Abstract: A security device (1) comprising an optically transparent layer (3) including a repeating first array of separate optical focussing elements (3) (e.g. having translational symmetry) wherein a pitch distance between repeated elements in the first array is a first pitch value (A). The device also includes a repeating second array of separate image elements (6) (e.g. having translational symmetry) collectively defining an image viewable through the first part. The device is structured such that a pitch distance between repeated or successive elements in the second array is a second pitch value (B) wherein the ratio (A/B) of the first pitch value and the second pitch value has a value, A/B=n±?, that differs from a positive integer value, n, according to an absolute difference, ?, not exceeding 0.01 and not less than 0.001.

Abstract: A diffusive reflector for a lighting apparatus comprising a backing part upon a surface of which is disposed an interface part(s) wherein the interface part(s) is at least partially diffusively reflective optically and/or the backing part is diffusively reflective optically. The interface part(s) is formed with a plurality of separate protrusions each adapted for making a separate respective contact interface with a surface of a light guide panel of the lighting apparatus to optically couple the backing part to the light guide panel via the interface part(s). The interface part(s) comprises an optically transmissive interface material arranged to form said contact interface such that the interfacial energy thereof is reduced so that air is driven from the contact interface. Consequently, the critical angle for total internal reflection of light guided by the light guide panel is increased at said contact interface.

Abstract: A tamper-evident security device including a first part comprising an optically transparent layer including an array of separate optical focussing elements. A second part comprises an array of separate image elements collectively defining an image viewable through the first part. Each of the optical focussing elements is positioned to reveal therethrough a view of one or more of said image element(s). An optically transparent adhesive layer between the first part and the second part which retains the optical focussing elements so positioned with respect to the image elements thereby in cooperation to reveal the image. The first part is mechanically separable from the second part by release of the adhesive layer to cease the cooperation.

Abstract: A diffusive reflector for a lighting apparatus comprising a backing part upon a surface of which is disposed an interface part(s) wherein the interface part(s) is at least partially diffusively reflective optically and/or the backing part is diffusively reflective optically. The interface part(s) is formed with a plurality of separate protrusions each adapted for making a separate respective contact interface with a surface of a light guide panel of the lighting apparatus to optically couple the backing part to the light guide panel via the interface part(s). The interface part(s) comprises an optically transmissive interface material arranged to form said contact interface such that the interfacial energy thereof is reduced so that air is driven from the contact interface. Consequently, the critical angle for total internal reflection of light guided by the light guide panel is increased at said contact interface.

Abstract: A security element includes a first layer, the first layer having opposing first and second surfaces, and being formed of a substantially transparent first material having a first refractive index, the first surface of the first layer having formed therein, in a first region, an array of focussing elements. An optically variable effect generating structure is located over the first layer in a second region at least partially overlapping the array of focussing elements in the first region. An array of image elements is arranged over the array of focussing elements such that a first image, formed from at least some of the image elements, is displayed to a viewer viewing the image elements via the array of focussing elements of the first layer. The optically variable effect generating structure is also configured to display, in the second region, a second image to the viewer.

Abstract: A security substrate has: a polymer substrate having first and second surfaces; array of focussing elements; an optical adjustment layer and masking layer. The array is formed of a surface relief. The optical adjustment layer is on the transparent base layer across a second region including the first. The optical adjustment layer has a first surface contacting the surface relief and an opposing second surface having a profile not operative to focus visible light. The optical adjustment layer has a first transparent material extending across a first sub-region of the array, the first transparent material having a refractive index different from that of the transparent base layer. The security substrate has a masking layer over the optical adjustment layer across a third region of the polymer substrate, the third region defining a gap in the masking layer(s), such that functional focusing elements of the array are revealed through the gap.

Abstract: The present invention relates to a method of producing a silica glass coating comprising the steps of: a) producing a sol comprising colloidal silica and an organic binder; b) forming a coating of said sol on a substrate; c) drying the sol coating so as to produce a gel coating on said substrate; and d) densifying the gel coating so as to produce a substantially crack-free glass coating. In accordance with the present invention there is used a cellulose based binder which enables the use of substantially reduced levels. of binder.

Abstract: The present invention provides an optical polyacrylate polymer wherein at least 20% w/w of the total monomer repeating units are of the general formula (I): —(—CH2—C(R1) (COOR2)—)— wherein R1 is H or a C1 to C12 aliphatic and/or aromatic group, and R2 is an aliphatic and/or aromatic moiety containing at least one S atom. In further aspects, the present invention provides methods of making the above polymers, as well as planar lightwave circuits formed from such polymers.

Abstract: Process for producing substrates with a layer comprising an inorganic gel, glass, glass-ceramic or ceramic material, in which a coating composition comprising nanosize particles and water soluble organic flexibilizers is applied to the substrate and heat treated. Crack-free and transparent thick films can be obtained by means of the process. The coated substrates are particularly suitable for optical, optoelectronic, electronic, micromechanical or dirt-repellent components.

Abstract: Thin SiO.sub.2 films can be produced by hydrolysis and condensation ofa) 40 to 100% by weight of one or more silanes of general formula (I)R.sub.x --Si--A.sub.4-x (I)in which the groups A are identical or different and stand for hydroxyl groups or hydrolytically separable groups, the groups R are identical or different and stand for hydrolytically non-separable groups, x has the value 0, 1, 2 or 3, x being not less than 1 for 70% by moles of said silanes;b) optionally in the presence of 0 to 50% by weight of colloidal SiO.sub.2 and/orc) 0 to 10% by weight of organic binder.The viscous sol thus obtained is worked into a gel film which is heat-treated.