. Based on the modal and birefringence behavior, three off-axis FBGs were fabricated with 3.0, 4.5 and 6.0 µm offsets from the core center, and then characterized in strain, temperature, and curvature. The tested off-axis FBGs exhibited a similar strain sensitivity of ~1.14 pm/µ? and a temperature sensitivity of ~12 pm/C. The curvature and orientation angle were simultaneously monitored by analyzing the intensity fluctuation and the wavelength shift of the LP1,1 Bragg resonance. A maximum curvature sensitivity of 0.53 dB/m-1 was obtained for the off-axis FBG with a 3.0 µm offset. © 2020 Elsevier Ltd
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    Fiber Loop Mirror Based on Optical Fiber Circulator for Sensing Applications
    ( 2023) Paulo Robalinho ; Beatriz Gomes Soares ; Lobo,A ; Susana Oliveira Silva ; Orlando Frazão ; 4061 ; 4678 ; 7405 ; 7700
    In this paper, a different Fiber Loop Mirror (FLM) configuration with two circulators is presented. This configuration is demonstrated and characterized for sensing applications. This new design concept was used for strain and torsion discrimination. For strain measurement, the interference fringe displacement has a sensitivity of (0.576 ± 0.009) pm?µe-1. When the FFT (Fast Fourier Transformer) is calculated and the frequency shift and signal amplitude are monitored, the sensitivities are (-2.1 ± 0.3) × 10-4 nm-1 µe-1 and (4.9 ± 0.3) × 10-7 µe-1, respectively. For the characterization in torsion, an FFT peaks variation of (-2.177 ± 0.002) × 10-12 nm-1/° and an amplitude variation of (1.02 ± 0.06) × 10-3/° are achieved. This configuration allows the use of a wide range of fiber lengths and with different refractive indices for controlling the free spectral range (FSR) and achieving refractive index differences, i.e., birefringence, higher than 10-2, which is essential for the development of high sensitivity physical parameter sensors, such as operating on the Vernier effect. Furthermore, this FLM configuration allows the system to be balanced, which is not possible with traditional FLMs.
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    Fiber microsphere coupled in a taper for a large curvature range
    ( 2019) Paulo Robalinho ; Orlando Frazão ; 4061 ; 7405
    This work consists of using an optical fiber microsphere as a sensor for a wide range of curvature radii. The microsphere was manufactured in a standard fiber with an electric arc. In order to maximize system efficiency, the microsphere was spliced in the center of a taper. This work revealed that the variations of the wavelength where the maxima and minima of the spectrum are located varies linearly with the curvature of the system with a maximum sensitive of 580 ± 20 (pm km). This is because the direction of the input beam in the microsphere depends on the system curvature, giving rise to interferometric variations within the microsphere. © 2019 by the authors.
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    Giant Displacement Sensitivity Using Push-Pull Method in Interferometry
    ( 2021) Paulo Robalinho ; Orlando Frazão ; 4061 ; 7405
    We present a giant sensitivity displacement sensor combining the push-pull method and enhanced Vernier effect. The displacement sensor consists in two interferometers that are composed by two cleaved standard optical fibers coupled by a 3 dB coupler and combined with a double-sided mirror. The push pull-method is applied to the mirror creating a symmetrical change to the length of each interferometer. Furthermore, we demonstrate that the Vernier effect has a maximum sensitivity of two-fold that obtained with a single interferometer. The combination of the push-pull method and the Vernier effect in the displacement sensors allows a sensitivity of 60 ± 1 nm/µm when compared with a single interferometer working in the same free spectral range. In addition, exploring the maximum performance of the displacement sensors, a sensitivity of 254 ± 6 nm/µm is achieved, presenting a M-factor of 1071 and MVernier of 1.9 corresponding to a resolution of 79 pm. This new solution allows the implementation of giant-sensitive displacement measurement for a wide range of applications.
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    High Enhancement Strain Sensor based on Vernier Effect using 2-Fiber Loop Mirrors
    ( 2020) Paulo Robalinho ; André Delgado Gomes ; Orlando Frazão ; 4061 ; 6406 ; 7405
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    High sensitivity strain sensor based on twin hollow microspheres
    ( 2019) Catarina Silva Monteiro ; Kobelke,J ; Schuster,K ; Bierlich,J ; Susana Oliveira Silva ; Orlando Frazão ; 4678 ; 6568 ; 4061
    A sensor based on 2 hollow core microspheres is proposed. Each microsphere was produced separately through fusion splicing and then joined. The resultant structure is a Fabry-Perot interferometer with multiple interferences that can be approximated to a 4-wave interferometer. Strain characterization was attained for a maximum of 1350 mu epsilon, achieving a linear response with a sensitivity of 3.39 /- 0.04 pm/mu epsilon. The fabrication technique, fast and with no chemical hazards, as opposed to other fabrication techniques, makes the proposed sensor a compelling solution for strain measurements in hash environments.
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    Micro-cantilever displacement detection based in optical fiber tip
    ( 2019) Paulo Robalinho ; Orlando Frazão ; 4061 ; 7405
    This work demonstrates the potential of combining a microsphere with a tip for the functionality of the contact sensor. This sensor consists of a tip aligned with the ?ber core and a microsphere, which appears during tip formation. This new structure was produced using the electric arc machine. The sensor operation consists of the variation of the tip curvature, which causes a variation of the optical paths and, consequently, a change in the output signal. The study of this micro-cantilever consisted of an exploration of the contact mode. In addition, the sensor was characterized by temperature, which shows very low sensitivity and vibration. This last characterization was performed with two con?gurations parallel and perpendicular to the oscillating surface. The perpendicular case showed higher sensitivity and has an operating band of 0 Hz to 20 kHz. In this con?guration, for frequencies up to 2 Hz, the intensity varies linearly with the frequencies and with a sensitivity of 0.032±0.001 (Hz-1). For the parallel case, the operating band was from 1.5 kHz to 7 kHz. © 2019 by the authors. Licensee MDPI, Basel, Switzerland.
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    Multipath Interferometer Polished Microsphere for Enhanced Temperature Sensing
    ( 2018) André Delgado Gomes ; Karami,F ; Zibaii,MI ; Latifi,H ; Orlando Frazão ; 6406 ; 4061