Gabriela Statkiewicz

Fiber Bragg Gratings in Germanium-Doped Highly Birefringent Microstructured Optical Fibers

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.

Experimental and theoretical investigations of birefringent holey fibers with a triple defect.

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 fibers 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.

Measurements of polarimetric sensitivity to hydrostatic pressure, strain and temperature in birefringent dual-core microstructured polymer fiber

We experimentally characterized a birefringent microstructured polymer fiber of specific construction, which allows for single mode propagation in two cores separated by a pair of large holes. The fiber exhibits high birefringence in each of the cores as well as relatively weak coupling between the cores. Spectral dependence of the group and the phase modal birefringence was measured using an interferometric method. We have also measured the sensing characteristics of the fiber such as polarimetric sensitivity to hydrostatic pressure, strain and temperature. Moreover, we have studied the effect of hydrostatic pressure and strain on coupling between the cores.

Measurements of polarimetric sensitivity to temperature in birefringent holey fibres

We measured spectral dependence of the polarimetric sensitivity to temperature in three birefringent holey fibres with different geometries. Our results show that thermal properties of the birefringent photonic crystal fibres depend very much on the air hole arrangement. Using the procedure which allows us to determine the sign of temperature sensitivity, we demonstrated that one of the investigated fibres is insensitive to temperature at a certain wavelength. We also measured the temperature sensitivities for the fibres with and without polymer coating and showed that the coating changes significantly the fibre response to temperature. Furthermore, we demonstrated experimentally that the spectral dependence of the polarimetric sensitivity to temperature in birefringent holey fibres obeys a scaling law.

Measurement and modelling of dispersion characteristics of a two-mode birefringent holey fibre

Employing several interferometric methods, we measured in a broad spectral range the wavelength dependences of the phase modal birefringence and the polarization mode dispersion for the LP01 and even LP11 spatial modes supported by a birefringent holey fibre. We also determined the wavelength dependence of the intermodal dispersion between the X- and Y-polarized LP01 and even LP11 spatial modes. Furthermore, using a full-vector finite-element method, we modelled all the measured dispersion characteristics and demonstrated good agreement between experimental and theoretical results.

Photonic crystal fibers: new opportunities for sensing

We review exceptional properties of the photonic crystal fibres enabling sensing applications of this new class of fibres. First, the sensing capabilities of highly birefringent index guided fibres are discussed. This includes dispersion characteristics of phase and group modal birefringence in different fibre structures, and sensitivity of these parameters to hydrostatic pressures and temperature. We demonstrate that index guided and photonic bandgap holey fibres of specific construction can be used as wide-band fibre-optic polarizer. We also show that combining of geometrical and stress effects makes it possible to design the holey fibres with either zero phase or group modal birefringence at virtually any given wavelength. Finally, different designs and performance of PCFs suitable for gas sensing are overviewed.

Polarizing Properties of Photonic Crystal Fibers

We show that index guided and photonic bandgap holey fibers of specific construction can be used as a wide-band fiber-optic polarizers. Similarly to traditional polarizing fibers, the operation principle of the index guided PCF polarizers is related to the difference in cut-off wavelengths of the two orthogonally polarized fundamental modes. Several fiber structures were analyzed and optimized for possibly highest polarization bandwidth. Furthermore, we investigated polarizing properties of four PBG PCFs with elliptical core. Our results show that after optimization of the cladding geometry, the polarization dependent loss in the analyzed PBG structures are so high that they can be used as fiber-optic polarizers in the full bandgap range

Sensing with photonic crystal fibres

Fast, frequent, accurate and reliable measurements of physical quantities such as temperature, stress or strain are known to be of utmost importance in areas such as process industry or structural health monitoring. Photonic crystal fibres (PCF) (Bjarklev et al., 2003) constitute a class of optical fibres that has a large potential for a number of novel applications in the sensing domain. The manufacturing flexibility of PCF allows fabricating different types of specialty microstructured fibres including endlessly single mode, double clad, germanium or rare earth doped, highly birefringent, and many other fibres with particular features. In this paper we analyse several of these and describe how they can be exploited for sensing applications. We pay particular attention to temperature and hydrostatic pressure sensitivities. We also report on new microstructure geometries dedicated to sensing applications and on Bragg gratings written in highly birefringent photonic crystal fibre.

Photonic crystal fibers for sensing applications

We report on research towards application of birefringent photonic crystal fibers as active and passive elements of fiber optic sensors for measurements of different physical parameters. Using experimental and theoretical methods, the sensing characteristics of different photonic structures are studied, including spectral behavior of phase and group modal birefringence, polarization dependent losses, sensitivity to temperature and hydrostatic pressure.

Sensing properties of Bragg grating in highly birefringent and single mode photonic crystal fiber

Microstructured fibers (MOF), also called photonic crystal fibers (PCF), constitute a class of optical fibers, which has a large potential for number of novel applications either in the telecom or in the sensing domain. However, some of the applications require the use of specialty fibers with a doped core. We have made a preliminary exploration of PCF with doped regions and with inscribed Bragg gratings. The extensive study of the fiber cross-section structure in respect to possibilities of writing the Bragg gratings and the sensitivities of PCF Bragg gratings was our main concern. Selective measurement of strain without temperature compensation is achieved with fiber Bragg grating (FBG) in highly birefringent (HB) PCF, since such grating is characterized by two reflection bands corresponding to the two polarization modes generated due to the fiber birefringence. The measurement range of such FBG in HB fiber sensor depends on how strong is the separation of the polarization modes, which is expressed as phase birefringence. In next step, we have modeled, designed and fabricated specialty PCF with Ge doped core in such way that after writing the Bragg grating into the fiber we have obtained a sensors exhibiting low sensitivity to any temperature drifts. Traditional optical fiber sensors are not able to make such a distinction between stress and temperatures and require complex temperature compensation mechanisms.