Parity–time synthetic photonic lattices

Abstract

The development of new artificial structures and materials is today one of the major research challenges in optics. In most studies so far, the design of such structures has been based on the judicious manipulation of their refractive index properties. Recently, the prospect of simultaneously using gain and loss was suggested as a new way of achieving optical behaviour that is at present unattainable with standard arrangements. What facilitated these quests is the recently developed notion of 'parity-time symmetry' in optical systems, which allows a controlled interplay between gain and loss. Here we report the experimental observation of light transport in large-scale temporal lattices that are parity-time symmetric. In addition, we demonstrate that periodic structures respecting this symmetry can act as unidirectional invisible media when operated near their exceptional points. Our experimental results represent a step in the application of concepts from parity-time symmetry to a new generation of multifunctional optical devices and networks.

Constant-intensity waves and their modulation instability in non-Hermitian potentials

“…We expect that our predictions can be verified by combining recent advances in shaping complex wave fronts 3 with new techniques to fabricate non-Hermitian scattering structures with gain and loss [7][8][9][10] . As the precise combination of gain and loss in the same device is challenging, we suggest using passive structures with only loss in the first place.…”

“…They also remain valid for any sign of Kerr nonlinearity and thus allow us to perform a modulational stability analysis for non-homogeneous potentials. The most appropriate context to study the MI of such solutions is that of PT -symmetric optics [6][7][8][9][10][11]14,[19][20][21][22]24 . We find that in the selffocusing regime, the waves are always unstable, whereas in the defocusing regime the instability appears for specific values of Bloch momenta.…”

“…Such non-Hermitian potential regions 4,5 , which serve as sources and sinks for waves, respectively, can give rise to novel wave effects that are impossible to realize with conventional, Hermitian potentials. Examples of this kind, which were meanwhile also realized in the experiment [6][7][8][9][10] , are the unidirectional invisibility of a gain-loss potential 11 , devices that can simultaneously act as laser and as a perfect absorber [12][13][14] and resonant structures with unusual features like non-reciprocal light transmission 10 or loss-induced lasing [15][16][17] . In particular, systems with a so-called parity-time (PT ) symmetry 18 , where gain and loss are carefully balanced, have recently attracted enormous interest in the context of nonHermitian photonics [19][20][21][22][23][24] .…”

High-density waveguide superlattices with low crosstalk

“…For example, waveguide arrays are widely used in emerging applications such as optical-phased arrays [18][19][20][21] , space-division multiplexing 22 and chip-scale optical interconnects 23,24 , and conventional applications such as wavelength-division multiplexers 25,26 . On the other hand, a waveguide array or a waveguide lattice can also be viewed 27 as fully analogous to a periodic chain of atoms, which lends itself to a broad spectrum of fascinating scientific possibilities ranging from Anderson localization of light 28,29 to parity-time symmetric effects 30 . Thus far, in most studies, the pitch associated with such relatively simple waveguide arrays/lattices has been typically large, ranging from a few micrometres to tens of micrometres (or a multiple of wavelengths) 18,19,21,31,32 .…”

PT symmetric Aubry–Andre model

“…Recent experimental realization of PT symmetric optical systems with balanced gain and loss has attracted a lot of attention [1][2][3]. The PT symmetric optical systems lead to interesting results such as unconventional beam refraction and power oscillation [4][5][6], nonreciprocal Bloch oscillations [7], unidirectional invisibility [8], an additional type of Fano resonance [9], and chaos [10].…”