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

摘要

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 0) 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 (sigma(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 sigma(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. (C) 2003 Elsevier Science B.V. All rights reserved. [References: 36]