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About

Graduated in Physics - Optics from the University of Minho (1999), he obtained a Masters in Optoelectronics and Laser from Faculty of Science from University of Porto (2003), a PhD in Physics from Faculty of Science from University of Porto (2011). He is Associate Professor in Instituto Politécnico de Viana do Castelo and Senior Researcher at the Applied Photonics Center INESC TEC. It is author and co-author of over 80 scientific articles related to optical fibers sensors, whispering gallery modes and long period grating.

Interest
Topics
Details

Details

  • Nationality

    Portugal
  • Centre

    Applied Photonics
  • Contacts

    +351220402301
    paulo.caldas@inesctec.pt
Publications

2021

Experimental investigation of a strain gauge sensor based on Fiber Bragg Grating for diameter measurement

Authors
Cardoso, VHR; Caldas, P; Giraldi, MTR; Frazao, O; de Carvalho, CJR; Costa, JCWA; Santos, JL;

Publication
Optical Fiber Technology

Abstract
A strain gauge sensor based on Fiber Bragg Grating (FBG) for diameter measurement is proposed and experimentally demonstrated. The sensor is easily fabricated inserting the FBG on the strain gauge—it was fabricated using a 3D printer—and fixing the FBG in two points of this structure. The idea is to vary the diameter of the structure. We developed two experimental setups, the first one is used to evaluate the response of the FBG to strain and the second one to assess the possibility of using the structure developed to monitor the desired parameter. The results demonstrated that the structure can be used as a way to monitor the diameter variation in some applications. The sensor presented a sensitivity of 0.5361 nm/mm and a good linear response of 0.9976 using the Strain Gauge with FBG and fused taper. © 2020 Elsevier Inc.

2021

Arc-Induced Long-Period Fiber Gratings at INESC TEC. Part I: Fabrication, Characterization and Mechanisms of Formation

Authors
Rego, G; Caldas, P; Ivanov, OV;

Publication
SENSORS

Abstract
In this work, we reviewed the most important achievements of INESC TEC related to the fabrication of long-period fiber gratings using the electric arc technique. We focused on the fabrication setup, the type of fiber used, and the effect of the fabrication parameters on the gratings' transmission spectra. The theory was presented, as well as a discussion on the mechanisms responsible for the formation of the gratings, supported by the measurement of the temperature reached by the fiber during an electric arc discharge.

2021

Arc-induced long-period fiber gratings at inesc tec. Part ii: Properties and applications in optical communications and sensing

Authors
Rego, G; Caldas, P; Ivanov, OV;

Publication
Sensors

Abstract
In this work, we review the most important achievements of INESC TEC related to the properties and applications of arc-induced long-period fiber gratings. The polarization dependence loss, the spectral behavior at temperatures ranging from cryogenic up to 1200 °C and under exposure to ultraviolet and gamma radiation is described. The dependence of gratings sensitivity on the fabrication parameters is discussed. Several applications in optical communications and sensing domains are referred. © 2021 by the authors. Licensee MDPI, Basel, Switzerland.

2021

Simulation of the Transmission Spectrum of Long-Period Fiber Gratings Structures with a Propagating Acoustic Shock Front

Authors
Ivanov, OV; Caldas, P; Rego, G;

Publication
SENSORS

Abstract
In this paper, we investigate modification of transmission spectra of long-period fiber grating structures with an acoustic shock front propagating along the fiber. We simulate transmission through inhomogeneous long-period fiber gratings, pi-shift and reflective pi-shift gratings deformed by an acoustic shock front. Coupled mode equations describing interaction of co-propagating modes in a long-period fiber grating structures with inhomogeneous deformation are used for the simulation. Two types of apodization are considered for the grating modulation amplitude, such as uniform and raised-cosine. We demonstrate how the transmission spectrum is produced by interference between the core and cladding modes coupled at several parts of the gratings having different periods. For the pi-shift long-period fiber grating having split spectral notch, the gap between the two dips becomes several times wider in the grating with the acoustic wave front than the gap in the unstrained grating. The behavior of reflective long-period fiber gratings depends on the magnitude of the phase shift near the reflective surface: an additional dip is formed in the 0-shift grating and the short-wavelength dip disappears in the pi-shift grating.

2021

Optical Fiber Interferometers Based on Arc-Induced Long Period Gratings at INESC TEC

Authors
Caldas, P; Rego, G;

Publication
SENSORS

Abstract
In this work, we review the most important achievements of an INESC TEC long-period-grating-based fiber optic Michelson and Mach-Zehnder configuration modal interferometer with coherence addressing and heterodyne interrogation as a sensing structure for measuring environmental refractive index and temperature. The theory for Long Period Grating (LPG) interferometers and coherence addressing and heterodyne interrogation is presented. To increase the sensitivity to external refractive index and temperature, several LPG interferometers parameters are studied, including order of cladding mode, a reduction of the fiber diameter, different type of fiber, cavity length and the antisymmetric nature of cladding modes.