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We designed, manufactured and characterized two birefringent microstructured fibers that feature a 5-fold increase in polarimetric sensitivity to hydrostatic pressure compared to the earlier reported values for microstructured fibers. We demonstrate a good agreement between the finite element simulations and the experimental values for the polarimetric sensitivity to pressure and to temperature. The sensitivity to hydrostatic pressure has a negative sign and exceeds -43 rad/MPa x m at 1.55 microm for both fibers. In combination with the very low sensitivity to temperature, this makes our fibers the candidates of choice for the development of microstructured fiber based hydrostatic pressure measurement systems.

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A Sagnac interferometer with a section of a polarization maintaining side-hole fiber for multiparameter measurement is proposed. The sensor was experimentally demonstrated to be sensitive to torsion, temperature, and longitudinal strain, simultaneously. The birefringence in the investigated side-hole fiber is induced simultaneously by the elliptical shape of a germanium-doped core and by field overlap with the air holes surrounding the core. The latter effect is purely geometrical and causes high chromatic dispersion of the group birefringence in the long wavelength range, which results in a different period of spectral interference fringes. A different wavelength response is obtained for each interference fringe peak when the fiber is subjected to torsion, temperature, or longitudinal strain. A matrix equation for simultaneous measurement of the three parameters--torsion, temperature, and longitudinal strain--is also proposed.

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We present a microstructured polymer fiber dedicated to long period grating (LPGs) inscription using a focused UV laser beam. The core and the microstructured cladding of the developed fiber are made of pure poly(methyl methacrylate) (PMMA). The external layer of the solid part of the cladding has increased UV absorption due to doping with trans-4-stilbenemethanol, which shows an absorption band at around 310 nm related to trans-cis photoisomerization. We present transmission characteristics of LPGs fabricated in this fiber using the point-by-point inscription technique with a He-Cd laser beam of 325 nm wavelength. We also demonstrate that in the proposed fiber, the fabrication process is shortened six times compared to pure PMMA fibers. Moreover, we report on temperature response and long-term stability of the fabricated gratings.

We demonstrate for the first time a possibility of fabrication of Bragg gratings in polymer microstructured fibers with multiple reflection peaks by using He-Cd laser (λ = 325 nm) and a phase mask with higher diffraction orders. We experimentally studied the growth dynamics of the grating with the primary Bragg peak at λ(B) = 1555 nm, for which we also observed good quality peaks located at λ(B)/2 = 782 nm and 2λ(B)/3 = 1040 nm. Temperature response of all the Bragg peaks was also investigated. Detailed numerical simulations of the interference pattern produced by the phase mask suggests that the higher order Bragg peaks originate from interference of UV beams diffracted in ± 1st, ± 2nd orders. We also demonstrated the grating with the reflection peak at λ(B)/2 = 659 nm, which is the shortest Bragg wavelength ever reported for polymer microstructured fibers. This peak was observed for the grating with primary Bragg wavelength at λ(B) = 1309 nm.

We report on the sensing characteristics of rocking filters fabricated in two microstructured fibers with enhanced polarimetric sensitivity to hydrostatic pressure. The filter fabricated in the first fiber shows a very high sensitivity to pressure ranging from 16.2 to 43.4 nm/MPa, depending on the resonance order and features an extremely low cross-sensitivity between pressure and temperature 28 ÷ 89 × 10(3) K/MPa. The filter fabricated in the second fiber has an extreme sensitivity to pressure ranging from -72.6 to -177 nm/MPa, but a less favorable cross-sensitivity between pressure and temperature of 1.05 ÷ 3.50 × 10(3) K/MPa. These characteristics allow using the rocking filters for pressure measurements with mbar resolution.