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

利用表面等离子体共振技术制备了非线性光学器件。在该装置中，通过离心机制备的细菌视紫红质膜沉积在薄银膜涂层的棱镜表面。随着入射光束强度的增加，反射率与入射角的共振倾角向低角度偏移。得到的非线性折射率为n_2=-0.054cm^2/W。然而，这种装置是不稳定的，因为细菌视紫红质薄膜会随着时间的推移而收缩并被移除。为了解决这一问题，开发了一种采用泄漏模光波导的替代器件，该器件采用掺杂染料的聚合物薄膜作为非线性波导层。在这种装置中，波导中的场比表面等离子体共振的场大。在实验中，用氩离子激光束测量了以双（4-二甲氨基-二噻吩）镍掺杂PMMA薄膜作为波导层的器件的反射率与入射角的关系。谐振角发生了几毫瓦的位移，光学双稳性达到了几十毫瓦。然而，由于热效应，高强度的波导层被破坏。为了获得更高的场增强，考虑了小胶体金颗粒在波导上的沉积。数值计算证实，粒子与波导之间的场增强了。本文还提出了用光束传播法分析光束在细菌-视紫红质膜等非线性光学介质中传播的数值方法。该方法的计算结果与实验结果非常吻合。

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.