A self-aligned assembling terahertz metasurface microfluidic sensor for liquid detection.

This paper reports a new terahertz metasurface microfluidic sensor, which is actually a kind of reflective terahertz metasurface absorber with a microfluidic-channel structure located in the strong field energy region of the absorber. The metasurface structure is made on an ultra-thin quartz substrate as the cap layer, while a two-step structure is made on a silicon substrate as the pedestal layer. In order to precisely control the thickness of the microfluidic channel, the cap layer is self-aligned assembled with the pedestal layer to form the terahertz metasurface microfluidic sensor. The obtained sensor could enhance the light-matter interaction, resulting in high sensing performance. The measured results show that the sensor has a perfect absorption peak at 2.60 THz and a high Q-factor of 62.59, which are basically consistent with the simulated results. The sensitivity and FOM calculated based on the measured results of different liquids with different refractive indices is 0.733 THz per RIU and 16.4, respectively. Compared with some recently related work, the sensitivity is increased by about 40%, the Q-factor is increased by 3-5 times, and the FOM is increased by 5 times, which make the sensor have great application potential for solution detection in the terahertz frequency band.

Optical metasurfaces for multiplex high-performance grating-type structural colors.

Optical metasurfaces provide a significant approach for the production of structural colors due to their excellent optical control abilities. Herein, we propose trapezoidal structural metasurfaces for achieving multiplex grating-type structural colors with high comprehensive performance originating from the anomalous reflection dispersion in the visible band. Single trapezoidal metasurfaces with different x-direction periods can tune the angular dispersion regularly from 0.036 rad/nm to 0.224 rad/nm to generate various structural colors, and composite trapezoidal metasurfaces with three kinds of combinations can achieve multiplex sets of structural colors. The brightness can be controlled by adjusting the distance between the trapezoids in a pair accurately. The designed structural colors have higher saturation than traditional pigmentary colors, whose excitation purity can reach 1.00. The gamut is about 158.1% of the Adobe RGB standard. This research has application potential in ultrafine displays, information encryption, optical storage, and anti-counterfeit tagging.

Polarization-controlled bifunctional metasurface for structural color printing and beam deflection.

We propose a polarization-controlled bifunctional metasurface composed of arrayed trapezoidal nanoantennas. Under orthogonal-polarized incidence, different types of gap-surface plasmons are generated, regulating the intensity and phase, respectively. Thus, structural color printing and beam deflection functions are achieved on a miniaturized chip. The color printing function works from 400 to 800 nm, exhibiting a subwavelength-scale chromatic image with a broad gamut. The beam deflection function works from 360 to 540 nm, mapping light to the first diffraction order with the anomalous angle from 40.4° to 76.6°. The proposed bifunctional metasurface could serve as a key component in integrated optics systems and will find many other wide-ranging applications in optical and biological areas.

Plasmonic color generation and refractive index sensing with three-dimensional air-gap nanocavities.

Three-dimensional (3D) air-gap metal-coated nanocavities with tunable geometries, changeable heights, and improved smoothness are fabricated by combining electron beam lithography (EBL), ultra dilute hydrofluoric acid solution wet etching (UDHFE), and metal magnetron sputtering technologies. With different shapes, heights, and separations of the nanocavities, the strong electromagnetic resonances inside the nanocavities are changed in different extent, resulting in broad gamut and sophisticated plasmonic color generation. The nanocavities-based metasurface is also used to construct a real-time and label-free refractive index sensor with 372 nm/RIU sensitivity, which shows distinct colorimetric change between different mediums. This nanocavities may find extensive potential applications in high-fidelity color printing, high-density information storage, and on-chip colorimetric label-free biomedical sensing.