Holographic angle sensor

An apparatus for determining the angular orientation of an object, comprising:

• (a) means for generating a partially coherent light beam;
• (b) reflector means positioned on said object, said reflector means including means for producing at least two derivative beams from an incident beam, said beam producing means being positioned relative to said reflector means such that a light beam passes through said beam producing means upon entry and exit from said reflector means, wherein said beam producing means produces two original derivative beams from an incident beam entering said reflector means in such a manner that said two original beams travel paths of different length within the reflector means between entry and exit thereof, the difference in path length between said two original beams being representative of the angular orientation of the object, and wherein said beam producing means produces at least two additional divergent beams from each of said two original beams upon exit of the original beams from said reflector, at least one additional beam produced from one of the original beams being parallel to one additional beam produced from the other of the original beams, said two parallel beams being characterized by a separation sufficiently small that the wavefronts thereof are substantially equally affected by changes in the index of refraction across the medium through which said two parallel means are moving;
• and
• (c) means for measuring the change in optical phase of said two parallel beams, which value of phase change is a function of the angular orientation of the object and hence is correlatable to a corresponding value of the angular orientation of the object.