title: Observation of exceptional points in reconfigurable non-Hermitian vector-field holographic lattices.
abstract: Recently, synthetic optical materials represented via non-Hermitian Hamiltonians have attracted significant attention because of their nonorthogonal eigensystems, enabling unidirectionality, nonreciprocity and unconventional beam dynamics. Such systems demand carefully configured complex optical potentials to create skewed vector spaces with a desired metric distortion. In this paper, we report optically generated non-Hermitian photonic lattices with versatile control of real and imaginary sub-lattices. In the proposed method, such lattices are generated by vector-field holographic interference of two elliptically polarized pump beams on azobenzene-doped polymer thin films. We experimentally observe violation of Friedel's law of diffraction, indicating the onset of complex lattice formation. We further create an exact parity-time symmetric lattice to demonstrate totally asymmetric diffraction at the spontaneous symmetry-breaking threshold, referred to as an exceptional point. On this basis, we provide the experimental demonstration of reconfigurable non-Hermitian photonic lattices in the optical domain and observe the purest exceptional point ever reported to date.
authors.affiliation: Department of Physics, Hanyang University, Seoul 133-791, Korea.
authors.forename: Choloong
authors.initials: C
authors.lastname: Hahn
authors.affiliation: Department of Physics, Hanyang University, Seoul 133-791, Korea.
authors.forename: Youngsun
authors.initials: Y
authors.lastname: Choi
authors.affiliation: Department of Physics, Hanyang University, Seoul 133-791, Korea.
authors.forename: Jae Woong
authors.initials: JW
authors.lastname: Yoon
authors.affiliation: Department of Physics, Hanyang University, Seoul 133-791, Korea.
authors.forename: Seok Ho
authors.initials: SH
authors.lastname: Song
authors.affiliation: Department of Physics, Hanyang University, Seoul 133-791, Korea.
authors.forename: Cha Hwan
authors.initials: CH
authors.lastname: Oh
authors.affiliation: School of Electrical Engineering and Computer Science, University of Ottawa, 800 King Edward Avenue, Ottawa, Ontario, Canada K1N 6N5.|Department of Physics, University of Ottawa, 150 Louis Pasteur, Ottawa, Ontario, Canada K1N 6N5.|Centre for Research in Photonics, University of Ottawa, 25 Templeton Street, Ottawa, Ontario, Canada K1N 6N5.
authors.forename: Pierre
authors.initials: P
authors.lastname: Berini