Generation of Ultra-Broadband Frequency Comb in Strongly Bistable Nonlinear Magnonic Resonator

TL;DR

This work introduces a fundamentally new route to ultrabroadband magnonic frequency combs using a highly nonlinear, chip-scale YIG magnonic microresonator coupled to a slow-wave SSPP waveguide and driven by a two-tone off-resonant pump. By entering a large-amplitude bistable regime and leveraging Suhl-type parametric excitation of spin waves, the system generates a broadband comb with over 350 lines spanning about 450 MHz, with tunable spacing set by the inter-tone difference $\delta$. The device is 4–6 orders of magnitude smaller than conventional YIG spheres and offers continuous spacing control and strong tunability through magnetic bias and pump parameters, enabling scalable on-chip microwave signal processing, neuromorphic computing, and precision sensing. This platform establishes a new paradigm for magnonic frequency combs, combining compactness, tunability, and high spectral richness without relying on multiple high-Q resonances.

Abstract

Magnonic frequency combs (MFCs) offer a promising route to compact, energy-efficient platforms for on-chip coherent microwave signal generation and processing. Conventional on-chip comb generation typically relies on nonlinear resonators supporting a series of equidistant, low-loss resonances driven by a strong monochromatic signal, resulting in fixed comb spacing defined by the resonator's free spectral range (FSR). Here we introduce and experimentally demonstrate a fundamentally different mechanism for ultrabroadband MFC generation using a highly nonlinear miniaturized magnonic resonator. The small resonator volume, combined with a slow-wave transducer, yields high intra-resonator power density, driving the system deep into the bistable regime where parametric excitation of propagating spin waves facilitates comb formation. Our approach yields more than 350 comb lines spanning a 450 MHz bandwidth, with spacing continuously tunable via a two-tone external drive, representing an order-of-magnitude enhancement over prior reports while operating at relatively low power. The platform is ultra-compact (4-6 orders of magnitude smaller in size than conventional YIG sphere resonators), fully scalable, and highly tunable, enabling precise control of comb properties through magnetic bias and pump manipulation. These results establish a new paradigm for frequency comb technology, unlocking transformative opportunities in microwave signal processing, neuromorphic computing, and precision sensing.

Figures (4)

• Figure 1: Concept and operating principles of the nonlinear magnonic microresonator.a, Schematic of the device architecture: a normally magnetized YIG microresonator flip-bonded onto a slow-wave microwave waveguide supporting spoof surface plasmon polaritons. The device is driven by a two-tone microwave pump consisting of two frequencies $f_s$ and $f_s+\delta$, which exhibits an time-varying envelope at the beat frequency $\delta$. The device output is analyzed using a spectrum analyzer. b,c, Magnon resonance spectra under different input powers. Red dots mark the achievable powers for small detuning ($f_s \approx f_0$) and large detuning ($f_s \gg f_0$) for $P_4$. d, Bistability and hysteresis in the magnon power at large detuning observed when sweeping the input power. Transitions occur from the lower (upper) branch to the upper (lower) branch at $P_\mathrm{max}$ ($P_\mathrm{min}$) during upward (downward) sweeps. In the presence of parametric pumping of spin waves, $P_\mathrm{max}$ is reduced to $P_\mathrm{par}$. e, Magnon dispersion (purple curves) and parametric pumping at $f_s > f_0$. Off-resonant driving of uniform magnon mode at $f_s$ excites incoherent large-wavevector spin-wave magnon pairs (purple shaded regions) at the same frequency. f, Temporal evolution of uniform magnon mode amplitude (blue) and parametric spin-wave magnons (red). $N_\mathrm{par}$ denotes the threshold for parametric excitation; $N_\mathrm{lim}$ marks the level where the uniform magnon mode shifts to $f_s$.
• Figure 2: Dynamic process of magnon frequency comb generation.a, Time trace of the microwave drive signal. $P_\mathrm{min}$, $P_\mathrm{max}$, and $P_\mathrm{par}$ correspond to the turning-point powers shown in Fig. \ref{['fig1']}d. b, Time trace of the uniform magnon mode power. Amp.: amplitude. c, Instantaneous states of the system during one modulation cycle at large detuning. Blue dots and lines: lower branch; red dots and lines: upper branch; arrows indicate sweep direction. d, Calculated spectrum of the magnon temporal response under periodic modulation. e, Calculated spectrum with the nonlinear dissipation via coupling to higher-order magnon modes accounted for.
• Figure 3: Experimental spectrum of the MFC.a,b, Device transmission spectra measured at low power ($-30$ dBm) and high power ($-7$ dBm), respectively. The high-power spectrum shows pronounced hysteresis, absent in the low-power regime. Periodic oscillations at high power originate from bulk acoustic phonon modes, a common feature in thin-film YIG magnonic devices 2021_PRAppl_Xu2025_PRL_Xu. c, MFC spectrum measured with a pump power of $P_s=-30$ dBm at $f_1 = f_0 = 10.05$ GHz. d, MFC spectrum measured with a pump power $P_s=-3$ dBm at $f_1 = 10.05$ GHz and $f_0 = 9.86$ GHz. e, Output spectra recorded at varying pump powers. f, Device output power versus pump power, showing a threshold at $-7$ dBm. g, Total MFC power as a function of pump power $P_s$ and frequency $f_1$. Yellow dots indicate extracted threshold points; blue curve shows quadratic fitting.
• Figure 4: Tuning of the MFC bandwidth.a,b, MFC characteristics--span, line count, and total on-chip comb power--as functions of the bias magnetic field and pump frequency difference $\delta$, respectively. c, Comparison of comb line count achieved in this work (red star) with state-of-the-art results, including experimental demonstrations (red circles) and theoretical proposals (blue squares), extracted from Refs.2024_NP_Wang_EPMFC2023_PRL_Xu_MagnomechanicalResonator2022_APL_Hula_SpinWaveFC2025_APLQuantum_Kani_SqueezedComb2023_FundResearch_Xiong2023_PRA_Liu_TwoToneDrive2025_PRA_Wang_MechanicalMFC2022_PRL_Wang_Twisted2024_NanoLett_Li_AsymmetricMFC2021_PRL_Wang_nonlinearMagnonSkyrmion2021_AdvEngMatt_Sun_StrainModulation2024_PRB_Liu_SyntheticFerrimagnets. Exp.: Experimental results. d, Measured MFC spectrum with a comb line spacing of 2 MHz and a total of 200 lines, obtained with uniform magnon mode frequency $f_0 = 9.35$ GHz, pump frequency $f_1 = 10.0232$ GHz and $f_2=10.0252$ GHz, and pump power $P_s = -3$ dBm. Right inset: magnified view of the comb spectrum. Left inset: magnified view of a single comb line with Gaussian fitting, revealing a linewidth of 26 Hz. e, MFC spectrum exhibiting period doubling, obtained with uniform magnon mode frequency $f_0 = 9.35$ GHz, pump frequency $f_1 = 10.0232$ GHz and $f_2=10.0265$ GHz, and pump power $P_s = -3$ dBm. The comb line spacing is $\delta/2 = 1.65$ MHz, with a total line count of 225. Inset: magnified view of the comb spectrum.