Patent GB-762678-A (GB)
Title: Improvements in and relating to polarization apparatus
IPC: F21S8/10
Filed: 1953-11-13
Abstract: 762,678. Polarizing apparatus. MARKS, A. M. Nov. 13, 1953 [Nov. 14, 1952], No. 31505/53. Class 97(1) A device for producing polarized light consists of means for directing light from a 'light source at a polarizing medium, depolarizing means -receiving directly light reflected from the polarizing medium and depolarizing it, and means gathering the depolarized light received from the said depolarizing means and causing it to impings on the said polarizing medium. As shown in Fig. 2 parallel light 38 formed by a parabolic reflector placed behind the source is incident on a member 26 and totally reflected by the prismatic surface 42 thereof to form an inclined beam 44 incident at an angle of about 60 degrees on a polarizer 30 comprising a number of superimposed layers after passage through a depolarizing layer 31. The portion 49 of the beam 44 transmitted by the polarizer 30 is polarized perpendicular to the plane of the Figure and emerges as a parallel beam 52 after reflection at the surface 50 of a prismatic member 27 .similar to the member 26. The beam 46 reflected by the polarizer 30 and polarized in the plane of the Figure is depolarized by the layer 31 and directed back to the light source as a beam 47 after total reflection at the surface 48 of the member 26. The beam 47 is thereafter reflected by the parabolic reflector and by an auxiliary reflector to be directed once more at the polarizing system. In an alternative construction the plates 26 and 27 are reversed and the layer 30 sandwiched between them, a separate layer being provided to depolarize the reflected beam. In the modification shown in Fig. 10 light from a source 23 falls directly, or after reflection by a spherical reflector 118, on a parabolic reflector 21 whence it passes as a parallel beam e.g. beam 119 to a depolarizer 31 and thence to a series of polarizing layers 117, 117<SP>1</SP>, arranged as shown. The transmitted beam 120 is plane polarized in one plane while the reflected beam 121, polarized in the perpendicular plane is incident normally on the polarizer 117<SP>1</SP> and is totally reflected to return to polarizer 117 and is again totally reflected thereby to form a beam 125, depolarized by the layer 31 and returned to the light source. Modifications are designed in which the polarizers 117, 117<SP>1</SP> are arranged at different angles. The polarizing layers may be formed of thin superimposed films of polystyrene or other plastic or may be formed as of thin flakes of glass suspended in an air stream and floated downwardly in a uniform layer on a glass plate and interspersed with a low-melting point glass the whole being subsequently heated to cause sintering. Alternatively, as shown in Fig. 17 the polarizer may comprise a glass plate 144 carrying high refractive index layers 145 and 147 of titanium dioxide and low index layers 146 of silica or magnesium fluoride. Alternatively a glass plate may be coated on both sides with a layer of titanium dioxide, zinc sulphide, stannic oxide or selenium. The depolarizer may consist of a number of glass balls, about one tenth of a millimeter in diameter, heated suddenly cooled to give optical stress and suspended in a plastic medium, or a plastic medium containing randomly oriented birefringent crystals. Alternatively the depolarizer may consist of three layers 71a, 71b, 71c, Fig. 5, of plastic oriented by stretching to be birefringent and cut out to the pattern shown, or to a hexagonal or other regular pattern so that different parts of an incident polarized beam will pass through different thicknesses of material and so be depolarized. The system may be used in automobile headlights to obviate dazzle. Specification 450,090 is referred to.