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Author: Frazão, Orlando × DDC: 530 ×

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    Optical Vernier Effect: Recent Advances and Developments
    (Weinheim : Wiley VCH, 2021) Gomes, André D.; Bartelt, Hartmut; Frazão, Orlando
    The optical analog of the Vernier effect applied to fiber interferometers is a recent tool to enhance the sensitivity and resolution of optical fiber sensors. This effect relies on the overlap between the signals of two interferometers with slightly detuned interference frequencies. The Vernier envelope modulation generated at the output spectrum presents magnified sensing capabilities (i.e., magnified wavelength shift) compared to that of the individual sensing interferometers that constitute the system, leading to a new generation of highly sensitive fiber sensing devices. This review analyses the recent advances and developments of the optical Vernier effect from a fiber sensing point-of-view. Initially, the fundamentals of the effect are introduced, followed by an extensive review on the state-of-the-art, presenting all the different configurations and types of fiber sensing interferometers used to introduce the optical Vernier effect. This paper also includes an overview of the complex case of enhanced Vernier effect and the introduction of harmonics to the effect.
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    A Brief Review of New Fiber Microsphere Geometries
    (Basel : MDPI, 2018-7-11) Delgado Gomes, André; Silva Monteiro, Catarina; Silveira, Beatriz; Frazão, Orlando
    A brief review of new fiber microsphere geometries is presented. Simple microspheres working as Fabry–Perot cavities are interrogated in reflection and in transmission. Two microspheres were also spliced together, and subjected to different physical parameters. These structures are an alternative solution for load measurement and, when read in transmission, it is also possible to apply strain. Moreover, the structure is capable of being used under extreme ambient temperatures up to 900 °C. Random signal in cleaved microspheres was demonstrated with the possibility of using it for random laser or sensing applications. All this work was developed at the Centre for Applied Photonics, INESC TEC.
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    Fiber Fabry-Perot interferometer for curvature sensing
    (Berlin ; Heidelberg : Springer, 2016) Monteiro, Catarina S.; Ferreira, Marta S.; Silva, Susana O.; Kobelke, Jens; Schuster, Kay; Bierlich, Jörg; Frazão, Orlando
    A curvature sensor based on an Fabry-Perot (FP) interferometer was proposed. A capillary silica tube was fusion spliced between two single mode fibers, producing an FP cavity. Two FP sensors with different cavity lengths were developed and subjected to curvature and temperature. The FP sensor with longer cavity showed three distinct operating regions for the curvature measurement. Namely, a linear response was shown for an intermediate curvature radius range, presenting a maximum sensitivity of 68.52 pm/m-1. When subjected to temperature, the sensing head produced a similar response for different curvature radii, with a sensitivity varying from 0.84 pm/°C to 0.89 pm/°C, which resulted in a small cross-sensitivity to temperature when the FP sensor was subjected to curvature. The FP cavity with shorter length presented low sensitivity to curvature.