Patent GB-369698-A (GB)
Title: Improvements in the electrical production of optical effects and in electric discharge and other apparatus therefor
IPC: G02F1/01
Filed: 1931-01-19
Abstract: 369,698. Producing optical effects electrically. WALTON, G. W., 2, Dean Street, Soho, London. Jan. 19, 1931, No. 1798. [Class 97 (i).] A lens, prism, or like optical effect is produced in a light-transmitting medium by means which subject the medium to an electrical influence of different intensity in different parts thereof. Figs. 1 and 2 show a thermionic discharge apparatus for producing a cylindrical lens effect, comprising a heated filament 5 surrounded by a cylinder 8 of transparent insulating material such as glass and contained within a vacuum tube 1. A high resistance translucent electrically-conducting coating 15 is deposited on the inner surface of the cylinder, and connection is made thereto by a lead 9 which extends over the coating in the form of a loop. The filament 5 is preferably brightly incandescent so as also to act as a source of illumination. Fig. 2 shows the electrical connections. When a thermionic current passes between the filament and the coating there is a variation of potential over the surface of the film which, if the film is of uniform thickness and resistance, is such that the potential is lowest at a point midway between the sides of the loop 9, and increases towards both sides of the loop. The optical result of this variation in potential is that light from the filament 5 has a different velocity in the direction 5-16, Fig. 3, from that in the directions 5-9 so that a wave front represented by the line 9-16-9 when no E.M.F. is applied is changed to a front represented by the line 9a-16-9a when the E.M.F. is applied, the result being that the source of light is apparently displaced to the position 5a. A spherical lens effect can be produced by making the film 15 and the loop 9 of circular form. The device can be used as a light-control means as shown in Fig. 8. When no E.M.F. is applied, the light from the source 5 is focused by the lens 18 to produce an image at 20 so that very little light passes through the slit in a diaphragm 19. When the E.M.F. is applied the image plane is displaced into the plane of the diaphragm and all the light passes through the slit. The device may be arranged to produce the optical effect of a prism by making connection to one edge only of the film 15, so that he other edge is at the lowest potential relatively to the filament 5. A combined prism and cylindrical lens effect can be obtained by providing a conductor along each edge of the film and connecting the conductors by a resistance so that they have different potentials. Fig. 16 shows an arrangement which does not i.nvolve a discharge apparatus. Films 15, 15a are deposited on opposite surfaces of a transparent insulating material 30 and are connected as shown to batteries 28, 29 so that the fall of potential along the film 15 is in the opposite direction to that along the film 15a. The potential difference between the films 15, 15a is thus greatest at the ends and zero at an intermediate point so that the refractive index of 30 is less at the edges than at the centre and a cylindrical effect is produced. By applying a battery to one end only of the films and connecting them at the other end by a conductor, a prism effect is obtained. Instead of the solid films shown, liquid or colloidal films may be used, the member 30 being then constructed as a cell. Fig. 22 shows a device having a reflecting surface and shaped to form a curved mirror. A single film 15 is used connected at its centre to one terminal and at its ends to the other terminal of a source of E.M.F. On the opposite face of the member 30 is a reflecting conductor 34 having little or no voltage drop across it. A reflector may also be used with the devices shown in Figs. 1 and 4 to cause the light to return through the transparent member and thus to enhance the optical effect. Also in any form of the apparatus a varying potential may be used. The source of light may be independent of the filament 5 and arranged outside the tube 1. The optical effects above described may be produced by means of a vacuum tube making use of photo-electric emission. In Fig. 29 the film 15 is of photo-electric material and the electrons emitted under the influence of light are collected by the anode 41 which consists of wire mesh and has applied positive potential. Any of the thermionic devices described may be provided with control electrodes ; for example in Fig. 30 a grid 43 is provided around the filament and a varying potential, such as television signals, is applied between the grid and the filament, a constant positive potential being applied to the film 15 relatively to the filament.