Antonio B. Lobo Ribeiro

Low coherence fiber optic system for remote sensors illuminated by a 1.3 μm multimode laser diode

A fiber optic sensor probe, with two low‐finesse Fabry–Perot cavities enabling the determination of displacement (in the range of a typical diaphragm pressure sensor) and temperature, is described. The sensors are connected in a reflective array network and their status is read using coherence tuned sensing based upon a multimode laser diode at 1.3 μm wavelength. Data are presented which show the resolution and linearity of the sensors for the measurement of displacement and temperature.

Simple multiplexing scheme for fiber optic grating sensor networks

A novel approach for the interrogation of multiplexed fiber optic Bragg grating sensors is described. Signal recovery is achieved by matching a receiving grating to a corresponding sensor grating. As a demonstration, the technique is applied to strain sensing.

A study of the optical properties of photopolymer Fabry-Perot microcavities by a dual-wavelength fibre optic architecture

We present a novel method to study the behaviour of the optical properties of photopolymer materials with temperature. The photopolymer is deposited on the tip of optical fibres by dip coating to fabricate low-finesse Fabry-Perot microcavities. The signal processing technique utilized to interrogate the cavity is based on the generation of two quadrature phase-shifted interferometric signals using two Bragg fibre gratings. This technique enables the determination of the values of the thermo-optical coefficient and the linear coefficient of thermal expansion of the photopolymer. The effectiveness of the processing technique is also exploited in the study of the dependence of the temperature sensitivity on the cavity thickness.

Bragg grating temperature and strain sensors.

wavelength changes when the fibre is placed under strain or subjected to a change in temperature so the grating may beused as a sensor.Many gratings may be written at arbritrary locations in the fibre so strain or temperature can be monitored atchosen discrete points over large distances. Possible applications include monitoring body temperature for medical

Optical fiber sources for measurement and imaging

An overview of the different type of fibre broadband sources and some fiber laser sources that operate as incoherent sources, are briefly discussed and some practical applications are presented. The optical performance and characteristics of several of these fiber sources are reviewed, including emission spectra profiles, autocorrelation functions, wavelength and power stabilities, and polarization behavior.

Simultaneously spatial-, time-, and wavelength-division multiplexed in-fiber Bragg grating sensor network

A simultaneous spatial, time and wavelength division multiplexing topology, with combination of a tunable wavelength filter and an interferometric wavelength scanner, is proposed to interrogate a range of in-fiber Bragg grating (FBG) sensors. An eleven-element FBG sensor network based upon this topology is demonstrated for quasi-static strain sensing. Preliminary experimental results show that a strain resolution of approximately 7 (mu) (epsilon) with an approximately 30 Hz bandwidth (approximately 1.3 (mu) (epsilon) /(root)Hz) for quasi-static strain measurement has been obtained.

Large range coherence tuned fiber optic interferometric system for application in accelerometers

A low coherence interferometric system with large tracking range and self‐initialization to be used for remote signal processing of fiber optic accelerometers is investigated. The tracking range of the low coherence system is 1.1 mm at low frequency. Phase resolution better than 1 mrad/√Hz at frequencies below 600 Hz is obtained, with a dynamic range of ≊90 dB. Data are presented which show that if the system were used to process the output from a compliant cylinder‐type accelerometer, resolutions of ∼10−7 g/√Hz could be achieved.

METAL-COATED OPTICAL FIBRE BRAGG GRATING FOR ELECTRIC CURRENT SENSING

The use of optical fibres as sensing elements for electric current measurement has been developed by several methods such as those utilising magnetic field to generate the Faraday effect, magnetomotive force to make fibres bend, magnetostrictive material bonded on a fibre to constrict or lengthen the fibre, and heating effect to change the fibre’s length and refractive index