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Extraordinary Fast Forward and Backward Light in Transparent Non‐Hermitian Systems
Author(s) -
Zhang Lingxuan,
Ying Lei,
Ge Li,
Zhao Wei,
Zhang Wenfu
Publication year - 2021
Publication title -
laser and photonics reviews
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 3.778
H-Index - 116
eISSN - 1863-8899
pISSN - 1863-8880
DOI - 10.1002/lpor.202000204
Subject(s) - superluminal motion , physics , slow light , photonics , hermitian matrix , optics , bandwidth (computing) , photonic crystal , quantum mechanics , telecommunications , computer science
The phenomenon of fast forward and backward light pulse propagation in effectively transparent non‐Hermitian photonic systems is reported. Specifically, the propagation eigenmodes are analyzed in several parity‐time‐symmetric coupled waveguides. In contrast to a previous finding that showed slow light due to an exceptional point in such systems, a critical point in its close proximity that displays a diverging dispersion is identified. Superluminal light pulse propagation in the forward and backward directions is then found and observed numerically on the two sides of the critical point, respectively. This abnormal phenomenon can be understood by a conservation relation of group velocities, which can be extended to other transparent non‐Hermitian photonic systems with different symmetries. More importantly, the abrupt transition across the critical point between the fast forward and backward light can be tuned, indicating the possibility of detecting atom‐scale movement of the waveguides with little time delay. In addition, bandwidth broadening and a passive superluminal propagation configuration are discussed.