Specimen identification apparatus utilizing an elliptically polarized optical autocorrelation function

1,013,129. Automatic character reading. INTERNATIONAL BUSINESS MACHINES CORPORATION. Oct. 1, 1962 [Oct. 5, 1961], No. 37076/62. Heading G4R. In a pattern identification apparatus of the kind in which the autocorrelation function of the pattern is derived optically, the light source is polarized in a first plane and the autocorrelation function is formed as a pattern of elliptically polarized light which is passed through an analyser opaque to the plane polarized light. In the form of Fig. 1, the character 28 is scanned to derive a succession of signals representing the elemental areas. These are impressed as compression-waves in a light valve 18, each compressed part having the property that the plane polarized light passing through it becomes elliptically polarized. At a certain instant after scanning the compressed areas representing the black parts of the character are positioned somewhere near the middle of the valve 18. This pattern is autocorrelated by an area of light 10 plane polarized at 12 and reflected from halfmirror through a collimating lens 16 and through the travelling pattern in light valve 18. A mirror 34 reflects the light and returns it through the light valve where light passing through the compressed parts are further elliptically polarized, and through the analyser 36 where the plane polarized light is cut out. A strip pattern of varying brightness therefore forms on ground glass screen 38 which represents the autocorrelation function of the character, as indicated in Figs. 3a, 3b. Transparencies 40, one for each possible character, are placed behind the screen each having 45 strips of varying opacity representing the autocorrelation functions of the corresponding characters. Behind each transparency 40 is a normalizing transparency 42 having an opacity such that the maximum light passed (i.e. when the corresponding character is being sensed) is the same in each case. The light transmitted is stored on a phosphor sheet 43 which serves as an integrator and strip photocells 44 give output signals proportional to the light passed the maximum signal coming from the mask and photo-cell corresponding to the character being scanned. Circuit 46 determines the lead having the highest signal. The normalizing transparencies 42 may be replaced by normalizing potentiometers in series with photo-conductors which replace the photo-cells. Since in practice the light valve is not optically perfect a compensator 32 is provided to remove elliptically p