Patent GB-1099237-A (GB)
Title: Improvements in or relating to optical devices for producing scanning light beams
IPC: G02F1/29
Filed: 1965-06-24
Abstract: 1,099,237. Deflecting light. INTERNATIONAL BUSINESS MACHINES CORPORATION. June 24, 1965 [Sept. 30, 1964], No. 26709/65. Heading H4F. An optical device for producing a scanning light beam comprises in a first embodiment, Figs. 1B and 1C, two parallel mirrors 3 and 4, a transparent optically activable medium 1 and a transparent birefringent element 2. A monochromatic plane polarized light beam R from a ruby laser S is directed between mirrors 3 and 4 and is reflected back and forth repeatedly through medium 1 and element 2. In this embodiment medium 1 comprises stressoptic material and a sonic pulse which is periodically generated by a piezoelectric transducer T is transmitted along the medium thereby causing the medium either to change from an optically isotropic state to an optically anisotropic state or to vary its degree of optical anisotropy. If medium 1 is an electro-optic medium it is associated with electrodes for periodically generating electric pulses that travel along the medium. In its normal state medium 1 does not effect any change in the polarization of the light rays R, however, in the position of the sonic pulse indicated by hatched region 5 the medium is rendered anisotropic or birefringent such that the light ray which passes twice therethrough has its direction of polarization effectively rotated through 90 degrees and thus is refracted by medium 2 as an extraordinary ray in such a way that it passes beneath the lower edge of mirror 4, Fig. Ic. Thus the light emerges from the device as a beam which transversely shifts its position along a desired scanning path in synchronism with the passage of the scanning pulse through medium 1. Local anisotropy may be induced in medium 1 by directing an electron beam along the medium, thereby imparting a transient electrical charge to the area of the medium on which the electron beam impinges. In a second embodiment, Fig. 2, the front and back faces of the optically activable medium 6 are used on internal reflecting surfaces for confining the light beam within the medium which is normally birefringent and is positioned adjacent a birefringent element 7. The materials of crystal 6 and element 7 are so chosen that their extraordinary refractive indices are approximately equal, crystal 6 having an ordinary refractive index greater than its extraordinary refractive index and element 7 having an ordinary refractive index smaller than its extraordinary refractive index. Monochromatic plane polarized light beam R is directed into crystal 6 through an oblique end face and is totally internally reflected back and forth through crystal 6. However when the " ordinary " ray R encounters the localized anisotropic region 8 it becomes an " extraordinary " ray E and passes through the interface 6a, element 7 and a non-reflective transparent coating 7a. In a third embodiment, Figs. 3A and 3B, not shown, a glass rod (9) of rectangular cross-section is positioned between parallel mirrors (10) and (11), and an elongated crystal (12) of optically activable material is positioned adjacent the reflecting surface of mirror (11) facing glass rod (9). Glass rod (9) extends longitudinally in parallel relation to the mirrors but inclined slightly from the vertical so that its front and back faces are at approximately 20 degrees relative to the mirror surfaces, the monochromatic plane polarized light beam being directed against the glass rod (9) so that its angle of incidence is equal to the Brewster angle of the material, i.e. glass. The light beam is thus repeatedly reflected by the mirrors and is transmitted without reflection by the glass rod until it encounters a local anisotropic region where its state of polarization is changed such that it is refracted and reflected by the glass rod, the reflected portion thereby escaping from the optical system above the edge of mirror (11).