Alicja Anuszkiewicz

Highly birefringent microstructured fibers with enhanced sensitivity to hydrostatic pressure

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.

Sensing characteristics of rocking filter fabricated in microstructured birefringent fiber using fusion arc splicer

We demonstrate that higher order rocking filters coupling energy between polarization modes at several wavelengths can be fabricated in a birefringent photonic crystal fiber using a fusion arc splicer. Three resonant couplings were identified, respectively at 855, 1271, and 1623 nm for the filter with a pitch distance of 8 mm characterized in this work. We also measured the filter response to temperature, elongation and hydrostatic pressure at the first and the second resonance. Our results show that the fabricated filter has very low sensitivity to temperature 1.77 and 1.38 pm/K, moderate sensitivity to elongation 1.35 and 1.12 nm/mstrain, and extremely high sensitivity to hydrostatic pressure 6.14 and 3.30 nm/MPa, respectively at the first and the second resonance.

Sensing and transmission characteristics of a rocking filter fabricated in a side-hole fiber with zero group birefringence

We report on sensing and transmission characteristics of rocking filters fabricated in a silica side-hole fiber with group birefringence changing its sign at certain wavelength (λ(G = 0)), which corresponds to parabolic-like spectral dependence of beat length. Unusual birefringence dispersion of the side-hole fiber is induced by an elliptical germanium doped core located in a narrow glass bridge between two holes. Rocking filters fabricated in such a fiber have two resonances of the same order located on both sides of λ(G = 0). The sensitivity of both resonances has an opposite sign, which makes it possible to double the response of the rocking filter by applying the differential interrogation scheme. We demonstrate that in this way a pressure sensitivity of the rocking filter can be enlarged to 132 nm/MPa. We also show that by fabricating the rocking filter with a period close to maximum beat length a coupling between polarization modes can be obtained in a broad band reaching 240 nm.

Sensing characteristics of the rocking filters in microstructured fibers optimized for hydrostatic pressure measurements

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.

Nonlinear frequency conversion in a birefringent microstructured fiber tuned by externally applied hydrostatic pressure

We studied vector frequency conversion in externally tuned microstructured fibers for applications as a novel, nonlinear fiber-optic sensor. We investigated both experimentally and numerically a possibility of shifting vector and scalar modulation instability gain bands by pressure-induced changes in the linear properties of a microstructured fiber. Our results show that polarization-dependent vector nonlinear processes sensitive to variation of fiber group velocity difference (group birefringence) exhibit a clear advantage for pressure-sensing applications compared with scalar nonlinear processes only sensitive to group velocity dispersion changes. Analytical predictions and numerical simulations confirm our measurement results.

Birefringence in microstructure fiber with elliptical GeO2 highly doped inclusion in the core.

We studied both numerically and experimentally a birefringence in a microstructure fiber with elliptical inclusion highly doped with GeO(2). We demonstrate that such inclusion increases the phase modal birefringence and modifies its dispersion in the short wavelength range, thus causing that group birefringence crosses zero value at a certain wavelength. Moreover, we numerically analyzed different factors contributing to the overall fiber birefringence, including geometrical birefringence induced by holes distribution and ellipticity of the inclusion as well as stress birefringence associated with thermal shrinkage of the doped glass.

Polarimetric sensitivity to hydrostatic pressure and temperature in a side-hole fiber with squeezed microstructure

We report on sensing characteristics of an endlessly single mode silica fiber with microstructure squeezed by very large side-holes. An elliptical shape of the cladding holes results in high phase and group modal birefringence, equal respectively to B = 3.33 × 10−4 and G = −6.62 × 10−4 at 1.55 μm. Thanks to a large diameter of the side-holes located in the solid part of the cladding, the fiber polarimetric sensitivity to hydrostatic pressure was increased two times compared to earlier reports and equals K p = −25.6 rad MPa−1 m−1 at 1.55 μm. Moreover, the fiber has a very low polarimetric sensitivity to temperature K T = −9.18 × 10−3 rad K−1 m−1 at 1.55 μm, thus allowing for hydrostatic pressure measurements with little cross-sensitivity to temperature. All measured parameters are in good agreement with the results of numerical simulations conducted using the finite element method.

Photonic crystal fibers for sensing applications

This paper discusses the sensing capabilities of the highly birefringent index-guided photonic crystal fibers (PCFs) such as dispersion characteristics of phase and group modal birefringence, polarization characteristics, sensitivity to hydrostatic pressures, temperature, and strain. Different types of applications including interferometric and polarimetric sensors of different physical parameters as well as evanescent field sensors for monitoring specific chemical compounds in gases and liquids are reported.

Formation of optical vortices with all-glass nanostructured gradient index masks

We report the development of microscopic size gradient index vortex masks using the modified stack-and-draw technique. The vortex mask has a form of flat surface all-glass plate. Its functionality is determined by an internal nanostructure composed of two types of soft glass nanorods. The generation of optical vortices with charges 1 and 2 is demonstrated.

Polarized all-normal dispersion supercontinuum reaching 2.5 µm generated in a birefringent microstructured silica fiber

We demonstrate a polarized all-normal dispersion supercontinuum generated in a birefringent silica microstructured fiber spanning beyond 2.5 µm. To our knowledge, this is the spectra reaching the furthest in mid-infrared ever generated in normal dispersion silica fibers. The generation process was studied experimentally and numerically with 70 fs pump pulses operating at different wavelengths on short propagation distances of 48 mm and 122 mm. The all-normal operation was limited by the zero-dispersion wavelength at 2.56 µm and spectral broadening was stopped by OH absorption peak at 2.72 µm. We identified the asymmetry between propagation in both polarization axes and showed that pumping along a slow fiber axis is beneficial for a higher degree of polarization. Numerical simulations of the generation process conducted by solving the generalized nonlinear Schrödinger equation (NLSE) and coupled NLSEs system showed good agreement with experimental spectra.