The rapid development of topological photonics has significantly facilitated the development of novel microwave and optical devices with richer electromagnetic properties. A stable and efficient guided wave is a neces...The rapid development of topological photonics has significantly facilitated the development of novel microwave and optical devices with richer electromagnetic properties. A stable and efficient guided wave is a necessary condition for optical information transmission and processing. However, most topological waveguides are confined at a domain wall around the interfaces and usually operate in a single-type topological mode, leading to low-throughput energy transmission over a single frequency band. Here, we propose, design, and experimentally demonstrate a novel planar microstrip heterostructure system based on topological LC circuits that supports a dual-type topological large-area waveguide state, and the system showcases tunable mode widths with different operating bandwidths. Inheriting from the pseudospin and valley topology, the topological large-area waveguides exhibit the pseudospin-and valley-locked properties at different frequency windows and have strong robustness against defects. Moreover, the large-area topological waveguide states of high-energy capacity channel intersections and beam expanders with topological pseudospin and valley mode width degrees of freedom are verified numerically and experimentally. We also show the distinct topological origins of large-area topological waveguide states that provide versatile signal routing paths by their intrinsic coupling properties. Our system provides an efficient scheme to realize the tunable width and the multi-mode bandwidth of topological waveguides, which can further promote the applications of multi-functional high-performance topological photonic integrated circuit systems in on-chip communication and signal processing.展开更多
Optical resonators with high quality(Q)factors are paramount for the enhancement of light–matter interactions in engineered photonic structures,but their performance always suffers from the scattering loss caused by ...Optical resonators with high quality(Q)factors are paramount for the enhancement of light–matter interactions in engineered photonic structures,but their performance always suffers from the scattering loss caused by fabrication imperfections.Merging bound states in the continuum(BICs)provide us with a nontrivial physical mechanism to overcome this challenge,as they can significantly improve the Q factors of quasi-BICs.However,most of the reported merging BICs are found atΓpoint(the center of the Brillouin zone),which intensively limits many potential applications based on angular selectivity.To date,studies on manipulating merging BICs at off-Γpoint are always accompanied by the breaking of structural symmetry that inevitably increases process difficulty and structural defects to a certain extent.Here,we propose a scheme to construct merging BICs at almost an arbitrary point in momentum space without breaking symmetry.Enabled by the topological features of BICs,we merge four accidental BICs with one symmetry-protected BIC at theΓpoint and merge two accidental BICs with opposite topological charges at the off-Γpoint only by changing the periodic constant of a photonic crystal slab.Furthermore,the position of off-Γmerging BICs can be flexibly tuned by the periodic constant and height of the structure simultaneously.Interestingly,it is observed that the movement of BICs occurs in a quasi-flatband with ultra-narrow bandwidth.Therefore,merging BICs in a tiny band provide a mechanism to realize more robust ultrahigh-Q resonances that further improve the optical performance,which is limited by wide-angle illuminations.Finally,as an example of application,effective angle-insensitive second-harmonic generation assisted by different quasi-BICs is numerically demonstrated.Our findings demonstrate momentum-steerable merging BICs in a quasi-flatband,which may expand the application of BICs to the enhancement of frequency-sensitive light–matter interaction with angular selectivity.展开更多
Metasurfaces with spin-selective transmission play an increasingly critical role in realizing optical chiral responses,especially for strong intrinsic chirality,which is limited to complex three-dimensional geometry.I...Metasurfaces with spin-selective transmission play an increasingly critical role in realizing optical chiral responses,especially for strong intrinsic chirality,which is limited to complex three-dimensional geometry.In this paper,we propose a planar metasurface capable of generating maximal intrinsic chirality and achieving dual-band spinselective transmission utilizing dual quasi-bound states in the continuum(quasi-BICs)caused by the structural symmetry breaking.Interestingly,the value of circular dichroism(CD)and the transmittance of two kinds of circular polarization states can be arbitrarily controlled by tuning the asymmetry parameter.Remarkable CD approaching unity with the maximum transmittance up to 0.95 is experimentally achieved in the dual band.Furthermore,assisted by chiral BICs,the application in polarization multiplexed near-field image display is also exhibited.Our work provides a new avenue to flexibly control intrinsic chirality in planar structure and offers an alternative strategy to develop chiral sensing,multiband spin-selective transmission,and high-performance circularly polarized wave detection.The basic principle and design method of our experiments in the microwave regime can be extended to other bands,such as the terahertz and infrared wavelengths.展开更多
基金National Key Research and Development Program of China (2021YFA1400602, 2020YFA0211402)National Natural Science Foundation of China (12474316,12274325)。
文摘The rapid development of topological photonics has significantly facilitated the development of novel microwave and optical devices with richer electromagnetic properties. A stable and efficient guided wave is a necessary condition for optical information transmission and processing. However, most topological waveguides are confined at a domain wall around the interfaces and usually operate in a single-type topological mode, leading to low-throughput energy transmission over a single frequency band. Here, we propose, design, and experimentally demonstrate a novel planar microstrip heterostructure system based on topological LC circuits that supports a dual-type topological large-area waveguide state, and the system showcases tunable mode widths with different operating bandwidths. Inheriting from the pseudospin and valley topology, the topological large-area waveguides exhibit the pseudospin-and valley-locked properties at different frequency windows and have strong robustness against defects. Moreover, the large-area topological waveguide states of high-energy capacity channel intersections and beam expanders with topological pseudospin and valley mode width degrees of freedom are verified numerically and experimentally. We also show the distinct topological origins of large-area topological waveguide states that provide versatile signal routing paths by their intrinsic coupling properties. Our system provides an efficient scheme to realize the tunable width and the multi-mode bandwidth of topological waveguides, which can further promote the applications of multi-functional high-performance topological photonic integrated circuit systems in on-chip communication and signal processing.
基金National Key Research and Development Program of China (2021YFA1400602)National Natural Science Foundation of China (11974261,12104105,12274325,61621001,62075213,91850206)Fundamental Research Funds for the Central Universities (22120190222)。
文摘Optical resonators with high quality(Q)factors are paramount for the enhancement of light–matter interactions in engineered photonic structures,but their performance always suffers from the scattering loss caused by fabrication imperfections.Merging bound states in the continuum(BICs)provide us with a nontrivial physical mechanism to overcome this challenge,as they can significantly improve the Q factors of quasi-BICs.However,most of the reported merging BICs are found atΓpoint(the center of the Brillouin zone),which intensively limits many potential applications based on angular selectivity.To date,studies on manipulating merging BICs at off-Γpoint are always accompanied by the breaking of structural symmetry that inevitably increases process difficulty and structural defects to a certain extent.Here,we propose a scheme to construct merging BICs at almost an arbitrary point in momentum space without breaking symmetry.Enabled by the topological features of BICs,we merge four accidental BICs with one symmetry-protected BIC at theΓpoint and merge two accidental BICs with opposite topological charges at the off-Γpoint only by changing the periodic constant of a photonic crystal slab.Furthermore,the position of off-Γmerging BICs can be flexibly tuned by the periodic constant and height of the structure simultaneously.Interestingly,it is observed that the movement of BICs occurs in a quasi-flatband with ultra-narrow bandwidth.Therefore,merging BICs in a tiny band provide a mechanism to realize more robust ultrahigh-Q resonances that further improve the optical performance,which is limited by wide-angle illuminations.Finally,as an example of application,effective angle-insensitive second-harmonic generation assisted by different quasi-BICs is numerically demonstrated.Our findings demonstrate momentum-steerable merging BICs in a quasi-flatband,which may expand the application of BICs to the enhancement of frequency-sensitive light–matter interaction with angular selectivity.
基金National Key Research and Development Program of China(2021YFA1400602)National Natural Science Foundation of China(11974261,62075213,12104105,12274325,11874286,61621001,91850206)。
文摘Metasurfaces with spin-selective transmission play an increasingly critical role in realizing optical chiral responses,especially for strong intrinsic chirality,which is limited to complex three-dimensional geometry.In this paper,we propose a planar metasurface capable of generating maximal intrinsic chirality and achieving dual-band spinselective transmission utilizing dual quasi-bound states in the continuum(quasi-BICs)caused by the structural symmetry breaking.Interestingly,the value of circular dichroism(CD)and the transmittance of two kinds of circular polarization states can be arbitrarily controlled by tuning the asymmetry parameter.Remarkable CD approaching unity with the maximum transmittance up to 0.95 is experimentally achieved in the dual band.Furthermore,assisted by chiral BICs,the application in polarization multiplexed near-field image display is also exhibited.Our work provides a new avenue to flexibly control intrinsic chirality in planar structure and offers an alternative strategy to develop chiral sensing,multiband spin-selective transmission,and high-performance circularly polarized wave detection.The basic principle and design method of our experiments in the microwave regime can be extended to other bands,such as the terahertz and infrared wavelengths.
