high-Q Resonator Research Articles

Can a terahertz metamaterial sensor be improved by ultra-strong coupling with a high-Q photonic resonator?

When a metamaterial (MM) is embedded in a one-dimensional photonic crystal (PC) cavity, the ultra-strong coupling between the MM plasmons and the photons in the PC cavity gives rise to two new polariton modes with high quality factor. Here, we investigate by simulations whether such a strongly coupled system working in the terahertz (THz) frequency range has the potential to be a better sensor than a MM (or a PC cavity) alone. Somewhat surprisingly, one finds that the shift of the resonance frequency induced by an analyte applied to the MM is smaller in the case of the dual resonator (MM and cavity) than that obtained with the MM alone. However, the phase sensitivity of the dual resonator can be larger than that of the MM alone. With the dielectric perturbation theory - well established in the microwave community - one can show that the size of the mode volume plays a decisive role for the obtainable frequency shift. The larger frequency shift of the MM alone is explained by its smaller mode volume as compared with the MM-loaded cavity. Two main conclusions can be drawn from our investigations. First, that the dielectric perturbation theory can be used to guide and optimize the designs of MM-based sensors. And second, that the enhanced phase sensitivity of the dual resonator may open a new route for the realization of improved THz sensors.

Metasurfaces with high-Q resonances governed by topological edge state.

Achieving high-quality (Q)-factor resonances in metasurfaces is essential for various applications, including nano-lasers, nonlinear optics, and quantum optics. In this work, we propose a high-Q metasurface using a topological strategy: constructing the metasurface by stacking two conjugated nanopillar arrays with different topological invariants. Our study shows that a topological edge state steadily appears at the interfaces of the nanopillars, and a sharp transmission resonance with a Q-factor of more than 1000 can be obtained. The sensing application of such high-Q topological metasurface is also demonstrated, whose figure of merit reaches approximately 145. The proposed strategy and underlying theory can open up new avenues to realize ultrasharp resonances, which can promote numerous potential applications, such as biosensing, optical modulation, and slow-light devices.

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.

Resonant mode approximation of the scattering matrix of photonic crystal slabs near several Wood-Rayleigh anomalies

The resonant mode approximation of the scattering matrix is considered for calculating the optical properties of multilayered periodic structures within the formalism of the Fourier-modal method for two diffraction thresholds in close proximity of the spectral-angular range of interest. The developed approximation opens up possibilities for the fast calculation of the scattering matrix of these structures when describing the integral characteristics of spectra and dispersion curves containing high-Q resonances, such as bound states in the continuum.

High-quality multi-band absorber in a hybrid all-dielectric system using the surface plasmon polaritons

High confinement of surface plasmon polaritons in graphene have important applications in many aspects. In this paper, we have demonstrated that high-quality multi-band absorption can be achieved by using a hybrid system where periodic monolayer graphene nanoribbons is coated on an all-dielectric nanostructure. The effect of the monolayer graphene nanoribbons on plasmonic resonances absorption is investigated theoretically and numerically. It is found that the high tunability and large near field enhancement of the system is observed by changing the grating period and Fermi level. After delicate optimization, the system can achieve high-Q resonances in the vicinity of the bound states in the continuum, and the Q factors of the two resonance modes are respectively significantly enhanced (＞450, 600). In addition, the multi-band light absorption enhancement with high quality can be observed by altering the carrier mobility of graphene. Wherein the optimized absorption efficiency up to 97% is reached. More interestingly, the proposed structure puts up palpable advantage in absorption stability when the incident angle is varied from 0° to 60°. Thus, this work may facilitate the design of high-performance optoelectronic devices based on all-dielectric configuration, such as tunable optical sensors and perfect absorbers.

Bound state in the continuum in an anisotropic photonic crystal supported by a full-wave phase plate

We consider bound states in the continuum (BICs) in a 1D multilayered system of an anisotropic defect layer embedded into an anisotropic photonic crystal. We analytically demonstrate that an anisotropic defect layer embedded into anisotropic photonic crystal supports accidental BICs. These BICs can be transformed to high-Q resonances by variation of one of the system’s parameters. At the same time, the BICs are remarkably robust in the sense that a true BIC can be recovered by further tuning any of the system’s other parameters, leading to tunability of the resonance position.

Single-frequency Brillouin lasing based on a birefringent fiber Fabry–Pérot cavity

Stimulated Brillouin scattering (SBS) in a high-Q resonator is capable for narrow-linewidth laser generation for various applications but is limited by on-resonance pump to SBS matching from single-longitudinal lasing. In this Letter, we present a narrow linewidth laser via SBS that is enhanced in a monolithic high-Q fiber resonator. The unique cross-polarization pump scheme based on fiber birefringence prevents high-order SBS and ensures single-frequency Brillouin lasing with high intracavity conversion efficiency. Fundamental linewidth of 50 Hz is achieved. Moreover, our scheme also allows precise characterization of Brillouin frequency shift and gain bandwidth of some nonlinear materials.

Bound States in the Continuum in Compact Acoustic Resonators.

We reveal that finite-size solid acoustic resonators can support genuine bound states in the continuum (BICs) completely localized inside the resonator. The developed theory provides the multipole classification of such BICs in the resonators of various shapes. It is shown how breaking of the resonator's symmetry turns BICs into quasi-BICs manifesting themselves in the scattering spectra as high-Q Fano resonances. We believe that the revealed novel states will push the performance limits of acoustic devices and will serve as high-Q building blocks for acoustic sensors, antennas, and topological acoustic structures.

High-Q Fano resonance in all-dielectric metasurfaces for molecular fingerprint detection

We present and numerically investigate a high-quality factor (high- Q ) meta-atom with Fano resonance. Numerical simulations indicate that the designed meta-atom has a single sharp Fano resonance in the 1350–1750 1/cm range. Moreover, the frequency of the single resonance can be tuned in this frequency range by scaling the meta-atom. We exploit these properties to design a pixelated metasurface for spectrometer-less molecular fingerprint retrieval. The proposed meta-atom with an average quality factor of 2000 makes it possible to decrease the scaling step of metapixels without introducing resonance overlap between the metapixels, leading to higher precision in label-free and nondestructive identification of molecular fingerprints.

High-Q localized surface plasmon resonance based on bound states in the continuum for enhanced refractive index sensing.

Nanophotonics based on localized surface plasmon resonance (LSPR) has emerged as a vibrant arena for research into enhanced light-matter interactions with potential applications in imaging, sensing, and computing. However, the low quality (Q) factor of LSPR is a significant barrier to comprehensive device applications. Here, we demonstrate that coupling the LSPR of a gold nanowire array with the optical bound states in the continuum (BIC) of a dielectric double-layer grating can significantly increase the Q factor of LSPR. We realize two hybrid modes with Q factors of up to 111 at 558 nm and 83 at 582 nm, which are about 14 and 10 times larger than those of an uncoupled gold nanowire array. Based on temporal coupled-mode theory, we further show that the resonance frequencies and Q factors of the hybrid modes can be modulated and optimized by varying relevant structural parameters. This coupled system provides a new platform for improving the figures of merit (FoMs) of LSPR-based refractive index sensors, and the concept of LSPR-BIC coupling can be extended to other similar nanosystems.

Externally Driven Nonlinear Time-Variant Metasurfaces

Resonant photonic nanostructures exhibiting enhanced nonlinear responses and efficient frequency conversion are an emergent platform in nonlinear optics. High-index semiconductor metasurfaces with rapidly tuned high-Q resonances enable a novel class of time-variant metasurfaces, which expands the toolbox of color management at the nanoscale. Here, we report on the dynamic control of the nonlinear optical response in time-variant semiconductor metasurfaces supporting high-quality factor resonances in the near-infrared spectral range. Pump-probe measurements of germanium metasurfaces at negative pump-probe time delays reveals frequency conversion in the fundamental beam and a blue-shift of 10~nm (3.05$\omega$) and 40% broadening in the third harmonic signal due to the photoinduced time-variant refractive index. A time-dependent coupled-mode theory, in excellent agreement with the experimental data, validated the time-variant nature of the system. Our findings expand the scope of time-variant metasurfaces and may serve as base for the next generation of nanoscale pulse shapers, optical switches and light sources.

A Kerr polarization controller

Kerr-effect-induced changes of the polarization state of light are well known in pulsed laser systems. An example is nonlinear polarization rotation, which is critical to the operation of many types of mode-locked lasers. Here, we demonstrate that the Kerr effect in a high-finesse Fabry-Pérot resonator can be utilized to control the polarization of a continuous wave laser. It is shown that a linearly-polarized input field is converted into a left- or right-circularly-polarized field, controlled via the optical power. The observations are explained by Kerr-nonlinearity induced symmetry breaking, which splits the resonance frequencies of degenerate modes with opposite polarization handedness in an otherwise symmetric resonator. The all-optical polarization control is demonstrated at threshold powers down to 7 mW. The physical principle of such Kerr effect-based polarization controllers is generic to high-Q Kerr-nonlinear resonators and could also be implemented in photonic integrated circuits. Beyond polarization control, the spontaneous symmetry breaking of polarization states could be used for polarization filters or highly sensitive polarization sensors when operating close to the symmetry-breaking point.

Generation of Reconfigurable Linearly Chirped Microwave Waveforms Based On Fourier domain Mode-Locked Optoelectronic Oscillator

We propose and experimentally demonstrate an approach to generating reconfigurable linearly chirped microwave waveforms (LCMWs) based on a Fourier domain mode-locked (FDML) optoelectronic oscillator (OEO), in which a tunable and reconfigurable microwave photonic filter (MPF) based on a high-Q microring resonator (MRR) is used for mode selection. The MPF can be electrically tuned to achieve Fourier domain mode-locking by using a micro-heater deposited on the MRR. Adjusting the state of polarization of the optical carrier, the MPF is reconfigured and multi-band and multi-format LCWMs can be generated based on the FDML OEO. In the experiment, a dual-chirp LCMW with a bandwidth of 12 GHz consisting of an up-chirped waveform from 7 to 13 GHz and a down-chirped waveform from 19 to 13 GHz is realized, with a time-bandwidth product (TBWP) as high as 1.004×10⁶. By reconfiguring the MPF, we can also obtain LCMWs with a single chirp at C-band (from 4 to 8 GHz), X-band (from 8 to 12 GHz) and Ku-band (from 13 to 19 GHz), respectively. Further, the bandwidth and center frequency of the LCMWs and the dual-chirp LCMWs can be changed by adjusting the magnitude of the driving signal and the laser wavelength, respectively. This kind of reconfigurable LCMWs can be applied to advanced multi-band radar and wireless communication systems.

Broad-band spatial light modulation with dual epsilon-near-zero modes

Epsilon-near-zero (ENZ) modes have attracted extensive interests due to its ultrasmall mode volume resulting in extremely strong light-matter interaction (LMI) for active optoelectronic devices. The ENZ modes can be electrically toggled between on and off states with a classic metal-insulator-semiconductor (MIS) configuration and therefore allow access to electro-absorption (E-A) modulation. Relying on the quantum confinement of charge-carriers in the doped semiconductor, the fundamental limitation of achieving high modulation efficiency with MIS junction is that only a nanometer-thin ENZ confinement layer can contribute to the strength of E-A. Further, for the ENZ based spatial light modulation, the requirement of resonant coupling inevitably leads to small absolute modulation depth and limited spectral bandwidth as restricted by the properties of the plasmonic or high-Q resonance systems. In this paper, we proposed and demonstrated a dual-ENZ mode scheme for spatial light modulation with a TCOs/dielectric/silicon nanotrench configuration for the first time. Such a SIS junction can build up two distinct ENZ layers arising from the induced charge-carriers of opposite polarities adjacent to both faces of the dielectric layer. The non-resonant and low-loss deep nanotrench framework allows the free space light to be modulated efficiently <italic>via</italic> interaction of dual ENZ modes in an elongated manner. Our theoretical and experimental studies reveal that the dual ENZ mode scheme in the SIS configuration leverages the large modulation depth, extended spectral bandwidth together with high speed switching, thus holding great promise for achieving electrically addressed spatial light modulation in near- to mid-infrared regions.

Magnetic excitation of high-Q resonance with split-ring resonators

Planar split-ring resonators (SRRs) with broken symmetry, excited by the electric field of incident wave, have been widely used to realize the high-Q resonance. In this paper, we report by theory and experiment an alternative scheme to induce the SRR-based high-Q resonance. The proposed scheme utilizes a two-dimensional array of vertical SRRs with vertical air gaps, which enables the excitation of narrow resonance with magnetic field and strong enhancement of local electromagnetic fields. The working mechanism correlates with the strong directional dependence of the dipole radiation (i.e., the elimination of electric-dipole radiation of the SRRs in the propagation direction), rather than the destructive interference due to the structural symmetry breaking. The dependence of Q factor on the structural parameters has also been studied theoretically, suggesting that a Q factor more than 2000 can be achieved. The results may be useful for designing narrow-band filters and sensors in the microwave or THz regime.

High-performance lasers for fully integrated silicon nitride photonics

Silicon nitride (SiN) waveguides with ultra-low optical loss enable integrated photonic applications including low noise, narrow linewidth lasers, chip-scale nonlinear photonics, and microwave photonics. Lasers are key components to SiN photonic integrated circuits (PICs), but are difficult to fully integrate with low-index SiN waveguides due to their large mismatch with the high-index III-V gain materials. The recent demonstration of multilayer heterogeneous integration provides a practical solution and enabled the first-generation of lasers fully integrated with SiN waveguides. However, a laser with high device yield and high output power at telecommunication wavelengths, where photonics applications are clustered, is still missing, hindered by large mode transition loss, non-optimized cavity design, and a complicated fabrication process. Here, we report high-performance lasers on SiN with tens of milliwatts output power through the SiN waveguide and sub-kHz fundamental linewidth, addressing all the aforementioned issues. We also show Hertz-level fundamental linewidth lasers are achievable with the developed integration techniques. These lasers, together with high-Q SiN resonators, mark a milestone towards a fully integrated low-noise silicon nitride photonics platform. This laser should find potential applications in LIDAR, microwave photonics and coherent optical communications.

Integrated Molecular Optomechanics with Hybrid Dielectric-Metallic Resonators.

Molecular optomechanics describes surface-enhanced Raman scattering using the formalism of cavity optomechanics as a parametric coupling of the molecule’s vibrational modes to the plasmonic resonance. Most of the predicted applications require intense electric field hotspots but spectrally narrow resonances, out of reach of standard plasmonic resonances. The Fano lineshapes resulting from the hybridization of dielectric–plasmonic resonators with a broad-band plasmon and narrow-band cavity mode allow reaching strong Raman enhancement with high-Q resonances, paving the way for sideband resolved molecular optomechanics. We extend the molecular optomechanics formalism to describe hybrid dielectric–plasmonic resonators with multiple optical resonances and with both free-space and waveguide addressing. We demonstrate how the Raman enhancement depends on the complex response functions of the hybrid system, and we retrieve the expression of Raman enhancement as a product of pump enhancement and the local density of states. The model allows prediction of the Raman emission ratio into different output ports and enables demonstrating a fully integrated high-Q Raman resonator exploiting multiple cavity modes coupled to the same waveguide.

Ultra-narrow passband-tunable filter based on a high-Q silicon racetrack resonator

An ultra-narrow narrow passband-tunable optical filter employing a high-Q silicon racetrack resonator is proposed and experimentally demonstrated on a SOI platform. The high-Q silicon racetrack resonator is realized by utilizing the multimode waveguide racetrack, and the Q factor is measured as high as 8.1×105. The structure of the device is based on a thermally tunable Mach-Zehnder interferometer coupled racetrack. The tunability of the bandwidth is realized by tuning the coupling coefficient between the racetrack resonator and the input or output ports. Finally, the bandwidth of the filter can be tuned from 1.92 to 11.00 pm (240 MHz to 1.375 GHz), and the free spectral range is about 0.28 nm (35 GHz), with the footprint of 0.21mm2.

Demonstration of MHz frequency domain multiplexing readout of 37 transition edge sensors for high-resolution x-ray imaging spectrometers

We report on the development and demonstration of MHz frequency domain multiplexing (FDM) technology to readout arrays of cryogenic transition edge sensor (TES) x-ray microcalorimeters. In our FDM scheme, TESs are AC biased at different resonant frequencies in the low MHz range through an array of high-Q LC resonators. The current signals of all TESs are summed at superconducting quantum interference devices (SQUIDs). We have demonstrated multiplexing for a readout of 31 pixels using room temperature electronics, high-Q LC filters, and TES arrays developed at SRON, and SQUID arrays from VTT. We repeated this on a second setup with 37 pixels. The summed x-ray spectral resolutions @ 5.9 keV are ΔE31pix MUX=2.14 ± 0.03 eV and ΔE37pix MUX=2.23 ± 0.03 eV. The demonstrated results are comparable with other multiplexing approaches. There is potential to further improve the spectral resolution, to increase the number of multiplexed TESs, and to open up applications for TES x-ray microcalorimeters.

High-Q two-groove resonator for all-dielectric Bloch surface wave platform

We propose a simple integrated resonant structure for the Bloch surface wave platform, which consists of two subwavelength grooves patterned on the surface of a one-dimensional dielectric photonic crystal. We demonstrate that the investigated structure can operate in a parasitic-scattering-free regime and, in this case, provide unity transmittance and zero reflectance at resonance conditions associated with the excitation of a leaky mode of the structure localized at the central ridge formed by the grooves. The proposed structure may find application in integrated photonic devices for optical filtering and analog optical computing.