Light control with Weyl semimetals

Weyl semimetals are topological materials whose electron quasiparticles obey the Weyl equation.They possess many unusual properties that may lead to new applications.This is a tutorial review of the optical properties and applications of Weyl semimetals.We review the basic concepts and optical responses of Weyl semimetals,and survey their applications in optics and thermal photonics.We hope this pedagogical text will motivate further research on this emerging topic.

Multi-dimensional band structure spectroscopy in the synthetic frequency dimension

The concept of synthetic dimensions in photonics provides a versatile platform in exploring multi-dimensional physics.Many of these physics are characterized by band structures in more than one dimensions.Existing efforts on band structure measurements in the photonic synthetic frequency dimension however are limited to either onedimensional Brillouin zones or one-dimensional subsets of multi-dimensional Billouin zones.Here we theoretically propose and experimentally demonstrate a method to fully measure multi-dimensional band structures in the synthetic frequency dimension.We use a single photonic resonator under dynamical modulation to create a multidimensional synthetic frequency lattice.We show that the band structure of such a lattice over the entire multidimensional Brillouin zone can be measured by introducing a gauge potential into the lattice Hamiltonian.Using this method,we perform experimental measurements of two-dimensional band structures of a Hermitian and a non-Hermitian Hamiltonian.The measurements reveal some of the general properties of point-gap topology of the non-Hermitian Hamiltonian in more than one dimensions.Our results demonstrate experimental capabilities to fully characterize high-dimensional physical phenomena in the photonic synthetic frequency dimension.

Metal-dielectric-metal plasmonic waveguide devices for manipulating light at the nanoscale

We review some of the recent advances in the development of subwavelength plasmonic devices for manipulating light at the nanoseale, drawing examples from our own work in metal-dielectric-metal （MDM） plasmonic waveguide devices. We introduce bends, splitters, and mode converters for MDM waveguides with no additional loss. We also demonstrate that optical gain provides a mechanism for on/off switching in MDM plasmonic waveguides. Highly efficient compact couplers between dielectric waveguides and MDM waveguides are also introduced.

Higher-order topological insulators in synthetic dimensions

Conventional topological insulators support boundary states with dimension one lower than that of the bulk system that hosts them,and these states are topologically protected due to quantized bulk dipole moments.Recently,higherorder topological insulators have been proposed as a way of realizing topological states with dimensions two or more lower than that of the bulk due to the quantization of bulk quadrupole or octupole moments.However,all these proposals as well as experimental realizations have been restricted to real-space dimensions.Here,we construct photonic higher-order topological insulators(PHOTIs)in synthetic dimensions.We show the emergence of a quadrupole PHOTI supporting topologically protected corner modes in an array of modulated photonic molecules with a synthetic frequency dimension,where each photonic molecule comprises two coupled rings.By changing the phase difference of the modulation between adjacent coupled photonic molecules,we predict a dynamical topological phase transition in the PHOTI.Furthermore,we show that the concept of synthetic dimensions can be exploited to realize even higher-order multipole moments such as a fourth-order hexadecapole(16-pole)insulator supporting 0D corner modes in a 4D hypercubic synthetic lattice that cannot be realized in real-space lattices.

Thermodynamic limits for simultaneous energy harvesting from the hot sun and cold outer space

The sun and outer space are two of the most important fundamental thermodynamic resources for renewable energy harvesting.A significant amount of work has focused on understanding the fundamental limit of energy harvesting from the sun.More recently,there have been several theoretical analyses of the fundamental limit of energy harvesting from outer space.However,far less is understood about the fundamental limits of simultaneous energy harvesting from both the sun and outer space.Here,we consider and introduce various schemes that are capable of simultaneous energy harvesting and elucidate the fundamental thermodynamic limits of these schemes.We show that the theoretical limits can far exceed the previously established limit associated with utilizing only one thermodynamic resource.Our results highlight the significant potential of simultaneous energy harvesting and indicate new fundamental opportunities for improving the efficiency of energy harvesting systems.

Structured 3D linear space–time light bullets by nonlocal nanophotonics

We propose the generation of 3D linear light bullets propagating in free space using a single passive nonlocal optical surface.The nonlocal nanophotonics can generate space–time coupling without any need for bulky pulse-shaping and spatial modulation techniques.Our approach provides simultaneous control of various properties of the light bullets,including the external properties such as the group velocity and the propagation distance,and internal degrees of freedom such as the spin angular momentum and the orbital angular momentum.

Thermal photonics with broken symmetries

Nanophotonic engineering provides an effective platform to manipulate thermal emission on-demand,enabling unprecedented heat management superior to conventional bulk materials.Amongst a plethora of nanophotonic structures,symmetries play an important role in controlling radiative heat transfer in both near-field and far-field.In physics,broken symmetries generally increase the degree of freedom in a system,enriching the understanding of physical mechanisms and bringing many exciting opportunities for novel applications.In this review,we discussed the underlying physics and functionalities of nanophotonic structures with broken geometrical symmetries,engineered mode symmetries,and broken reciprocity for the control of thermal emission.We overview a variety of physical phenomena and interesting applications,and provide the outlook for future development.

Temporal modulation brings metamaterials into new era

Temporal modulations in photonics bring many exotic optical phenomena in the time dimension while metamaterials provide powerful ways in manipulating light in the spatial domain.The authors envision the connection,Floquet Metamaterials,may deliver novel opportunities in nanophotonics.

Low-overhead distribution strategy for simulation and optimization of large-area metasurfaces

Fast and accurate electromagnetic simulation of large-area metasurfaces remains a major obstacle in automating their design.In this paper,we propose a metasurface simulation distribution strategy which achieves a linear reduction in the simulation time with the number of compute nodes.Combining this distribution strategy with a GPU-based implementation of the Transition-matrix method,we perform accurate simulations and adjoint sensitivity analysis of large-area metasurfaces.We demonstrate ability to perform a distributed simulation of large-area metasurfaces(over 600λ×600λ),while accurately accounting for scatterer-scatterer interactions significantly beyond the locally periodic approximation.

Creating locally interacting Hamiltonians in the synthetic frequency dimension for photons

The recent emerging field of synthetic dimension in photonics offers a variety of opportunities for manipulating different internal degrees of freedom of photons such as the spectrum of light.While nonlinear optical effects can be incorporated into these photonic systems with synthetic dimensions,these nonlinear effects typically result in long-range interactions along the frequency axis.Thus,it has been difficult to use the synthetic dimension concept to study a large class of Hamiltonians that involves local interactions.Here we show that a Hamiltonian that is locally interacting along the synthetic dimension can be achieved in a dynamically modulated ring resonator incorporatingχ3nonlinearity,provided that the group velocity dispersion of the waveguide forming the ring is specifically designed.As a demonstration we numerically implement a Bose–Hubbard model and explore photon blockade effect in the synthetic frequency space.Our work opens new possibilities for studying fundamental many-body physics in the synthetic space in photonics,with potential applications in optical quantum communication and quantum computation.

Angle-selective perfect absorption with two-dimensional materials

Two-dimensional(2D)materials have great potential in photonic and optoelectronic devices.However,the relatively weak light absorption in 2D materials hinders their application in practical devices.Here,we propose a general approach to achieve angleselective perfect light absorption in 2D materials.As a demonstration of the concept,we experimentally show giant light absorption by placing large-area single-layer graphene on a structure consisting of a chalcogenide layer atop a mirror and achieving a total absorption of 77.6%in the mid-infrared wavelength range(~13μm),where the graphene contributes a record-high 47.2%absorptivity of mid-infrared light.Construction of such an angle-selective thin optical element is important for solar and thermal energy harvesting,photo-detection and sensing applications.Our study points to a new opportunity to combine 2D materials with photonic structures to enable novel device applications.

Design of a multichannel photonic crystal dielectric laser accelerator

To be useful for most scientific and medical applications,compact particle accelerators will require much higher average current than enabled by current architectures.For this purpose,we propose a photonic crystal architecture for a dielectric laser accelerator,referred to as a multi-input multi-output silicon accelerator(MIMOSA),that enables simultancous acceleration of multiple electron beams,increasing the total electron throughput by at least I order of magnitude.To achieve this,we show that the photonic crystal must support a mode at the I point in reciprocal space,with a normalized frequency equal to the normalized speed of the phase-matched electron.We show that the figure of merit of the MIMOSA can be inferred from the eigenmodes of the corresponding infinitely periodic structure,which provides a powerful approach to design such devices.Additionally,we extend the MIMOSA architecture to electron deflectors and other clectron manipulation functionalities.These additional functionalities,combined with the increased electron throughput of these devices,permit all-optical on-chip manipulation of electron beams in a fully integrated architecture compatible with current fabrication technologies,which opens the way to unconventional electron beam shaping,imaging,and radiationg encration.

Dissipation in few-photon waveguide transport[Invited]

We develop a formulation of few-photon Fock-space waveguide transport that includes dissipation in the form of reservoir coupling.We develop the formalism for the case of a two-level atom and then show that our formalism leads to a simple rule that allows one to obtain the dissipative description of a system from the nondissipative case.