GB256611A - Method and device for modulating the intensity of a luminous source particularly applicable to television and like systems - Google Patents

Abstract

256,611. Tawil, E. P. Aug. 7. 1925, [Convention date]. Television apparatus.-The intensity of a beam of light is controlled electrically by utilizing the variations in shape or optical properties of a piezo-electric crystal to which the varying potential is applied, the arrangement being such that the beam is incident directly on the surface of the crystal. To obtain maximum effects the current used may be of a frequency corresponding to the natural frequency of the crystal. In the arrangement of Fig. 1, light from a source S is concentrated by a lens C on a very narrow slot f in a screen e, and a second lens L<1> produces an image of the slot at I of a size comparable with the elongations of the quartz plate Q of which one end is arranged in the plane of the image. The degree of interception of the rays is thus varied in accordance with the variations of length of the plate, and a third lens L<2> concentrates at P the light of varying intensity. In a modification. Fig. 2, the light is reflected from the surface of the plate Q, and the lens L<2> concentrates the reflected rays at P. Two or more plates may replace the single plate Q. In the arrangement of Fig. 3 the end of the plate Q extends into a parallel beam from a source S<3> and a lens L' to vary the length of shadow on a slot extending between B and B<1>. Fig. 4 shows the use of a quartz plate Q<5> fixed between end stops H, H<1> so that the potential variations produce a curvature of the plate. A parallel beam from a source S<5> and a lens L<5> is reflected by a mirior M on the plate, and the beam reflected by the plate, of varying divergence in accordance with the curvature, is incident on a perforated screen G. The light passing through the screen is thus of an intensity dependent on the degree of divergence of the beam, and is concentrated at P by a lens L<2>. The use of interference phenomena by arranging a reflecting surface on the quartz plate to constitute one of two Fresnel mirrors, and the use of double refraction phenomena in connection with the deformations of the plate, are referred to. The Specification as open to inspection under Sect. 91 (3) (a) comprises also an arrangement shown in Fig. 4 (Cancelled), comprising two quartz plates secured together, the inner sides being earthed by a wire d and the outer sides being connected to the variable potential circuit d<1>. The resulting deformations are used, to vary the light reflected from a beam T by a mirror m. This subect-matter does not apjpear in the Specification as accepted.