Enhancement Of Light-matter Interaction Research Articles

Nonlinear response of Q-boosting metasurfaces beyond the time-bandwidth limit

Abstract Resonant nanostructures, such as photonic metasurfaces, have created an unprecedented case for enhanced light–matter interactions through local field engineering. However, the presence of resonances fundamentally limits the bandwidth of such interactions. Here, we report on amending the nonlinear optical response of a semiconducting metasurface through Q-boosting, where the Q-factor of a metasurface rapidly increases with time. The coupled-mode theory reveals overcoming the bandwidth limit by coupling a broadband signal to a bandwidth-matched resonance and Q-boosting at a timescale faster than a resonator lifetime. A control–excitation experiment simulation using a tailored Q-boosting silicon-germanium metasurface predicts the third-harmonic enhancement by factors of 8 (peak) and 4.5 (integrated) against the best-case static metasurface. An analysis of free-carrier losses based on experimental data shows robustness to nonradiative losses and offers a viable pathway to increasing the light–matter interactions beyond the bandwidth limit, with implications in nonlinear and quantum optics, sensing, and telecommunication technologies.

Engineering a mechanically stable hybrid photonic crystal cavity coupled to color defects in diamond

Wavelength scale photonic, high-quality factor (Q-factor), cavities are crucial for enhancing light–matter interaction. Such on-chip hybrid devices could potentially provide a route towards scalable quantum technologies with color defects in diamond. A variety of designs for photonic crystal cavities have been proposed; however, the challenging and multi-step fabrication processes required for such designs limit the experimentally observed Q-factors in addition to significant radiation loss. One possible way to minimize the radiation loss in a one-dimensional (1D) photonic crystal cavity is by introducing a so-called Gaussian defect region around the cavity. In this work, we propose a versatile approach to design a Gaussian defect region by changing the lattice parameter in a 1D photonic crystal. Further, to circumvent the problem of creating freestanding cavities for achieving high-Q factor in a 1D photonic crystal cavity, we propose a novel hybrid diamond-titanium dioxide (TiO2) based materials for color defects in diamond, in particular the nitrogen-vacancy (NV−) center. Our proposed mechanically stable and high-Q cavity could be crucial for on-chip integration of different nanophotonic components for chip-scale photonic devices. We show via simulations that Q-factor 105 can be achieved with the device.

Non-Ultrawide Bandgap Semiconductor GaSe Nanobelts for Sensitive Deep Ultraviolet Light Photodetector Application.

In this paper, the authors report the fabrication of a sensitive deep ultraviolet (DUV) photodetector by using an individual GaSe nanobelt with a thickness of 52.1nm, which presents the highest photoresponse at 265nm illumination with a responsivity and photoconductive gain of about 663AW-1 and 3103 at a 3V bias, respectively, comparable to or even better than other reported devices based on conventional wide bandgap semiconductors. According to the simulation, this photoelectric property is associated with the wavelength-dependent absorption coefficient of the GaSe crystal, for which incident light with shorter wavelengths will be absorbed near the surface, while light with longer wavelengths will have a larger penetration depth, leading to a blueshift of the absorption edge with decreasing thickness. Further finite element method (FEM) simulation reveals that the relatively thin GaSe nanobelt exhibits an enhanced transversal standing wave pattern compared to its thicker counterpart at a wavelength of 265nm, leading to an enhanced light-matter interaction and thereby more efficient photocurrent generation. The device can also function as an effective image sensor with acceptable spatial resolution. This work will shed light on the facile fabrication of a high-performance DUV photodetector from non-ultrawide bandgap semiconductors.

3D printed metamaterial absorbers for mid-infrared surface-enhanced spectroscopy

The resonant nature and geometric scalability make metamaterials an ideal platform for an enhanced light–matter interaction over a broad frequency range. The mid-infrared (IR) spectral range is of great importance for vibrational spectroscopy of molecules, while IR metamaterials created from lithography-based planar nanostructures have been used to demonstrate enhanced molecular detection. Compared with visible and near-infrared, the relative long wavelengths of IR light make it possible to achieve three-dimensional (3D) IR metamaterials via the state-of-the-art 3D fabrication techniques. Here, we design and fabricate a 3D printed plasmonic metamaterial absorber (MMA), and by performing Fourier-transform IR spectroscopy, we demonstrate that a series of molecular fingerprint vibrations of glycine can be significantly enhanced by the high absorption mode supported by the 3D meta-atoms of the MMA. The observed enhanced IR detection can also be partially attributed to the improved accessibility offered by the 3D architecture of the MMA. In particular, due to capillary forces during the drying process, the microscale 3D printed features lead to selective analyte deposition in high-field regions, which provides another degree of freedom in the design of the 3D printed structures for surface-enhanced IR detection. Our study shows the flexibility of metastructures based on advanced 3D printing technology in tailoring the interaction between IR light and materials on a subwavelength scale.

Hybrid plasmonic-photonic microcavity for enhanced light-matter interaction

Cavity quantum electrodynamics focuses on enhancing the light-matter interactions for a broad spectrum of applications, including lasers, quantum information processing, spectroscopy, and imaging. As photonic cavities confine light with the constraint of diffraction limit while plasmonic cavities suffer from Ohmic loss, hybrid plasmonic-photonic microcavities have emerged as a versatile platform to overcome the limitations in pure systems and enhance lightmatter interactions reaching the strong coupling regime. The present Perspective starts from the fundamentals of light-matter interaction, followed by the review of both theoretical and experimental developments achieved recently in hybrid plasmonic-photonic systems. Together with the fascinating optical properties of hybrid systems, diverse potential applications are discussed, for example, quantum state preparation and operation, nonlinear optics, molecular spectroscopy, and sensing. The possible challenges posed to nanofabrication and characterization are also briefly covered.

Symmetry-protected bound states in the continuum in graphene nanoribbons

Bound states in the continuum (BICs) have emerged as a significant design principle for producing systems with high-quality (Q) factor states to enhance light–matter interactions. As a particular case, symmetry-protected BICs are flexible to be designed, commonly by utilizing two identical lossless dielectric elements. Herein, different from previous studies, we propose symmetry-protected BICs in a plasmonic structure of two contacting graphene nanoribbons (GNRs), in which two GNRs are not identical and lossy. We show that BICs are achieved when two GNRs are perpendicular to each other, and as the vertical GNR deviates from the vertical direction (inversion symmetry breaking), it will evolve into quasi-BICs, with a new resonance dip appearing in the transmission spectrum. The spectrum curve can be well described by the coupled-mode theory, from which the variation of two fundamental states is clearly seen. Since in the presence of internal loss, the Q-factor of quasi-BICs does not follow the linear formula that is generally valid for symmetry-protected BICs. Alternatively, an extended formula is derived, which predicts exactly the behavior of the Q-factor of quasi-BICs. Besides BICs, the structure can also support plasmonically induced transparency (PIT) like effects, through rotating the vertical GNR to a particular angle. Therefore, a mechanically tunable switch, from BIC to PIT, is achieved here. Our work demonstrates an alternative scheme for BICs, and a new degree of freedom for tuning plasmonic coupling related effects.

Bound states in the continuum on flatbands of symmetry-broken photonic crystal slabs

Bound states in the continuum (BICs) are localized states despite in a radiation continuum, rendering the ultra-high quality factor for enhanced light–matter interactions and supporting exotic topological properties. So far, most of studied BICs in photonic crystal (PhC) slabs are only vertically localized, i.e. allowing propagations in the plane of slab therein but forbidding radiations, and the density of optical states (DOS) at their frequencies is limited due to the steep dispersion characteristics. Here, we report a BIC existing on a flatband of symmetry-broken PhC slab. The flatband, associated with largely reduced group velocity, significantly sharpens the DOS at the frequency of BIC, which can be realized via finely controlling broken vertical symmetry in the PhC slab. The effect of broken symmetry is revealed in a simple effective Hamiltonian near the second-order Γ point of such system. Our results show the simultaneous engineering of dispersion and leaky characteristics of modes, offering new opportunities to boost light–matter interactions and to enhance the performance of photonic devices.

Enhanced sensing of terahertz surface plasmon polaritons in graphene/J-aggregate coupler using FDTD method

J-aggregates nanostructure proposed for realization of plasmonic manufactories like switchable localized surface resonances (LSR) due to their optical nonlinearities' properties. J-aggregates to enhancement of light-matter interaction is applied. In this regard, we propose a novel graphene/J-aggregate plasmonics coupler with subwavelength structure at telecommunication range. Utilizing device geometries and optical properties optimized for enhanced light-matter interactions lets us to harness the propagation of TM (TE) modes without the change of configuration. Here, the coupling parameters have been numerically and investigated using the finite-difference time-domain (FDTD) method. The results show that the coupling condition can be tuned by optical properties of graphene in turn leads to a tunable plasmonics coupler. It is shown that, by considering magnetic field of 0.01 T and graphene chemical potential of mc = 0.45 eV, the TM mode, and magnetic field of 0.02 T and graphene chemical potential of mc = 0.4 eV, the TE mode can be propagated in the selected ports. With the above behavior, the proposed structure may potentially be applied in telecommunication links.

Tunable and enhanced optical force with bound state in the continuum.

Light-actuated motors, vehicles, and even space sails have drawn tremendous attention for basic science and applications in space, biomedical, and sensing domains. Optical bound states in the continuum (BIC) are topological singularities of the scattering matrix, known for their unique light-trapping capability and enhanced light-matter interaction. We show that BIC modes enable the generation of enhanced and tunable optical forces and torques. A sharp and controllable line shape is observed in force and torque spectra when approaching high-Q resonance BIC modes. Wavelength and polarization tunability are presented as an effective method to control forces on BIC enclosed structures. Finally finite-size simulations are performed to evaluate the practical applications for a BIC-assisted metavehicle.

Centimeter‐Scale Propagation of Optical Surface Waves at Visible Wavelengths

AbstractGuiding and confining light at interfaces is crucial for applications involving light–matter interactions, such as surface spectroscopy, nonlinear optics, and quantum information technology. While dielectric surface waves offer promising perspectives for strong light confinement at non‐absorbing interfaces, their capacity has not yet been widely explored. This article focuses on the propagation properties of optical modes supported at the free surface of a 1D photonic crystal. The contributions of intrinsic and extrinsic loss mechanisms are investigated. Structures optimized to support long propagating optical surface waves are designed and fabricated. This work experimentally demonstrates, for the first time, the existence of optical surface waves capable of propagating over centimeter‐scale distances in the visible spectral range. The results open new perspectives for the use of optical surface waves in integrated optics and enhanced light–matter interactions.

Correction to: Enhanced light–matter interaction in a hybrid photonic–plasmonic cavity

Correction to: Enhanced light–matter interaction in a hybrid photonic–plasmonic cavity

Bound states in the continuum based on the total internal reflection of Bloch waves.

A photonic-crystal slab can support bound states in the continuum (BICs) that have infinite lifetimes but are embedded into the continuous spectrum of optical modes in free space. The formation of BICs requires a total internal reflection (TIR) condition at both interfaces between the slab and the free space. Here, we show that the TIR of Bloch waves can be directly obtained based on the generalized Fresnel equations proposed. If each of these Bloch waves picks up a phase with integer multiples of 2πfor traveling a round trip, light can be perfectly guided in the slab, namely forming a BIC. A BIC solver with low computational complexity and fast convergence speed is developed, which can also work efficiently at high frequencies beyond the diffraction limit where multiple radiation channels exist. Two examples of multi-channel BICs are shown and their topological nature in momentum space is also revealed. Both can be attributed to the coincidence of the topological charges of far-field radiations from different radiation channels. The concept of the generalized TIR and the TIR-based BIC solver developed offer highly effective approaches for explorations of BICs that could have many potential applications in guided-wave optics and enhanced light-matter interactions.

Sensitivity Dependence of Single Nanoparticle Mass Detection Using Mechanical Oscillations in Optical Microcavities

Single nanoparticle detection is demanding in fields such as early-stage diagnostics, environmental monitoring and biochemical researches. Microcavities are becoming excellent platforms for ultrasensitive detection due to the extremely strong enhancement of light-matter interactions. However, the analytes to be detected will introduce optical losses, which eventually spoils the detection limit of the optical sensor. The strong light confinement enables optical induced mechanical oscillations that is also sensitive to analyte attachments and can thus be applied as an alternative sensing signal in microcavity sensors. In this work, the mass sensitivities of the mechanical oscillations of a microcavity are theoretically discussed. The sensitivity dependence on different modes, analyte sensing position and microcavity structure are explored via finite-element-method simulations, which are consistent with theoretical predictions. Our results provide an effective guideline for the sensitivity optimization during microcavity design aiming for single nanoparticle mass detection.

Silicon Nanosphere with Accessible Magnetic Hotspot

AbstractHigh refractive index dielectric nanoparticles supporting the magnetic dipole (MD) Mie resonance are capable of inducing strongly enhanced magnetic field at an optical frequency, and have great potential for enhancing light–matter interactions such as magnetic dipole transitions of ions and molecules. However, the magnetic hotspot is usually located inside a nanoparticle and thus the development of technology to access the hotspot remains an urgent issue. Here, a silicon (Si) nanosphere having an access hole to the magnetic hotspot is proposed. Numerical simulations for a Si nanosphere with a hole of different diameters and depths are performed. Then, a solution‐based process to dig an access hole to a Si nanosphere is developed. A spectroscopic method to analyze nanohole‐induced anisotropy of a spherical nanoantenna is also developed. Finally, in combination with numerical simulations and angle‐resolved scattering measurements of a Si nanosphere with a nanohole, it is shown that the magnetic field intensity is 100‐fold enhanced at the nanohole.

SnSe-Coated Microfiber Resonator for All-Optical Modulation.

In this study, a tin monoselenide (SnSe)-based all-optical modulator is firstly demonstrated with high tuning efficiency, broad bandwidth, and fast response time. The SnSe nanoplates are deposited in the microfiber knot resonator (MKR) on MgF2 substrate and change its transmission spectra by the external laser irradiation. The SnSe nanoplates and the microfiber are fabricated using the liquid-phase exfoliation method and the heat-flame taper-drawing method, respectively. Due to the strong absorption and enhanced light–matter interaction of the SnSe nanoplates, the largest transmitted power tunability is approximately 0.29 dB/mW with the response time of less than 2 ms. The broad tuning bandwidth is confirmed by four external pump lights ranging from ultraviolet to near-infrared. The proposed SnSe-coated microfiber resonator holds promising potential for wide application in the fields of all-optical tuning and fiber sensors.

Bidirectional Rainbow Trapping in 1-D Chirped Topological Photonic Crystal

The rainbow trapping effect has attracted gathering attention due to its potential application in data processing, energy storage, and light-matter interaction enhancement. The interest has increased recently with the advent of topological photonic crystals (PCs), as the topological PC affords a robust platform for nanophotonic devices. We proposed a chirped one-dimensional (1D) PC as a sandwiched trapped between two1D topological PCs to realize two topological edge states (TESs) for topological protection and trap the formed rainbow. Through graded the thickness of dielectric layers of the chirped 1D PC, light of different wavelengths components localizes and stores at different spatial positions leading to rainbow trapping formation. Unidirectional rainbow trapping can be observed by progressively increasing the thicknesses of the chirped PC. Nonetheless, changing increasingly one of its thicknesses and solidifying the other leads to bidirectional rainbow trapping. Achieving bidirectional rainbow trapping will reduce the footprint of nanophotonic devices in the future. This work brings inspiration to the realization of the rainbow trapping effect and provides a way to design topological nanophotonic devices.

Deep Learning-Assisted Enhanced Fano Resonances in Symmetry-Breaking SOI Metasurface

Metasurfaces analogues of Fano resonances provide a powerful platform for high sensitivity sensing, nonlinear optics, and light manipulation. However, previous Fano-resonant metasurfaces usually are not compatible with silicon complementary metal-oxide semiconductor circuits due to their hybrid material structures and large non-radiative loss. Herein, we theoretically demonstrate a silicon-on-insulator metasurface (SOIM) enhancing Fano resonances by using a tandem neural network design. Multiple Fano resonances with high Q-factor have been observed in the symmetry-breaking SOIM. The Fano-resonant mechanism of the SOIM is analyzed. Additionally, the spectral features of the Fano-resonant SOIM as a function of the symmetry tuning factor of the double silicon nanobars and the environment refractive index are also investigated. The result shows that the Fano-resonant SOIM as a methanol sensor with a sensitivity of 310 nm/RIU can achieve an overall figure of merit of 195 in the near-infrared spectral regime. The designed Fano-resonant SOIM shows enormous potential applications in highly sensitive sensors and light-matter interaction enhancement.

Spin‐Lasing in Bimodal Quantum Dot Micropillar Cavities

AbstractSpin‐controlled lasers are highly interesting photonic devices and have been shown to provide ultrafast polarization dynamics in excess of 200 GHz. In contrast to conventional semiconductor lasers their temporal properties are not limited by the intensity dynamics, but are governed primarily by the interaction of the spin dynamics with the birefringent mode splitting that determines the polarization oscillation frequency. Another class of modern semiconductor lasers are high‐β emitters, which benefit from enhanced light–matter interaction due to strong mode confinement in low‐mode‐volume microcavities. In such structures, the emission properties can be tailored by the resonator geometry to realize for instance bimodal emission behavior in slightly elliptical micropillar cavities. This attractive feature is utilized to demonstrate and explore spin‐lasing effects in bimodal high‐β quantum dot micropillar lasers. The studied microlasers with a β‐factor of 4% show spin‐laser effects with experimental polarization oscillation frequencies up to 15 GHz and predicted frequencies up to about 100 GHz, which are controlled by the ellipticity of the resonator. These results reveal appealing prospects for very compact, ultrafast, and energy‐efficient spin‐lasers and can pave the way for future purely electrically injected spin‐lasers enabled by short injection path lengths.

Investigation of dual-band perfect absorption and their hybridization on multilayer tungsten disulfide (WS2) gratings

We investigate the dual-band perfect absorption and their hybridization on multilayer tungsten disulfide (WS2) gratings with metallic substrates by the finite-difference time-domain method and the coupled-mode theory. Numerical results suggest that, under the illumination of the transverse magnetic polarized plane wave, the special multilayer WS2 grating with high refractive index not only allows the circulating-current-drove magnetic resonance but also provides additional wavevectors to excite the plasmonic resonance on the substrate surface simultaneously. Consequently, the dual-band perfect absorption is obtained in the single-port system by two independent critical coupling. The effect of small changes in the grating period, width, and height on spectral positions of absorption peaks is presented. The inherent multiple dielectric resonances on the WS2 grating under the illumination of the transverse electric polarized plane wave are also demonstrated. Intriguingly, the simultaneous existence of angle-independent magnetic resonances and angle-dependent plasmonic resonances gives rise to the obvious hybridization between the two types of resonances under the oblique incidence. Numerical results are in excellent agreement with theoretical calculations. The structure under study undoubtedly opens perspectives for enhancing light–matter interactions in two-dimensional materials.

Engineering Chiral Light-Matter Interactions in a Waveguide-Coupled Nanocavity.

Spin-dependent, directional light–matter interactions form the basis of chiral quantum networks. In the solid state, quantum emitters commonly possess circularly polarized optical transitions with spin-dependent handedness. We demonstrate numerically that spin-dependent chiral coupling can be realized by embedding such an emitter in a waveguide-coupled nanocavity, which supports two near-degenerate, orthogonally polarized cavity modes. The chiral behavior arises due to direction-dependent interference between the cavity modes upon coupling to two single-mode output waveguides. Notably, an experimentally realistic cavity design simultaneously supports near-unity chiral contrast, efficient (>95%) cavity-waveguide coupling and enhanced light–matter interaction strength (Purcell factor FP > 70). In combination, these parameters enable the development of highly coherent spin–photon interfaces ready for integration into nanophotonic circuits.