Patent GB-1388925-A (GB)
Title: Electrically-controlled graphic reproduction system
IPC: G02F1/33
Filed: 1972-03-03
Abstract: 1388925 Recording apparatus THOMSON CSF 3 March 1972 [5 March 1971] 10192/72 Heading G1J [Also in Divisions B6 and H4 In a system for reproducing an oscillogram of an electrical signal, a pattern built up in a manner similar to a television roster, or a text having characters arranged in successive lines, one or more acoustic-optic devices are employed to intensity modulate a monochromatic light beam e.g. a laser beam and to deflect it in at least one direction over a photo-sensitive recording medium. In the embodiment Fig. 8, a Bragg diffraction cell 110 receives a variable amplitude, constant frequency, acoustic signal from transducer 111 whereby the intensity of the undiffracted beam 132 is varied. The diffracted beam 131 is passed out of the system, and beam 132 is deflected in a system comprising a Bragg cell 114, receiving variable frequency, constant amplitude, acoustic waves from a transducer 117, together with prisms 112, 113, 115, 116. These prisms have an apex angle equal to the complement of the Brewster angle for the material of the prism, as described in detail in Specification 1369909. After passing a fixed lens 118 and mirror 119 the deflected and modulated beam 134 falls on a recording web 121 which is moved under the control of signals Sy to provide the second scanning direction. Alternatively a second deflection system similar to 112-116 may be arranged to provide an orthogonal deflection over a stationary web, Fig. 4 (not shown). A beam splitter may be interposed between the lens and the web in this case, for providing an image on a ground glass screen. In a further variant two dimensional scanning of a fixed web, achieved by rotating a single Bragg deflector about its axis i.e. using polar co-ordinates. The modulation and deflection may be effected by a single Bragg cell if it is provided with a variable amplitude, variable frequency signal. In a further variation, the intensity modulator 110 is replaced by a cell of the type wherein a plane polarized light beam in an optically unisotropic medium is diffracted into an orthogonal polarization by a collinear acoustic wave when the optical and acoustic frequencies satisfy a phase matching condition. Fig. 5 shows a system comprising such a cell 62, provided with a plurality of selectively addressable transducers 63 and having an inclined optical input/output face whereby a diffracted light beam 95 is shaped for example as an alphanumeric symbol, and separated from the undiffracted input and output beams 94, as described in detail in Specification 1350821. The generated letter is directed to a predetermined position by deflector 64-68 and movement of the web 72, and subsequently the light source 59 is energized. As described the recording medium may comprise a metallized film between a semiconductor layer and an insulating substrate. The semi-conductor is electrostatically charged in the dark, selectively discharged by the action of the light beam, and the charge image developed using charged particles and fixed by heating. The charge image may be transferred to an insulating substrate if a number of copies are required. The medium is alternatively a dry silver paper, which is developed by thermal radiation.