Light in a birefringent crystal

The two polarization eigenstates acquire different phases. Their sum changes shape.

Polarization 1Polarization 2Sum E

Input Output axis 1 axis 2

One frequency · different wavelengths

Input polarization β0° 0°90°180° Axes rotation α45° 0°90°180° Thickness L1.00 λ₀ 02 λ₀4 λ₀

Two equal components shifted in phase by π/2 give circular polarization.

Δφ = π/2