Ultrafast Nonreciprocal Transmission Modulation in Metasurfaces with Epsilon-Near-Zero Materials

Nonreciprocity refers to the difference in received to transmitted ratio when the source and detector are inter-changed [1]. Optical isolator - component which allows transmission in one direction - is a canonical example of a nonreciprocal device. Nonreciprocity can be achieved through three known pathways; (i) materials with asymmetric permittivity or permeability tensors, such as ferrites; (ii) nonlinear light-matter interactions [2]–[4]; and (iii) time-varying systems[5]. While traditionally nonreciprocal components are quite large in size, nanofabrication of metasurfaces has enabled their miniaturisation to the nanoscale. However, ultrafast nonreciprocal responses at the nanoscale remain still a challenge. Here we design and study metasurface with an epsilon near zero material indium tin oxide (ITO) that enables ultrafast switching of refractive index via Kerr nonlinearity, in order to achieve optical isolation.