Guided-mode Resonance Research Articles

Longwave infrared polarization independent monolithic guided-mode resonance filters with double-sided orthogonal linear gratings

We present novel polarization independent, high-quality monolithic spectral filters based on the guided-mode resonance (GMR) effect with orthogonal linear gratings on either side of the substrate operating in the longwave infrared (LWIR) spectral region. We employ high-spatial resolution e-beam lithography and reactive-ion etching (RIE) nanofabrication techniques to achieve large-area (10×10 mm2) notch filters with subwavelength features. We fabricated prototype filters and characterized their polarization independent spectral performance with both coherent and incoherent incident light using a tunable quantum cascade laser (QCL) system that spans the ∼8–12 µm spectral band as well as a Fourier transform infrared (FTIR) spectrometer with collimated incident beam.

A Theoretical Description of Node-Aligned Resonant Waveguide Gratings

Waveguide gratings are used for applications such as guided-mode resonance filters and fiber-to-chip couplers. A waveguide grating typically consists of a stack of a single-mode slab waveguide and a grating. The filling factor of the grating with respect to the mode intensity profile can be altered via changing the waveguide’s refractive index. As a result, the propagation length of the mode is slightly sensitive to refractive index changes. Here, we theoretically investigate whether this sensitivity can be increased by using alternative waveguide grating geometries. Using rigorous coupled-wave analysis (RCWA), the filling factors of the modes of waveguide gratings supporting more than one mode are simulated. It is observed that both long propagation lengths and large sensitivities with respect to refractive index changes can be achieved by using the intensity nodes of higher-order modes.

Weakly coupled hybrid guided mode resonance optical transmission filter

Hybrid metal-dielectric guided mode resonance devices have an advantage over the all-dielectric guided mode resonance device for having a thin metal grating conductive layer that can be used as an electrode for tunable applications. In this work, we investigate the coupling between the waveguide mode and surface plasmons of the gold nanoslits grating in the hybrid guided mode resonance filter. It is shown that the coupling between the waveguide mode and surface plasmons can be engineered by increasing either the thickness of the low index of the refraction spacing layer or the thickness of the high index of the refraction waveguide layer. Therefore, a narrow spectral linewidth and a high finesse of hybrid guided mode resonance filters can be obtained by increasing the thickness of the low index of the refraction spacing layer or the thickness of the high index of the refraction waveguide layer. A hybrid guided mode resonance transmission filter with a narrow spectral linewidth of 2.8 nm is designed at the 1660.2 nm center wavelength.

Terahertz bound states in the continuum with incident angle robustness induced by a dual period metagrating

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 metasurfaces are limited to specified incident angles that seriously dim their application prospects. Here, we propose that a dual-period dielectric metagrating can support multiple families of BICs that originate from guided mode resonances in the dielectric grating and exhibit infinite quality factors at arbitrarily tilted incidence. This robustness was analyzed based on the Bloch theory and verified at tilted incident angles. We also demonstrate that inducing geometric asymmetry is an efficient way to manipulate the leakage and coupling of these BICs, which can mimic the electromagnetically induced transparency (EIT) effect in our dual-period metagrating. In this demonstration, a slow-light effect with a measured group delay of 117 ps was achieved. The incidence-insensitive BICs proposed here may greatly extend the application scenarios of the BIC effect. The high Q factor and outstanding slow-light effect in the metagrating show exciting prospects in realizing high-performance filters, sensors, and modulators for prompting terahertz applications.

Broadband terahertz guided-mode resonance filter using cyclic olefin copolymer.

We propose an all-dielectric single-layer guided-mode resonance filter (GMRF) operating in the high-frequency terahertz (THz) region. For the fabrication of thin gratings to achieve strong resonance in the high-frequency region, the refractive index and absorption must be small, while the tensile strength must be high. Cyclic olefin copolymer (COC) films have a lower refractive index and absorption than polyethylene terephthalate (PET) films and a higher tensile yield strength than polytetrafluoroethylene (PTFE) films. Therefore, the COC film was found suitable to fabricate a GMRF operating in the high-frequency THz region. We fabricated COC-based single-layer GMRFs with a thickness of 50 µm and grating periods of 500, 400, 300, 200, and 100 µm; the resonance frequencies of the TE0,1 mode were 0.576, 0.712, 0.939, 1.329, and 2.759 THz, respectively. A shorter grating period caused a greater shift of the resonance to a higher frequency. In particular, the COC film enabled the fabrication of a 100-µm grating period with a ridge width of 32 µm and length of 2 mm, enabling the GMRF to operate up to 2.759 THz, which is very high frequency compared to the previous highest frequency of 0.7 THz. These results were in good agreement with a simulation using rigorous coupled-wave analysis.

High-Q and tunable analog of electromagnetically induced transparency in terahertz all-dielectric metamaterial.

We propose a novel all-dielectric metamaterial (ADMM), to the best of our knowledge, with a simple structure to achieve the analog of electromagnetically induced transparency (EIT) in the terahertz range. The ADMM is constructed by unit cells with two same silicon bar resonators on a quartz substrate. By breaking the symmetrical array of silicon resonators, the guided-mode resonance can be excited in the substrate, and the destructive interference between a broadband electric-dipole resonance and a narrowband guided-mode resonance gives rise to an EIT-like response. The EIT window can reach a high quality factor (Q-factor) over 1500 by carefully adjusting the asymmetry degree within the unit cell. A dynamically tunable ADMM was further developed by employing photoactive doped silicon. By varying the carrier density of the doped silicon through optical pump, the strength of the EIT-like resonance can be actively modulated, enabling an on-to-off switch of the slow-light effect. The designed ADMM can achieve a high-Q EIT-like response and dynamic modulation, which may give potential applications in bio/chemical sensing, optical switching, and slow-light devices.

Fabrication and Investigation of Spectral Properties of a Dielectric Slab Waveguide Photonic Crystal Based Fano-Filter

In this paper, we discuss the fabrication of a dielectric photonic crystal (PhC)-based Fano-filter device, as well as a numerical investigation of its spectral characteristics. The process parameters affecting the structural and physical properties of the fabricated device are discussed in detail, along with their influence on the spectral properties of the filter. The considered experimental problem is a three-layered PhC structure, fabricated using focused ion-beam (FIB) technology, designed to operate in the near-infrared (NIR) range. The studied parameters include the shape of PhC elements, depth of the structures, cladding layer thicknesses, and the refractive index of the material. Numerical design and simulations are performed using an open-source python-based Finite-difference time-domain (FDTD) simulation tool. The proposed optical filter device operates based on the principle of guided-mode resonance, and achieved a maximum quality factor value in the range of 800.

High-Sensitivity Phase Detection of Reflection-Type Guided-Mode Resonance Sensor Based on Rotating Azimuth Angle Using a Heterodyne Interferometer

A high-sensitivity phase-detection system is proposed for a reflection-type guided-mode resonance (GMR) sensor, which achieves the resonance condition by rotating the azimuth angle and utilizes an electro-optic (EO) heterodyne interferometer. By rotating the GMR sensor azimuthally, the direction of the reflected light can be maintained in reflection-type detection, and the optical system can be compactly constructed because the light-tracking rotation stage is not required. The phase-detection sensitivity can be enhanced in this common-path EO heterodyne interferometer by rotating the analyzer in front of the photodetector; therefore, this system can achieve both a high sensitivity and low limit of detection. Numerical and experimental results of the reflectivity and phase response curves versus the azimuth angle were compared. The proposed system was used to perform gas sensing, and its detection sensitivity and limit were 3.73 × 104 deg/RIU and 2.68 × 10−7 RIU, respectively.

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.

Plasmon-Induced Transparency for Tunable Atom Trapping in a Chiral Metamaterial Structure.

Plasmon-induced transparency (PIT), usually observed in plasmonic metamaterial structure, remains an attractive topic for research due to its unique optical properties. However, there is almost no research on using the interaction of plasmonic metamaterial and high refractive index dielectric to realize PIT. Here, we report a novel nanophotonics system that makes it possible to realize PIT based on guided-mode resonance and numerically demonstrate its transmission and reflection characteristics by finite element method simulations. The system is composed of a high refractive-index dielectric material and a two-dimensional metallic photonic crystal with 4-fold asymmetric holes. The interaction mechanism of the proposed structure is analyzed by the coupled-mode theory, and the effects of the parameters on PIT are investigated in detail. In addition, we first consider this PIT phenomenon of such fields on atom trapping (87Rb), and the results show that a stable 3D atom trapping with a tunable range of position of about ~17 nm is achieved. Our work provides a novel, efficient way to realize PIT, and it further broadens the application of plasmonic metamaterial systems.

Polarization-independent optical spatial differentiation with a doubly-resonant one-dimensional guided-mode grating.

We report on the design and experimental characterization of a suspended silicon nitride subwavelength grating possessing a polarization-independent guided-mode resonance at oblique incidence. At this resonant wavelength we observe that the transverse intensity profile of the transmitted beam is consistent with a first-order spatial differentiation of the incident beam profile in the direction of the grating periodicity, regardless of the incident light polarization. These observations are corroborated by full numerical simulations. The simple one-dimensional and symmetric design, combined with the thinness and excellent mechanical properties of these essentially loss-free dieletric films, is attractive for applications in optical processing, sensing and optomechanics.

Independently tunable multi-band terahertz absorber based on graphene sheet and nanoribbons.

A multi-band terahertz (THz) absorber based on graphene sheet and nanoribbons is proposed and investigated. In the studied frequency range, five absorption peaks are observed, with four originate from lateral Fabry-Perot resonance (LFPR) and one originates from guided-mode resonance (GMR). The LFPR and GMR peaks behave differently when geometric parameters are adjusted, which makes independent tuning possible. When period increases, the GMR peak red shifts and the frequencies of LFPR peaks remain almost unchanged. On the contrary, as nanoribbon width increases, the frequency of GMR remains almost unchanged while that of LFPRs decrease significantly. With increasing top dielectric layer thickness, the LFPR peaks blue shift while the GMR peak red shifts. In addition, the absorber has the merit of multi-band high absorptivity and frequency stability under large angle oblique incidence. The proposed terahertz absorber may benefit the areas of medical imaging, sensing, non-destructive testing, THz communications and other applications.

Near-infrared spectroscopy using period-chirped Si/SiO/SiO2-based guided mode resonance filter.

We demonstrate a Si/SiO/SiO2-based period-chirped guided mode resonance (GMR) filter to discriminate telecom o-band wavelengths by spatially resolved horizontal movement. Continuously period-chirped silicon gratings were fabricated by using a Lloyd's laser interferometer with a convex mirror. Due to the large waveguide effective index, the GMR filter can be realized with a short grating period, thus enabling a slow grating period transition along the sample position and high optical resolution in wavelength discrimination. Depositing a SiO/SiO2 stack on top of silicon gratings enables a narrowband GMR filter with a linewidth of 1-1.5 nm over a wavelength range of 1260-1360 nm. By using the chirped GMR filter as a dispersive device, the optical spectra of a near-infrared broadband light source are reconstructed. An optimized aspheric mirror is proposed to further improve the linearity of chirped gratings. Such a period-chirped GMR filter is promising for compact on-chip spectroscopy and sensing applications.

Giant and controllable Goos-Hänchen shift of monolayer graphene strips enabled by a multilayer dielectric grating structure.

The discovery of monolayer graphene allows the unprecedented chance for exploring its Goos-Hänchen (GH) shift. However, most of the pronounced GH shifts are achieved in various structures with two-dimensional continuous monolayer graphene. Here, we report on the giant GH shift of reflected wave in monolayer graphene strips by constructing the multilayer dielectric grating structure under them. The observed GH shift here is as high as 7000 times that of the incident wave at the near-infrared frequency region, whose magnification is significantly larger than that of the monolayer graphene ribbon array. We further elucidate that the enhanced GH shift originates from the guided mode resonance of the dielectric grating structure and its magnitude and sign can be manipulated by chemical potential of the monolayer graphene strip. Our work enables a promising route for enhancing and controlling the GH shifts of reflected wave in monolayer graphene strips, which might contribute to their applications in biosensors and detectors.

(INVITED)A review on dielectric resonant gratings: Mitigation of finite size and Gaussian beam size effects

Resonant gratings made of dielectrics and semiconductors sustain guided mode resonances with very high lifetime due to the intrinsic lossless properties of the materials involved. Upon out of plane multi-wavelength illumination, resonant grating present very sharp peaks and/or dips in the reflection and/or transmission spectrum at specific resonant wavelength. Theoretical quality factors of the spectral features (which reach values in the order of 105) can be obtained only considering an infinite grating area and an incident plane wave. In practice, the finite dimension of the patterning area and the non-ideal characteristics of the input optical beam (typically with a Gaussian-like profile) cause a broadening and a visibility reduction of the resonant peaks/dips. This prevents from the effective exploitation of micro-sized dielectric structures in many applications, including their integration onto the optical fibers for the realization of High-Q Lab-on-fiber resonant optrodes. In this framework, this review shades light on the non–idealities of the guided mode resonances in dielectric gratings, browsing the solutions proposed by the scientific community during the last decades aimed at overcoming the finite size and finite beam effects, such as the use of distributed Bragg reflectors, and the exploitation of bi-periodic gratings.

Switchable optics based on guided mode resonance in lithographically patterned vanadium dioxide

Vanadium dioxide as a phase change material is usually known for its consideration in smart window applications. However, the attention shifts to using it in actively switched optical elements. The main challenges are the deposition of vanadium dioxide with the correct stoichiometry and phase and the patterning of the material. We propose a design with a corresponding manufacturing process for an actively switchable reflector at 1550 nm wavelength with a contrast near 105 by using the thermochromic effect of vanadium dioxide. The reflectance of the proposed optical element can be controlled between an ultra-low and a high reflecting state. We elaborate on the proposed optical design, the manufacturing process including deposition, annealing and patterning processes, and discuss already achieved results.

Strong coupling of excitons in patterned few-layer WS2 with guided mode and bound state in the continuum.

The strong coupling of excitons in few-layer transition-metal dichalcogenide (TMDC) with guided mode resonance (GMR) and bound state in the continuum (BIC) is investigated. It is shown that the strong coupling between excitons and GMR or BIC can enable a large Rabi splitting, where up to 155 meV or 162 meV Rabi splitting could be realized through changing the grating period, respectively. The physical origins behind this behavior are revealed by studying the electric field distributions at resonance. In addition, such behaviors are further theoretically verified according to the coupled-oscillator model. Moreover, the effect of the geometric dimensions on the strong coupling is also studied, which can be employed to guide real fabrication. The results will provide a new route for realization of few-layer TMDC-based light-matter interactions and may pave the way toward novel, compact, few-layer TMDC-based polaritonic devices.

Extremely broadband light absorption by bismuth-based metamaterials involving hybrid resonances.

An ultra-broadband polarization-insensitive perfect absorber for the 400-4000 nm spectral range is proposed and studied. The absorber is composed of a dielectric film and a phase change material film sandwiched between a bismuth square ring array and a continuous bismuth mirror. Greater than 94% absorptivity across the wavelength range of 400-4000 nm and an averaged absorptivity of about 97% can be achieved. The physical origin results from the mixed effect of guided mode resonance (GMR), cavity resonance (CR) and surface plasmon resonance (SPR). In addition, such a property is maintained excellent in a very large viewing angle range. Furthermore, the proposed scheme exhibits certain geometrical parameter tolerance, which is beneficial for practical fabrication with low cost. Finally, the potential application of the solar cells is investigated as an illustration. The designed metamaterial absorber will find promising applications in solar cells, thermo-photovoltaics and detection.

A membrane reflector, polymer hybrid infrared emitter for better radiative cooling performance

Due to the increasing power consumption for air-conditioning, the power-free passive radiative cooling technique has drawn great attentions in recent years. Blackbody-like broadband emitter and 8–13 μm selective emitter are the two major types of emitters used in current techniques. In this work, we put forward a new type of emitter which has high emissivity in the two atmospheric windows (8–13 μm & 16–25 μm) while maintaining high reflectance at other wavelengths. The proposed emitter has greater cooling potential than both selective and broadband emitters according to our calculations, expect for the extreme sub-ambient conditions. To approach this new emissive characteristic, based on PDMS film, we exploited the guided-mode resonance in the two-dimensional photonic crystal, which introduces a reflectance window between the two atmospheric windows. As the simulation results indicate, the emitter with structural optimization is able to achieve a temperature drop approaching 15 K for ambient temperature Ta = 300 K, non-radiative heat transfer coefficient hc = 2.0 W/m2/K and 3% solar absorption. We believe that it is the first attempt to exploit guided mode resonance in passive radiative cooling applications. Hopefully, this work may provide the researchers a new scheme in terms of the spectral property when designing radiative coolers.

High-Q refractive index sensors based on all-dielectric metasurfaces.

Possessing fantastic abilities to freely manipulate electromagnetic waves on an ultrathin platform, metasurfaces have aroused intense interest in the academic circle. In this work, we present a high-sensitivity refractive index sensor excited by the guided mode of a two-dimensional periodic TiO2 dielectric grating structure. Numerical simulation results show that the optimized nanosensor can excite guided-mode resonance with an ultra-narrow linewidth of 0.19 nm. When the thickness of the biological layer is 20 nm, the sensitivity, Q factor, and FOM values of the nanosensor can reach 82.29 nm RIU−1, 3207.9, and 433.1, respectively. In addition, the device shows insensitivity to polarization and good tolerance to the angle of incident light. This demonstrates that the utilization of low-loss all-dielectric metasurfaces is an effective way to achieve ultra-sensitive biosensor detection.