Space-invariant optical correlator using a photorefractive medium

Abstract Scale and rotation invariant polar-logarithmic coordinate transformation is used to achieve deformation invariant pattern recognition. The coordinate transformation is produced by a computer generated hologram (CGH). The mask fabricated by a photo (ultra-violet light) pattern generator for the In( r )-θ coordinate transformation is made of the CGH whose transmission function is derived by the use of the stationary phase method. The optically produced coordinate transformed input pattern is interfaced to an optical correlator. A BaTiO 3 single crystal is used as a real-time matched filter based on real-time holography.