Longqing Cong

Longqing Cong
Southern University of Science and Technology | SUSTech · Department of Electrical and Electronic Engineering

Doctor of Philosophy

About

65
Publications
20,103
Reads
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4,158
Citations
Introduction
Terahertz technologies, Next-generation wireless communications, Metamaterials & Metasurfaces, Nonlinear Optics, Photonic crystals
Additional affiliations
August 2019 - July 2020
University of Pennsylvania
Position
  • PostDoc Position
April 2017 - July 2019
Nanyang Technological University
Position
  • Research fellow
January 2014 - August 2017
Nanyang Technological University
Position
  • PhD Student

Publications

Publications (65)
Article
Terahertz (THz) waves have exhibited promising applications in imaging, sensing, and communications, especially for the next-generation wireless communications due to the large bandwidth and abundant spectral resources. Modulators and waveguides to manipulate THz waves are becoming key components to develop the relevant technologies where metamater...
Article
Full-text available
Bound state in the continuum (BIC) refers to the trapped state in the radiation continuum of a system. In the terahertz band, BIC provides a unique and feasible method to design devices with ultra-high quality factor (Q factor) and to achieve intense terahertz-matter interaction, which is of great value to terahertz science and technology. Here, mu...
Article
Full-text available
Metasurface-empowered bound state in the continuum (BIC) provides a unique route for fascinating functional devices with infinitely high quality factors. This method is particularly attractive to the terahertz community because it may essentially solve the deficiencies in terahertz filters, sensors, lasers, and nonlinear sources. However, most BIC...
Article
Full-text available
Metasurfaces with a strongly enhanced local field are envisioned as a powerful platform for ultrasensitive optical sensors to significantly amplify imperceptible differences between compatible bioanalytes. Through the use of phototunable silicon-based terahertz (THz) metasurfaces, we experimentally demonstrate ultrafast switchable sensing functions...
Article
Full-text available
Losses are ubiquitous and unavoidable in nature inhibiting the performance of most optical processes. Manipulating losses to adjust the dissipation of photons is analogous to braking a running car that is as important as populating photons via a gain medium. Here, we introduce the transient loss boundary into a photon populated cavity that function...
Preprint
Full-text available
Losses are ubiquitous and unavoidable in nature inhibiting the performance of most optical processes. Manipulating losses to adjust the dissipation of photons is analogous to braking a running car that is as important as populating photons via a gain medium. Here, we introduce the transient loss boundary into a photon populated cavity that function...
Article
Full-text available
Next‐generation devices for low‐latency and seamless communication are envisioned to revolutionize information processing, which would directly impact human lives, technologies, and societies. The ever‐increasing demand for wireless data traffic can be fulfilled by the terahertz band, which has received tremendous attention as the final frontier of...
Article
Full-text available
Recently emerged dielectric resonators and metasurfaces offer a low-loss platform for efficient manipulation of electromagnetic waves from microwave to visible. Such flat meta-optics can focus electromagnetic waves, generate structured beams and vortices, enhance local fields for sensing as well as provide additional functionalities for advanced MR...
Article
Bound state in the continuum (BIC) is a mathematical concept with an infinite radiative quality factor (Q) that exists only in an ideal infinite array of resonators. In photonics, it is essential to achieve high Q resonances for enhanced light‐mater interactions that could enable low‐threshold lasers, ultrasensitive sensors, and optical tweezers. H...
Article
Full-text available
Optical chirality is central to many industrial photonic technologies including enantiomer identification, ellipsometry-based tomography, and spin multiplexing in optical communications. However, a substantial chiral response requires a three-dimensional constituent, thereby making the morphology highly complex to realize structural reconfiguration...
Article
Full-text available
Optical chirality is central to many industrial photonic technologies including enantiomer identification, ellipsometry-based tomography, and spin multiplexing in optical communications. However, a substantial chiral response requires a three-dimensional constituent, thereby making the morphology highly complex to realize structural reconfiguration...
Preprint
Bound state in the continuum (BIC) is a mathematical concept with an infinite radiative quality factor (Q) that exists only in an ideal infinite array. It was first proposed in quantum mechanics, and extended to general wave phenomena such as acoustic, water, elastic, and electromagnetic waves. In photonics, it is essential to achieve high Q resona...
Article
Full-text available
Miniaturized ultrafast switchable optical components with an extremely compact size and a high-speed response will be the core of next-generation all-optical devices instead of traditional integrated circuits, which are approaching the bottleneck of Moore's Law. Metasurfaces have emerged as fascinating subwavelength flat optical components and devi...
Article
Full-text available
Polarization manipulation is essential in developing cutting-edge photonic devices ranging from optical communication displays to solar energy harvesting. Most previous works for efficient polarization control cannot avoid utilizing metallic components that inevitably suffer from large ohmic loss and thus low operational efficiency. Replacing metal...
Article
The interaction between microscopic particles is always a fascinating and intriguing area of science. Direct interrogation of such interactions is often difficult. Structured electromagnetic systems offer a rich toolkit for mimicking and reproducing the key dynamics that govern the microscopic interactions, and thus provides an avenue to explore an...
Preprint
Full-text available
Optical chirality is central to many industrial photonic technologies including enantiomer identification, ellipsometry-based tomography and spin multiplexing in optical communication. However, a substantial chiral response requires a typical three-dimensional (3D) constituent, thereby making the paradigm highly complex. Photonic devices integrated...
Article
The mechanism of Cooper pair formation and underlying physics has long occupied the investigation into high temperature (high-Tc ) cuprate superconductors. One of the ways to unravel this is to observe ultrafast response present in charge carrier dynamics of a photoexcited specimen. This results in an interesting approach to exploit the dissipation...
Article
Full-text available
The interaction between microscopic particles has always been a fascinating and intriguing area of science. Direct interrogation of such interactions is often difficult. Structured electromagnetic systems offer a rich toolkit for mimicking and reproducing the key dynamics that governs the microscopic interactions, and thus provide an avenue to expl...
Conference Paper
We report the observation of extremely high-quality factors in all-dielectric subwavelength terahertz metasurfaces. We further demonstrate an active ultrafast switching of the high-Q resonances via direct optical excitation of the supercavities.
Article
Sensing technologies based on terahertz waves have immense potential due to their non-destructive, transparent, and fingerprint spectral response of several materials that are opaque to other parts of the electromagnetic spectrum. Terahertz metasensors reported so far merely exploit the fringing electric field on the top of the subwavelength resona...
Article
Incorporating semiconductors as active media into metamaterials offers opportunities for a wide range of dynamically switchable/tunable, technologically relevant optical functionalities enabled by strong, resonant light–matter interactions within the semiconductor. Here, a germanium-thin-film-based flexible metaphotonic device for ultrafast optical...
Article
The toroidal dipole moment, a localized electromagnetic excitation of torus magnetic fields, has been observed experimentally in metamaterials. However, the metamaterial based toroidal moment was restricted at higher frequencies by the complex three-dimensional structure. Recently, it has been shown that toroidal moment could also be excited in a p...
Article
Full-text available
The multipoles play a significant role in determining the resonant behavior of subwavelength resonators that form the basis of metamaterial and plasmonic systems. Here, we study the impact of multipoles including toroidal dipole on the resonance intensity and linewidth of the fundamental inductive-capacitance (LC) resonance of a metamaterial array....
Article
Full-text available
Controlling the phase of local radiation by using exotic metasurfaces has enabled promising applications in a diversified set of electromagnetic wave manipulation such as anomalous wavefront deflection, flat lenses, and holograms. Here, we theoretically and experimentally demonstrate an active phase transition in a micro-electromechanical system-ba...
Article
Fano resonances offer exciting features in enhancing the non-linearity and sensing capabilities in metamaterial systems. An active photoswitching of Fano resonances in a terahertz metadevice at low optical pump powers is demonstrated, which signifies the extreme sensitivity of the high-quality-factor resonant electric field to the external light il...
Article
Metasurfaces have provided a novel route to control the local phase of electromagnetic radiation through subwavelength scatterers where the properties of each element remain passive. A passive metasurface design can only achieve a specific functionality as it is extremely challenging to reconfigure each element that contributes toward the control o...
Article
Recent advances in graphene photonics reveal promising applications in the technologically important terahertz spectrum, where graphene-based active terahertz metamaterial modulators have been experimentally demonstrated. However, the sensitivity of the atomically thin graphene monolayer towards sharp Fano resonant terahertz metasurfaces remains un...
Article
A toroidal dipole in metasurfaces provides an alternate approach for the excitation of high-Q resonances. In contrast to conventional multipoles, toroidal dipole interaction strength depends on the time derivative of the surrounding electric field. A characteristic feature of a toroidal dipole is tightly confined loops of oscillating magnetic field...
Article
Toroidal multipoles have recently been explored in various scientific communities, ranging from atomic and molecular physics, electrodynamics, and solid-state physics to biology. Here we experimentally and numerically demonstrate a three-dimensionsal toroidal metamaterial where two different toroidal dipoles along orthogonal directions have been ob...
Article
The inductive coupling of the identical bianisotropic meta-atoms has been demonstrated to be dependent on the spatial distance. Here, a nonintuitive orientation dependent switchable coupling phenomenon is experimentally studied and the applications in polarization control of the proposed metasurface are shown.
Article
Full-text available
Metamaterials have recently enabled coupling induced transparency due to interference effects in coupled subwavelength resonators. In this work, we present a three dimensional (3-D) metamaterial design with six-fold rotational symmetry that shows electromagnetically induced transparency with a strong polarization dependence to the incident electrom...
Article
The near field meta-molecular interactions in a lattice play an important role in determining the collective behavior of the metamaterials. Here, we exploit the nearest neighbor inter unit cell interactions and the intra near-field coupling in metamolecules to manipulate the co- and the cross-polarized light. We observed large enhancement in the ba...
Article
Full-text available
Fano resonances in metasurfaces are important due to their low loss subradiant behavior that allows excitation of high-quality (Q) factor resonances extending from the microwave to the optical regime. High-Q Fano resonances have recently enabled applications in the areas of sensing, modulation, filtering, and efficient cavities for lasing spasers....
Article
A microelectromechanically reconfigurable digital metamaterial for dynamic switching of terahertz anisotropy is experimentally demonstrated. Out-of-plane reconfigurable microcantilevers placed in orthogonal direction with isolated control allows active making and breaking of unit cell symmetry. The electrical control, miniaturized size, and ease of...
Article
It is extremely challenging to control the phase of light at will in free space. Here, Pancharatnam-Berry-phase-enabled, tunable phase control of free-space light is experimentally demonstrated in an ultrathin flexible dispersion-free metadevice. This metadevice enables the broadband conversion of linearly polarized light into any desired output po...
Article
Full-text available
We report the simulation, fabrication, and experimental characterization of a multichannel metamaterial absorber with the aim to be used as a label-free sensing platform in the terahertz regime. The topology of the investigated resonators deposited on a thin flexible polymer by means of optical lithography is capable of supporting multiple resonanc...
Article
An operation range of the figure of merit (FoM) that reflects the trade-off between Q factor and resonance intensity of the Fano resonance is provided. The structural asymmetry parameter α = (l1 − l2)/(l1 + l2) × 100% in the resonator determines the FoM that has an optimized band of operation for asymmetry ranging from 4% to 8% in the terahertz Fan...
Article
Full-text available
We experimentally study the effect of near field coupling on the transmission of light in terahertz metasurfaces, possessing slightly distinctive SRR resonances. Our results show that the interplay between the strengths of electric and magnetic dipoles, modulates the amplitude of resulting electromagnetically induced transmission, probed under diff...
Article
Full-text available
Planar metasurfaces and plasmonic resonators have shown great promise for sensing applications across the electromagnetic domain ranging from the microwaves to the optical frequencies. However, these sensors suffer from lower figure of merit and sensitivity due to the radiative and the non-radiative loss channels in the plasmonic metamaterial syste...
Article
Full-text available
Near-field coupling between orthogonally twisted bright and dark mode resonances gives rise to sharp Fano-like resonances and electromagnetically induced transparency. We demonstrate that by varying the orientation of the near-field coupled bright and dark metamolecule with respect to the incident electric field, the shape and linewidth of the coup...
Article
Metamaterials can harvest electromagnetically induced transparency (EIT) phenomena due to the induced high-order multipolar interference, which is generally characterized as plasmonic hybridization process. Inspired by the multipolar hybridization concept, we construct 3D metamaterials to numerically and experimentally realize the EIT phenomena. Fu...
Article
Full-text available
By utilizing the vector nature of light as well as the inherent anisotropy of artificial meta-atoms, we investigate parity time symmetry breaking in polarization space using a metasurface with anisotropic absorption, whose building blocks consist of two orthogonally orientated meta-atoms with the same resonant frequency but different loss coefficie...
Article
Full-text available
The coupling of multiple plasmonic resonators that sustain bright or dark modes provide intriguing spectral signatures. However, probing the onset of coupling effects while engaging the resonators with an increasing proximity has not yet been studied experimentally in detail. Nevertheless, this is of utmost importance to bridge the phenomenological...
Article
Full-text available
Metamaterial perfect absorbers from microwaves to optical part of the electromagnetic spectrum has been intensely studied for its ability to absorb electromagnetic radiation. Perfect absorption of light by metamaterials have opened up new opportunities for application oriented functionalities such as efficient sensors and emitters. We present an ab...
Article
Metamaterials offer exciting opportunities that enable precise control of light propagation, its intensity and phase by designing an artificial medium of choice. Inducing birefringence via engineered metamolecules presents a fascinating mechanism to manipulate the phase of electromagnetic waves and facilitates the design of polarimetric devices. He...
Article
Full-text available
High quality factor resonances are extremely promising for designing ultra-sensitive refractive index label-free sensors since it allows intense interaction between electromagnetic waves and the analyte material. Metamaterial and plasmonic sensing has recently attracted a lot of attention due to subwavelength confinement of electromagnetic fields i...
Article
Full-text available
As the potential applications of terahertz science and technology become extremely important, there is an increasing demand for improved terahertz optical components. One of such devices on demand is the class of polarization control devices. Recently, metasurfaces have emerged as designer structures with excellent control, design flexibility, and...
Article
Full-text available
Polarization conveys valuable information for electromagnetic signal processing exhibiting tremendous potential in developing application driven photonic devices. Manipulation of polarization state of an electromagnetic wave has drawn a lot of research interests in many different fields, especially in the terahertz regime. Here, we propose a unique...
Article
Experimental tests are presented to investigate the stress effect on terahertz (THz) waves with a THz time-domain spectroscopy system. Through the Jones matrix method, an experimental principle is derived according to the experimental system. Experimental results indicate the linear relationship between a polytetrafluoroethylene refractive index an...
Article
Full-text available
We present a double-ring-chain metamaterial that enables efficient polarization conversion of terahertz waves. The experimental results and numerical simulations reveal that the linear-to-linear polarization rotation and linear-to-elliptic polarization transformation are simply accomplished by altering the dimensional parameters of the metamaterial...