
Chair: Stefan Rotter

09:00  09:40

Mercedeh Khajavikhan
(University of Central Florida, Orlando)
NonHermitian Photonics: Lasers and Sensors
I will talk about some of the practical applications of nonHermiticity and exceptional points, which can lead to novel lasers and ultrasensitive sensors.

09:40  10:20

Jan Wiersig
(OttovonGuerickeUniversity Magdeburg)
Exceptional points in whisperinggallery microcavities
In this talk, I will discuss the formation of exceptional points in whisperinggallery microcavities. We distinguish three different mechanisms based on weak deformation or perturbation of the cavity's boundary: asymmetric backscattering of counterpropagating waves, interaction of modes with different angular momentum, and coupling of internal and external modes. Finally, we discuss sensors for singleparticle detection based on exceptional points in optical microcavities.

10:20  10:30

discussions

10:30  11:00

coffee break

11:00  11:40

Seok Ho Song
(Hanyang University Seoul)
Dynamic encircling an exceptional point at telecomm wavelength
We experimentally demonstrate siliconphotonic waveguide devices that function as a broadband asymmetric transmission mode converter while dynamically encircling an EP (EEP) in the optical domain. The silicon device consists of two coupled channel waveguides with complex propagationindex profiles configured such that excited photonic modes undergo timeasymmetric EEP parametric evolutions. Real and imaginary propagationindex profiles required for the EEP evolution are realized by tuning waveguide width and photonic tunnelgap size, respectively. We explain the underlying design principle, theoretical analyses, fabrication, and measurement of the proposed photonic EEP device. Comprehensive theoretical and experimental analyses show robust timeasymmetry in the optical transmission over a broad spectral domain from 1,250 nm to 1,650 nm. We may establish robust EEP device in the optical domain and an important step toward realization of onchip optical isolators taking advantages of the unique nonHermitian wave dynamics.
[1] Y. Choi, C. Hahn, J. W. Yoon, S. H. Song and P. Berini, “Extremely broadband, onchip optical nonreciprocity enabled by mimicking nonlinear antiadiabatic quantum jumps near exceptional points,” Nat. Commun. 8, 14154 (2017).
[2] J. W. Yoon, Y. Choi, C. Hahn, G. Kim, S. H. Song, K.Y. Yang, J. Y. Lee, Y. Kim, C. S. Lee, J. K. Shin, H.S. Lee, and P. Berini, “Broadband timeasymmetry of light through a topological loop around an exceptional point,” submitted (Feb. 2018).

11:40  12:20

Peter Rabl
(Vienna University of Technology)
Energy transport phenomena in microscopic gainloss systems
I this talk I will describe the transport of energy through a network of coupled harmonic oscillators with active gain and loss sites. Despite it simplicity such a network exhibits a range of anomalous transport phenomena, which arise from the competition between coherent and incoherent processes in combination with nonlinear saturation effects. These phenomena become in particular interesting for microscopic networks, where the presence of thermal and quantum noise leads to a transition between a chaotic and a noiseless transport regime. This transition is closely related to PT symmetry breaking in balanced gainloss systems, but occurs more generally and therefore has important consequences for energy transport at the microscopic level.

12:20  12:30

discussions

12:30  13:30

lunch break

13:30  14:00

discussions


Chair: Li Ge

14:00  14:40

Paul M. Walker
(University of Sheffield)
ExcitonPolariton Nonlinear Photonics
Exciton polaritons, the hybrid quasiparticles formed from strong coupling of photons to semiconductor excitons, have emerged as promising candidates for implementing novel photonic devices such as ultrafast optical information processors [13], sources of quantum light [4,5] and nonlinear optical simulators based on arrays of coupled microresonators [6]. Polaritons can propagate like photons but their excitonic component allows for giant effective third order nonlinearity, gain, and sensitivity to real magnetic fields. These properties are advantageous for incorporation of strong nonlinearity into devices with nontrivial topological features [7,8] or PT symmetry [9,10].
In this talk I will review our experimental results on low power bright [11] and dark [12] solitons and continuum generation in polariton waveguides as well as spontaneous pattern formation [13] in FabryPerot microcavities. I will also discuss polariton lasing in a Lieblattice of coupled optical microresonators [14] and the role of spinorbit coupling in Lieb and onedimensional zigzag lattices.
[1] T. EspinosaOrtega and T. C. H. Liew, Phys. Rev. B 87, 195305 (2013)
[2] D. Ballarini et. al., Nat. Commun., 4, 1778 (2014)
[3] A. Dreismann et., al. Nat. Materials, 15, 1074 (2016)
[4] T. Boulier, et. al., Nat. Commum. 5, 3260 (2014)
[5] A. Delteil, T. Fink, A. Schade, S. Höfling, C. Schneider, and A. Imamoğlu, arXiv:1805.04020 (2018)
[6] A. Amo and J. Bloch, C. R. Physique 17, 934945 (2016).
[7] A. V. Nalitov, D. D. Solnyshkov, and G. Malpuech, Phys. Rev. Lett. 114, 116401 (2015)
[8] T. Karzig, C. E. Bardyn, N. H. Lindner, and G. Refael, Phys. Rev. X, 5, 031001 (2015)
[9] I. Yu. Chestnov, et. al., Sci. Rep. 6 19551 (2016)
[10] S. V. Suchkov et. al., Laser Photon. Rev. 10 177213 (2016)
[11] P. M. Walker et. al., Nat. Commun. 6, 8317 (2015)
[12] P. M. Walker et. al., Phys. Rev. Lett. 119, 097403 (2017)
[13] C. E. Whittaker et. al. Phys. Rev. X 7, 031033 (2017)
[14] C. E. Whittaker et. al., Phys. Rev. Lett. 120, 097401 (2018)

14:40  15:20

Uwe Bandelow
(Weierstrass Institute for Applied Analysis and Stochastics)
Semiconductor Laser Instabilities and Dynamics emerging from Mode Degeneracy
In the context of linear optics typical models for semiconductor lasers consist of a set of linear evolution equations for the optical fields, that is nonlinearly coupled to a nonlinear system of transport equations for the charge carriers in the active region of these lasers.
The latter system is typically evolving along the recombination time scale, which is usually 3 orders of magnitude slower than the photon lifetime in semiconductor lasers.
This special structure of the model motivates a spectral representation of the optical subsystem, which is nonhermitian by nature, because of radiating boundary conditions, as well as by the presence of gain and losses in the resonator.
As a first consequence, the spectrum of the optical subsystem is complex, where the real part can be interpreted as the optical frequency of the corresponding mode, whereas the imaginary part is the (reverse) lifetime of the mode, such that the modes with the smallest imaginary part are favoured for lasing.
As a second consequence, the modes are not powerorthogonal, but biorthogonal with respect to their adjoint partners. This implies counterintuitive effects, as the appearance of Petermanns Kfactor in the evolution of the optical fields, which measures the „nonhermiticity’’ of the optical resonator.
As a third consequence, the modes can completely degenerate in socalled exceptional points,
where the Petermann Kfactor reaches infinity, with even more striking consequences.
Several examples will show new types of instabilities and dynamic scenaria in semiconductor lasers that arise from these facts, and demonstrate their practical use in photonic technologies for highspeed applications.

15:20  16:00

EvaMaria Graefe
(Imperial College London)
Blochoscillations in nonHermitian lattices

16:00  16:30

coffee break

16:30  17:00

JungWan Ryu
(Center for Theoretical Physics of Complex Systems Daejeon)
Robust localized states in a twisted interface of PTsymmetric Moebius ladder lattices
Moebius strip is a continuous onesided surface formed from a rectangular strip by rotating one end 180 degrees and attaching to the other end. This marvelous structure with only one side and only one boundary is the epitome of the topologically nontrivial phenomenon and shows various curious properties due to its unorientability. Besides fundamental studies on topology, the unorientability enable the Moebius strip to be applicable to many useful applications in various field. Here, we investigate eigenfunctions in Moebius ladder lattice which can be considered as the prototype for eigenfunction analysis of real space Moebius strip. PTsymmetry is applied to the Moebius ladder lattices and then the PTphase transitions in PTsymmetric Moebius ladder lattice appear at new transition points because of the combination between PTsymmetry and nontrivial topology of real space. Finally, we report the interface states are localized at the twisted interface and protected by PTsymmetry.

17:00  17:30

Kai Wang
(Australian National University)
Synthetic multidimensional photonic lattices and novel manifestations
Kai Wang (1), Lukas J. Maczewsky (2), Alexander A. Dovgiy (1), Andrey E. Miroshnichenko (3), Alexander Moroz (4), Demetrios N. Christodoulides (5), Alexander Szameit (2), and Andrey A. Sukhorukov (1)
(1) Nonlinear Physics Centre, The Australian National University, Canberra, Australia
(2) Institute for Physics, Universität Rostock, Rostock, Germany
(3) School of Engineering and Information Technology, University of New South Wales, Canberra, Australia
(4) Wavescattering.com
(5) CREOL, The College of Optics and Photonics, University of Central Florida, Orlando, Florida 32816, USA
Discrete lattices play an important role in fundamental physics, due to the universality of wave propagation and localization spanning from electrons in atomic potentials to light in periodic photonic structures. The latest research reveals unique benefits of two and higherdimensional structures for tailoring light confinement and emission [1], implementing imperfectionsinsensitive transmission [2], and even realization of optical neural networks [3]. Yet, it remains an open question on the potential for implementing multidimensional photonics on planar integrated alloptical platforms. Here, we introduce a new, general and practical approach for mapping arbitrary multidimensional tightbinding lattices to a planar (1D) lattice, where the photon dynamics remains exactly equivalent, and theoretically demonstrate an application in ultrasensitive optical detection and lowthreshold nonlinear switching.
Our mapping procedure is based on Lanczos matrix tridiagonalization. Whereas this algorithm was traditionally formulated in an abstract form for linear matrices, we find that it is applicable to coupledmode discrete Schrödinger equation describing completely the nonstationary light dynamics. Our approach allows multidimensional structures to be mapped to a 1D semiinfinite lattice with only nearestneighbour couplings. Importantly, Lanczos algorithm allows us to map any initial multidimensional excitation to the first site of the equivalent planar lattice. It is also possible to add defect to the excitation site, where the wave dynamics in that site is exactly the same as in the defect site of the multidimensional lattice.
Our concept can enable fundamental advances in optical switching and sensing. Specifically, we find that the excitation efficiency, i.e. the amount of light remaining trapped at the defect, exhibits unique features in highdimensional space. In directly accessible dimensions of N = 1,2,3, the excitation efficiency grows gradually as the defect strength is increased. However, only for highdimensional (N = 4,5,...) lattices, the excitation suddenly jumps from zero to a finite value as the defect strength crosses a critical threshold. This effect was absent in previous studies of linear optical lattices, and it corresponds to an ultrahigh sensitivity to extremely small changes in defect strength. Although photonic lattices with N= 4, 5, . . . are out of reach for direct experimental realizations, we successfully applied our approach to mapping the multidimensional lattice into a planar (1D) structure, where the special variation of couplings can be achieved by engineering the separations between the waveguides [4]. Moreover, we introduce Kerrnonlinearity to the defect waveguide and numerically demonstrate a lowthreshold switching controlled by the input power.
In conclusion, we introduced a powerful approach for designing practical synthetic photonic structures behaving as complicated multidimensional structures. As an important application, we predicted a sharp switching from zero to strong localization at critical surface defect strength in four and higherdimensional synthetic lattices, demonstrating the potential for optical detection with fundamentally enhanced sensitivity and optical switching with ultralow threshold in both linear and nonlinear regimes. By proper use of loss and gain, our concept may also be generalized to the synthesis of nonHermitian highdimensional lattices.
References
[1] J. D. Joannopoulos, R. D. Meade, et al., Photonic Crystals: Molding the Flow of Light, 2nd ed. (Princeton University Press, Princeton, 2008).
[2] M. C. Rechtsman, J. M. Zeuner, et al., Nature 496, 196 (2013).
[3] P. R. Prucnal and B. J. Shastri, Neuromorphic Photonics (CRC Press, 2017).
[4] M. Heinrich, M. A. Miri, et al., Nat. Commun. 5, 3698 (2014).

17:30  19:00

discussions

19:00  21:00

dinner

20:00  21:30

poster session
