| 摘要 |
PROBLEM TO BE SOLVED: To optionally design the center wavelength and the wavelength range from a vertical wave to oblique wave by stacking a grating layers with grating pitch smaller than the wavelength of applied light, through void layers or dielectric layers, and specifying the thickness of each layer. SOLUTION: Grating layers with a grating pitch smaller than the wavelength of the light are stacked through void layers or dielectric layers, and the thickness of each layer is to be about a quarter of either wavelength of two orthogonal polarized components of the light in each layer. That is, when grating structure is formed of isotropic material, and the grating pitch is made smaller than the wavelength, an effective refractive index in the direction of an arrow mark L (perpendicular to a grating face) differs between polarized light in a TE direction of the electric field and polarized light in a TM direction out of light entering this grating, and the refractive index of polarized light in the TM direction is larger. Such a grating is horizontally sliced and stacked with thin layers of isotropic material (or different material) placed in between, and its stack pitch P is to satisfy the effective refractive index of TE or TM polarized light×P=1/4 wavelength + 1/4 wavelength.
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