Optoelectronic Devices Based on the Nonlinear Optical Properties of Bacteriorhodopsin

András Dér, László Fábián, Loránd Kelemen, László Oroszi and Pál Ormos

Institute of Biophysics, Biological Research Centre of the Hungarian Academy of Sciences, P.O. Box 521, H-6701 Szeged, Hungary

e-mail: pali@everx.szbk.u-szeged.hu

Non linear optical (NLO) materials change their optical properties upon external effects, most prominently the index of refraction and absorption upon illumination. They offer great possibilities in optically active devices, applications in optoelectronics.

Recently, materials of biological origin have emerged as an interesting option for NLO materials with practical possibilities. Bacteriorhodopsin, the light driven transmembrane proton pump from the cell membrane of Halobacterium salinarium in a promising candidate for such applications. The function of bacteriorhodopsin is based on a light induced sequence of photochemical reactions, the photocycle. The photocycle proceeds through several well defined steps, the intermediate states. The intermediates have different light absorption maxima. During the photocycle, primarily due to the immense absorption shifts during the reactions between the intermediates (e.g. > 200 nm between the K and M forms), bacteriorhodopsin is also expected to exhibit also large changes in the refractive index as it can be estimated from the Kramers-Kronig relation. The change of these optical properties may be utilised in practical applications.

We explored the possibility to apply bacteriorhodopsin as an active nonlinear material in combination with optical waveguides, the fundamental component of integrated optoelectronic devices. Using waveguides into which the light is coupled by grating, we determined both the static optical properties of bacteriorhodopsin as well as the changes of the refractive index during the photocycle. The waveguide with grating coupler in combination with bacteriorhodopsin provides a proof-of-concept optically controlled optical switch - the basic element for promising complex optoelectronic applications.