Theoretical Modelling of Ion Exchange Processes in Glass: Advances and Challenges

In the last few years, some advances have been made in the theoretical modelling of ion exchange processes in glass. On the one hand, the equations that describe the evolution of the cation concentration were rewritten in a more rigorous manner. This was made into two theoretical frameworks. In the first one, the self-diffusion coefficients were assumed to be constant, whereas, in the second one, a more realistic cation behaviour was considered by taking into account the so-called mixed ion effect. Along with these equations, the boundary conditions for the usual ion exchange processes from molten salts, silver and copper films and metallic cathodes were accordingly established. On the other hand, the modelling of some ion exchange processes that have attracted a great deal of attention in recent years, including glass poling, electro-diffusion of multivalent metals and the formation/dissolution of silver nanoparticles, has been addressed. In such processes, the usual approximations that are made in ion exchange modelling are not always valid. An overview of the progress made and the remaining challenges in the modelling of these unique processes is provided at the end of this reviewThis research was funded by Xunta de Galicia, Consellería de Educación, Universidades e FP, Grant GRC Number ED431C2018/11, and Ministerio de Economía, Industria y Competitividad, Gobierno de España, Grant Number AYA2016-78773-C2-2-P, European Regional Development FundS

A Polygonal Model to Design and Fabricate Ion-Exchanged Diffraction Gratings

We propose a simple polygonal model to describe the phase profile of ion-exchanged gratings. This model enables the design of these gratings, as well as the characterization of the ion-exchange process itself. Several ion-exchanged gratings were fabricated to validate the model and to characterize the process involved in their fabrication. From this characterization, we show the practical utility of the model by designing and fabricating both a grating that removes the zero order and a three splitter. The performance of these two elements was good, although the first one stood out especially because only 0.5% of the power remained in the zero order after diffraction. This polygonal model could be useful to design more complex diffractive elementsThis research was funded by Xunta de Galicia, Consellería de Educación, Universidades e FP, Grant GRC number ED431C2018/11, and Ministerio de Economía, Industria y Competitividad, Gobierno de España, Grant Number AYA2016-78773-C2-2-PS

Quantum Photonic Simulation of Spin-Magnetic Field Coupling and Atom-Optical Field Interaction

In this work, we present the physical simulation of the dynamical and topological properties of atom-field quantum interacting systems by means of integrated quantum photonic devices. In particular, we simulate mechanical systems used, for example, for quantum processing and requiring a very complex technology such as a spin-1/2 particle interacting with an external classical time-dependent magnetic field and a two-level atom under the action of an external classical time-dependent electric (optical) field (light-matter interaction). The photonic device consists of integrated optical waveguides supporting two collinear or codirectional modes, which are coupled by integrated optical gratings. We show that the single-photon quantum description of the dynamics of this photonic device is a quantum physical simulation of both aforementioned interacting systems. The two-mode photonic device with a single-photon quantum state represents the quantum system, and the optical grating corresponds to an external field. Likewise, we also present the generation of Aharonov–Anandan geometric phases within this photonic device, which also appear in the simulated systems. On the other hand, this photonic simulator can be regarded as a basic brick for constructing more complex photonic simulators. We present a few examples where optical gratings interacting with several collinear and/or codirectional modes are used in order to illustrate the new possibilities for quantum simulationXunta de Galicia, Consellería de Educación, Universidades e FP, Grant GRC Number ED431C2018/11; Ministerio de Economía, Industria y Competitividad, Gobierno de España, Grant Number AYA2016-78773-C2-2-PS

Quantum projectors implemented with optical directional couplers in ion-exchanged glasses

Ion-exchanged glass as a platform for quantum photonics is proposed. Quantum projectors are implemented with integrated optical directional couplers fabricated by ion-exchange K+/Na+ in soda-lime glass. We consider devices composed of concatenated directional couplers which implement N-dimensional quantum projective measurements, and concomitantly the production of 1-qudit states. The fundamental units of these devices are 2 × 2 directional couplers that are experimentally studied in order to obtain, through an optical characterization, empiric relationships between fabrication and optical parameters of such couplers. Likewise, a two-dimensional quantum projector is demonstrated so that projective measurements are obtained for the states of bases X (diagonal) and Y (circular)S

Quaternary adaptive optics

We present a new Point Diffraction Interferometer (PDI). Binary adaptive optics (BAO) and Quaternary Adaptive Optics (QAO) can be performed with the help of this PDI as a wavefront sensor. The PDI interferogram, once binarized, is used in two consecutive steps to produce a quaternary mask with phase values 0, π/2, π and 3π/2. The addition of the quaternary mask compensates for the aberrated wavefront and allows us to reach a Strehl ratio of about 0.81. We have verified through computer simulations that the use of QAO depends on the number of actuators of the compensating device to achieve effective compensation. The technique was successfully validated through an experiment.Ministerio de Economía y Competitividad (MINECO) (AYA2016-78773-C2-1-P)

Design of Spatial-Mode (De)Multiplexer for Few-Mode Fibers Based on a Cyclically Used Michelson-Like Interferometer

Few mode optical fibers are a promising way to continue increasing the data rate in optical communications. However, an efficient method to launch and extract separately each mode is essential. The design of a interferometric spatial mode (de)multiplexer for few mode optical fibers is presented. It is based on a single Michelson-like interferometer which consists of standard optical elements and has a reflective image inverter in one arm. Particular care has been taken in its design so that both polarizations behave the same. Moreover, this interferometer can process several pairs of modes simultaneously. The multiplexer also consists of: a phase plate, focusing optics at both ports of the interferometer and elliptical core fibers to recirculate some outputs. It can multiplex ten spatial and polarization modes and it presents low losses and no intrinsic crosstalk between modes. Additionally, it is polarization insensitive, achromatic, compact and inexpensive. The same system can work as a demultiplexer when used in reverse. In this case, both the losses and the crosstalk remain very low. Similar designs that perform other functions, like an add-drop mode multiplexing, are also suggestedThis research was funded by: Ministerio de Economía, Industria y Competitividad, Gobierno de España, grant number AYA2016-78773-C2-2-P; Xunta de Galicia, Consellería de Educación, Universidades e FP, Grant GRC number ED431C2018/11; and European Regional Development FundS

Interferometric space-mode multiplexing based on binary phase plates and refractive phase shifters

A Mach-Zehnder interferometer (MZI) that includes in an arm either a reflective image inverter or a Gouy phase shifter (RGPS) can (de)multiplex many types of modes of a few mode fiber without fundamental loss. The use of RGPSs in combination with binary phase plates for multiplexing purposes is studied for the first time, showing that the particular RGPS that shifts π the odd modes only multiplexes accurately low order modes. To overcome such a restriction, we present a new exact refractive image inverter, more compact and flexible than its reflective counterpart. Moreover, we show that these interferometers remove or reduce the crosstalk that the binary phase plates could introduce between the multiplexed modes. Finally, an experimental analysis of a MZI with both an approximated and an exact refractive image inverter is presented for the case of a bimodal multiplexing. Likewise, it is proven experimentally that a RGPS that shifts π/2 demultiplexes two odd modes which can not be achieved by any image inverter.Ministerio de Economía y Competitividad, Central Government of Spain, Contract number FIS2013-46584-C2-1-R; Fondo Europeo de Desenvolvemento Rexional 2007-2013 (FEDER).S

Experimental validation of Lyot stop apodization in ground-based coronagraphy

ABSTRACT We show that the use of apodizing functions at the coronagraph Lyot plane may be useful for improving the image contrast of ground-based coronagraphs. An experimental set-up consisting of a tip–tilt mirror, a coronagraph and a low-noiseEMCCDcamerawas implemented at theWilliam Herschel Telescope. Images were taken in the I band, which meant that the D/r0 value was around 10. Experimental results confirm that, for moderately aberrated wavefronts, our instrument works as theoretically expected, and that the contrast value attained is high enough to provide direct detection of faint companions.This research was supported by the Ministerio de Economía y Competitividad under project FIS2012-31079 and the Fundación Séneca of Murcia under projects 15419/PI/10 and 15345/PI/10

Straw mulching is not always a useful post-fire stabilization technique for reducing soil erosion.

Mulching is increasingly employed to stabilize burnt areas, making necessary to elucidate where and how it should be used. The effects of mulching and the efficiency of two straw application strategies in reducing nutrient losses were evaluated in a steep area (burnt with moderate severity) with twelve experimental plots split into three sets: control burnt plots (BS), burnt plots with straw mulching in narrow bands along the contour lines (NM, global dose 800 kg ha!1) and in wide bands (WM, global dose 1000 kg ha!1). None of the mulching strategies had a significant effect on most of the 16 soil and sediment variables analysed (pH, nutrient and trace element concentrations). The principal component analyses show that soil and sediment samples change with time after the fire regardless treatment, decreasing progressively the differences between successive sampling dates. In sediments, pHKCl, Ca, Mg, Mn and Zn fitted to curvilinear regression models with time after fire as independent variable, while the other variables showed no clear temporal trend. During the first post-fire year, <500 kg ha!1 of sediments were eroded and mulching had no effect on the total mass of lost sediments and nutrients. We conclude that the erosion rate was rather low that year due to moderate precipitation rates and therefore mulching did not significantly reduce soil erosion. Nevertheless, the concentration of Mo, Mn and Zn in sediments exceeded reference levels for ecosystem protection and can lead to deficiency problems for on-site vegetation and to soil and water pollution off-site.Peer reviewe