Multiple Grating Optical Processing in Barium Titanate

Nonlinear optical image subtraction and Boolean XOR operations have been demonstrated in Michelson interferometers with phase conjugate mirrors [1-3], The two interferometer arms each contain a light modulating transmission or reflection element which must be carefully registered and imaged at the interferometer output. Destructive interference between the output images of the two arms arises because one image undergoes a extra π phase change on reflection from a dielectric interface. Image subtraction has also been achieved in photorefractives via double exposure holography [4] where two gratings are formed by displacing the reference beam in phase by π. A π phase shift on one of the writing beams in four wave mixing has also been used to selectively erase volume holograms in photoreffactive media [5-7].