Dynamics of a Spin-Wave Active Ring Resonator Driven by Harmonic-Null Square-Wave and Unipolar 8-bit Walsh Code Modulations

TL;DR

This paper introduces practical methods to characterize and optimize the nonlinear dynamics of spin-wave active ring resonators for reservoir computing, using harmonic null elimination and Walsh code decomposition.

Contribution

It presents systematic experimental techniques for analyzing nonlinear behavior and memory in SWARRs, enhancing their design for physical reservoir computing applications.

Findings

Identified five nonlinear regions within 2.15-2.2 GHz drive frequency range.

Estimated SWARR's STM duration to be approximately 300 ns.

Demonstrated Walsh code decomposition of the nonlinear response.

Abstract

Spin-wave active ring resonators (SWARRs) based on yttrium iron garnet (YIG) films exhibit rich nonlinear dynamics that make them promising platforms for physical reservoir computing. We present systematic and experimentally simple methods to characterize a SWARR's nonlinear behavior and memory. We first use a third harmonic elimination method to probe the nonlinear response. A drive frequency $f_\mathrm{d}$ is modulated by a square-wave pattern engineered to have a spectral null at $3/T$, which is then applied as input to the SWARR. The power spectra at the output of the YIG delay line allow us to identify five distinct regions within a drive frequency range of $2.15 < f_\text{d} < 2.2\ \text{GHz}$ where nonlinearity was observed as frequency peaks at $f_\mathrm{d} \pm \frac{3}{T}$. The STM duration of the SWARR was estimated to be approximately 300 ns using a modulation pattern derived from the sequency-ordered 8-bit unipolar Walsh family. The nonlinear dynamics of the SWARR were further quantified by decomposing its temporal response to analog Walsh pulses in terms of the input Walsh codewords. The proposed methods of harmonic elimination and Walsh-function decomposition together provide a practical and general framework for the design and optimization of tunable spin-wave reservoir computers.