Patent GB-1057439-A (GB)
Title: Method and apparatus for the deflection and amplitude modulation of monochromatic linearly-polarised electromagnetic radiation
IPC: G02F1/29
Filed: 1963-10-21
Abstract: 1,057,439. Modulating and deflecting light; modulating light by electromagnetic radiation. SIEMENS & HALSKE A.G. Oct. 21, 1963 [Oct. 25, 1962], No. 41435/63. Heading H3R and H4F. To controllably deflect and amplitude modulate a monochromatic plane polarized light beam from a generator 21, e.g. a laser, Fig. 2, the light beam is directed through a wedgeshaped crystal 22 to which is applied an electric or magnetic modulating field from generator 23 which varies the refractive index of said crystal and thus varies the angle of deflection of the light beam, the beam 24 which leaves the crystal passing to a greater or lesser extent (determined by the degree of deflection) through a fixed iris 26 in the form of an amplitude-modulated ray 27. Crystal 22 is denoted in Fig. 1 by reference numeral 1 and comprises an electro-optic or magneto-optic crystal such as an alkali dihydrogen phosphate crystal, e.g. a potassium dihydrogen phosphate (KDP) crystal, or an alkali dihydrogen arsenate crystal, e.g. a deuterium-substituted ammonium dihydrogen arsenate crystal, or a cubic copperchloride crystal having properties of electrical double-refraction. Coherent monochromatic plane-polarized light from a laser 6 enters face 2 of the crystal, the plane of polarization being parallel to the plane of the drawing that is perpendicular to the plane of the principal section, this being given by the ray direction and the optical axis of the field-free crystal. The ray 3<SP>1</SP> leaving the field-free crystal is deflected to the directions 3<SP>11</SP> or 3<SP>111</SP> in the presence of a field perpendicular to the plane of the drawing depending upon the field direction, the angular change with respect to 3<SP>1</SP> being determined by the field strength, the prism angle α and the electro-optical constants of the material (see specification). Unpolarized light would result in the proportion of the light polarized perpendicular to the plane of the drawing forming an extraordinary ray 5, but this would not be influenced by the field. Where high and ultrahigh ranges of modulating frequencies are concerned waveguide couplings are employed between the field generator and the crystal, the crystal being arranged within the waveguide at a point of maximum magnetic or electric field strength. In a further embodiment, Fig. 3, angle α<SP>1</SP>, of prism 1 is so large that the central ray 33 of convergent beam 31 focused to point 32 is refracted to lie flush with crystal face 4 when no field is applied. When an electric field is applied a greater or lesser proportion of the beam is totally reflected with consequent modulation, the totally reflected beam portion 37 being removed by an additional prism 35. For fluids, wedge-shaped vessels constructed from plane-parallel plates are used. The electrooptical constants are temperature dependant and the field-dependant change in the refractive index is large at temperatures near the Curie temperature i.e. the temperature at which conversion of the crystal lattice takes place.