Extreme Contrast Enchantment of an All-Optical AND Gate

We experimentally demonstrate a 31.2-dB-contrast all-optical AND gate based on a Fabry-Pérot semiconductor optical amplifier (SOA). Typically, cross phase modulation is the dominant nonlinearity as it shifts a FPSOA resonance to trigger the AND-gate functionality. Cross polarization modulation (XPolM) is introduced here to produce a distinct output SOP for the high-state power that is different from the low-state power. A linear polarizer is used to block the low-state power to enhance the contrast by 24 dB, far exceeding previous demonstrations for such FPSOA gates

Polarization Dynamics in Nonlinear Photonic Resonators

The global market demand for higher-bandwidth communication is increasing exponentially. Although optical networks provide high transmission speed using light to transmit signals, a bottleneck-inducing conversion is often needed to perform the processing of optical signals in the electrical domain. Such processing imposes a major barrier that would limit the high transmission speed of fiber-optic communications. This bottleneck conversion may be mitigated by extending signal-processing capabilities directly into the optical domain itself. Thus, I have studied the dynamics of optical polarization in a nonlinear photonic resonator to understand a new optical physical behavior to enhance the capabilities of optical signal processing. I present a theoretical model and experimental investigation to study the simultaneous occurrence of two optical nonlinear processes---nonlinear polarization rotation (NPR) and dispersive optical bistability. These two optical nonlinear processes within a nonlinear photonic resonator produce an optical signal exhibiting hysteresis curves in its state of polarization (SOP). Bistable action accompanied with simultaneous NPR is a significant departure from traditional optical memory, where the optical signal only exhibits hysteresis curves in the output power. Bistable polarization rotation (BPR) term is used to refer to the new physical process of bistable action accompanied by simultaneous NPR. I have leveraged this new physical process of the bistable polarization rotation to realize a hysteresis-shape transformation and optimization. A diversity of hysteresis shapes are demonstrated in optical power including the canonical counter-clockwise (CCW) shape (S-shape), the clockwise (CW) shape (inverted S-shape), and butterfly shapes. The control of the shape is performed downstream of the nonlinear photonic resonator within which the bistable signal is generated. I have derived a mathematical model to study this transformation process. Critical to our model, a generalized Malus\u27 law of a non-ideal linear polarizer and an elliptical input polarization. Since all hysteresis shapes originate from the same bistable signal, all shapes exhibit the same switching input powers. Moreover, the shape-control process is used to enhance the bistable switching contrast to surpass 20 dB for the CCW and CW shapes. Additionally, the new technique of hysteresis shape control enables the ability of simultaneous distribution of the bistable signal into multiple paths. In each path, the optical signal can be independently controlled to produce a hysteresis shape. For example, CCW and CW shapes can be configured in two locations using the same BPR signal. The theoretical and experimental work reported here is carried out for the case of a Fabry-Perot semiconductor optical amplifier as the nonlinear photonic resonator. Both the new physical process and the new control capability presented here are extendable to other nonlinear media (such as Kerr media) and other photonic resonators (such as ring and distributed feedback resonators). The dissertation outcomes detail processes and techniques to enhance the performance of all-optical combinational gates, such as photonic AND and XOR gates, as well as all-optical sequential devices, such as photonic flip-flops

Greenhouse Gas Fluxes from Created Wetlands: How Management Techniques Impact Emissions and Implications for Climate Change

Wetlands are one of the most valuable ecosystems, providing services such as carbon sequestration and nitrogen removal. Studies suggest that created wetlands may not function the same as natural wetlands and management techniques, such as organic matter addition (OM), have been proposed to promote natural functions. The objective of this study was to understand the effects of OM additions on greenhouse gas (GHG) emissions in created wetlands with different vegetation, hydrology and soil characteristics. This study was conducted from 2016 to 2017 at two created wetlands (A2S and A3A) at High Acres Nature Area in Fairport, New York. There was high seasonal and inter-annual variability in weather conditions during the study period and rainfall and temperature were the dominant factors controlling GHG fluxes within both wetlands. Drought condition during 2016 limited soil respiration and C uptake by plants. In 2017, when moisture conditions were more typical, OM addition increased soil respiration rates at A2S in the fall. There was a trend towards higher ecosystem respiration at this time; however, OM addition also increased gross primary production, resulting in no net change in CO2 exchange. Due to dry conditions, methane (CH4) emissions were low during much of the study. When emissions were high, fluxes were significantly higher in the light than the dark at A2S, but not A3A, suggesting that vegetation differences between the site impact CH4 transport pathways. While OM addition did not change anaerobic CH4 or CO2 production potential, there were significant differences between the sites, with higher production rates in A2S, where hydrologic conditions in the field may have selected for microbial communities adapted to anaerobic environments. These findings highlight the importance of precipitation and hydrology in controlling C cycling in created wetlands and suggest that wetland characteristics will influence their responses to management techniques

Hybrid Nano-scale Carbon Sensors for Improved Detection of Vital Neurotransmitters

Electrochemical detection of vital biomolecules using nano-carbon materials has attracted great attention to effectively carry-out electrochemical sensing of important neurotransmitters in the brain. Multi-walled carbon nanotubes (MWNTs) and graphene (G) have been employed as promising nano-carbon materials according to physical, electrical, optical, and thermal properties along with remarkable electrochemical performance. Modified MWNTs and G, on the same hand, exhibited greater electrocatalytic activity and improved redox signals of the targeted analytes. For this reason, the primary goal of this study is to fabricate simple, low cost, biocompatible, and modified MWNTs sensor appropriate for dopamine (DA) neurotransmitter detection. To obtain improved sensitivity and selectivity of DA compared to conventional electrodes, our MWNTs electrode was fabricated by a direct draw of MWNTs fibers from MWNTs forest converted into yarn/probe style by twisting then modified with nafion. The second goal was based on applying reduced graphene oxide (RGO) as graphene derivative along with poly (ethylenedioxythiophene): poly (styrenesulfonate) PEDOT:PSS to prepare RGO/PEDOT:PSS dispersion modified with nafion. RGO/PEDOT:PSS-nafion composite drop-casted onto gold mylar sheets to prepare films at specific dimensions. The deposited films were divided into strips in order to be tested for serotonin (5-HT) neurotransmitter detection. The electrocatalytic activity of both electrodes was investigated via electrochemical analytical methods including cyclic voltammetry (CV) and differential pulse Vvoltammetry (DPV) towards mentioned neurotransmitters in the presence of common interferences. The voltammetric studies included different parameters such as modifying with concentric or diluted nafion, number of nafion layer coated the electrode, varied dip-coating times in nafion, and different films thickness which were all investigated

Hybrid Graphene/Conducting Polymer Strip Sensors for Sensitive and Selective Electrochemical Detection of Serotonin

© 2019 American Chemical Society. There is an urgent need for electrochemical sensor materials that exhibit electrochemically compliant properties while also retaining high durability under physiological conditions. Herein, we demonstrate a novel strip-style electrochemical sensor using reduced graphene oxide (rGO) and poly(ethylene dioxythiophene)/poly(styrene sulfonic acid) (PEDOT/PSS) nanocomposite films. The fabricated rGO-PEDOT/PSS sensor with and without nafion has shown an effective electrochemical response for both selectivity and sensitivity of the serotonin (5-hydroxytryptamine, 5-HT) neurotransmitter. The developed high-performance hybrid graphene/conducting polymer strip sensors are likely to find applications as chip electrochemical sensor devices for patients diagnosed with Alzheimer\u27s disease

Probe Sensor Using Nanostructured Multi-Walled Carbon Nanotube Yarn for Selective and Sensitive Detection of Dopamine

The demands for electrochemical sensor materials with high strength and durability in physiological conditions continue to grow and novel approaches are being enabled by the advent of new electromaterials and novel fabrication technologies. Herein, we demonstrate a probe-style electrochemical sensor using highly flexible and conductive multi-walled carbon nanotubes (MWNT) yarns. The MWNT yarn-based sensors can be fabricated onto micro Pt-wire with a controlled diameter varying from 100 to 300 µm, and then further modified with Nafion via a dip-coating approach. The fabricated micro-sized sensors were characterized by electron microscopy, Raman, FTIR, electrical, and electrochemical measurements. For the first time, the MWNT/Nafion yarn-based probe sensors have been assembled and assessed for high-performance dopamine sensing, showing a significant improvement in both sensitivity and selectivity in dopamine detection in presence of ascorbic acid and uric acid. It offers the potential to be further developed as implantable probe sensors

The Composition of Dissolved Organic Matter in Arable Lands: Does Soil Management Practice Matter?

Dissolved organic matter (DOM) is a key soil quality property, indicative of the organic matter stored in the soil, which may also be a function of temporal variation. This study examines whether DOM is a robust property of the soil, controlling fertility, or if it may change with time. Altogether eight sets of soil samples were collected in 2018 and 2019 from the cultivated topsoil (0–10 cm) of cropland and from a nearby grassland near Martonvásár, Hungary. The study sites were characterized by Chernozem soil and were part of a long-term experimental project comparing the effects of manure application and fertilization to the control under maize and wheat monocultures. DOM was extracted from the samples with distilled water. The dissolved organic carbon (DOC), total dissolved nitrogen (DN), biological index (BIX), fluorescence index (FI), humification index (HIX), carbon nitrogen (C/N) ratio and specific ultraviolet absorbance at 254 nm (SUVA254) index were studied in the arable soils, and the results showed that all the DOM samples were humified, suggesting relevant microbiological contributions to the decomposition of OM and its conversion into more complex molecules (FI = 1.2–1.5, BIX = ~0.5, and HIX = ~0.9). Temporal variations were detected only for the permanent grassland where higher DOM concentration was found in spring. This increased DOM content mainly originated from humified, solid phase associated, recalcitrant OM. In contrast, there were no differences among fertilization treatments and sampling dates under cropfield conditions. Moreover, climatic conditions were not proven as a general ruler of DOM properties. Therefore, momentary DOM alone is not necessarily the direct property of soil organic matter under cropfield conditions. The application of this measure needs further details of sampling conditions to achieve adequate comparability