| 摘要 |
A security device comprises a substrate having a region provided with an antireflective grating, and is configured to generate a security image when visible light is incident on the grating to provide authentication for an observer, wherein the grating comprises a combined broadband antireflective and narrowband reflective structure, the structure is antireflective for visible light between 400 and 700 nm which is incident within ±45° of a normal to the grating and the structure produces a narrowband reflection of light having a wavelength of less than 550 nm at glancing angles to the grating when visible light is incident at an angle greater than ±45° from the grating normal, wherein the security device is configured to generate the security image from the narrowband reflection. |
