An embarrassment of riches: what to do with a material on million times more nonlinear than silica

Research reported in 2016 (Science 352, 795) showed that materials such as indium tin oxide (ITO) display an unprecedentedly large nonlinear refractive index when excited at a frequency where the dielectric permittivity is nearly vanishing. The large nonlinear response of these epsilon-near-zero (ENZ) materials, some million times larger than that of silica glass, suggest that these materials would prove extremely useful in the development of new classes of photonic devices. In this contribution, we review the history of the understanding of nature of the nonlinear response of ENZ materials and the development of ENZ-based photonic devices. Specific investigations over the past eight years have led to increased under-standing of topics including (1) the origin of the enhancement of the nonlinear optical response, (2) the possibility of using nanofabrication methods to create ENZ behavior at any specified wavelength, and (3) the exploration of what interactions and devices are enabled through use of ENZ materials. In this contribution, we review the recent history of the development of the field of ENZ science and of the development of ENZ applications.