The difference is in the amount of aluminium wire deposited on the surface of the substrate. The higher extinction ratio (HER) polarizers have more material, which is equivalent to increasing the thickness of the wires.
In the case of free standing wire grids, we define the distance between the centrelines of the wires as ‘a‘ and the diameter or width of the wires as ‘d‘. As the ratio d/a increases the transmission of light through the polarizer decreases and begins to approximate a flat mirror. The transmission of light polarized parallel to the wires is affected by a greater amount, so the result is a higher overall extinction ratio. The light polarized perpendicular to the wires is affected only slightly, so the trade off between extinction ratio and overall transmittance is a good one.
In the case of holographic wire grid polarizers, we cannot control the thickness of the ‘wires’ with the same precision, but we can still achieve a similar effect by increasing the amount of material deposited when the grid is laid on the substrate.
