Exceptional Points of Degeneracy in Periodic Coupled Waveguides and the Interplay of Gain and Radiation Loss: Theoretical and Experimental Demonstration

Abdelshafy, Ahmed F.; Othman, Mohamed A. K.; Oshmarin, Dmitry; Almutawa, Ahmad T.; Capolino, Filippo

doi:10.1109/tap.2019.2922778

Cited by 48 publications

(35 citation statements)

References 46 publications

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“…One issue that must be considered when implementing this design in the gigahertz frequency range and above, is the decrease of inductor quality factor with increasing frequency, especially in the integrated circuit technology where inductor Q is only 20–30. An obvious workaround the inductor low Q e limitation is the elimination of all lumped elements by means of implementation of the unit cell with degeneracy condition in another technology, such as microstrip or waveguide where there is no need for lumped elements [14, 16, 43, 44]. As previously mentioned, the simple lumped element structure of this paper already mimics the RF/microwave distributed TL model and, with minor alteration, can easily be translated to a different technology such as TLs, and more specifically microstrip waveguides.…”

Section: Conclusion and Remarksmentioning

confidence: 99%

New oscillator concept based on band edge degeneracy in lumped double‐ladder circuits

Oshmarin

Yazdi

Othman

et al. 2019

IET Circuits, Devices & Systems

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An oscillator scheme based on the degenerate band edge (DBE) in a periodic, double-ladder resonant circuit made of lumped elements is proposed for the first time. The circuit exhibits a DBE in the dispersion diagram of its phase-frequency eigenstates and possesses unique resonance features associated with a high loaded Q-factor resonance, compared to a singleladder circuit. This oscillator is shown to have an oscillation threshold that is half that of a single LC ladder circuit having the same total quality factor, and thus is more robust than an LC oscillator in the presence of losses. Moreover, the double-ladder oscillators have a unique mode selection scheme that leads to stable single-frequency oscillations even when the load is varied. It is also shown that the output amplitude of the double-ladder oscillator is much less sensitive to the output loading compared to single-ladder oscillators. The authors show the analysis and design of such oscillators that potentially lead to enhancing the efficiency of RF components and sources.

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Section: Conclusion and Remarksmentioning

confidence: 99%

New oscillator concept based on band edge degeneracy in lumped double‐ladder circuits

Oshmarin

Yazdi

Othman

et al. 2019

IET Circuits, Devices & Systems

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“…In this paper, we present an example of a DBE oscillator based on two periodic, coupled transmission lines (CTLs) as in one of the configurations proposed in [20] and shown in Fig. 1(a).…”

Section: Introductionmentioning

confidence: 99%

Distributed Degenerate Band Edge Oscillator

Abdelshafy

Oshmarin

Othman

et al. 2021

IEEE Trans. Antennas Propagat.

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We propose a new class of oscillators by engineering the dispersion of two-coupled periodic waveguides to exhibit a degenerate band edge (DBE). The DBE is an exceptional point of degeneracy (EPD) of order four, i.e., representing the coalescence of four eigenmodes of a waveguide system without loss and gain. We present a distributed DBE oscillator realized in periodic coupled transmission lines with a unique mode selection scheme that leads to a stable single-frequency oscillation, even in the presence of load variation. The DBE oscillator potentially leads to a boost of the efficiency and performance of RF sources, thanks to the unique features associated to the EPD concept. This class of oscillators is promising for improving discrete-distributed coherent sources and can be extended to radiating structures to achieve a new class of active integrated antenna arrays.

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“…In order to quantify the coalescence of the eigenvectors we use the concept of "coalescence parameter" introduced in [22] for the DBE and in [4] for the SIP. Here, we use a coalescence parameter σ defined similarly to that in [4].…”

Section: A Analytic Dispersion Relation For An Sipmentioning

confidence: 99%

“…Here, θ mn is the angle between two 6-dimensional complex vectors ψ m , ψ n , which is defined as stated in equation ( 16) using the inner product < ψ i |ψ j >= ψ † i ψ j with the dagger symbol † representing the complex conjugate transpose operation and ψ m denotes the norm of ψ m [4]. In this paper, we calculate the coalescence parameter using the norm based on the euclidean distance between the parameters θ mn , ∀m, n, and zero, [23], instead of using the arithmetic average used in [4,22]. The reason for this change is that the optimization algorithm converges faster using the euclidean distance than the arithmetic average, as long as the algorithm does not generate a lot of points far from the optimization goal (known as outliers) [24].…”

Section: A Analytic Dispersion Relation For An Sipmentioning

confidence: 99%

Frozen mode in an asymmetric serpentine optical waveguide

Parareda,

Vitebksiy,

Scheuer

et al. 2021

Preprint

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We show the existence of a frozen mode in a periodic serpentine waveguide with broken longitudinal symmetry. The frozen mode is associated with a stationary inflection point (SIP) of the Bloch dispersion relation, where three Bloch eigenmodes collapse on each other. Indeed, we show that the SIP is an exceptional point of degeneracy of order three. The frozen mode regime is characterized by vanishing group velocity and enhanced field amplitude, which can be very attractive in various applications including dispersion egineering, lasers, and delay lines. We show the trend in group delay and quality factor with waveguide length that is peculiar of the frozen mode. In a finite length waveguide, full transmission occurs at the resonance frequency very close to the SIP frequency.

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Exceptional Points of Degeneracy in Periodic Coupled Waveguides and the Interplay of Gain and Radiation Loss: Theoretical and Experimental Demonstration

Cited by 48 publications

References 46 publications

New oscillator concept based on band edge degeneracy in lumped double‐ladder circuits

New oscillator concept based on band edge degeneracy in lumped double‐ladder circuits

Distributed Degenerate Band Edge Oscillator

Frozen mode in an asymmetric serpentine optical waveguide

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