Abstract
Microwave isolators, developed after World War II, are essential non-reciprocal devices widely used to minimize signal reflections and interference across various applications, including mobile base stations, satellite communications, radar systems, magnetic resonance imaging and industrial microwave heating. A typical commercial microwave isolator provides 20 dB of isolation, reducing the backward power by two orders of magnitude. Although higher isolation is always desired for systems that require greater power or lower noise, such as superconducting quantum computing, further reduction in the backward signal will inevitably lead to an unacceptable degradation in the forward transmission in traditional designs. Here we introduce the principle of a topological isolator, based on a unique one-way edge waveguide that spatially separates forward and backward waves, allowing for the complete absorption of the backward-propagating mode without compromising any forward signal. This ideal isolation mechanism produces an unprecedented isolation level, analytically derived to be 200 dB within a single-wavelength-size device. It is limited only by the evanescent fields within the topological bandgap in the ferrite material that spans two octaves around 10 GHz. We experimentally demonstrate this topological isolator in a stripline configuration with a minimal insertion loss of 1 dB and a backward signal deeply attenuated to the instrument noise floor. This results in an ultrahigh isolation exceeding 100 dB—an eight-orders-of-magnitude improvement over conventional counterparts. Our work not only paves the way for higher-performance isolators in the aforementioned technologies but also sets the stage for innovation in a variety of related microwave components.
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Data availability
The data presented in the main text are available via Figshare at https://doi.org/10.6084/m9.figshare.29554457 (ref. 44). All other data that support the findings of this work are available from the corresponding author on reasonable request.
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Acknowledgements
We thank Q. Yan, X. Zhao, R. Liu, W. Sun, T. Zheng and Z. Li for discussions. This work was supported by the Natural Science Foundation of China (12025409), by the Chinese Academy of Sciences through the Project for Young Scientists in Basic Research (YSBR-021) and through the IOP-HKUST-Joint Laboratory for Wave Functional Materials Research, and by the Beijing Natural Science Foundation (Z200008).
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G.W. performed the design, simulations, experiments and wrote the paper with L.L., who initiated and supervised the project.
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Extended data
Extended Data Fig. 1 Simulation results of topological isolators with different sizes in y-direction.
The left panel presents the scattering parameters of a device with a ferrite length of 50.8 mm, identical to Fig. 2d, along with the corresponding energy distributions at 3.5 GHz. The right panel presents the scattering parameters of a device with a ferrite length of 25 mm, along with the energy distributions at 3.5 GHz and 10 GHz. The absorber used in these simulations is the same as that in Fig. 2d,e, as listed in Supplementary Table S1.
Extended Data Fig. 2 Comparison between 1 topological isolator and 5 junction isolators (UIYCI1318A10T13SF) connected in series.
Note that, even in this case, our topological isolator could have higher transmission, higher isolation, and lower group delay. The group delay time of the forward signal in the device is \(t=\frac{d\varphi }{d\omega }\), where φ represents the phase of S21 and ω is the angular frequency. Consequently, a single topological isolator exhibits about 1/3 group delay compared to 5 junction isolators.
Extended Data Fig. 3 Ultrawideband response (up to 43.5 GHz) of the topological microwave isolator.
a. Experimental scattering parameters with the phase of S21. b. Propagation constants of stripline one-way edge mode extracted from experimental data using (Phase of S21)/(Propagation distance of S21), which fit well with the analytical results.
Extended Data Fig. 4 S21 dip due to surface effect of ferrite.
a. Photonic band structure of bulk ferrite. b. Photonic band structure of surface ferrite. c. Comparison between simulated and experimental scattering parameters after surface ferrite modification. The saturation magnetization of the surface layer is determined by the dip frequency, which equals the Larmor frequency (\({\omega }_{0}^{{\prime} }\)) of the surface ferrite, being higher than the bulk Larmor frequency (ω0). The Larmor resonance linewidth (ΔH’) of the surface layer is determined by the spectral width of the transmission dip. The thickness of the surface layer is determined by the depth of the S21 dip. The details of the modeling are in Supplementary Section VI.
Extended Data Fig. 5
SEM images of the sidewall cross-section of the 400 μm-thick nickel spinel ferrite used in the topological isolator, exhibiting micron-scale grain sizes.
Extended Data Fig. 6 Permeability parameters of nickel spinel ferrite, when H = 5,100 Oe, Ms = 4,850 Oe, and ΔH = 80 Oe.
a. Band structure of nickel spinel ferrite. b. Real part of permeability. c. Imaginary part of permeability.
Supplementary information
Supplementary Information
Supplementary Sections I–VI, Figs. 1–7, Table 1 and discussion.
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Wang, G., Lu, L. Topological microwave isolator with >100-dB isolation. Nat. Photon. 19, 1064–1069 (2025). https://doi.org/10.1038/s41566-025-01750-w
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DOI: https://doi.org/10.1038/s41566-025-01750-w
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