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 × m at 1.55 μm 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.

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.

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.

We present a dedicated fiber Bragg grating (FBG) inscription experiment to investigate the compatibility of a microstructured optical fiber (MOF) with conventional FBG inscription setups. For the studied MOF, the angular orientation of the fiber in the interferometric excimer laser setup was found to have no significant influence on the final reflection of the inscribed FBGs. We also show that an array of multiplexed FBGs can be inscribed in a single MOF with a repeatability and quality that match fiber sensing requirements.

We have systematically measured the differential stress-optic coefficient, $\mathrm{\Delta }C$, in a number of poly(methyl methacrylate) (PMMA) fibers drawn with different stress, ranging from 2 up to $27\mathrm{MPa}$. $\mathrm{\Delta }C$ was determined in transverse illumination by measuring the dependence of birefringence on additional axial stress applied to the fiber. Our results show that $\mathrm{\Delta }C$ in PMMA fibers has a negative sign and ranges from $-4.5$ to $-4.5\times {10}^{-12}{\mathrm{Pa}}^{-1}$, depending on the drawing stress. Increase of the drawing stress results in greater initial fiber birefringence and lower $\mathrm{\Delta }C$.