Charles Jewart

Ultrafast femtosecond-laser-induced fiber Bragg gratings in air-hole microstructured fibers for high-temperature pressure sensing

We present fiber Bragg grating pressure sensors in air-hole microstructured fibers for high-temperature operation above 800 degrees C. An ultrafast laser was used to inscribe Type II grating in two-hole optical fibers. The fiber Bragg grating resonance wavelength shift and peak splits were studied as a function of external hydrostatic pressure from 15 psi to 2000 psi. The grating pressure sensor shows stable and reproducible operation above 800 degrees C. We demonstrate a multiplexible pressure sensor technology for a high-temperature environment using a single fiber and a single-fiber feedthrough.

Sensitivity enhancement of fiber Bragg gratings to transverse stress by using microstructural fibers

We present simulation and experimental results of fiber Bragg grating responses to transverse stress in microstructure fibers. The grating wavelength shifts and peak splits are studied as a function of external load and fiber orientation. Both simulation and measurement results indicate that the sensitivity of grating sensors to the transverse stress can be enhanced by a factor of eight in a two-hole fiber over that in a standard fiber.

Design of a highly-birefringent microstructured photonic crystal fiber for pressure monitoring

We present the design of an air hole microstructured photonic crystal fiber for pressure sensing applications. The air-hole photonic crystal lattices were designed to produce a large intrinsic birefringence of 1.16 x 10(-3). The impact of the surrounding air holes for pressure sensing to the propagation mode profiles and indices were studied and improved, which ensures single mode propagation in the fiber core defined by the photonic crystal lattice. An air hole matrix and a practical chemical etching process during the fiber perform preparation stage is proposed to produce an optical fiber with a birefringence-pressure coefficient of 43.89 x 10 (-6)MPa(-1) or a fiber Bragg grating pressure responsivity of 44.15 pm/MPa, which is a 17 times improvement over previous photonic crystal fiber designs.

Distributed high-temperature pressure sensing using air-hole microstructural fibers

We present spatially resolved Rayleigh scattering measurements in different polarization-maintaining (PM) fibers for high-temperature pressure sensing. The pressure-induced birefringence in the fiber cores is interrogated using polarization-resolved frequency-swept interferometry. The pressure responses of a PM photonic crystal fiber and a twin-air-hole PM fiber are investigated for a pressure range of 0 to 13.8 MPa (0-2000 psi) at room temperature and at temperatures as high as 800 °C. The proposed sensing system provides, for the first time to our knowledge, a truly distributed pressure-sensing solution for high-temperature applications.

Suspended-core fiber Bragg grating sensor for directional-dependent transverse stress monitoring

This Letter presents simulation and experimental results of orientation-dependent transverse stress fiber sensors using fiber Bragg gratings (FBGs) inscribed in four-hole suspended-core fibers. Resonant peak shifts and splitting of FBGs were studied as functions of the applied transverse load and fiber orientation. Both simulation and experimental results revealed that the response of FBGs in suspended-core fibers is sensitive to both the orientation and magnitude of an applied transverse stress.

Bending insensitivity of fiber Bragg gratings in suspended-core optical fibers

This Letter presents simulation and experimental results that explore bending insensitivity of fiber Bragg gratings in suspended-core optical fibers. The implementation of thin silica bridge in the fibers enhances index contrast of the fiber core and reduces bending-induced strain transfer to the fiber core. This fiber design lead to a reduction of over 7 times in strain-induced fiber Bragg grating resonant peak shifts in the suspended-core fiber compared with that in standard telecommunication fiber, and an 0.14 dB bending loss at a bending radius of 6.35 mm.

Structure optimization of air-hole fibers for high-sensitivity fiber Bragg grating pressure sensors

This paper presents sensitivity enhancement of fiber Bragg grating sensors written in two hole fibers to external hydrostatic pressure. Finite element analysis was used to optimize the size, diameter, and configuration of air holes. The fiber core was then fabricated in the region with the maximum birefringence induced by external pressure. Resonant peak splitting of fiber Bragg gratings were used to gauge the external hydrostatic pressures. By using 220-μm diameter two hole fibers with 90-μm air holes, the optimized fiber structure with a fiber core fabricated on the edge of the air hole registered 0.102 pm/psi hydrostatic pressure response, yielding 6.5 times enhancement than previously reported in two hole fibers. The sensitivity enhancement of fiber sensors is further demonstrated by controlling the size of air holes.

Thermally regenerated fiber Bragg gratings in twin-air-hole microstructured fibers for high temperature pressure sensing

We present thermally regnenerated fiber Bragg grating in air-hole microstructured fibers for high temperature hydrostatic pressure sensing application. Saturated type I gratings were inscribed in hydrogen-loaded two-hole optical fibers using 248-nm KrF laser, and regenerated during annealing at 800ºC. The fiber Bragg grating resonance wavelength shift and peak splits were studied as a function of external hydrostatic pressure from 15 psi to 2400 psi. The grating pressure sensor shows stable and reproducible operation up to 800ºC. This paper demonstrates a multiplexible pressure sensor network technology for high temperature harsh environment using a single fiber feedthrough.

Fiber Bragg Grating Transverse Load Sensors Using Suspended Core Fibers for Directional Dependent Strain Measurement

This paper presents simulation and experimental results of orientation-dependent transverse load fiber sensors using fiber Bragg gratings written in four-hole suspended core fibers. Resonant peak shifts and splitting of fiber Bragg gratings were studied as functions of the applied transverse load and its orientation. Both simulation and experimental results revealed that response of fiber Bragg grating in suspended core fibers are sensitive to both orientation and magnitude of transverse strains.

High-temperature fiber Bragg grating sensors in microstructured fibers for harsh environment applications

In this paper, we present fiber Bragg grating pressure sensors written in twin-hole microstructured fibers for high temperature operation above 800 °C. A Ti: Sapphire ultrafast laser is used to inscribe type II grating in two-hole optical fibers. The fiber Bragg grating resonance wavelength shift and peak splits are studied as a function of external hydrostatic pressure from 15 psi to 2000 psi. The ultrafast laser inscribed grating pressure sensor shows stable and reproducible operation above 800 °C. This paper demonstrates highly multiplexible pressure sensor technology for high temperature environment.