An investigation into the performance of an optically-interrogated Rogowski coil over temperatures up to 80 °C is presented. Preliminary thermal tests reveal that the sensor response is temperature-dependent and the measurement errors are increased at higher temperatures. Compensation of temperature effects is, therefore, necessary in order for the sensors to meet the requirements of protection and metering classes specified by relevant IEC standards over the considered operating temperature range. This can, however, only be achieved when the utilised sensor interrogator is adapted to ensure sufficient resolution and accuracy from a generally low-output transducer. As such, the design of a new multiplexing, interferometric interrogation platform is also proposed in this paper.
We present a solid-state FBG array interrogator and multiplexer capable of determining absolute FBG wavelengths and of providing high-speed, high-resolution static and dynamic measurements. Using a described procedure, deployable on multiplexing passive-interferometric schemes, the system is able to determine initial sensor wavelengths and thereafter track wavelength changes with interferometric resolution. The scheme allows high-resolution interrogation of FBG sensor arrays to be applied to many industrial applications, where previously the lack of combined absolute and quasistatic wavelength measurement precluded the use of interferometric techniques. Using a preliminary laboratory embodiment, we demonstrate a wavelength determination accuracy of <0.3 nm and a measurement resolution of 10 fm/√Hz, and propose pathways to improved performance and miniaturisation.
We report on the design and preliminary testing of an interferometric interrogator capable of large-scale time-division
multiplexing of FBG sensors. The scheme employs a passive algorithm for phase demodulation, allowing changes in
FBG sensor reflected wavelengths to be calculated instantaneously upon arrival, and incorporates a technique for
identification of initial absolute sensor wavelengths in order to overcome the measurement ambiguity associated with
interferometric schemes. The proposed system will allow for high-speed interrogation of large-scale FBG sensor arrays
with interferometric resolution and the capability for dynamic, static, and absolute FBG wavelength measurement.
In this paper we demonstrate through simulation the potential for phase-shifted fibre Bragg gratings incorporating
structural slow light to enable intrinsic reflection-mode point sensors for electric field or voltage. It is shown that lo-bi
FBGs incorporating multiple phase shifts yield large enhancements in group index (group delay) at resonance, thus
amplifying and localizing time-dependent non-reciprocal effects. A relative, multiplexable measurement of electric field
by comparison of the phase unbalance between linear modes on and off resonance is proposed, yielding static resolutions
of 24 V and 18 mV respectively in unpoled (dc Kerr effect) and poled (Pockels effect) fibres.
We present an FBG interrogation system incorporating a fast polarization selection mechanism that enables the
independent detection of sensor responses to orthogonal polarizations. By configuring the polarization-switching
subsystem in two example schemes - switching between either orthogonal linearly or circularly polarized FBG
reflections - we demonstrate the system's capability to interrogate single transducers for both fiber bend and longitudinal
strain, or for both magnetic field strength and temperature. With each embodiment the capability for serial multiplexing
of sensors is retained. The technique allows magnetic field or bend to be measured using intrinsic multiplexable
wavelength-encoded sensors, and will be applicable to a number of other polarization-dependent measurements such as
electric field or transverse strain.
Magneto-optical activity giving rise to circular birefringence and Faraday rotation is not usually an appropriate basis for
point measurement of magnetic field strength, acting as it must over extended lengths. In this paper we report on
investigations into the dispersion characteristics of structured fibre Bragg gratings for the purposes of implementing
novel polarimetric point sensors. Phase-shifts inscribed along the grating profile introduce windows in transmission that
correspond to highly resonant wavelengths undergoing large group delay. We demonstrate through fabrication of
structured gratings that their dispersion characteristics can be tailored, producing regions of spectrally co-located
reflection and large group delay. Importantly, it is shown how a number of such regions can contribute to a single
enhanced group delay in reflection. Through simulation we discuss the potential for implementing polarimetric magnetic
field sensors which operate in reflection.
We present a solution to the simultaneous intrinsic point sensing of bi-directional magnetic field strength and
temperature. Using a passive, retroactive method for polarisation selection based on a local chiral fibre device, a series of
dual-wavelength fibre Bragg gratings written in polarisation-maintaining fibre may be interrogated for both measurands
over long distance using linearly polarised light. Through simulation we identify and evaluate sources of error in the
scheme in order to find the design that yields the optimal sensitivity and noise level, which for the multiplexing
interferometric interrogator are 3.0 μrad/mT and 22 mT rms respectively at a rate of up to 10 kHz.
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