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About

About

O. Frazão, Graduated in Physics Engineering (optoelectronics and electronics) from the University of Aveiro, Portugal. He received the Ph. D. degree in Physics from the University of Porto, Portugal in 2009. Portugal. From 1997 to 1998, he was with the Institute of Telecommunications, Aveiro. Presently, he is a Researcher at Optoelectronics and Electronic Systems Unit, INESC Porto. He has published about 200 papers, mainly in international journals and conference proceedings, and his present research interests included optical fiber sensors and optical communications. He is member of the Optical Society of America (OSA) and The International Society for Optical Engineering (SPIE).

Interest
Topics
Details

Details

010
Publications

2019

High sensitivity strain sensor based on twin hollow microspheres

Authors
Monteiro, CS; Kobelke, J; Schuster, K; Bierlich, J; Silva, SO; Frazao, O;

Publication
MICROWAVE AND OPTICAL TECHNOLOGY LETTERS

Abstract
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.

2019

Multimode Fabry?Perot Interferometer Probe Based on Vernier Effect for Enhanced Temperature Sensing

Authors
Gomes, AD; Becker, M; Dellith, J; Zibaii, MI; Latifi, H; Rothhardt, M; Bartelt, H; Frazao, O;

Publication
Sensors (Basel, Switzerland)

Abstract
New miniaturized sensors for biological and medical applications must be adapted to the measuring environments and they should provide a high measurement resolution to sense small changes. The Vernier effect is an effective way of magnifying the sensitivity of a device, allowing for higher resolution sensing. We applied this concept to the development of a small-size optical fiber Fabry?Perot interferometer probe that presents more than 60-fold higher sensitivity to temperature than the normal Fabry?Perot interferometer without the Vernier effect. This enables the sensor to reach higher temperature resolutions. The silica Fabry?Perot interferometer is created by focused ion beam milling of the end of a tapered multimode fiber. Multiple Fabry?Perot interferometers with shifted frequencies are generated in the cavity due to the presence of multiple modes. The reflection spectrum shows two main components in the Fast Fourier transform that give rise to the Vernier effect. The superposition of these components presents an enhancement of sensitivity to temperature. The same effect is also obtained by monitoring the reflection spectrum node without any filtering. A temperature sensitivity of -654 pm/°C was obtained between 30 °C and 120 °C, with an experimental resolution of 0.14 °C. Stability measurements are also reported.

2019

Bi-core optical fiber for sensing o temperature, strain and torsion

Authors
Lobo Ribeiro, ABL; Silva, SFO; Frazao, O; Santos, JL;

Publication
MEASUREMENT SCIENCE AND TECHNOLOGY

Abstract
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.

2019

Optical Fiber Humidity Sensor Based on Polyvinylidene Fluoride Fabry-Perot

Authors
Vaz, A; Barroca, N; Ribeiro, M; Pereira, A; Frazao, O;

Publication
IEEE PHOTONICS TECHNOLOGY LETTERS

Abstract
An optical fiber Fabry-Perot (FP) for relative humidity (RH) sensing is proposed. The FP cavity is fabricated by splicing a short length of hollow silica tube in a single mode fiber. The fiber is then coated with a polyvinylidene fluoride (PVDF) thin film to work as a mirror. The fabrication process of the FP interferometer with a dip coating process in a PVDF/dimethyl formamide solution is presented. The pattern fringes of the FP suffer a wavelength shift due to the change in the PVDF's refractive index with the ambient RH variation. A short overview of the cavity's formation and stability is presented. The RH response of the FPI cavity is tested. The sensor presented a sensitivity of 32.54 pm/%RH at constant temperature and -15.2 pm/degrees C for temperature variation.

2019

Microfiber Knot Resonators for Sensing Applications

Authors
Gomes, AD; Frazão, O;

Publication
Springer Series in Optical Sciences

Abstract
Microfiber knot resonators are widely applied in many different fields of action, of which an important one is the optical sensing. Microfiber knot resonators can easily be used to sense the external medium. The large evanescent field of light increase the interaction of light with the surrounding medium, tuning the resonance conditions of the structure. In some cases, the ability of light to give several turns in the microfiber knot resonator allows for greater interaction with deposited materials, providing an enhancement in the detection capability. So far a wide variety of physical and chemical parameters have been possible to measure using microfiber knot resonators. However, new developments and improvements are still being done in this field. In this chapter, a review on sensing with microfiber knot resonators is presented, with particular emphasis on the application of these structures as temperature and refractive index sensors. A detailed analysis on the properties of these structures and different assembling configurations is presented. An important discussion regarding the sensor stability is presented, as well as alternatives to increase the device robustness. An overview on the recent developments in coated microfiber knot resonators is also addressed. In the end, other microfiber knot configurations are explored and discussed. © 2019, Springer Nature Switzerland AG.

Supervised
thesis

2018

Indicadores de Desempenho em Equipas de Desenvolvimento de Software

Author
João Pedro Pacheco de Figueiredo

Institution
UP-FEUP

2018

Sistema de recomendação para proteção de código

Author
Luís Filipe Rodrigues Carvalho

Institution
UP-FEUP

2018

Data Mining techniques for Prediction of secondary and 3D structures of proteins

Author
Luís Miguel da Costa Oliveira

Institution
UP-FEUP

2016

Cavity Ring-down Characterization Technique

Author
regina Magalhâes

Institution
UP-FCUP

2016

Polymer fiber based sensors

Author
Miguel Fernandes Soares Ferreira

Institution
UP-FCUP