SWITCHABLE HOLOGRAMS

摘要

Holographic fringes recorded in a substrate (10) can be activated and de-activated by the application of an electrical signal to electrodes (13, 14) on opposed surfaces (11, 12) of the substrate. At least one of the electrodes (13, 14) is composed of separate portions (17, 18) having interdigitated fingers (20). When an electric signal is applied across the electrodes (13, 14) and electric field is produced generally in a first direction perpendicular to the surfaces (11, 12). In contrast, when an electric signal is applied across the electrode portions (17, 18) an electric field is produced generally in a second direction parallel to the surfaces (11, 12) and orthogonal to the said first direction. In this latter condition, the respective state of the substrate (i.e. activated or de-activated, as the case may be) is reinforced by the electric field.