Nonlinear Optical Device using Bacteriorhodopsin and Surface Plasmon Resonance and Its Applications

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A nonlinear optical device using surface plasmon resonance was fabricated. In the device a bacteriorhodopsin film, which was prepared by a centrifuge, was deposited on a thin-silver-film coated prism surface. The resonance dip shown in the reflectance versus the angle of incidence shifted toward lower angle as the intensity of the incident beam increased. The obtained nonlinear index of refraction was n_2=-0.054cm^2/W.However, the device is unstable because the bacteriorhodopsin film shrinks and is removed with time. To solve this problem an alternative device using a leaky-mode optical waveguide, in which a dye-doped polymer film was used as a nonlinear waveguide layer, was developed. In this device the field in the waveguide is larger than that by the surface plasmon resonance. In the experiments the reflectance versus the angle of incidence was measured with argon-ion laser beam for a device using bis (4-dimethylamino-dithiobenzil) nickel doped PMMA film as the waveguide layer. The resonance angle shifted for a few mW and optical bistability was observed for a few ten mW.However, the waveguide layer is damaged for the high intensity due to a thermal effect. For the higher field enhancement the deposition of small colloidal gold particles on the waveguide was considered. It was numerically confirmed that the field between the particles and the waveguide was much enhanced. The numerical method analyzing the propagation of beams in nonlinear optical media, e. g. bacterio-rhodopsin film, using the beam propagation method was also developed. The results using this method agreed very much with the experimental ones.