Patent GB-1399994-A (GB)
Title: Multiple colour image projection method apparatus and photographic records
IPC: H04N9/00
Filed: 1973-01-25
Abstract: 1399994 Modulating light; facsimile apparatus EASTMAN KODAK CO 25 Jan 1973 [28 Jan 1972] 3787/73 Heading H4F A plurality of light beams R, B and G each having a known wavelength are diffracted by a corresponding plurality of amplitude modulated waves in an acousto-optic medium 102, the carrier frequency of each acoustic wave being selected with respect to a respective optical wavelength so as to produce a single desired diffracted beam of that wavelength (in addition to the undiffracted beam and diffracted beams of the other wavelengths) in a direction 136 common to the desired beams of the other wavelengths. Thus, in Fig. 3, there are 3 acoustic waves (standing or travelling) providing diffracted RG and B beams 118, 120,122; 124, 126, 128; and 130, 132, 134 respectively in addition to undiffracted beams 114<SP>1</SP> and 1161. The desired beams 118, 126, 134 are selected by an aperture, Fig. 1 (not shown), to provide a composite beam with variable amplitude colour components. Methods of finding the required optical beam diameter, modulation bandwidth, acoustic frequencies, and aperture size are described. The incident beams may all be collinear, or angularly separated, Figs. 1 and 2 (not shown) or a combination thereof, Fig. 3, and are preferably laser beams. A single electroacoustic transducer 104 is shown, driven by different frequency sources 106, 108, 110 and summing amplifier 103, but a transducer may be provided for each frequency, the acoustic waves meeting in the acousto-optic interaction region, or they may sequentially interact with the incident light beams. When large amounts of diffraction occur, there may be interaction between the different frequencies, for instance a variation in the intensity of one diffracted beam when the intensity of another is varied. Non- linear electronic circuitry, or alternatively a negative feedback technique in which the output light is sampled and compared, may be provided to overcome this. The arrangement of Figs. 1-3 may be used in system for copying, e.g. negatives, or reflectance prints, by scanning the original and controlling the modulation of the beam 136 as it is scanned over a photosensitive medium, in response to the output of a plurality of photocells each responsive to a different wavelength, e.g. RG and B, Figs. 4 and 5 (not shown). Scanning of the original is by a flying spot scanner, or a reading beam deflected by a single mirror (moving original) or two mirrors. One or two scanning mirrors deflect the recording beam in synchronism with scanning of the original. In Figs. 6 and 6a (not shown) one or two doublesided mirrors effect simultaneous scanning of the reading and recording beams which are derived from the same light source. The arrangement may also be used for recording television video signals on film, Fig. 7 (not shown) or for providing a television or other display, Figs. 7-9 (not shown). The screen receiving such a display may be vibrated to reduce laser speckle. Additional beams, non- collinear with the composite beam 136 may be produced and used. In interlaced scanning the beam 136 may be (B+G) and the additional beam the R beam.