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Optimizing optical trap stiffness for Rayleigh particles with an Airy array beams

RAFAEL BONILLA, Antonio Neves, and Marcos Gesualdi

DOI: 10.1364/JOSAB.379247 Received 02 Oct 2019; Accepted 04 Dec 2019; Posted 05 Dec 2019  View: PDF

Abstract: The Airy array beams are attractive for optical manipulation of particles owing to their non-diffraction and auto-focusing properties. An Airy array beams is composed of N Airy beams which accelerate mutually and symmetrically in opposite direction, for different ballistics trajectories, that is, with different initial launch angles. Based on this, we investigate the optical force distribution acting on Rayleigh particles. Results show that is possible to obtain greater stability, for optical trapping, increasing the number of beams in the array. Also, the intensity focal point and gradient and scattering force of array on Rayleigh particles can be controlled through a launch angle parameter.

Design and analysis of slow-light Bloch slot waveguides for on-chip gas sensing

Guizhen Xu, Jin Wang, Qizheng Ji, Ming Yang, Tianye Huang, jianxing pan, Yuan Xie, and Ping Shum

DOI: 10.1364/JOSAB.380251 Received 14 Oct 2019; Accepted 04 Dec 2019; Posted 05 Dec 2019  View: PDF

Abstract: The performance of on-chip gas sensors based on light absorption is mainly determined by the light-gas interaction. In this paper, the slow-light Bloch slot waveguides (BSWs) are proposed to improve sensing performance. The sensing performance is enhanced in two mechanisms. On one hand, light is highly confined in the slot to increase the overlap of the mode field and the gas. On the other hand, the slow-light effect is achieved by adjusting the subwavelength grating period to increase the group index. By joint engineering the evanescent fields and group index, for a low pump power of 10 mW and a propagation loss of 3 dB/cm, the detection limit of 0.034 ppm in the near-infrared and the detection limit of 0.29 ppm in the mid-infrared at the optimum propagation length of 1.45 cm are obtained, respectively. The proposed BSW provides a promising platform for high performance gas sensing.

Refractive index and group velocity of electromagnetic modes in a relativistic Fermi gas at finite temperatures

J. D. Mazo-Vasquez, L. M. Hincapie-Zuluaga, and Ernesto Reyes-Gomez

Doc ID: 374789 Received 06 Aug 2019; Accepted 03 Dec 2019; Posted 03 Dec 2019  View: PDF

Abstract: A theoretical study on the optical properties of a relativistic Fermi gas at a finite temperature is performed. The results are obtained from Maxwell's equations, assuming bianisotropic constitutive relations for the relativistic gas. The longitudinal and transverse spatial directions are defined according to the properties of the electric permittivity tensor. The electromagnetic modes and the refractive index of the relativistic gas are calculated along such directions. The longitudinal and transverse group velocities corresponding to the respective propagation modes are also obtained. No typical characteristics of metamaterials are observed, neither in the refractive index nor in the group velocities corresponding to the transverse modes. However, in the case of longitudinal modes, negative values of the group velocity are observed in a region of the reciprocal space where particle-antiparticle excitations can occur.

Segmented Bayesian optimization of meta-gratings for deep sub-wavelength light focusing

Jun Jun Xiao, Dasen Zhang, Feifei Qin, Zhenzhen Liu, Guochao Wei, and Qiang Zhang

Doc ID: 376263 Received 26 Aug 2019; Accepted 03 Dec 2019; Posted 03 Dec 2019  View: PDF

Abstract: Using inverse design tools to engineer functional photonic nanostructures has been a subject of great interest over the past several years. We report combing a segmented Bayesian optimization (SBO) algorithm with the rigorous coupled wave analysis (RCWA) to design meta-gratings for sub-wavelength light focusing. Specifically, the meta-gratings comprise one-dimensional periodic arrays of large-scale supercells, each of which consists of dozens of dielectric bars. By optimizing geometry of the structure, we demonstrate two kinds of meta-gratings operating at single and double wavelengths, respectively. Both of them can focus the incoming light into periodic sub-wavelength spots with high energy density. The full-width at half maximum (FWHM) of the focusing spots for the single wavelength (λ=633 nm) case can be as small as 0.36λ, while FWHMs of the focusing spots at double wavelengths (λ=533 nm and 633 nm) are about 0.4λ. This proposed approach provides an affordable method to tackle the problem of complex photonic structure design.

Ultra-broadband TE-pass Polarizer Based on Hybrid Plasmonic-assisted Contra-directional Couplers

Xiaohan Sun and Zhengying Xu

Doc ID: 378732 Received 10 Oct 2019; Accepted 03 Dec 2019; Posted 03 Dec 2019  View: PDF

Abstract: An ultra-broadband and compact TE-pass polarizer assisted by contra-directional coupling is proposed, which consists of two identical hybrid plasmonic waveguides (HPWs) and a middle strip grating waveguide (SGW). The grating pitch of the SGW is properly designed to make TM polarization satisfy the phase-matching condition. Therefore, the launched TE mode passes through the middle SGW directly with a very low propagation loss, while the launched TM mode is contra-directional coupled to the two HPWs evenly and finally absorbed by the top metal layers. Simulation results show the proposed polarizer has a compact coupling length of ~16.48 µm, the insertion loss, extinction ratio, and the reflection loss are 0.269 dB, 27.7 dB and -16.5 dB for the fundamental TE mode at 1550 nm, respectively. In the wavelength range of 1430~1700 nm, the ER is more than 20 dB and the IL is less than 1 dB, exceeding the operating spectral to 270 nm.

Tunable double electromagnetically induced gratingwith an incoherent pumping field

Azar Vafafard and Mostafa Sahrai

Doc ID: 379540 Received 04 Oct 2019; Accepted 01 Dec 2019; Posted 03 Dec 2019  View: PDF

Abstract: We introduce double electromagnetically induced grating(DEIG) using a tripod atomic structure wherein twofields, known as probe and signal fields, with differentfrequencies experience an atomic grating, simultaneously.Properties of presented DEIG can be substantiallymodified by the detunings of the appliedfields. It is also found that applying an incoherentpumping field has a remarkable influence on the high-orderdiffraction efficiencies. Amplification of travellingweak lights via the incoherent pumping field resultsin large diffraction efficiencies in first-order andsecond-order directions. Such a novel scheme mightopen the possibility for designing the two-qubit switchwith the quantum implementation that could be advantageousin quantum information processing and quantumnetworking.

Separation of organic dye molecules to their selective photo-excitation

Gordei Anchutkin, Semen Plyastsov, George Miroshnichenko, and Igor Meshkovsky

Doc ID: 375762 Received 11 Sep 2019; Accepted 30 Nov 2019; Posted 03 Dec 2019  View: PDF

Abstract: The paper presents the results of experimental studies of the effect of selective photo-excitation on the diffusion of molecules of organic dyes Rhodamine 6G and Oxazine 1 perchlorate through silica gel. The experimental results are compared with the theoretical model presented in our previous work, which describes a decrease in the diffusion rate of molecules being excited by laser radiation and brought into triplet state. The experimental data obtained in course of present study are in qualitative agreement with the model mentioned above. It was shown that after selective photo-excitation of Rhodamine 6G molecules and their transition into triplet state, the diffusion rate decreases by 40% compared with molecules in the ground state.

Generation of higher-order sidebands based on the magnetostrictive interaction in a hybrid cavity electro-opto-magnomechanical system

Wang Bao and Yan Wei

Doc ID: 382009 Received 31 Oct 2019; Accepted 30 Nov 2019; Posted 03 Dec 2019  View: PDF

Abstract: Magnetostrictive interaction, as a nonlinear effect, provides a great opportunity to establish a tunable cavity magnomechanical system and may bring many interesting physical phenomena and potential applications. Here, we theoretically investigate the generation and control of higher-order sidebands phenomenon in a hybrid cavity electro-opto-magnomechanical system, in which the geometrical deformation of yttrium iron garnet (YIG) can be treated as an excellent mechanical resonator. We show that the amplitude of sideband can be considerably enhanced in the case of blue detuning of the microwave cavity field, and we also find an interesting pump-field-detuning-controlled optical switch effect. Furthermore, numerical calculations of the system dynamic equations show an excellent agreement with our analytical results. Our results will contribute to the understanding of nonlinear coherent phenomena and have the potential to greatly advance the fields of cavity electro-opto-magnomechanical system and nonlinear optics.

Multi-hop Nondestructive Teleportation via Different Non-maximally Entangled Channels

Fenxiang Fu and Min Jiang

Doc ID: 374489 Received 01 Aug 2019; Accepted 29 Nov 2019; Posted 03 Dec 2019  View: PDF

Abstract: In quantum communication networks, multi-hop teleportation protocols are introduced to transfer an unknown quantum state between two remote nodes which have no direct entangled pairs. We propose a faithful teleportation scheme for realizing multi-hop generalized nondestructive teleportation with different non-maximally entangled Bell pairs. With entanglement among the source node, intermediate nodes and the destination node in advance, a direct entangled channel between the source node and the destination node could be established via independent and simultaneous entanglement swapping. The integrity of initial unknown state can be kept even if teleportation fails. Thus, although the channels linking the adjacent nodes are different, faithful teleportation is still achievable with a shorter delay.

Ultrabroadband and highly coherent mid-infrared supercontinuum generation in all-normal dispersion Te-based chalcogenide all-solid microstructured fiber

Yuan Yuan, Peilong Yang, Xuefeng Peng, Zhenfei Cao, Shengjie Ding, Nan Zhang, Zijun Liu, Peiqing Zhang, Xunsi Wang, and Shixun Dai

Doc ID: 380556 Received 14 Oct 2019; Accepted 29 Nov 2019; Posted 03 Dec 2019  View: PDF

Abstract: We report an ultrabroadband supercontinuum (SC) generation with high coherence property in all-normal-dispersion (ANDi) Te-based chalcogenide all-solid microstructured optical fiber (AS-MOF). The fiber was fabricated using a rod-in-tube method that presents four As2S3 glass rods selected as low refractive index material (n = 2.4) embedded in a Ge20As20Se20Te40 glass matrix (n = 3.1). The highly symmetrical four-hole MOF preform was fabricated through the computerized numerical control precision mechanical drilling method. By engineering the structure of the fiber, we determined an ANDi characteristic in the range of 2–13.5 μm when the core diameter of the fiber was 10 μm. Under pumping at 5 μm, a highly coherent SC generation in the range of 2–13.2 μm was generated in a 16-cm-long AS-MOF with core diameter of 9.8 μm.

Smoothing Scheme for Intensity Sweep and Polarization Rotation at Subpicosecond Timescale

Bin Zhang, Muyu Yi, and Zheqiang Zhong

Doc ID: 379647 Received 02 Oct 2019; Accepted 28 Nov 2019; Posted 03 Dec 2019  View: PDF

Abstract: A novel scheme for decreasing the scattering levels of stimulated Raman scattering (SRS) and stimulated Brillouin scattering (SBS), as well as for improving illumination uniformity of focal spots is proposed. In this scheme, non-adjacent beamlets in a laser quad are frequency shifted, spatial phase shaped by conjugate phase plates, and counter-rotating circularly polarized by polarization control plates before focused by wedged lenses. Consequently, the intensity sweep and the polarization rotation of the focal spot in the timescale of subpicosecond are achieved, resulting in the reduction of the scattering level of SRS and SBS, and also the improvement of the illumination uniformity when the frequency shift between non-adjacent beamlets are comparable to the parametric backscattering growth rate and the filamentation instability growth rate. The theoretical model of the novel smoothing scheme has been established, and the influences of some key parameters including spatial modulation type, peak-to-mean value of phase distortion and frequency shift have been discussed. Results show that, the uniformity of the focal spot of this novel scheme is improved much faster than that of the conventional temporal smoothing scheme, i.e., smoothing by spectral dispersion (SSD). The parametric instabilities are significantly reduced and both phase distortion and modulation depth of the laser quad have a large tolerance, which opens a new dimension for controlling the incident light in laser plasma interaction.

Fluorescence of rubidium vapor in a transient interaction regime

Artur Aleksanyan, Svetlana Shmavonyan, Emil Gazazyan, Aleksandr Khanbekyan, Hrayr Azizbekyan, Marina Movsisyan, and Aram Papoyan

Doc ID: 377995 Received 16 Sep 2019; Accepted 26 Nov 2019; Posted 26 Nov 2019  View: PDF

Abstract: We have studied modification of the fluorescence spectra of a room-temperature atomic rubidium vapor in the region of ⁸⁵Rb and ⁸⁷Rb D₂ line while changing the temporal rate of linear (triangular) scanning of laser radiation frequency. Increase of the ramping speed over certain value (~10⁶ MHz/s) results in essential modification of magnitudes of individual atomic transitions, different on rising and falling slopes, which characterize transition from a steady-state interaction regime to a transient one. Our experimental results are well consistent with the developed theoretical model. The obtained results can be used for determination of atomic system parameters such as ground-state relaxation rate. Possible follow-up actionson addressed control of atomic levels population is discussed.

Coupling silica waveguides to photonic crystal waveguides through multilayered Luneburg lens

Seyed Hadi Badri and Mohsen Mohammadzadeh Gilarlue

Doc ID: 375310 Received 13 Aug 2019; Accepted 25 Nov 2019; Posted 25 Nov 2019  View: PDF

Abstract: We present a detailed analysis of a coupler based on the Luneburg lens to couple a silica waveguide to a photonic crystal waveguide. The dependence of coupling efficiency on the lens’s truncation, cut position of the photonic crystal structure, coupler tip width, and misalignment are investigated with two-dimensional finite element method. We implement the lens with a concentric ring-based multilayer structure. We also present a method to replace layers with very narrow widths by layers of predetermined minimum widths in the structure of the lens. The coupling loss of the designed 2.7 µm-long coupler, connecting a 2.79 µm-wide silica waveguide to a photonic crystal structure with a rod-type square lattice, is lower than 0.49 dB in the C-band. The average coupling loss in the entire S, C, L, and U bands of optical communications is 0.70 dB.

Propagation characteristics of vortex beam in anisotropic atmospheric turbulence

Rongzhu Zhang, Shanfa Tang, Jiawei Yan, and KANG yong

Doc ID: 375711 Received 19 Aug 2019; Accepted 25 Nov 2019; Posted 25 Nov 2019  View: PDF

Abstract: The phase distortion of vortex beam caused by atmospheric turbulence is calculated by power spectral inversion method. An analytical expression of the fundamental mode Gaussian vortex beam that propagates through anisotropic atmospheric turbulence has been deduced. The influences of altitude, anisotropic factor and topological charge on the propagation characteristics of vortex beam are discussed in detail. The results show that when the altitude is in the region of 3~6km, the change of altitude has little influence on the quality of vortex beam. When the altitude is in the region of 6~8km, beam quality will become better along with the increasing of altitude. Otherwise, the ability to resist distortion will be stronger with the increasing of topological charge.

Atomic switch for control of heat transfer in coupled cavities

Nilakantha Meher and S. Sivakumar

Doc ID: 370277 Received 17 Jun 2019; Accepted 21 Nov 2019; Posted 22 Nov 2019  View: PDF

Abstract: Controlled heat transfer and thermal rectification in a system of two coupled cavities connected to thermal reservoirs are discussed. Embedding a dispersively interacting two-level atom in one of the cavities allows switching from a thermally conducting to resisting behavior. By properly tuning the atomic state and system-reservoir parameters in particular system-reservoir couplings and resonance frequencies, direction of current can be reversed. It is shown that a large thermal rectification is achievable in this system by tuning the cavity-reservoir and cavity-atom couplings. Partial recovery of diffusive heat transport in an array of $N$ cavities containing one dispersively coupled atom is discussed.

Normal-mode splitting in a linear and quadraticoptomechanical system with an ensemble of two-levelatoms

He Qing, Fazal Badshah, THAMER ALHARB, LIPING LI, and Linfeng Yang

Doc ID: 371105 Received 27 Jun 2019; Accepted 21 Nov 2019; Posted 22 Nov 2019  View: PDF

Abstract: We theoretically calculate normal-mode splitting (NMS) in a linear and quadratic optomechanical system (OMS) with an ensemble of two-level atoms, where the interaction between the mechanical membrane and the optical cavity includes the linear optomechanical coupling (LOC) and the quadratic optomechanicalcoupling (QOC). In the presence of atomic ensemble, a negative QOC strength is instrumental for generating NMS, while the positive QOC restricts NMS and eventually it disappears. Further, for the hybrid OMS assisted with the atomic ensemble, the displacement spectrum of the mechanical resonator displays three peaks, where the middle peak results from the effective coupling strength between the cavity field and the atomic ensemble. Here the negative QOC strength and the effective ensemble-fieldcoupling can provide an efficient control of the amplitude and position of the three peaks.

Revisiting comparison between entanglement measures for two-qubit pure states

Urbasi Sinha, ASHUTOSH SINGH, Ijaz Ahamed, and Dipankar Home

Doc ID: 374930 Received 12 Aug 2019; Accepted 21 Nov 2019; Posted 22 Nov 2019  View: PDF

Abstract: Given a non-maximally entangled state, an operationally significant question is to quantitatively assess as to what extent the state is away from the maximally entangled state, which is of importance in evaluating the efficacy of the state for its various uses as a resource. It is this question which is examined in this paper for two-qubit pure entangled states in terms of different entanglement measures like Negativity(N), Logarithmic Negativity(LN) and Entanglement of Formation(EOF). Theoretical estimates show that percentage deviations from the maximally entangled state of any given entangled state, quantified by N vis-a-vis EOF, can differ quite appreciably, even up to ~ 15 % for states further away from the maximally entangled state, while for LN vis-a-vis EOF, the maximum value of this difference is around %. This analysis is complemented by illustration of these differences in terms of empirical results obtained from a suitably planned experimental study. Thus, such appreciable amount of quantitative non-equivalence between the entanglement measures in addressing the experimentally relevant question considered in the present paper highlights the requirement of an appropriate quantifier for such intent. We indicate directions of study that can be explored towards finding such a quantifier.

Symmetry-Engineered Waveguide Dispersion in PT Symmetric Photonic Crystal Waveguides

Adam Mock

Doc ID: 375314 Received 28 Aug 2019; Accepted 19 Nov 2019; Posted 22 Nov 2019  View: PDF

Abstract: This work demonstrates how the crystal symmetry of photonic crystal defect waveguides interacts with simple, experimentally realizable parity-time(PT) symmetric regions of chip-scale absorption and amplification to control the existence and location of exceptional points in the first Brillouin zone.Our analysis is based on Heesh-Shubnikov group theory and is generalizable to a large class of devices for which the symmetry groups can be identified.Transverse, longitudinal and transverse-longitudinal hybrid PT symmetries are considered, and for each, a triangular lattice photonic crystal waveguide with lattice-aligned and lattice-shifted cladding orientations are analyzed. We find that various symmetry combinations produce either strictly real-valued or strictly complex-valued eigenfrequencies at the Brillouin zone boundary. We also show how symmetry can be used to predict PT transitions at accidental degeneracies in the waveguide bands. It is shown how symmetry can be used to design single-mode waveguides, and we discovered exceptional points whose propagation constants are highly sensitive to the non-Hermiticity factor.

Effective detection of weak THz pulses in electro-optic sampling at kHz repetition rate

Julien Réhault, Philipp Krauspe, and Natalie Banerji

Doc ID: 378839 Received 26 Sep 2019; Accepted 19 Nov 2019; Posted 22 Nov 2019  View: PDF

Abstract: The standard THz detection mechanism known as electro optic sampling can be improved in sensitivity by biasing the polarization of the sampling field. In this work, we show theoretically and experimentally how weak signals can be amplified without inducing distortions. Our study identifies the influence of THz field strength, the polarization quality and biasing amplitude on signal amplification and distortion. Here we present a distortion free amplification of a factor of 28 while at the same time reducing the measurement time significantly.

Development and nonlinear optical characterization of phthalocyanine incorporated stable natural dye with wideband absorption for solarcell applications

Riya Sebastian and S SANKARARAMAN

Doc ID: 379747 Received 04 Oct 2019; Accepted 18 Nov 2019; Posted 22 Nov 2019  View: PDF

Abstract: The increasing demand for energy led to the development of the non-conventional energy source, solar cell, and the materials capable of harvesting light energy from sun. Of various types of solar cells dye-sensitized solar cells (DSSC) are low cost despite the lesser efficiency. The paper reports the development of cobalt phthalocyanine incorporated natural dye with high broad absorption in the 400-800 nm region and exhibiting excellent stability on ageing. The nonlinear absorption coefficient and the refractive index, studied using the open and closed aperture Z-scan technique, is also found to be high, making it best suitable for DSSC applications.

Non-reciprocity using quadrature-phase time-varying slab resonators

Mahdi Chegnizadeh, Mohammad Memarian, and Khashayar Mehrany

Doc ID: 375512 Received 19 Aug 2019; Accepted 13 Nov 2019; Posted 13 Nov 2019  View: PDF

Abstract: In this paper, it is shown that non-reciprocity can be observed in time-varying media without employing spatio-temporal modulated permittivities. We show that by using only two one dimensional Fabry-Perot slabs with time-periodic permittivities having quadrature phase difference, it is possible to achieve considerable non-reciprocity in transmission at the incidence frequency. To analyze such scenario,generalized transfer matrices are introduced to find the wave amplitudes of all harmonics in all space. The results are verified by in-house FDTD simulations. Moreover, in order to have a simple model of such time-varying slab resonators, a time-perturbed coupled mode theory is developed for multiple resonances, and it is shown that the results obtained by this method and the analytical method are in excellent agreement.

Reverse-strip-structure Ge28Sb12Se60 chalcogenide glass waveguides prepared by micro-trench filling and lift-off

Chengdong Li, Panpan Guo, Wei Huang, Wei Zhang, Peipeng Xu, and Peiqing Zhang

Doc ID: 376320 Received 26 Aug 2019; Accepted 12 Nov 2019; Posted 12 Nov 2019  View: PDF

Abstract: We propose a reverse-strip-structure chalcogenide Ge28Sb12Se60 glass waveguide prepared through micro-trench filling and lift-off technique. This fabrication method avoids processes that are directly applied to chalcogenide glass films, such as photolithography and dry etching, thereby yielding waveguides with excellent surface profiles. The nonlinear refractive index (n2), nonlinear absorption coefficient (β), and third-order nonlinear susceptibility (χ3) of the Ge28Sb12Se60 glass films are estimated by Z-scan technique, and excellent nonlinearities were observed. The linear optical losses of the as-prepared waveguide samples with cross-sectional area of 3.0 × 1.0 and 5.0 × 1.0 μm2 are measured and calculated to be 2.2 and 1.7 dB/cm at 1550 nm, respectively, using the lensed fiber and cut-back method. This study predicts that reverse-strip-structure waveguides based on micro-trench filling and lift-off technique are promising candidates for high-quality on-chip integrated nonlinear optical devices and warrant further research.

Flexible Pulse Shaping for Sum Frequency Microspectroscopies

Niklas Müller, Tiago Buckup, and Marcus Motzkus

Doc ID: 377232 Received 04 Sep 2019; Accepted 11 Nov 2019; Posted 11 Nov 2019  View: PDF

Abstract: The complexity of experimental schemes still challenges the broad application of multimodal microscopy beyond fundamental research. Pulse shaping has been a promising candidate to assist in the implementation of flexible and compact schemes. In this work, its application is demonstrated for vibrational resonant Sum Frequency (SF) spectroscopy in a nonlinear Raman microscope. The mixing of an ultrabroadband NIR laser pulse with a difference-frequency generated MIR spectrum provides spectral access from 1750 cm-¹ to beyond 3000 cm-¹ via two shaping methods: (i) a homodyne MIR scanning and (ii) a heterodyne multiplex method. The versatility of shaper-based SF is demonstrated in the spectroscopy and microscopy of crystalline cholesterol and cysteine.

Strong Purcell effect for magnetic dipole emission with spoof plasmonic spiral structure

Hongwei Wu, Jia-Qi Quan, Yun-Qiao Yin, and Zong-Qiang Sheng

Doc ID: 374201 Received 30 Jul 2019; Accepted 05 Nov 2019; Posted 25 Nov 2019  View: PDF

Abstract: The ability to manipulate the interaction between light and optical emitters is essential for enhancing the capability of optical devices. Multifarious metallic and all-dielectric structures have been proposed frequently to enhance the emission of electromagnetic dipole through the Purcell effect, which its performances depend on two confinement mechanisms: temporal confinement (photon cavity period) and spatial confinement (localized light in an enclosed space), which can be described by the quality factor and mode volume, respectively. Here, we demonstrate that a hollow spoof plasmonic spiral structure in deep-subwavelength scale, which is constituted by periodically inserting spiral-shaped metallic arms into a hollow silicon cylinder, can drastically enhance emission of magnetic dipole. Particularly, ultra-high quality factor and ultra-small mode volume of the magnetic resonance can be realized by further increasing the spiral degree of metallic arms. The results indicate that the quality factor of magnetic dipole mode in the structure can be enhanced to 2600 (silicon5.5 for same scale) for spiral degree 4, and the Purcell factor can be enhanced to 5×106 (silicon5.1) for a magnetic dipole emission. These results may provide a new avenue for designing optical cavities and enhancing magnetic dipole emission in low frequency.

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