Free Space Optical Polarization De-multiplexing and Multiplexing by means of Conical Refraction

Polarization de-multiplexing and multiplexing by means of conical refraction is proposed to increase the channel capacity for free space optical communication applications. The proposed technique is based on the forward-backward optical transform occurring when a light beam propagates consecutively along the optic axes of two identical biaxial crystals with opposite orientations of their conical refraction characteristic vectors. We present experimental proof of usefulness of the conical refraction de-multiplexing and multiplexing technique by increasing in one order of magnitude the channel capacity at optical frequencies in a propagation distance of 4m

Coherent injecting, extracting, and velocity filtering of neutral atoms in a ring trap via spatial adiabatic passage

We introduce here a coherent technique to inject, extract, and velocity filter neutral atoms in a ring trap coupled via tunneling to two additional waveguides. By adiabatically following the transverse spatial dark state, the proposed technique allows for an efficient and robust velocity dependent atomic population transfer between the ring and the input/output waveguides. We have derived explicit conditions for the spatial adiabatic passage that depend on the atomic velocity along the input waveguide as well as on the initial population distribution among the transverse vibrational states. The validity of our proposal has been checked by numerical integration of the corresponding two dimensional Schr\"odinger equation with state-of-the-art parameter values for $^{87}$Rb atoms and an optical dipole ring trap.Comment: To be published in European Physical Journal

Laser beams with conical refraction patterns

Laser beams with cone-refracted output from the plane mirror is demonstrated for the first time in lasers based on intracavity conical refraction (CR) phenomenon. Transverse profile of such lasers comprises a crescent ring of CR-like distribution, where any opposite points are of orthogonal linear polarizations. We confirm the existence of such mode of CR lasers by two observations. First, cascaded CR in reflection geometry has been demonstrated for first time and it provides experimental prove that a light beam passed along optic axis of a biaxial crystal, reflected back from a plane mirror and passed again through the crystal is restored. Second, CR cavity mode with CR-like pattern through the plane mirror is experimentally and theoretically demonstrated for the first time

Multiple rings formation in cascaded conical refraction

When a light beam passes through a cascade of biaxial crystals (BCs) with aligned optic axes, the resulting transverse intensity pattern consists of multiple concentric rings. We provide a simple formulation for the pattern formation for both circularly and linearly polarized input beams, that could be applied for a cascade of an arbitrary number of BCs. We have experimentally investigated multiple ring formation with up to three cascade BCs, showing that the theoretical formulation is in full agreement with the experimental results

Conical Refraction Multiplexing for Free-space Optical Communications

Conical refraction (CR) is proposed to increase the channel capacity for free space optical communication applications. We present the first investigations of cascaded CR with a linearly polarized input beam and experimentally prove that two oppositely oriented consecutive identical biaxial crystals perform a forward-backward transformation of the incident light beam. This forward-backward transformation is reported for different input beams with Gaussian, elliptical and angularly modulated transverse intensity profiles and is the basis for our novel proposal on multiplexing and demultiplexing of optical beams. We present experimental proof of usefulness and perspective of the CR multiplexing technique by increasing in one order of magnitude the channel capacity at optical frequencies. The technique is applicable to any wavelength in optical and telecommunication bands. It can be also properly upgraded with the WDM technique

Free-space optical polarization demultiplexing and multiplexing by means of conical refraction

Polarization demultiplexing and multiplexing by means of conical refraction is proposed to increase the channel capacity for free-space optical communication applications. The proposed technique is based on the forward-backward optical transform occurring when a light beam propagates consecutively along the optic axes of two identical biaxial crystals with opposite orientations of their conical refraction characteristic vectors. We present an experimental proof of usefulness of the conical refraction demultiplexing and multiplexing technique by increasing in one order of magnitude the channel capacity at optical frequencies in a propagation distance of 4 m

DNA-Binding Protein Dps Protects <i>Escherichia coli</i> Cells against Multiple Stresses during Desiccation

Gradual dehydration is one of the frequent lethal yet poorly understood stresses that bacterial cells constantly face in the environment when their micro ecotopes dry out, as well as in industrial processes. Bacteria successfully survive extreme desiccation through complex rearrangements at the structural, physiological, and molecular levels, in which proteins are involved. The DNA-binding protein Dps has previously been shown to protect bacterial cells from many adverse effects. In our work, using engineered genetic models of E. coli to produce bacterial cells with overproduction of Dps protein, the protective function of Dps protein under multiple desiccation stresses was demonstrated for the first time. It was shown that the titer of viable cells after rehydration in the experimental variants with Dps protein overexpression was 1.5–8.5 times higher. Scanning electron microscopy was used to show a change in cell morphology upon rehydration. It was also proved that immobilization in the extracellular matrix, which is greater when the Dps protein is overexpressed, helps the cells survive. Transmission electron microscopy revealed disruption of the crystal structure of DNA–Dps crystals in E. coli cells that underwent desiccation stress and subsequent watering. Coarse-grained molecular dynamics simulations showed the protective function of Dps in DNA–Dps co-crystals during desiccation. The data obtained are important for improving biotechnological processes in which bacterial cells undergo desiccation

Sistema, método, transmisor y receptor de comunicaciones ópticas

Sistema, método, transmisor y receptor de comunicaciones ópticas.El sistema comprende:- un transmisor (T) formado por un demultiplexor y un multiplexor con unos elementos ópticos (C1, C2) que, junto con un modulador (M1) dispuesto entre ellos, permiten utilizar los sub-haces que componen un haz de luz de entrada (H1) como canales ópticos para la transmisión de datos, en la forma de un haz de luz multiplexado (HM); y- un receptor (R) dispuesto para recibir dicho haz, tras haber viajado por el medio de transmisión, y que comprende un demultiplexor con un elemento óptico (C3) que recupera los canales ópticos del haz de luz multiplexado (HM).El método está adaptado para implementarse utilizando el sistema de la invención.El transmisor y el receptor están adaptados para realizar las funciones de, respectivamente, el transmisor y el receptor del sistema de la invención

Morphological peculiarities of the DNA-protein complexes in starved Escherichia coli cells.

One of the adaptive strategies for the constantly changing conditions of the environment utilized in bacterial cells involves the condensation of DNA in complex with the DNA-binding protein, Dps. With the use of electron microscopy and electron tomography, we observed several morphologically different types of DNA condensation in dormant Escherichia coli cells, namely: nanocrystalline, liquid crystalline, and the folded nucleosome-like. We confirmed the presence of both Dps and DNA in all of the ordered structures using EDX analysis. The comparison of EDX spectra obtained for the three different ordered structures revealed that in nanocrystalline formation the majority of the Dps protein is tightly bound to nucleoid DNA. The dps-null cells contained only one type of condensed DNA structure, liquid crystalline, thus, differing from those with Dps. The results obtained here shed some light on the phenomenon of DNA condensation in dormant prokaryotic cells and on the general problem of developing a response to stress. We demonstrated that the population of dormant cells is structurally heterogeneous, allowing them to respond flexibly to environmental changes. It increases the ability of the whole bacterial population to survive under extreme stress conditions