A simple refractive index sensor based on a fat long period fiber grating (FLPFG) in a single-mode fiber is constructed
and demonstrated. The sensor consists of periodical fattening region in a short piece of single-mode fiber. In this method,
the fiber fattening is realized by applying a standard fusion splicing procedure on single mode optical fiber. The
sensitivity of the sensor is 7.5 x 10-5 which the sensitivity is enhanced to the other kinds of long period fiber grating
(LPFG).
A hybrid long period fiber grating (HLPFG) sensor was utilized for sensing the refractive index and pressure for downhole
applications. The HLPFG is fabricated by fattening and tapering on a single mode fiber, utilizing a standard fusion
splicing and a CO2 laser, respectively. The limit of detection (LOD) of the HLPFG for the RI measurement in the range
from 1.3150 to 1.3559 is 4x10-5 as a refractometer sensor which can be used for analysis of multicomponent in native
petroleum. Pressure sensitivity of the HLPFG sensors in the range from 500 to 6000 psi is -0.6 pm/psi. With a 10 pm
resolution for the wavelength shift detection our OSA, the LOD of the device at room temperature for pressure
measurement is calculated to be 17 psi. This sensor can be used as a high pressure sensor in downhole application.
We report fabrication of a high pressure optical fiber sensor by using a fat long period fiber grating (FLPFG) for
downhole applications. The pressure sensitivity of the bare optical fiber is low so we have designed a mechanical
transducer for increasing the pressure sensitivity and possibility of installation the sensor in downhole. The pressure
along the longitudinal direction changes the physical characteristic of the FLPFG and result in shifting the resonance
wavelength. The FLPFG sensor has been installed on transducer and the pressure sensitivity of the fiber sensor has been
measured. Since the temperature changes can affect the FLPFG output, the high pressure vessel was isolated and the
temperature was kept constant during the experiment. Pressure sensitivity of the FLPFG sensors has been measured by
increasing the pressure from 1500 psi to 10000 psi in steps of 700 psi which is equal to -1.04 pm/psi. With a 10 pm
resolution for the wavelength shift detection our OSA, detection limit of our device at room temperature for pressure
measurement is calculated to be 10 psi.
We report fabrication of a high pressure nonadiabatic tapered optical fiber (NATOF) for downhole applications by using a
mechanical transducer. The mechanical transducer has been used for increasing the pressure sensitivity and possibility of
installation the sensor in downhole. The NATOF is fabricated by heat pulling method, utilizing a CO2 laser. The limit of
detection of the NATOF was 15 psi.
In this work, two all-fibre interferometric configurations based on suspended core fibres (SCF) are
investigated. A Fabry-Pérot cavity made of SCF spliced in-between segments of single-mode and hollow-core
fiber is proposed. An alternative sensing head configuration formed by the insertion of a length of
SCF as a birefringence element in a Sagnac interferometer is also demonstrated. The sensitivity to pressure
and temperature was determined for both configurations.
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