A multifocus optical vortex metalens, with enhanced signal-to-noise ratio, is presented, which focuses three longitudinal vortices with distinct topological charges at different focal planes. The design largely extends the flexibility of tuning the number of vortices and their focal positions for circularly polarized light in a compact device, which provides the convenience for the nanomanipulation of optical vortices.

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Abstract-The two-dimensional photonic crystal (2-D PhC) structure has been investigated as a method for lateral mode control of vertical-cavity surface-emitting lasers (VCSELs). The 2-D PhC structures were designed using an equivalent index model developed for photonic crystal fibers combined with a plane wave expansion method. The etching depth dependence of the PhC structure was incorporated for the first time to design practical devices. 2-D PhC-confined VCSELs are demonstrated to operate in single PhC-confined mode using either a single-or seven-point defect.

In this letter, we propose and experimentally demonstrate a color filter based on an annular aperture geometry working in the visible range. The device is built by configuring an array of annular apertures in a gold film suitable for transmission measurement. We show effective fine tuning of resonance peaks through precise geometric control of the aperture dimensions. Selective transmission through annular apertures of various sizes leads to continuous color tuning of transmitted electromagnetic waves. This may find potential for application in high-definition displays, optical filters, ultrafast switching, and bio-sensing.

Low-cost controllable solution-based processes for preparation of titanium oxide (TiO(2)) thin films are highly desirable, because of many important applications of this oxide in catalytic decomposition of volatile organic compounds, advanced oxidation processes for wastewater and bactericidal treatments, self-cleaning window glass for green intelligent buildings, dye-sensitized solar cells, solid-state semiconductor metal-oxide solar cells, self-cleaning glass for photovoltaic devices, and general heterogeneous photocatalysis for fine chemicals etc. In this work, we develop a solution-based adsorptive self-assembly approach to fabricate anatase TiO(2) thin films on different glass substrates such as simple plane glass and patterned glass at variable compositions (normal soda lime glass or solar-grade borofloat glass). By tuning the number of process cycles (i.e., adsorption-then-heating) of TiO(2) colloidal suspension, we could facilely prepare large-area TiO(2) films at a desired thickness and with uniform crystallite morphology. Moreover, our as-prepared nanostructured TiO(2) thin films on glass substrates do not cause deterioration in optical transmission of glass; instead, they improve optical performance of commercial solar cells over a wide range of incident angles of light. Our as-prepared anatase TiO(2) thin films also display superhydrophilicity and excellent photocatalytic activity for self-cleaning application. For example, our investigation of photocatalytic degradation of methyl orange indicates that these thin films are indeed highly effective, in comparison to other commercial TiO(2) thin films under identical testing conditions.

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