Guided Mode Resonance Structure Research Articles

Low-threshold lasing behavior assisted by the asymmetric grating profile in the guided-mode resonance structure

We present a nanoscale laser based on an asymmetric guided-mode resonance (AGMR) structure. The AGMR creates hybrid resonant modes, which consist of the newly generated quasi-bound states in the continuum (quasi-BICs) and the intrinsic GMR mode. By modifying the structural parameters, the GMR and quasi-BICs modes can be matched with the pump and emission wavelengths of the gain medium, respectively. Therefore, high-intensity near fields of the GMR as the resonant optical pumping mode and high quality (Q) factor of the quasi-BICs as the resonant-emitting mode jointly contribute to the low-threshold lasing behavior. The finite-difference time-domain method is used to analyze the lasing characteristics, and a threshold of 14.2 μJ/cm2 is obtained, which is approximately ten times lower than that of a single-coupled mode laser. By adjusting the asymmetry parameters and fill factor of the grating, the threshold can be further reduced to 8.9 μJ/cm2. Additionally, we have also studied the feasibility of the AGMR structure by adjusting the simulation boundary conditions from periodic to perfectly matched layer to simulate a finite-sized structure. The findings provide a new way to excite hybrid modes, opening up possibilities for applications that demand highly confined fields and high Q-factors.

Strong coupling in an asymmetric two-dimensional guided mode resonance metasurface structure and enhancement for optical third-harmonic generation

A two-dimensional guided mode resonance structure supports a transverse magnetic (TM) resonant mode in the direction of incident polarization and a transverse electric (TE) resonant mode in the direction perpendicular to the polarization. In this work, the coupling between the transverse magnetic and the transverse electric resonant modes in an asymmetric two-dimensional dielectric metasurface structure is investigated. The asymmetric structure consists of a two-dimensional square nanohole array etched in a titanium dioxide thin film on a transparent silica substrate. With finite difference time domain simulations, anti-crossing of the resonant spectra of the TM and TE modes is observed by adjusting the asymmetry of the structure. The anti-crossing indicates that the interaction between TM and TE resonant modes results in a strong coupling state. A coupled harmonic oscillator model is used to explain the strong coupling effect. The results of the coupled harmonic oscillator modeling agree well with the results of numerical simulations. Furthermore, it is shown that the strong coupling can significantly enhance the third harmonic generation intensity compared with the uncoupled TM and TE resonant modes.

Exploring tunable single-wavelength detection schemes for guided-mode resonance sensors

We explore guided-mode resonant (GMR) structures in an unconventional way for low-cost yet effective bio-sensing applications. In contrast to regular broadband source-based wavelength interrogation techniques, single wavelength-based measurements can successfully eliminate the requirement of a costly spectrometer for rapid label-free detection and analysis. We have fabricated a silicon–nitride grating-waveguide structure and investigated it theoretically as well as experimentally under normal, angular, and conical incidences following an all-in-one transmission geometry. Such studies avoid unnecessary fabrication of multiple chips and promote a wide operational range of the GMR sensor. To validate the proposed cost-effective intensity-based sensing, we have analyzed our fabricated single GMR chip under different combinations of two-axis rotation to confirm its suitability under commonly available laser sources. Finally, using a He-Ne laser, a sensitivity of ∼ 166 mW/RIU is recorded experimentally on an average for the fabricated GMR device, operating at the resonant wavelength of 632.8 nm. The current study provides an in-depth investigation to promote possibilities for utilizing GMR structures in an inexpensive intensity-based bio-detection scheme through the demonstrated proof-of-concept.

Design of narrowband infrared emitters by hybridizing guided-mode resonance structures with van der Waals materials

In this paper, narrowband emitters have been designed using particle swarm optimization (PSO) in the 10–20 μm infrared range. The device structure consists of an anisotropic α-MoO3 layer combined with the one- and two-dimensional guided-mode resonance structures. Well-defined absorption lines are present in the reflection spectrum for both TE and TM polarizations, thereby yielding narrowband emissivity at desired wavelengths. The band structure of the designed emitters under TM polarization demonstrates distinct features unlike its TE counterpart. These features are attributed to the interaction between guided-mode resonances and phonon polaritons. The results are relevant for applications in active and passive photonic elements in mid- and long-wave IR bands.

Multimode experimental band dynamics of resonant nanophotonic lattices.

Subwavelength resonant lattices provide a host of interesting spectral expressions on broadside illumination. The resonance mechanism is based on generation of lateral Bloch modes phase matched to evanescent diffraction orders. The leaky mode structure and mode count determine the spectra and the number of resonance states. Here, we study band flips and bound-state transitions in guided-mode resonant structures supporting multiple resonant modes. We present theoretical simulations and experimental results for a subwavelength silicon-nitride lattice integrated with a liquid film with adjustable boundary. The relatively thick liquid waveguiding region supports additional modes such that the first four transverse-electric (TE) leaky modes are present and generate observable resonance signatures. By varying the duty cycle of the basic lattice in experiment, the 4 bands undergo band transitions and band closures as quantified herein. The experimental results taken in the 1400-1600 nm spectral region agree reasonably well with numerical analysis.

Guided mode resonance aided polarization insensitive in-plane spectral filters for an on-chip spectrometer.

We demonstrate an on-chip in-plane polarization independent multi-spectral color filter in the visible to near-infrared wavelength band. We experimentally show a four-channel transmission and in-plane spectral filter characteristics spanning a 400-nm spectral range. Engineered 2D guided mode resonance structures in a silicon nitride-on-sapphire substrate are used to realize the filters. The in-plane color filters could provide the necessary impetus for developing robust integrated photonic platforms for on-chip devices and applications.

Analytical Investigation and Systematic Design Approach for High-Sensitivity Guided Mode Resonance Sensors With Graphene-Enabled Tunability

The high quality factor of guided mode resonance (GMR) structures and their sensitivity to the adjacent media’s refractive index (RI) make them excellent candidates for sensing applications. In this study, we derive analytical sensitivity equations for the GMR structures for the first time, which can be utilized to better understand and optimize their behavior. The simulated structures (based on the finite element method) show excellent agreement with the analytical sensitivities for both the transverse electric and magnetic (TE and TM) modes. The effects of waveguide height, working wavelength, and material RIs on the obtained sensitivities were surveyed, which helped achieve a design approach based on the analytical equations. The substrate RI should be as low as possible for any application. For analytes, the RI of the waveguide thin film should be low, whereas this trend is different for gas sensors; there is an optimum RI for the waveguide in the TE mode, and in the TM mode, the waveguide should have a higher possible RI. Moreover, the TM-mode gas sensors exhibit optimum sensitivity for a specified waveguide height. The design approach was used for a gas sensor operating at methane resonance wavelength (1653.7 nm), which can be tuned using a double-layer graphene sheet. A linear tunability of up to 5 nm was achieved using 1 eV chemical potential adjustment, whereas the device sensitivity remains between 291.9 to 295.5 nm/RIU. Moreover, higher sensitivities up to 950 nm/RIU can be obtained for analyte sensors at 1550 nm.

Focus-engineered sub-diffraction imaging in infrared-sensitive third-order sum frequency generation microscope.

We experimentally demonstrate sub-diffraction imaging in infrared-sensitive third-order sum frequency generation (TSFG) microscope using focal-field engineering technique. The TSFG interaction studied here makes use of two mid infrared photons and a single 1040 nm pump photon to generate up-converted visible photons. Focal field engineering scheme is implemented using a Toraldo-style single annular phase mask imprinted on the 1040 nm beam using a spatial light modulator. The effect of focal field engineered excitation beam on the non-resonant-TSFG process is studied by imaging isolated silicon sub-micron disks and periodic grating structures. Maximum reduction in the measured TSFG central-lobe size by ∼43% with energy in the central lobe of 35% is observed in the presence of phase mask. Maximum contrast improvement of 30% is observed for periodic grating structures. Furthermore, to validate the infrared sensitivity of the focus engineered TSFG microscope, we demonstrate imaging of amorphous Germanium-based guided-mode resonance structures, and polystyrene latex beads probed near the O-H vibrational region. We also demonstrate the utility of the focus engineered TSFG microscope for high resolution imaging of two-dimensional layered material. Focus-engineered TSFG process is a promising imaging modality that combines infrared selectivity with improved resolution and contrast, making it suitable for nanostructure and surface layer imaging.

Third harmonic generation enhancement from silicon-based multilayer guided mode resonance structures under a conical mounting condition

We experimentally demonstrate more than four-orders of magnitude enhancement in third harmonic generation from an amorphous silicon layer as thin as 10 nm deposited above silicon nitride guided mode resonance (GMR) structures under a conical mounting condition using a rectangular aperture as a pupil plane mask for the fundamental excitation. The multilayer GMR structure studied here consists of shallow etched one-dimensional silicon dioxide gratings with a silicon nitride intermediate layer and an amorphous silicon nonlinear medium. Under conical mounting, by restricting the fundamental excitation angles along the grating vector direction, while retaining the angles supported by the objective lens along the grating lines, the resonances are made angle insensitive. The forward detected THG enhancement increases from 2860 in the absence of any pupil plane mask, with a uniform fundamental excitation angular span of 2.3° to 4740 and 1.7 × 104 in the presence of rectangular apertures that selectively reduce the excitation angular span along the grating vector direction to 0.86° and 0.43°, respectively. Conical mounting using rectangular aperture pupil masks to engineer the fundamental excitation is a promising approach to enhance nonlinear optical processes from angle sensitive GMR structures.

Controllable lasing behavior enabled by the transmission guided-mode resonance effect in coupled gratings

A new type of dye laser is proposed based on a guided-mode resonance (GMR) transmission structure using coupled gratings. By distributing the laser dye in the coupled gratings, controllable transmission lasing behavior was simulated. The structure excites the transmission GMR effect and causes a strong local electric field in the coupled gratings, inducing the slow light effect, which in turn enhances the interaction between light and matter. The proposed GMR structure guides laser emission in the transmission direction. Two structures with resonant wavelengths of 820 nm and 870 nm were designed and compared. A higher laser intensity can be obtained in the structure with resonance at 870 nm and a corresponding threshold and half-height width of 1.24 × 107 V/m and 0.8 nm, respectively. In addition, the lasing wavelength can be tuned by changing the relative position of the coupled gratings. The proposed structure is desirable for the construction of other light-emitting devices.

Mid-infrared quasi-BIC resonances with sub-wavelength slot mode profiles in germanium-based coupled guided-mode resonance structures

We experimentally demonstrate a novel quasi-bound state in the continuum (BIC) resonance in the mid-infrared wavelength region with the resonant electric field confined as a slot mode within a low-refractive-index medium sandwiched between high-index layers. The structures studied here comprise coupled amorphous germanium guided-mode resonance (GMR) structures with a top one-dimensional grating layer and bottom uniform layer separated by a low-index silicon nitride layer. The slot-mode profile within the silicon nitride layer with mode field confinement > 30 % is achieved as a solution to the electromagnetic wave propagation through the coupled GMR structure with the dominant field component being perpendicular to the layers. The quasi-BIC resonance in symmetric 1D grating structures can be observed even at normal incidence when considering a realistic excitation beam with finite angular spread. The measured transmission peak is found to redshift (remain almost unchanged) under classical (full-conical) mounting conditions. The highest quality factor of ∼ 400 is experimentally extracted at normal incidence under a classical mounting condition with a resonance peak at 3.41 μm wavelength. Such slot-mode GMR structures with appropriately chosen low-index intermediate layers can find applications in resonantly enhanced sensing and active photonic devices.

Resonant mode engineering in silicon compatible multilayer guided-mode resonance structures under Gaussian beam excitation condition

In this work we present detailed electromagnetic design, fabrication, and experimental study of silicon-compatible, step-index, multilayer guided-mode resonance structures. The proposed multilayer stack consists of an amorphous silicon overlayer deposited above a silicon nitride layer on top of one-dimensional sub-wavelength silicon dioxide grating structures. The silicon nitride layer combined with the underlying silicon dioxide gratings define the high-quality factor resonances in the 1500–1600 nm wavelength range. The addition of the amorphous silicon overlayer with varying thickness further red-shifts the resonance combined with the ability to engineer the resonant field profile and its evanescent field fraction. Realistic Gaussian beam excitation with increasing angular spread exciting finite extent gratings results in reduced contrast and quality factor of the designed resonances are found to decrease. We experimentally study the linear transmission spectra for the fabricated structures with amorphous silicon overlayer thickness of 10, 50 and 100 nm. The measured optical resonances are at 1580, 1813 and 2104 nm respectively, showing good agreement with Gaussian-beam excitation studies. As an application of the proposed structures, we demonstrate third-harmonic generation (THG) enhancement from the 10 nm amorphous silicon overlayer showing 19 and 178-times enhancement in THG for fundamental excitation with 11° and 4° angular spread respectively. The present work utilizes the thinnest amorphous silicon layer to achieve optical resonances in the near-infrared wavelength and consequently ensures minimum absorption of the generated THG signal when used for nonlinear optical enhancement studies.

Resonant reflection by microsphere arrays with AR-quenched Mie scattering.

Periodic guided-mode resonance structures which provide perfect reflection across sizeable spectral bandwidths have been known for decades and are now often referred to as metasurfaces and metamaterials. Although the underlying physics for these devices is explained by evanescent-wave excitation of leaky Bloch modes, a growing body of literature contends that local particle resonance is causative in perfect reflection. Here, we address differentiation of Mie resonance and guided-mode resonance in mediating resonant reflection by periodic particle assemblies. We treat a classic 2D periodic array consisting of silicon spheres. To disable Mie resonance, we apply an optimal antireflection (AR) coating to the spheres. Reflectance maps for coated and uncoated spheres demonstrate that perfect reflection persists in both cases. It is shown that the Mie scattering efficiency of an AR-coated sphere is greatly diminished. The reflectance properties of AR-coated spherical arrays have not appeared in the literature previously. From this viewpoint, these results illustrate high-efficiency resonance reflection in Mie-resonance-quenched particle arrays and may help dispel misconceptions of the basic operational physics.

Tunable dual-wavelength absorption switch with graphene based on an asymmetric guided-mode resonance structure.

We propose a tunable dual-wavelength absorption (TDWA) switch based on an asymmetric guided mode resonance (AGMR) structure. A TDWA switch consists of a graphene layer and an AGMR structure sandwiched by cap and slab layers on a buffer/silicon substrate. The AGMR structure adds a smaller grating unit cell next to a larger one, exciting a second resonance close to but distinct from the first resonance. For switching, the TDWA between an absorptive or reflective mode with each on-/off-state, the chemical potential of graphene is tuned from 0.0 eV to 0.6 eV. For the absorptive mode, two absorption peaks of ≥ 96.2% are separated by 23 nm, both having an on-off ratio of ∼15.52. For the reflective mode, two reflectance peaks of ≥ 93.8% are separated by 23 nm, having on-off ratios of 15.56 dB and 18.95 dB. The maximum on-off ratios of 39.98 dB and 34.55 dB are achieved near the reflectance peaks. Both the period of the AGMR and the cap thickness alters the two peak wavelengths linearly, while the grating width of the AGMR varies nonlinearly from 17 nm to 28 nm. The buffer excites a weak Fabry-Perot resonance, which interacts with the TDWA structure, the result of which is the two absorption peaks are varied. Finally, as the incidence angle of light increases up to 5.3°, the distance of the two peak wavelengths is tuned from ∼22 nm to ∼77 nm with ≥ 96% absorption or ≥ 93% reflectance in each mode.

Optimization of two-dimensional metal-assisted guided mode resonance based structures for sensing applications in the visible region

The design, optimization, and analysis of two-dimensional metal-assisted guided mode resonance (MAGMR) based sensing structures have been presented focusing on the visible range of operation. The study has been conducted for square and hexagonal lattice geometries and the sensing properties and performance of the MAMGR structures have been compared with the traditional guided-mode resonance (GMR) structures sharing identical design parameters. The effect of various design parameters on the individual resonant polarization modes has also been investigated and the superior bulk sensitivities of the MAGMR structures have been highlighted in comparison with the GMR structures.

Enhanced dye lasing emission by guided-mode resonance grating with mesoporous silica as spacing layer

<sec>The enhancement of lasing emission intensity of dye laser is particularly important and urgently required due to a broad range of optical and electrical applications. The guided-mode resonance (GMR) effect occurs in a periodic waveguide structure where an incident wave is coupled to a leaky waveguide mode, and yields a resonance peak. The resonance wavelength can be easily controlled by adjusting the period of the grating, thickness of the waveguide layer, and refractive index of the covering materials. By using band edge states, one may be able to excite optical resonances extended over the entire structure surface, thereby achieving field enhancement over a large area. In this study, mesoporous silica with low refractive index is introduced between the grating layer and the substrate layer of the GMR structure to significantly enhance the contact between local electric field and gain medium. For comparison, another structure using SU-8 with high refractive index as the spacing layer is also proposed. It is clearly observed that the maximum of the electric field intensity is highly localized inside the SU-8 waveguide grating layer. However, it is shifted upward to the gain medium layer in the mesoporous silica structure due to the reverse symmetry waveguide structure design. Therefore, the interaction between laser dye and electric field is increased to further enhance the lasing emission.</sec><sec>Besides the refractive index, the waveguide layer, other structural parameters such as thickness of each layer and grating period also affect the electric field distribution in the GMR structure. Based on the finite-difference time-domain method, the structural parameters are analyzed and optimized. According to the simulation results, the structure parameters T<sub>WG</sub> = 3.5 μm, <i>Λ</i> = 700 nm, and <inline-formula><tex-math id="Z-20201229080229-1">\begin{document}$ T_{\rm TiO_2} = 20 $\end{document}</tex-math><alternatives><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="1-20201017_Z-20201229080229-1.jpg"/><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="1-20201017_Z-20201229080229-1.png"/></alternatives></inline-formula> nm are chosen as the guideline for designing the dye laser, which generates the resonance wavelength of 820 nm the same as the absorption wavelength of dye molecules. Additionally, the laser characteristics excited by pump light with the wavelength of 820 nm are studied. The continuous laser output is obtained. The energy threshold is about 2.5 mJ/cm<sup>2</sup>, and the linewidth is about 0.3 nm. The proposed structure can effectively regulate the surface local electric field and enhance the interaction between pump light and gain medium. It can not only be used in lasers, but also provide reference for designing other light-emitting devices.</sec>

Guided-mode resonance-based bandpass filter operating at full conical mounting.

We propose a cost-effective narrow bandpass filter based on a guided-mode resonance (GMR) structure, operating at full conical mounting configuration. Two additional layers above the GMR structure with designed geometry is considered to create a large angle of incidence (AOI) on the GMR structure with an almost normal AOI on the entire structure. In the visible wavelength range, the transmission spectrum contains three peaks: two peaks that are due to the GMR effect and one that is due to thin-film interference. The modal characteristic of the two GMR peaks is identified using a matrix method for the n-layer waveguide structure. The two GMR peaks with bandwidths of ∼1nm and ∼0.5nm correspond to the fundamental TE and TM modes, respectively. The GMR peaks can be pushed away from the thin-film interference peak by modulating the grating depth.

High azimuthal angle tolerant dual-channel wavelength filter from visible to NIR using conically mounted guided mode resonance structures.

We present a concept to design narrow linewidth dual-channel wavelength filters using the principle of wavelength tuning under conical mounting of guided mode resonance structure. The general procedure for the design of such filters from visible to NIR wavelength range is presented and validated experimentally. We show that already fabricated guided mode resonance structures that do not show dual wavelength filtering at these wavelengths in classical mounting can exhibit dual wavelength filtering in conical mounting. Using this principle, we design high azimuthal angle tolerant guided mode resonance dual wavelength filters at C-band communication wavelengths (1310 and 1550 nm) that are insensitive to azimuthal angle over a range of up to 20 deg, achieved in expense of a tolerance in the angle of incidence that is less than 3 deg.

Enhanced sensitivity of guided mode resonance sensor through super-mode excitation at near cut-off diffraction

This work theoretically and experimentally demonstrates sensitivity enhancement in dielectric guided mode resonance (GMR) sensor via controlling a super-mode resonance at nearly cut-off diffraction (or at Rayleigh wavelength.) A bulk refractive index sensitivity can reach the upper limit at the value linearly proportional to the grating’s periodicity. Super-mode excitation in the multilayer configuration of the 2D GMR sensor (a high refractive index film coated on a low refractive index imprinted grating) is demonstrated. This concept is verified using numerical calculations: Rigorous Coupled Wave Analysis (RCWA) and Homogeneous Waveguide Approximation (HWA). Modal allocation for each resonance in the GMR structure is performed using the approximated four-layer waveguide. The measured super-mode resonance has shown sensitivity enhancement almost three folds of that of the traditional guide mode resonance. Also, this realization occurs in a broad dynamic range through optimization of the structure’s parameters. This guarantees a usage in multiple sensing applications.

Polarization-independent absorption enhancement in graphene for light incidence in conical mounting

A terahertz graphene tunable absorber consisting of monolayer graphene on a dielectric grating and a substrate separated by a waveguide layer is designed and investigated. The absorber exhibits polarization-independent absorption enhancement at resonance for fully conical light incidence, which is attributed to the simultaneous excitation of two identical guided modes in the waveguide layer. Moreover, the absorber possesses an ultranarrow absorption profile with an ultrahigh quality factor. To intuitively confirm the potential physical mechanism of such phenomena, the electromagnetic field distributions for both polarized light are described. Finally, the influences of Fermi level and relaxation time on the absorption properties are investigated, which present the flexible tunability of the proposed device. It is believed that the conclusions will enable the development of optoelectronic devices by simply combining graphene with a guided-mode resonance structure.