Polarization encoding using number of stacking sheets as additional key information

Polarization encoding is one of encryption techniques that employ physical keys. Secret information is decoded without any calculations and can be distributed on social contacts. In this paper, we propose two types of compositions of polarization-encrypted sheets. A film-based type is composed of two quarter-wave retarder films that are attached together. The other type is composed of pieces of retarder film that are pasted on a glass substrate. We have developed polarization-encrypted sheets in both types. Decoding with 26-layered sheets has been demonstrated. Furthermore, contrast of decoded results are compared experimentally.