Ultrafast all-optical temporal differentiators based on CMOS-compatible integrated-waveguide Bragg gratings

We report the first realization of integrated, all-optical first- and higher-order photonic differentiators operating at terahertz (THz) processing speeds. This is accomplished in a Silicon-on-Insulator (SOI) CMOS-compatible platform using a simple integrated geometry based on (π-)phase-shifted Bragg gratings. Moreover, we achieve on-chip generation of sub-picosecond Hermite-Gaussian pulse waveforms, which are noteworthy for applications in next-generation optical telecommunications.

Second harmonic generation in AlGaAs photonic wires using low power continuous wave light

We report modal phase matched (MPM) second harmonic generation (SHG) in high-index contrast AlGaAs sub-micron ridge waveguides, by way of sub-mW continuous wave powers at telecommunication wavelengths. We achieve an experimental normalized conversion efficiency of ~14%/W/cm2, obtained through a careful sub-wavelength design supporting both the phase matching requirement and a significant overlap efficiency. Furthermore, the weak anomalous dispersion, robust fabrication technology and possible geometrical and thermal tuning of the device functionality enable a fully integrated multi-functional chip for several critical areas in telecommunications, including wavelength (time) division multiplexing and quantum entanglement.

Observation of PT-symmetry breaking in complex optical potentials

In 1998, Bender and Boettcher found that a wide class of Hamiltonians, even though non-Hermitian, can still exhibit entirely real spectra provided that they obey parity-time requirements or PT symmetry. Here we demonstrate experimentally passive PT-symmetry breaking within the realm of optics. This phase transition leads to a loss induced optical transparency in specially designed pseudo-Hermitian guiding potentials.

Low power four wave mixing in an integrated, micro-ring resonator with Q = 1.2 million

We demonstrate efficient, low power, continuous-wave four-wave mixing in the C-band, using a high index doped silica glass micro ring resonator having a Q-factor of 1.2 million. A record high conversion efficiency for this kind of device is achieved over a bandwidth of 20 nm. We show theoretically that the characteristic low dispersion enables phase-matching over a tuning range > 160 nm.

Two-photon photodetector in a multiquantum well GaAs laser structure at 1.55 microm

We report two-photon photocurrent in a GaAs/AlGaAs multiple quantum well laser at 1.55 microm. Using 1ps pulses, a purely quadratic photocurrent is observed. We measure the device efficiency, sensitivity, as well as the two-photon absorption coefficient. The results show that the device has potential for signal processing, autocorrelation and possibly two-photon source applications at sub-Watt power levels.

A self-included cyclomaltoheptaose derivative studied by NMR spectroscopy and molecular modelling

The 3D structure of 6-deoxy-6-L-tyrosinylamidocyclomaltoheptaose, a self-complexing beta-cyclodextrin derivative, was determined by NMR and molecular modelling. The aminoacyl side-chain is included in the cavity and induces chemical-shift variations in the CD proton signals, allowing their complete assignment. Dipolar interactions between protons of the tyrosine ring and internal protons of the cyclodextrin were used to obtain distance constraints. Then 42 structures were calculated from 32 distance constraints--21 shorter than 4 A involve the host-guest interactions--using a simulated annealing procedure. Starting from one of the resulting structures, a 250-ps molecular dynamics simulation was carried out in a waterbox without constraint. The simulation data are in agreement with NMR data such as nOe and ring-current effects. The cyclodextrin part takes an elliptical shape, which tightly fits the aromatic moiety. As a consequence, the respective motion of the host and the guest moieties have the same amplitude and time scale: the self-inclusion complex shows only little flexibility.

The optimization and application of two direct viable count methods for bacteria in distributed drinking water

The optimal incubation conditions for the direct viable count method with nalidixic acid were determined. They do not differ from those proposed in the literature for a laboratory strain and a mixed bacterial population isolated from drinking water. The direct viable count method with 5-cyano-2,3-ditolyl tetrazolium chloride (CTC) was performed under in situ conditions. The bacteria were incubated with CTC at concentration of 1 mM for 4-6 h at the temperature of the water in the pipes and without the addition of an exogenous substrate. The results obtained for a laboratory strain using the two direct count methods were similar. However, for a mixed bacterial population, the counts were always higher with the CTC method than with the nalidixic acid method.

Folding trends in a flexible peptide: two-dimensional NMR study of deltorphin-I, a delta selective opioid heptapeptide

Deltorphin-I, H-Tyr-(D)ala-Phe-Asp-Val-Val-Gly-NH2 and dermenkephalin, H-Tyr-(D)met-Phe-His-Leu-Met-Asp-NH2 are 2 members of small but growing family of D-amino acid containing opioid peptides isolated from the frog skin. Both peptides exhibit high affinity and selectivity for the delta-opioid receptor. Two-dimensional NMR study of deltorphin-I in DMSO-d6 revealed a close conformational homology with dermenkephalin. However, the temperature dependency of NOE correlations issued from Val5 and Val6 of deltorphin-I reflects a high intrinsic flexibility of the carboxyend. Whereas most of the JN alpha coupling constants and interresidue alpha N NOE effects were compatible with an extended structure, some sequential NOEs together with several medium and long range correlations involving Tyr1, Val6 and Asp4 may reflect an equilibrium mixture of extended and folded conformers in which the C- and the N-terminal parts of deltorphin-I are in close proximity. Finally, g- is the preferential conformer in the side chain of Phe3 in both deltorphin-I and dermenkephalin.