Infrared metasurface-enabled compact polarization nanodevices

Infrared metasurface, especially that having a working range covering wavelengths from 0.75 to 25 μm, has been exploited as a revolutionary tool to manipulate the properties of electromagnetic waves owing to its potential applications in military and civilian fields. It owns the capacity to steer electromagnetic waves within subwavelength scale, with full degrees of freedom such as phase, amplitude and polarization, allowing the development of a number of planar meta-devices including the metalens, hologram, wave-plate and polarimeter. In particular, polarization, which determines the interaction of electromagnetic waves with matter, is important in almost every area of science. However, conventional materials for infrared polarization control inevitably introduce extra optical components and bulky configurations, hindering future miniaturization and integration. Moreover, compared with their short wavelength counterparts, polarization nanodevices in the infrared band and especially those in the long-wavelength infrared region have been far less explored due to the loss of material and immature fabrication techniques. Here, we review recent progress in the development of infrared metasurfaces in terms of generating, manipulating and detecting the polarization on standard and higher-order Poincaré spheres. The principles, typical strategies and emerging applications of these processes are introduced. We also discuss the challenges and outlook of future developments in this emerging field.