Abstract-Plasmons in two-dimensional semiconductor devices will be reflected by discontinuities, notably, junctions between gated and non-gated electron channels. The transmitted and reflected plasmons can form spatially-and frequency-varying signals, and their understanding is important for the design of terahertz detectors, oscillators, and plasmonic crystals. Using mode decomposition, we studied terahertz plasmons incident on a junction between a gated and a non-gated channel. The plasmon reflection and transmission coefficients were found numerically and analytically, and studied between 0.3 and 1 THz for a range of electron densities. At higher frequencies, we could describe the plasmons by a simplified model of channels in homogeneous dielectrics, for which the analytical approximations were accurate. At low frequencies, however, the full geometry and mode spectrum had to be taken into account. The results agreed with simulations by the finite-element method. Mode decomposition thus proved to be a powerful method for plasmonic devices, combining the rigor of complete solutions of Maxwell's equations with the convenience of analytical expressions.
A multilevel microcontact printing (μCP) system that avoids the use of optical alignment and precision manipulation equipment is demonstrated. Most of the complexity is transferred to the poly(dimethylsiloxane) (PDMS) stamp itself by forming the features, a mechanical self-alignment mechanism, and an elastic membrane by wafer scale replica molding on a Si master. Flexible 50-μm-thick photoetched stainless steel sheets are bonded to PDMS prior to demolding to improve the mechanical stability. The Si master itself is made using conventional MEMS fabrication tools such as photolithography, reactive ion etching, and anisotropic wet etching. Self-alignment is achieved by introducing protrusions on the stamp that mate onto corresponding grooves on a machined substrate. Complete 10 mm × 10 mm prototypes are fabricated, and six-level μCP is demonstrated with an average layer-to-layer misalignment of 5-10 μm.
The control of large-scale quantum information processors based on arrays of trapped ions requires a means to route and focus multiple laser beams to each of many trapping sites in parallel. Here, we combine arrays of fibres, 3D laser-written waveguides and diffractive microlenses to demonstrate the principle of a micro-optic interconnect suited to this task. The module is intended for use with an ion microtrap of 3D electrode geometry. It guides ten independent laser beams with unique trajectories to illuminate a pair of spatially separated target points. Three blue and two infrared beams converge to overlap precisely at each desired position. Typical relative crosstalk intensities in the blue are 3.6 × 10 −3 and the average insertion loss across all channels is 8 dB. The module occupies ∼10 4 times less volume than a conventional bulk-optic equivalent and is suited to different ion species.
Abstract-A magnetic resonance imaging (MRI) duodenoscope is demonstrated, by combining nonmagnetic endoscope components with a thin-film receiver based on a magneto-inductive waveguide. The waveguide elements consist of figure-of-eight shaped inductors formed on either side of a flexible substrate and parallel plate capacitors that use the substrate as a dielectric. Operation is simulated using equivalent circuit models and by computation of two-and three-dimensional sensitivity patterns. Circuits are fabricated for operation at 127.7 MHz by double-sided patterning of copper-clad Kapton and assembled onto non-magnetic flexible endoscope insertion tubes. Operation is verified by bench testing and by 1 H MRI at 3T using phantoms. The receiver can form a segmented coaxial image along the length of the endoscope, even when bent, and shows a signal-to-noise-ratio advantage over a surface array coil up to three times the tube diameter at the tip. Initial immersion imaging experiments have been carried out and confirm an encouraging lack of sensitivity to RF heating.
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