| 摘要 |
643,210. Light valves. FARNSWORTH TELEVISION & RADIO CORPORATION. July 23, 1946, No. 21944. Convention date, Aug. 13, 1945. [Class 40 (iii)] In a light-modulating system in which mechanical waves are propagated through a light valve comprised of an elastic transparent medium to cause diffraction of a light beam, the mechanical waves are produced by a carrier oscillation which is amplitude-modulated by a sub-carrier oscillation, itself amplitude-modulated by a modulation signal. The light valve comprises a container 2 (Fig. 1) formed with two glass sides 4, 5 and filled with a suitable liquid (e.g. water, heptane or butyl bromide), through which mechanical waves are propagated by means of a piezo-electric crystal 6 energized by a carrier oscillation (e.g. 10 Mc/s.) source 13 which is amplitude-modulated in 14 by a subcarrier (e.g. 1 Mc/s.) source 11 itself amplitudemodulated in 12 by an audio-frequency signal source 10 which may have a maximum frequency of about 10 kc/s. The diffraction grating effect resulting from the propagation of the mechanical (i.e. compressional) waves in the liquid of the cell is employed to control a parallel light beam from source 25 in accordance with the modulated sub-carrier and, to this end, the diffracted component of the light which emerges from the light valve is separated from the emergent undiffracted component by means of a first series of opaque bars 27 separated by spaces 28 of the same width as the bars 27 and a similar series of opaque bars and spaces 30, 31, separated from the first series by a distance, determined by calculation, so that light of the first diffraction order only is permitted to pass through the spaces 28 and 31 whilst the transmission of undiffracted light is prevented. The emergent diffracted light is then collimated by lens 35 and employed for transmission to a distant receiver. Instead of positioning the two series of opaque bars on the emergent side of the cell one series may be positioned on the incident side. The undiffracted emergent light may be utilized for transmission instead of the diffracted light by shifting the bars 30 to either side by a distance equal to their width. In a receiving system for use with the modulating system provided by the invention (Fig. 5, not shown) the received modulated light is transformed into an electrical signal by means of a photo-electric cell, the output from which is detected to recover the modulation signal and then amplified and fed to a loudspeaker. In an application of the invention to multiplex signalling (Figs. 6 and 7, not shown) three light valves, each energized by a common carrier oscillation but by different sub-carriers, each of which is modulated by a different audio signal, control a single light beam, the three modulation channels of which are separated at the receiver by electric filter means. |
