An electro optical random access memory uses a film of bacteriorhodopsin or similar photochromic substance which can change between two light absorbing states in response to light of each of two wavelengths. In one embodiment combined red and green laser beams are steered in two orthogonal directions...http://www.google.com.au/patents/US5228001?utm_source=gb-gplus-sharePatent US5228001 - Optical random access memory
