Logarithmic Output from Cascaded Two-beam Coupling Interactions in Photorefractive Crystals

A scheme is presented that uses cascaded two-beam coupling interactions to optically generate a log transform. By optimizing the two free parameters of gain coefficient and beam intensity ratio for each interaction region, we have generated a computed output intensity that is the natural log of the input intensity, with an accuracy of better than 1% over a four decade dynamic range.