  Here, we present an exploratory study of the potential applications of
electrically biased materials that possess a nonreciprocal and non-Hermitian
electromagnetic response analogous to the electronic response of field-effect
transistors. The most distinctive feature of such materials is their
chiral-gain, meaning that their response can be active or dissipative depending
on the handedness of the wave polarization. Here, we show how the chiral-gain
can be harnessed to develop novel electromagnetic devices with unique
properties such as chiral lasers, polarization-dependent mirrors, and
coherent-perfect-absorber lasers. Furthermore, it is demonstrated that
materials with chiral-gain can bypass a reciprocity constraint that typically
limits the external coupling strength, thus facilitating the excitation of
cavities with extremely large quality factors.
