GB1126392A - Optical polariser - Google Patents

Abstract

1,126,392. Polarizing devices. STANDARD TELEPHONES & CABLES Ltd. May 19, 1967, No. 23388/67. Heading G2J. A linear optical polarizer comprising multiple layers 50 of transparent thin film dielectric layers on a glass plate 51 is arranged such that for a particular wavelength and angle of incidence, an incident beam of light plane polarized normal to the plane of incidence gives rise to a reflected beam which is the resultant sum of the components reflected from each layer, whereas, a similar incident beam plane polarized parallel to the planes of incidence is incident on some layers at more than the Brewster angle and on other layers at less than the Brewster angle, so that the resultant of the reflected components has zero amplitude. This system gives 99% reflection of incident light polarized normal to the plane of incidence, and 99% transmission of light polarized parallel to the plane of incidence. The thin film layers are alternately of 1À35 and 1À50 refractive index and are of a thickness giving an optical path difference which is an odd number of half wavelengths between light reflected at the top and bottom of each layer. The layers are of cryolite and a higher oxide of silicon, and an anti-reflection layer 52 of zinc sulphide is provided on the underside of the glass 51.