One-dimensional time-Floquet photonic crystal
One-dimensional time-Floquet photonic crystal
复制标题
一维时间-Floquet光子晶体
DOI：
10.1088/1367-2630/ac2c2d
复制
发表时间：
2021-04
影响因子：
3.3
通讯作者：
Guo Ping Wang
中科院分区：
文献类型：
--
作者：
Neng Wang;Guo Ping Wang
利用基于含时微扰理论导出的Floquet哈密顿量，研究了一维含时Floquet光子晶体的准能带。PC包含两个交替层，在静态情况下具有不同的折射率，标记为A和B。层A的介电常数在时间上被周期性地调制。我们考虑了两种情况，第一种情况下，调制函数是时间的函数，第二种情况下，它是时间和空间的函数，通过一个独特的组合。在前一种情况下，虽然整个介质的介电常数是时空调制的，但准能带是对称的，因为反演对称性被保留。与以前经常讨论的时空调制介质不同，例如，具有根据类波函数时空调制的介电常数的均匀介质，其中仅产生例外点（EP）或仅产生准能隙，正向和负向之间的耦合是不存在的。（消极）和积极时间-Floquet PC中的（负）带导致准能隙，而正负带之间的耦合导致EP对，当调制在介电常数的真实的部分时，使得准能隙和EP共存。在后一种情况下，准能带变得不对称，因为时间反演和反转对称性同时被打破。正（负）带和正（负）带之间的耦合仍然导致准能隙，而正带和负带之间的耦合在小调制速度下导致准能隙，在高调制速度下导致EP对。
Using the Floquet Hamiltonian derived based on the time-dependent perturbation theory, we investigated the quasienergy bands of a one-dimensional time-Floquet photonic crystal (PC). The PC contains two alternating layers with different permittivies in the static case which are labeled as A and B. The permittivity of layer A is modulated periodically in time. We considered two cases, first the modulation function is a function of time only and second it is a function of both time and space through an unique combination. In the former case, although the permittivity of the whole medium is space-time-modulated, the quasienergy bands are symmetric because inversion symmetry is preserved. Different from the space-time-modulated medium often discussed previously, e.g. a homogeneous medium with the permittivity space-time-modulated according to a wavelike function, where either only exception points (EPs) or only quasienergy gaps generate, the coupling between the positive (negative) and positive (negative) bands in the time-Floquet PC results in quasienergy gaps, while the coupling between the positive and negative bands leads to pairs of EPs, enabling the coexistence of quasienergy gaps and EPs, when the modulation is on the real part of the permittivity. In the latter case, the quasienergy bands become asymmetric since time-reversal and inversion symmetries are simultaneously broken. The coupling between the positive (negative) and positive (negative) bands still results in quasienergy gaps, while the coupling between the positive and negative bands leads to quasienergy gaps at a small modulation speed and pairs of EPs at a high modulation speed.
DOI：
--
发表时间：
--
期刊：
--
影响因子：
--
作者：
Bit
通讯作者：
Bit