Frequency correlation requirements on the biphoton wavefunction in an induced coherence experiment between separate sources

There is renewed interest in using the coherence between beams generated in separate down-converter sources for new applications in imaging, spectroscopy, microscopy and optical coherence tomography (OCT). These schemes make use of continuous wave (CW) pumping in the low parametric gain regime, which produces frequency correlations, and frequency entanglement, between signal-idler pairs generated in each single source. But can induced coherence still be observed if there is no frequency correlation, so the biphoton wavefunction is factorable? We will show that this is the case, and this might be an advantage for OCT applications. High axial resolution requires a large bandwidth. For CW pumping this requires the use of short nonlinear crystals. This is detrimental since short crystals generate small photon fluxes. We show that the use of ultrashort pump pulses allows improving axial resolution even for long crystal that produce higher photon fluxes

Effects of wind turbine rotor positioning on tornado induced loads

This study investigates the loads induced by a large-scale tornado simulation on a horizontal axis wind turbine (HAWT) to assess the influence of three-dimensional flows with respect to the HAWT position. The loads were analyzed under two rotor operational conditions, idling and parked, at five radial distances. Subsequently, experimental validation of the numerical code HIW-TUR was conducted by evaluating the induced moments for various yaw and pitch angles. The experimental results demonstrated that the bending moment was the most important in terms of magnitude and variation with respect to the HAWT position. Furthermore, The HIW-TUR code accurately identified the magnitude and HAWT configuration that leads to the maximum mean moments induced by the tornado. It was proved that by varying the yaw angle of the rotor plane and blade orientation to parallel to the tornado tangential component, the overall loads could be reduced to the minimum values

Low-loss inverted taper edge coupler in silicon nitride

"This paper is a postprint of a paper submitted to and accepted for publication in IET Optoelectronics and is subject to Institution of Engineering and Technology Copyright. The copy of record is available at IET Digital Library"[EN] An inverted lateral taper with one vertical discrete step was designed for a medium confinement silicon nitride waveguide platform in the C-band, as a chip edge coupler, with a predicted insertion loss of 0.58¿dB. The design is supported by an extensive study to evaluate the impact of fabrication process variations on the performance of such a coupler. The device was manufactured and measured, showing an insertion loss of 1.47 dB, which was traced back to fabrication process variations as cross-checked with simulations. To the authors¿ knowledge, the reported edge coupler is the shortest and among the best performing found for silicon nitride platforms.The authors acknowledge financial support through projects TEC2015-69787-REDT PIC4TB, TEC2016-80385-P SINXPECT, TEC2014-54449-C3-1-R, GVA PROMETEO 2017/103, EC H2020-ICT-27-2015 PICs4all CSA 68777.Fernández-Vicente, J.; Baños Lopez, R.; Doménech Gómez, JD.; Domínguez-Horna, C.; Muñoz Muñoz, P. (2019). Low-loss inverted taper edge coupler in silicon nitride. IET Optoelectronics. 13(2):62-66. https://doi.org/10.1049/iet-opt.2018.5065S6266132Marcatili, E. A. J. (1969). Dielectric Rectangular Waveguide and Directional Coupler for Integrated Optics. Bell System Technical Journal, 48(7), 2071-2102. doi:10.1002/j.1538-7305.1969.tb01166.xMiller, S. E. (1969). Integrated Optics: An Introduction. Bell System Technical Journal, 48(7), 2059-2069. doi:10.1002/j.1538-7305.1969.tb01165.xTomlinson, W. J., & Brackett, C. A. (1987). Telecommunications applications of integrated optics and optoelectronics. Proceedings of the IEEE, 75(11), 1512-1523. doi:10.1109/proc.1987.13912Lim, A. E.-J., Junfeng Song, Qing Fang, Chao Li, Xiaoguang Tu, Ning Duan, … Tsung-Yang Liow. (2014). Review of Silicon Photonics Foundry Efforts. IEEE Journal of Selected Topics in Quantum Electronics, 20(4), 405-416. doi:10.1109/jstqe.2013.2293274Smit, M., Leijtens, X., Ambrosius, H., Bente, E., van der Tol, J., Smalbrugge, B., … van Veldhoven, R. (2014). An introduction to InP-based generic integration technology. Semiconductor Science and Technology, 29(8), 083001. doi:10.1088/0268-1242/29/8/083001Taillaert, D., Bogaerts, W., Bienstman, P., Krauss, T. F., Van Daele, P., Moerman, I., … Baets, R. (2002). An out-of-plane grating coupler for efficient butt-coupling between compact planar waveguides and single-mode fibers. IEEE Journal of Quantum Electronics, 38(7), 949-955. doi:10.1109/jqe.2002.1017613Dillon, T., Murakowski, J., Shi, S., & Prather, D. (2008). Fiber-to-waveguide coupler based on the parabolic reflector. Optics Letters, 33(9), 896. doi:10.1364/ol.33.000896Li, H., Cao, Z., Lu, H., & Shen, Q. (2003). Free-space coupling of a light beam into a symmetrical metal-cladding optical waveguide. Applied Physics Letters, 83(14), 2757-2759. doi:10.1063/1.1616205Cardenas, J., Poitras, C. B., Luke, K., Luo, L.-W., Morton, P. A., & Lipson, M. (2014). High Coupling Efficiency Etched Facet Tapers in Silicon Waveguides. IEEE Photonics Technology Letters, 26(23), 2380-2382. doi:10.1109/lpt.2014.2357177Shiraishi, K., Yoda, H., Ohshima, A., Ikedo, H., & Tsai, C. S. (2007). A silicon-based spot-size converter between single-mode fibers and Si-wire waveguides using cascaded tapers. Applied Physics Letters, 91(14), 141120. doi:10.1063/1.2795337Tao, H., Song, J., Fang, Q., Yu, M., Lo, G., & Kwong, D. (2008). Improving coupling efficiency of fiber-waveguide coupling with a double-tip coupler. Optics Express, 16(25), 20803. doi:10.1364/oe.16.020803Muñoz, P., Micó, G., Bru, L., Pastor, D., Pérez, D., Doménech, J., … Domínguez, C. (2017). Silicon Nitride Photonic Integration Platforms for Visible, Near-Infrared and Mid-Infrared Applications. Sensors, 17(9), 2088. doi:10.3390/s17092088Papes, M., Cheben, P., Benedikovic, D., Schmid, J. H., Pond, J., Halir, R., … Vašinek, V. (2016). Fiber-chip edge coupler with large mode size for silicon photonic wire waveguides. Optics Express, 24(5), 5026. doi:10.1364/oe.24.005026Cheben, P., Schmid, J. H., Wang, S., Xu, D.-X., Vachon, M., Janz, S., … Picard, M.-J. (2015). Broadband polarization independent nanophotonic coupler for silicon waveguides with ultra-high efficiency. Optics Express, 23(17), 22553. doi:10.1364/oe.23.022553Shani, Y., Henry, C. H., Kistler, R. C., Orlowsky, K. J., & Ackerman, D. A. (1989). Efficient coupling of a semiconductor laser to an optical fiber by means of a tapered waveguide on silicon. Applied Physics Letters, 55(23), 2389-2391. doi:10.1063/1.102290Zhuang, L., Marpaung, D., Burla, M., Beeker, W., Leinse, A., & Roeloffzen, C. (2011). Low-loss, high-index-contrast Si_3N_4/SiO_2 optical waveguides for optical delay lines in microwave photonics signal processing. Optics Express, 19(23), 23162. doi:10.1364/oe.19.02316

Creating a three dimensional intrinsic electric dipole on rotated CrI3_3 bilayers

Two-dimensional (2D) materials are being explored as a novel multiferroic platform. One of the most studied magnetoelectric multiferroic 2D materials are antiferromagnetically-coupled (AFM) CrI$_3$ bilayers. Neglecting magnetism, those bilayers possess a crystalline point of inversion, which is only removed by the antiparallel spin configuration among its two constituent monolayers. The resultant intrinsic electric dipole on those bilayers has a magnitude no larger than 0.04 pC/m, it points out-of-plane, and it reverts direction when the--Ising-like--cromium spins are flipped (toward opposite layers {\em versus} away from opposite layers). The combined presence of antiferromagnetism and a weak intrinsic electric dipole makes this material a two-dimensional magnetoelectric multiferroic. Here, we remove the crystalline center of inversion of the bilayer by a relative $60^{\circ}$ rotation of its constituent monolayers. This process {\em enhances} the out-of-plane intrinsic electric dipole tenfold with respect to its magnitude in the non-rotated AFM bilayer and also creates an even stronger and switchable in-plane intrinsic electric dipole. The ability to create a three-dimensional electric dipole is important, because it enhances the magnetoelectric coupling on this experimentally accessible 2D material, which is explicitly calculated here as well.Comment: Accepted at PRB on May 1, 202

Italian Mutual Banks: Performance, Efficiency and Mergers and Acquisitions

1) Are Italian mutual banks efficient? Evidence from two different cost frontier techniques, by Juan Sergio Lopez, Alessandra Appenini, and Stefania P.S. Rossi. The aim of the first paper is to analyze the efficiency of co-operative banks in Italy. The increasing competition induced by the ongoing process of liberalization in Europe has been affecting also these small financial institutions that used to operate in a more protected environment. Based on a panel of about 450 banks covering the period 1995-99, two different techniques were employed: non-parametric frontier analysis, and parametric frontier analysis. By means of this analysis it is possible to compare the results obtained using these two methodologies and analyze the determinants of bank inefficiency 2) Mergers and acquisitions between mutual banks in Italy: an analysis of the effects on performance and productive efficiency, by Roberto Di Salvo, Maria Carmela Mazzilis, and Andrea Guidi. The second paper is aimed at testing the hypothesis that the M&A wave over the past ten years has increased the level of efficiency of co-operative credit banks (CCBs), both in terms of overall performance and productive efficiency. The logical development is hinged on two steps: 1) an explorative analysis which is based on the observation of balance sheet ratios by quantiles, 2) a DEA application for estimating productive efficiency scores. The analysis refers to 94 CCBs which have been involved in M&As over the period 1995-98 and is carried out on both merged and non-merged banks, either before concentration or in the subsequent years. The explorative analysis mainly shows a higher level of fee-based income for merged banks, which is consistent with the hypothesis that concentration strategies enhance diversification. It also detects some degree of cost reduction just after merging. The DEA application models (CRS and VRS) tends to confirm the results of the previous analysis and estimates higher efficiency for merged banks, a lower efficiency degree for pre-merger banks, and a significant degree of scale econonomies.