Direct observation of topological edge states in silicon photonic crystals: Spin, dispersion, and chiral routing

Parappurath, Nikhil; Alpeggiani, Filippo; Kuipers, L.; Verhagen, Ewold

doi:10.1126/sciadv.aaw4137

Cited by 190 publications

(145 citation statements)

References 46 publications

(75 reference statements)

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“…Most implementations so far have been limited to indirect probing of topological states such as transmission spectra [11,[18][19][20], which cannot provide spatially-resolved information about the edge modes and suffer from input/output coupling losses. Other recentlydemonstrated linear approaches such as near-field imaging [21], cathodoluminescence [22], and far-field imaging [23] suffer from poor spatial resolution or small field of view, leaving the edge states almost completely hidden in the background noise. Direct high-contrast imaging of the edge states is essential for assessing the fidelity of the topological waveguides, identifying potential sources of backscattering, and for optimizing the coupling between the edge states and localized emitters [5].…”

mentioning

confidence: 99%

Third-Harmonic Generation in Photonic Topological Metasurfaces

et al. 2019

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We study nonlinear effects in two-dimensional photonic metasurfaces supporting topologicallyprotected helical edge states at the nanoscale. We observe strong third-harmonic generation mediated by optical nonlinearities boosted by multipolar Mie resonances of silicon nanoparticles. Variation of the pump-beam wavelength enables independent high-contrast imaging of either bulk modes or spin-momentum-locked edge states. We demonstrate topology-driven tunable localization of the generated harmonic fields and map the pseudospin-dependent unidirectional waveguiding of the edge states bypassing sharp corners. Our observations establish dielectric metasurfaces as a promising platform for the robust generation and transport of photons in topological photonic nanostructures.Topological photonics describes optical structures with the properties analogous to electronic topological insulators [1]. These systems are distinguished by bulk band gaps that host disorder-robust states localized at edges or interfaces and provide a novel approach for designing non-reciprocal or localized modes for optical isolators, photonic-crystal waveguides, and lasers. Since the original demonstration of backscattering-immune photonic topological edge states with the use of a gyrotropic microwave photonic crystal under a strong magnetic field [2], there has been a concerted effort towards realizing topological photonics at the nanoscale. Recently suggested optical designs compatible with non-magnetic alldielectric structures [3][4][5][6][7][8] are now emerging as a promising platform for quantum and nonlinear topological photonics [9][10][11][12].Stimulated by the progress in nanofabrication techniques, a new favourable ground for topological photonics based on dielectric nanoparticles with high refractive index has recently emerged [13,14]. Strong optical resonances and low Ohmic losses make it feasible for practical implementation of topological order for light at subwavelength scales. The underlying conceptual framework is to use arrays of meta-atoms with judiciously engineered shape and lattice structure, with topologically nontrivial features arising from pseudospin degrees of freedom. It bridges fundamental physics of topological phases with resonant nanophotonics and multipolar electrodynamics [15,16]. Topological metasurfaces could form a ground for a new class of ultra-thin devices with functionalities based on novel physical principles through engineering light-matter interactions in synthetic photonic potentials [17]. Their pseudospindependent physics may be useful for manipulation of internal degrees of freedom of light such as polarization and angular momentum.However, the experimental characterization of topological photonic structures becomes much more challenging at the nanoscale. Most implementations so far have been limited to indirect probing of topological states such as transmission spectra [11,[18][19][20], which cannot provide spatially-resolved information about the edge modes and suffer from input/output coupling losses. ...

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confidence: 99%

Third-Harmonic Generation in Photonic Topological Metasurfaces

et al. 2019

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“…In Figure 4d we plot the power for the blue path shown in Figure 4a. This path is similar to scanning perpendicularly across a zig-zag interface, as in [21]. Compared to the red path, there is wider range of y-values that yield the expected directionality.…”

Section: Far-field Circularly-polarized Excitationsmentioning

confidence: 90%

“…A number of experimental works have investigated the directionality of these edge states under far-field excitation in a range of frequency regimes [17,21,22]. In each of these experiments, purely unidirectional modes are observed.…”

Section: Far-field Circularly-polarized Excitationsmentioning

confidence: 99%

“…This result is true for any bosonic breathing honeycomb lattice [16], since it is rooted in time-reversal symmetry and the absence of Kramer's degeneracy for bosons as opposed to fermions. There have been a range of experimental investigations on the breathing honeycomb photonic crystal [17][18][19][20], including the observation of edge modes in the visible regime [21,22]. Despite this, comprehensive theoretical studies of the directional excitation of pseudospin edge modes in the breathing honeycomb lattice based on an analysis of their inhomogeneous electromagnetic angular momentum are scarce; in particular, modelling with a circularly polarised incident beam, as used in recent experiments [17,21,22] are needed.…”

Section: Introductionmentioning

confidence: 99%

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Near- and Far-Field Excitation of Topological Plasmonic Metasurfaces

et al. 2020

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The breathing honeycomb lattice hosts a topologically non-trivial bulk phase due to the crystalline-symmetry of the system. Pseudospin-dependent edge states, which emerge at the interface between trivial and non-trivial regions, can be used for the directional propagation of energy. Using the plasmonic metasurface as an example system, we probe these states in the near- and far-field using a semi-analytical model. We provide the conditions under which directionality was observed and show that it is source position dependent. By probing with circularly-polarised magnetic dipoles out of the plane, we first characterise modes along the interface in terms of the enhancement of source emissions due to the metasurface. We then excite from the far-field with non-zero orbital angular momentum beams. The position-dependent directionality holds true for all classical wave systems with a breathing honeycomb lattice. Our results show that a metasurface in combination with a chiral two-dimensional material, could be used to guide light effectively on the nanoscale.

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“…In recent years, it has been proposed that "topological" photonic structures can help mitigate the problem of disorderinduced losses in PCS waveguides, thanks to the special properties of their photonic edge states. These edge states of topological waveguides may allow scatter-free propagation for nanoscale PCs and have applications in quantum technologies due to their strong interactions with quantum emitters [40][41][42][43][44][45][46][47]. Experimentally, electromagnetic modes for these topological edge states have been measured by Barik et al [48] in 2018, indicating that these topological edge states can function as waveguides, with localized spin control.…”

Section: Introductionmentioning

confidence: 99%

Theory of intrinsic propagation losses in topological edge states of planar photonic crystals

Sauer

Vasco

Hughes

2020

Phys. Rev. Research

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Using a semianalytic guided-mode expansion technique, we present theory and analysis of intrinsic propagation losses for topological photonic crystal slab waveguide structures with modified honeycomb lattices of circular or triangular holes. Although conventional photonic crystal waveguide structures, such as the W1 waveguide, have been designed to have lossless propagation modes, they are prone to disorder-induced losses and backscattering. Topological structures have been proposed to help mitigate this effect as their photonic edge states may allow for topological protection. However, the intrinsic propagation losses of these structures are not well understood and the concept of the light line can become blurred. For four example topological edge state structures, photonic band diagrams, loss parameters, and electromagnetic fields of the guided modes are computed. Two of these structures, based on armchair edge states, are found to have significant intrinsic losses for modes inside the photonic bandgap, more than 100 dB/cm, which is comparable to or larger than typical disorder-induced losses using slow-light modes in conventional photonic crystal waveguides, while the other two structures, using the valley Hall effect and inversion symmetry, are found to have a good bandwidth for exploiting lossless propagation modes below the light line (at least in the absence of disorder).

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Direct observation of topological edge states in silicon photonic crystals: Spin, dispersion, and chiral routing

Cited by 190 publications

References 46 publications

Third-Harmonic Generation in Photonic Topological Metasurfaces

Third-Harmonic Generation in Photonic Topological Metasurfaces

Near- and Far-Field Excitation of Topological Plasmonic Metasurfaces

Theory of intrinsic propagation losses in topological edge states of planar photonic crystals

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