Landers S, Tuxbury W, Vitebskiy I, Kottos T
Opt Lett. 2024 Sep 1;49(17):4967-4970. doi: 10.1364/OL.530371.
A stationary inflection point (SIP) is a spectral singularity of the Bloch dispersion relation ω(k) of a periodic structure where the first and the second derivatives of ω with respect to k vanish. An SIP is associated with a third-order exceptional point degeneracy in the spectrum of the unit-cell transfer matrix, where there is a collapse of one propagating and two evanescent Bloch modes. At the SIP frequency, the incident wave can be efficiently converted into the frozen mode with greatly enhanced amplitude and vanishing group velocity. This can be very attractive for applications, including light amplification. Due to its non-resonant nature, the frozen mode regime (FMR) has fundamental advantages over common cavity resonances. Here, we propose, a novel, to the best of our knowledge, scheme for FMR-based unidirectional amplifiers by leveraging a tailored amplification/attenuation mechanism and a single nonlinear defect. The defect breaks the directional symmetry of the periodic structure and enables nonlinearity-related unidirectional amplification/attenuation in the vicinity of the SIP frequency. We demonstrate the robustness of the amplification mechanism to local impurities and parasitic nonlinearity.
固定拐点（SIP）是周期性结构的布洛赫色散关系ω(k)的一种光谱奇点，其中ω关于k的一阶和二阶导数都为零。SIP与单胞传输矩阵谱中的三阶例外点简并相关联，此时一个传播的布洛赫模式和两个倏逝布洛赫模式发生坍缩。在SIP频率下，入射波可以有效地转换为冻结模式，其幅度大大增强且群速度为零。这对于包括光放大在内的应用可能非常有吸引力。由于其非共振性质，冻结模式 regime（FMR）相对于普通腔共振具有根本优势。在此，据我们所知，我们提出了一种基于FMR的单向放大器的新颖方案，该方案利用了定制的放大/衰减机制和单个非线性缺陷。该缺陷打破了周期性结构的方向对称性，并在SIP频率附近实现了与非线性相关的单向放大/衰减。我们展示了放大机制对局部杂质和寄生非线性的鲁棒性。
