分类: 光学 >> 量子光学 提交时间: 2023-02-19
摘要: Time metamaterials exhibit a great potential for wave manipulation, drawing increasing attention in recent years. Here, we explore the exotic wave dynamics in an anisotropic photonic time crystal (APTC), formed by an anisotropic medium whose optical properties are uniformly and periodically changed in time. Based on a temporal transfer matrix formalism, we show that a stationary charge embedded in an APTC can emit radiation, in contrast to the case of an isotropic photonic time crystal, and its distribution in momentum space is controlled by the APTC band structure. Our approach extends the functionalities of time metamaterials, offering new opportunities for simultaneous radiation generation and control, with implications for both classical and quantum applications.
分类: 光学 >> 量子光学 提交时间: 2023-02-19
摘要: Temporal interfaces introduced by abrupt switching of the constitutive parameters of unbounded media enable unusual wave phenomena. So far, their explorations have been mostly limited to lossless media. Yet, non-Hermitian phenomena leveraging material loss and gain, and their balanced combination in parity-time (PT)-symmetric systems, have been opening new vistas in photonics. Here, we unveil the role that temporal interfaces offer in non-Hermitian physics, introducing the dual of PT symmetry for temporal boundaries. Our findings reveal unexplored interference mechanisms enabling extreme energy manipulation, and open new scenarios for time-switched metamaterials, connecting them with the broad opportunities offered by non-Hermitian phenomena.
分类: 光学 >> 量子光学 提交时间: 2023-02-19
摘要: Resonance coupling in non-Hermitian systems can lead to exotic features, such as bound states in the continuum (BICs) and exceptional points (EPs), which have been widely employed to control the propagation and scattering of light. Yet, similar tools to control diffraction and engineering spatial wavefronts have remained elusive. Here, we show that, by operating a suitably tailored metagrating around a BIC and EPs, it is possible to achieve an extreme degree of control over coupling to different diffraction orders in metasurfaces. We stack subwavelength metallic slit arrays on a metal-insulator-metal waveguide, enabling a careful control of the coupling between localized and guided modes. By periodically tuning the coupling strength from weak to strong, we largely tailor the overall spectrum and enable the emergence of singular features, like BICs and EPs. Perfect unitary diffraction efficiency with large spectrum selectivity is achieved around these singular features, with promising applications for arbitrary wavefront shaping combined with filtering and sensing.
分类: 光学 >> 量子光学 提交时间: 2023-02-19
摘要: Optical skyrmions have recently been constructed by tailoring electric or spin field distributions through the interference of multiple surface plasmon polaritons, offering promising features for advanced information processing, transport and storage. Here, we construct topologically robust plasmonic skyrmions in a wisely tailored space-coiling meta-structure supporting magnetic localized spoof plasmons (LSPs), which are strongly squeezed down to {\lambda}3/106 and do not require stringent external interference conditions. By directly measuring the spatial profile of all three vectorial magnetic fields, we reveal multiple {\pi}-twist target skyrmion configurations mapped to multi-resonant near-equidistant LSP eigen-modes. The real-space topological robustness of these skyrmion configurations is confirmed by arbitrary deformations of the meta-structure, demonstrating flexible skyrmionic textures with arbitrary shapes. The observed magnetic LSP skyrmions pave the way to ultra-compact and topologically robust plasmonic devices, such as flexible sensors, wearable electronics and ultra-compact antennas.
分类: 光学 >> 量子光学 提交时间: 2023-02-19
摘要: Optical metasurfaces with high-Q chiral resonances can boost light-matter interaction for various applications of chiral response for ultrathin, active, and nonlinear metadevices. Usually, such metasurfaces require sophisticated depth-resolved nanofabrication to realize subwavelength stereo-nanostructures, posing overwhelming challenges, especially in the short-wavelength range. Here, we suggest a novel planar design for chiral metasurfaces supporting bound states in the continuum (BICs) and demonstrate experimentally chiroptical responses with record-high Q-factors (Q=390) and near-perfect circular dichroism (CD=0.93) at optical frequencies. The symmetry-reduced meta-atoms are highly birefringent and support winding elliptical eigen-polarizations with opposite helicity surrounding the BIC polarization singularity, providing a convenient way for achieving maximal planar chirality tuned by either breaking in-plane symmetry or changing illumination direction. Such sharply resonant chirality realized in planar metasurfaces promises various practical applications in classical and quantum optics including chiral sensing, enantiomer selection, and chiral quantum emitters.