18 research outputs found
All-dielectric reciprocal bianisotropic nanoparticles
The study of high-index dielectric nanoparticles currently attracts a lot of
attention. They do not suffer from absorption but promise to provide control on
the properties of light comparable to plasmonic nanoparticles. To further
advance the field, it is important to identify versatile dielectric
nanoparticles with unconventional properties. Here, we show that breaking the
symmetry of an all-dielectric nanoparticle leads to a geometrically tunable
magneto-electric coupling, i.e. an omega-type bianisotropy. The suggested
nanoparticle exhibits different backscatterings and, as an interesting
consequence, different optical scattering forces for opposite illumination
directions. An array of such nanoparticles provides different reflection phases
when illuminated from opposite directions. With a proper geometrical tuning,
this bianisotropic nanoparticle is capable of providing a phase change
in the reflection spectrum while possessing a rather large and constant
amplitude. This allows creating reflectarrays with near-perfect transmission
out of the resonance band due to the absence of an usually employed metallic
screen.Comment: 7 pages, 6 figure
Controlling surface waves with temporal discontinuities of metasurfaces
Static reactive metasurfaces allow excitation and propagation of surface waves. In this paper, we theoretically elucidate how surface-wave propagation along a reactive boundary is affected by temporal discontinuities of effective parameters characterizing the boundary. First, we show that by switching the value of the surface reactance, the velocity of surface waves is fully controlled, and the power of reflected and transmitted surface waves can be amplified. Second, we indicate that when a boundary supporting waves with transverse-electric polarization is switched to the one allowing only transverse-magnetic polarization, the propagating surface wave is “frozen” and converted to a static magnetic-field distribution. Moreover, efficiently, these fields can be “melted”, restoring propagating surface waves when the boundary is switched back to the initial state. Finally, we demonstrate that temporal jumps of the boundary reactance couple free-space propagating waves to the surface wave, in an analogy to a spatial prism. All these intriguing phenomena enabled by temporal discontinuities of effective properties of reactive metasurfaces open up interesting possibilities for the generation and control of surface waves
Metasurface-Based Realization of Photonic Time Crystals
Photonic time crystals are artificial materials whose electromagnetic
properties are uniform in space but periodically vary in time. The synthesis of
such materials and experimental observation of their physics remain very
challenging due to the stringent requirement for uniform modulation of material
properties in volumetric samples. In this work, we extend the concept of
photonic time crystals to two-dimensional artificial structures --
metasurfaces. We demonstrate that time-varying metasurfaces not only preserve
key physical properties of volumetric photonic time crystals despite their
simpler topology but also host common momentum bandgaps shared by both surface
and free-space electromagnetic waves. Based on a microwave metasurface design,
we experimentally confirmed the exponential wave amplification inside a
momentum bandgap as well as the possibility to probe bandgap physics by
external (free-space) excitations. The proposed metasurface serves as a
straightforward material platform for realizing emerging photonic space-time
crystals and as a realistic system for the amplification of surface-wave
signals in future wireless communications.Comment: 21 pages, 3 figure
Controlling surface waves with temporal discontinuities of metasurfaces
Funding Information: Research funding: This work was supported by the Academy of Finland under Grant No. 330260. Publisher Copyright: © 2023 the author(s), published by De Gruyter, Berlin/Boston 2023.Static reactive metasurfaces allow excitation and propagation of surface waves. In this paper, we theoretically elucidate how surface-wave propagation along a reactive boundary is affected by temporal discontinuities of effective parameters characterizing the boundary. First, we show that by switching the value of the surface reactance, the velocity of surface waves is fully controlled, and the power of reflected and transmitted surface waves can be amplified. Second, we indicate that when a boundary supporting waves with transverse-electric polarization is switched to the one allowing only transverse-magnetic polarization, the propagating surface wave is "frozen"and converted to a static magnetic-field distribution. Moreover, efficiently, these fields can be "melted", restoring propagating surface waves when the boundary is switched back to the initial state. Finally, we demonstrate that temporal jumps of the boundary reactance couple free-space propagating waves to the surface wave, in an analogy to a spatial prism. All these intriguing phenomena enabled by temporal discontinuities of effective properties of reactive metasurfaces open up interesting possibilities for the generation and control of surface waves.Peer reviewe
Physical Meaning of the Dipole Radiation Resistance in Lossless and Lossy Media: What is the Radiation Resistance of Antennas in Lossy Media?
Spin-dependent phenomena at chiral temporal interfaces
Temporally varying electromagnetic media have been extensively investigated recently to unveil new means for controlling light. However, spin-dependent phenomena in such media have not been explored thoroughly. Here, we reveal the existence of spin-dependent phenomena at a temporal interface between chiral and dielectric media. In particular, we show theoretically and numerically that due to the material discontinuity in time, linearly polarized light is split into forward-propagating right-handed and left-handed circularly polarized waves having different angular frequencies and the same phase velocities. This salient effect allows complete temporal separation of the two spin states of light with high efficiency. In addition, a phenomenon of spin-dependent gain/loss is observed. Furthermore, we show that when the dielectric medium is switched back to the original chiral medium, the right- and left-handed circularly polarized light waves (with different angular frequencies) merge to form a linearly polarized wave. Our findings extend spin-dependent interactions of light from space to space-time