Observation of localized modes at effective gauge field interface in synthetic mesh lattice

We predict a generic mechanism of wave localization at an interface between uniform artificial gauge fields, arising due to propagation-dependent phase accumulation similar to Aharonov-Bohm phenomenon. We realize experimentally a synthetic mesh lattice with real-time control over the vector gauge field, and observe robust localization under a broad variation of gauge strength and direction, as well as structural lattice parameters. This suggests new possibilities for confining and guiding waves in diverse physical systems through the synthetic gauge fields.This work was supported by the Russian Science Foundation (16-12-10402). A.A.S. acknowledges support by the Australian Research Council (ARC) (DP160100619). I.D.V. acknowledges support of Ministry of Education and Science of the Russian Federation (3.7672.2017/8.9)

Anderson localization in synthetic photonic lattices

Synthetic photonic lattices provide unique capabilities to realize theoretical concepts emerging in different fields of wave physics via the utilization of powerful photonic technologies. Here we observe experimentally Anderson localization for optical pulses in time domain, using a photonic mesh lattice composed of coupled fiber loops. We introduce a random potential through programmed electro-optic pulse phase modulation, and identify the localization features associated with varying degree of disorder. Furthermore, we present a practical approach to control the band-gap width in photonic lattices by varying the coupling between the fiber loops, and reveal that the strongest degree of localization is limited and increases in lattices with wider band-gaps. Importantly, this opens a possibility to enhance or reduce the effect of disorder and associated localization of optical pulses

Nonlinear transition between PT-symmetric and PT-broken modes in coupled fiber lasers

We present a systematic analysis of the stationary regimes of nonlinear parity-time (PT) symmetric laser composed of two coupled fiber cavities. We find that power-dependent nonlinear phase shifters broaden regions of existence of both PT-symmetric and PT-broken modes, and can facilitate transitions between modes of different types. We show the existence of non-stationary regimes and demonstrate an ambiguity of the transition process for some of the unstable states. We also identify the presence of higher-order stationary modes, which return to the initial state periodically after a certain number of round-trips.Australian Research Council (DP160100619, DP190100277); Foundation for the Advancement of Theoretical Physics and Mathematics (18-1-3-39-1); Russian Foundation for Basic Research (19-0200633); Ministry of Education and Science of the Russian Federation (FSUS-2020-0034)

Influence of Kerr nonlinearity on PT-transition in coupled fibre lasers

This work investigates a concept of coupled fiber lasers exhibiting PT-symmetry and a PT-transition between PTsymmetric and PT-broken lasing states. We consider a system operated via Raman gain comprising two fiber loops (ring cavities) connected to each other by means of two fiber couplers with adjustable phase shift between them. By changing the phase shift or/and amplification (loss) in fiber loops, one can switch between generation regimes, realizing either PTsymmetric or PT-broken solution. In the PT-symmetric lasing regime, equal powers are generated in both cavities despite only active one is pumped. We make theoretical and numerical description of the proposed coupled fiber lasers starting with the simple discrete matrix model taking into account coupling, phase delays, gain (which is assumed to be saturated), losses and nonlinear phase shift. We show how the PT-transition is affected by self-phase modulation inside the fiber cavity and investigate requirements that should be met in order to observe PT-transition experimentally despite Kerr effect that violates exact symmetry conditions. In particular, we show that PT-transition may be observable only near lasing threshold. Further on we adopt more sophisticated model based on Nonlinear Schrödinger equation for PT fiber laser. Taking into account quasi-CW polychromatic radiation with typical spectral bandwidth of fiber Raman lasers, chromatic dispersion and Kerr nonlinearity, we demonstrate both PT-symmetric and PT-broken lasing in a fiber laser

Assessing Distribution Network Flexibility via Reliability-based P-Q Area Segmentation

This paper proposes a framework to assess the flexibility of active distribution networks (ADNs) via P-Q area segmentation, considering the reliability of flexible units (FUs). A mixed-integer quadratically constrained programming (MIQCP) model is formulated to analyse flexible active and reactive power support at the interface with transmission networks, explicitly capturing the contributions and reliability of FUs that provide flexibility services within an ADN. The numerical simulations performed for a real 124-bus UK distribution network demonstrate the optimal flexibility provision by different FUs, as well as the corresponding reliability and the impact of network reconfiguration. Distribution system operators (DSOs) can use the proposed framework to identify critical units, select an adequate combination of flexibility volumes, and manage its reliability.Comment: Submitted to PSCC 2022, then resubmitted to IEEE PowerTech 2023 conferenc

Tracing, Ranking and Pricing DER Flexibility in Active Distribution Networks

This paper presents a framework for analysing the aggregated flexibility of active distribution networks (ADNs) with distributed energy resources (DER). The analysis takes a different perspective than existing studies, which focus on characterising flexibility as the limits of the flexible power provision, i.e., the set of the network feasible operating points in the P-Q space. Instead, this work aims to estimate the contributions of different flexible units to the aggregated flexibility, which is essential for flexible power ranking and pricing. The proposed framework exploits cost-minimising OPF models complemented with cooperative game formulations that are able to capture the combinatorial nature of activating multiple flexible units. Moreover, in contrast to existing studies that imply perfect coordination of units, the proposed framework specifies the actions needed to reach feasible operating points, reflecting the nonlinearities of the network flexibility model. Extensive simulations are performed for different flexibility metrics to demonstrate the applicability of the framework. Depending on the metric selected (capacity, cost, or economic surplus of flexibility), distribution system operators (DSOs) can identify the most critical flexible units or remunerate units for participating in flexibility services provision