Nonreciprocal topological mode conversion by encircling an exceptional point in dynamic waveguides

The topology of exceptional points (EPs) has been revealed by taking stationary or dynamical encircling around them, which induces eigenstate exchange or chiral mode conversion. However, the conversions are usually reciprocal obeying restricted transmittances. Here we propose the concept of nonrecip...

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Veröffentlicht in:Optics letters 2023-08, Vol.48 (15), p.4089-4092
Hauptverfasser: Liu, Qingjie, Wang, Tiantian, Lei, Quan, Zhao, Dong, Ke, Shaolin
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Sprache:eng
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Zusammenfassung:The topology of exceptional points (EPs) has been revealed by taking stationary or dynamical encircling around them, which induces eigenstate exchange or chiral mode conversion. However, the conversions are usually reciprocal obeying restricted transmittances. Here we propose the concept of nonreciprocal encircling of EPs in a dynamic waveguide under complex modulation. The waveguide allows direction-dependent EPs in their quasienergy spectra due to different phase-matching conditions for opposite propagation direction. We design a closed loop that will encircle the EP in the backward direction but not in the forward direction. In this way, a nonreciprocal topological conversion is achieved as the forward transmittance from the even to odd mode significantly exceeds the backward transmittance from the odd to even mode. As a result, the forward propagation produces two modes with equal strength while the backward propagation leads to a specific mode regardless of the input. The structure is promising for making robust optical isolators.
ISSN:0146-9592
1539-4794
DOI:10.1364/OL.496988