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.

We have manufactured and characterized a birefringent holey fiber of a new construction. The birefringence in this fiber is induced by the highly elliptical shape of the core, which consists of a triple defect in a hexagonal structure. Using a hybrid edge-nodal finite-element method, we calculated the spectral dependence of phase and group modal birefringence for spatial modes E11 and E21 in idealized and in real fiber, whose geometry we determined by using a scanning-electron microscope. Results of our calculations show that technological imperfections significantly affect the fiber's birefringence. Normalized cutoff wavelengths for higher-order modes relative to the filling factor were also determined for the idealized structure. We observed a significant disagreement between theoretical and experimental values of cutoff wavelengths, which was attributed to high confinement losses near the cutoff condition. We also measured the spectral dependence of the phase and the group modal birefringence for spatial modes E11 and E21. The measured parameters showed good agreement with the results of modeling.

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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.

We report on experimental studies of polarimetric sensitivity to hydrostatic pressure and temperature in two highly birefringent index guided photonic crystal fibers, in which birefringence is induced by one row of the cladding holes with diameters smaller than the other cladding holes. The sensitivity measurements were carried out in the spectral range from 0.6 µm to 1.6 µm. Our results show that absolute value of the polarimetric sensitivity to hydrostatic pressure can reach 23 rad/MPa×m, which is almost one order of magnitude higher than in conventional fibers with elliptical core. Simultaneously, polarimetric sensitivity to temperature is at least two orders of magnitude lower than in conventional highly birefringent fibers. Moreover, we proved experimentally that one of the investigated fibers is completely insensitive to temperature at certain wavelength.