Bound states in the continuum (BICs) have exhibited extraordinary properties in photonics for enhanced light-matter interactions that enable appealing applications in nonlinear optics, biosensors, and ultrafast optical switches. The most common strategy to apply BICs in a metasurface is by breaking symmetry of resonators in the uniform array that leaks the otherwise uncoupled mode to free space and exhibits an inverse quadratic relationship between quality factor (Q) and asymmetry. Here, we propose a scheme to further reduce scattering losses and improve the robustness of symmetry-protected BICs by decreasing the radiation density with a hybrid BIC lattice. We observe a significant increase of radiative Q in the hybrid lattice compared to the uniform lattice with a factor larger than 14.6. In the hybrid BIC lattice, modes are transferred to Г point inherited from high symmetric X, Y, and M points in the Brillouin zone that reveal as multiple Fano resonances in the far field and would find applications in hyperspectral sensing. This work initiates a novel and generalized path toward reducing scattering losses and improving the robustness of BICs in terms of lattice engineering that would release the rigid requirements of fabrication accuracy and benefit applications of photonics and optoelectronic devices.
Terahertz (THz) waves have exhibited promising applications in imaging, sensing, and communications, especially for the next-generation wireless communications due to the large bandwidth and abundant spectral resources. Modulators and waveguides to manipulate THz waves are becoming key components to develop the relevant technologies where metamaterials have exhibited extraordinary performance to control free-space and on-chip propagation, respectively. In this review, we will give a brief overview of the current progress in active metadevices and topological photonic crystals, for applications of terahertz free-space modulators and on-chip waveguides. In the first part, the most recent research progress of active terahertz metadevices will be discussed by combining metamaterials with various active media. In the second part, fundamentals of photonic topological insulations will be introduced where the topological photonic crystals are an emerging research area that would boost the development of on-chip terahertz communications. It is envisioned that the combination of them would find great potential in more advanced terahertz applications, such as reconfigurable topological waveguides and topologically-protected metadevices.
Recent advancements in photonic bound states in the continuum (BICs) have opened up exciting new possibilities for the design of optoelectronic devices with improved performance. In this perspective article, we provide an overview of recent progress in photonic BICs based on metamaterials and photonic crystals, focusing on both the underlying physics and their practical applications. The first part of this article introduces 2 different interpretations of BICs, based on far-field interference of multipoles and near-field analysis of topological charges. We then discuss recent research on manipulating the far-field radiation properties of BICs through engineering topological charges. The second part of the article summarizes recent developments in the applications of BICs, including chiral light and vortex beam generation, nonlinear optical frequency conversion, sensors, and nanolasers. Finally, we conclude with a discussion of the potential of photonic BICs to advance terahertz applications in areas such as generation and detection, modulation, sensing, and isolation. We believe that continued research in this area will lead to exciting new advancements in optoelectronics, particularly in the field of terahertz devices.
The microstructure and shape memory behavior of Ti-rich Ti-Ni melt-spun ribbons with various Ni-contents were investigated. Ti-xNi(x=40~48at%) ribbons were fabricated by the melt-spinning method at the rotation speed of 5000rpm. They were heat-treated at 1073K for 3.6ks. It was found that the Ti-40at%Ni as-spun ribbon exhibited almost complete amorphous structure, while the specimen with more Ni-content, such as 48at%Ni ribbon exhibited the coexistence of amorphous and crystalline structures. It was also found that the maximum shape recovery strain increased with increasing Ni-content. The Ti-40at%Ni ribbon was very brittle because of many Ti2Ni precipitates formed.
Topological photonic crystals with robust pseudo-spin and valley edge states have shown promising and wide applications in topological waveguides, lasers, and antennas. However, the limited bandwidth and intrinsic coupling properties of a single pseudo-spin or valley edge state have imposed restrictions on their multifunctional applications in integrated photonic circuits. Here, we propose a topological photonic crystal that can support pseudo-spin and valley edge states simultaneously in a single waveguiding channel, which effectively broadens the bandwidth and enables a multipath routing solution for terahertz information processing and broadcasting. We show that distorted Kekulé lattices can open two types of bandgaps with different topological properties simultaneously by molding the inter- and intra-unit cell coupling of the tight-binding model. The distinct topological origins of the edge states provide versatile signal routing paths toward free space radiation or on-chip self-localized edge modes by virtue of their intrinsic coupling properties. Such a powerful platform could function as an integrated photonic chip with capabilities of broadband on-chip signal processing and distributions that will especially benefit terahertz wireless communications.
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