The use of polarization-maintaining photonic crystal fiber in a Sagnac interferometer configuration operating at 850 nm
shows large response to applied pressure. The sensor demonstrates a 300% improvement in sensitivity than when
operating at 1550 nm. Using wavelengths at the 850 nm window enable the use of low-cost CCD-interrogator which
also provides a much higher spectrum scanning speed than the much more expensive optical spectrum analyzers.
We present a highly sensitive salinity sensor realized with a polyimide-coated polarization-maintaining photonic crystal
fiber (PM-PCF) based on a Sagnac interferometer configuration. The achieved salinity sensitivity is as high as 0.616
nm/M which is 37 times more sensitive than that of previous reported polyimide-coated fiber grating sensor. It has a low
temperature sensitivity of -0.0122 pm/°. The performance of the sensor in aqueous solution of NaCl with concentrations
up to 5.12 mol/L has been experimentally investigated. The proposed fiber optic salinity sensor is a promising candidate
for salinity measurement.
The viability of an all-optical fibre optical thermocoupler for remote sensing of ultra-high temperatures, independent of
electronics, is explored. Simple packaging of regenerated fibre Bragg gratings (FBGs) within silica capillaries were
shown to protect the fibre structure sufficiently to allow the temperature measurement of a furnace element to >1500 °C;
a temperature at which the regenerated FBG, which was written in relatively soft boron-codoped germano silicate glass,
was shown to decay rapidly.
Rapid annealing of Regenerated fibre Bragg gratings observed at temperatures approaching 1500
°C. Simple packaging within a dry silica tube is found to resolve issue of brittleness of fibres at
extreme temperatures.
We experimentally demonstrate a high pressure sensor based on a polarization-maintaining photonic crystal fiber (PMPCF)
with Sagnac loop configuration for downhole application. The pressure sensitivity of the proposed sensor is 4.21
nm/MPa and 3.27 nm/MPa at ~1320 nm and ~1550 nm respectively. High pressure measurement up to 20 MPa has been
achieved in our experiment. The sensor also shows reduced temperature sensitivity, making it an ideal candidate for
pressure sensing in harsh environment.
We proposed and demonstrated the application of a polarization-maintaining photonic crystal fiber for torsion sensing.
The sensor has high twist angle resolution and exhibits reduced temperature sensitivity, making it an ideal candidate for
torsion sensing.
A novel interrogation method for optical fiber Bragg grating (FBG) sensors has been proposed by converting the change
of the FBG wavelength into the phase difference between two radio frequency (RF) signals. As a result, the beating-induced
RF signal power changes with the FBG wavelength shift. This technique could be used for high speed FBG
interrogation and, due to the use of a second FBG to produce the reference RF signal, temperature cross-sensitivity effect
is compensated automatically. Theoretical analysis and experimental demonstration have been carried out. Performances
of the FBG sensor interrogation scheme have been studied.
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