Terahertz Spin-Selective Perfect Absorption Enabled by Quasi-Bound States in the Continuum

Abstract Hot electrons generated in metallic nanostructures have shown promising perspectives for photodetection. This has prompted efforts to enhance the absorption of photons by metals. However, most strategies require fine-tuning of the geometric parameters to achieve perfect absorption, accompanied by the demanding fabrications. Here, we theoretically propose a Ag grating/TiO2 cladding hybrid structure for hot electron photodetection (HEPD) by combining quasi-bound states in the continuum (BIC) and plasmonic hot electrons. Enabled by quasi-BIC, perfect absorption can be readily achieved and it is robust against the change of several structural parameters due to the topological nature of BIC. Also, we show that the guided mode can be folded into the light cone by introducing a disturbance to become a guided resonance, which then gives rise to a narrow-band HEPD that is difficult to be achieved in the high loss gold plasmonics. Combining the quasi-BIC and the guided resonance, we also realize a multiband HEPD with near-perfect absorption. Our work suggests new routes to enhance the light-harvesting in plasmonic nanosystems.

Download Full-text

Graphene perfect absorber with loss adaptive Q-factor control function enabled by quasi-bound states in the continuum

Scientific Reports ◽

10.1038/s41598-021-02318-8 ◽

2021 ◽

Vol 11 (1) ◽

Author(s):

Sangjun Lee ◽

Joohyung Song ◽

Sangin Kim

Keyword(s):

Bound States ◽

Control Function ◽

Incident Angle ◽

Leakage Rate ◽

Slab Waveguide ◽

Monolayer Graphene ◽

Perfect Absorber ◽

Coupling Condition ◽

Perfect Absorption ◽

The Continuum

AbstractNumerous device structures have been proposed for perfect absorption in monolayer graphene under single-sided illumination, all of which requires the critical coupling condition, i.e., the balance between the loss of graphene and the leakage rate of the device. However, due to the difficulty of the precise control of the quality of synthesized graphene and unwanted doping in graphene transferred to the substrate, the loss of graphene is rather unpredictable, so that the perfect absorption is quite difficult to achieve in practice. To solve this problem, we designed a novel perfect absorber structure with a loss adaptive leakage rate control function enabled by the quasi-bound states in the continuum (BIC) and numerically demonstrated its performance. Our designed device is based on a slab-waveguide grating supporting both the quasi-BIC and the guided-mode resonance (GMR); the quasi-BIC with an adjustable leakage rate controlled by an incident angle is responsible for absorption, while the GMR works as an internal mirror. Since the proposed device scheme can have an arbitrarily small leakage rate, it can be used to implement a perfect absorber for any kind of ultrathin absorbing media. Due to the simple structure avoiding an external reflector, the device is easy to fabricate.

Download Full-text

Bound states in the continuum in double-hole array perforated in a layer of photonic crystal slab

Applied Physics Express ◽

10.7567/1882-0786/ab5346 ◽

2019 ◽

Vol 12 (12) ◽

pp. 125002 ◽

Cited By ~ 1

Author(s):

Suxia Xie ◽

Changzhong Xie ◽

Song Xie ◽

Jie Zhan ◽

Zhijian Li ◽

...

Keyword(s):

Photonic Crystal ◽

Bound States ◽

Hole Array ◽

Photonic Crystal Slab ◽

The Continuum

Download Full-text

Differentiating and quantifying exosome secretion from a single cell using quasi-bound states in the continuum

Nanophotonics ◽

10.1515/nanoph-2020-0008 ◽

2020 ◽

Vol 9 (5) ◽

pp. 1081-1086 ◽

Cited By ~ 4

Author(s):

Abdoulaye Ndao ◽

Liyi Hsu ◽

Wei Cai ◽

Jeongho Ha ◽

Junhee Park ◽

...

Keyword(s):

Single Cell ◽

Optical Sensors ◽

Figure Of Merit ◽

Bound States ◽

Single Cell Analysis ◽

Optical Cavity ◽

High Sensitivity ◽

Cell Secretion ◽

The Continuum ◽

Refractive Index Detection

AbstractOne of the key challenges in biology is to understand how individual cells process information and respond to perturbations. However, most of the existing single-cell analysis methods can only provide a glimpse of cell properties at specific time points and are unable to provide cell secretion and protein analysis at single-cell resolution. To address the limits of existing methods and to accelerate discoveries from single-cell studies, we propose and experimentally demonstrate a new sensor based on bound states in the continuum to quantify exosome secretion from a single cell. Our optical sensors demonstrate high-sensitivity refractive index detection. Because of the strong overlap between the medium supporting the mode and the analytes, such an optical cavity has a figure of merit of 677 and sensitivity of 440 nm/RIU. Such results facilitate technological progress for highly conducive optical sensors for different biomedical applications.

Download Full-text

Metasurfaces with Bound States in the Continuum Enabled by Eliminating First Fourier Harmonic Component in Lattice Parameters

Physical Review Letters ◽

10.1103/physrevlett.126.013601 ◽

2021 ◽

Vol 126 (1) ◽

Author(s):

Sun-Goo Lee ◽

Seong-Han Kim ◽

Chul-Sik Kee

Keyword(s):

Bound States ◽

Harmonic Component ◽

Lattice Parameters ◽

Fourier Harmonic ◽

The Continuum

Download Full-text

Active nonlocal metasurfaces

Nanophotonics ◽

10.1515/nanoph-2020-0375 ◽

2020 ◽

Vol 10 (1) ◽

pp. 655-665

Author(s):

Stephanie C. Malek ◽

Adam C. Overvig ◽

Sajan Shrestha ◽

Nanfang Yu

Keyword(s):

Bound States ◽

Fano Resonances ◽

Spatial Control ◽

Technical Challenge ◽

Materials Engineering ◽

Narrow Bandwidth ◽

Wavefront Shaping ◽

Mechanical Stretching ◽

Proof Of Principle ◽

The Continuum

AbstractActively tunable and reconfigurable wavefront shaping by optical metasurfaces poses a significant technical challenge often requiring unconventional materials engineering and nanofabrication. Most wavefront-shaping metasurfaces can be considered “local” in that their operation depends on the responses of individual meta-units. In contrast, “nonlocal” metasurfaces function based on the modes supported by many adjacent meta-units, resulting in sharp spectral features but typically no spatial control of the outgoing wavefront. Recently, nonlocal metasurfaces based on quasi-bound states in the continuum have been shown to produce designer wavefronts only across the narrow bandwidth of the supported Fano resonance. Here, we leverage the enhanced light-matter interactions associated with sharp Fano resonances to explore the active modulation of optical spectra and wavefronts by refractive-index tuning and mechanical stretching. We experimentally demonstrate proof-of-principle thermo-optically tuned nonlocal metasurfaces made of silicon and numerically demonstrate nonlocal metasurfaces that thermo-optically switch between distinct wavefront shapes. This meta-optics platform for thermally reconfigurable wavefront shaping requires neither unusual materials and fabrication nor active control of individual meta-units.

Download Full-text

Near-Field Excitation of Bound States in the Continuum in All-Dielectric Metasurfaces through a Coupled Electric/Magnetic Dipole Model

Nanomaterials ◽

10.3390/nano11040998 ◽

2021 ◽

Vol 11 (4) ◽

pp. 998

Author(s):

Diego R. Abujetas ◽

José A. Sánchez-Gil

Keyword(s):

Magnetic Dipole ◽

Density Of States ◽

Bound States ◽

Local Density ◽

Near Field ◽

Field Pattern ◽

Local Density Of States ◽

Optical Modes ◽

Source Excitation ◽

The Continuum

Resonant optical modes arising in all-dielectric metasurfaces have attracted much attention in recent years, especially when so-called bound states in the continuum (BICs) with diverging lifetimes are supported. With the aim of studying theoretically the emergence of BICs, we extend a coupled electric and magnetic dipole analytical formulation to deal with the proper metasurface Green function for the infinite lattice. Thereby, we show how to excite metasurface BICs, being able to address their near-field pattern through point-source excitation and their local density of states. We apply this formulation to fully characterize symmetry-protected BICs arising in all-dielectric metasurfaces made of Si nanospheres, revealing their near-field pattern and local density of states, and, thus, the mechanisms precluding their radiation into the continuum. This formulation provides, in turn, an insightful and fast tool to characterize BICs (and any other leaky/guided mode) near fields in all-dielectric (and also plasmonic) metasurfaces, which might be especially useful for the design of planar nanophotonic devices based on such resonant modes.

Download Full-text