Topological microwave isolator with >100-dB isolation

Microwave isolators are key non-reciprocal devices that protect sensitive components by blocking backward signals. Commercial junction isolators typically offer 20 dB isolation, but higher isolation is needed in demanding systems such as superconducting quantum computing. Cascading isolators increases isolation but adds loss, bulk, and complexity. To address this bottleneck, we demonstrate a topological isolator based on a one-way edge waveguide that spatially separates forward and backward modes, enabling complete absorption of the backward signal without affecting the forward transmission. Its isolation limit is set by the evanescent field. A ferrite stripline configuration is analytically shown to achieve 200 dB isolation within a wavelength-scale device, while experiments demonstrate 1 dB insertion loss and >100 dB isolation—eight orders of magnitude higher than conventional isolators. These results highlight the potential of topological photonics to drive innovation in microwave technology and enable next-generation high-performance isolators.