Infrared Polarizer Based on Direct Coupling to Surface Plasmon Polaritons

We propose a new type of reflective polarizer based on polarization-dependent coupling to surface plasmon polaritons (SPPs) from free space. This inexpensive polarizer is relatively narrowband but features an extinction ratio of up to 1000 with efficiency of up to 95% for the desired polarization (numbers from a calculation) and thus can be stacked to achieve extinction ratios of 10⁶ or more. As a proof of concept, we experimentally realized a polarizer based on nanoporous aluminum oxide that operates around a wavelength of 10.6 μm, corresponding to the output of a CO₂ laser, using aluminum anodization, a low-cost electrochemical process.