Four-wave mixing in a silicon microring resonator using a self-pumping geometry

We report on four-wave mixing in a silicon microring resonator using a self-pumping scheme instead of an external laser. The ring resonator is inserted in an external-loop cavity with a fibered semiconductor amplifier as a source of gain. The silicon microring acts as a filter and we observe lasing in one of the microring's resonances. We study correlations between signal and idler generated beams using a Joint Spectral Density experiment

Suppression of Parasitic Nonlinear Processes in Spontaneous Four-Wave Mixing with Linearly Uncoupled Resonators

We report on a signal-to-noise ratio characterizing the generation of identical photon pairs of more than 4 orders of magnitude in a ring resonator system. Parasitic noise, associated with single-pump spontaneous four-wave mixing, is essentially eliminated by employing a novel system design involving two resonators that are linearly uncoupled but nonlinearly coupled. This opens the way to a new class of integrated devices exploiting the unique properties of identical photon pairs in the same optical mode

Structural correlates of early and late onset Alzheimer's disease: voxel based morphometric study

Methods: We studied nine patients with early onset (age ⩽65 years), nine with late onset (age >65) Alzheimer's disease (EOAD and LOAD, respectively) of mild-moderate severity, and 26 controls who were stratified into younger (YC, age ⩽65, n = 9) and older (OC, age >65, n = 17) subjects. The patients were closely matched for clinical severity: 3/2/3/1 patients had clinical dementia rating of 0.5/1/2/3, respectively, in both the groups. High resolution magnetic resonance images of the brain of the EOAD and YC groups and the LOAD and OC groups were compared on a voxel by voxel basis with statistical parametric mapping to detect areas specifically atrophic. Results: The patients with EOAD showed greater neocortical atrophy at the temporoparietal junction while the patients with LOAD showed greater hippocampal atrophy. The results could not be accounted for by the apolipoprotein E genotype. Conclusions: Since genetic factors are believed to play a relevant pathogenetic role in EOAD and environmental factors in LOAD, genetic and environmental factors may differentially predispose the neocortical and limbic areas to the development of Alzheimer's neuropathology

APOE and modulation of Alzheimer's and frontotemporal dementia

To investigate the difference in the morphologic expression of frontotemporal dementia (FTD) and Alzheimer's disease (AD) in patients carrying and not carrying the epsilon4 allele of APOE, MR images of 26 controls, 18 AD patients (11 carrying the epsilon4 allele, seven non-carriers), and eight FTD (two carriers, six non-carriers) were compared using voxel by voxel analysis. Greater atrophy was found in the disease-specific regions of the epsilon4 carriers vs the non-carriers at P < 0.05 corrected: medial temporal atrophy was greater in the AD carrying the epsilon4 allele, right ventral striatal atrophy in the FTD carrying the allele. The non-carriers did not have atrophic regions compared to the carriers. The epsilon4 allele of the APOE might modulate the expression of degenerative dementias by enhancing the specific effects of neurodegenerative diseases on the brain

Silicon source of frequency-bin entangled photons

We demonstrate an integrated source of frequency-entangled photon pairs on a silicon photonics chip. The emitter has a coincidence-to-accidental ratio exceeding 103. We prove entanglement by showing two-photon frequency interference with a visibility of 94.6% ± 1.1%. This result opens the possibility of on-chip integration of frequency-bin sources with modulators and the other active and passive devices available in the silicon photonics platform

Detection of grey matter loss in mild Alzheimer's disease with voxel based morphometry

Objectives: To test the applicability of an automated method of magnetic resonance image analysis (voxel based morphometry) to detect presence and severity of regional grey matter density reduction—a proxy of atrophy—in Alzheimer's disease. Methods: Twenty nine probable Alzheimer's patients and 26 non-demented controls (mini-mental state examinations mean (SD) 21 (4) and 29 (1)) underwent high resolution 3D brain magnetic resonance imaging. Spatial normalisation to a stereotactic template, segmentation into grey matter, white matter, and cerebrospinal fluid, and smoothing of the grey matter were carried out based on statistical parametric mapping (SPM99) algorithms. Analyses were carried out: (a) contrasting all Alzheimer's patients with all controls (p<0.05 corrected for multiple comparisons); (b) contrasting the three Alzheimer's patients with mini-mental state of 26 and higher with all controls (p<0.0001 uncorrected); and (c) correlating grey matter density with mini-mental state score within the Alzheimer's group (p<0.0001 uncorrected). Results: When all Alzheimer's patients were compared with controls, the largest atrophic regions corresponded to the right and left hippocampal/amygdalar complex. All parts of the hippocampus (head, body, and tail) were affected. More localised atrophic regions were in the temporal and cingulate gyri, precuneus, insular cortex, caudate nucleus, and frontal cortex. When the mildest Alzheimer's patients were contrasted with controls, the hippocampal/amygdalar complex were again found significantly atrophic bilaterally. The mini-mental state score correlated with grey matter density reduction in the temporal and posterior cingulate gyri, and precuneus, mainly to the right. Conclusions: Voxel based morphometry with statistical parametric mapping is sensitive to regional grey matter density reduction in mild Alzheimer's disease

Hippocampal shape differences in dementia with Lewy bodies

To assess the morphological changes of the hippocampus in Lewy body dementia (LBD) patients we used radial atrophy mapping, a mathematical modeling method sensitive to subtle differences in hippocampal shape. T1-weighted high resolution magnetic resonance (MR) scans were acquired from 14 LBD and 28 controls of similar age and gender, and were compared to those of 28 patients with Alzheimer's disease (AD) described previously. MR images were normalized by linear (12 parameter) transformation to a customized template. The hippocampal formation was isolated by manual tracing. Group differences were assessed with algorithms that average hippocampal shapes across subjects, using three-dimensional parametric surface mesh models. In LBD patients, significant tissue loss amounting to 10-20% was found in the hippocampal subregions corresponding to the anterior portion of the CA1 field on both sides, along the longitudinal midline in the dorsal aspect within the CA2-3 field, and in the subiculum and presubiculum. The direct comparisons between LBD and AD patients showed that this pattern of local atrophy is different from that characteristic of AD. LBD pattern of hippocampal atrophy might be related to the peculiar neuropathology of the disease

Electrically driven source of time-energy entangled photons based on a self-pumped silicon microring resonator

Time-energy entangled photon pairs are fundamental resources for quantum communication protocols since they are robust against environmental fluctuations in optical fiber networks. Pair sources based on spontaneous four-wave mixing in silicon microring resonators usually employ expensive external tunable lasers to compensate for ambient fluctuations; adopting self-pumped configurations, instead, lifts the need for such external source. Here we demonstrate the emission of time-energy entangled photon pairs at telecom wavelengths from a silicon self-pumped ring, obtaining a Franson interference fringe with 93.9% ± 0.9% visibility

Emission of time-energy entangled photon pairs by a self-pumped silicon microresonator

We demonstrate emission of photon pairs from a Silicon integrated microresonator under electrical self-pumping. By controlling excitation conditions, the photon pairs are time-energy entangled, with fringe visibility in a Franson experiment of 93.9% ± 0.9%