Performance and modeling of advanced Ti:LiNbO3 digitaloptical switches

High-performance Y-branch digital optical switches realized in Ti:LiNbO₃ are presented. Their switching response functions have been optimized in terms of switch voltage and crosstalk ratio. The optimization is based on analyzing different types of waveguide shaping and switching arrangements using coupled mode theory and computer simulations. Excellent switching characteristics are achieved with devices exploiting a specially shaped waveguide branch in a dilated switch arrangement. Demonstrated performances include switching voltage as low as 9 V with crosstalk suppression better than 45 dB and fiber-to-fiber losses as low as 4 dB. Polarization independence with crosstalk suppression better than 40 dB over a 1520- to 1570-nm wavelength range is achieved for any applied switch voltage greater than 18 V. These optimized digital optical switches have further demonstrated the capability to reshape electrical input signals at switching rates of several hundred megahertz     

Use of a doubly polarized laser for remote powering of anintegrated optical modulator

Stable operation of an integrated optic modulator is demonstrated using a 1.3 μm doubly polarized laser as a depolarized source in conjunction with a long run of ordinary fiber. The laser is found to be unusually susceptible to feedback due to gain competition between the polarization modes. The resulting low-frequency polarization noise is significantly reduced by the addition of fiber isolators to the system     

A pyridine-thiol ligand with multiple bonding sites for heavy metal precipitation

There are immediate concerns with current commercial ligands that are used for heavy metal precipitation, especially the limited arrays of bonding sites. Previous research has indicated that not only do commercial reagents lack sufficient bonding criteria, but they also fail to provide long-term stability as ligand-metal complexes. For this reason, we have developed a pyridine-based thiol ligand (DTPY) which not only offers multiple bonding sites for heavy metals but also should form stable metal-ligand precipitates. In this study, we used the divalent metals cadmium and copper to model the reactivity and pH stability of divalent metal complexes with the DTPY ligand. Using inductively-coupled plasma spectrometry (ICP), results indicate that a 50.00ppm (parts per million) copper solution, pH of 4.5, can be reduced to below the ICP detection limits of 0.00093ppm (>99.99% removal), and a 50.00ppm cadmium solution, pH of 6.0, can be reduced to 0.06ppm (99.88%).     

Irreversible precipitation of mercury and lead

There are immediate concerns with current commercial reagents that are used for heavy metal precipitation; in particular the fact that the reagents are not specifically designed to bind the targeted metals. The current literature reveals that not only do commercial reagents lack sufficient ability to strongly bind the metals, but they also fail to provide long-term stability as ligand-metal complexes under a variety of moderate conditions. For this reason a new ligand was designed and synthesized: 1,3-benzenediamidoethanethiol (BDETH2). It offers multiple, concerted, bonding sites for heavy metals and forms a stable metal-ligand precipitate. In this study, the formation of compounds comprised of this ligand with the divalent metals, lead and mercury, was explored and the pH stability of the water insoluble precipitates was determined. The leaching properties of the metal-ligand precipitates were determined using inductively coupled plasma (ICP) spectroscopy and cold vapor atomic fluorescence spectroscopy (CVAF). The results indicate that a 50.00 ppm lead solution at a pH of 4.0 may be reduced to a concentration of 0.05 ppm (99.9% lead removal) and to 0.13 ppm (99.7% lead removal) at a pH 6.0. A 50.00 ppm mercury solution at pH 4.0 may be reduced to a concentration of 0.02 ppm (99.97% mercury removal) and to 0.02 ppm (99.97% mercury removal) at a pH of 6.0.     

Reflective digital optical switch (RDOS) for DWDM optical networkapplications

A novel, high-performance, reflective digital optical switch for use in dense wavelength-division-multiplexed (WDM) network applications is presented. Highly reliable Ti-LiNbO₃ devices show high-speed polarization-independent reflection modulation with 30-dB ON-OFF ratios over a wavelength range from 1520 to 1570 nm     

Effect of intrinsic phase mismatch on linear modulator performanceof the 1×2 directional coupler and Mach-Zehnderinterferometer

The performance of 1×2 directional couplers and Mach-Zehnder interferometers as linear modulators is compared. Models describing the operation of each device, incorporating the intrinsic phase mismatch Δβ₀ which is present in nonideal devices, are developed. Distributions of Δβ₀ are obtained for each device and are shown to be independent of device type. Linear dynamic range and sensitivity measurements showing how Δβ₀ affects performance agree with theory. The additional effect of the coupling coefficient in the 1×2 directional coupler is demonstrated. This information can be used to predict device yield when combined with the measured Δβ₀ distributions     

Advanced mercury removal from gold leachate solutions prior to gold and silver extraction: a field study from an active gold mine in Peru

Mercury contamination in the Gold-Cyanide Process (GCP) is a serious health and environmental problem. Following the heap leaching of gold and silver ores with NaCN solutions, portions of the mercury-cyano complexes often adhere to the activated carbon (AC) used to extract the gold. During the electrowinning and retorting steps, mercury can be (and often is) emitted to the air as a vapor. This poses a severe health hazard to plant workers and the local environment. Additional concerns relate to the safety of workers when handling the mercury-laden AC. Currently, mercury treatment from the heap leach solution is nonexistent. This is due to the fact that chelating ligands which can effectively work under the adverse pH conditions (as present in the heap leachate solutions) do not exist. In an effort to economically and effectively treat the leachate solution prior to passing over the AC, a dipotassium salt of 1,3-benzenediamidoethanethiol (BDET2-) has been developed to irreversibly bind and precipitate the mercury. The ligand has proven to be highly effective by selectively reducing mercury levels from average initial concentrations of 34.5 ppm (parts per million) to 0.014 ppm within 10 min and to 0.008 ppm within 15 min. X-ray powder diffraction (XRD), proton nuclear magnetic resonance (1H NMR), Raman, and infrared (IR) spectroscopy demonstrate the formation of a mercury-ligand compound, which remains insoluble over pH ranges of 0.0-14.0. Leachate samples from an active gold mine in Peru have been analyzed using cold vapor atomic fluorescence (CVAF) and inductively coupled plasma optical emission spectroscopy (ICP-OES) for metal concentrations before and after treatment with the BDET2- ligand.     

SBS suppression using a depolarized source for high power fiberapplications

A depolarized source for fiber applications is demonstrated using a traveling wave LiNbO₃ phase modulator. The source suppresses stimulated Brillouin scattering (SBS) in the fiber when operated at high drive frequencies, enabling more power to be delivered to a remote location. The threshold for SBS is examined in detail using optical powers up to 150 mW and drive frequencies up to 4 GHz. A resonant enhancement technique is demonstrated which reduces the drive power requirement for frequencies <2 GHz by up to 7.6 dB     

A thin-film waveguide photodetector using hydrogenated amorphoussilicon

Metal-silicon-metal cladding layers on dielectric waveguides exhibit coupling and absorption characteristics that make them useful as photodetectors for integrated optical applications. Multilayer computer-modeling techniques were applied to waveguide photodetectors in order to investigate field and power distributions, as well as the attenuation and phase response in the guiding region. A waveguide photodetector based on amorphous silicon was fabricated and demonstrated     

Sequential effects of reinforcement magnitude on fixed-interval performance in rats.

Conducted 2 experiments each with 10 male hooded laboratory rats. In Exp I, Ss responded on an FI schedule in which several differentially cued 1 or 3 food-pellet intervals preceded cued 2 food-pellet intervals. Exp II contained only intervals ending with 1 or 3 pellets and presorted in a quasi-random order. In both experiments, absolute performance varied as a function of the preceding and the current amount of reinforcement and the minute of the interval. The distribution of responses within an interval varied as a function of the preceding amount of reinforcement and the amount of reinforcement which would be delivered at the end of the current interval. Results are discussed in terms of a frustration interpretation and of an alternative hypothesis based on an extension of the inhibitory effects of reinforcement. (PsycINFO Database Record (c) 2010 APA, all rights reserved)