![]() However, this technique and its variants 17, 18, 19, 20, 21, 22 lead to structures much larger than the wavelength, owing to the weak electro-optic or acousto-optic effects on which they rely, and require complex modulation schemes. This concept is especially attractive for integrated optical networks, as it may be fully realized in silicon photonics 16. Another interesting approach to magnetic-free non-reciprocity has been introduced 15, using asymmetric mode conversion in spatiotemporally modulated waveguides. Also these solutions impose severe restrictions on the input power levels, generally degrading the signal quality because of noise or signal distortion. More recently, non-reciprocity has been achieved in transistor-loaded metamaterials 9, 10 and nonlinear devices 11, 12, 13, 14. However, such approaches traded the absence of magnetic bias with other significant drawbacks, such as the strong nonlinearities and poor noise-performance of transistors, or the large size and complexity of the required electro-optical networks. ![]() Furthermore, the device topology is tunable in real time, and can be directly embedded in a conventional integrated circuit.Įarly attempts to realize magnetic-free non-reciprocity were based on the non-reciprocal properties of transistors at microwave frequencies 4, and on networks of electro-optical modulators at optical frequencies 5, 6, 7, 8. We observe giant non-reciprocity, with up to six orders of magnitude difference in transmission for opposite directions. Their resonant frequencies are modulated by external signals with the same amplitude and a relative phase difference of 120°, imparting an effective electronic angular momentum to the system. The scheme is based on the parametric modulation of three identical, strongly and symmetrically coupled resonators. Inspired by this concept, here we demonstrate a subwavelength, linear radio-frequency non-reciprocal circulator free from magnetic materials and bias. Angular-momentum biasing was recently proposed as a means of realizing isolation for sound waves travelling in a rotating medium 1, and envisaged as a path towards compact, linear integrated non-reciprocal electromagnetic components 2, 3. A practical and inexpensive route to magnetic-free non-reciprocity could revolutionize radio-frequency and nanophotonic communication networks. Non-reciprocal components, which are essential to many modern communication systems, are almost exclusively based on magneto-optical materials, severely limiting their applicability.
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