Ultrathin Cavity Research Articles

Exciton-induced Fano resonance in metallic nanocavity with tungsten disulfide atomic layer.

Photon-exciton coupling behaviors in optical nanocavities attract broad attention due to their crucial applications in light manipulation and emission. Herein, we experimentally observed a Fano-like resonance with asymmetrical spectral response in an ultrathin metal-dielectric-metal (MDM) cavity integrated with an atomic-layer tungsten disulfide (WS2). The resonance wavelength of an MDM nanocavity can be flexibly controlled by adjusting dielectric layer thickness. The results measured by the home-made microscopic spectrometer agree well with the numerical simulations. A temporal coupled-mode theoretical model was established to analyze the formation mechanism of Fano resonance in the ultrathin cavity. The theoretical analysis reveals that the Fano resonance is attributed to a weak coupling between the resonance photons in the nanocavity and excitons in the WS2 atomic layer. The results will pave a new way for exciton-induced generation of Fano resonance and light spectral manipulation at the nanoscale.

Stimulated whispering gallery modes emission from green to UVA realized by AlInGaN based quantum wells microtube

Self-rolling GaN quantum wells microtubes have been fabricated by a photoresist-assisted electrochemical etching method. Different microtubes with whispering gallery modes emitting from the green to ultraviolet range have been demonstrated. Stimulated whispery gallery mode emission from 370 to 460 nm was achieved with lasing line-width less than 0.087 nm and a threshold as low as 0.12 mJ cm−2. Such advanced optical properties can be attributed to the larger mode gain obtained by overlapping the active region with the optical confinement layers. The number of modes was greatly suppressed simultaneously leaving only basic radial modes due to the ultra-thin cavity wall.

Dual-functional ultrathin wearable 3D particle-in-cavity SF-AAO-Au SERS sensors for effective sweat glucose and lab-on-glove pesticide detection

A novel approach is developed to fabricate an ultra-thin layered flexible wearable Surface-Enhanced Raman Scattering (SERS) substrate named silk fibroin-anodic aluminum oxide-Au nanoparticles (SF-AAO-Au), which consists of biocompatible SF film as flexible support, ultrathin cavity AAO as template, and plasmonic Au NPs. The SF-AAO-Au sensor exhibits excellent SERS mechanical flexibility, homogeneity and sensitivity for its effective enhancement ability and highly ordered 3D periodic porous particle-in-cavity (PIC) arrays structure. The humidity-driven interface structure of biocompatible SF film provides good skin adhesion under various fitness tests and excellent mechanical flexibility as a wearable SERS sensor on natural skin (deformation within 5%). The flexible SF-AAO-Au can be developed as quantitative sweat glucose sensor in the concentration range of 10−7 to 10−3 M with a limit of detection (LOD) of 1.68×10−7 M and qualitative human sweat glucose detection ability. This SF-AAO-Au substrate can be further designed as lab-on-glove SERS sensing platform for ultrasensitive (LOD ~5.7 ppt) quantitative on-site detection of agricultural residues in a wide range. The effective dual-functional SERS wearable sensor realized for the first time paves a new way to develop smart wearable and non-destructive devices in environmental safety, forensic identification and point-of-care testing (POCT) diagnosis of physiological disease.

Ultrasensitive terahertz sensing with broadside coupled polarization insensitive graphene metamaterial cavities

The ubiquitous property of metamaterials to confine energy at deep-subwavelength scale paves the way to leverage strong light (or terahertz)-matter interactions towards the development of efficient, state-of-the-art sensing technologies at the terahertz (THz) frequencies. In two-dimensional active metamaterials, for instance, graphene metasurfaces; THz-matter interactions are largely governed by the near-field coupling, where strong field confinement is predominantly achieved within very small areas (compared to total device area), viz, in split gaps, narrow apertures etc. Here, we demonstrate a polarization insensitive broadside coupling mechanism in graphene- metamaterials, which is beneficial for realization of miniaturized, compact, ultra-sensitive THz thin film sensors with substantially large effective areas for strong THz-matter interaction. Proposed structure entails ultrathin layer of dielectric spacer (cavity) sandwiched between two “plus” shaped sub-wavelength graphene resonators. In order to investigate the sensing capabilities, obscure materials are placed in ultrathin cavity region to detect its refractive indices. A record high refractive index sensitivity of around 2.8 THz/RIU substantiates the utility of introducing the concept of broadside coupling in graphene metamaterials. Further, we employ the Lorentz oscillator based coupled mode theory in order to elucidate the numerical outcomes.

Surface-enhanced Raman scattering of CoV-SARS-2 viral proteins in a strong coupling regime

Fast, sensitive, high-throughput detection of coronavirus antigens at physiologically relevant levels is essential for population screening that could prevent epidemics such as the current COVID-19 global pandemic. Optical methods based on surface-enhanced Raman scattering (SERS) spectroscopy are promising for this purpose because they ensure quick detection of even single biological molecules in a sample. For achieving such a high sensitivity, it is crucial to design SERS-active systems concentrating incident radiation into small sample volumes. Here, metal-dielectric cavities have been obtained through interaction of protein sulfhydryl groups with a SERS-active silver surface. The concentration of light in these cavities allows the differential detection of spike glycoprotein and nucleocapsid protein of SARS-COV-2, which are its key antigens, at physiologically relevant concentrations. The cavity Q-factor can be increased by additionally covering the dielectric protein film with a silver shell to form an ultrathin cavity, which provides an at least tenfold enhancement of the detection signal. The results could be used to design high-throughput systems for specific and sensitive detection of viral antigens and quick diagnosis of viral infections.

Controlling the Bidirectional Circular Polarization States Using Ultrathin Back-to-Back Quarter-Wave Plates Cavity

Efficiently manipulating the polarization states of electromagnetic waves is of great importance for communication, imaging, and sensing. In this paper, we aim to control the circular polarization states, e.g., left-hand, or right-hand, for the bidirectional radiated waves utilizing a pair of back-to-back quarter-wave plates, which are integrated within an ultrathin cavity. As an example, a bidirectional circularly polarized wave with the same helicity in forward and backward is generated based on numerical analyses, and proved by experiments in microwave region. The proposed ultrathin back-to-back quarter-wave plates cavity can be adopted to higher frequencies, e.g., terahertz and mid-infrared ranges, with lower metallic conductivity. The proposed method exhibits the advantages of compact dimension and low-cost implementation in engineering the bidirectional polarization states of electromagnetic waves.

High-Frequency Fiber-Optic Ultrasonic Sensor Using Air Micro-Bubble for Imaging of Seismic Physical Models.

A micro-fiber-optic Fabry-Perot interferometer (FPI) is proposed and demonstrated experimentally for ultrasonic imaging of seismic physical models. The device consists of a micro-bubble followed by the end of a single-mode fiber (SMF). The micro-structure is formed by the discharging operation on a short segment of hollow-core fiber (HCF) that is spliced to the SMF. This micro FPI is sensitive to ultrasonic waves (UWs), especially to the high-frequency (up to 10 MHz) UW, thanks to its ultra-thin cavity wall and micro-diameter. A side-band filter technology is employed for the UW interrogation, and then the high signal-to-noise ratio (SNR) UW signal is achieved. Eventually the sensor is used for lateral imaging of the physical model by scanning UW detection and two-dimensional signal reconstruction.

Hybridization of plasmonic antenna and cavity modes: Extreme optics of nanoparticle-on-mirror nanogaps

The precise structural details of metallic nanogaps within optical antennae are found to dramatically modify the plasmonic response, producing a complex pattern of electromagnetic modes that can be directly observed in scattering experiments. We analyze this situation theoretically in the nanoparticle-on-mirror construct, which forms a plasmonic nanogap sensitive to even atomic-scale restructuring of nanoparticle morphology. We focus on the effect of nanoparticle faceting, which allows the formation of ultrathin cavities between the particle and the underlying metallic film in the nanoparticle-on-mirror geometry. Two different sets of modes are identified: longitudinal antenna modes, which are strongly radiative and excited for all facet width ranges, and transverse cavity modes produced at large facets and exhibiting extreme confinement. The interaction and hybridization of antenna and cavity modes is determined by their symmetry and the precise morphology of the nanogap edges. Understanding such complex optics from nanoparticle-on-mirror structures is important to elucidate a wide variety of emerging photochemical and optoelectronic processes.

High‐gain ultrathin resonant cavity antenna

AbstractHigh‐gain and ultrathin cavity antennas consisting of conventional rectangular patch antenna and partially reflective surface (PRS) are investigated in the article.PRS is made of periodic distinct metallic patterns on the both sides of the single dielectric slab. The geometry is simpler and has not been used in the pervious references. The proposed cavity antenna has the advantages of ultrathin cavity (λ/70), high gain and high directivity. Compared with the conventional patch antenna, the results show the gain of the proposed antenna is higher by 4.5 dB. In addition, it is interesting that the antenna with the sectoral form radiation pattern can be realized when the defects are introduced in the periodic PRS structure. This special sectoral form radiation pattern has the characteristics of the narrow half‐power bandwidth (HPBW) of 30° in the E plane and the broad HPBW of 90° in the H plane, which is needed urgently by the station antennas of the mobile communication. © 2011 Wiley Periodicals, Inc. Microwave Opt Technol Lett, 2011; View this article online at wileyonlinelibrary.com. DOI 10.1002/mop.26213

A Dual-Band Tunable Ultra-Thin Cavity Antenna

A dual-band ultra-thin cavity antenna with a wide tuning range is designed and fabricated. The overall dimensions are 31 × 15 × 0.5 mm3. The proposed cavity antenna is realized by making two adjacent side walls of a rectangular dielectric-filled resonant cavity open as radiating ports. The achievable frequency ratio changes from 1.2 to 2.2 with different aspect ratios. With a varactor diode installed at the front open port, the dual frequency bands can be tuned over a wide range. When the applied reverse biasing voltage varies from 3 to 13 V, the realized |S11| <; -6 dB impedance bandwidth is 420 MHz (12.5%) and 960 MHz (20.5%) for the low band and the high band, respectively. The designed antenna occupies no area on a circuit board, and a 0.5-mm-thin volume inside a device cover is enough for installation. The dual bands can be scaled to other desired bands within the frequency ratio range.

Transition from edge to vertical cavity operation of tunnel contact AlGaAs–GaAs–InGaAs quantum well heterostructure lasers

Al x Ga 1−x As–GaAs–In y Ga 1−y As quantum well heterostructure lasers with thin sharply defined cavities that operate longitudinally or vertically are demonstrated. Longitudinally, the cavity is defined by cleaving (edge emission) while vertical definition is provided by a lower AlxOy/GaAs distributed Bragg reflector (DBR) and an upper SiO2/Si DBR that form a resonant structure. A reverse-biased tunnel contact junction provides lateral electron current to support hole injection through a native-oxide-defined aperture. This ultrathin cavity configuration produces low threshold high efficiency (η∼91%, L=140 μm) edge emission (longitudinal operation) in the case of long lasers (L≳90 μm), and vertical emission for shorter lasers (L≲65 μm). The transition from longitudinal to vertical laser operation as a function of cavity length, L, is demonstrated.