Bistability and Stationary Gap Solitons in Quasiperiodic Photonic Crystals Based on Thue-Morse Sequence

Victor Grigoriev, Fabio Biancalana

The nonlinear properties of quasiperiodic photonic crystals based on Thue-Morse sequence are investigated. The intrinsic asymmetry of these 1D structures for odd generation numbers results in bistability thresholds which are sensitive to propagation direction. Along with resonances of perfect transmission, this feature allows to obtain strongly nonreciprocal propagation and to create an all-optical diode (ADD). The efficiency of two schemes is compared: passive and active when an additional short-term pump signal is applied. The existence of stationary gap solitons for quasiperiodic photonic crystals is shown numerically, and their difference from the Bragg case is emphasized.

Optimization of Dispersion-Imbalanced Loop Mirror for Phase-Preserving Amplitude Regeneration

T. Roethlingshoefer, K. Sponsel, C. Stephan, G. Onishchukov, B. Schmauss, G. Leuchs

The adaptation and optimization of a dispersion-imbalance loop mirror for phase-preserving amplitude 2R regeneration is shown by numerical simulations. Its performance has been evaluated for DPSK transmission. A 4.8dB Q-factor improvement has been demonstrated.

Propagation of a decentered astigmatic partially coherent beam in a turbulent atmosphere

Yangjian Cai, Qiang Lin

Propagation properties of a decentered general astigmatic partially coherent beam (i.e., decentered twisted anisotropic Gaussian Schell-model beam) in a turbulent atmosphere are investigated. Analytical formulas for the cross-spectral density and decentered parameter of a decentered astigmatic partially coherent beam propagating in a turbulent atmosphere are derived. Irradiance properties of a decentered astigmatic partially coherent beam in a turbulent atmosphere are studied graphically, and are found to be quite different from its properties in free space. (C) 2007 Elsevier GmbH. All rights reserved.

Coherent Superposition of Terahertz Beams from a Phased Linear Photomixer Array

Sebastian Bauerschmidt, Sascha Preu, Stefan Malzer, Gottfried H. Doehler, Lijun Wang, Hong Lu, Arthur C. Gossard

We report on a 4 element linear array of free standing, tunable THz n-i-pn-i-p superlattice photomixers. The individual THz beams are coherently combined at a target plane distance of 4.2 m. The measurements of the interference pattern confirm the theoretically expected quadratic intensity increase of the center beam with the number of sources. At the same time, the beam waist is reduced in one dimension by a factor of 6 compared to a single beam. This technique allows for high resolution, THz stand off imaging.

Characterization of the absolute frequency stability of an individual reference cavity

T. Liu, Y. N. Zhao, V. Elman, A. Stejskal, L. J. Wang

We demonstrated for the first time (to our knowledge) the characterization of absolute frequency stability of three reference cavities by cross beating three laser beams that are independently locked to these reference cavities. This method shows the individual feature of each reference cavity, while conventional beat note measurement between two cavities can provide only an upper bound. This method allows for numerous applications such as optimizing the performance of the reference cavity for optical clockwork. (C) 2009 Optical Society of America

4OD-mediated solitonic radiations in HC-PCF cladding

F. Biancalana, F. Benabid, P. S. Light, F. Couny, A. Luiten, P. J. Roberts, Jiahui Peng, A. V. Sokolov

We observe for the first time the simultaneous emission of two resonant radiation frequencies by optical solitons in a small waveguiding glass-feature within the cladding of a HC-PCF. We attributes this phenomenon to the unusually large 4th-order GVD coefficient of the waveguide. (C)2009 Optical Society of America

Cascaded Phase-Preserving Amplitude Regeneration in a DPSK Transmission System

Ch Stephan, K. Sponsel, G. Onishchukov, B. Schmauss, G. Leuchs

Experimental results obtained on 10 Gb/s RZ-DPSK transmission in a recirculating fiber-loop setup show that nonlinear amplifying loop mirrors can efficiently enhance system performance. Main limiting factor is amplified Rayleigh backscattering in highly nonlinear fiber.

Temperature response of turbulent premixed flames to inlet velocity oscillations

B. Ayoola, G. Hartung, C. A. Armitage, J. Hult, R. S. Cant, C. F. Kaminski

Flame-turbulence interactions are at the heart of modern combustion research as they have a major influence on efficiency, stability of operation and pollutant emissions. The problem remains a formidable challenge, and predictive modelling and the implementation of active control measures both rely on further fundamental measurements. Model burners with simple geometry offer an opportunity for the isolation and detailed study of phenomena that take place in real-world combustors, in an environment conducive to the application of advanced laser diagnostic tools. Lean premixed combustion conditions are currently of greatest interest since these are able to provide low NO (x) and improved increased fuel economy, which in turn leads to lower CO(2) emissions. This paper presents an experimental investigation of the response of a bluff-body-stabilised flame to periodic inlet fluctuations under lean premixed turbulent conditions. Inlet velocity fluctuations were imposed acoustically using loudspeakers. Spatially resolved heat release rate imaging measurements, using simultaneous planar laser-induced fluorescence (PLIF) of OH and CH(2)O, have been performed to explore the periodic heat release rate response to various acoustic forcing amplitudes and frequencies. For the first time we use this method to evaluate flame transfer functions and we compare these results with chemiluminescence measurements. Qualitative thermometry based on two-line OH PLIF was also used to compare the periodic temperature distribution around the flame with the periodic fluctuation of local heat release rate during acoustic forcing cycles.

Heralded entanglement of arbitrary degree in remote qubits

U. Schilling, C. Thiel, E. Solano, T. Bastin, J. von Zanthier

Incoherent scattering of photons off two remote atoms with a Lambda-level structure is used as a basic Young-type interferometer to herald long-lived entanglement of an arbitrary degree. The degree of entanglement, as measured by the concurrence, is found to be tunable by two easily accessible experimental parameters. Fixing one of them to certain values unveils an analog to the Malus' law. An estimate of the variation in the degree of entanglement due to uncertainties in an experimental realization is given.

Generation and Direct Detection of Broadband Mesoscopic Polarization-Squeezed Vacuum

Timur Iskhakov, Maria V. Chekhova, Gerd Leuchs

Using a traveling-wave optical parametric amplifier with two orthogonally oriented type-I BBO crystals pumped by picosecond pulses, we generate vertically and horizontally polarized squeezed vacuum states within a broad frequency-angular range. Depending on the phase between these states, fluctuations in one or another Stokes parameter are suppressed below the shot-noise limit. Because of the large number of photon pairs produced, no local oscillator is required, and 3 dB squeezing is observed by means of direct detection.