Based on various combinations of chalcogenides such as sulfur, tellurium and selenium, chalcogenide glasses are attractive optical materials due to their wide infrared transmission windows and potential nonlinear properties.

Second harmonic wave (SHG) is a typical nonlinear optical phenomenon. The fundamental frequency light of a certain intensity passes through the nonlinear optical crystal, and the second harmonic signal of double frequency is generated.

An MIT research effort has developed an active zoom metalens that requires no deformation or physical motion for applications such as optical devices, drones, and cameras.