Non-linear photoluminescence from graphene

Graphene is in the focus of research due to its unique electronic and optical properties. Intrinsic graphene is a zero gap semiconductor with a linear dispersion relation for E-k leading to zero-effective-mass electrons and holes described by Fermi-Dirac theory. Since pristine graphene has no bandgap no photoluminescence would be expected. However, recently several groups showed non-linear photoluminescence from pristine graphene putting forward different physical models explaining this remarkable effect [1-3]. © 2011 IEEE.

Non-linear conductance of disordered quantum wires

The self-consistent electron potential in a current-carrying disordered quantum wire is spatially inhomogeneous due to the formation of resistivity dipoles across scattering centres. In this paper it is argued that these inhomogeneities in the potential result in a suppression of the differential conductance of such a wire at finite applied voltage. A semi-classical argument allows this suppression, quadratic in the voltage, to be related directly to the amount of intrinsic defect scattering in the wire. This result is then tested against numerical calculations.

Studies on some nonlinear schrodinger type equations describing pulse propagation through optical fibers

The discovery of the soliton is considered to be one of the most significant events of the twentieth century. The term soliton refers to special kinds of waves that can propagate undistorted over long distances and remain unaffected even after collision with each other. Solitons have been studied extensively in many fields of physics. In the context of optical fibers, solitons are not only of fundamental interest but also have potential applications in the field of optical fiber communications. This thesis is devoted to the theoretical study of soliton pulse propagation through single mode optical fibers.

Fractional order and non-linear system identification algorithms for biomedical applications

We discuss the modelling of dielectric responses of amorphous biological samples. Such samples are commonly encountered in impedance spectroscopy studies as well as in UV, IR, optical and THz transient spectroscopy experiments and in pump-probe studies. In many occasions, the samples may display quenched absorption bands. A systems identification framework may be developed to provide parsimonious representations of such responses. To achieve this, it is appropriate to augment the standard models found in the identification literature to incorporate fractional order dynamics. Extensions of models using the forward shift operator, state space models as well as their non-linear Hammerstein-Wiener counterpart models are highlighted. We also discuss the need to extend the theory of electromagnetically excited networks which can account for fractional order behaviour in the non-linear regime by incorporating nonlinear elements to account for the observed non-linearities. The proposed approach leads to the development of a range of new chemometrics tools for biomedical data analysis and classification.

Lorentz symmetry breaking and planar effects from non-linear electrodynamics

We propose a modification of standard linear electrodynamics in four dimensions, where effective non-trivial interactions of the electromagnetic field with itself and with matter fields induce Lorentz violating Chern-Simons terms. This yields two consequences: it provides a more realistic and general scenario for the breakdown of Lorentz symmetry in electromagnetism and it may explain the effective behavior of the electromagnetic field in certain planar phenomena (for instance, Hall effect). A number of proposals for non-linear electrodynamics is discussed along the paper. Important physical implications of the breaking of Lorentz symmetry, such as optical birefringence and the possibility of having conductance in the vacuum are commented on.

1.5 mu m and visible up-conversion emissions in Er3+/Yb3+ co-doped tellurite glasses and optical fibers for photonic applications

Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)

Giant non-linear absorption in Er3+-doped fluoroindate glass

Non-linear absorption is observed in Er3+-doped fluoroindate glass (in mol% 37InF2:20ZnF2:20SrF2:16BaF2:2GdF2: 2NaF:1GaF3:2ErF3) when the sample is irradiated with a CW laser emitting at 650 nm. An intensity dependence of the optical transmittance is detected. Saturation and sequential absorption of two photons are responsible for the decrease of 50% in the transmittance. The results are explained by simple models which are solved based on rate-equations for the populations of energy levels.

Study of the glass transition temperature of as-s glasses for the fabrication of chalcogenide optical fibers

Values of glass transition temperature (Tg) and of linear expansion coefficient (α) for Asx S100-x glasses were measured in the range of concentrations 35 × 42. Because of the importance of the glass formation region 35 × 42 for the optical fibers elaboration, special attention was made on high-pure Asx S100-x glasses. For the glass in the range of 35 × 38, we measure Tg with the interval of x equal to 1 at.% of arsenic. We also measured the Tg values with the interval of x equal to 0.5 at.% of As. We obtained nonlinear behavior of Tg, reflecting the change in molecular composition of As-S glass in the glass composition range studied. The control of such parameters is important to produce optical fibers with specific numerical aperture. © 2013 The American Ceramic Society and Wiley Periodicals, Inc.

Vidros óxidos contendo átomos pesados para aplicações em óptica não linear e fotônica na região do infravermelho

Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)

Magneto-optic current sensor with Faraday mirror for linear birefringence compensation

Fiber optic sensors have some advantages in subjects related with electrical current and magnetic field measurement. In spite of the optical fiber utilization advantages we have to take into account undesirable effects, which are present in real non-ideal optical fibers. In telecommunication and sensor application fields the presence of inherent and induced birefringence is crucial. The presence of birefringence may cause an undesirable change in the polarization state. In order to compensate the linear birefringence a promising method has been chosen. This method employs orthogonal polarization conjugation in the back propagation direction of the light wave in the fiber. A study and a simulation of an experimental setup are realized with the advantage of a significant sensitivity improvement.

UWB Monocycle Generator based on the non-linear effects of an SOA-integrated structure

In this letter, we propose and experimentally demonstrate a novel and single structure to generate ultra-wideband (UWB) pulses by means of the cross-phase modulation present in a semiconductor optical amplifier unified structure. The key components of this system is an integrated Mach-Zehnder interferometer with two semiconductor optical amplifiers and an optical processing unit. The fusion of these two components permits the generation and customization of UWB monocycle pulses. The polarity of the output pulses is easily modified through the single selection of a specific input port. Moreover, the capacity of transmitting several data sequences is demonstrated and the potentiality to adapt the system to different modulation formats is analyzed.

A detector based on silica fibers for ion beam monitoring in a wide current range

A detector based on doped silica and optical fibers was developed to monitor the profile of particle accelerator beams of intensity ranging from 1 pA to tens of µA. Scintillation light produced in a fiber moving across the beam is measured, giving information on its position, shape and intensity. The detector was tested with a continuous proton beam at the 18 MeV Bern medical cyclotron used for radioisotope production and multi-disciplinary research. For currents from 1 pA to 20 µA, Ce3+ and Sb3+ doped silica fibers were used as sensors. Read out systems based on photodiodes, photomultipliers and solid state photomultipliers were employed. Profiles down to the pA range were measured with this method for the first time. For currents ranging from 1 pA to 3 µA, the integral of the profile was found to be linear with respect to the beam current, which can be measured by this detector with an accuracy of ∼1%. The profile was determined with a spatial resolution of 0.25 mm. For currents ranging from 5 µA to 20 µA, thermal effects affect light yield and transmission, causing distortions of the profile and limitations in monitoring capabilities. For currents higher than ∼1 µA, non doped optical fibers for both producing and transporting scintillation light were also successfully employed.

Non-linear photoluminescence from purified aqueous PbS nanocrystals

A simple and effective method for purifying photoluminescent water-soluble surface passivated PbS nanocrystals has been developed. Centrifuging at high speeds removes PbS nanocrystals that exhibit strong red band edge photoluminescence from an original solution containing multiple nanocrystalline species with broad photoluminescence spectra. The ability to purify the PbS nanocrystals allowed two-photon photoluminescence spectroscopy to be performed on water-soluble PbS nanocrystals and be attributed to band edge recombination. (c) 2006 Elsevier B.V. All rights reserved.

Thermal response of Bragg gratings in PMMA microstructured optical fibers

We report on the thermal characteristics of Bragg gratings fabricated in polymer optical fibers. We have observed a permanent shift in the grating wavelength at room temperature which occurs when the grating has been heated above a threshold temperature. This threshold temperature is dependent on the thermal history of the grating, and we attribute the effect to a shrinking of the fiber. This effect can be avoided by annealing the fiber before grating inscription, resulting in a linear response with temperature and an increased linear operating temperature range of the grating.

Approaching the non-linear Shannon limit

We review the recent progress of information theory in optical communications, and describe the current experimental results and associated advances in various individual technologies which increase the information capacity. We confirm the widely held belief that the reported capacities are approaching the fundamental limits imposed by signal-to-noise ratio and the distributed non-linearity of conventional optical fibres, resulting in the reduction in the growth rate of communication capacity. We also discuss the techniques which are promising to increase and/or approach the information capacity limit.