Longhi Stefano
Opt Lett. 2014 Mar 15;39(6):1697-700. doi: 10.1364/OL.39.001697.
This Letter shows that bound states in the continuum (BIC), which are normalizable modes with energy embedded in the continuous spectrum of scattered states, exist in certain optical waveguide lattices with PT-symmetric defects. There are two distinct types of BIC modes: BIC states that exist in the broken PT phase, and correspond to exponentially localized modes with either exponentially damped or amplified optical power; and BIC modes with sub-exponential spatial localization that also can exist in the unbroken PT phase. These two types of BIC modes at the PT symmetry breaking point behave differently: in the former case, spatial localization is lost and the defect coherently radiates outgoing waves with an optical power that linearly increases with the propagation distance; in the latter case, localization is maintained and the optical power increase is quadratic.
这封信表明，连续谱束缚态（BIC），即能量嵌入散射态连续谱中的可归一化模式，存在于某些具有PT对称缺陷的光波导晶格中。有两种不同类型的BIC模式：存在于PT对称性破缺相中且对应于光功率呈指数衰减或放大的指数局域化模式的BIC态；以及在PT对称性未破缺相中也能存在的具有亚指数空间局域化的BIC模式。这两种BIC模式在PT对称破缺点处表现不同：在前一种情况下，空间局域性丧失，缺陷相干地辐射出光功率随传播距离线性增加的出射波；在后一种情况下，局域性得以维持，光功率呈二次方增加。
