Patent GB-1076096-A (GB)
Title: Improvements in or relating to electro-optical light deflectors
Inventor: DORE MARCUS JOHN
IPC: G02F1/29
Filed: 1965-02-02
Abstract: 1,076,096. Deflecting light. MINISTER OF AVIATION. Jan. 31, 1966 [Feb. 2, 1965], No. 4429/65. Heading H4F. An electro-optical light deflector comprises a prism P, Fig. 1, formed of a single crystal of electro-optic material so cut that a beam of coherent light, indicated by rays I1 and I2, is totally internally reflected into a direction of maximum electro-optic effect within the crystal, the prism being disposed between electrodes which apply a uniform electric field in the direction of the crystal c-axis, i.e. normal to the plane of the paper, causing the phase velocity of the light propagating in the direction of maximum electro-optic effect within the crystal to vary and thus the reflected light rays R1 and R2 to be refracted into direction R<SP>1</SP> and to be further refracted into the direction R<SP>11</SP> on emerging from the face F2 of the prism. Crystal axes a1 and a2 are the directions of minimum electro-optic effect in the prism and lines O1 and 02 represent the directions of maximum electro-optic effect, i.e. when an electric field is applied the refractive index effectively varies with direction of propagation. The light beam I1, I2 is incident normally on face F1 which is normal to the crystal axis a1 face F2 being normal to the direction O1 and face F3 equally inclined to faces F1 and F2. The Hughens wavefronts 0 to 5 indicated in Fig. 1 show the effect of a reduction of the phase velocity after reflection at face F3. By reversing the field the light beam is deflected to the other side of ray R1. Face F2 of the crystal prism may be formed in two plane sections meeting at an edge which is parallel to the crystal c-axis and across which the emerging beam may be deflected and if ray R<SP>1</SP> becomes incident on a part of the face F2 at an angle greater than the critical angle the light beam is switched from one path to a quite different path. Since the electro-optic effect becomes comparatively large at temperatures slightly above the Curie point of the material the crystal is maintained at a temperature exceeding the dielectric Curie point temperature of the material by less than 50‹ C. by means of a temperature-controlling servo system, Figs. 2 and 3, not shown. This system includes means for deriving an error signal representative of a deviation from a preset value of the capacitance between the electrodes and means controllable by this error signal for altering the temperature of the prism to restore the capacitance towards the preset value, e.g. a thermoelectric cooling device. Instead of using the same electrodes as those used for applying the field, Fig. 3, not shown, separate electrodes may be used for the temperature-stabilizing system or else the electrodes of the temperature-stabilizing system may be on a separate crystal in good thermal contact with the prism P and formed of the same electro-optic material, Fig. 4, not shown. The material of the single crystal prism may comprise potassium di-deuterium phosphate, mixed crystals of potassium niobate and potassium tatalate, or isomers of potassium dihydrogen phosphate.