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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    100 km-Ultralong Raman Fiber Laser using a Distributed Rayleigh Mirror for Sensing Applications
    ( 2012) Manuel Joaquim Marques ; Hugo Fidalgo Martins ; Orlando Frazão
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    250 km ultra long sensor system based on a Fiber Loop Mirror interrogated by an OTDR
    ( 2011) M. Lopez-Amo ; José Manuel Baptista ; José Luís Santos ; Orlando Frazão ; M. Bravo
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    2D computational modeling of optical trapping effects on malaria-infected red blood cells
    ( 2017) Joana Isabel Paiva ; Ribeiro,RSR ; Pedro Jorge ; Carla Carmelo Rosa ; Guerreiro,A ; João Paulo Cunha
    A computational method for optical fiber trapping of healthy and Malariainfected blood cells characterization is proposed. A trapping force relation with the infection stage was found, which could trigger the development of a diagnostic sensor. © OSA 2017.
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    300 km-Ultralong Raman Fiber Lasers using a Distributed Mirror for Sensing Applications
    ( 2011) Manuel Joaquim Marques ; Hugo Fidalgo Martins ; Orlando Frazão
    H. Martins, M. B. Marques, O. Frazão, 300 km-Ultralong Raman Fiber Lasers using a Distributed Mirror for Sensing Applications, Opt. Express, 19 (19), 18149-18154, September 2011.
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    Absorption-line-locked fiber laser for gas-sensing applications
    ( 2007) Nome Apelido ; Francisco Araújo ; Luís Alberto Ferreira
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    Acetone evaporation and water vapor detection using a caterpillar-like microstructured fiber
    ( 2016) André Delgado Gomes ; Ferreira,MFS ; Moura,JP ; Ricardo Melo André ; Kobelke,J ; Bierlich,J ; Wondraczek,K ; Schuster,K ; Orlando Frazão
    A new microstructured optical fiber is presented as a sensor of acetone evaporation. Sensing is performed by observing the time response of the reflected signal at 1550 nm when the device is dipped in acetone or a 50% acetone-50% water mixture. The sensor consists on a caterpillar-like microstructured fiber spliced to a single-mode fiber, where the spliced end of the sensor has a transversal microfluidic channel etched using focused ion beam. Upon heating, different behaviors are visible between the dipping and the evaporation of acetone. The sensor is able to track the evaporation of acetone and to distinguish between pure acetone and a 50% acetone-50% water mixture. The sensor is also able to detect when the acetone in a mixture with water is fully evaporated. The detection of water vapor with no particular orientation of the sensor is achieved due to the presence of the microfluidic channels. (c) 2016 Wiley Periodicals, Inc.
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    Acetone evaporation monitoring using a caterpillar-like microstructured fiber
    ( 2015) André Delgado Gomes ; Ferreira,MFS ; Moura,JP ; Ricardo Melo André ; Susana Oliveira Silva ; Kobelke,J ; Bierlich,J ; Wondraczek,K ; Schuster,K ; Orlando Frazão
    A new microstructured optical fiber is demonstrated to detect acetone evaporation by observing the time response of the reflected signal at 1550nm. The sensor consists on a caterpillar-like fiber, with a transversal microfluidic channel created with a Focused Ion Beam technique, spliced to a single-mode fiber. Different stages were visible between the dipping and the evaporation of acetone and of a mixture of water and acetone. It was also possible to detect the presence of water vapor.
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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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    Active Illumination Single-Pixel Camera Based on Compressive Sensing
    ( 2011) Mehrdad Abolbashari ; Francisco Araújo ; Miguel Velhote Correia ; Faramarz Farahi ; Filipe Tiago Magalhães
    In this paper an optical imaging system based on compressive sensing (CS) is presented along with its principal mathematical aspects. Although CS is undergoing significant advances and empowering many discussions and applications throughout various fields, this article focus on the analysis of a single-pixel camera. This work was the core for the development of a single-pixel camera approach based on active illumination. Therefore, the active illumination concept is described along with experimental results, which were OSA Published by 2 very encouraging towards the development of compressive sensing based cameras for various applications, such as pixel level programmable gain imaging.
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    Adam Hilger revisited: a museum instrument as a modern teaching tool
    ( 2015) Carvalhal,MJ ; Manuel Joaquim Marques
    Spectroscopy can be historically traced down to the study of the dispersion of light by a glass prism. In the early 19th century, inspired by Newton's experiment, Fraunhofer creates a device where an illuminated slit and a lens are placed before the prism; such a device is later transformed, by Kirchoff and Bunsen, into a much handier and more precise observation and measurement instrument, the spectroscope. In the 1930's, the Physics Laboratory of the Faculty of Science of the University of Porto would buy, from Adam Hilger, Ltd., London, a constant deviation spectrometer. The ultimate purpose was to set up a spectroscopy laboratory for teaching and research. This model's robust construction (the telescope and the collimator are rigidly fixed) makes it adequate for student's practice. To sweep across the spectrum, all it takes is to rotate the high quality, constant deviation prism -known as Pellin-Broca prism. Spectra in the 390-900 nm interval are observed, either directly, or through photographic recording, or even by using a thermopile and associated galvanometer, when working in the infra-red range. The wavelength of the line under observation is read straight on a drum, which is fixed to the prism's rotation mechanism. Details of the construction and operation of this spectrometer are explored, against the background of present day spectrometers, automatic and computerized, thereby offering a deeper understanding of spectroscopic analysis: for instance, the use of the raies ultimes powder, a mixture of 50 chemical elements whose emission spectra provide a way of calibrating the instrument.
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    Addressing the Fabrication Difficulties of Femtosecond Laser Written Surface Waveguides for Enhanced Evanescent Coupling
    ( 2019) Vítor Oliveira Amorim ; João Miguel Maia ; Viveiros,D ; Marques,PVS ; 6407 ; 6596
    In this work, the fabrication of optical waveguides embedded in fused silica (Suprasil1) and boro-aluminosilicate glass (Eagle2000) is demonstrated with femtosecond laser direct writing, as well as their suitability to be brought to the surface, through wet etching, for enhanced evanescent coupling with the external dielectric medium. Fused silica demonstrated to be inappropriate in this particular application, as the guiding region is at the bottom of the induced modification, creating a barrier between the guided mode and the substrate’s boundary. Furthermore, the existence of nanogratings meant that, upon contact of the top of the induced modification with the substrate’s boundary, the waveguide is quickly etched. Eagle2000 demonstrated to be superior to fused silica due to its characteristic modification cross-section and absence of nanogratings, which allowed the placement of the guiding region as close to the substrate’s surface as required. However, surface roughness arising from the creation of insoluble products in the HF solution was found. The addition of HCl to dissolve these products was implemented.
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    An adjustable sensor platform using dual wavelength measurements for optical colorimetric sensitive films
    ( 2014) Carlos Manuel Machado ; Gouveia,C ; João Ferreira ; Kovacs,B ; Pedro Jorge ; Luís Lopes
    We present a new and versatile sensor platform to readout the response of sensitive colorimetric films. The platform is fully self-contained and based on a switched dual-wavelength scheme. After filtering and signal processing, the system is able to provide self-referenced measures of color intensity changes in the film, while being immune to noise sources such as ambient light and fluctuations in the power source and in the optical path. By controlling the power and the switching frequency between the two wavelengths it is possible to fine tune the output gain as well as the operational range of the sensor for a particular application, thus improving the signal conditioning. The platform uses a micro-controller that complements the analog circuit used to acquire the signal. The latter pre-amplifies, filters and conditions the signal, leaving the micro-controller free to perform sensor linearization and unit conversion. By changing the sensitive film and the wavelength of the light source it is possible to use this platform for a wide range of sensing applications. © 2014 IEEE.
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    Advanced experiments with an Erbium doped fiber laser
    ( 2014) Paulo Vicente Marques ; Manuel Joaquim Marques ; Carla Carmelo Rosa
    This communication describes an optical hands-on fiber laser experiment aimed at advanced college courses. Optical amplifiers and laser sources represent very important optical devices in numerous applications ranging from telecommunications to medicine. The study of advanced photonics experiments is particularly relevant at undergraduate and master level. This paper discusses the implementation of an optical fiber laser made with a cavity built with two tunable Bragg gratings. This scheme allows the students to understand the laser working principles as a function of the laser cavity set-up. One or both of the gratings can be finely tuned in wavelength through applied stress; therefore, the degree of spectral mismatch of the two gratings can be adjusted, effectively changing the cavity feedback. The impact of the cavity conditions on the laser threshold, spectrum and efficiency is analyzed. This experiment assumes that in a previous practice, the students should had already characterized the erbium doped fiber in terms of absorption and fluorescent spectra, and the spectral gain as a function of pump power.
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    Advances in Fs-Laser Micromachining Towards the Development of Optofluidic Devices
    ( 2019) João Miguel Maia ; Vítor Oliveira Amorim ; Daniel Alexandre ; Paulo Vicente Marques ; 4287 ; 4382 ; 6407 ; 6596
    In this chapter the developments made in femtosecond laser micromachining for applications in the fields of optofluidics and lab-on-a-chip devices are reviewed. This technology can be applied to a wide range of materials (glasses, crystals, polymers) and relies on a non-linear absorption process that leads to a permanent alteration of the material structure. This modification can induce, for instance, a smooth variation of the refractive index or generate etching selectivity, which can be used to form integrated optical circuits and microfluidic systems, respectively. Unlike conventional techniques, fs-laser micromachining offers a way to produce high-resolution three-dimensional components and integrate them in a monolithic approach. Recent advances made in two-photon polymerization have also enabled combination of polymeric structures with microfluidic channels, which can provide additional functionalities, such as fluid transport control. In particular, here it is emphasised the integration of microfluidic systems with optical layers and polymeric structures for the fabrication of miniaturized hybrid devices for chemical synthesis and biosensing. © 2019, Springer Nature Switzerland AG.
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    All fiber Mach-Zehnder interferometer based on suspended twin-core fiber
    ( 2010) Orlando Frazão ; J. Kobelke ; K. Schuster ; Susana Oliveira Silva ; José Luís Santos ; José Manuel Baptista
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    An all-fiber Fabry-Perot interferometer for pressure sensing in different gaseous environments
    ( 2014) Susana Oliveira Silva ; Luís Carlos Coelho ; Orlando Frazão
    A gas pressure sensor based on an all-fiber Fabry-Perot interferometer (FFPI) is reported. The sensing head consists of a small section of silica rod spliced with a large offset between two single-mode fibers. The silica rod is used only as mechanical support so that an air cavity can be formed between both SMF. It is shown that the FFPI sensor is sensitive to gas pressure variation and when submitted to different gaseous environments, namely carbon dioxide, nitrogen and oxygen - sensitivities of 6.2, 4.1 and 3.6 nm/MPa, respectively, were attained. The refractive index change on nitrogen environment by means of gas pressure variation was also determined and a sensitivity of 1526 nm/RIU was obtained. The response of the sensing device to temperature variations in air was also studied and a sensitivity of -14 pm/degrees C was attained.
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    All-fibre Wavelength Conversion Based on Four-Wave-Mixing in a Ring Erbium Doped Fibre Laser
    ( 2003) ; Orlando Frazão ; Manuel Joaquim Marques ; Joel Pedro Carvalho ; Henrique Salgado
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    AMINOSQUARYLIUM CYANINES DYES AND EVALUATION OF THEIR EFFECT ON THE PROLIFERATION AND VIABILITY OF HEPG-2 CELLS AND CACO-2 IN CULTURE
    ( 2012) José Ramiro Fernandes ; Sara Guerra ; Amélia Silva ; Lucinda Reis ; Paulo Almeida
    Photodynamic therapy (PDT) is an attractive alternative to the traditional cancer therapies. It involves the administration of a photosensitizing drug that accumulates preferentially in the neoplasic cells, which, by itself, is harmless and has no effect on either healthy or abnormal tissue. PDT photosensitizer candidates must fulfil some requirements, e.g., strong absorption (>105 M-1cm-1) ideally in the so-called 'photodynamic window' (600-850 nm), should be able to generate reactive species such as singlet oxygen in quantitative yields, have minimal dark toxicity and only be cytotoxic when the photosensitizer is irradiated with light of an appropriated wavelength.[1
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    Analysis of a fibre-optic sensor design based on SPR in nanowire metamaterial films
    ( 2014) Leite,IT ; Fernandes,P ; Aurélio Hierro Rodriguez ; Teixeira,JM ; Pedro Jorge ; Ariel Guerreiro
    This paper investigates numerically the performance of a design for an optical sensor of the refractive index of gases and liquids based on smart or functional metamaterial films (smart optical metamembranes).
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    Analysis of Phase Interrogated SPR Fiber Optic Sensors With Bimetallic Layers
    ( 2014) Hamed Moayyed ; Leite,IT ; Luís Carlos Coelho ; José Luís Santos ; Diana Viegas
    An effective analytical model combining geometrical optics with the transfer-matrix theory for stratified optical media is applied to investigate the sensing properties of tapered optical fiber surface plasmon resonance (SPR) sensors incorporating Ag-Au bimetallic layers, particularly in the context of phase interrogation. The performance of the sensing structures is studied as a function of the tapering parameters and thickness of the metallic layers. It is shown that the Ag-Au bimetallic combination is capable of improving the resolution and tuning working region of SPR fiber-optic sensors and that by tapering the sensing structures enhanced sensitivity can be achieved when phase interrogation is considered.