| 摘要 |
<p>A diffractive optical filter comprises a bulk material (1) having a first refractive index, a volume diffraction grating structure (2,3) having a second, different, refractive index embedded in the bulk material (1), and a mirror(4) formed within or on the surface of the bulk material (1) behind the grating structure (2,3). By placing the mirror (4) immediately behind the grating structure (2,3) the diffractive structure is effectively doubled and consequently the number of effective optically active layer is doubled. Such diffractive optical filters may be used as diffractive identification devices bonded to articles whose authenticity needs to be established.</p> |
