Biomedical subjects

Ulf Peschel

Publications and source records attributed to Ulf Peschel.

6 recordsLinked to original sources

PubMed2006

Correlation between single-cylinder properties and bandgap formation in photonic structures.

The origin of frequency gaps in the dispersion relation of periodic, quasi-periodic, and random photonic structures consisting of different arrangements of dielectric cylinders has been investigated. For TM polarization it was found that the formation and properties of gaps are strongly affected by Mie resonances of a single cylinder. Both the spectral position and size depend on the properties of this single scatterer. In contrast, for TE polarization no correlation between the scattering properties and bandgap formation was found, as Mie resonances are spectrally not well separated. For the inverted structure consisting of air cylinders in a dielectric material, the frequency gaps depend on the spatial arrangement of the cylinders because no pronounced Mie resonances exist in this case.

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PubMed2006

Bloch oscillations and Zener tunneling in two-dimensional photonic lattices.

We report on the first experimental observation of photonic Bloch oscillations and Zener tunneling in two-dimensional periodic systems. We study the propagation of an optical beam in a square lattice superimposed on a refractive index ramp. We observe oscillations of the beam inside the first Brilloin zone and tunneling of light from the first to the higher-order bands of the lattice band gap spectrum.

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PubMed2006

Visual observation of Zener tunneling.

We experimentally investigate photonic Zener tunneling between the bands of a waveguide array by directly monitoring the propagating light inside this structure. For strong transverse index gradients we observe Zener breakdown as regular outbursts of radiation escaping from the Bloch oscillations. Tunneling to higher order photonic bands and Bloch oscillations in different bands have been detected.

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PubMed2004

Nonlinearity and disorder in fiber arrays.

We experimentally investigate light propagation in a disordered two-dimensional array of mutually coupled optical fibers. In the linear case light either spreads in a diffusive manner or localizes at a few sites. For high excitation power diffusive spreading is arrested by the focusing nonlinearity, i.e., forming a discrete soliton. By contrast, fields, which are localized in the linear regime, can experience both spreading and contraction caused by the nonlinearity.

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PubMed2004

Discrete diffraction in two-dimensional arrays of coupled waveguides in silica.

The propagation of light in 5 x 5 and 7 x 7 cubic lattices of evanescently coupled waveguides is investigated for the first time, to the authors' knowledge. The results reveal ideal discrete diffraction and demonstrate the excellent quality of the waveguide arrays, which were manufactured in fused silica by femtosecond-laser-induced refractive-index modifications.

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PubMed2003

All-optical switching in quadratically nonlinear waveguide arrays.

We demonstrate a scheme for efficient switching and routing of low-power signals in waveguide arrays with second-order nonlinearity. With control beams the signal can be switched to different output positions and can be simultaneously converted to another wavelength with low cross talk.

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