Patent GB-1054129-A (GB)
IPC: G02F1/31
Abstract: 1,054,129. Light modulating and deflecting apparatus; television. INTERNATIONAL BUSINESS MACHINES CORPORATION. Nov. 4, 1964 [Nov. 8, 1963], No. 44880/64. Heading H4F. [Also in Division G4] The principle of the invention is illustrated in Fig. 1 wherein a beam control element e.g. an electro-optic plate 14, having transparent electrodes 15 and 16 adjacent its front and rear faces, and a doubly refracting crystal 22, intensity modulates and/or selectively deflects from a first position to a second position an input beam 12 of plane polarized substantially monochromatic radiation e.g. from a laser. The electrodes 15 and 16 are electrically coupled to a switch S and a voltage source 20, the potential being sufficient when switch S is closed to switch the plane of polarization of beam 12 through 90 degrees. The doubly refracting crystal 22 is so orientated that with its plane of polarization thus altered (effectively rotated through 90 degrees) the beam is propagated therethrough as an ordinary (O) ray i.e. undeflected on path 29. By opening switch S the beam passes through the electro-optic plate 14 unchanged and is thus deflected in crystal 22 as an extraordinary (E) ray i.e. on path 28. A mask plate 30 is located behind crystal 22 having an aperture T, to allow the deflected (E) ray to leave the apparatus, and a depression 34, serving as a heat sink, for absorbing, by means of a circulated coolant, the energy of the undeflected ray on path 29. Thus if switch S is intermittently operated in accordance with a pulsed information signal representing binary coded data a beam detector aligned with aperture T will receive the coded data as intermittent bursts of radiation. As a beam intensity modulator, the apparatus of Fig. 1 operates with the switch S continuously closed and the voltage source 20 is varied in magnitude between 0 and half-wave voltage by an externally generated AM information signal. The beam 12 is circularly or elliptically polarized for voltages intermediate 0 and halfwave voltage, thus giving rise to a splitting of the beam between the paths 28 and 29, and a photomultiplier tube positioned opposite aperture T will receive the AM information carried on the output beam. The electro-optic crystal 13 may comprise KDP, potassium dideuterium phosphate, ADP, ammonium dideuterium phosphate or cuprous chloride. A Kerr cell or a magnetically operated Faraday rotator may be substituted for crystal 13 with certain changes in wave plate thickness and field magnitude. Crystal 22 may be of any birefrigent medium, either uniaxial or biaxial e.g. calcite, quartz, anthracene, naphthalene or sodium nitrate. The invention relates to a beam deflector having multiple output paths, Fig. 2, employing the principles of operation for deflection of Fig. 1 which is constructed by superimposing a number of the apparatuses of Fig. 1. In this embodiment four output paths T1-T4 are shown, the apparatus comprising a pair of plane mirrors 42 and 54, a pair of quarter-wave plates 44 and 52, a selectively operable half-wave plate 48 and a pair of doubly refracting crystals 46 and 50. Wave plate 48 has four individuallycontrollable pairs of transparent electrodes 56, 58, 60 and 62 vertically spaced across its front and rear faces. In operation the collinated input beam 40 is directed through the output aperture T1 as follows, Fig. 3a, (not shown). The vertically polarized beam 40 enters the deflector through apertures 66 and 70 in mirror 42 and quarter-wave plate 44. In double refracting crystal 46 it is refracted upward into path 45 and by applying a potential across the first electrodes 62 of plate 48 the beam's plane of polarization is effectively rotated to horizontal. The beam thus passes through the doubly refracting crystal 50 undeviated and leaves the apparatus polarized in a horizontal plane through a lower aperture 68 in quarterwave plate 52 and output aperture T1 in mirror 54. To channel the beam through upper output aperture T4, Fig. 3b (not shown), a potential is only applied across the fourth upper pair of electrodes 56 of plate 48. The beam thus passes through wave plate 48 undisturbed from its vertical status of polarization in the region of electrodes 62, is refracted up to the level of path 47 in doubly refracting crystal 50 and is effectively rotated through 90 degrees upon passing twice through quarter-wave plate 52 being reflected from mirror 54. Still at the level of path 47 the now horizontally polarized beam is propagated undeviated through crystal 50, wave plate 48 and crystal 46 to the quarter-wave plate 44. After the beam passes through the quarter-wave plate 44 twice, being reflected from mirror 42, its plane of polarization is effectively rotated to the vertical so that the crystal 46 refracts the beam into the path 49. The beam will thus continue to work its way up until it emerges from crystal 46 in the upper path 51 and encounters the wave plate 48 between activated electrodes 56 and is switched to a horizontal status of polarization, whereupon it propagates undeviated through crystal 50 and out of the system via upper apertures 68 and T4. Instead of using manually operable contact points for the switches S1- S4, Fig. 2, the natural capacitance of the opposed pair of electrodes 56, 58, 60 and 62 may be utilized by building these electrodes into a pulse propagating circuit, Fig. 5 (not shown), in which the electrodes of like polarity are coupled together by individual inductors 63, thus forming a L-C delay line. A train of scanning pulses 65 may then be propagated down the delay line resulting in sequential activation of the several electrodes and thus high-speed beam scanning. A beam deflector having a two-dimensional co-ordinate array of output apertures, Fig. 6 (not shown), may be formed from a vertical deflection stage A and a horizontal deflection stage B. Stage A comprises a single straight line deflector identical to that of Fig. 2, and stage B is identical to that of stage A except that it is orientated at right angles thereto and has four input apertures each adjacent to one of the four output apertures T1-T4 of the A stage deflector. This deflector may be used as a " flying spot " scanner to interrogate a photographic memory plate. Further, the input beam may be supplied by the apparatus of Fig. 1 and may thereby be modulated in either a digital " onoff " manner or in an intensity varying analogue fashion. Stage B may comprise a plurality of single vertical deflection stages one on top of the other thus producing an expanded version of the deflector of Fig. 2, light-conducting rods or a lens arrangement being employed to " fan out " the output paths from the first stage deflector.