Narrow-band Resonance Research Articles

A Theory for Energy-Optimized Operation of Self-Adaptive Vibration Energy Harvesting Systems with Passive Frequency Adjustment.

Self-adaptive vibration energy harvesting systems vary their resonance frequency automatically to better exploit changing environmental conditions. The energy required for the adjustment is taken from the energy storage of the harvester module. The energy gained by an adjustment step has to exceed the energy expended on it to justify the adjustment. A smart self-adaptive system takes this into account and operates in a manner that maximizes the energy output. This paper presents a theory for the optimal operation of a vibration energy harvester with a passive resonance-frequency adjustment mechanism (one that only requires energy for the adjustment steps proper, but not during the hold phases between the steps). Several vibration scenarios are considered to derive a general guideline. It is shown that there exist conditions under which a narrowing of the adjustment bandwidth improves the system characteristics. The theory is applied to a self-adaptive energy harvesting system based on electromagnetic transduction with narrowband resonators. It is demonstrated that the novel optimum mode of operation increases the energy output by a factor of 3.6.

Self-Assembled, Ultrahigh Refractive Index Pseudo-Periodic Sn Nanostructures for Broad-Band Infrared Photon Management in Single Layer Graphene

Graphene is a two-dimensional material with intriguing electrical and optical properties for infrared photonic devices. However, single layer graphene (SLG) suffers from a very low optical absorption of ∼1–2% depending on the substrate, which significantly limits its efficiency as photonic devices. In this Letter, we address this challenge by coating SLG with self-assembled, pseudoperiodic ultrahigh refractive index (n = 8–9 at λ = 1600–5000 nm) semimetal Sn nanostructures for highly effective, broad-band infrared photon management in SLG, offering a new approach for light trapping beyond plasmonics and high refractive index dielectric photonics. The infrared absorption in SLG on fused quartz (SiO2) is greatly increased from 15% in a very broad spectral range of λ = 900–2000 nm due to the near-field electromagnetic interactions between the ultrahigh refractive index Sn nanostructures and SLG, a significant advantage over relatively narrow-band plasmonic resonances for photon management in SLG. T...

Nanoscale Core-Shell Hyperbolic Structures for Ultralow Threshold Laser Action: An Efficient Platform for the Enhancement of Optical Manipulation.

Plasmonic material has emerged with multifunctionalities for its remarkable tailoring light emission, reshaping density of states (DOS), and focusing subwavelength light. However, restricted by its propagation loss and narrowband resonance in nature, it is a challenge for plasmonic material to provide a broadband DOS to advance its application. Here, we develop a novel nanoscale core-shell hyperbolic structure that possesses a remarkable coupling effect inside the multishell nanoscale composite owing to a higher DOS and a longer time of collective oscillations of the electrons than the plasmonic-based pure-metal nanoparticles. Subsequently, a giant localized electromagnetic wave of surface plasmon resonance is formed at the surface, causing pronounced out-coupling effect. Specifically, the nanoscale core-shell hyperbolic structure confines the energy well without being decayed, reducing the propagation loss and then achieving an unprecedented stimulated emission (random lasing action by dye molecule) with a record ultralow threshold (∼30 μJ/cm2). Besides, owing to the radial symmetry of the nanoscale core-shell hyperbolic structure, the excitation of high wavevector modes and induced additional DOS are easily accessible. We believe that the nanoscale core-shell hyperbolic structure paves a way to enlarge the development of plasmonic-based applications, such as high optoelectronic conversion efficiency of solar cells, great power extraction of light-emitting diodes, wide spectra photodetectors, carrying the emitter inside the core part as quantitative fluorescence microscopy and bioluminescence imaging system for in vivo and in vitro research on human body.

Guided-mode resonant narrowband terahertz filtering by periodic metallic stripe and patch arrays on cyclo-olefin substrates

We experimentally and theoretically demonstrate a class of narrowband transmissive filters in the terahertz spectrum. Their operation is based on the excitation of guided-mode resonances in thin films of the low-loss cyclo-olefin polymer Zeonor, upon which aluminum stripe and patch arrays are patterned via standard photolithography. The filters are engineered to operate in low atmospheric loss THz spectral windows, they exhibit very high transmittance and quality factors, compact thickness, and mechanical stability. The dependence of their filtering properties on the geometrical parameters, the substrate thickness and the angle of incidence is investigated, discussing the physical limitations in their performance. This class of filters provides a cost-effective solution for broadband source or channel filtering in view of emerging terahertz wireless communication systems.

Broadband Light Harvesting for Highly Efficient Hot-Electron Application Based on Conformal Metallic Nanorod Arrays

The utilization of nonradiative decay of surface plasmons (SPs) in the form of hot electrons in metallic nanostructures has a great potential for applications in photovoltaics, photocatalysis, photodetection, and surface imaging. Unfortunately, the metallic nanostructures usually support only narrowband plasmon resonances; moreover, the hot-electron thermalization loss during the transport to Schottky interface and the confined momentum space for hot-electron injection into semiconductor together result in an inefficient internal quantum process. In this study, we propose and experimentally demonstrate a broadband super absorber based on the metallic nanorod arrays (NRs). Optically, the average absorption across the entire visible band is up to 0.8, which is over 16-fold enhancement of the planar reference. Electrically, the hot electrons are controlled to be preferentially generated near Schottky interface within the mean free path, relieving the severe hot-electron thermalization loss. Moreover, the thr...

Towards an on-chip optical microsystem for spectroscopic detection of gastrointestinal dysplasia

This paper presents a CMOS optical microsystem with a 4 × 4 photodiodes array and their readout electronics, based on 16 light-to-frequency converters, and 16 high selective optical filters, for spectrophotometric measurement of diffuse reflectance and fluorescence signals, applied to the detection of gastrointestinal dysplasia. The photodiodes array is based on n+/p-epilayer junction silicon photodiodes. Their readout electronics outputs a digital signal, with a frequency proportional to the photodiode current, featuring a sensitivity of 26 Hz/nA at 550 nm, a spectral resolution of 9 MHz and a power consumption of 1 mW. The optical filters are based on 16 thin-film narrow-band Fabry-Perot resonators, in which dielectric mirrors are used. They feature high transmittances and low full-width-half-maximum. Experimental measurements, using phantoms representative of the main absorbing, scattering and fluorescence properties of gastrointestinal tissues, proved the viability of the CMOS optical microsystem with the optical filters to extract those signals, when comparing the obtained results with commercial equipment. The implemented apparatus is ready to be used as a portable system on a surgery room to verify the total removing of gastrointestinal cancer tissue. Moreover, the developed approach is a step forward in the implementation of a gastrointestinal dysplasia detection miniaturized tool.

A refractive index sensor based on an analogy T shaped metal–insulator–metal waveguide

A refractive index sensor based on plasmonics metal–insulator–metal (MIM) waveguide coupled with an analogy T shaped resonator is proposed. The analogy T shaped resonator consists of two perpendicular rectangle cavities. At visible light range, the transmission characteristics of the sensor are investigated by using the finite-difference time-domain (FDTD) method. The transmission spectrum exhibits a Fano resonance shape, which is caused by the interaction between the broadband and narrowband resonances of the two rectangle cavities. The refractive index sensing property is systematically studied with varied structural parameters and refractive indices. The result shows the maximum sensitivity of the sensor is 680 nm/RIU. The sensor may be potential applied in integrated of optical circuits.

A graphene-based tunable guided-mode resonance narrowband mid-infrared filter

We report a graphene-based tunable ultra-narrowband mid-infrared filter which can be tuned from 4.45122 [Formula: see text]m to 4.44675 [Formula: see text]m by tuning the Fermi level from 0.2 eV to 0.6 eV. Furthermore, the reflection bandwidth is less than 0.2 nm and the reflection rate is more than 0.55. The ultra-narrowband filter is designed based on the guided-mode resonance (GMR) effect. The shift of reflection peak is mainly caused by the change of the real part of the graphene’s permittivity. This tunable ultra-narrowband mid-infrared filter can be applied in the mid-infrared microscopy.

Resonance fluorescence from an atomic-quantum-memory compatible single photon source based on GaAs droplet quantum dots

Single photon sources, which are compatible with quantum memories, are important components of quantum networks. In this article, we show optical investigations on isolated GaAs/Al0.25Ga0.75As quantum dots grown via droplet epitaxy, which emit single photons on resonance with the Rb-87-D2 line (780 nm). Under continuous wave resonant excitation conditions, we observe bright, clean, and narrowband resonance fluorescence emission from such a droplet quantum dot. Furthermore, the second-order correlation measurement clearly demonstrates the single photon emission from this resonantly driven transition. Spectrally resolved resonance fluorescence of a similar quantum dot yields a linewidth as narrow as 660 MHz (2.7 μeV), which corresponds to a coherence time of 0.482 ns. The observed linewidth is the smallest reported so far for strain free GaAs quantum dots grown via the droplet method. We believe that this single photon source can be a prime candidate for applications in optical quantum networks.

Wide-Band Circularly Polarized ReflectarrayUsing Graphene-Based Pancharatnam-Berry Phase Unit-Cells for Terahertz Communication.

A wide-band and high gain circularly polarized (CP) graphene-based reflectarray operating in the THz regime is proposed and theoretically investigated in this paper. The proposed reflectarray consists of a THz CP source and several graphene-based unit-cells. Taking advantages of the Pancharatnam Berry (PB) phase principle, the graphene-based unit-cell is capable of realizing a tunable phase range of 360° in a wide-band (1.4–1.7 THz) by unit-cell rotating, overcoming the restriction of intrinsic narrow-band resonance in graphene. Therefore, this graphene-based unit-cell exhibits superior bandwidth and phase tunability to its previous counterparts. To demonstrate this, a wide-band (1.4–1.7 THz) focusing metasurface based on the proposed unit-cell that exhibits excellent focusing effect was designed. Then, according to the reversibility of the optical path, a CP reflectarray was realized by placing a wide-band CP THz source at the focal point of the metasurface. Numerical simulation demonstrates that this reflectarray can achieve a stable high gain up to 15 dBic and an axial ratio around 2.1 dB over the 1.4–1.7 THz band. The good radiation performance of the proposed CP reflectarray, as demonstrated, underlines its suitability for the THz communication applications. Moreover, the design principle of this graphene-based reflectarray with a full 360° phase range tunable unit-cells provides a new pathway to design high-performance CP reflectarray in the THz regime.

CMOS compatible metamaterial absorbers for hyperspectral medium wave infrared imaging and sensing applications.

We experimentally demonstrate a CMOS compatible medium wave infrared metal-insulator-metal (MIM) metamaterial absorber structure where for a single dielectric spacer thickness at least 93% absorption is attained for 10 separate bands centred at 3.08, 3.30, 3.53, 3.78, 4.14, 4.40, 4.72, 4.94, 5.33, 5.60 μm. Previous hyperspectral MIM metamaterial absorber designs required that the thickness of the dielectric spacer layer be adjusted in order to attain selective unity absorption across the band of interest thereby increasing complexity and cost. We show that the absorption characteristics of the hyperspectral metamaterial structures are polarization insensitive and invariant for oblique incident angles up to 25° making them suitable for practical implementation in an imaging system. Finally, we also reveal that under TM illumination and at certain oblique incident angles there is an extremely narrowband Fano resonance (Q > 50) between the MIM absorber mode and the surface plasmon polariton mode that could have applications in hazardous/toxic gas identification and biosensing.

Extraordinary Transmission Through a Single Dielectric-Loaded Slot in a Thick Metallic Shield

Extraordinary transmission through a thick slot in a metallic shield loaded with high-permittivity dielectric is demonstrated using an analytical approximation based on the slot being small compared to a free space wavelength. In addition to previously known resonant transmission based on the fundamental waveguide mode of the slot, we show the existence of extremely narrowband resonances associated with the presence of higher order modes in the slot. Numerical simulations have been used to confirm the existence of these resonant transmission phenomena.

Analysis of high-efficiency widely-tunable N-resonances in Cs vapor

The narrow-band coherent N-type resonance, promising for the development of advanced atomic clocks, can be considered as a type of three-photon resonance, where a two-photon Raman excitation is combined with a resonant optical pumping field. In this communication, we present an experimental study and a theoretical analysis related to three-photon, bi-chromatic excitation of Cs atomic vapor contained in an 8-mm long cell with 20 Torr of neon. If a coupling laser is fixed at a frequency that is lower by several GHz than the position of the absorption profile of the Fg = 4 set of transitions, and a probe laser is tuned over the D2 line (λ = 852 nm), a narrow high-contrast enhanced absorption N-resonance will be observed in the probe light profile, superimposed on the absorption profile of the Fg = 4 set of transitions. We present theoretical modeling aimed to clarify the processes behind the efficiency of the N-resonance preparation for different frequency positions of the coupling laser within the D2 line of Cs.

Highly improved, non-localized field enhancement enabled by hybrid plasmon of crescent resonator/graphene in infrared wavelength.

The development of surface enhanced infrared absorption has been constrained by the limited field enhancement and narrow-band resonance of commonly used metal resonators. In this theoretical work, the design of a crescent resonator (CR) combined with graphene-enabled plasmon tuning is proposed to settle the drawbacks. The CR is similar to a split ring resonator (SRR), but exhibits a much improved field enhancement. The influence of graphene on the field enhancement of the CR has been systematically investigated. Coupling from localized plasmon of CR to propagating plasmon of graphene has been observed, and the constructive interference of the plasmon wave has led to not only better enhancement inside the gap but also usable enhancements all over the graphene film, which go beyond the localized nature of metal plasmons.

Universal mechanism for the binding of temporal cavity solitons

We present theoretical and experimental evidence of a universal mechanism through which temporal cavity solitons of externally-driven, passive, Kerr resonators can form robust long-range bound states. These bound states, sometime also referred to as multi-soliton states or soliton crystals in microresonators, require perturbations to the strict Lugiato-Lefever mean field description of temporal cavity solitons. Binding occurs when the perturbation excites a narrowband resonance in the soliton spectrum, which gives long oscillatory tails to the solitons. Those tails can then interlock for a discrete set of temporal separations between the solitons. The universality of this mechanism is demonstrated in fiber ring cavities by providing experimental observations of long-range bound states ensuing from three different perturbations: third-order dispersion (dispersive wave generation), the periodic nature of the cavity (Kelly sidebands), and the random birefringence of the resonator. Sub-picosecond resolution of bound state separations and their dynamics are obtained by using the dispersive Fourier transform technique. Good agreement with theoretical models, including a new vector mean-field model, is also reported.

Dual band monopole antenna based on metamaterial structure with narrowband and UWB resonances with reconfigurable quality

In this article, an Ultra Wide Band (UWB) monopole antenna based on Metamaterial (MTM) unit cell with reconfigurable feature has been developed. The proposed antenna covers 3.1–10.6GHz for UWB applications and it has a reconfigurable narrow-band for L-band (1.27GHz) and wireless applications. The gaps in Split Rings Resonator (SRR) element are made for the Left-hand capacitance and Ω-shape strip layer by four via junctions are used for Left-hand inductance. The antenna is printed on FR-4 low cost substrate with relative permittivity of 4.4 and thickness of 1.6mm. The total size of the antenna is 40mm×40mm. The simulation is carried out using HFSS commercial full-wave software. In addition, the experimental results are presented and compared with simulated results. The antenna gives a maximum peak gain of 6dBi with Omni-Directional radiation pattern and high efficiency of more than 70%. By embedding four switches in Ω-shape strip layer, a reconfigurable antenna has been successfully designed for wireless applications with sufficient qualification. The monopole part covers the UWB spectrum and the CRLH is responsible for the controllable narrowband resonance. The simulation and experimental results are confirmed by the numerical results.

A comparison of Lenz lenses and LC resonators for NMR signal enhancement.

High signal‐to‐noise ratio (SNR) of the NMR signal has always been a key target that drives massive research effort in many fields. Among several parameters, a high filling factor of the MR coil has proven to boost the SNR. In case of small‐volume samples, a high filling factor and thus a high SNR can be achieved through miniaturizing the MR coil. However, under certain circumstances, this can be impractical. In this paper, we present an extensive theoretical and experimental investigation of the inductively coupled LC resonator and the magnetic Lenz lens as two candidate approaches that can enhance the SNR in such circumstances. The results demonstrate that the narrow‐band LC resonator is superior in terms of SNR, while the non‐tuned nature of the Lenz lens makes it preferable in broadband applications.

Tunable Fano Resonance in Asymmetric MIM Waveguide Structure.

A plasmonic waveguide coupled system that uses a metal-insulator-metal (MIM) waveguide with two silver baffles and a coupled ring cavity is proposed in this study. The transmission properties of the plasmonic system were investigated using the finite element method. The simulation results show a Fano profile in the transmission spectrum, which was caused by the interaction of the broadband resonance of the Fabry-Perot (F-P) cavity and the narrow band resonance of the ring cavity. The Fabry-Perot (F-P) cavity in this case was formed by two silver baffles dividing the MIM waveguide. The maximum sensitivity of 718 nm/RIU and the maximum figure of merit of 4354 were achieved. Furthermore, the effects of the structural parameters of the F-P cavity and the ring cavity on the transmission properties of the plasmonic system were analyzed. The results can provide a guide for designing highly sensitive on-chip sensors based on surface plasmon polaritons.

Design of High-Temperature Superconducting Wideband Bandpass Filter With Narrow-Band Notch Resonators for Radio Telescope Application

This paper presents a compact wideband bandpass filter (BPF) integrating with two narrow-band notch resonators, for preventing the wideband communication system from interfering. The wideband filter adopts an asymmetric stub-loaded multimode resonator to obtain a bandwidth of 66.7%, with excellent passband fluctuation. In addition, two multiloop resonators are used to implement a 0.56% narrow-band. To illustrate its usefulness, a high-temperature superconducting wideband BPF with built-in narrow-band notch resonators is designed. It is fabricated on 20.8 mm × 16.15 mm YBCO films deposited on a 0.5-mm-thick MgO substrate with a relative permittivity ϵr of 9.78. The proposed wideband filter works at L-band, i.e., 1–2 GHz, and the return loss is greater than 19 dB. The notch-band resonator centered at 1.805 GHz provides more than 25 dB maximum attenuation for avoiding interferences from the global system for mobile communication. Finally, the circuit is measured, and the results agree well with the simulations.

On the resonant behavior of laminated accelerating structures

The laminated round metallic waveguide is one of the promising options for high frequency single-mode accelerating structures. Under certain conditions the longitudinal impedance of such type structures has a narrow-band resonance that corresponds to slowly propagating synchronous TM01 fundamental mode. In this paper the resonant properties of two parallel plates and rectangular cavity with laminated walls are studied. The first measurement results performed for the copper cavity of rectangular cross section with inner germanium layers at top and bottom walls are presented. The measurements show the existence of a dedicated resonant frequency being in a good agreement with the one predicted for the corresponding laminated parallel plates.