Patent GB-601237-A (GB)
Title: Improvements in a pick-up or relay system using modulated light beams
IPC: H04B10/00
Filed: 1945-05-11
Abstract: 601,237. Light valves photo-electric signalling apparatus. RAIBOURN, P. May 11, 1945, No. 11897. [A Specification was laid open to inspection under Sect. 91 of the Acts, Aug. 25, 1945.] [Class 40 (iii)] [Also in Group XL (a)] A system for transmitting or relaying signals varies the opacity of an ionic crystal in accordance with the said signals and the variation is then used to modulate a beam of light projected through the crystal, the opacity of the crystal being controlled by directing a modulated radiant beam upon it. 1st Embodiment. Fig. 1. In this embodiment which is described as being applied to a television system, the output from an iconoscope 3 is applied between the cathode and grid of a cathode-ray tube 7, the anodes 8 and 9 of which disperse the electron beam so that it falls upon a considerable portion of the surface of an ionic crystal 10, the opacity of which varies in accordance with the intensity of the electron beam. In place of a single crystal, a microcrystalline layer supported in various ways may be used, or a single crystal may have its exposed surface covered with some substance such as beryllium which yields additional electrons on being struck and thus increases the opacity effect. A source of light 11, preferably in the near infra-red region, is focused upon the crystal, the transmitted light which is consequently modulated in accordance with the signals from the iconoscope being brought to a parallel beam by the lens 31 and directed towards the receiving or relay station. The restoration time of the crystal 10 may be varied in accordance with the characteristics desired. Several ways of accomplishing this are shown. A transparent conductive electrode 27 at a high potential may be placed on the surface of the crystal, which may also be surrounded by a heating element 28 and irradiated by an auxiliary source 30 of infrared radiation of such a wavelength that the amplitude of vibration of ions in the crystal is increased. These elements all tend to increase the rate at which elements all bend to increase the rate at which the opacity effect disappears. If desired, the source 11 may be made to fulfil the functions of both the source of heat 28 and source of auxiliary infra-red light 30. Selected impurities also may be used to control the restoration time. The invention is not limited to the use of an electron beam as a source of the desired opacity and any suitable radiant beam may be used. In alternative methods, the voltage on electrode 27 or the infra-red light source 30 are modulated while a constant beam of cathode rays, X-rays, ultra-violet rays or of positive ions is directed on to the crystal. A relay station, Fig. 2 (not shown), comprises a reflector which receives the light from the transmitter :of Fig. 1 and focuses it upon a photo-electric cell, the output from which is applied to a cathode-ray tube as described in relation to Fig. 1 which then modulates a further beam of light. 2nd Embodiment, Fig. 3. An evacuated container, bounded by a parabolic surface covered by a microcrystalline layer of ionic crystals. 42 and a lens 34, houses a filament 35 producing infra-red light which is reflected from the. parabolic surface. The light is thence projected through the lens 34 and filter 37 to a receiving station. The electron source, light beam source and auxiliary infra-red beam source of the 1st Embodiment are all replaced by the filament 35. The modulation voltage may be applied between the reflector and the filament 35 or to a grid 41.