Browsing by Subject "PT-symmetry"

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Open Access
Anderson localization in non-hermitian systems: skin effect and scale-free localization
(2024-08) Yılmaz, Burcu
Localization properties of eigenstates change according to the lattice model. A Hatano-Nelson model with asymmetric hopping constants exhibit non-Hermitian skin effect(NHSE) where eigenstates localize near the edge of the lattice, the localization length is finite and does not depend on the system size. With introducing disorder to the Hatano-Nelson model, skin states start to become Anderson localized states. At a critical disorder strength all skin states become Anderson localized states. Since localization length of skin states does not depend on the system size, this model exhibits a size-independent Anderson localization. When the Hatano-Nelson model is modified as a 1D Hermitian lattice with an impurity, new model exhibits scale-free localized (SFL) states where unlike skin states, localization length scales with the system size. SFL states have a spatial profile that does not change as the system size varies. With the introduction of disorder into the system with SFL states, the interplay between SFL and Anderson localized states is observed. At the critical disorder strength, all states become Anderson localized states. Since localization length of SFL states scales with system size, a size-dependent Anderson transition occurs.
Open Access
Quasi PT-symmetric edge-emitting lasers outperform PT-symmetric ones
(IEEE, 2025-04) Olyaeefar, Babak; Şeker, Enes; El-Ganainy, Ramy; Demir, Abdullah
In recent years, engineering the spatial distribution of optical gain and loss has emerged as a new paradigm for tailoring light transport, trapping, and its interaction with matter. In this regard, it was shown that the notion of PT-symmetry can be employed to build new on-chip laser devices that operate in single longitudinal/transverse mode. Until recently, however, obtaining realistic power output and beam qualities from these systems was impossible. A recent study on quasi-PT-symmetric (q-PTS) lasers has changed this landscape by demonstrating up to 0.5 W output power with a high-quality Gaussian beam profile. In that work, PTS was implemented only for the higher-order mode in what can be considered a two-mode supersymmetric laser. Encouraged by these results and to present a clear roadmap for building practical chip-scale lasers with high performance, here we present a detailed comparison between the performance of PTS and q-PTS lasers in terms of power, mode filtering, and beam quality. Our experimental results, which are also supported by theoretical analysis, indicate that both q-PTS and PTS lasers scale similarly in terms of output power levels as a function of the pump current. However, when it comes to mode filtering and beam quality, our results clearly indicate that quasi-PTS lasers outperform PTS counterpart devices by a large margin. This can be explained by noting that while PTS geometry provides modal filtering for the higher order modes in the lasing cavity, it introduces side lobe contribution from the passive cavity which degrades the far-field emission pattern.