Time-bandwidth relation for cavities with nonreciprocal coupling
The time-bandwidth relation that states that the longer a resonator stores energy, the narrower the bandwidth of supported frequencies and it is an intrinsic limitation to conventional resonators. However, this relation can be overcome, allowing the storage of broader frequency ranges for long times, for certain classes of resonators, for example, ones with a time-varying coupling or quality factor.
In this paper, we theoretically and numerically study the dependence of the achievable time-bandwidth product of a resonator on the degree of non-reciprocity of the coupling interface. Simply put a completely reciprocal coupling interface has equally coupling of light into the resonator and out of it, while a completely non-reciprocal resonator would allow coupling in only one direction (in or out).
We show that as the degree of non-reciprocity increases (more in coupling than outcoupling) the achievable time-bandwidth product increases as well and is no longer limited by the conventional relation. Furthermore, we show that the power enhancement within the resonator is directly proportional to the time-bandwidth product of the device.
This work was completed together with our collaborators from EPFL, the University of Ottawa, the University of Pavia and the National and Kapodistrian University of Athens and is published in Physical Review A.