Possibility of complete broadband traveling‑wave isolation without forward penalty

Determine whether complete and broadband traveling‑wave optical isolation can be achieved in principle while leaving the forward‑propagating light entirely unaffected (i.e., without attenuation or induced modulation), in integrated photonic waveguides that rely on spatiotemporal traveling‑wave modulation rather than magnetic materials or resonant elements.

Background

Integrated traveling‑wave optical isolators break reciprocity via spatiotemporal modulation, but prior implementations typically suffer from narrow bandwidth, residual modulation sidebands, or attenuation of forward‑propagating light. Despite multiple approaches (phase modulation in single waveguides, mode‑coupling schemes, and multi‑channel configurations), the field had not established whether it is fundamentally feasible to realize an isolator that simultaneously provides broadband isolation and leaves the forward transmission unaffected.

The paper frames this as a previously unresolved question in the literature and motivates the proposed dynamic rotating destructive interference (DRDI) scheme as a potential resolution, emphasizing the historical uncertainty around achieving complete and broadband isolation without penalties to forward transmission.