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Mode-Locked Topological Insulator Laser Utilizing Synthetic Dimensions
摘要： We propose a system that exploits the fundamental features of topological photonics and synthetic dimensions to force many semiconductor laser resonators to synchronize, mutually lock, and under suitable modulation emit a train of transform-limited mode-locked pulses. These lasers exploit the Floquet topological edge states in a 1D array of ring resonators, which corresponds to a 2D topological system with one spatial dimension and one synthetic frequency dimension. We show that the lasing state of the multielement laser system possesses the distinct characteristics of spatial topological edge states while exhibiting topologically protected transport. The topological synthetic-space edge mode imposes a constant-phase difference between the multifrequency modes on the edges, and together with modulation of the individual elements forces the ensemble of resonators to mode lock and emit short pulses, robust to disorder in the multiresonator system. Our results offer a proof-of-concept mechanism to actively mode lock a laser diode array of many lasing elements, which is otherwise extremely difficult due to the presence of many spatial modes of the array. The topological synthetic-space concepts proposed here offer an avenue to overcome this major technological challenge and open new opportunities in laser physics.
关键词： Synthetic Dimensions,Topological Insulators,Mode-Locked Lasers,Photonics
更新于2025-09-23 15:21:01
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THz photodetector using sideband-modulated transport through surface states of a 3D topological insulator
摘要： The transport properties of the surface charge carriers of a three dimensional topological insulator under a terahertz (THz) field along with a resonant double barrier structure is theoretically analyzed within the framework of Floquet theory to explore the possibility of using such a device for photodetection purposes. We show that due to the contribution of elastic and inelastic scattering processes in the resulting transmission, side-bands are formed in the conductance spectrum. This side band formation is similar to the side-bands formation in cavity transmission spectra in an optical cavity and this information can be used to detect the frequency of unknown THz radiation. The dependence of the conductance on the bias voltage, the effect of THz radiation on resonances and the influence of zero energy points on the transmission spectrum are also discussed.
关键词： THz radiation,Floquet theory,surface states of topological insulators,side bands in transmission spectrum
更新于2025-09-23 15:21:01
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Resonant pumping of polaritonic SSH chains
摘要： An optical-lattice realization of a Su-Schrieffer-Heeger chain is theoretically investigated. The topological state is controlled by the relative phase of the lasers constructing the lattice. The hopping amplitudes are calculated within the harmonic approximation to the optical potential in the vicinity of its minima. Finally, we examine polaritons loaded into adiabatically shaken optical lattices with damping and pumping and demonstrate that, in the case of resonant pumping, the system manifests different quantitative and qualitative behaviour for topologically trivial and non-trivial phases.
关键词： Su-Schrieffer-Heeger chain,topological insulators,polaritons,resonant pumping,optical lattices
更新于2025-09-23 15:21:01
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Transmission-Line Model for Materials with Spin-Momentum Locking
摘要： We provide a transmission-line representation for channels exhibiting spin-momentum locking (SML) that can be used for both time-dependent and steady-state transport analysis on a wide variety of materials with spin-orbit coupling such as topological insulators, Kondo insulators, transition metals, semimetals, oxide interfaces, and narrow band-gap semiconductors. This model is based on a time-dependent four-component di?usion equation obtained from the Boltzmann transport equation assuming linear response and elastic scattering in the channel. We classify all electronic states in the channel into four groups (U+, D+, U?, and D?) depending on the spin index [up (U), down (D)] and the sign of the x component of the group velocity (+, ?) and assign an average electrochemical potential to each of the four groups to obtain the four-component di?usion equation. For normal metal channels, the model decouples into the well-known transmission-line model for charge and a time-dependent version of the Valet-Fert equation for spin. We ?rst show that, in the steady-state limit, our model leads to simple expressions for charge-spin interconversion in SML channels in good agreement with existing experimental data on diverse materials. We then use the full time-dependent model to study spin-charge separation in the presence of SML, a subject that has been controversial in the past. Our model shows that the charge and spin signals travel with two distinct velocities, resulting in well-known spin-charge separation, which is expected to persist even in the presence of SML. However, our model predicts that the lower velocity signal is purely spin, while the higher velocity signal is largely charge with an additional spin component proportional to the degree of SML, which has not been noted before. Finally, we note that our model can be used within standard circuit simulators such as SPICE to obtain numerical results for complex geometries.
关键词： spin-orbit coupling,spin-charge separation,transmission-line model,topological insulators,charge-spin interconversion,spin-momentum locking
更新于2025-09-23 15:21:01
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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) - Theoretical Analysis of a Non-Quantized Square-Root Topological Insulator using Photonic Aharonov-Bohm Cages
摘要： Topological insulators have to date seen a variety of manifestations. All available realizations of topological insulators, however, share a common feature: their spectral bands are attributed with a nonlocal topological index that is quantized. In this work, we report a new type of insulator exhibiting spectral bands with nonquantized indices, yet robust boundary states. We provide a theoretical analysis based on the quantization of the indices in the corresponding system where the square of the Hamiltonian is taken and exemplify the general paradigm using photonic Aharonov-Bohm cages. Taking the square-root of the Klein-Gordon Hamiltonian has opened up an entirely new realm of physics: the resulting Dirac operator provided a relativistic quantum description of massive spin-1/2 fermionic particles, thus disclosing the fine-structure spectra of atoms or the anomalous Zeeman effect. Along a similar line, we consider a three-band model that can have nonquantized topological indices, but with a spectral symmetry that gives rise to quantized topological invariants when the square of the Hamiltonian is taken. This relation generates the topological characterization of the square-root model and allows us to establish a topological bulk-boundary correspondence with states that can be used as in-gap, protected and controllable qubits. Notably, whereas taking the square of the Dirac operator leads to the topologically trivial Klein-Gordon model, in our case, the squared model maps to an effective Su-Schrieffer-Heeger (SSH) model in its nontrivial phase. Optical settings prove to be ideally suited for realizing various topological phenomena. In this vein, we employ photonic waveguide lattices with effective negative hopping amplitudes to realize a 3-band quasi-1D chain made of photonic Aharonov-Bohm cages that exemplifies our general description. In summary, we predict and demonstrate the physics of a square-root topological insulator, using a photonic platform. Specifically, we show that the AB cages have in-gap states, above bands possessing nonquantized Zak’s phases. Furthermore, we find that these states are robust, both in energy and localization, against symmetry-preserving perturbation and disorder. We show that this robustness stems from the corresponding system where the square of the Hamiltonian is taken and where the bands exhibit quantized topological indices with associated in-gap boundary states.
关键词： nonquantized indices,photonic Aharonov-Bohm cages,square-root topological insulator,robust boundary states,Topological insulators
更新于2025-09-23 15:19:57
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Quantum cascade laser lives on the edge
摘要： Electromagnetic waves with frequencies in the terahertz range (300?GHz to 10?THz) have applications in many areas, from imaging and security screening to the atmospheric and biological sciences. Semiconductor devices called quantum cascade lasers (QCLs) provide the most compact and efficient way to generate terahertz radiation. In QCLs, electrons cascade down in energy through a series of discrete quantum energy levels, emitting a photon at each step1. But, as with all compact semi conducting lasers, QCLs are notoriously sensitive to fabrication imperfections, which results in device-to-device variability of the laser output frequency. Now, on page 246, Zeng et al.2 report the realization of a terahertz QCL that is insensitive to such disorder. This achievement opens the door for terahertz lasers and optoelectronics that have unprecedented stability and fabrication reproducibility.
关键词： topological protection,terahertz radiation,topological insulators,photonics,quantum cascade lasers
更新于2025-09-19 17:13:59
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Recent progress in ultrafast lasers based on 2D materials as a saturable absorber
摘要： Two-dimensional (2D) materials are crystals with one to a few layers of atoms and are being used in many fields such as optical modulator, photodetector, optical switch, and ultrafast lasers. Their exceptional optoelectronic and nonlinear optical properties make them as a suitable saturable absorber for laser cavities. This review focuses on the recent progress in ultrafast laser use 2D materials as a saturable absorber. 2D materials traditionally include graphene, topological insulators, transition metal dichalcogenides, as well as new materials such as black phosphorus, bismuthene, antimonene, and MXene. Material characteristics, fabrication techniques, and nonlinear properties are also introduced. Finally, future perspectives of ultrafast lasers based on 2D materials are also addressed.
关键词： saturable absorber,MXene,antimonene,bismuthene,graphene,ultrafast lasers,transition metal dichalcogenides,black phosphorus,2D materials,topological insulators
更新于2025-09-19 17:13:59
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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) - Switching Quasi-Flat Modes at the Interface between Detuned Anomalous Floquet Topological Insulators
摘要： Anomalous Floquet Topological Insulators (A-FTIs) [1–3] are time-dependent arrangements with topologically non-trivial phases. These recently discovered systems are characterized by an integer Winding number W [4]. We theoretically investigate photonic A-FTI comprised of honeycomb lattices of waveguides (see Fig. 1(a)). Crucially, the couplings between adjacent lattice sites are periodically modulated in time so that, at any point in time, a site is coupled to only one of its three next neighbors. This system exhibits a number of non-degenerate bands separated by a gap centered on the quasi-energy (cid:2) = 0. Since time-periodicity translates to periodicity in quasi-frequency, another band gap appears around (cid:2) = ±π. By varying the coupling angle θc, we obtain di?erent values (W0, Wπ) for the Winding numbers of the two gaps, as well as for the band’s Chern numbers (C). We ?nd that C = 0 if topological modes appear across both gaps. In contrast, the Winding numbers ful?ll (W0 ∨Wπ) = 1 and correctly count the number of protected modes across each gap, as predicted in [4] (see Fig. 1(b)). Based on these considerations, we explore the interface between two mutually detuned realizations of the aforementioned A-FTI, placed next to one another. The detuning is implemented by a constant on site potential and results in a relative shift of the respective band structures. If, as a result, the π-gap of the second system becomes matched with the 0-gap of the non detuned system, the boundary between these two domains identi?es a transition between di?erent, albeit topologically equivalent, media that share the same band gap. While the bulk-edge correspondence principle doesn’t allow topological modes to exist on such interfaces, we can nevertheless observe a number of seemingly trivial, quasi-?at, defect modes (see Fig. 1(c) inset). Their existence is enabled by the interplay between counter-propagating modes on the inside edges of each sub-system. Both interface modes are phase-matched with the edge modes for exactly one value of the wave vector k. This behaviour is con?rmed by tight-binding simulations of the dynamics of a broad beam (i.e. a narrow wave packet in k-space), which show no coupling between the topological mode and the trivial interface state except for the phase-matching points between the two (see Fig. 1(c)). This mechanism can be harnessed to selectively extract a fraction of light that is propagating in a topologically protected edge channel by depositing it into quasi-static defect modes.
关键词： honeycomb lattices,Anomalous Floquet Topological Insulators,quasi-?at defect modes,topological modes,Chern numbers,Winding number,photonic A-FTI
更新于2025-09-16 10:30:52
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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) - Topological Cylindrical Resonators and Optical Fibers
摘要： We propose optical resonators based on the edge modes of a cylindrical multilayer structure with nontrivial topological configuration. We calculate the field confinement and resonator dispersion by a recursive approach able to tackle with arbitrary arrangements of annular concentric layers. We apply the method to a periodical structure with Harper modulation and study the resulting cylindrical edge modes. Conventional circular optical resonators are designed exploiting the effect of total internal reflection or by Bragg structured claddings. The Bragg reflection mechanism allows to decouple the detrimental link between cavity dimensions and cavity losses present if total internal reflection is exploited. Reducing bending losses requires a large core radius, while for achieving a high quality factor small dimensions are needed. We consider photonic topological insulators, sustaining edge states, as a viable alternative for the cladding patterning to achieve optical resonators operating on protected states, immune to disorder and perturbations.
关键词： photonic topological insulators,optical resonators,topological configuration,edge modes,Harper modulation
更新于2025-09-16 10:30:52
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Topological strong-field physics on sub-laser-cycle timescale
摘要： The sub-laser-cycle timescale of the electronic response to strong fields enables attosecond dynamical imaging in atoms, molecules and solids, with optical tunnelling and high-harmonic generation the hallmarks of attosecond optical spectroscopy. Topological insulators are intimately linked with electron dynamics, as manifested via the chiral edge currents, but it is unclear if and how topology leaves its mark on optical tunnelling and sub-cycle electronic response. Here, we identify distinct bulk topological effects on directionality and timing of currents arising during electron injection into conduction bands. We show that electrons tunnel differently in trivial and topological insulators, for the same band structure, and identify the key role of the Berry curvature in this process. These effects map onto topologically dependent attosecond delays and helicities of emitted harmonics that record the phase diagram of the system. Our findings create new roadmaps in studies of topological systems, building on the ubiquitous properties of the sub-laser-cycle strong-field response—a unique mark of attosecond science.
关键词： high-harmonic generation,attosecond science,Berry curvature,topological insulators,strong-field physics
更新于2025-09-12 10:27:22