Low loss coupling to sub-micron thick rib and nanowire waveguides by vertical tapering.

Highly nonlinear planar glass waveguides have been shown to be useful for all optical signal processing. However, the typical SMF-28 fiber to waveguide coupling loss of ~5dB/end remains a barrier to practical implementation. Low loss coupling to a fiber using vertical tapering of the waveguide film is analyzed for rib and nanowire waveguides and experimentally demonstrated for ribs showing polarization and wavelength independence over >300nm bandwidth. Tapers with essentially zero excess loss led to total losses from the waveguide to fiber core of 1.1dB per facet comprising only material absorption (0.75dB) and mode overlap loss (0.36dB), both of which can be eliminated with improvements to processing and materials.

Optical phase conjugation by an As(2)S(3) glass planar waveguide for dispersion-free transmission of WDM-DPSK signals over fiber.

We report the first demonstration of optical phase conjugation (OPC) transmission of phase encoded and wavelength-division multiplexed (WDM) signals by the Kerr effect in a planar structured waveguide. The phase conjugated electric field of the signal is produced by four wave mixing pumped by a CW laser during co-propagating with the signal in a highly nonlinear waveguide fabricated in As(2)S(3) glass. Experiments demonstrate the capability of the device to perform dispersion-free transmission through up to 225 km of standard single mode fiber for a 3 × 40 Gb/s WDM signal, with its channels encoded as return-to-zero differential phase shift keying and spaced either 100 or 200 GHz apart. This work represents an important milestone towards demonstrating advanced signal processing of high-speed and broadband optical signals in compact planar waveguides, with the potential for monolithic optical integration.

Photonic chip based transmitter optimization and receiver demultiplexing of a 1.28 Tbit/s OTDM signal.

We demonstrate chip-based Tbaud optical signal processing for all-optical performance monitoring, switching and demultiplexing based on the instantaneous Kerr nonlinearity in a dispersion-engineered As(2)S(3) planar waveguide. At the Tbaud transmitter, we use a THz bandwidth radio-frequency spectrum analyzer to perform all-optical performance monitoring and to optimize the optical time division multiplexing stages as well as mitigate impairments, for example, dispersion. At the Tbaud receiver, we demonstrate error-free demultiplexing of a 1.28 Tbit/s single wavelength, return-to-zero signal to 10 Gbit/s via four-wave mixing with negligible system penalty (< 0.5 dB). Excellent performance, including high four-wave mixing conversion efficiency and no indication of an error-floor, was achieved. Our results establish the feasibility of Tbaud signal processing using compact nonlinear planar waveguides for Tbit/s Ethernet applications.

Simultaneous multi-impairment monitoring of 640 Gb/s signals using photonic chip based RF spectrum analyzer.

We report the first demonstration of simultaneous multi-impairment monitoring at ultrahigh bitrates using a THz bandwidth photonic-chip-based radio-frequency (RF) spectrum analyzer. Our approach employs a 7 cm long, highly nonlinear (gamma approximately 9900 /W/km), dispersion engineered chalcogenide planar waveguide to capture the RF spectrum of an ultrafast 640 Gb/s signal, based on cross-phase modulation, from which we numerically retrieve the autocorrelation waveform. The relationship between the retrieved autocorrelation trace and signal impairments is exploited to simultaneously monitor dispersion, in-band optical signal to noise ratio (OSNR) and timing jitter from a single measurement. This novel approach also offers very high OSNR measurement dynamic range (> 30 dB) and is scalable to terabit data rates.

Terahertz bandwidth RF spectrum analysis of femtosecond pulses using a chalcogenide chip.

We report the first demonstration of the use of an RF spectrum analyser with multi-terahertz bandwidth to measure the properties of femtosecond optical pulses. A low distortion and broad measurement bandwidth of 2.78 THz (nearly two orders of magnitude greater than conventional opto-electronic analyzers) was achieved by using a 6 cm long As(2)S(3) chalcogenide waveguide designed for high Kerr nonlinearity and near zero dispersion. Measurements of pulses as short as 260 fs produced from a soliton-effect compressor reveal features not evident from the pulse's optical spectrum. We also applied an inverse Fourier transform numerically to the captured data to re-construct a time-domain waveform that resembled pulse measurement obtained from intensity autocorrelation.

Long, low loss etched As(2)S(3) chalcogenide waveguides for all-optical signal regeneration.

We report on the fabrication and optical properties of etched highly nonlinear As(2)S(3) chalcogenide planar rib waveguides with lengths up to 22.5 cm and optical losses as low as 0.05 dB/cm at 1550 nm - the lowest ever reported. We demonstrate strong spectral broadening of 1.2 ps pulses, in good agreement with simulations, and find that the ratio of nonlinearity and dispersion linearizes the pulse chirp, reducing the spectral oscillations caused by self-phase modulation alone. When combined with a spectrally offset band-pass filter, this gives rise to a nonlinear transfer function suitable for all-optical regeneration of high data rate signals.

Visual hallucinations in Parkinson's disease: clues to separate origins.

Our paper discusses two experimental studies suggesting that Visual Hallucinations (VH) in Parkinson's Disease (PD) may have separate origins. The first is a prospective 8years study evaluating the appearance of VH, visual abnormalities assessed by Visual Evoked Potentials (VEPs) and REM sleep Behaviour Disorder (RBD), in 80 PD patients treated with l-Dopa and Dopaminoagonists (DA). In chronically treated, cognitively unimpaired, PD patients VH were statistically related (p=0.001) to RBD occurrence and high DA doses. Visual abnormalities were significantly reduced by l-Dopa or DA intake, and were statistically unrelated to VH. The second study involved PD patients placed in a Virtual Reality Environment, to decontextualize visual input. When motor symptoms worsened and VEP abnormalities developed patients consistently described hallucinatory dysperceptions of the virtual environment. The two studies therefore show that VH can occur in two seemingly distinct conditions, one is related to chronic treatment and to a sleep disorder frequently observed in PD, the other is probably related to a hypodopaminergic state. Our studies support a recently proposed integrative model of VH, and show that the neural circuits purported to explain VH must include the retinal dopaminergic system and the REM sleep regulatory system.

Noun verb dissociation in Parkinson's disease.

A noun/verb dissociation with a relative verb deficit was found in patients affected by Parkinson's disease, even in relatively early stages, when mental deterioration is not severe. This finding is compatible with earlier observations, according to which verbs are dealt with in more anterior regions with respect to nouns. It also supports the speculation that the co-ordination and the manipulation of information associated with a verb world rely on the frontostriatal system.

Exploración radisotopica de la función ventricular basal izquierda del tránsito esofágico, de la vía urinaria superior y de la función vesical en pacientes chagásicos cronicos predominantemente asintomáticos / Radioisotopic exploration of basal left ventricular function of the esophageal transit, of upper urinary duct and of bladder function of patients with chronic Chagas' disease predominantly en assymptomatic

Estudou-se em 56 pacientes chagásicos crônicos (45 assintomáticos e os restantes portadores de transtornos cardiovasculares e digestivos) a funçäo ventrícular esquerda (ejeçäo basal, motilidade parietal segmentar e o histograma); em 29 deles, o trânsito esofagiano e em outros 25 enfermos explorou-se a via urinária, respectivamente com o 99m - TC coloidal e o 99ml - TC b + PA. Observou-se que a fraçäo de ejeçäo do ventrículo esquerdo entre os indivíduos normais era de 0,66 + ou - 0,07, enquanto nos chagásicos crônicos com alteraçöes cardiovasculares (Grupo II) verificou-se 0,49 + ou - 0,21. A motilidade parietal esteve alterada em 60% do mesmo grupo de enfermos e o desvio standard do histograma foi de 1,98 + ou - 0,45, para 1,29 + ou - 0,17 no grupo de voluntários. O trânsito esofágico foi considerado normal em 9 casos e alterado em 20, sendo que em 6 foi do tipo prolongado, em 4 adinâmico e em 10 incoordenado. Nos 25 pacientes nos quais investigaram a via urinária superior, foi encontrada alteraçäo em 22 (dilataçäo piélica uni ou bilateral) e a funçäo vesical nestes pacientes foi normal em apenas quatro casos. Concluem os pesquisadores que o 99 - TC representa um grande avanço tecnológico no estudo da funçäo cardíaca, esofágica e das vias urinárias em pacientes chagásicos crônicos e assintomáticos