Vitamin A, all-trans-retinol is the presursor of 11-cis-retinal. The retinal prosthetic group is a light-absorbing component known as a chromophore in rhodopsin and bacteriorhodopsin. Rhodopsin is the chromoprotein found in the visual system of higher invertebrates and vertebrates(Oesterhelt and Stoeckenius, 1971). The bacteriorhodopsin is the counterparts in Halobacterium halobium, a salt-loving bacterium, growing optimally in salt marsh with sodium chloride concentration of 4M or more. Upon light excited, the common chromophore structure- a 11-cis-retinal molecule-in both rhodopsin and bacteriorhodopsin must undergo a photocycle-series of structural changes, and thereby alters the conformation of the rest of the protein. Because rhodopsin and bacteriorhodopsin adopts different, readily detectable states in response to light( Henderson et al, 1990; Mathies et al., 1991: Khorana, 1988: Osterhelt et al., 1989), and especially for bacteriorhodopsin's stability to withstand changes in its environment and its availability in large quantities, they can serve as logic gates, or switches, in protein-based optical computers( Birge, 1995). Because of the structural similarity between bacteriorhodopsin and rhodopsin, and the common retinal function, the cheaper and more abundant bacteriorhodopsin can be exploited for use as an artificial retina to substitute rhodopsin(Freedman, 1991).