El-Ganainy Ramy, Levy Miguel
Opt Lett. 2015 Nov 15;40(22):5275-8. doi: 10.1364/OL.40.005275.
We introduce a new type of optical isolator based on breaking time reversal symmetry in dissipative finite Su-Schrieffer-Heeger (SSH) waveguide arrays that support topological edge states at one end of the structure. In the forward propagation direction, light is launched into the edge waveguide to excite the localized topological midgap state. As a result, most of the input optical power is transmitted to the output port. On the other hand, backward reflected light encounters a propagation constant mismatch in that same channel which shifts the otherwise midgap state into one of the bands and hence becomes delocalized over the whole array. We show that under these conditions, a judicious spatial distribution of the optical dissipation across the structure can produce an isolation ratio of -50 dB. The required nonreciprocal phase shift is introduced by depositing a magnetic garnet film only on the edge waveguide and, thus, the required magnetic field can be generated by an integrated micromagnet. Similar concepts can also be applied to SSH arrays made from optical resonators.
我们介绍了一种新型光学隔离器，它基于打破耗散有限Su-Schrieffer-Heeger（SSH）波导阵列中的时间反演对称性，该阵列在结构的一端支持拓扑边缘态。在正向传播方向上，光被注入边缘波导以激发局域化的拓扑中隙态。结果，大部分输入光功率被传输到输出端口。另一方面，反向反射光在同一通道中遇到传播常数失配，这会将原本的中隙态转移到能带之一中，从而在整个阵列上变得离域。我们表明，在这些条件下，结构中光损耗的合理空间分布可以产生-50 dB的隔离比。所需的非互易相移通过仅在边缘波导上沉积磁性石榴石薄膜来引入，因此所需的磁场可以由集成微磁体产生。类似的概念也可以应用于由光学谐振器制成的SSH阵列。
