  In recent years there has been significant fundamental research into phonon
polaritons, owing to their ability to compress light to extremely small
dimensions, low-losses, and ability to support anisotropic propagation. In this
perspective, after briefly reviewing the present state of mid-infrared
optoelectronics, we will assess the potential of phonon-polariton based
nanophotonics for infrared (3-100$\mathrm{\mu}$m) light sources, detectors and
modulators. These will operate in the Reststrahlen region where conventional
semiconductor light sources become ineffective. Drawing on the results from the
past few years, we will sketch some promising paths to create such devices and
we will evaluate their practical advantages and disadvantages when compared to
other approaches to infrared optoelectronics.
