Resonator Losses Research Articles

Numerical analysis of the pump’s spectral linewidth impact on single and multi-wavelength Brillouin fiber lasers

Brillouin fiber lasers (BFLs) are a promising optical source technology for industrial and academic purposes that have experienced continuous progress in recent years. Currently, part of this development is focused on delivering laser solutions with low resonator loss, relatively low pump threshold, high efficiency, very small linewidth, and multi-wavelength architecture. In this perspective, this study employs an accurate numerical model based on an analytical solution to investigate the effect of the pump’s spectral linewidth on BFLs working both in single and cascaded multi-wavelength configurations. Output powers, thresholds, and the Stokes lines number simulated are analyzed here using a standard single-mode optical fiber as the Brillouin gain medium. The numerical results obtained not only allow identifying the regions of the pump’s spectral linewidth in which there is greater, moderate, or even no suppression of the stimulated Brillouin scattering inside the laser cavity but also provides a deep understanding of the internal dynamics of the BFLs cavities.

Modal parameter calculation for viscoelastic composite structures from reduced order models

The moduli and loss factors of viscoelastic materials are frequency-dependent, which brings difficulty to solve the eigenvalue problems. In this note, an estimation method for resonance frequencies and loss factors of viscoelastic composite structures from reduced order models is presented. The reduced order model could be constructed from calculated or measured forced vibration data, and there is no need to know the specific structural matrices or to solve the eigenvalue problem of the vibration system directly. Thus, the difficulties caused by frequency-dependent behaviors of moduli and loss factors of viscoelastic materials are avoided. Numerical examples are presented to illustrate and validate the method.

Using thermo-optical nonlinearity to robustly separate absorption and radiation losses in nanophotonic resonators.

Key for optical microresonator engineering, the total intrinsic loss is easily determined by spectroscopy; however, quantitatively separating absorption and radiative losses is challenging, and there is not a general and robust method. Here, we propose and experimentally demonstrate a general all-optical characterization technique for separating the loss mechanisms with high confidence using only linear spectroscopic measurements and an optically measured resonator thermal time constant. We report the absorption, radiation, and coupling losses for ten whispering-gallery modes of three different radial orders on a Si microdisk. Although the total dissipation rates show order-of-magnitude differences, the small absorptive losses are successfully distinguished from the overwhelming radiation losses and show similar values for all the modes as expected for the bulk material absorption.

Simulation design of silver nanoparticle coated photonic crystal fiber sensor based on surface plasmon resonance

Surface Plasmon Resonance (SPR) is the charge density excitation oscillation (surface Plasmon’s, (SP)) caused by the polarized light along with the metal-dielectric interface by agreeing to phase-matching condition between polarized light and SPR. SPR method has unusual advantages like label-free, real-time and high resolutions with less than 10-7 RIU which is not consenting with other sensing methods. Photonic Crystal Fiber (PCF) presents unique features like design elasticity, geometric flexible and extraordinary guiding mechanism which head for better performance contrast conventional optical fibre, Additionally, the presence of air holes gives the possibility to insert multi able materials, that can recognize the interaction of travelling light and materials operatively. Adding the advantages of PCF to the properties of SPR, lead to design very strong and unique devices in different applications. In this paper, the PCF sensor based on SPR technique had been presented. The inner holes of PCF were coated with silver and then filled with air and ethanol. This was achieved theoretically by Finite Element Method (FEM). When the phase-matching condition was achieved at a fixed wavelength, the energy of the core-guided mode is shifted to the plasmon area and a resonant loss peak is observed at this wavelength. The simulated results show that a blue shifting is obtained when the outer air holes of PCF is filling with ethanol while the inner ring is filled with silver nano-particles. The maximum resolution and sensitivity are 5.66*10-4 RIU, 132.3 nm/RIU respectively in the sensing range of air refractive index to ethanol refractive index are obtained. The submitted design could be very useful in many fields like refractive index and temperature sensing applications.

Heterocoagulation method for preparation of composite fluoropolymer particles with core–shell structure for optimized electromagnetic performance

Tetrafluoroethylene-hexafluoropropylene copolymer (FEP) plays an important role in 5G communication era. Nevertheless, FeSiCr ferrite as inorganic particles were hardly incorporated in fluoropolymer phase. Heterocoagulation process represents an ideal solution making the inorganic particles disperse uniformly in the fluoropolymer phase. In this work, cetyltrimethylammonium bromide (CTAB) assumes a double-sided role in heterocoagulation for preparing C-FeSiCr@FEP5 with core–shell structure. Here, CTAB can not only make C-FeSiCr favorable dispersibility initially but also breaks FEP/C-FeSiCr-mixed dispersion system accelerating the heterocoagulation process. Due to the safeguard of FEP, natural resonance and eddy current loss as main attenuation mechanisms could be avoided for C-FeSiCr@FEP5 in the testing frequency range (1–18 GHz). The dielectric constant values of C-FeSiCr@FEP5 sample keep 2.11 from1.0 to 18.0 GHz with low dielectric loss, while their magnetic permeabilities are still above 1.00 with decreasing trend of magnetic loss at the same frequency range. C-FeSiCr@FEP5 composites with optimized electromagnetic performance are expected to have a broad range of applications in 5G communication, especially for miniature antenna.

Design of two miniaturized and broadband polarization filters based on two types of square-lattice gold-filled photonic crystal fibers

Two ultra-broadband polarization filters based on Structure 1 and Structure 2 are reported and characterized in terms of attenuation, crosstalk, bandwidth, and polarization filtering properties by the finite element method. Structure 1 is formed by introducing partial elliptical air holes in the first layer of the square-lattice gold-filled photonic crystal fiber. Based on the design solution of Structure 1, Structure 2 is arranged by using circular air holes with the changed transverse pitch to replace elliptical ones. Numerical results show that high resonance intensities of 2265.07 and 1831.83 dB/cm for y polarization, together with the corresponding x polarization losses of 0.50 and 0.18 dB/cm at respective communication wavelengths of 1.55 and 1.31 μm can be achieved by varying the gold film thickness for Structure 1.Moreover, the design of Structure 2 with all circle holes can also realize a high resonance loss of 1942.54 dB/cm for y polarization with a low loss of 0.43 dB/cm for x polarization at 1.55 μm. Structure 1 and Structure 2 with the fixed fiber length of 300 μm can obtain the crosstalk values of −590.09 and −506.07 dB at 1.55 μm, together with the bandwidths of 1500 and 900 nm, respectively. Additionally, two types of designs represent good produce tolerances. These results show a high potential of the suggested fiber for application in polarization-dependent filtering and other polarizing devices.

Lossy Microwave Filters With Active Shape Correction

Obtaining the prescribed microwave filter response is highly desirable for proper frequency selectivity in RF transceivers. As the traditional microwave filter design methods do not take into account finite unloaded quality factors, lossy resonators cause significant deviations from the prescribed filter response, especially in filters with narrow bandwidths or of high orders. This deviation gets more severe as the resonator losses increase. Building on the lossy filter design techniques by using an active shape correction mechanism, this paper proposes a new approach to recover the filter response when the filter has moderately-to-highly lossy resonators. Being different than most active filter topologies, where all of the resonators are loss-compensated, this study aims at achieving the shape correction with $N-2$ active elements. To characterize the design, a novel lossy-active coupling matrix is introduced by extending the $(N+2) \times (N+2)$ lossy coupling matrix. The proposed theory is verified with the design and fabrication of two $3^{rd}$ order 5 % bandwidth filters operating at 1 GHz and employing resonators with quality factors of 100 and 28, respectively. It has been shown that the method can recover the response in both designs and the theoretical and measured responses are in good agreement.

Synthesis of nitrogen-doped reduced graphene oxide/cobalt-zinc ferrite composite aerogels with superior compression recovery and electromagnetic wave absorption performance.

Graphene aerogels possessing a three-dimensional (3D) porous netlike structure, good electrical conductivity and ultralow density have been widely regarded as a promising candidate for high-efficiency electromagnetic wave (EMW) absorption. Herein, nitrogen-doped reduced graphene oxide/cobalt-zinc ferrite (NRGO/Co0.5Zn0.5Fe2O4) composite aerogels were synthesized through a solvothermal and subsequent hydrothermal self-assembly two-step method. The results of micromorphology analysis showed that the 3D networks were well constructed through the partial stacking of adjacent NRGO sheets, which were decorated with numerous Co0.5Zn0.5Fe2O4 microspheres. The as-synthesized NRGO/Co0.5Zn0.5Fe2O4 composite aerogels have a very low density (12.1-14.6 mg cm-3) and good compression recovery. Moreover, excellent EMW absorption performance could be achieved through facilely regulating the additive volume of ethylenediamine (i.e. nitrogen doping contents) and filler contents. Impressively, the composite aerogel with a doped nitrogen content of 2.5 wt% displayed the optimal minimum reflection loss (RLmin) of -66.8 dB in the X-band at a thickness of 2.6 mm and the broadest effective absorption bandwidth of 5.0 GHz under an ultrathin thickness of merely 1.6 mm. Meanwhile, the RLmin of NRGO/Co0.5Zn0.5Fe2O4 composite aerogels below -20 dB could be reached in almost the whole tested thickness range (1.4-5.0 mm). Additionally, the potential EMW absorption mechanisms were revealed, which was mainly due to the unique 3D porous netlike structure, synergistic effects among conduction loss, magnetic resonance loss and polarization loss, as well as the balanced attenuation capacity and impedance matching. It was believed that this work provided an alternative way for fabricating strong mechanical graphene-based 3D magnetic/dielectric composites as light-weight and high-efficiency EMW absorbers.

A flexible metamaterial based on liquid metal patterns embedded in magnetic medium for lightweight microwave absorber

Lightweight electromagnetic absorbing materials with thinner thickness and low density are highly desired for practical applications. In this work, a thin and lightweight magnetic metamaterial absorber was proposed by embedding liquid metal resonant patterns in magnetic composites medium with a low filling rate. Due to the coupling of magnetic medium and metamateria as demonstrated by CST (Computer Simulation Technology) simulation, the strong electromagnetic resonant loss and multiple reflections were rationally introduced. The obtained metamaterial absorber endows the strong absorption performance of −23.63 dB, an effective absorption bandwidth (EAB, with RL less than −10 dB) of 2.46 GHz under 0.9 mm and with a 1.91 g/cm3 density merely. The introduction of resonance patterns in the magnetic composites medium is an efficient way to fabricate lightweight and thin thickness metamaterials for high-performance microwave absorbers.

Sandwich-like sulfur-free expanded graphite/CoNi hybrids and their synergistic enhancement of microwave absorption

Sulfur-free expanded graphite (EG) was prepared by chemical oxidation, then EG-based cobalt-nickel alloy hybrid (EG@CoNi) was obtained via hydrothermal method in this work. CoNi particles with the diameter of 0.1–0.5 µm were tightly attached to the surface of the layered EG. The incorporation of CoNi was conducive to the absorption of electromagnetic waves due to the increase in Ms and Hc, which enhanced the soft magnetization of EG@CoNi hybrids. The resulting EG@CoNi hybrids exhibited better dielectric loss than CoNi particles, and the optimal value of reflection loss (RL) reached − 50 dB, while the optimal bandwidth less than − 10 dB was 4 GHz, indicating enhanced microwave absorption characteristics. The well impedance matching and electromagnetic wave attenuation of EG@CoNi hybrids benefited from the synergy and double-loss mechanism between CoNi nanoparticles and EG. The dielectric loss in the double-loss mechanism was mainly dipole polarization and interface polarization, while the magnetic loss was mainly the natural ferromagnetic resonance and eddy current loss of CoNi nanoparticles. These multi-layer EG@CoNi hybrids with light weight and high dielectric characteristics would show good application prospects in high-efficiency electromagnetic wave absorbers.

Nonlinear vibration analysis of circular/annular/sector sandwich panels incorporating magnetorheological fluid operating in the post-yield region

This study offers a comprehensive analysis on the nonlinear vibratory behavior of circular, annular, and sector sandwich panels containing magnetorheological (MR) fluid as the core layer. Due to the large deformation experienced by the sandwich structures, the MR fluid operates in the post-yield region, in which the shear strain and shear stress are nonlinearly dependent. The post-yield characteristics of the MR fluid are quantified using the experimental results available in the literature. The present study also employs the experimental results presented in the literature on the dynamic characteristics of a MR based sandwich circular plate to demonstrate accuracy of the results. To identify governing equations of motion of the structures, a finite element approach based on von Karman formulations is employed. Moreover, displacement control strategy is used to solve the extracted nonlinear equations and evaluate dynamic characteristics of the MR based circular/annular/sector sandwich plates in terms of resonant frequencies and loss factors. This study highlights the effect of post-yield behavior of the MR fluid in the nonlinear vibration attenuation of MR sandwich structures, under different levels of magnetic field. Also, the effects of maximum deformation and magnetic field on the functionality of the MR fluid are comprehensively investigated.

Facile preparation of cotton-derived carbon fibers loaded with hollow Fe3O4 and CoFe NPs for significant low-frequency electromagnetic absorption

Nowadays, the fast progress of wireless-communication, radar reconnaissance and electronic technology induces many serious problems such as electromagnetic interference and superfluous electromagnetic radiation. Herein, the cotton-derived CFs@H-Fe3O4/CoFe hybrid was prepared via a simple two-stage method of hydrothermal and calcination. For the synergistic effect of magnetic and dielectric loss, the mentioned ternary hybrid possesses outstanding low-frequency microwave absorbing capacity, concretely owing to the better dipole and interface polarization, conduction loss, eddy-current and natural resonance loss, multi-ply scattering and reflection, improved impedance matching etc. The maximal RL values can reach −40.15 dB at 0.71GHz and −40.85 dB at 0.59GHz for the thickness of 3 mm and 3.5 mm respectively, and a board low-frequency EAB of 0.79–2.93GHz can be also achieved at only 1.5 mm thickness. This biomass-based hybrid could be employed as a novel low-frequency microwave absorbent for its good properties and simple preparation process.

Continuous-wave efficient cyan-blue Pr:YAlO$$_3$$ laser pumped by InGaN laser diode

We report on the first continuous-wave quasi three-level laser emitting in the cyan-blue spectral range in praseodymium-doped oxide materials, as we believe. Pr:YAlO $$_3$$ crystal, cooled to the cryogenic temperatures, was used as an active medium. To minimize resonator losses, the cavity mirrors were directly deposited on the crystal faces to form a microchip geometry. More than half-Watt of the output power at 493 nm wavelength with a slope efficiency of 26% has been obtained under 3 W InGaN laser diode pumping at 447 nm wavelength.

Tunable and weakly invasive probing of a superconducting resonator based on electromagnetically induced transparency

Superconducting cavities with high quality factors play an essential role in circuit quantum electrodynamics and quantum computing. In measurements of the the intrinsic loss rates of high frequency modes, it can be challenging to design an appropriate coupling to the measurement circuit in such a way that the resulting signal is sufficiently strong but also that this coupling does not lead to unwanted loading circuit, obscuring the intrinsic internal loss rates. Here, we propose and demonstrate a spectroscopic probe of high-Q resonators based on the phenomena of electromagnetically-induced transparency (EIT) between the resonator and qubit in the weak dispersive coupling regime. Applying a sideband drive signal to the qubit, we observe an interference dip originated from EIT in the qubit spectroscopy, originating from the quantum interference between the qubit probe signal and sideband transition. From the width and the depth of the dip, we are able to extract the single-photon linewidth of the resonator from an analytical model. Working in a previously unexplored regime in which the qubit has a larger linewidth than the resonator reduces the technical challenge of making a high-coherence qubit and is advantageous for remaining in the weakly-invasive limit of coupling to the resonator. Furthermore, the sideband and the dispersive coupling between the resonator and the qubit can be tuned $in~situ$ controlling the strength of the sideband drive power. This $in-situ$ tuneability allows the technique to be applied for efficient measurement of the resonator loss rate for any quality factor below a fixed upper bound, on the order of $10^8$ for our device, allowing a wide range of quality factors to probed using a single design.

Full-orbit simulation of fast ion loss under resonant magnetic perturbations in the EAST tokamak

A new full-orbit Monte Carlo code (SOFT) has been developed and used to investigate how resonant magnetic perturbation (RMP) affects the loss of neutral beam injection ions in EAST. Benefiting from the calculation of real orbits in cylindrical coordinates, the simulation can take into account the first wall and provide a more realistic evaluation of the losses than previous results. The two co-current beams in EAST are chosen for the study. Depending on the spectrum used, losses can be significantly enhanced by low-n (n ≤ 2) RMPs. From the quantity perspective, the prompt loss and the resonant loss are the two loss channels of concern. The former is mainly related to the ion source, while the latter is closely related to RMP and quantitatively more dominant. It is found that both linear and non-linear resonances play an important role, which is consistent with previous results. The inclusion of plasma response, to a large extent, heals the magnetic topology, but does not necessarily lead to a better confinement of fast ions. Detailed analyses reveal the significant loss of passing ions in the presence of the response, which highlights the importance of the non-resonant components. A better understanding of the loss channels and their relation to the RMP spectrum helps to avoid the detrimental effects and to provide support for goals like phase-space engineering.

Breaking plasmonic symmetry through the asymmetric growth of gold nanorods

The optoelectronic properties of asymmetric metal nanostructures are of current interest for applications in photonics, sensing, and catalysis. Here, we break the symmetry of the localized surface plasmon resonance of gold nanorods by selective overgrowth of a single tip via a high-yield ( > 80 % ) wet-chemical method. While optical spectroscopy exhibits a bathochromic shift of the nanoparticle plasmon resonance, cathodoluminescence and electron energy loss spectroscopy measurements reveal a breaking of the symmetry of the associated localized surface plasmon resonance mode, which results in the subwavelength concentration of electromagnetic energy. The simple, one-step postsynthetic modification allows control of nanoparticle structural parameters, and we demonstrate how the asymmetric energy redistribution leads to increases in the surface-enhanced Raman scattering of a model analyte attached to the surface of the nanostructures. The spatial localization of energy in these nanostructures may find applications in nanofocusing, nanoimaging, and light harvesting.

Synthesis of 3D flower-like ZnO/ZnCo2O4 composites with the heterogeneous interface for excellent electromagnetic wave absorption properties

Reasonable structure and composition are essential for electromagnetic wave absorption (EMW). Herein, ZnO hollow spheres were prepared with carbon spheres as templates and then synthesized ZnO/ZnCo2O4 composites by the solvothermal method and annealing treatment. The flower-like ZnCo2O4 material was produced by self-assembly of ZnCo2O4 nanosheets. The absorbing material with the complex structure has multiple scattering and reflection, conduction loss, resonance, and eddy current loss characteristics. Furthermore, the addition of ZnO hollow spheres has a significant impact on electromagnetic parameters and absorption properties. As a result, the addition of ZnO hollow spheres can greatly enhance the complex permittivity of the ZnO/ZnCo2O4 composites and obtain excellent EMW absorbing properties. It is worth noting that ZnO/ZnCo2O4 composites show the best EMW absorption properties when the ZnO hollow spheres were added up to 5 mg. The minimum reflection loss is −55.42 dB and a matching thickness of 1.99 mm while the maximum effective absorption bandwidth can also reach 7.44 GHz with a matching thickness of 2.4 mm. Our research can prove that the structure and composition have a significant influence on the properties of the absorbing material, which provides ideas for the development of absorbing materials with high-performance.

Recycling of waste straw in sorghum for preparation of biochar/(Fe,Ni) hybrid aimed at significant electromagnetic absorbing of low-frequency band

Due to the rapid development of wireless electrommunication and electronic techniques in current age, electromagnetic radiation and electromagnetic interference (EMI) have brought serious threat to the normal operation of precision electronic instruments and human health. Herein, the reclaimed straw of sorghum derived biochar/(Fe,Ni) hybrid has been prepared via a facile calcination process. The as-prepared hybrid possesses an outstanding low-frequency electromagnetic absorbing performance i.e. the maximum RL of T-600 can achieve −44.18 dB with effective absorption bandwidth (EAB) of 0.17~0.99 GHz for 2 mm and a board EAB of 0.53~2.49 GHz for only 1 mm. Meanwhile, the maximum RL of T-700 can attain −46.36 dB with EAB of 0.49~1.43 GHz and the board EAB of 0.89~2.81 GHz for the same thickness, which are owing to the cooperative effect of interface polarization, dipole polarization, natural resonance, eddy current and conduction loss, multi-reflection and scatter, better impedance matching and so on. This environmentally-friendly biochar/(Fe,Ni) hybrid can be employed as a novel low-frequency microwave absorbent for its good performance and reclamation of waste straw in sorghum.

Self-organized synchronization of mechanically coupled resonators based on optomechanics gain-loss balance

We investigate collective nonlinear dynamics in a blue-detuned optomechanical cavity that is mechanically coupled to an undriven mechanical resonator. By controlling the strength of the driving field, we engineer a mechanical gain that balances the losses of the undriven resonator. This gain-loss balance corresponds to the threshold where both coupled mechanical resonators enter simultaneously into self-sustained limit cycle oscillations regime. Rich sets of collective dynamics such as in-phase and out-of-phase synchronizations therefore emerge, depending on the mechanical coupling rate, the optically induced mechanical gain and spring effect, and the frequency mismatch between the resonators. Moreover, we introduce the quadratic coupling that induces enhancement of the in-phase synchronization. This work shows how phonon transport can remotely induce synchronization in coupled mechanical resonator array and opens up new avenues for metrology, communication, phonon-processing, and novel memories concepts.

A Micro Structure POF Relative Humidity Sensor Modified With Agarose Based on Surface Plasmon Resonance and Evanescent Wave Loss

A novel high sensitivity relative humidity (RH) sensor was proposed by using micro structure plastic optical fiber (POF) based on the surface plasmon resonance (SPR) effect and the evanescent wave (EW) loss. The micro structure was fabricated on the POF and coated with a gold layer and agarose, adopting the sputtering and dip-coating technique. These construction effects on the attenuation of power caused by the SPR effect and the EW loss were used to perform RH detections. The agarose’s different refractive indexes (RIs) caused fluctuations in the transmission power when the humidity increased. The demonstrated experimental results showed that the proposed sensor achieved a linear response from 20% RH to 80% RH with a high sensitivity of 0.595µW/%. The proposed sensor had the advantages of fast response and recovery. Furthermore, the temperature dependence and the repeatability test of the sensor were also performed.