Metal-dielectric metameric filters for optically variable devices

A pair of metal-dielectric metameric filters that could create a hidden image was presented for the first time. The structure of the filters is simple and only six layers for filter A and five layers for filter B. The prototype filters were designed by using the film color target optimization method and the designed results show that, at normal observation angle, the reflected colors of the pair of filters are both green and the color difference index between them is only 0.9017. At observation angle of 60°, the filter A is violet and the filter B is blue. The filters were fabricated by remote plasma sputtering process and the experimental results were in accordance with the designs.