物理
低语长廊波浪
窃窃私语画廊
光学
相干后向散射
散射
哈密顿量(控制论)
不对称
谐振器
量子力学
数学
数学优化
标识
DOI:10.1103/physreva.84.063828
摘要
It is a well-known fact that a single nanoparticle placed in the evanescent field of an optical microdisk leads to coherent backscattering of light between counterpropagating whispering-gallery modes. This backscattering lifts the spectral degeneracy giving rise to a doublet of standing-wave modes. Here, we show that the evanescent coupling of two or more nanoparticles leads in general to asymmetric backscattering (i.e., the strength of the scattering of light from the clockwise to the counterclockwise propagation direction is different than the other way around). Even if the strength of the backscattering is weak its asymmetry can have a dramatic impact on the mode structure. In the regime of overlapping resonances the modes do not have a standing-wave character. Instead nonorthogonal pairs of mainly copropagating modes are formed. In the extreme case the pair of optical modes coalesce at a so-called exceptional point. We derive an effective Hamiltonian within a two-mode approximation which reveals that this unexpected behavior is due to interference of the scattered waves which can be destructive or constructive depending on the propagation direction of the light.
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