A Mach-Zehnder Interferometer (MZI) liquid sensor, employing ultra-compact double-slot hybrid plasmonic (DSHP) waveguide as active sensing arm, is developed. Numerical results show that extremely large optical confinement factor of the tested analytes (as high as 88%) can be obtained by DSHP waveguide with optimized geometrical parameters, which is larger than both, conventional SOI waveguides and plasmonic slot waveguides with same widths. As for MZI sensor with 40μm long DSHP active sensing area, the sensitivity can reach as high value as 1061nm/RIU (refractive index unit). The total loss, excluding the coupling loss of the grating coupler, is around 4.5dB.

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An ultra-high sensitivity double-slot hybrid plasmonic (DSHP) ring resonator, used for optical sensors and modulators, is developed. Due to high index contrast, as well as plasmonic enhancement, a considerable part of the optical energy is concentrated in the narrow slots between Si and plasmonic materials (silver is used in this paper), which leads to high sensitivity to the infiltrating materials. By partial opening of the outer plasmonic circular sheet of the DSHP ring, a conventional side-coupled silicon on insulator (SOI) bus waveguide can be used. Experimental results demonstrate ultra-high sensitivity (687.5 nm/RIU) of the developed DSHP ring resonator, which is about five-times higher than for the conventional Si ring with the same geometry. Further discussions show that a very low detection limit (5.37 × 10 −6 RIU) can be achieved after loaded Q factor modifications. In addition, the plasmonic metal structures offer also the way to process optical and electronic signals along the same hybrid plasmonic circuits with small capacitance (~0.275 fF) and large electric field, which leads to possible applications in compact high-efficiency electro-optic modulators, where no extra electrodes for electronic signals are required.

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A Mach-Zehnder interferometer (MZI)-based liquid refractive index sensor, utilizing a hollow hybrid plasmonic (HP) waveguide as the sensing element, has been investigated, showing large sensitivity to the refractive index changes of the tested liquids, as well as lower propagation loss in comparison to typical plasmonic waveguide-based ones. The sensor is fabricated using conventional silicon-on-insulator (SOI) technology; therefore, it is compatible to other standard SOI devices. The waveguide sensitivity, S_w, is experimentally demonstrated to be 0.64, with a propagation loss less than 0.25 dB/μm. Using a 20  μm long hollow HP waveguide in the sensing arm, the sensitivity of the MZI sensor (device sensitivity, S_d) is about 160 nm/RIU, with an extinction ratio larger than 40 dB.

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Ferrate is a powerful oxidant and disinfectant that has been proposed for use in drinking water treatment for more than a decade. The main obstacles in the application are costs and stability. In water treatment, using wet oxidation method to prepare liquid ferrate can save production costs. Saturated ferric nitrate solution can get higher efficiency and productivity to generate ferrate. Water quality has no obvious effect on the productivity of ferrate. The optimum alkaline concentration is 10-13 mol/L. The reaction time and temperature affect the quality of liquid ferrate product. The larger the mole ratio of sodium hypochlorite to ferric nitrate is, the greater the productivity of ferrate is. The proportion of sodium hypochlorite to ferric nitrate should be adjusted appropriately.