Fabry-Perot Resonator Research Articles

Acoustic Metamaterials for Low-Frequency Noise Reduction Based on Parallel Connection of Multiple Spiral Chambers.

Acoustic metamaterials based on Helmholtz resonance have perfect sound absorption characteristics with the subwavelength size, but the absorption bandwidth is narrow, which limits the practical applications for noise control with broadband. On the basis of the Fabry–Perot resonance principle, a novel sound absorber of the acoustic metamaterial by parallel connection of the multiple spiral chambers (abbreviated as MSC-AM) is proposed and investigated in this research. Through the theoretical modeling, finite element simulation, sample preparation and experimental validation, the effectiveness and practicability of the MSC-AM are verified. Actual sound absorption coefficients of the MSC-AM in the frequency range of 360–680 Hz (with the bandwidth Δf1 = 320 Hz) are larger than 0.8, which exhibit the extraordinarily low-frequency sound absorption performance. Moreover, actual sound absorption coefficients are above 0.5 in the 350–1600 Hz range (with a bandwidth Δf2 = 1250 Hz), which achieve broadband sound absorption in the low–middle frequency range. According to various actual demands, the structural parameters can be adjusted flexibly to realize the customization of sound absorption bandwidth, which provides a novel way to design and improve acoustic metamaterials to reduce the noise with various frequency bands and has promising prospects of application in low-frequency sound absorption.

Enhanced photonic spin Hall effect of reflected light from a doubly linear gradient-refractive-index material.

The photonic spin Hall effect (SHE), manifesting itself as spin-dependent splitting of light, holds potential applications in nano-photonic devices and precision metrology. However, the photonic SHE is generally weak, and therefore its enhancement is of great significance. In this paper, we propose a simple method for enhancing the photonic SHE of reflected light by taking advantage of the gradient-refractive-index (GRIN) material. The transverse shifts for a normal (homogeneous) layer and linear GRIN structure with three different types (singly increasing, singly decreasing, and doubly linear ones) are theoretically investigated. We found that the doubly linear GRIN materials exhibit the prominent photonic SHE of reflected light, which is mainly due to the Fabry-Perot resonance. By optimizing the thickness and the lower (higher) refractive index of the doubly linear GRIN layer, the transverse shift for a horizontally polarized incident beam can nearly reach its upper limitation (i.e., half of the beam waist). These findings provide us a potential method to enhance the photonic SHE, and therefore establish a strong foundation for developing spin-based photonic devices in the future.

Underwater metamaterial absorber with impedance-matched composite.

By using a structured tungsten-polyurethane composite that is impedance matched to water while simultaneously having a much slower longitudinal sound speed, we have theoretically designed and experimentally realized an underwater acoustic absorber exhibiting high absorption from 4 to 20 kHz, measured in a 5.6 m by 3.6 m water pool with the time-domain approach. The broadband functionality is achieved by optimally engineering the distribution of the Fabry-Perot resonances, based on an integration scheme, to attain impedance matching over a broad frequency range. The average thickness of the integrated absorber, 8.9 mm, is in the deep subwavelength regime (~λ/42 at 4 kHz) and close to the causal minimum thickness of 8.2 mm that is evaluated from the simulated absorption spectrum. The structured composite represents a new type of acoustic metamaterials that has high acoustic energy density and promises broad underwater applications.

Terahertz hybrid optical-plasmonic modes: tunable resonant frequency, narrow linewidth, and strong local field enhancement.

Hybrid optical-plasmonic modes have the characteristics of low loss and small mode volume, which will result in the strong localization and enhancement of electromagnetic field. Such advantages of hybrid optical-plasmonic mode are important for the enhancement of light-matter interactions. Here, terahertz (THz) hybrid modes of Fabry-Perot resonances (FPRs) and spoof surface plasmon polaritons (SSPPs) in the modified Otto scheme are investigated both in theoretical and experimental aspects. The device structure is composed of a metal grating silicon waveguide (MGSW) and a metal slit grating (MSG). The two components are vertically stacked with a variable air gap between them. The THz hybrid modes are originated from the far-field coupling of the FPRs and the SSPP supported by the air gap and the MSG, respectively. By changing the thickness of the air gap, the resonant frequency of the FPR-SSPP modes can be tuned in a frequency range of about 0.1 THz. An anti-crossing behavior between two reflection dips corresponding to the guided-mode resonance in the MGSW and the FPR-SSPP mode is observed, which leads to the narrowing of the reflection dips in the anti-crossing region. Numerical simulations show that at the resonant frequencies of FPR-SSPP mode, there is a huge volume-averaged electromagnetic energy enhancement of about 1600 times in the grooves of the MSG, which is around 8.7 times larger than that induced by the SSPP directly launched by free-space electromagnetic field. The hybrid FPR-SSPP modes can be used to construct THz sensors and detectors with high sensitivity.

A self-aligned lithography method based on Fabry-Perot resonator effect

Fabry-Perot (F-P) resonator is widely applied in the field of optics such as micro-ring resonator and photonic crystal, but there are not yet relevant reports about optical imaging. We propose a self-aligned lithography method based on F-P resonator effect and realize self-aligned effect successfully by controlling film stack parameters. The self-aligned structure is composed of Ag/photoresist/Ag film stack and wafer layer which contains SiO2 layer and SiO2/Si gratings. A rapid simulation model based on Rigorous Coupled Wave Analysis algorithm is established to optimize the best parameters of the self-aligned structure. Then rigorous Finite Difference Time Domain model and Finite Element Method model are used to verify the self-aligned effect and the results show that such process has extremely large mask critical dimension (CD) and overlay variation. The mask CD could be tuned more than 50% of structure period while the wafer CD maintains in the range less than 10%, and the maximum mask overlay offset could be ± 25% of half pitch while the wafer pattern center maintains unchanged. All the results show that the proposed method has lots of process robustness and could increase the application area of imaging lithography technology.

Scattering Properties of an Acoustic Anti-Parity-Time-Symmetric System and Related Fabry–Perot Resonance Mode

The pursuit of artificial structures exhibiting unusual acoustic properties is a major scientific endeavor, in which anti-parity-time (PT) symmetry has been coming into view recent years. At the same time, with the emergence of new acoustic metamaterials, the classical Fabry–Perot resonance mode also exhibits fascinating scattering features similar to those of the anti-PT-symmetric system. We derive the generalized relation for the scattering parameters of an acoustic anti-PT-symmetric system with a transfer matrix, including conjugate bidirectional reflection coefficients and pure real feature of transmission coefficient. In the absence of the real or the imaginary (representing gain/loss) part of the refractive index, the anti-PT-symmetric system degrades into a pair of complementary media, resulting in the bidirectional total transmission. Moreover, a Fabry–Perot resonance mode exhibiting conjugate bidirectional reflection coefficients and a pure imaginary transmission coefficient has been demonstrated. Our results are meaningful for guiding the experimental test of an acoustic anti-PT-symmetric system and the design of associated bidirectional response prototype devices.

Room-temperature plasmonic mid-infrared photodetector based on PtSi/p-Si low Schottky-barrier junction.

In this study, a low Schottky-barrier photodetector with a plasmonic assist using a two-dimensional (2D) nanohole array was demonstrated, which receives mid-infrared (MIR) light at room temperature. In the structural design, it was confirmed that the 2D nanohole-array photodetector has high absorbance in the MIR region using rigorous coupled-wave analysis. The result showed that the nanoholes formed in p-type silicon (p-Si), platinum silicide (PtSi), to form Schottky barriers, and gold (Au), for photocurrent extraction, had high absorbance in the MIR region along with the Fabry-Perot resonance mode toward the depth of the nanohole. The 2D nanohole array, with Au/PtSi/p-Si layers, has high absorbance for illuminating MIR light near 3.46 µm from the backside. The current-voltage characteristics indicated a low Schottky barrier of 0.32 eV, confirming the photoresponsive potential in the MIR photodetection. The photocurrent response to the modulation signal was obtained at room temperature. In addition, signal processing through transimpedance and lock-in amplifiers enabled us to obtain characteristics with high linearity for light intensities in milliwatts. Light acquisition for 2.5-3.8-µm-long MIR wavelength became possible, and applications in gas sensing, including vibrational absorption bands of alkane groups, are expected.

Plasmonic metasurface with quadrilateral truncated cones for visible perfect absorber

Solar radiation is mainly concentrated in the visible and infrared spectra ranges, and its perfect absorption has great significance to solar cell, energy harvester, emitter, perfect stealth, and hot-electron device fields. In this study, we theoretically design and numerically demonstrate a highly efficient broadband visible perfect absorber (VPA) using plasmonic metasurface , which consists of quadrilateral truncated cones configuration. The electromagnetic properties of VPA are discussed by changing the geometrical parameters, especially to the absorption intensity of VPA. VPA processes perfect absorption (100%) at the wavelength of 490 nm and the minimum absorption is 99.51% at the wavelength of 772 nm. The averaged absorption is 99.91% spanned the whole visible spectrum. The excellent absorption performance is revealed by the Fabry-Perot resonance, localized surface plasmon resonance (SPR), and propagating SPR . VPA exhibits ultrahigh absorption, wide incident angle, and polarization-independent characteristics. It proves that the designed VPA has great potential in thermal photovoltaics and energy harvesting applications. • A highly efficient broadband visible perfect absorber (VPA) using plasmonic metasurface is presented. • VPA processes perfect absorption (100%) at the wavelength of 490 nm. • The average absorption is 99.91% spanned the whole visible spectrum. • The averaged absorption intensities are 99.91%, 99.8%, and 94.7% at the incident angles of 0°, 20°, and 60°, respectively. • VPA exhibits ultrahigh absorption, wide incident angle, and polarization-independent characteristics.

Dual-Band Aperture-Shared Fabry–Perot Cavity-Integrated Patch Antenna for Millimeter-Wave/Sub-6 GHz Communication Applications

This letter presents a dual-band antenna with a large frequency ratio of 11.7 (2.4 GHz/28 GHz) by integrating an mm-wave Fabry–Perot cavity (FPC) antenna into a sub-6 GHz patch antenna. The patch with periodic slots functions as both the 2.4 GHz radiator and the partially reflective surface (PRS) of the 28 GHz FPC antenna. By properly tuning the length of the periodic slot, the PRS's reflection can be easily adjusted. As the periodic slot's length and width operating at 28 GHz are much smaller than the wavelength at 2.4 GHz, periodic slot operating at 28 GHz have little impact on the radiation of the patch. Furthermore, because of the Fabry–Perot resonance, the antenna can have a peak gain reaching 15 dBi at 28 GHz band with an easy feeding structure. For demonstration, a prototype is fabricated and experimentally verified. Note that the frequency ratio is not limited to the proposed design (11.7 for demonstration). It can be easily adjusted based on the same principle.

A Dual-Band Circularly Polarized Shared-Aperture Antenna for 1U CubeSat Applications

This communication presents a design of a dual-band circularly polarized antenna with structure reuse for one cubic unit (1U) CubeSat applications. It is a challenging to design an antenna with the limited space of a CubeSat platform. To improve the space utilization, an antenna is designed inspired by the concept of structure reuse. A meshed-like-structure is designed, which works as the radiator of a microstrip antenna at UHF band. However, it works as a partial reflective sheet for a Fabry–Perot resonator cavity antenna at C-band. Therefore, a microstrip patch antenna and a Fabry–Perot resonator cavity antenna share only single aperture. A shaped ground is used to decrease the resonance at the lower band. Then, the aperture of the antenna is only <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$0.3\lambda _{0} \,\times \, 0.3\lambda _{0}$ </tex-math></inline-formula> , which makes it easy to integrate with a 1U CubeSat. The measurement reveals that the antenna has a common bandwidth of ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\vert \text{S}_{11}\vert &lt; -10$ </tex-math></inline-formula> dB, AR < 3 dB) 1% and 1.4%, an isolation higher than 35 and 20 dB, a peak gain of 5.82 and 13.75 dBic at UHF and C-band, respectively. The frequency ratio of these two bands reaches 6.4. The above properties make the proposed antenna suitable for a CubeSat system.

Light Emission from Vibronic Polaritons in Coupled Metalloporphyrin-Multimode Cavity Systems.

In this study, we explore how one can use cavity polariton formation and a non-Condon vibronic coupling mechanism to form a type of hybrid light-matter state we denote as Herzberg-Teller (HT) vibronic polaritons. We use simple models to define the basic characteristics of these hybrid light-matter excitations including their dispersive energies. Experimentally, we find evidence of HT polaritons in the light emission spectra from copper(II) tetraphenylporphyrin (CuTPP) molecules strongly coupled to both single and multimode Fabry-Perot resonator structures. For specific resonator designs, we find evidence of significant enhancement of light emission from a short-lived sing-doublet state of CuTPP, which couples to a higher energy singlet state via a non-Condon vibronic mechanism. The results of a two-state model support the conclusion that this enhancement and the temperature-dependent dispersion of the light emission peak energy stem from radiative relaxation into cavity photon states dressed by collective vibrations of the molecules participating in polariton formation. These results show how researchers can leverage the complex interplay of electronic and nuclear degrees of freedom in light absorbing molecules to form a vaster array of coherent light-matter states and potentially transform platforms in optoelectronic and photocatalytic technologies.

Plasmonic origami: tuning optical properties by periodic folding of a gold nano film

Novel plasmonic structures are on the rise, with applications varying from sensing and spectroscopy to solar cells and biological therapies. In this work, we introduce a plasmonic metasurface with a very rich dispersion spectrum, measured both experimentally and numerically. It shows a tunable absorption that depends on the folding angle and periodicity. A detailed numerical analysis identifies the presence of quasi-omnidirectional absorption. This broad directional absorption mode matches a Fabry–Perot resonance of a surface plasmon polariton along an elementary segment of the periodic structure. This geometry induced wide directional absorption is highly promising for a variety of photonic, light harvesting, and sensing applications.

Wide-angle polarization selectivity based on anomalous defect mode in photonic crystal containing hyperbolic metamaterials.

Conventional defect modes in all-dielectric 1D photonic crystals (PCs) are polarization-insensitive. This poses a great challenge in achieving high-performance polarization selectivity. In this Letter, we introduce a defect layer into a 1D PC containing hyperbolic metamaterials to achieve an anomalous defect mode with polarization-sensitive characteristics. As the incident angle increases, such a defect mode remains almost unshifted under transverse magnetic polarization, while strongly shifting toward shorter wavelengths under transverse electric polarization. The polarization-sensitive characteristics of the defect mode can be well explained by the Fabry-Perot resonance condition. Assisted by the polarization-sensitive defect mode, wide-angle polarization selectivity with an operating angle width up to 54.8° can be realized. Our work provides a route to designing wide-angle linear polarizers using simple 1D structures, which would be useful in liquid crystal display and Q-switched lasers.

Topological phase singularities in atomically thin high-refractive-index materials

Atomically thin transition metal dichalcogenides (TMDCs) present a promising platform for numerous photonic applications due to excitonic spectral features, possibility to tune their constants by external gating, doping, or light, and mechanical stability. Utilization of such materials for sensing or optical modulation purposes would require a clever optical design, as by itself the 2D materials can offer only a small optical phase delay – consequence of the atomic thickness. To address this issue, we combine films of 2D semiconductors which exhibit excitonic lines with the Fabry-Perot resonators of the standard commercial SiO2/Si substrate, in order to realize topological phase singularities in reflection. Around these singularities, reflection spectra demonstrate rapid phase changes while the structure behaves as a perfect absorber. Furthermore, we demonstrate that such topological phase singularities are ubiquitous for the entire class of atomically thin TMDCs and other high-refractive-index materials, making it a powerful tool for phase engineering in flat optics. As a practical demonstration, we employ PdSe2 topological phase singularities for a refractive index sensor and demonstrate its superior phase sensitivity compared to typical surface plasmon resonance sensors.

Continuous-wave operation of 405 nm distributed Bragg reflector laser diodes based on GaN using 10th-order surface gratings

Single longitudinal mode continuous-wave operation of GaN-based distributed Bragg reflector (DBR) laser diodes with 10th-order surface gratings is demonstrated. The DBR consists of periodic V-shaped grooves on a 2 μm wide ridge waveguide fabricated by using electron-beam lithography and plasma etching. The effect of different lengths of the DBR section and the gain section on the device performance has been studied. Periodic mode hops to the adjacent longitudinal Fabry–Perot resonator mode at shorter wavelength have been observed when increasing the operation current. Between the mode hops, single longitudinal mode emission at around 405 nm is achieved with a full width at half-maximum of 0.03 nm. A linear redshift of the emission wavelength with increasing temperature of 0.019 nm/K was derived.

Reflective Metasurfaces with Multiple Elastic Mode Conversions for Broadband Underwater Sound Absorption

Unlike their electromagnetic and acoustic counterparts, elastic waves involve different wave modes. The interplay and the coupling among them increase the complexity of the problem while also offering a larger space for wave manipulation. Elastic bulk wave conversion in an elastic metamaterial has recently shown great promise in medical ultrasound and nondestructive testing. Unlike the transmission-type conversion, however, reflective elastic mode conversion has been explored less in terms of analysis and design, despite the enormous possibilities that it might offer for energy trapping and dissipation. In this work, we develop a theoretical framework for constructing elastic anisotropic metasurfaces that can enable reflective longitudinal-to-transverse (L-to-T) and transverse-to-longitudinal (T-to-L) wave conversions. We capitalize on the mechanism of multiple reflective mode conversion to achieve broadband, subwavelength, and near perfect sound absorption in the underwater environment. The reflective scattering properties of the metasurfaces are systematically exploited for incident longitudinal or transverse waves. The conversion mechanism is rooted in reflective Fabry-Perot (FP) resonance, whose occurrence conditions and features are predicted for prescribed effective parameters of the metasurface. We then establish an inverse-design framework for conceiving an underwater coating system formed by a viscoelastic rubber layer and the metasurface. A series of metasurfaces allowing for customized mode conversions are realized for delivering broadband low-frequency and high-efficiency underwater sound absorption. Specifically, an ultrathin rubber-metasurface layer in which the metasurface with a thickness of approximately \ensuremath{\lambda}/70 can lead to nearly 100% sound absorption. Furthermore, we demonstrate that a persistently high absorption (over 80%) can be obtained in a rather robust manner within a wide range of wave incidence angle from \ensuremath{-}60\ifmmode^\circ\else\textdegree\fi{} to 60\ifmmode^\circ\else\textdegree\fi{}. More importantly, high-efficiency acoustic absorption exceeding 75% can be readily achieved through multiple mode conversions within the ultrabroadband range featuring a relative bandwidth of 119%. We reveal the combined FP resonance mechanism of underwater sound absorption, i.e., the FP resonance of the metaconverter, which determines the L-to-T and T-to-L conversion ratio, and the FP resonance of the rubber-metasurface layers, which enhances the wave attenuation inside the rubber. The proposed reflective multiple mode-conversion mechanism and metasurface design methodology open a route towards a class of elastic-wave-based devices with promising potential for underwater applications.

Broadband Absorption Antenna Based on High Refractive Index Tungsten Metal-Insulator-Meta Metamaterial Nano Ring Array

Antennas for solar energy collection, for the problem of complex antenna structure and narrow absorption band, a metal-insulator-metal (MIM) nano ring array antenna based on metamaterial is proposed, which has high-efficiency light absorption characteristics in the broadband range of visible light and near-infrared light. Based on surface plasma theory, the proposed antenna is only composed of two W layers of metal and one Al2O3 layer of insulator medium, and has an a verage absorption rate of 96.93% in the range of 400–1600 nm. In addition, it is found that this kind of super light-absorbing capability is independent of the incoming light polarization state and can maintain an average of 91% for an incident angle as large as±60°. Furthermore, the perfect absorption performance of MIM nano ring array antenna based on metamaterial can be explained by the synergistic effect of localized surface plasmon resonance enhancement and Fabry-Perot resonance.

2-D Tilt Sensor Based on Coaxial Cable Fabry–Perot Resonators With Submicroradian Resolution

For the past 50 years, open-ended coaxial lines were commonly employed for the determination of electromagnetic properties of various materials. In this article, the application of an open-ended hollow coaxial cable resonator (OE-HCCR) as a 1-D inclinometer for tilt measurements with 110 nanoradian (nrad) resolution is proposed and demonstrated. The coaxial cable resonant structure is formed between a metal post welded within the coaxial cable at the RF input end and the open end of the coaxial cable. A metal mass block, suspended in proximity to the open end in parallel is used to construct a pendulum structure, serving as the element responsive to a tilt. When the device is tilted, the distance between the mass block and the open end varies due to the displacement of the suspended pendulum. The change in the gap distance modifies the phase reflection coefficient associated with the open end, causing the resonance frequency of the coaxial cable resonator to change. By tracking the resonance frequency, the coaxial line resonator is effectively used as an inclinometer. The experimental results demonstrated that the novel device has a measurement resolution of 110 nrad over a range of 0–3 milliradians (mrad). Additionally, based on the same principle, a 2-D inclinometer based on two perpendicularly aligned OE-HCCRs, useful for simultaneous tilt measurements in two orthogonal dimensions is demonstrated. The open-ended coaxial cable resonator-based inclinometer holds several advantages, including high resolution, robustness, cost effectiveness, ease of signal interrogation, and user-configurable sensitivity and dynamic range.

Phase resonance and sensing application of an acoustic metamaterial based on a composite both-sides-open disk resonator arrays

We designed a composite both-sides-open disk resonator (CBSODR) structure by alternately arranging two types of BSODRs in a square lattice array. The simulation spectra of CBSODR structure showed two transmission peaks split by a sharp phase resonance (PR) dip with high quality factor. Previously developed PR structures based on Fabry–Perot resonance require a trade-off between resonant frequency and structural thickness. In contrast, we examined the mechanism underlying the PR effect induced by the CBSODR array by varying the diameters of the BSODR holes. We analyzed the PR effect by calculating the pressure and velocity fields of the CBSODR and further investigated the relationship between the operating frequency and geometric parameters. We could tune the resonant frequencies of the CBSODR structure while maintaining its thinness. We also applied the structure in a 1-propanol liquid concentration sensor. The results indicated a significant improvement in the sensor’s figure of merit, which could be because the quality factor of the PR dip was high. At last, the experiment results showed the verification of the PR effect in CBSODR structure. The proposed CBSODR structure can be applied in underwater acoustic sensors and acoustic filters.

Theories of indirect chiral coupling and proposal of Fabry–Perot resonance as a flexible chiral-coupling interface

The chiral coupling of an emitter to waveguide mode, i.e., the propagation direction of the excited waveguide mode is locked to the transverse spin (T-spin) of a circularly polarized emitter, has exhibited unprecedented applications in nanophotonics and quantum information processing. This chiral coupling can be largely enhanced in terms of unidirectivity, efficiency, and spontaneous emission rate by introducing resonant modes as coupling interfaces. However, this indirect chiral coupling still undergoes limitations in flexibility and miniaturization, and the underlying physical mechanisms are to be clarified. Here, we present an intuitive and rigorous approach for analyzing the direct/indirect chiral coupling, and thereout, derive some general relations between the chiral-coupling directionality and the T-spin of the field or emitter. Based on the theories, we propose an indirect chiral-coupling system on the platform of surface plasmon polariton (SPP), with a nanocavity supporting Fabry–Perot (FP) resonance of dual SPP modes serving as a novel coupling interface. The FP resonance provides flexible design freedoms which can modulate the chirality of the T-spin (and the resultant chiral-coupling directionality) to flip or disappear. A unidirectivity up to 99.9% along with a high coupling efficiency and enhancement of spontaneous emission rate is achieved. Two first-principles-based SPP models for the reciprocal and original problems are built up to verify the decisive role of the FP resonance in achieving the chiral coupling. The proposed theories and novel chiral-coupling interface will be beneficial to the design of more compact and flexible chiral-coupling systems for diverse applications.