An integrated multi-THz tunable linear isolator based on electro-optic non-reciprocal strong coupling.

Optical isolators are essential for laser protection and robust signal routing, and several integrated non-magnetic isolators based on acousto-optic (AO) and electro-optic (EO) spatio-temporal modulation have been proposed. The most significant remaining concerns, however, are on mitigating undesirable sidebands, achieving wide bandwidth or wide tunability, and having a design that is practical to deploy. Most of these challenges can be addressed through non-reciprocal strong coupling between waveguide or resonator modes, with the intent to produce asymmetric optical dispersion, but this has never been accomplished with electro-optics. Here we demonstrate a compact EO optical isolator, using thin film lithium niobate, that is the first EO device to reach the non-reciprocal strong coupling regime. In this new regime, the isolator produces a very high isolation figure of merit and, due to its architecture, achieves linear operation with negligible sideband generation. We additionally demonstrate THz-scale (8 nm) tunability of the isolation band that is not fundamentally limited, and can be extended to multi-THz operation.