Half-wave plate
= Half-wave plate
{title2=$\delta=\pi\pmod{2\pi}$}
A <half-wave plate> reverses the relative sign of the two components. For initial <linear polarization> at <angle> $\alpha$ to the fast axis, the outgoing line is at $-\alpha$ modulo $\pi$. The $45^\circ$ input therefore rotates by $90^\circ$.