Recent developments in optical fibre based optoelectronic oscillators

The paper reports recent progress on new types of low noise and high spectral purity optoelectronic oscillators operating at optical wavelengths around 1550nm and radio frequencies (RF) up to 40GHz with RF linewidths <1kHz

Investigation of mid-infrared AlInSb LEDs with an n-i-p structure

We report on the investigation on mid-infrared AlInSb LEDs with an n-i-p structure. Compared to the conventional AlInSb LEDs with a p-i-n structure, a better current spreading corresponding to a uniform current distribution in the active region is expected in the n-i-p structure because of a high electron mobility in the n-type AlInSb material. The output optical power of laterally injected LEDs were investigated as a function of the device geometry by COMSOL simulations and confirmed by experimental results

Machine learning classification of human joint tissue from diffuse reflectance spectroscopy data

Objective: To assess if incorporation of DRS sensing into real-time robotic surgery systems has merit. DRS as a technology is relatively simple, cost-effective and provides a non-contact approach to tissue differentiation. Methods: Supervised machine learning analysis of diffuse reflectance spectra was performed to classify human joint tissue that was collected from surgical procedures. Results: We have used supervised machine learning in the classification of a DRS human joint tissue data set and achieved classification accuracy in excess of 99%. Sensitivity for the various classes were; cartilage 99.7%, subchondral 99.2%, meniscus 100% and cancellous 100%. Full wavelength range is required for maximum classification accuracy. The wavelength resolution must be larger than 8nm. A SNR better than 10:1 was required to achieve a classification accuracy greater than 50%. The 800-900nm wavelength range gave the greatest accuracy amongst those investigated. Conclusion: DRS is a viable method for differentiating human joint tissue and has the potential to be incorporated into robotic orthopaedic surgery

Hot probe measurements on neutron irradiated, isotope enriched ZnO nanorods

We report on neutron transmutation doping (NTD) of isotopically (64Zn) enriched ZnO nanorods to produce material with holes as the majority mobile carrier. Nanorods of ZnO enriched with 64Zn were synthesised and the abundance of 64Zn in these samples is ∼ 71%, compared to the natural abundance of ∼ 49 %. The enriched material was irradiated with thermal neutrons which converts some 64Zn to 65Zn. The 65Zn decays to 65Cu with a half-life of 244 days and the Cu can act as an acceptor dopant. After 690 days, a hot probe technique was used to determine the majority charge carriers in non-irradiated and neutron irradiated nanorod samples. Non-irradiated samples were measured to be to have electrons as the majority mobile carrier and the irradiated samples were measured to have holes as the majority mobile carrier

Photo-detectors integrated with resonant tunneling diodes

We report on photo-detectors consisting of an optical waveguide that incorporates a resonant tunneling diode (RTD). Operating at wavelengths around 1.55 μm in the optical communications C band we achieve maximum sensitivities of around 0.29 A/W which is dependent on the bias voltage. This is due to the nature of RTD nonlinear current-voltage characteristic that has a negative differential resistance (NDR) region. The resonant tunneling diode photo-detector (RTD-PD) can be operated in either non-oscillating or oscillating regimes depending on the bias voltage quiescent point. The oscillating regime is apparent when the RTD-PD is biased in the NDR region giving rise to electrical gain and microwave self-sustained oscillations Taking advantage of the RTD’s NDR distinctive characteristics, we demonstrate efficient detection of gigahertz (GHz) modulated optical carriers and optical control of a RTD GHz oscillator. RTD-PD based devices can have applications in generation and optical control of GHz low-phase noise oscillators, clock recovery systems, and fiber optic enabled radio frequency communication systems.info:eu-repo/semantics/publishedVersio

Atom probe microscopy of zinc isotopic enrichment in ZnO nanorods

We report on atomic probe microscopy (APM) of isotopically enriched ZnO nanorods that measures the spatial distribution of zinc isotopes in sections of ZnO nanorods for natural abundance natZnO and 64Zn and 66Zn enriched ZnO nanorods. The results demonstrate that APM can accurately quantify isotopic abundances within these nanoscale structures. Therefore the atom probe microscope is a useful tool for characterizing Zn isotopic heterostructures in ZnO. Isotopic heterostructures have been proposed for controlling thermal conductivity and also, combined with neutron transmutation doping, they could be key to a novel technology for producing p-n junctions in ZnO thin films and nanorods

Limitation Due To 3-Photon Absorption On The Useful Spectral Range For Nonlinear Optics In Algaas Below Half Band-Gap

We report measurements of the spectral dispersion and the magnitude of three-photon absorption in Al0.18Ga0.82As for photon energies between one half and one third the band gap and show that a two-parabolic-band model is valid in this material. These results indicate that there is a limited spectral range below half the band gap in AlGaAs (and presumably all semiconductors) in which the bound electronic optical nonlinearity can be used without significant multiphoton absorption

Photo-detectors integrated with resonant tunneling diodes

We report on photo-detectors consisting of an optical waveguide that incorporates a resonant tunneling diode (RTD). Operating at wavelengths around 1.55 m in the optical communications C band we achieve maximum sensitivities of around 0.29 A/W which is dependent on the bias voltage. This is due to the nature of RTD nonlinear current-voltage characteristic that has a negative differential resistance (NDR) region. The resonant tunneling diode photo-detector (RTD-PD) can be operated in either non-oscillating or oscillating regimes depending on the bias voltage quiescent point. The oscillating regime is apparent when the RTD-PD is biased in the NDR region giving rise to electrical gain and microwave self-sustained oscillations Taking advantage of the RTD's NDR distinctive characteristics, we demonstrate efficient detection of gigahertz (GHz) modulated optical carriers and optical control of a RTD GHz oscillator. RTD-PD based devices can have applications in generation and optical control of GHz low-phase noise oscillators, clock recovery systems, and fiber optic enabled radio frequency communication systems.FCT under the project WOWi [PTDC/EEA-TEL/100755/2008]; programme POCTI/FEDER [REEQ/1272/EEI/2005]; FCT Portugal [SFRH/BPD/84466/2012]info:eu-repo/semantics/publishedVersio

Assessment of β-amyloid deposits in human brain: a study of the BrainNet Europe Consortium

β-Amyloid (Aβ) related pathology shows a range of lesions which differ both qualitatively and quantitatively. Pathologists, to date, mainly focused on the assessment of both of these aspects but attempts to correlate the findings with clinical phenotypes are not convincing. It has been recently proposed in the same way as ι and α synuclein related lesions, also Aβ related pathology may follow a temporal evolution, i.e. distinct phases, characterized by a step-wise involvement of different brain-regions. Twenty-six independent observers reached an 81% absolute agreement while assessing the phase of Aβ, i.e. phase 1 = deposition of Aβ exclusively in neocortex, phase 2 = additionally in allocortex, phase 3 = additionally in diencephalon, phase 4 = additionally in brainstem, and phase 5 = additionally in cerebellum. These high agreement rates were reached when at least six brain regions were evaluated. Likewise, a high agreement (93%) was reached while assessing the absence/presence of cerebral amyloid angiopathy (CAA) and the type of CAA (74%) while examining the six brain regions. Of note, most of observers failed to detect capillary CAA when it was only mild and focal and thus instead of type 1, type 2 CAA was diagnosed. In conclusion, a reliable assessment of Aβ phase and presence/absence of CAA was achieved by a total of 26 observers who examined a standardized set of blocks taken from only six anatomical regions, applying commercially available reagents and by assessing them as instructed. Thus, one may consider rating of Aβ-phases as a diagnostic tool while analyzing subjects with suspected Alzheimer’s disease (AD). Because most of these blocks are currently routinely sampled by the majority of laboratories, assessment of the Aβ phase in AD is feasible even in large scale retrospective studies