All-optical light modulation in pharaonis phoborhodopsin and its application to parallel logic gates

Abstract

All-optical light modulation in pharaonis phoborhodopsin (ppR) protein has been analyzed considering its ppRO state dynamics based on nonlinear intensity-induced excited-state absorption. Amplitude modulation of a cw probe laser beam transmission at 560nm corresponding to the peak absorption of ppRO intermediate state through ppR, by a modulating cw pump laser beam at 498nm corresponding to the peak absorption of initial ppR state has been analyzed considering all six intermediate states in its photocylce using the rate equation approach. The transmission characteristics have been shown to exhibit a dip at relatively lower pump intensity values compared to bacteriorhodopsin, which is sensitive to normalized small-signal absorption coefficient (β), rate constants of ppRM and ppRO states, and absorption of the ppRO state at 498nm. There is an optimum value of β for a given pump intensity range for which maximum modulation can be achieved. It is shown that 100% modulation can be achieved if the initial state of ppR does not absorb the probe beam. The results have been used to design low power all optical parallel NOT, AND, OR, XNOR, and the universal NAND and NOR logic gates for two cases: (i) only changing the output threshold and (ii) considering a common threshold with different β values. At typical parameters, wild-type (WT) ppR based logic gates can be realized at considerably lower pump powers than WT-bR.