The ability to control the polarization of light at the extreme nanoscale has long been a major scientific and technological goal for photonics. Here we predict the phenomenon of polarization splitting through van der Waals heterostructures of nanoscale thickness, such as graphene-hexagonal boron nitride (hBN) heterostructures, at infrared frequencies. The underlying mechanism is that the designed heterostructures possess an effective relative permittivity with its in-plane (out-of-plane) component being unity (zero); such heterostructures are transparent to the transverse-electric (TE) waves while opaque to the transverse-magnetic (TM) waves, without resorting to the interference effect.Moreover, the predicted phenomenon is insensitive to incident angles. Our work thus indicates that van der Waals heterostructures are a promising nanoscale platform for the manipulation of light, such as the design of polarization beam nano-splitters and epsilon-near-zero materials, and the exploration of superscattering for TM waves while zero scattering for TE waves from deep-subwavelength nanostructures.
With the ability to focus and rotate the acoustic field in a given region while keeping the outside region unchanged, the acoustic concentrator and rotator has been developed for the versatile manipulations of acoustic wave. In this letter, we report the design of acoustic concentrator and rotator facilitated by linear coordinate transformation. Compared with the previous ones that have inhomogeneous parameter distributions, the designed devices are composed of several parts with homogeneous parameters, which can be achieved with the help of few homogeneous layered structures. Simulations are also performed to verify the functions of the designed device. The proposed acoustic concentrators and rotators would be useful in numerous applications such as acoustic sensing and communication.
The altering permittivity tensor of a hyperbolic medium from diagonal to off-diagonal by the constructive manipulation of the optical axis (also called tilted hyperbolic medium) has attracted much interest recently. Here, the electromagnetic field solutions of waves interacting with a tilted hyperbolic medium are established. Detailed calculations reveal that when a transverse magnetic (TM) polarized wave is incident from a tilted hyperbolic medium to a dielectric medium, tangential components of electric fields are expected to be discontinuous at the interface. Extraordinary surface voltages are induced at the inner boundary of the tilted hyperbolic medium, which prevents the reflection of electromagnetic waves. This alternative behavior of induced extraordinary surface voltages enriches the understanding of continuity across the boundary and provides a novel perspective for their realizations among multiple experimental platforms.
Unidirectional cloaks or carpet cloaks have become an essential branch of invisibility cloaks due to non-extreme parameters that are relatively easy for realization and potential applications. So far, a unidirectional cloak for transverse electric (TE) polarized wave has been successfully realized to hide an object in the air along a single direction with almost ideal performance. However, a practical method to achieve a unidirectional cloak for transverse magnetic (TM) polarization is still missing. In this paper, we successfully have designed, fabricated, and measured a full-parameter unidirectional TM-wave cloak in free space. In comparison to the previously-realized TE-wave counterpart, our cloak uses a perfect electric conductor boundary to obey the free-space symmetry condition of the TM incident wave and is therefore much more convenient to fabricate. The cloaking performance of the fabricated sample has been demonstrated via both full-wave numerical simulation and near-field measurement.
Two-dimensional (2D) materials offer several unique advantages for high-performance light detection including fast response, high responsivity, broadband response and relatively low noise levels. 2D materials integrated photodetectors often use chemical vapor deposition grown materials, which despite their good quality are relatively high cost and not easily scalable. 2D materials based inks, fabricated through liquid phase exfoliation of bulk crystals, are attractive alternatives due to their low cost, ease of processing and scalable production. Combined with these advantages, mature printing methods available for 2D inks allow large scale electronic device fabrication for a variety of high performance applications including energy storage, solar cells, photodetectors, etc. In this review, we summarize production of 2D materials based inks, their printing methods, and applications for high performance photodetection.
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