HOLOGRAPHIC SECURITY DEVICES AND SYSTEMS

摘要

An identifiable security device comprises a carrier (1), such as a key card, credit card or document, supporting a thick film hologram (5) including at least one discrete reflective region (6) which, when illuminated reflects strongly in a specific, predetermined direction. A reader (2) incorporates a light source (7) and one or more photodiode detectors (8, 11) arranged to detect the directional reflections, to discriminate against non-holographic reflections and to perform a security function on detection of appropriate reflections. The function may comprise authentication of a carrier bearing a simple hologram, but more complex holograms having a plurality of reflective regions arranged in a coded array are used, for example, on bank cheque cards to operate automatic bank dispensers and on pass cards for gaining entry to secure areas. A method is also described for making holograms for such security devices in which a panel, such as an LCD panel, having an arry of discrete areas which can be switched between different states of transmission and reflection is set up as the subject of a holographic photography system, the panel being located very close to the film. Laser light is incident on the film both through the transparent areas of the panel and via a mirror inclined to the film and interferes within the emulsion to create the discrete reflective regions, in positions corresponding to the transparent areas. The areas can be switched between photographic exposures to produce different coded arrays and the inclination of the mirror can be changed to alter the direction and angle of reflections from the reflective regions of the developed holograms.