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Switching and dynamic memory applications using
nonuniform system of coupled waveguides with local
parity-time symmetry

Anatole Lupu, Vladimir Konotop, H. Benisty

► To cite this version:

Anatole Lupu, Vladimir Konotop, H. Benisty. Switching and dynamic memory applications using nonuniform system of coupled waveguides with local parity-time symmetry. Photonics North 2015, Jun 2015, Ottawa, Canada. 10.1109/PN.2015.7292525. hal-01714370

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Submitted on 30 Aug 2022

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Distributed under a Creative Commons Attribution 4.0 International License
Switching and dynamic memory applications using
nonuniform system of coupled waveguides
with local parity-time symmetry

Anatole Lupu, Institut d'Electronique Fondamentale, Univ. Paris-Sud, CNRS UMR 8622, Orsay, France
anatole.lupu@u-psud.fr

Vladimir V. Konotop, Centro de Física Teórica e Computacional, Universidade de Lisboa, Lisboa, Portugal

Henri Benisty, Laboratoire Charles Fabry, IOGS, CNRS, Univ. Paris-Sud, Palaiseau, France

***Abstract***— We address the potential of a nonuniform coupled waveguides system with gain and loss featuring a PT-symmetry configuration for the realization of switching and dynamic memory applications based on a non-reciprocal modal behavior. The possibility for a perfect switching operation in such a non-conservative layout combining loss and gain is demonstrated.

***Keywords***—optical switching; buffer memory; gain-loss modulation, Parity-Time symmetry; plasmonics, metamaterials.

I. INTRODUCTION

The development of photonics enabled by the advent of
nanofabrication technologies during the past decades has
triggered the emergence of new types of artificial structures
such as photonic crystals, metamaterials, plasmonic structures,
and more recently the so-called PT-symmetric devices,
referring to Parity-Time symmetry. The characteristic feature
of PT-symmetry is that the refractive index profile of the
structures is complex-valued due to the presence of alternating
gain and loss regions in the system. These particular spatial
repartitions can either occur in the direction transverse to the
light propagation direction, as in the case of the coupled
directional coupler [1] or in the longitudinal direction, as in the
case of the PT-symmetric Bragg grating [2]. Apart from
fundamental research motivations, the tremendous interest in
these artificial systems is strongly driven by the practical
functionalities that can be achieved by modulating the values
of gain and loss in such structures.

II. PT-SYMMETRY RELATED FUNCTIONALITIES

A disruptive paradigm of the PT-symmetry concept is that
combination and modulation of gain and loss can be
advantageously used for obtaining additional functionalities,
well beyond the simple idea of loss compensation.

A. *Gain-loss modulation optical switching*

The effective detuning of the propagation constants in a
system of PT-symmetric coupled waveguides is first gradually
reduced upon increasing the level of combined gain/loss in the
system, until they become imaginary above the critical point.
The variation of the effective detuning (i.e. the propagation

eigenvalue difference) can be advantageously exploited for the
implementation of a switching or modulation through the
variation of the gain-loss level below the critical point. This
avenue would largely mitigate the lack of electro-optical
tunability in fiber optics, metamaterials and plasmonics.

Our theoretical findings also predict a remarkable feature,
genuinely connected to the PT-symmetry. The gain level
required for switching can be reduced by increasing the loss
contribution, with a penalty that turns out to be quite affordable
on the transmission level. A further reduction of the
amplification level could be expected through the additional
implementation of the variable gain-loss profile. We
demonstrate the possibility for a perfect switching operation in
such local PT-symmetric system and provide derivation for the
optimal gain-loss profile corresponding to the switching
operation requiring the minimal amplification level that
produces switching.

B. *Buffer memory operation based on spatial non-reciprocity*

This functionality, different from non-reciprocity based on
the Faraday magneto-optical effect, is based on the non-
reciprocity of mode coupling. In the case of a system of PT-
symmetric coupled waveguides the transmission differs
depending whether light injection is performed in the gain or
loss waveguides. This kind of asymmetric operation can be
used for the implementation of a buffer memory function. The
remarkable feature is that tailoring of gain-loss or coupling
profiles brings an additional degree of freedom allowing for
example to provide a strong re-amplification of the signal
circulating in the buffer memory loop.

Overall, such non-reciprocal PT-symmetric network
systems provides an avenue for novel computational/logic
architectures with perspectives for potentially groundbreaking
applications.

REFERENCES

1. A. Lupu, et al, “Switching using PT-symmetry in plasmonic systems: positive role of the losses,” Opt. Express 21, 21651-21668 (2013).

2. M. Kulishov, et al, “Nonreciprocal waveguide Bragg gratings,” Opt. Express 13, 3068–3078 (2005).