The effect of pressures up to 200 kPa on pi-phase-shifted Bragg gratings was investigated in several types of
fibers placed in a pressure chamber. Standard and alternative types of pi-phase shifted gratings were studied,
and changes in reflection spectra caused by pressure changes were monitored. The alternative pi-phase shifted
grating was fabricated using a phase mask with 536-nm pitch exhibiting features at twice the Bragg
wavelength near 1552 nm due to the interleaved refractive index modulations along the fiber core with the
periodicity of the phase mask. The three gratings studied exhibited quite different variation in Bragg
wavelength with increased pressure for the different fiber types, and the alternative pi-phase-shifted grating in
Corning HI 1060 FLEX fiber also suffered a significant change in the shape of the peaks.
The effect of transverse strain on a uniquely etched phase-shifted fiber Bragg grating (FBG) was investigated. The
relevant phase-shifted FBG was fabricated by the application of a non-uniform wet chemical etching technique. The
prospect of providing temperature independent transverse strain measurements is also explored using this FBG.
The effect of bending on the twin peaks of an alternative type of pi-phase shifted fibre Bragg grating (FBG) (embedded
in a resin) at twice the Bragg wavelength, has been investigated. Variation of the direction of bending resulted in
corresponding changes in the relative intensity of these peaks. Temperature independent bend measurements were
realised by monitoring the change of ratio of the reflected intensities of these peaks.
A multipoint fiber optic refractive index sensor is presented, that is potentially capable of simultaneous
measurement from many samples. The operation of this sensor is based on the reflection of light from a
cleaved fiber end when the sensor is moved from one medium to another, while the sensor consists of two
fiber couplers and an optical fiber Bragg grating (FBG). Experimental characterization of the sensor shows
excellent agreement with numerical analysis and a precision of 0.002 and resolution of the order of 10-3.
Through the use of multiple Bragg wavelengths measurement at multiple points is achieved.
The effect of transverse strain on a fiber Bragg grating fabricated using a phase mask with 536-nm pitch has
been investigated through the study of its reflection and transmission features at twice the Bragg wavelength
near 1552 nm, that are due to reflection/transmission from FBG periodicities associated with the phase mask
periodicity. The occurrence of two peaks in the reflection spectrum is due to the interleaved refractive index
modulations along the fiber core, with the periodicity of the phase mask that produces a type of π-phaseshifted
grating. The response of these features to transverse strain is similar to that observed previously for
features at 2/3 of the Bragg wavelength that also arise from the same complex refractive index structure.
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