DIRECTION SENSING ROTATIONAL FILTER FOR AN OPTICAL CORRELATOR

The output of an optical correlator is sensitive to rotations of the i nput object. However, the correlator cannot distinguish the direction of this rotation (clockwise or counterclockwise). We introduce a rotat ionally sensitive multiplexed filter that senses both the direction an d amount of rotation of the input object without employing iterative f ilter techniques. Our filter simultaneously forms three correlation ou tputs at three different spatial locations. Each output represents the correlation of the input object with a different rotated Version of t he reference object. Comparison of the three correlation outputs enabl es the direction and amount of rotation to be determined. This approac h is insensitive to changes in the input object intensity because the various correlation peaks are formed simultaneously. Experimental resu lts show an angular sensitivity of less than 0.5 deg. (C) 1998 Society of Photo-Optical Instrumentation Engineers. [S0091-3286(98)00401-2].