The biological leaching of an auriferous pyrite ore

The oxidation of an auriferous pyrite ore sample was evaluated in biological leaching experiments for subsequent gold recovery via cyanidation. In batch cultures, organisms derived from the mine site oxidized pyrite and ferrous iron at pH values as low as pH 0.6. The recovery of gold was variable in shake flask experiments. In stirred tank bioreactor leaching, gold recovery was proportional to the extent of iron dissolution by bioleaching. The leaching of arsenic from the sample was also directly proportional to iron dissolution.     

Sub-/spl mu/s switching time in silicon-on-insulator Mach-Zehnder thermooptic switch

We have demonstrated both rise and fall times below 1 /spl mu/s with 10%-90% modulation in a silicon-on-insulator thermooptical Mach-Zehnder switch. The switch is based on 9-/spl mu/m-thick and 10-/spl mu/m-wide single-mode rib waveguides. Very fast switching was achieved by using a differential control method. The switch was driven with a digital signal processor accompanied by simple electronic circuitry.     

Thermally tunable integrated optical ring resonator with poly-Sithermistor

Doped polysilicon is applied as a thermo-optic heating element to temperature tune the ring resonator based on silicon nitride rib waveguides on silicon. The ring diameter is 2 mm allowing a large free spectral range of 26 GHz. For the first time, a poly-Si resistor is used as a thermistor to measure waveguide temperature. The temperature coefficient of the poly-Si thermistor is 9.5×10^-4/°C. The reproducibility of the temperature measurement is 0.3°C. The finesse of the ring resonator is 77. The propagation loss of silicon nitride rib waveguide is 0.5 dB/cm at the wavelength of 1.312 μm. The temperature tuning of the ring resonator and the in situ supervision of the temperature on chip based on the same poly-Si fabrication process may find use especially in optical sensor applications     

Birefringence control and dispersion characteristics of silicon oxynitride optical waveguides

The design, fabrication and characterisation of birefringent silicon oxynitride planar optical waveguides are described for applications at the wavelength of 1.54 mu m. Form birefringence is attained by interposing a thin silicon nitride film in the waveguide stack, and can be controlled by adjusting the nitride layer thickness. Dispersion characteristics of the oxynitride waveguides have been measured and compared with theory.<>     

Tunable silicon etalon for simultaneous spectral filtering andwavelength monitoring of a DWDM transmitter

A temperature-tunable Fabry-Perot filter made of silicon has been developed and applied for simultaneous spectral filtering and wavelength monitoring of a directly modulated DFB laser. This novel device decreases the dispersion penalty of a cost-effective dense wavelength-division-multiplexing (DWDM) transmitter in a long-haul transmission link. Moreover, it allows the operating wavelength of the transmitter to be accurately monitored in real time