- 标题
- 摘要
- 关键词
- 实验方案
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Mechanical Deformation–Assisted Fabrication of Plasmonic Nanobowties with Broken Symmetry and Tunable Gaps
摘要： A symmetry broken and gap tunable gold nanobowtie array is demonstrated by nanosphere lithography performed on a mechanically uniaxially pre-stretched elastomeric substrate. Due to symmetry breaking of each nanotriangle with its three neighboring nanotriangles once the uniaxial prestretch is released, the structure exhibits polarization-dependent optical properties. In addition, the decrease in the gap between adjacent triangles provided by mechanical relaxation of the substrate enhances the electric field enhancement between adjacent triangles, which in turn results in enhanced Raman scattering from molecules present in the gap. Triangle apex-to-apex gaps as small as 20 nm are generated using a colloidal crystal formed from 500 nm colloids on at 30% prestretched substrate (gaps formed when an unstretched substrate is used are ≈115 nm).
关键词： mechanical deformation-assisted,tunable gaps,broken symmetry,plasmonic nanobowties
更新于2025-09-16 10:30:52
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Spontaneous phase symmetry breaking in a gas coupled-cavity ring laser
摘要： A theoretical model is proposed that describes the lasing dynamics in a gas ring laser (GRL) with coupled cavities. The conditions are found under which spontaneous phase symmetry of counterpropagating waves is broken in the GRL with an antiphase optical coupling of the cavities. It is shown that in the case of spontaneous phase symmetry breaking, two branches appear on the GRL frequency characteristic. In some region of frequency non-reciprocity of a ring cavity, both branches can exist under the same conditions. In this case, radiation bistability appears in the GRL, and hysteresis phenomena can be observed.
关键词： spontaneous symmetry breaking,phase non-reciprocity,beat mode,gas ring laser,coupled cavities
更新于2025-09-16 10:30:52
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Parity–Time Symmetry in Bidirectionally Coupled Semiconductor Lasers
摘要： We report on the numerical analysis of intensity dynamics of a pair of mutually coupled, single-mode semiconductor lasers that are operated in a con?guration that leads to features reminiscent of parity–time symmetry. Starting from the rate equations for the intracavity electric ?elds of the two lasers and the rate equations for carrier inversions, we show how these equations reduce to a simple 2 × 2 effective Hamiltonian that is identical to that of a typical parity–time (PT)-symmetric dimer. After establishing that a pair of coupled semiconductor lasers could be PT-symmetric, we solve the full set of rate equations and show that despite complicating factors like gain saturation and nonlinearities, the rate equation model predicts intensity dynamics that are akin to those in a PT-symmetric system. The article describes some of the advantages of using semiconductor lasers to realize a PT-symmetric system and concludes with some possible directions for future work on this system.
关键词： parity–time symmetry,intensity dynamics,semiconductor laser
更新于2025-09-16 10:30:52
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[IEEE 2019 21st International Conference on Transparent Optical Networks (ICTON) - Angers, France (2019.7.9-2019.7.13)] 2019 21st International Conference on Transparent Optical Networks (ICTON) - Real-DFT Based DCO-OFDM and ACO-OFDM for Optical Communications Systems
摘要： In this paper, a new solution is proposed for optical OFDM systems that eliminates the need for applying the Hermitian symmetry in the generation of optical OFDM signals. Our technique can completely reconstruct the OFDM signal from its pure real part without the need to transmit the imaginary data. Applying such technique has improved the performance on many aspects, where the power requirements has been reduced by 50% when compared to conventional ACO and DCO OFDM systems, the computational complexity has improved by 17%, 28% for radix-2 and radix-4 based FFT systems respectively whilst having same BER as traditional optical OFDM systems.
关键词： optical communications,Hermitian symmetry,optical OFDMA
更新于2025-09-16 10:30:52
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Universal numerical calculation method for the Berry curvature and Chern numbers of typical topological photonic crystals
摘要： Chern number is one of the most important criteria by which the existence of a topological photonic state among various photonic crystals can be judged; however, few reports have presented a universal numerical calculation method to directly calculate the Chern numbers of different topological photonic crystals and have denoted the in?uence of different structural parameters. Herein, we demonstrate a direct and universal method based on the ?nite element method to calculate the Chern number of the topological photonic crystals by dividing the typical Brillouin zone into small zones, establishing new properties to obtain the discrete Chern number, and simultaneously drawing the Berry curvature of the ?rst Brillouin zone. We also explore the manner in which the topological properties are in?uenced by the different structure types, air duty ratios, and rotating operations of the unit cells; meanwhile, we obtain large Chern numbers from – 2 to 4. Furthermore, we can tune the topological phase change via different rotation operations of triangular dielectric pillars. This study provides a highly ef?cient and simple method for calculating the Chern numbers and plays a major role in the prediction of novel topological photonic states.
关键词： Chern number,?nite element method,symmetry,topological photonic crystal
更新于2025-09-16 10:30:52
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Data processing for atomic resolution holography
摘要： In photoelectron holography, the intensity of the angular distribution of photoelectrons is measured to obtain a hologram. Thus, a hologram can be defined as a function on a sphere. X-ray fluorescence holography is similar to photoelectron holography. In this study, we describe methods for representing spherical functions that are suitable for atomic resolution holography, and the theory of conversion from the coordinate system of measurement to the various projections. We describe methods for rotational transformations and symmetry operations for atomic resolution hologram and the image composition from measured hologram fragments. In addition, several ways to remove the background from the raw hologram data are discussed.
关键词： atomic resolution holography,photoelectron holography,X-ray fluorescence holography,background removal,spherical functions,symmetry operations,rotational transformations,image composition
更新于2025-09-16 10:30:52
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Embedded waveguide band: New localized states from parity-time symmetric photonic crystal waveguide
摘要： Using conventional photonic crystal waveguides combined with the Parity-Time (PT) symmetry configuration, we study the evolution of the waveguide mode bands, and the mechanism of the band merging and the exceptional point forming. A special waveguide mode band occurs in the band evolution with a part of the band embedded in the bulky bands. The embedded band takes on a new localized state with its mode field is mainly localized in the waveguide. The frequency on the bottom of the embedded band excites a huge localized field. The exceptional point on the special band excites an asymmetric mode field in the waveguide and an amplified transmission.
关键词： Localized state,Exceptional point,Parity-time symmetry,Photonic crystal waveguides
更新于2025-09-12 10:27:22
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[IEEE 2019 Conference on Lasers and Electro-Optics Europe & European Quantum Electronics Conference (CLEO/Europe-EQEC) - Munich, Germany (2019.6.23-2019.6.27)] 2019 Conference on Lasers and Electro-Optics Europe & European Quantum Electronics Conference (CLEO/Europe-EQEC) - Different Lasing Regimes of Parity-Time Symmetric Fiber Ring Laser
摘要： The concept of parity-time (PT) symmetry in optics attracts great deal of attention. Recently, a parity-time symmetry-breaking laser consisted of two coupled microrings has been experimentally demonstrated [1, 2]. A single-mode operation in an initially multimode system was achieved through stronger mode discrimination close to a PT-symmetry breaking transition. Further on, a single transverse mode operation in a system of coupled microring lasers was demonstrated near the exceptional point [3]. A possible route to a PT symmetry-based mode-locking has been theoretically discussed in paper [4]. This work develops a recently proposed concept of PT-symmetric fiber laser [5]. The laser layout [5] comprises two fiber loops of the same length cross-coupled via a set of two fiber 50:50 couplers with incorporated adjustable phase shifts ((cid:77)1, (cid:77)2) between them. Changing phase shift difference one can control coupling ratio between two fiber loops and get either PT-symmetric or PT-broken lasing regime [5]. Using exhaustive numerical modeling based on generalized nonlinear Schr?dinger equation we investigated into spectral and spatio-temporal dynamics [6] of this PT-symmetric fiber Raman laser. In particular we demonstrate that such laser is capable to operate in a variety of lasing regimes, including turbulent [7] (stochastic quasi-stationary), laminar (coherent quasi-stationary) lasing, as well as generation of a single pulse or multiple pulses per cavity round-trip, see Fig. 1. We analyze PT-symmetry of laser radiation in each regime and show how the laser can switch between these lasing regimes by means of adjustment of pump power and phase shift between fiber loops. In particular, when (cid:77)1 ≈ (cid:77)2 the gain and loss fiber loops are almost uncoupled, the radiation is almost completely concentrated in the gain loop, so that the laser operates in PT-broken turbulent regime irrespective to pump power. In the opposite limiting case (cid:77)1 - (cid:77)2 ≈ (cid:83), two fiber loops are fully coupled. Once the pump power is above the threshold and (cid:77)1 - (cid:77)2 ≈ (cid:83), the laser always operates in PT-symmetric regime thus having equal powers in the middle of gain and loss segments. The laser produces highly coherent narrow-bandwidth radiation (laminar regime [7]) near the lasing threshold and stochastic (turbulent) radiation with broad optical spectrum and low coherence well above the threshold. We show that at intermediate phase shift 0 < (cid:77)1 - (cid:77)2 < (cid:83) where PT-transition takes place, the laser may operate in pulsed regimes with “partial” (local) symmetry, i.e. temporal areas of PT-symmetric and PT-broken radiation interleave. The laser pulses correspond to areas of PT-broken regime with power concentrated mainly inside gain loop, whereas between adjacent pulses there’s a PT-symmetric laminar background with equal extremely low-level powers at the middle of gain and loss loops.
关键词： laminar,turbulent,parity-time symmetry,fiber laser,PT-broken,PT-symmetric,pulsed,lasing regimes
更新于2025-09-12 10:27:22
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Parity-Time Symmetry in Laterally Coupled Bragg Waveguides
摘要： We investigate theoretically, in the frame of Coupled-Mode Theory (CMT), a system made of two laterally coupled, index-coupled Bragg waveguides, the modal gain of the amplifying one compensating exactly the modal losses of the other. Reverting to the supermode eigenbasis of the underlying “naked” (non-periodic) Parity-Time Symmetric (PTS) directional coupler, we derive analytically the scattering parameters of the whole structure. We also consider a system made of two purely gain-coupled Bragg waveguides, either in phase or in anti-phase. In each case, we comment upon the gain requirement for achieving a laser oscillation.
关键词： Parity-Time Symmetry (PTS),Coupled-Mode Theory (CMT),Distributed Feedback (DFB),Distributed Bragg Reflector (DBR)
更新于2025-09-12 10:27:22
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Glide-Symmetric Lens Antenna in Gap Waveguide Technology
摘要： In this paper, we propose a wideband fully-metallic impedance-matching horn lens antenna based on glide symmetry realized in the gap waveguide technology. A multiple iterative method is adopted, which overcomes the limitation of large phase deviations at the interface of traditional lens antennas, thus increases the directivity as a result. Moreover, the glide-symmetric configurations of inner metallic pins within the gap waveguide are employed to construct the artificial dielectric lens, with the advantage of the ultra-low dispersion, which is especially helpful to broaden the working bandwidth and improve the lens performance. The antenna is fed by a stepped double ridged gap waveguide which can easily excite the antenna working in a wide band. To reduce the undesired reflections at the antenna aperture, the antenna is ended with a tapered structure as an impedance transition. A prototype of the horn lens antenna is manufactured and measured, showing a broad operation bandwidth from 12 to 18.5 GHz with S11 less than -10 dB. The antenna can be further extended to the millimeter band due to the low losses of the gap waveguide at high frequencies and the iterative method can also be applied to other types of lens antenna designs.
关键词： glide symmetry,gap waveguide,Horn lens antennas
更新于2025-09-12 10:27:22