Vibrational signature of broken chemical order in a GeS2 glass: a molecular dynamics simulation

Using density functional molecular dynamics simulations, we analyze the broken chemical order in a GeS$_2$ glass and its impact on the dynamical properties of the glass through the in-depth study of the vibrational eigenvectors. We find homopolar bonds and the frequencies of the corresponding modes are in agreement with experimental data. Localized S-S modes and 3-fold coordinated sulfur atoms are found to be at the origin of specific Raman peaks whose origin was not previously clear. Through the ring size statistics we find, during the glass formation, a conversion of 3-membered rings into larger units but also into 2-membered rings whose vibrational signature is in agreement with experiments.Comment: 11 pages, 8 figures; to appear in Phys. Rev.

Propagation of light polarization in a birefringent medium: Exact analytic models

Driving the analogy between the coherent excitation of a two-state quantum system and the torque equation of motion, we present exact analytic solutions to different models for manipulation of polarization in birefringent medium. These models include the one-dimensional model, the Landau-Zener model, and the Demkov-Kunike model. We also give an example for robust, broadband manipulation of polarization by suitably tailoring the birefringence vector.Comment: 7 pages, 8 figure

Electro-optic barium titanate modulators on silicon photonics platform

Single crystal barium titanate with both c-axis and a-axis orientation have been epitaxially integrated on silicon-on-insulator wafers. Electro-optic Mach-Zehnder modulators with both X-cut and Z-cut configurations are fabricated that exhibit Pockels coefficients of 180 and 130 pm/V, respectively, with Vpi-length values of &lt;5 V-mm. </p