Ultra-high-Q substrate-mode coupled resonances in complementary THz metamaterial.

Achieving high-Q resonances in the THz frequency range is significant for applications such as sensors, filters, and emitters. A promising approach for obtaining such resonances is by using metamaterials. However, high-Q resonances in THz metamaterials are usually limited by metallic radiation losses in the meta-atoms. In this Letter, we investigate both experimentally and numerically a complementary metallic disk-hole array (CMA) that uses the coupling between lattice resonances and Fabry-Pérot cavity resonances, and features in-substrate modes with experimentally obtained record breaking Q-factors of up to 750. To the best of our knowledge, this is the highest quality factor measured for free-space-coupled metallic metamaterial structure at THz frequencies.

Terahertz Fresnel-zone-plate thin-film lens based on a high-transmittance double-layer metamaterial phase shifter.

Planar diffractive lenses, with metamaterial artificial structures and subwavelength thickness, provide unique and flexible platforms for optical design in the terahertz (THz) regime. Here, we present a metamaterial-based Rayleigh-Wood Fresnel-zone-plate (FZP) thin-film lens designed to focus a monochromatic THz beam at 1.0 THz with a high transmittance of 80%, short focal length of 24 mm, and subwavelength thickness of 48 µm. Specifically, the FZP lens is composed of 8 alternating concentric zones through a polymer film substrate, where odd zones are patterned with double-layer un-split ring resonators (USRRs) that provide a polarization-independent phase shift of π/2 compared to un-patterned even zones. Both simulation and experiment confirm that our FZP lens creates a focused beam at the designed frequency of 1.0 THz by constructive interference through alternating concentric metamaterial-patterned and un-patterned zones, producing a diffraction-limited resolution of 0.6 mm for imaging applications. In contrast to conventional approaches in which the uniform periodic array of metamaterial unit cells has been treated as an effective material, we newly find that double-layer USRRs can work as an independent meta-atom without degradation of its performances, which benefits the behavior of small arrays of double-layer USRRs located in the outer zones of the FZP lens. Such a planar thin-film lens would enable us to realize compact and lightweight THz systems.

Off-resonance and in-resonance metamaterial design for a high-transmission terahertz-wave quarter-wave plate.

This Letter describes a novel metamaterial design by employing off-resonance and in-resonance excitation for a high-transmission terahertz-wave quarter-wave plate (QWP). The device is demonstrated with a thin film metamaterial with double-layer split ring resonators (SRRs). Different from a usual resonant metamaterial device, here we design the work frequency off from the inductor-capacitor (LC) resonance for the TE mode, while in a dipole resonance for the TM mode to obtain the artificial birefringence. Rectangular SRRs in this Letter provide a choice to optimize the off-resonance and in-resonance excitation, to assist the double-layer design for high transmission. Converting a linearly polarized wave to circular polarization with our QWP, the experiment confirms a transmittance of 0.8 and an ellipticity of 0.99 at 0.98 THz. The developed thin film device is flexible and has a thickness of 48 µm (sub-wavelength). This is an advantage for potential integration in systems where overall device compactness is required.

Thin terahertz-wave phase shifter by flexible film metamaterial with high transmission.

Thin terahertz (THz)-wave optical components are fundamentally important for integrated THz-wave spectroscopy and imaging systems, especially for phase manipulation devices. As described herein, a thin THz-wave phase shifter was developed using a flexible film metamaterial with high transmission and polarization independent properties. The metamaterial unit structure employs double-layer un-split ring resonators (USRRs) with a designed distance between the two layers to obtain phase retardance of π/2, thus constituting a THz-wave phase shifter. The metamaterial design keeps the transmission coefficient as high as 0.91. The phase shifter also has polarization independence due to the four-fold symmetry of the USRR structure. Because of the subwavelength feature size of the USRR, this shifter can offer benefits for manipulating the spatial profile for the THz-wave phase through design of a binary optics phase plate by arranging a USRR array. The thickness of 48 µm has benefits for developing integrated THz optics and other applications that demand compactness and flexibility. The developed film size of 5 cm × 5 cm from the device fabrication process is suitable for THz lenses or gratings of large optical components.

MEMS reconfigurable metamaterial for terahertz switchable filter and modulator.

We demonstrate a reconfigurable metamaterial developed by surface micromachining technique on a low loss quartz substrate for a tunable terahertz filter application. The device implements a reconfigurable RF-MEMS (radio frequency - micro electro mechanical systems) capacitor within a split-ring resonator (SRR). Time-domain spectroscopy confirms that the tunability of the SRR resonance and thus the terahertz transmittance are electrostatically controlled by the RF-MEMS capacitor. Due to the high transparency and low loss of quartz used as a substrate, the device exhibits a high contrast switching performance of 16.5 dB at 480 GHz, which is also supported by the terahertz dynamic modulation measurement results. The device shows promise for tunable transmission terahertz optics.

MEMS cantilever-controlled plasmonic colors for sustainable optical displays.

Conventional optical displays using indium tin oxide and liquid crystal materials present challenges for long-term sustainability. We show here a cost-effective and complementary metal-oxide semiconductor (CMOS)-compatible fast and full-range electrically controlled RGB color display. This is achieved by combining transmission-based plasmonic metasurfaces with MEMS (microelectromechanical systems) technology, using only two common materials: aluminum and silicon oxide. White light is filtered into RGB components by plasmonic metasurfaces made of aluminum nanohole arrays. The transmission through each color filter is modulated by MEMS miniaturized cantilevers fabricated with aluminum and silicon oxide on top of the color filters. We show that the relative transmission of a color subpixel can be freely modulated from 35 to 100%. The pixels can also operate well above 800 Hz for future ultrafast displays. Our work provides a road to future circular economic goals by exploiting advances in structural colors and MEMS technologies to innovate optical displays.

[Reconstruction and analysis of three-dimensional finite element model of human middle ear].

OBJECTIVE: To reconstruct a finite element model of human middle ear and measure characteristic dimensions of this model and calculate the mass properties of the ossicles. METHODS: The proposed method starts with the histologic section preparation of human temporal bone. Through tracing outlines of the middle ear components on the sections in AutoCAD2005, a set of exterior contours of the components is obtained. The three-dimensional solid model of middle ear, including tympanic membrane, ossicular bones, middle ear suspensory ligaments/muscles, are reconstructed using these contours in Unigraphics (UG). To prepare for finite element analysis (FEA) of the middle ear, all surfaces of the solid model are translated into ADINA, a commercial FE model package. Based on these surfaces, FE meshes of the middle ear are created, and material properties and boundaries are set up. The characteristic dimensions of this model are measured and the mass properties of the ossicles are calculated to confirm the accuracy of the geometric model constructed following the proposed method. RESULTS: The three-dimensional finite element model of the human middle ear that included tympanic membrane, ossicular bones and middle ear suspensory ligaments/muscles was reconstructed. The accuracy of this geometric model was confirmed with the outcome of the characteristic dimensions of this model and the mass properties of the ossicles. CONCLUSIONS: The proposed method not only provides an effective, convenient, economic, accurate way to reconstruct the three dimensional finite element model of human middle, but also provides a detailed knowledge of middle ear geometry that is required for finite element analysis.