Patent GB-1224331-A (GB)
Title: Improvements in or relating to optical deflectors
Inventor: KOMPFNER RUDOLF
IPC: G02F1/29
Filed: 1968-04-16
Abstract: 1,224,331. Light deflectors. WESTERN ELECTRIC CO. Inc. 16 April, 1968 [17 April, 1967 (2)], No. 17794/68. Heading H4F. A multiple-pass optical deflection apparatus comprises electro-optical deflector 32, Fig. 1, positioned at the common focal point of mirrors (reflectors) 31 and 33 whose effective diameters are larger than the effective diameters of the elements forming the deflector 32, and a coherent-light beam from a laser 34 which is directed through a central aperture or uncoated portion of mirror 31 via deflection apparatus 32 to mirror 33 (beam 1) and then via mirror 31 (beams 2 and 3) to be deflected further in deflector 32 &c., until it is deflected (beam 10) beyond the edge of reflector 33 in a conical scan. The deflector 32 comprises two electro-optical crystals 52, 62, Fig. 3, separated by a halfwave plate 45 and energized with X and Y-coordinate deflection signals 90 degrees out of phase and equal amplitude, the deflection being increased if the time for two passes between mirrors 31 and 33 equals half a period of the deflection signal frequency fm. A shielding structure encompasses both deflection stages. The horizontal deflection crystal 52, e.g. a KDP crystal, is orientated with its Z axis orthogonal to, and its X and Y axes both at 45 degrees to, the plane including the common axis and the deflection co-ordinate. The crystal is energized through symmetrically disposed strip lines 53 and 54 each of which is slightly less than a halfwavelength long at the deflection frequency fm and is orientated parallel to the direction of the deflection co-ordinate. Metal steps 56 and 55, which separate the strip lines 54 and 53 from the crystal, help to shape the driving electric field which due to the symmetrical disposition of lines 53 and 54 provides an effective ground plane halfway therebetween. In operation the X-co-ordinate deflection signal is applied to strip lines 53 and 54 so that the former has a positive-to-negative voltage gradient in one direction when the other has a negative-topositive voltage gradient in the same direction. Both gradients have the same potential at a point midway between the ends (directly above and below the centre of crystal 52) and are sustained on the lines because they are nearly a half-wavelength long at the modulating frequency fm and behave as transmission lines at that frequency. In the crystal the effects of the voltage gradients are additive and the voltage differences across the crystal vary from left to right in a linear manner, which voltage slope varies with line. The voltage slope produces a corresponding slope (profile) in the refractive index and to obtain maximum response (deflection) the light beam is horizontally polarized. Half-wave plate 45 converts the horizontally polarized light into vertically polarized light which is deflected in vertical deflection crystal 62 in a similar manner. In a second embodiment, Fig. 2 (not shown), the deflector is positioned adjacent one of the mirrors which mirror need not have a larger effective diameter than the effective diameter of the deflector. The input and output paths of the light beam from the apparatus may be interchanged. Magneto-optic instead of electrooptic crystals may be utilized. Reference has been directed by the Comptroller to Specification 1,060,954.