GB1180334A - Optical Scanner - Google Patents

Abstract

1,180,334. Light deflectors. MULLARD Ltd. 5 April, 1968, No. 16542/68. Heading H4F. Optical scanning apparatus comprises an array of magneto-optical Faraday effect elements each intercepting a different elemental portion of an optical path, and means for magnetically energizing the elements with an energization cycle such that each element of the array sequentially rotates the polarization plane of light travelling therethrough to an orientation such that thereafter the light is transmitted by an analyser, the other elements' light outputs being stopped by the analyser. The elements may be arranged to be effectively transparent when magnetically unsaturated and effectively opaque when saturated or vice versa. Alternatively the elements may be effectively transparent when magnetically saturated in one sense and effectively opaque when saturated in the other sense. The apparatus may be used in an image converter or in a televisiontype picture display. The Faraday effect material may comprise doped yttrium iron (or aluminium) garnet. The elements of the array may be subjected to a constant magnetic field Ho, Fig. 1, which exceeds the saturation magnetic field, an element being rendered unsaturated when energized by both a row control lead R 1 and a column control lead C 1 ; an element which is excited by either a row or a column control lead but not both being still saturated. In a second embodiment each element has its own control wire, Fig. 3 (not shown), and this embodiment may operate without a constant bias field Ho, only saturated fields rendering an element effectively transparent. In a further embodiment an array of elements 1, Fig. 5, are subjected to a time varying field H ac which at any one time is spatially uniform over the area of the array, and to a time constant bias field H dc which is spatially non- uniform with positive gradients from top to bottom and from right to left of the array as shown by the straight line plots 11 and 12. All the elements including 1 MIN which is subjected to the smallest H dc are saturated by H dc in the absence of other fields. The scan may start at 1 MIN by applying field H ac in the opposite direction to H dc , for as H ac increases it passes through H MIN , desaturating 1 MIN rendering it transparent, and then increases to saturate 1 MIN rendering it again opaque, at which time the next element is rendered transparent by the increased field H ac , and so on.