Broadband quarter-wave plates using the dispersion of form birefringence

亚波长结构引起强烈的光学各向异性和波长色散。本研究的目的就是利用这些特性来设计和制造“消色差四分之一波片”。研究了介质亚波长光栅的透明四分之一波片和金属光栅的反射四分之一波片。为了设计透明的四分之一波片，我们利用有效介质理论对光栅轮廓进行了粗略估计。在此基础上，通过严格的计算对光栅轮廓进行校正，以减小色差。准夹层结构光栅在波长偏移10%的情况下仍能保持90度的相位延迟，且相位延迟偏差小于3度。讨论了二维亚波长光栅的有效介质理论，并验证了有效介质理论的有效性。另一方面，还讨论了金属亚波长光栅的有效介质理论。人们发现，有效理论只适用于周期远小于十分之一波长的非常精细的结构。然后，通过严格的光栅分析，设计了10.6mum波长的金属光栅反射四分之一波片。我们试着做波浪板。但由于有相当大的侧蚀刻效应，难以获得设计的光栅轮廓。波浪片的制作在本研究中尚未成功。提出了一种测量各向异性分布的方法。该方法不仅可以测量全指数分布，而且可以测量三维分布。实验成功地测量了各向异性沿几毫米厚度方向的变化。

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.