Patent GB-1385230-A (GB)
Title: Apparatus and method for reproducing stored information
IPC: G11B7/125
Filed: 1972-03-30
Abstract: 1385230 Modulating light EASTMAN KODAK CO 30 March 1972 [12 April 1971] 15098/72 Heading H4F [Also in Division B6] Apparatus for producing an optical image formed of a plurality of segments each of a predetermined number N of elemental areas, e.g. an alpha-numeric character based on a 5 column (segment) by 7 row array of elements, comprises an acoustic-optic diffraction cell 26, the transducer 28 thereof being simultaneously energized at selected ones of N predetermined different frequencies to deflect a collimated monochromatic laser beam 24 from a beam expander 22 through a corresponding plurality of angles to provide an instantaneous image segment, successive segments being imaged 42, 46 in a plane 48 and being disposed adjacent each other by the action of a scanner 44. Undeflected light is blocked at 38. The image at 48 may be viewed on a screen or recorded on a photosensitive medium, e.g. direct print-out, dry or wet processing. The scanner 44 may be a rotating prism, flat mirror or mirror drum, or an acoustic-optic or electro-optic deflector. Successive spaced or overlapping lines of characters are recorded by movement of the film 48. In Fig. 3 (not shown) the film is stationary and scanned in two directions by scanner 44 and a further deflector, e.g. a mirror, prism, lens or acoustic-optic device. Successive pages, or groups of pages are recorded by moving the film. The cell 26, which may have non-parallel sides or comprise a plastics acoustic absorbing container to avoid standing waves, or alternatively may be such that standing waves are formed, may include water, LiNbO 3 , glass or PbMoO 4  as the acoustic-optic material. As particularly described, the images to be reproduced are determined by the output of a storage unit or computer 100 (32), Fig. 4, e.g. in binary coded decimal form. A memory circuit 104 converts the output of a temporary storage register 102 into an output format comprising N outputs corresponding to the number of elements per segment, for controlling different frequency oscillators 106, e.g. via diode switches. The oscillator outputs are added 110 and passed to transducer 28, which may be a single device, or N devices each responsive to a different one of the frequencies. The different frequencies are preferably equally spaced and may be such as to produce separate or overlapped light spots in plane 48. By modulating the amplitude from individual oscillators 106 grey scale modulation of the recorded elements is possible. The oscillators may be phase locked to reduce distortion in the electrical circuitry, and variations in image intensity caused by varying the number of operative oscillators 106 may be reduced by a suitable switching arrangement, Fig. 6 (not shown). An output from the scanner 116 (44) is applied to a position sensor 118, e.g. a photo-cell, for controlling information supply to circuit 102 and controlling a counter 122 enabling feed of each image segment from circuit 104. A further light sensor 119 receives the output from 116 and controls the gain of amplifier 110 in response to fluctuations in the laser beam intensity. Oscillators 106 may be replaced by a single multi-frequency oscillator, the desired frequencies being selected from the output thereof, or by controlling which frequencies are produced thereby. Some of the frequencies may be multiplexed instead of being added at 110. The system is said to be particularly useful for recording on microfilm, and may be used for graphs and drawings in addition to characters.