Porous anodic alumina films were studied to realize artificial metal-dielectric composites for polarizers. By the improved anodizing and electroplating procedures, nickel was deposited successfully as thick as50 µm in the pores. Optical transmittance of the film was measured in the wavelength range of 0.63-1.55 µm and a notable polarizing function was confirmed. The extinction ratio and the insertion loss were evaluated to be 41 dB and 1.3 dB, respectively, at the wavelength of 1.55 µm.

The complex refractive indices n-jχ of typical magnetic fluids were evaluated for the sake of utilizing them as optical materials. Transmission and reflection spectra were measured in the wavelength range of 0.6-1.6 µm by using monochromators. Magnetic fluids were put into glass cells of 2.5-14-µm thickness for transmission measurement. Due to the absorption by magnetic fluids, the transmittance decreased notably with the increase of the sample thickness. The extinction coefficient χ was evaluated from the dependence of the transmittance on the sample thickness. χ was found to vary between 0.003 and 0.03 depending upon wavelength. The refractive index n was evaluated by fitting theoretical curves to the reflectances that were measured for various incident angles. n was found to vary between 1.6 and 1.7 depending slightly on wavelength. Since a magnetic fluid is a composite of ferrite particles and a solvent, the refractive index can be calculated by using the effective medium theory. The calculated value agreed well with the experimental value. Preliminary experiment of optical switching was also demonstrated by utilizing the mobility of a magnetic fluid.