Signal translating systems

摘要

1,132,511. Read-only memories. WESTERN ELECTRIC CO. Inc. 16 Dec., 1965 [24 Dec., 1964], No. 53377/65. Heading G4A. [Also in Division H4] To increase the signal to noise ratio in a system operable to route an input light beam along a selected one of a plurality of paths to one of a plurality of output positions e.g. a multistage digital beam deflector wherein each stage comprises a uniaxial birefringeat crystal and a polarization modulator, the light from the selected output position is directed along a path that is a reversal of the selected path before it is detected. As shown, Fig. 1, plane polarized light from source 11 is directed through optical circulator 15, beam deflector 12 and storage medium 13 and is reflected back through the arrangement by mirror 14 along the same path, circulator 15 directing the reflected light to photodetector 16. Circulator 15 comprises a tube filled with an optical medium which exhibits the Faraday rotation effect and terminated at each end with a birefringent crystal or a Wollaston prism, and is arranged to rotate the plane of polarization of the light beam by 45 degrees so that the reflected light beam is polarized at 90 degrees to the input light beam and is thus deflected by the birefringent crystal of the circulator to photodetector 16. Medium 13 may comprise a photographic plate having a plurality of opaque spots developed therein. A half-silvered mirror may be used instead of the circulator. Each stage of the deflector 12 may comprise a single calcite crystal or a Wollaston prism (see Bell System Technical Journal, Volume 43, page 1153, May 1964) and the modulator material may comprise electro-optic KTN. In a second embodiment, Fig. 3 (not shown), mirror 14 is replaced by a second beam deflector (121) back to back with beam deflector (12), and in this embodiment circulator 15 is unnecessary. A polarizer may be used between deflector (121) and detector (16) to permit passage of only that light polarized in the direction of that comprising the selected signal. The Specification includes a mathematical analysis of the system which shows that the signal (S) to noise (N) ratio is increased by the present arrangement from where a is the light intensity-transmitted along the selected path at each stage in the beam deflector, b is the light intensity transmitted along the unselected path at each stage and n the number of stages.