Patent GB-1158675-A (GB)
Title: Optical Device
IPC: F21V9/40
Filed: 1967-01-24
Abstract: 1,158,675. Glass coated glass. BAUSCH & LOMB Inc. 24 Jan., 1967 [7 Feb., 19661, No. 3621/67. Heading C1M. [Also in Divisions C7, G2 and H4] An electro-chemical device comprises a pair of electron conducting electrodes separated by a solid state electrolytic reactive film which in response to an electrical potential applied across the electrodes initiates a current conduction by an ionic transport phenomenon resulting in reversible reducing and oxidizing reactions in the reactive film thereby changing the optical properties, i.e. refractive index or optical density, of the device. The reactive film may comprise a glass film containing lead fluoride ions or crystalline film containing lead and fluoride ions. The device may comprise, Fig. 1 conducting layers 14 and 16 and solid electrolytic layer 18 disposed between glass substrates 10 and 12. Layers 14 and 16 may comprise a semi-conducting coating of tin oxide, indium oxide, nickel oxide or cadmium fluoride, or a thin coating of gold, silver or copper. Reactive layer 18 may comprise a glass film containing lead fluoride having lead cations available for reducing and oxidizing reactions, and mobile fluoride anions, such as PhO.¢PbF 2 .SiO 2  or PbO.¢PbF 2 .¢B 2 O 3  or PbO.¢PbF 2 ¢SiO 2 B 2 O 3  or compositions including bismuth fluoride or lanthanum fluoride doped with strontium and cerium. In operation a potential 20 is applied across layers 14 and 16 and an ionic current flows through reactive layer 18 changing the optical properties of the device. The rate at which the optical properties of the device change is a function of the magnitude of the potential and the temperature of the device. The change in optical properties may be considered to be a result of the formation of reduced lead (Pb) forming in reactive layer 18 adjacent negative electrode 16. Ionic conduction in the reactive layer 18 can result when the electrons stored on electrode 16 repel fluoride ions into openings in the amorphous structure of layer 18 resulting in ionic conduction away from electrode 16. Electrons from the tin oxide layer 16 combine with the divalent lead ions to produce reduced lead increasing the optical density of the device. As the fluoride ions move towards electrode 14 divalent lead is changed to tetra-valent lead. The optical properties of the device remain unchanged when the potential is removed (i.e. functions as an electro-chemical storage cell) but it may be reversed to its original condition by shorting electrodes 14 and 16 or by applying an opposite potential. In a second embodiment, Fig. 2, not shown, the device comprises a glass substrate on which is formed a conducting film followed by a reactive layer and second conducting film. The device may comprise a plurality of layers consecutively stacked, Fig. 3, not shown. Two devices may be included as the lenses in a pair of electrically variable density sun glasses, Figs. 4 and 5, not shown. The optical device of Fig. 1 may be produced by depositing a coating of tin oxide by a " sputtering " process on the glass substrates. A glass bead of a composition containing lead fluoride is placed on one of the tin oxide surfaces and heated so that the bead fuses and slowly spreads over the substrate. The other preheated tin oxide surface of the second substrate is placed on the lead fluoride composition and the substrates are firmly pressed together. The device is then cooled to produce an amorphous reactive layer.