Engineering Epsilon‐Near‐Zero Media with Waveguides

Epsilon‐Near‐Zero (ENZ) media have attracted widespread interest due to their unique electromagnetic properties, which have brought distinctive characteristics and phenomena, such as spatiotemporal decoupling, supercoupling and tunneling, constant phase transmission, near‐field enhancement, and so on. However, these ENZ characteristics are existed in natural plasmonic materials at their intrinsic plasma frequencies and accompanied by significant losses, thus limiting their applications in engineering. Different from the effect ENZ media with artificially periodic structures, the waveguide ENZ media offers a promising platform with non‐periodic architectures. Unlike the natural plasmonic materials and the periodic‐structured ENZ media, the waveguide ENZ media utilizes waveguide dispersion to achieve effective ENZ characteristics and phenomena with lower loss and smaller dimensions. This review begins with an exploration of the fundamental properties of the waveguide ENZ media and then introduces the design principles of different ENZ‐based electromagnetic devices. Finally, the review concludes with the challenges and potential development directions encountered by the ENZ media in the realm of electromagnetic applications.