摘要 |
AN OPTICALLY VARIABLE SECURITY DEVICE COMPRISES A PHOTONIC CRYSTAL WHICH, UPON RECEIPT OF INCIDENT LIGHT, GENERATES A FIRST OPTICAL EFFECT, AND WHICH, WHEN THE DEVICE IS SUBJECTED TO AN EXTERNAL STIMULUS, GENERATES A SECOND OPTICAL EFFECT THAT IS DIFFERENT FROM THE FIRST OPTICAL EFFECT. AT LEAST ONE OF THE FIRST AND SECOND OPTICAL EFFECTS IS AN OPTICALLY VARIABLE EFFECT OBSERVABLE OVER A SET OF DIRECTIONS. THE OPTICALLY VARIABLE EFFECT IS CAUSED BY THE LIGHT BEING SELECTIVELY REFLECTED OR TRANSMITTED BY THE CRYSTAL. |