Bacteriorhodopsin films as spatial light modulators for nonlinear-optical filtering.

The application of dry purple membrane films for nonlinear-optical filtering is described. The biological photochrome bacteriorhodopsin (BR) is contained in the purple membrane (PM) from Halobacterium halobium. BR has two dominant photoactive states, B and M, which have well-separated absorption bands with maxima at 570 nm (B) and 412 nm (M). Since the local transmission of a PM film depends on the ratio between the forward (B ? M) and the backward (M ? B) photoreactions, PM films can be used as light-controlled absorptive spatial light modulators. A model describing the nonlinear transmission of PM films containing the wild-type form of BR or one of its mutated variants, e.g., BR(D96N), and examples of their application in spatial filtering, e.g., edge enhancement, are presented.