http://oar.a-star.edu.sg:80/jspui/handle/123456789/108 Tue, 27 Jun 2017 07:05:30 GMT 2017-06-27T07:05:30Z http://oar.a-star.edu.sg:80/jspui/handle/123456789/1917 Title: Wideband nonlinear spectral broadening in ultra-short ultra-silicon rich nitride waveguides Authors: Choi, Ju Won; Chen, George F. R.; Ng, D. K. T.; Ooi, Kelvin J. A.; Tan, Dawn T. H. Abstract: CMOS-compatible nonlinear optics platforms with high Kerr nonlinearity facilitate the generation of broadband spectra based on self-phase modulation. Our ultra – silicon rich nitride (USRN) platform is designed to have a large nonlinear refractive index and low nonlinear losses at 1.55 μm for the facilitation of wideband spectral broadening. We investigate the ultrafast spectral characteristics of USRN waveguides with 1-mm-length, which have high nonlinear parameters (γ ∼ 550 W−1/m) and anomalous dispersion at 1.55 μm wavelength of input light. USRN add-drop ring resonators broaden output spectra by a factor of 2 compared with the bandwidth of input fs laser with the highest quality factors of 11000 and 15000. Two – fold self phase modulation induced spectral broadening is observed using waveguides only 430 μm in length, whereas a quadrupling of the output bandwidth is observed with USRN waveguides with a 1-mm-length. A broadening factor of around 3 per 1 mm length is achieved in the USRN waveguides, a value which is comparatively larger than many other CMOS-compatible platforms. Wed, 08 Jun 2016 00:00:00 GMT http://oar.a-star.edu.sg:80/jspui/handle/123456789/1917 2016-06-08T00:00:00Z http://oar.a-star.edu.sg:80/jspui/handle/123456789/1916 Title: Multiple broken symmetries in striped La2−xBaxCuO4 detected by the field-symmetric Nernst effect Authors: Soumyanarayanan, Anjan; Tee, X. Y.; Ito, T.; Ushiyama, T.; Tomioka, Y.; Panagopoulos, C. Abstract: We report a thermoelectric investigation of the stripe and superconducting phases of the cuprate La2−xBaxCuO4 near x = 1/8.We vary the doping and the magnetic field to identify features in the field-symmetric Nernst effect consistent with the reports of time-reversal symmetry breaking above the superconducting Tc. Crucially, we further detect a field-invariant peak at the stripe charge order temperature, TCO. Our observations suggest the onset of a nontrivial charge ordered phase at TCO, and the subsequent presence of spontaneously generated vortices before the emergence of bulk superconductivity. Thu, 11 Feb 2016 00:00:00 GMT http://oar.a-star.edu.sg:80/jspui/handle/123456789/1916 2016-02-11T00:00:00Z http://oar.a-star.edu.sg:80/jspui/handle/123456789/1915 Title: Generalized Brewster effect in dielectric metasurfaces Authors: Paniagua-Domínguez, Ramón; Yu, Ye Feng; Miroshnichenko, Andrey E.; Krivitsky, Leonid A.; Fu, Yuan Hsing; Valuckas, Vytautas; Gonzaga, Leonard; Toh, Yeow Teck; Kay, Anthony Yew Seng; Luk’yanchuk, Boris; Kuznetsov, Arseniy I. Abstract: Polarization is a key property defining the state of light. It was discovered by Brewster, while studying light reflected from materials at different angles. This led to the first polarizers, based on Brewster’s effect. Now, one of the trends in photonics is the study of miniaturized devices exhibiting similar, or improved, functionalities compared with bulk optical elements. In this work, it is theoretically predicted that a properly designed all-dielectric metasurface exhibits a generalized Brewster’s effect potentially for any angle, wavelength and polarization of choice. The effect is experimentally demonstrated for an array of silicon nanodisks at visible wavelengths. The underlying physics is related to the suppressed scattering at certain angles due to the interference between the electric and magnetic dipole resonances excited in the nanoparticles. These findings open doors for Brewster phenomenon to new applications in photonics, which are not bonded to a specific polarization or angle of incidence. Tue, 19 Jan 2016 00:00:00 GMT http://oar.a-star.edu.sg:80/jspui/handle/123456789/1915 2016-01-19T00:00:00Z http://oar.a-star.edu.sg:80/jspui/handle/123456789/1914 Title: Perfect valley filter in strained graphene with single barrier region Authors: Yesilyurt, Can; Tan, Seng Ghee; Liang, Gengchiau; Jalil, Mansoor B. A. Abstract: We present a single barrier system to generate pure valley-polarized current in monolayer graphene. A uniaxial strain is applied within the barrier region, which is delineated by localized magnetic field created by ferromagnetic stripes at the region’s boundaries. We show that under the condition of matching magnetic field strength, strain potential, and Fermi energy, the transmitted current is composed of only one valley contribution. The desired valley current can transmit with zero reflection while the electrons from the other valley are totally reflected. Thus, the system generates pure valley-polarized current with maximum conductance. The chosen parameters of uniaxial strain and magnetic field are in the range of experimental feasibility, which suggests that the proposed scheme can be realized with current technology. Tue, 01 Mar 2016 00:00:00 GMT http://oar.a-star.edu.sg:80/jspui/handle/123456789/1914 2016-03-01T00:00:00Z