A. B. Lobo Ribeiro

Simple multiplexing scheme for a fiber-optic grating sensor network

A new approach for the interrogation of a large number of fiber-optic grating sensors is proposed and demonstrated for a small number of sensors in which signal recovery is achieved by matching a receiving grating to its corresponding sensor. This technique is demonstrated for both quasi-static and periodic measurands, and the resolution achieved for a single sensor–receiving grating pair for quasi-static strain is 4.12 μ∊.

Analysis of the reflective-matched fiber Bragg grating sensing interrogation scheme.

A technique for the demodulation of fiber Bragg grating (FBG) sensors based on the use of a second wavelength-matched FBG receiver to track wavelength shifts from the FBG sensor is analyzed, particularly regarding its sensitivity as determined by primary noise sources. Numerical and experimental results show that there is an optimum Bragg wavelength difference between the two FBGs that maximizes the sensitivity for this demodulation technique.

Simultaneous spatial, time and wavelength division multiplexed in-fibre grating sensing network

Abstract 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-fibre 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 ∼7 μϵ with a ∼30 Hz bandwidth (∼1.3 μϵ⧸ Hz for quasi-static strain measurement has been obtained.

Simultaneous measurement of displacement and temperature using a low finesse cavity and a fiber Bragg grating

An optical sensor capable of simultaneously measuring displacement and temperature is presented. It incorporates a fiber Bragg grating temperature sensor and a low-finesse extrinsic Fabry-Perot cavity. A white light tandem interferometric technique is used to recover signal from the low finesse cavity. Signals obtained from the interferometer and the Bragg grating provide required information to simultaneously determine temperature and displacement. Experimental results are presented which demonstrate the feasibility of this sensor topology in practical applications.

Multipoint Fiber-Optic Hot-Spot Sensing Network Integrated Into High Power Transformer for Continuous Monitoring

A multipoint fiber-optic temperature sensor network integrated inside a power transformer for continuous monitoring of hot-spots on windings, cellulose insulations, and oil, is demonstrated and tested. The temperature sensors are based on proprietary encapsulated fiber Bragg grating (FBG) sensors and the optical interrogation unit uses a special designed narrowband high power broadband fiber source. The fiber-optic sensing network is integrated into a 20 MVA, 345/radic3 kV -20 kV power transformer (CORE type) having 12 temperature sensing points, distributed over several physical locations inside the transformer (windings, cellulose insulators, magnetic circuit, and cooling oil entrance and exit).

Demultiplexing of fibre Bragg grating temperature and strain sensors

We describe a demultiplexing scheme for fibre optic Bragg grating sensors in which signal recovery is achieved by locking each sensor grating to a corresponding receiver grating. As a demonstration, the technique is applied to strain and temperature sensing, achieving a resolution of 3.0 µe and 0.2°C, respectively.

Fiber-Optic Inclinometer Based on Taper Michelson Interferometer

A compact fiber-optic inclinometer based on a fiber-taper Michelson interferometric sensor is constructed and demonstrated. The sensor consist of a single symmetrically taper waist of 80 μm distanced 30 mm from the single-mode fiber end-tip right-angled cleaved. The amplitude of the bending angle of the fiber taper interferometer is obtained by passive interferometric interrogation based on the generation of two quadrature phase-shifted signals from two fiber Bragg gratings with different resonant wavelengths. Optical phase-to-bending sensitivity of ~ 1.13 rad/degree and a bend angle resolution of ~ 0.014 degree/√ Hz were achieved.

Simultaneous displacement and temperature sensing using a white light interrogated low finesse cavity in line with a fiber Bragg grating

A fiber optic sensing system for simultaneous measurement of displacement and temperature is presented. It is based on the use of a low finesse extrinsic Fabry-Perot cavity and a fiber Bragg grating for temperature compensation. A white light tandem interferometric technique is used to recover the signal from the low finesse cavity, providing both fringe visibility and phase measurements. These, together with the fiber grating signal, give two equations that can be used to simultaneously determine temperature and displacement. Theoretical analysis of the sensing scheme is performed. Experimental results are presented which validate theoretical predictions and also demonstrate the feasibility of this sensing system in practical applications.

Time-and-spatial-multiplexing tree topology for fiber-optic Bragg-grating sensors with interferometric wavelength-shift detection.

A combined time-and-spatial-division-multiplexed tree topology with eight fiber-optic Bragg-grating sensors operating at the 830-nm wavelength was constructed and tested for both quasistatic and periodic strain and temperature measurements. The system uses a interferometric wavelength-shift discriminator and incorporates a reference channel for thermal drift compensation in the output. Dynamic sensor sensitivity, as determined by primary noise sources, is evaluated, and numerical results are presented and compared with experimental results.

Multiplexing interrogation of interferometric sensors using dual multimode laser diode sources and coherence reading

Abstract A multiplexing topology with virtually no cross-talk is demonstrated for a sensor network based upon low coherence interferometry, in which a scanning interferometer simultaneously interrogates all the sensors. Dual wavelength operation using two multimode laser diode sources is implemented. The concept is demonstrated by multiplexing two bulk optical Michelson interferometers. For both sensors the achieved resolution was of the order of 1 nm, with a working range of 45 μm.