Sketch of the simple design. Unpolarized (green) light enters on the left. This is split into vertically (red) and horizontal (blue) polarized light by the first Wollaston prism (W1). Inside the birefringent element, the polarization of the light depends on wavelength and position. After the birefringent element, the light is split by the second Wollaston prism (W2), with twice the offset angle of the first. The transmissions of the four beams as a function of wavelength are shown on the right. The top (A) and bottom (D) beams are identically modulated. Similarly, the middle two beams (B and C) are identically modulated. For illustrative purposes, the relative distances are not to scale, the angles are vastly exaggerated and are not two-to-one, and only the center ray of each col-limated beam is shown. In reality, the collimated beam would nearly fill the element, the spacing of the rays would be on the order of the fiber diameter, and α₂ ≈ 2α₁ or α₂ ≈ α₁/2. For clarity, the Wollaston prisms are spaced away from the element. In reality, they would likely be in contact. Also, they are shown with zero thickness.