Disorder, which qualitatively describes some measure of irregularities in spatial patterns, is ubiquitous in many-body systems, equilibrium and non-equilibrium states of matter, network structures, ...biological systems and wave–matter interactions. In photonics, the introduction of order and disorder for device applications has traditionally been treated separately. However, recent developments in nanofabrication and design strategies have enabled the use of materials that lie between the extremes of order and disorder that can yield innovative optical phenomena owing to their engineered disordered patterns. Here, we review recent achievements in the emerging field of engineered disorder in photonics by outlining milestones in the control of the spectrum, transport, wavefront and topology of light in disordered structures. We show that engineered disorder has begun to transform the traditional landscape of photonics by introducing a greatly enhanced design freedom and, hence, has great potential for the rational design of the next generation of materials.In photonics, the introduction of order and disorder has traditionally been treated separately. However, recent developments in nanofabrication and design strategies have enabled the use of materials that lie between the extremes of order and disorder that can yield innovative optical phenomena. This Review surveys the basics and recent achievements of engineered disorder in photonics.
One of the most striking phenomena in condensed-matter physics is the quantum Hall effect, which arises in two-dimensional electron systems subject to a large magnetic field applied perpendicular to ...the plane in which the electrons reside. In such circumstances, current is carried by electrons along the edges of the system, in so-called chiral edge states (CESs). These are states that, as a consequence of nontrivial topological properties of the bulk electronic band structure, have a unique directionality and are robust against scattering from disorder. Recently, it was theoretically predicted that electromagnetic analogues of such electronic edge states could be observed in photonic crystals, which are materials having refractive-index variations with a periodicity comparable to the wavelength of the light passing through them. Here we report the experimental realization and observation of such electromagnetic CESs in a magneto-optical photonic crystal fabricated in the microwave regime. We demonstrate that, like their electronic counterparts, electromagnetic CESs can travel in only one direction and are very robust against scattering from disorder; we find that even large metallic scatterers placed in the path of the propagating edge modes do not induce reflections. These modes may enable the production of new classes of electromagnetic device and experiments that would be impossible using conventional reciprocal photonic states alone. Furthermore, our experimental demonstration and study of photonic CESs provides strong support for the generalization and application of topological band theories to classical and bosonic systems, and may lead to the realization and observation of topological phenomena in a generally much more controlled and customizable fashion than is typically possible with electronic systems.
Rapid scaling of semiconductor devices has led to an increase in the number of processor cores and integrated functionalities onto a single chip to support the growing demands of high‐speed and ...large‐volume consumer electronics. To meet this burgeoning demand, an improved interconnect capacity in terms of bandwidth density and active tunability is required for enhanced throughput and energy efficiency. Low‐loss terahertz silicon interconnects with larger bandwidth offer a solution for the existing inter‐/intrachip bandwidth density and energy‐efficiency bottleneck. Here, a low‐loss terahertz topological interconnect–cavity system is presented that can actively route signals through sharp bends, by critically coupling to a topological cavity with an ultrahigh‐quality (Q) factor of 0.2 × 106. The topologically protected large Q factor cavity enables energy‐efficient optical control showing 60 dB modulation. Dynamic control is further demonstrated of the critical coupling between the topological interconnect–cavity for on‐chip active tailoring of the cavity resonance linewidth, frequency, and modulation through complete suppression of the back reflection. The silicon topological cavity is complementary metal–oxide–semiconductor (CMOS)‐compatible and highly desirable for hybrid electronic–photonic technologies for sixth (6G) generation terahertz communication devices. Ultrahigh‐Q cavity also paves the path for designing ultrasensitive topological sensors, terahertz topological integrated circuits, and nonlinear topological photonic devices.
A low‐loss terahertz (THz) silicon topological interconnect–cavity system that can actively route signals through sharp bends by critically coupling to a topological cavity with an ultrahigh‐quality (Q) factor of 0.2 × 106 is shown. On‐chip active tailoring is demonstrated of the cavity resonance linewidth, frequency, and modulation at extremely low power through complete suppression of the back reflection, essential for sixth generation (6G) communication with THz topological integrated photonic circuits.
In the time-reversed counterpart to laser emission, incident coherent optical fields are perfectly absorbed within a resonator that contains a loss medium instead of a gain medium. The incident ...fields and frequency must coincide with those of the corresponding laser with gain. We demonstrated this effect for two counterpropagating incident fields in a silicon cavity, showing that absorption can be enhanced by two orders of magnitude, the maximum predicted by theory for our experimental setup. In addition, we showed that absorption can be reduced substantially by varying the relative phase of the incident fields. The device, termed a "coherent perfect absorber," functions as an absorptive interferometer, with potential practical applications in integrated optics.
Topological photonic states, inspired by robust chiral edge states in topological insulators, have recently been demonstrated in a few photonic systems, including an array of coupled on-chip ring ...resonators at communication wavelengths. However, the intrinsic difference between electrons and photons determines that the 'topological protection' in time-reversal-invariant photonic systems does not share the same robustness as its counterpart in electronic topological insulators. Here in a designer surface plasmon platform consisting of tunable metallic sub-wavelength structures, we construct photonic topological edge states and probe their robustness against a variety of defect classes, including some common time-reversal-invariant photonic defects that can break the topological protection, but do not exist in electronic topological insulators. This is also an experimental realization of anomalous Floquet topological edge states, whose topological phase cannot be predicted by the usual Chern number topological invariants.
Unconventional chiral particles have recently been predicted to appear in certain three-dimensional crystal structures containing three- or more-fold linear band degeneracy points (BDPs)1–4. These ...BDPs carry topological charges, but are distinct from the standard twofold Weyl points or fourfold Dirac points, and cannot be described in terms of an emergent relativistic field theory1. Here we report on the experimental observation of a topological threefold BDP in a three-dimensional phononic crystal. Using direct acoustic field mapping, we demonstrate the existence of the threefold BDP in the bulk band structure, as well as doubled Fermi arcs of surface states consistent with a topological charge of 2. Another novel BDP, similar to a Dirac point but carrying non-zero topological charge, is connected to the threefold BDP via the doubled Fermi arcs. The Fermi arcs form double helicoids spanning a broad frequency range (relative bandwidth >25%). We show that the non-contractibility of these arcs gives rise to the phenomenon of topologically protected negative refraction of surface states on all surfaces of the sample. Our work paves the way to using these unconventional particles for exploring new emergent physical phenomena, and may find applications in symmetry-stabilized three-dimensional zero-index metamaterials.In acoustic metamaterials, unconventional chiral quasiparticles exhibit multifold band degeneracy points, each carrying non-zero topological charges, giving rise to the topologically protected negative surface refraction.
Observation of antichiral edge states in a circuit lattice Yang, YuTing; Zhu, DeJun; Hang, ZhiHong ...
Science China. Physics, Mechanics & Astronomy/Science China. Physics, mechanics & astronomy,
05/2021, Letnik:
64, Številka:
5
Journal Article
Recenzirano
Odprti dostop
We construct an electrical circuit to realize a modified Haldane lattice exhibiting the phenomenon of antichiral edge states. The circuit consists of a network of inductors and capacitors with ...interconnections reproducing the effects of a magnetic vector potential. The next nearest neighbor hoppings are configured differently from the standard Haldane model, and as predicted by earlier theoretical studies, this gives rise to antichiral edge states that propagate in the same direction on opposite edges and coexist with bulk states at the same frequency. Using pickup coils to measure voltage distributions in the circuit, we experimentally verify the key features of the antichiral edge states, including their group velocities and ability to propagate consistently in a Möbius strip configuration.
Ultrashort electron bunches are useful for applications like ultrafast imaging, coherent radiation production, and the design of compact electron accelerators. Currently, however, the shortest ...achievable bunches, at attosecond time scales, have only been realized in the single- or very few-electron regimes, limited by Coulomb repulsion and electron energy spread. Using ab initio simulations and complementary theoretical analysis, we show that highly-charged bunches are achievable by subjecting relativistic (few MeV-scale) electrons to a superposition of terahertz and optical pulses. We provide two detailed examples that use realistic electron bunches and laser pulse parameters which are within the reach of current compact set-ups: one with bunches of >240 electrons contained within 20 as durations and 15 m radii, and one with final electron bunches of 1 fC contained within sub-400 as durations and 8 m radii. Our results reveal a route to achieve such extreme combinations of high charge and attosecond pulse durations with existing technology.
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