An electromagnetic wave in vacuum has the electric and magnetic field $\mathop E\limits^ \to $and $\mathop B\limits^ \to $, which are always perpendicular to each other. The direction of polarization is given by $\mathop X\limits^ \to $ and that of wave propagation by $\mathop k\limits^ \to $. Then
$\mathop X\limits^ \to ||\mathop B\limits^ \to $ and $\mathop X\limits^ \to ||\mathop B\limits^ \to \times \mathop E\limits^ \to $
$\mathop X\limits^ \to ||\mathop E\limits^ \to $ and $\mathop k\limits^ \to ||\mathop E\limits^ \to \times \mathop B\limits^ \to $
$\mathop X\limits^ \to ||\mathop B\limits^ \to $ and $\mathop k\limits^ \to ||\mathop E\limits^ \to \times \mathop B\limits^ \to $
$\mathop X\limits^ \to ||\mathop E\limits^ \to $ and $\mathop k\limits^ \to ||\mathop B\limits^ \to \times \mathop E\limits^ \to $
