Integrated Optical Switching Based on the Protein Bacteriorhodopsin†

According to our earlier pioneering study, a dry film containing native bacteriorhodopsin (bR) shows unique nonlinear optical properties (refractive index change, controllable by light of different colors, greater than 2 × 10−3) that are in many respects superior to those of the materials presently applied in integrated optics. Here, we report on the first integrated optical application based on a miniature Mach–Zehnder interferometer (see 1, 2) demonstrating a real switching effect by bR (efficiency higher than 90%) due to the M-state. Our results also imply that the refractive index change of the K-state (9 × 10−4) is high enough for fast switching. Figure 1Open in figure viewerPowerPoint Electron micrograph images of the photopolymeric Mach–Zehnder interferometer (two oppositely joined Y-junctions, symmetrically dividing and rejoining the beams, respectively). (a) Cross-sectional view of a single strip. (b) Side view of a single strip. (c) View of a Y-branch. (d) View of the whole Mach–Zehnder structure (shaded inside). Figure 2Open in figure viewerPowerPoint Photographs of the Mach–Zehnder interferometer guiding green light (488 nm line of an Ar-ion laser).