分类： 光学 >> 量子光学 提交时间： 2023-02-19
Fujia Chen
Zhen Gao
Li Zhang
Qiaolu Chen
Qinghui Yan
Rui Xi
Liqiao Jing
Erping Li
Wenyan Yin
Hongsheng Chen
Yihao Yang
摘要： Exploiting topological ideas has been a major theme in modern photonics, which provides unprecedented opportunities to design photonic devices with robustness against defects and flaws. While most previous works in topological photonics have focused on band theory, recent theoretical advances extend the topological concepts to the analysis of scattering matrices and suggest a topological route to complete polarization conversion (CPC), a unique photonic phenomenon without an electronic counterpart. Here, we report on the experimental observation of the topological effect in reflection matrices of a photonic crystal slab, enabling CPC between two linear polarizations over a wide range of frequencies. Using angle-resolved reflection measurements, we observe CPC occurring at vortex singularities of reflection coefficients in momentum space, verifying the topological nature of CPC. In addition, the topological effect also guarantees the spin-preserved reflection of a circularly polarized wave. Remarkably, we experimentally establish a connection between two seemingly unrelated topological phenomena--CPC and bound states in the continuum (BICs): BICs lie on the critical coupling curves that define the condition for CPC. Our work paves the way to exploring the topological properties in scattering matrices for controlling light polarization and spin and creating robust photonic devices.
分类： 光学 >> 量子光学 提交时间： 2023-02-19
Fujia Chen
Haoran Xue
Yuang Pan
Maoren Wang
Yuanhan Hu
Li Zhang
Qiaolu Chen
Song Han
Gui-geng Liu
Zhen Gao
Peiheng Zhou
Wenyan Yin
Hongsheng Chen
Baile Zhang
Yihao Yang
摘要： Slow-light devices are able to significantly enhance light-matter interaction due to the reduced group velocity of light, but a very low group velocity is usually achieved in a narrow bandwidth, accompanied by extreme sensitivity to imperfections that causes increased disorder-induced attenuation. Recent theories have suggested an ideal solution to this problem - unidirectional chiral photonic states, previously discovered in structures known as photonic topological insulators, not only resist backscattering from imperfections but can also be slowed down in the entire topological bandgap with multiple windings in the Brillouin zone. Here, we report on the experimental demonstration of broadband topological slow light in a photonic topological insulator. When coupled with periodic resonators that form flat bands, the chiral photonic states can wind many times around the Brillouin zone, achieving an ultra-low group velocity in the entire topological bandgap. This demonstration extends the scope of topological photonics into slow light engineering and opens a unique avenue in the dispersion manipulation of chiral photonic states.
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