The time-bandwidth limit in optical nanostructures and its relation to nonreciprocity

The time-bandwidth limit refers to the trade-off between the time-delay that can be applied to a signal and the signal bandwidth. Recently, there have been several studies showing that this bound can be broken in nonreciprocal nano-structures, including nonreciprocal cavities and terminated unidirectional waveguides. Here, we clarify the nature of these claims and the physical mechanisms involved in such structures.