GB1291692A - Light modulator - Google Patents

Abstract

1291692 Modulating light MULLARD Ltd 9 Jan 1970 1173/70 Heading H4F An electro-optic crystal of the m3m class, e.g. barium titanrate above its Curie point, KTN, or other perovskites, is provided with a pair of transport electrodes e.g. of tin oxide, for setting up an electric field in the crystal which is not parallel to any of the crystallographic axes. Light e.g. of wavelength 0.3-6 Ám for KTN, may be directed through the crystal in a direction which is not parallel to the crystallographic axes and which is not normal to the field direction. The light and field may be applied in substantially parallel directions and a maximum effect is then obtained when that direction is at 45 degrees to the crystal axes. Thus in Fig. 1 (not shown) such a crystal is disposed between crossed polarizers and has electroded (0, 11) faces perpendicular to the optic axis. In one embodiment, monochromatic light is intensity modulated by applying voltage pulses to the crystal and detected by an indium antimonide detector. The amplitude of such pulses may be reduced if a D.C. bias is also applied due to the square law dependence of the retardation. If the light source is broad band, the crystal and polarizers may form a variable filter. In a light deflector, Fig. 3, plane polarized light is passed through a series of such crystals interleaved with a series of uniaxial crystals e.g. of calcite, which are orientated so that their privileged directions are at 45 degrees to those of the preceding and following active crystals. Each uniaxial crystal has half the thickness of the preceding uniaxial crystal, so that application of a half wave voltage to one of the active crystals results in the appropriate binary deflection. Such an arrangement may be used for a display on a screen, of for addressing an optical storage bank such as an array of photo-diodes. Reference has been directed by the Comptroller to Specification- 1,258,633.