On Time-Modulation-Enabled Nonreciprocity

This letter is to provide a review of recent works carried out on time-modulation-based nonreciprocal devices. It first provides an introduction of various modulation mechanisms and device architectures used in those studies and discusses the commonality and difference among the concepts of those approaches. Examples of on-chip implementations are presented. Potentials and challenges of time-modulation approaches in replacing ferrite-based nonreciprocal devices have also been discussed.