Near-unity uniformity and efficiency broadband meta-beam-splitter/combiner.

Subwavelength planar structured interfaces, also known as metasurfaces, are ultra-thin optical elements modulating the amplitude, phase, and polarization of incident light using nanostructures called meta-atoms. The optical properties of such metasurfaces can be controlled across wavelengths by selecting geometries and materials of the meta-atoms. Given recent technological developments in optical device miniaturization, components for beam splitting and beam combining are sought for use within these devices as two quintessential components of every optical setup. However, realizing such devices using metasurfaces typically leads to poor uniformity of diffraction orders and narrow-band operation. Using a modified version of particle swarm optimization, we propose and numerically demonstrate a broadband, reciprocal metasurface beam combiner/splitter with uniformity > 97% and diffraction efficiency > 90% in the continuous band from λ=1525 nm to λ=1575 nm. The proposed approach significantly extends the current state of the art of metasurfaces design in terms of uniformity, bandwidth, and efficiency, and opens the door for devices requiring high power or near-unit uniformity.

Far-field position-tunable trapping of dielectric particles using a graphene-based plasmonic lens.

In this report, a graphene-based plasmonic lens is designed for far-field position-tunable trapping of dielectric particles at a wavelength of 1550 nm, in which target particles can be floated at a variable z-position, using a variable gate voltage applied to the graphene ribbons. Preventing proximity of the trapped particle and the metallic lens structure, we can diminish general thermal issues in plasmonic tweezers, while realizing higher degrees of freedom in studying target characteristics of the particles by achieving position-tunable 3D trapping. These advantageous aspects are impossible in conventional plasmonic tweezers, because of the highly evanescent nature of the plasmonic field at the metal interface. The proposed structure is comprised of two concentric circular slit-sets (S1, S2), each capable of sending a directive beam, which can lead to a constructive interference, and forming a subwavelength focal spot in the far-field. Taking advantage of the epsilon-near-zero (ENZ) behavior of graphene, each of the radiating slit-sets can be switched ON/OFF, with a radiation switching ratio of about 49, by applying a small electric pulse of 80 meV to change the Fermi energy of the corresponding graphene ribbon from 0.535 eV to 0.615 eV. Hence, inverting the radiation state of the designed lens, from (S1:ON, S2:OFF) to (S1:OFF, S2:ON), we can change the z-position of the focal trapping site from 5000 nm to 9800 nm. This configuration can be proposed as a new generation of long-range, electrostatically tunable 3D plasmonic tweezing, without the need for any external bulky optomechanical equipment.

Immunoengineering in glioblastoma imaging and therapy.

Patients diagnosed with glioblastoma have poor prognosis. Conventional treatment strategies such as surgery, chemotherapy, and radiation therapy demonstrated limited clinical success and have considerable side effects on healthy tissues. A central challenge in treating brain tumors is the poor permeability of the blood-brain barrier (BBB) to therapeutics. Recently, various methods based on immunotherapy and nanotechnology have demonstrated potential in addressing these obstacles by enabling precise targeting of brain tumors to minimize adverse effects, while increasing targeted drug delivery across the BBB. In addition to treating the tumors, these approaches may be used in conjunction with imaging modalities, such as magnetic resonance imaging and positron emission tomography to enhance the prognosis procedures. This review aims to provide mechanistic understanding of immune system regulation in the central nervous system and the benefits of nanoparticles in the prognosis of brain tumors. This article is characterized under: Diagnostic Tools > in vivo Nanodiagnostics and Imaging Nanotechnology Approaches to Biology > Cells at the Nanoscale Nanotechnology Approaches to Biology > Nanoscale Systems in Biology.