Browsing by Author "Wilkey, Andrew"

Now showing 1 - 7 of 7
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    Exceptional points in a time-delayed anti-parity-time symmetric system
    (Optica, 2021) Wilkey, Andrew; Joglekar, Yogesh N.; Vemuri, Gautam; Physics, School of Science
    We report on the experimental realization of an anti-PT symmetric system in a pair of time-delay coupled semiconductor lasers, and via numerical and analytical modeling investigate the properties of exceptional points in it.
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    Exceptional points in anti-PT symmetric system of delay coupled semiconductor lasers
    (SPIE, 2021-08) Vemuri, Gautam; Wilkey, Andrew; Joglekar, Yogesh; Physics, School of Science
    This paper will report on some features of a platform for the realization of an anti parity-time (anti-PT) symmetric system in a pair of time-delay coupled semiconductor lasers, with special emphasis on the delay induced dynamics in the system. The system is modeled by a modified Lang-Kobayashi rate equations model, augmented to include delayed coupling. The role of a phase accumulation factor that arises from the delayed coupling is elucidated. Finally, the novel exceptional point(s) behavior that is characteristic of the time-delay is investigated via numerics as well as analytically via the Lambert W function.
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    Investigation of PT Symmetry Breaking and Exceptional Points in Delay-coupled Semiconductor Lasers
    (2021-08) Wilkey, Andrew; Vemuri, Gautam; Joglekar, Yogesh; Liu, Jing; Ou, Jeff; Petrache, Horia
    This research investigates characteristics of PT (parity-time) symmetry breaking in a system of two optically-coupled, time-delayed semiconductor lasers. A theoretical rate equation model for the lasers' electric fields is presented and then reduced to a 2x2 Hamiltonian model, which, in the absence of time-delay, is PT-symmetric. The important parameters we control are the temporal separation of the lasers, the frequency detuning, and the coupling strength. The detuning is experimentally controlled by varying the lasers' temperatures, and intensity vs. detuning behavior are examined, specifically how the PT-transition and the period and amplitude of sideband intensity oscillations change with coupling and delay. Experiments are compared to analytic predictions and numerical results, and all are found to be in good agreement. Eigenvalues, eigenvectors, and exceptional points of the reduced Hamiltonian model are numerically and analytically investigated, specifically how nonzero delay affects existing exceptional points.
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    Lambert function methods for laser dynamics with time-delayed feedback
    (2017-12-30) Joglekar, Yogesh N.; Vemuri, Gautam; Wilkey, Andrew; Physics, School of Science
    Time-delayed differential equations arise frequently in the study of nonlinear dynamics of lasers with optical feedback and because the analytical solution of such equations can be intractable, one resorts to numerical methods. In this manuscript, we show that under some conditions, the rate equations model that is used to model semiconductor lasers with feedback can be analytically solved by using the Lambert W function. In particular, we discuss the conditions under which the coupled rate equations for the intracavity electric field and carrier inversion can be reduced to a single equation for the field, and how this single rate equation can be cast in a form that is amenable to the use of the Lambert W function.
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    Non-hermitian dynamics in delay coupled semiconductor lasers
    (SPIE, 2019-08) Wilkey, Andrew; Suelzer, Joseph S.; Joglekar, Yogesh; Vemuri, Gautam; Physics, School of Science
    This paper describes our work on the realization of a non-hermitian Hamiltonian system in time-delay coupled semiconductor lasers consisting of two identical lasers, operated with a small frequency detuning between them, and bidirectionally coupled to each other through optical injection. The effective Hamiltonian for this system is non-hermitian, and, under some assumptions and conditions, reminiscent of two-site paritytime (PT) symmetric Hamiltonians, a topic that is under intense investigation. The dynamical response of the intensity of the lasers as a function of the detuning between them reveals characteristics of a PT symmetric system, and our emphasis is on the features that arise from the delayed coupling. Experimental measurements are in good agreement with numerical simulation of the nonlinear rate equation model that describes the coupled system.
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    Parity–Time Symmetry in Bidirectionally Coupled Semiconductor Lasers
    (MDPI, 2019-12) Wilkey, Andrew; Suelzer, Joseph; Joglekar, Yogesh; Vemuri, Gautam; Physics, School of Science
    We report on the numerical analysis of intensity dynamics of a pair of mutually coupled, single-mode semiconductor lasers that are operated in a configuration that leads to features reminiscent of parity–time symmetry. Starting from the rate equations for the intracavity electric fields of the two lasers and the rate equations for carrier inversions, we show how these equations reduce to a simple 2 × 2 effective Hamiltonian that is identical to that of a typical parity–time (PT)-symmetric dimer. After establishing that a pair of coupled semiconductor lasers could be PT-symmetric, we solve the full set of rate equations and show that despite complicating factors like gain saturation and nonlinearities, the rate equation model predicts intensity dynamics that are akin to those in a PT-symmetric system. The article describes some of the advantages of using semiconductor lasers to realize a PT-symmetric system and concludes with some possible directions for future work on this system.
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    Theoretical and experimental characterization of non-Markovian anti-parity-time systems
    (Springer, 2023-10-20) Wilkey, Andrew; Suelzer, Joseph; Joglekar, Yogesh N.; Vemuri, Gautam; Physics, School of Science
    Open systems with anti-parity-time (APT) or PT symmetry exhibit a rich phenomenology absent in their Hermitian counterparts. To date all model systems and their diverse realizations across classical and quantum platforms have been local in time, i.e., Markovian. Here we propose a non-Markovian system with anti-PT-symmetry where a single time-delay encodes the retention of memory, and experimentally demonstrate its consequences with two time-delay coupled semiconductor lasers. A transcendental characteristic equation with infinitely many eigenvalue pairs sets our model apart. We show that a sequence of amplifying-to-decaying dominant mode transitions is induced by the time delay in our minimal model. The signatures of these transitions quantitatively match results obtained from four, coupled, nonlinear rate equations for laser dynamics, and are experimentally observed as constant-width sideband oscillations in the laser intensity profiles. Our work introduces a paradigmatic non-Hermitian system with memory, paves the way for its realization in classical systems, and may apply to time-delayed feedback-control for quantum systems.