Guided-mode Resonance Research Articles

Quasi-bound states in the continuum in a metal nanograting metasurface for a high figure-of-merit refractive index sensor.

In this work, we investigate the bound states in the continuum (BICs) in a gold nanograting metal-insulator-metal metasurface structure at oblique angles of incidence. The nanograting metasurface consists of a gold nanograting patterned on a silicon dioxide dielectric film deposited on a thick gold film supported by a substrate. With rigorous full-wave finite difference time domain simulations, two bound states in the continuum are revealed upon transverse magnetic wave angular incidence. One BIC is formed by the interference between the surface plasmon polariton mode of the gold nanograting and the FP cavity mode. Another BIC mode is formed by the interference between the metal-dielectric hybrid structure guided mode resonance mode and the FP cavity mode. While true BIC modes cannot be observed, quasi-BIC modes are investigated at angles of incidence slightly off from the corresponding true BIC angles. It is shown that quasi-BIC modes can suppress radiation loss, resulting in narrow resonance spectral linewidths and high quality-factors. The quasi-BIC mode associated with the surface plasmon polariton mode is investigated for refractive index sensing. As a result, a high sensitivity refractive index sensor with a large figure-of-merit of 364 has been obtained.

Phase of Topological Lattice with Leaky Guided Mode Resonance.

Topological nature in different areas of physics and electronics has often been characterized and controlled through topological invariants depending on the global properties of the material. The validity of bulk-edge correspondence and symmetry-related topological invariants has been extended to non-Hermitian systems. Correspondingly, the value of geometric phases, such as the Pancharatnam-Berry or Zak phases, under the adiabatic quantum deformation process in the presence of non-Hermitian conditions, are now of significant interest. Here, we explicitly calculate the Zak phases of one-dimensional topological nanobeams that sustain guided-mode resonances, which lead to energy leakage to a continuum state. The retrieved Zak phases show as zero for trivial and as π for nontrivial photonic crystals, respectively, which ensures bulk-edge correspondence is still valid for certain non-Hermitian conditions.

Guided mode resonances for angular and spectral filtering

The development of devices based on compact waveguides is a rapidly evolving field. A unique variation of such devices is the Fano-like resonance dielectric spectral and spatial filtre, made from a dielectric conformal thin film on a surface relief grating. It can be used in a normal (or oblique) angle-of-incidence configuration. This device facilitates directional selectivity, which is useful for transverse-mode cleaning in short optical cavities. It can also be enhanced by using leaky-mode effects to produce even sharper spectral features. However, a perfect spatial filtre should be as invariant as possible in the spectral and enhanced angular domains. Here, we solved the inverse design problem to produce such an effect. Numerically, we tuned the surface profile of the substrate grating, assuming a conformal layer on top. This resulted in trapezoidal relief patterns followed by narrow flat-top angular features. The combination of leaky mode effect and enhanced device topology will enable efficient and useful devices with a bandwidth of 50 nm and even more in the future.

Strong dual-channel nonreciprocal radiation with guided mode resonances

A dual-channel thermal emitter, which is composed of an InAs layer atop an aluminum grating backed with a continuous aluminum film, is proposed and studied. Two resonant absorption and emission peaks are achieved at different wavelengths, leading to the achievement of dual-channel strong nonreciprocal radiations at two different wavelengths for an applied magnetic field of 2 T when the angle of incidence is 17°. The physical origin is revealed through illustrating the electromagnetic field distributions at both resonances and also verified through impedance matching. In addition, the perfect nonreciprocity remains stable within a wide range of structure parameters, lowering the cost of manufacture. Moreover, the nonreciprocal radiations for different incident angles and different magnetic fields are also investigated in detail. The concept and conclusions proposed here will be interesting for the development of novel energy conversion and capture devices.

Gradient Guided-Mode Resonance Biosensor with Smartphone Readout.

Integrating biosensors with smartphones is becoming an increasingly popular method for detecting various biomolecules and could replace expensive laboratory-based instruments. In this work, we demonstrate a novel smartphone-based biosensor system with a gradient grating period guided-mode resonance (GGP-GMR) sensor. The sensor comprises numerous gratings which each correspond to and block the light of a specific resonant wavelength. This results in a dark band, which is observed using a CCD underneath the GGP-GMR sensor. By monitoring the shift in the dark band, the concentration of a molecule in a sample can be determined. The sensor is illuminated by a light-emitting diode, and the light transmitted through the GGP-GMR sensor is directly captured by a smartphone, which then displays the results. Experiments were performed to validate the proposed smartphone biosensor and a limit of detection (LOD) of 1.50 × 10-3 RIU was achieved for sucrose solutions. Additionally, multiplexed detection was demonstrated for albumin and creatinine solutions at concentrations of 0-500 and 0-1 mg/mL, respectively; the corresponding LODs were 1.18 and 20.56 μg/mL.

Polymer-Based Guided-Mode Resonance Sensors: From Optical Theories to Sensing Applications

Polymer-Based Guided-Mode Resonance Sensors: From Optical Theories to Sensing Applications

Ultra-broadband and wide-angle solar absorber with hierarchical nanohole design based on MXene

MXene has received a lot of attention from researchers in the fields of photothermal and photovoltaic due to its excellent optical properties. However, research on MXene-based solar absorbers has rarely been carried out. In this work, we proposed a MXene-based solar absorber with absorption broadband, wide-angle, and polarization insensitive. The absorber has excellent light capture capability, with its average absorption in the solar band as high as 97.8 % and an energy absorption ratio of 98.9 % in the AM1.5 solar radiation spectrum. The electric and magnetic field distributions indicate that the unique hierarchical nanohole design can effectively excite multiple resonance couplings of surface plasmon resonance, cavity resonance, and guided mode resonance. The proposed absorber can still maintain the broadband absorption characteristics within a certain manufacturing tolerances. Moreover, the absorber is insensitive to polarization and has a high light absorption under a large incident angle. We believe that this work holds great promise for solar thermal conversion and heat utilization.

Perfect Absorption and Reflection Modulation Based on Asymmetric Slot-Assisted Gratings without Mirrors.

As a perfect graphene absorber without any external mirrors, we proposed asymmetric slot-assisted grating structures supporting two degenerate resonant modes of the guided-mode resonances (GMR) and the quasi-bound states in the continuum (quasi-BIC). The GMR mode functions as an internal mirror in conjunction with the background scattering, while the quasi-BIC, which is responsible for perfect graphene absorption, stems from the horizontal symmetry breaking by an asymmetric slot. By properly shifting the slot center from the grating center, the leakage rate of quasi-BIC can be controlled in such a way as to satisfy the critical coupling condition. We provide a comprehensive study on the coupling mechanism of two degenerate resonant modes for a one-port system mimicking the resonance. We also numerically demonstrated that our proposed grating structures show an excellent reflection-type modulation performance at optical wavelength ranges when doped double-layer graphene is applied. Due to the perfect absorption at the OFF state, a high modulation depth of ~50 dB can be achieved via a small Fermi level variation of ~0.05 eV. To obtain the lower insertion loss at the ON state, the higher Fermi level is required to decrease the graphene absorption coefficient.

Large nonreciprocity of thermal radiation for transverse electric wave with extremely small incident angle

Violating of traditional Kirchhoff’s law has been a topic of active research because of the possibilities for engineering thermal radiation. An alternative paradigm consisting of zero-contrast gratings (ZCGs) and Weyl semimetal (WSM) interlayer sitting on a silver (Ag) substrate is proposed. Strong nonreciprocal thermal radiation (NTR) has been observed for transverse electric (TE) incidence wave. This structure is highly favorable for standard mask-based nano-fabrication processes. Moreover, the nonreciprocity larger than 0.8 is realized with an extremely small angle of 1°. The mechanism of this proposal is owing to the guided-mode resonance (GMR) supported by the ZCGs and nonreciprocal radiation of WSM, which is confirmed by investigating the amplitude distribution of electric field. The high performance of the NTR can be maintained within wide ranges of structural parameters, which is highly favorable for practical fabrication. The nonreciprocal emitter described herein allows simultaneous control of spectral distribution and polarization of radiation, which will facilitate the active design and application of mid-infrared (MIR) thermal emitters.

Near-infrared switch effect of polarization modulation induced by guided-mode resonance in dielectric grating

Light intensity modulation is crucial for the development of optical imaging, optical sensing, and optical switch. Light intensity modulation methods, such as changing structural parameters, external temperature, or external voltage, make the control process time consuming and complex. The plasmonic polarization modulation is an effective strategy to modulate the light intensity, but this method is limited by the excitation of surface plasmons with transverse magnetic (TM) polarized light. Herein, we report another polarization modulation method for light intensity based on guided mode resonance in a dielectric grating excited by transverse electric (TE) polarized light. The nanosystem comprises a Si grating and a TiN substrate. By adjusting the polarization states of the incident light from TE to TM, the proposed nanosystem exhibits an outstanding light intensity modulation performance with a relative modulation depth of 25833%. The presented method provides another way for modulating the light intensity, which has potential applications in optical switching, optical imaging, and optical anti-counterfeiting.

Merging and Band Transition of Bound States in the Continuum in Leaky‐Mode Photonic Lattices

AbstractBound states in the continuum (BICs) theoretically have the ability to confine electromagnetic waves in limited regions with infinite radiative quality (Q) factors. However, in practical experiments, resonances can only exhibit finite Q factors due to unwanted scattering losses caused by fabrication imperfections. Recently, it has been shown that ultrahigh‐Q guided‐mode resonances (GMRs), which are robust to fabrication imperfections, can be realized by merging multiple BICs in momentum space. This study analytically and numerically investigates the merging and band transition of accidental BICs in planar photonic lattices. Accidental BICs can merge at the edges of the second stop band, either with or without a symmetry‐protected BIC. The results show that as the thickness of the photonic lattice gradually increases, the merged state of BICs transitions from the upper to the lower band edge. Using coupled‐mode analysis, the analytical merging thickness at which multiple accidental BICs merge at the second‐order Γ point is presented. The coupled‐mode analysis can be beneficial for achieving ultrahigh‐Q GMRs in various photonic lattices composed of materials with different dielectric constants.

Promoting second-harmonic generation in the LiNbO3 film combined with metasurface using plasmonic quasi bound states in the continuum

Metasurfaces have become a fascinating framework for nonlinear optics, with the advantages of a compact footprint and unprecedented flexibility to manipulate light. However, further advancements are necessary to enhance the efficiency of metasurfaces in nonlinear devices. Here, a novel approach for second harmonic generation (SHG) based on the LiNbO3 metasurface using leaked plasmonic bound states in the continuum (BIC) is proposed. The behavior of SHG in the guided mode resonance (GMR) under TE polarization and plasmonic modes under TM polarization is investigated. The structure consists of a plasmonic grating overlying a nonlinear lithium niobate dielectric waveguide layer that supports two different BIC, namely plasmonic BIC and GMR BIC. The evolution of second harmonics generation(SHG) near two groups of BIC is explored. The SHG of the plasmonic quasi-BIC is stronger than that based on the GMR quasi-BIC. In addition, the plasmonic accidental quasi-BIC produces stronger harmonic effects than the quasi-BIC based on symmetry-broken. Specifically, at a pump intensity of 30 MW/cm2, this accidental quasi-BIC results in SHG efficiency of 1.86 × 10−3. This work provides a valuable approach to achieving enhanced SHG using plasmonic and BIC. It opens up new possibilities for the utilization of LiNbO3 in integrated nonlinear nanophotonics and paves the way for the development of advanced nonlinear photonic devices.

Molecular Fingerprint Detection with a Mid-infrared Guided-Mode Resonance

Molecular Fingerprint Detection with a Mid-infrared Guided-Mode Resonance

High-resolution biosensing with C-band guided-mode Fano resonance in an all-dielectric structure

An all-dielectric Fano resonance sensor is proposed, and its sensing characteristics are numerically investigated in the near-infrared region. The proposed device comprises two planar waveguides and a grating. The coupling between high- and low-quality-factor guided modes of the waveguides leads to a sharp Fano resonance at the optical communication wavelength of . Owing to the transparency of constituent dielectric layers in the near-infrared region, a sharp, low-loss Fano resonance appears in the reflection spectrum, which is favorable in sensing applications. The proposed sensor can detect small changes in the refractive index of the sensing medium as low as . The high sensitivity of a structure is promising in biochemical applications, such as measuring the refractive indices of organic solvents, the level of water content in ethanol and aqueous solutions, and blood glucose levels. The refractive index sensitivity is as high as λ=1550nm, and a figure of merit of Δn=0.001 is achieved.

Ultra-narrowband circular dichroism in all-dielectric chiral nanohole arrays based on griddings and monolayer MoS2

The strong circular dichroism (CD) of metallic chiral nanostructures can be applied to polarization conversion, negative refraction materials, and chiral molecule detection. However, metallic chiral nanostructures with losses struggle to produce dynamically tunable ultra-narrow band circular dichroism signals, which greatly limits their applications in sensing. In this paper, the MoS2 and Sb2S3 with phase change characteristics are introduced into all-dielectric chiral nanopore arrays (ACNAs) based on gridding to generate dynamically tunable ultra-narrow band circular dichroism signals. Simulation results show that ACNAs/MoS2 produce two strong narrow-band CD signals in the visible range. The maximum CD intensity can reach 0.75, and the maximum half-width can reach 0.8 nm. The electric field distribution indicates that two CD signals are mainly caused by the guided mode resonance. The ultra-narrow band CD signals both lie on their geometric parameters and can realize the dynamic regulation by changing the incidence angle of lights and the crystalline state of Sb2S3. Furthermore, the sensing characteristics of this device were evaluated by analyzing the effects of different concentrations of SARS-CoV-2 solutions on the CD spectra. These findings will facilitate the design of all-dielectric chiral nanostructures with dynamically tunable ultra-narrow band CDs and facilitate their applications in biosensing.

Design and performance evaluation of a novel metamaterial broadband THz filter for 6G applications

Terahertz (THz) radiation, which has applications in the imaging of objects, non-destructive testing, satellite communication, medical diagnostics, and biosensing, has generated a great deal of attention due to its remarkable properties. This paper proposes a novel broadband filter for THz applications. The main idea is to overcome the insertion loss and bandwidth issues by modeling a frequency-domain finite difference method and guided-mode resonance (GMR). The optimal design scheme of the wideband pass filter based on the circular resonant ring is discussed by comparing the transmission parameters under various parameters. This scheme overcomes the restriction of the narrow passband bandwidth of the prior THz filters and achieves approximately 3 dB bandwidth of 0.54 THz. The proposed THz filter paper also has the advantages of a straightforward structure, low processing costs, and ease of conformal with other structures, and it can be used for stealth fighters, new communication technology, and precise instruments. In addition, when compared to existing models, the suggested filter offers higher 3 dB BW operation, increased transmittance, low insertion loss, and stable performance at various oblique angles.

High-Q Quasi-Bound States in the Continuum in Terahertz All-Silicon Metasurfaces.

Bound states in the continuum (BIC)-based all-silicon metasurfaces have attracted widespread attention in recent years because of their high quality (Q) factors in terahertz (THz) frequencies. Here, we propose and experimentally demonstrate an all-silicon BIC metasurface consisting of an air-hole array on a Si substrate. BICs originated from low-order TE and TM guided mode resonances (GMRs) induced by (1,0) and (1,1) Rayleigh diffraction of metagratings, which were numerically investigated. The results indicate that the GMRs and their Q-factors are easily excited and manipulated by breaking the lattice symmetry through changes in the position or radius of the air-holes, while the resonance frequencies are less sensitive to these changes. The measured Q-factor of the GMRs is as high as 490. The high-Q metasurfaces have potential applications in THz modulators, biosensors, and other photonic devices.

Guided mode resonance immunosensor for label-free detection of pathogenic bacteria Pseudomonas aeruginosa

Photonic biosensors are promising platforms for the rapid detection of pathogens with the potential to replace conventional diagnostics based on microbiological culturing methods. Intricately designed sensing elements with robust architectures can offer highly sensitive detection at minimal development cost enabling rapid adoption in low-resource settings. In this work, an optical detection scheme is developed by structuring guided mode resonance (GMR) on a highly stable, transparent silicon nitride (SiN) substrate and further biofunctionalized to identify a specific bacteria Pseudomonas aeruginosa. The resonance condition of the GMR chip is optimized to have relatively high bulk sensitivity with a good quality factor. The biofunctionalization aims at oriented immobilization of specific antibodies to allow maximum bacteria attachment and improved specificity. The sensitivity of the assays is evaluated for clinically relevant concentrations ranging from 102 to 108 CFU/mL. From the calibration curves, the sensitivity of the chip is extracted as 0.134nm/Log10 [concentration], and the detection modality possesses a favorably good limit of detection (LOD) 89 CFU/mL. The use of antibodies as a biorecognition element complemented with a good figure of merit of GMR sensing element allows selective bacteria identification compared to other non-specific pathogenic bacteria that are relevant for testing physiological samples. Our developed GMR biosensor is low-cost, easy to handle, and readily transformable into a portable handheld detection modality for remote usage.

Near-perfect multi-band graphene absorber with a compound grating-based resonant structure

We proposed a multi-band graphene absorber composed of a resonant compound grating (RCG), monolayer graphene, a thin silver layer, and a distributed Bragg reflector (DBR). A multi-band near-perfect absorption spectrum can be determined by three different physical mechanisms, including guided mode resonance (GMR), quasi-bound states in the continuum (quasi-BIC), and Tamm plasmon polaritons states (TPPs). Interestingly, the quasi-BIC mode can be achieved by changing grating layer spacing. In addition, the BIC mode can also be realized by varying grating periods. The variation of the absorption peak can be observed by changing the spacing layer thickness of the DBR structure, and the waveguide layer and grating layer thickness of the compound grating. Simulation results show that the absorption peaks of the three modes excited by our proposed absorbers are high as 80% at an incident light angle of 25°.

Design of multi-wavelength demultiplexing coupler based on DBS algorithm

The optical coupler can couple the light from the fiber into the waveguide, and the wavelength demultiplexer can split light into different wavelengths. Both devices play a significant role in optical chips, and combing them together can further reduce the chip footprint and improve the operating efficiency. In this work, based on the direct-binary-search (DBS) inverse design algorithm, we design two metamaterial couplers that can realize multi-wavelength demultiplexing. The two devices are based on silicon on insulator (SOI) and cover an ultra-compact footprint of 3.6 μm × 3.6 μm. The first device can couple and split 1310 nm and 1550 nm light into two separate waveguides with coupling efficiencies of 0.26 and 0.27, respectively. The second device can couple and split 1310 nm, 1490 nm, and 1550 nm light into three separate waveguides with coupling efficiencies of 0.25, 0.2, and 0.23, respectively. This effect is caused by the large number of guide-mode resonances in the device. The two couplers, especially the three-wavelength demultiplexing coupler, can be used as splitters for monolithically silicon-integrated transceivers at the commonly used wavelengths of 1310 nm, 1490 nm, and 1550 nm in the optical fiber communication, which potentially meets the low-cost and ultra-compact requirements for future passive optical networks.