Nonlinear control of photonic higher-order topological bound states in the continuum

AbstractHigher-order topological insulators (HOTIs) are recently discovered topological phases, possessing symmetry-protected corner states with fractional charges. An unexpected connection between these states and the seemingly unrelated phenomenon of bound states in the continuum (BICs) was recently unveiled. When nonlinearity is added to the HOTI system, a number of fundamentally important questions arise. For example, how does nonlinearity couple higher-order topological BICs with the rest of the system, including continuum states? In fact, thus far BICs in nonlinear HOTIs have remained unexplored. Here we unveil the interplay of nonlinearity, higher-order topology, and BICs in a photonic platform. We observe topological corner states that are also BICs in a laser-written second-order topological lattice and further demonstrate their nonlinear coupling with edge (but not bulk) modes under the proper action of both self-focusing and defocusing nonlinearities. Theoretically, we calculate the eigenvalue spectrum and analog of the Zak phase in the nonlinear regime, illustrating that a topological BIC can be actively tuned by nonlinearity in such a photonic HOTI. Our studies are applicable to other nonlinear HOTI systems, with promising applications in emerging topology-driven devices.

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Geometry symmetry-free and higher-order optical bound states in the continuum

Nature Communications ◽

10.1038/s41467-021-24686-5 ◽

2021 ◽

Vol 12 (1) ◽

Author(s):

Qingjia Zhou ◽

Yangyang Fu ◽

Lujun Huang ◽

Qiannan Wu ◽

Andrey Miroshnichenko ◽

...

Keyword(s):

Significant Role ◽

Bound States ◽

Higher Order ◽

Multiple Objects ◽

Material Parameters ◽

Geometrical Symmetry ◽

Geometric Symmetry ◽

Symmetry Protected ◽

Zero Index ◽

The Continuum

AbstractGeometrical symmetry plays a significant role in implementing robust, symmetry-protected, bound states in the continuum (BICs). However, this benefit is only theoretical in many cases since fabricated samples’ unavoidable imperfections may easily break the stringent geometrical requirements. Here we propose an approach by introducing the concept of geometrical-symmetry-free but symmetry-protected BICs, realized using the static-like environment induced by a zero-index metamaterial (ZIM). We find that robust BICs exist and are protected from the disordered distribution of multiple objects inside the ZIM host by its physical symmetries rather than geometrical ones. The geometric-symmetry-free BICs are robust, regardless of the objects’ external shapes and material parameters in the ZIM host. We further show theoretically and numerically that the existence of those higher-order BICs depends only on the number of objects. By practically designing a structural ZIM waveguide, the existence of BICs is numerically confirmed, as well as their independence on the presence of geometrical symmetry. Our findings provide a way of realizing higher-order BICs and link their properties to the disorder of photonic systems.

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Geometry symmetry-free and Higher-order Optical Bound States in the Continuum

10.21203/rs.3.rs-138091/v1 ◽

2021 ◽

Author(s):

Qingjia Zhou ◽

Yangyang Fu ◽

Lujun Huang ◽

Qiannan Wu ◽

Andrey Miroshnichenko ◽

...

Keyword(s):

Significant Role ◽

Bound States ◽

Higher Order ◽

Multiple Objects ◽

New Approach ◽

Geometrical Symmetry ◽

Symmetry Protected ◽

Zero Index ◽

The Continuum

Abstract Geometrical symmetry plays a significant role in realizing robust, symmetry-protected, bound states in the continuum (BICs). However, this benefit is only theoretical in many cases since the unavoidable imperfections of fabricated samples may easily break the stringent geometrical requirements. Here we propose an essentially new approach by introducing the concept of geometrical-symmetry-free but symmetry-protected BICs, realized using the static-like environment induced by a zero-index metamaterial (ZIM). We find that robust BICs exist and are protected from the disordered distribution of multiple objects inside ZIM host by its physical symmetries rather than geometrical ones. We further show theoretically and numerically that the existence of those higher-order BICs depends only on the number of objects. By practically designing a structural ZIM waveguide, the existence of BICs is numerically confirmed, as well as their independence on the presence of geometrical symmetry. Our findings provide a new way of realizing higher-order BICs and link their properties to disorder of photonic systems.

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Accidental and symmetry-protected bound states in the continuum in a photonic-crystal slab: A resonant-state expansion study

Physical Review B ◽

10.1103/physrevb.103.155112 ◽

2021 ◽

Vol 103 (15) ◽

Author(s):

Sam Neale ◽

Egor A. Muljarov

Keyword(s):

Photonic Crystal ◽

Bound States ◽

Resonant State ◽

State Expansion ◽

Photonic Crystal Slab ◽

Symmetry Protected ◽

The Continuum

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Polarization-selective modulation of supercavity resonances originating from bound states in the continuum

Communications Physics ◽

10.1038/s42005-020-00453-8 ◽

2020 ◽

Vol 3 (1) ◽

Author(s):

Chan Kyaw ◽

Riad Yahiaoui ◽

Joshua A. Burrow ◽

Viet Tran ◽

Kyron Keelen ◽

...

Keyword(s):

Strong Coupling ◽

Bound States ◽

Photonic Band Gap ◽

Incidence Angle ◽

Polarization State ◽

Normal Incidence ◽

Polarization Angle ◽

Sensing Applications ◽

Symmetry Protected ◽

The Continuum

AbstractBound states in the continuum (BICs) are widely studied for their ability to confine light, produce sharp resonances for sensing applications and serve as avenues for lasing action with topological characteristics. Primarily, the formation of BICs in periodic photonic band gap structures are driven by symmetry incompatibility; structural manipulation or variation of incidence angle from incoming light. In this work, we report two modalities for driving the formation of BICs in terahertz metasurfaces. At normal incidence, we experimentally confirm polarization driven symmetry-protected BICs by the variation of the linear polarization state of light. In addition, we demonstrate through strong coupling of two radiative modes the formation of capacitively-driven Freidrich-Wintgen BICs, exotic modes which occur in off-Γ points not accessible by symmetry-protected BICs. The capacitance-mediated strong coupling at 0° polarization is verified to have a normalized coupling strength ratio of 4.17% obtained by the Jaynes-Cummings model. Furthermore, when the polarization angle is varied from 0° to 90° (0° ≤ ϕ < 90°), the Freidrich-Wintgen BIC is modulated until it is completely switched off at 90°.

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High Quality-Factor Dual-Band Fano Resonances Induced by Bound States in The Continuum Using A Planar Nanohole Slab

10.21203/rs.3.rs-598706/v1 ◽

2021 ◽

Author(s):

Tian Sang ◽

Qing Mi ◽

Yao Pei ◽

Chaoyu Yang ◽

Shi Li ◽

...

Keyword(s):

Bound States ◽

Near Field ◽

Dual Band ◽

Q Factor ◽

Fano Resonances ◽

High Quality ◽

Potential Applications ◽

Q Factors ◽

Symmetry Protected ◽

The Continuum

Abstract In photonics, it is essential to achieve high quality (Q)-factor resonances to enhance light-mater interactions for improving performances of optical devices. Herein, we demonstrate that high Q-factor dual-band Fano resonances can be achieved by using a planar nanohole slab (PNS) based on the excitation of bound states in the continuum (BICs). By shrinking or expanding the tetramerized holes of the superlattice of the PNS, symmetry-protected BICs can be excited and the locations of Fano resonances as well as their Q-factors can be flexibly tuned. Physical mechanisms for the dual-band Fano resonances can be interpreted as the resonant couplings between the electric-toroidal dipoles or the magnetic-toroidal dipoles based on the far-field multiple decompositions and the near-field distributions of the superlattice. The dual-band Fano resonances of the PNS possess polarization independent feature, they can be survived even the geometric parameters of the PNS are significantly altered, making them more suitable for potential applications.

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Bound states in the continuum in periodic structures with structural disorder

Nanophotonics ◽

10.1515/nanoph-2021-0475 ◽

2021 ◽

Vol 0 (0) ◽

Author(s):

Ekaterina E. Maslova ◽

Mikhail V. Rybin ◽

Andrey A. Bogdanov ◽

Zarina F. Sadrieva

Keyword(s):

Bound States ◽

Periodic Structures ◽

Structural Disorder ◽

Practical Implementation ◽

Photonic Structure ◽

Mode Localization ◽

Effective Reduction ◽

System Length ◽

Symmetry Protected ◽

The Continuum

Abstract We study the effect of structural disorder on the transition from the bound states in the continuum (BICs) to quasi-BICs by the example of the periodic photonic structure composed of two layers of parallel dielectric rods. We uncover the specificity in the robustness of the symmetry-protected and accidental BICs against various types of structural disorder. We analyze how the spatial mode localization induced by the structural disorder results in an effective reduction of the system length and limits the Q factor of quasi-BICs. Our results are essential for the practical implementation of BICs especially in natural and self-assembled photonic structures, where the structural disorder plays a crucial role.

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