Broadband quarter-wave plates using the dispersion of form birefringence

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Subwavelength structures cause strong optical anisotropy and wavelength dispersions. The purpose of this research is to design and fabricate "achromatic quarter-wave plates" by using such features. We studied a transparent quarter-wave plate of dielectric subwavelength grating and a reflective quarter-wave plate of metal grating.To design the transparent quarter-wave plate we make a rough estimation of the grating profile by using the effective medium theory. After this estimation, the grating profile was corrected by the rigorous calculation to reduce the chromatism. A quasi-sandwich structure grating can be retain 90 degree phase retardation with deviations smaller than 3 degree for wavelength shifts by 10%. Moreover, we discussed the effective medium theory for two-dimensional subwavelength gratings and verified the validity of the effective theory.On the other hand, the effective medium theory for metallic subwavelength gratings was discussed also. It was found that the effective theory was useful only for a very fine structure of which the period was much smaller than one tenth of the wavelength. Then the reflective quarter-wave plate of metal grating was designed for 10.6mum wavelength by using a rigorous grating analysis. We tried to make the wave-plate. But it was difficult to obtain the grating profile designed because of a considerable side-etching effect.Fabrication of the wave-plates has not succeeded in this research. However a method of measurement for the distribution of anisotropy was proposed. This method can be used to measure not only plenary index distributions but also three dimensional distributions. An experiment succeeded to measure the change in anisotropy along a direction of the thickness of a few millimeters.