Birefringence analysis of segmented cladding fiber

We present a full-vectorial modal analysis of a segmented cladding fiber (SCF). The analysis is based on the H-field vectorial finite element method (VFEM) employing polar mesh geometry. Using this method, we have analyzed the circular SCF and the elliptical SCF. We have found that the birefringence of the circular SCF is very small (1.0×10−8). Birefringence of a highly elliptical SCF can be altered to some extent by the number of segments and duty cycle of segmentation in the segmented cladding. However, the change is not profound. The analysis shows that the circular SCF possesses low birefringence and that the segmented cladding does not add any significant birefringence in an elliptical fiber. This result strongly indicates that small deviations in the segmented cladding parameters arising from fabrication process do not significantly affect the birefringence of the fiber

Enhanced photoinduced nematic reorientation in mixture with azo-dye-substituted polymer

The optically induced reorientation of nematic liquid crystal doped with azo-dye substituted polymer is investigated measuring photoinduced birefringence. These measurement reveal the value (Dn~0.1) of induced birefringence of liquid crystal with dye polymer which significantly exceeds the value of birefringence previously obtained in nematic mixture with the low molecular weight dye. More than one order of enhancement is connected with lower diffusivity of polymer.Comment: 11 pages, 3 figure

Including birefringence into time evolution of CMB: current and future constraints

We introduce birefringence effects within the propagation history of CMB, considering the two cases of a constant effect and of an effect that increases linearly in time, as the rotation of polarization induced by birefringence accumulates during photon propagation. Both cases result into a mixing of E and B modes before lensing effects take place, thus leading to the fact that lensing is acting on spectra that are already mixed because of birefringence. Moreover, if the polarization rotation angle increases during propagation, birefringence affects more the large scales that the small scales. We put constraints on the two cases using data from WMAP 9yr and BICEP 2013 and compare these results with the constraints obtained when the usual procedure of rotating the final power spectra is adopted, finding that this dataset combination is unable to distinguish between effects, but it nevertheless hints for a non vanishing value of the polarization rotation angle. We also forecast the sensitivity that will be obtained using data from Planck and PolarBear, highlighting how this combination is capable to rule out a vanishing birefringence angle, but still unable to distinguish the different scenarios. Nevertheless, we find that the combination of Planck and PolarBear is sensitive enough to highlight the existence of degeneracies between birefringence rotation and gravitational lensing of CMB photons, possibly leading to false detection of non standard lensing effects if birefringence is neglected.Comment: 20 pages, 10 figures. New version matching the one accepted by JCAP. Corrected typos in equations 2.17-2.1

Ion-Exchanged Glass Waveguides with Low Birefringence for a Broad Range of Waveguide Widths

Optical communications networks require integrated photonic components with negligible polarization dependence, which typically means that the waveguides must feature very low birefringence. Recent studies have shown that waveguides with low birefringence can be obtained, e.g., by use of silica-on-silicon waveguides or buried ion-exchanged glass waveguides. However, many integrated photonic circuits consist of waveguides with varying widths. Therefore low birefringence is consequently required for waveguides having different widths. This is a difficult task for most waveguide fabrication technologies. We present experimental results on waveguide birefringence for buried silver–sodium ion-exchanged glass waveguides. We show that the waveguide birefringence of the order of 106 for waveguide mask opening widths ranging from 2 to 10 μm can be obtained by postprocessing the sample through annealing at an elevated temperature. The measured values are in agreement with the values calculated with our modeling software for ion-exchanged glass waveguides. This unique feature of ion-exchanged waveguides may be of significant importance in a wide variety of integrated photonic circuits requiring polarization independent operation