All-optical switching in bacteriorhodopsin based on M state dynamics and its application to photonic logic gates

Abstract

All-optical switching has been theoretically analyzed in bacteriorhodopsin (bR) based on nonlinear intensity induced excited state absorption of the M state. The transmission of a cw probe laser beam at 410 nm corresponding to the peak absorption of M state through a bR film is switched by a pulsed pump laser beam at 570 nm that corresponds to the maximum initial B state absorption. The switching characteristics have been numerically simulated using the rate equation approach considering all the six intermediate states (B, K, L, M, N and O) in the bR photocycle. The switching characteristics are shown to be sensitive to various parameters such as the pump pulse width, pump intensity, life time of the M state, thickness of the film and absorption cross-section of the B-state at probe wavelength ( σ Bp). It has been shown that the probe laser beam can be completely switched off (100% modulation) by the pump laser beam at relatively low pump powers, for σ Bp=0. The switching characteristics have also been used to theoretically design all-optical NOT, OR, AND and the universal NOR and NAND logic gates with two pulsed pump laser beams using the six state model.