Chiral modes and directional lasing at exceptional points.
Controlling the emission and the flow of light in micro- and nanostructures is crucial for on-chip information processing. Here we show how to impose a strong chirality and a switchable direction of light propagation in an optical system by steering it to an exceptional point (EP)-a degeneracy universally occurring in all open physical systems when two eigenvalues and the corresponding eigenstates coalesce. In our experiments with a fiber-coupled whispering-gallery-mode (WGM) resonator, we dynamically control the chirality of resonator modes and the emission direction of a WGM microlaser in the vicinity of an EP: Away from the EPs, the resonator modes are nonchiral and laser emission is bidirectional. As the system approaches an EP, the modes become chiral and allow unidirectional emission such that by transiting from one EP to another one the direction of emission can be completely reversed. Our results exemplify a very counterintuitive feature of non-Hermitian physics that paves the way to chiral photonics on a chip.
Department of Electrical and Systems Engineering, Washington University, St. Louis, MO 63130;
Bo
B
Peng
Department of Electrical and Systems Engineering, Washington University, St. Louis, MO 63130; ozdemir@wustl.edu yang@seas.wustl.edu.
Şahin Kaya
ŞK
Özdemir
Institute for Theoretical Physics, Vienna University of Technology (TU Wien), Vienna A-1040, Austria;
Matthias
M
Liertzer
Department of Electrical and Systems Engineering, Washington University, St. Louis, MO 63130;
Weijian
W
Chen
Institute for Theoretical Physics, Otto-von-Guericke University, Magdeburg D-39016, Germany.
Johannes
J
Kramer
Department of Electrical and Systems Engineering, Washington University, St. Louis, MO 63130;
Huzeyfe
H
Yılmaz
Institute for Theoretical Physics, Otto-von-Guericke University, Magdeburg D-39016, Germany.
Jan
J
Wiersig
Institute for Theoretical Physics, Vienna University of Technology (TU Wien), Vienna A-1040, Austria;
Stefan
0000-0002-4123-1417
S
Rotter
Department of Electrical and Systems Engineering, Washington University, St. Louis, MO 63130; ozdemir@wustl.edu yang@seas.wustl.edu.
Lan
L
Yang
asymmetric backscattering; chiral modes; directional lasing; exceptional points; whispering-gallery-mode resonator