Patent GB-1275725-A (GB)
Title: Solid state scanning systems
Inventor: SANDBANK CARL PETER
IPC: H01L47/00
Filed: 1968-08-23
Abstract: 1275725 Optical scanning; light modulators & deflectors STANDARD TELEPHONES & CABLES Ltd 21 Aug 1969 [23 Aug 1968 16 April 1969] 40342/68 and 19339/69 Heading H4F. A scanning device comprises a piezo-electric semi-conductor body e.g. of CdS, having electrodes at opposite ends for applying an electric field greater than a threshold value to the body whereby, due to high field instability effects (a "piezo-electric Gunn effect") a propagating high field domain of high acoustic amplitude is produced therein so that in use when a beam of radiation is incident on the body, that part of the beam instantaneously interacting with the moving acoustic domain is diffracted thereby to provide a line scan. The applied field may be continuously above the threshold value to give sequential scans, since a second domain will form immediately the first domain has traversed the body, or it may be pulsed to give single domains, or groups of sequential domains, depending on the pulse length. To produce single domains using field pulses of a length less than the domain transit time through the body, a steady state field of 50-75% threshold is also applied, either continuously or pulsed. For a television line scan time, a single CdS crystal of 11 cm. would be required, but a plurality of bodies may be connected in series so that the output pulse of one body provides an input (domain nucleating) pulse for the next body, Fig. 6 (not shown). The scanning effect may be provided by normal Bragg diffraction, Fig. 4 (not shown), or by a process in which each different wavelength of plane polarized (white) light interacts with that one of the randomly oriented acoustic waves within the domain having an orientation and frequency to give 90 degrees polarization rotation upon diffraction through the Bragg angle thereby, so that after the output light has been passed through an analyser a beam moving at the speed of the domain is produced, Fig. 5A (not shown). This figure shows a CdS body between a polarizer and analyser, for successively sampling portions across an input light beam of spatially varying intensity, the transmitted light being received on a photomultiplier. Most of the applied field in excess of that required to form the acoustic domain appears across the domain, altering the phonon population therein and the amount of diffraction produced thereby. Therefore modulating the applied field leads to a modulation of the intensity of the diffracted or polarization rotated beam as it scans across the body which is of use in providing a display. In a film scanning and display unit, Figs. 7 and 8, a narrow strip 19 of light is passed through a moving film 20 and focused on a semi-conductor body 10, operating in the Bragg diffraction node for example. Deflected light is focused on a photomultiplier 25 feeding a video signal to a recorder 26 or a display unit such as shown in Fig. 8, where a light source 28 illuminates one side of, and is variably modulated by, an array of semi-conductor body elements 27. Each element may comprise a plurality of series connected semi-conductor bodies as described above, and in addition, the elements are connected in series from line to line so that a domain propagates throughout the whole array. Alternatively the display unit may be such as is described in Specification 1,136,254.