Sinusoidal plane-wave solutions of the electromagnetic wave equation

Sinusoidal plane-wave solutions are particular solutions to the wave equation. The general solution of the electromagnetic wave equation in homogeneous, linear, time-independent media can be written as a linear superposition of plane-waves of different frequencies and polarizations.

Source: Wikipedia — Sinusoidal plane-wave solutions of the electromagnetic wave equation (CC BY-SA 4.0)