All-optical light modulation in bacteriorhodopsin films

We report a convenient method to obtain all-optical light modulation in bacteriorhodopsin films using a degenerate four-wave mixing geometry. Chemically stabilized films of bacteriorhodopsin in a polymer matrix for which the lifetime of the excited M state is tens of seconds were used to demonstrate all-optical light intensity modulation. The films are observed to be stable over a period of 4 years. Due to the sensitivity of the films, small intensities of order microwatt/ cm2 are required in the modulation experiments. Furthermore the fast photochemical transition from M to B permit reasonably fast modulation speeds independent of the slow thermal M and B relaxation time. The experimental system also acts as an all-optical switch where a low power blue pulse turns on a signal red beam.