More Like this

1. Measuring the growth of Alfvén wave parametric decay instability using counter-propagating waves: Theory and simulations

   https://doi.org/10.1103/4phq-zl19  

   Li, Feiyu; Dorfman, Seth; Fu, Xiangrong (August 2025, Physical Review E)

   The parametric decay instability (PDI) of Alfvén waves—where a pump Alfvén wave decays into a backward-propagating child Alfvén wave and a forward ion acoustic wave—is a fundamental nonlinear wave-wave interaction and holds significant implications for space and laboratory plasmas. However, to date there has been no direct experimental measurement of PDI. Here, we propose a novel and experimentally viable scheme to quantify the growth of Alfvén wave PDI on a linear device using a large pump Alfvén wave and a small counter-propagating seed Alfvén wave, with the seed-wave frequency tuned to match the backward Alfvén wave generated by standard PDI. Using hybrid simulations, we show that energy transfer from the pump to the seed reduces the latter’s spatial damping. By comparing seed-wave amplitudes with and without the pump wave, this damping reduction can be used as a direct and reliable proxy for PDI growth. The method is validated in our simulations across a range of plasma and wave parameters and agrees well with theoretical predictions. Notably, the scheme exhibits no threshold for PDI excitation and is, in principle, readily implementable under current laboratory conditions. This scheme is a critical step toward solving the challenge of experimentally accessing Alfvén wave PDI and provides an elegant method that may be used to validate fundamental theories of parametric instabilities in controlled laboratory settings. 

   more » « less
2. Self phase-matched broadband amplification with a left-handed Josephson transmission line

   Kow, C; Podolskiy, V; Kamal, A (January 2022, ArXivorg)

   Josephson Traveling Wave Parametric Amplifiers (J-TWPAs) are promising platforms for realizing broadband quantum-limited amplification of microwave signals. However, substantial gain in such systems is attainable only when strict constraints on phase matching of the signal, idler and pump waves are satisfied -- this is rendered particularly challenging in the presence of nonlinear effects, such as self- and cross-phase modulation, which scale with the intensity of propagating signals. In this work, we present a simple J-TWPA design based on left-handed (negative-index) nonlinear Josephson metamaterial, which realizes autonomous phase matching without the need for any complicated circuit or dispersion engineering. The resultant efficiency of four-wave mixing process can implement gains in excess of 20 dB over few GHz bandwidths with much shorter lines than previous implementations. Furthermore, the autonomous nature of phase matching considerably simplifies the J-TWPA design than previous implementations based on right-handed (positive index) Josephson metamaterials, making the proposed architecture particularly appealing from a fabrication perspective. The left-handed JTL introduced here constitutes a new modality in distributed Josephson circuits, and forms a crucial piece of the unified framework that can be used to inform the optimal design and operation of broadband microwave amplifiers. 

   more » « less
3. Frequency dependent parametric radiation through a nonlinear fundamentally slow travelling wave structure

   https://doi.org/10.1002/mop.32950  

   Li, Shuping; Zhu, Minning; Yuan, Yichao; Wu, Chung‐Tse Michael (June 2021, Microwave and Optical Technology Letters)

   Abstract This article presents a nonlinear leaky wave antenna (LWA) with frequency dependent parametric radiation based on a fundamentally slow‐wave transmission line (TL) structure. Unlike a conventional LWA that radiates at the excitation frequency, the radiation for the proposed travelling wave structure relies on the parametric frequencies based on the injected pump signals. The proposed nonlinear fundamentally slow wave structure utilizes a periodic sharply bend TL loaded by varactor diodes as nonlinear elements. By utilizing then = −1 spatial harmonic, the fundamentally slow wave structure can enter the leaky wave region at higher frequencies, where the parametric radiation results from the bifurcation of the injected pump signals. Such TL‐based nonlinear LWA reduces the design complexity and fabrication difficulty. The resulting parametric frequency radiation can be used for beam steering, which provides additional degree of design freedom. 

   more » « less
4. Elastic Metasurfaces for Full Wavefront Control and Low-Frequency Energy Harvesting

   https://doi.org/10.1115/1.4050275  

   Lin, Zhenkun; Tol, Serife (December 2021, Journal of Vibration and Acoustics)

   null (Ed.)

   Abstract Controlling and manipulating elastic/acoustic waves via artificially structured metamaterials, phononic crystals, and metasurfaces have gained an increasing research interest in the last decades. Unlike others, a metasurface is a single layer in the host medium with an array of subwavelength-scaled patterns introducing an abrupt phase shift in the wave propagation path. In this study, an elastic metasurface composed of an array of slender beam resonators is proposed to control the elastic wavefront of low-frequency flexural waves. The phase gradient based on Snell’s law is achieved by tailoring the thickness of thin beam resonators connecting two elastic host media. Through analytical and numerical models, the phase-modulated metasurfaces are designed and verified to accomplish three dynamic wave functions, namely, deflection, non-paraxial propagation, and focusing. An oblique incident wave is also demonstrated to show the versatility of the proposed design for focusing of wave energy incident from multiple directions. Experimentally measured focusing metasurface has nearly three times wave amplification at the designed focal point which validates the design and theoretical models. Furthermore, the focusing metasurface is exploited for low-frequency energy harvesting and the piezoelectric harvester is improved by almost nine times in terms of the harvested power output as compared to the baseline harvester on the pure plate without metasurface. 

   more » « less
5. On-chip non-Hermitian optical parametric amplifiers with a large bandwidth

   https://doi.org/10.1364/JOSAB.426956  

   Ahmed, Asif; Meng, Xiang; Zhong, Qi; El-Ganainy, Ramy; Osgood, Richard_M; Dadap, Jerry_I (June 2021, Journal of the Optical Society of America B)

   Recently, our groups have introduced the notion of optical parametric amplification based on non-Hermitian phase matching wherein the incorporation of loss can lead to gain in this nonlinear optical process. Previous simulation results using second-order nonlinear optical coupled-mode theory have demonstrated the potential of this technique as an alternative to the stringent phase-matching condition, which is often difficult to achieve in semiconductor platforms. Here we fortify this notion for the case of third-order nonlinearity by considering parametric amplification in silicon nanowires and illustrate the feasibility of these devices by employing rigorous finite-difference time-domain analysis using realistic materials and geometric parameters. Particularly, we demonstrate that by systematic control of the optical loss of the idler in a four-wave mixing process, we can achieve efficient unidirectional energy conversion from the pump to the signal component even when the typical phase-matching condition is violated. Importantly, our simulations show that a signal gain of $\sim <\#comment/>9\mathrm{d}\mathrm{B}$for a waveguide length of a few millimeters is possible over a large bandwidth of several hundreds of nanometers ( $\sim <\#comment/>600\mathrm{n}\mathrm{m}$). This bandwidth is nearly 2 orders of magnitude larger than what can be achieved in the conventional silicon-photonics-based four-wave mixing process. 

   more » « less