| 摘要 |
A beam splitting element having a diffraction grating improves the reduction and polarization dependence of a diffraction efficiency while achieving a desired splitting angle. In a beam splitting element constituted by a diffraction grating that splits an incident luminous flux into a plurality of luminous fluxes according to wavelengths, the diffraction grating satisfies the following condition: n.d.w/p>=0.670(mum) where a refraction index of grating material is n, grating depth is d, a grating period is p and grating width is w. And the grating period p satisfies the following condition: lambd0/(n.sintheta+n')<p<=2.lambd0/(n.sintheta+n') where a design wavelength is lambd0, an incident angle is theta, and a refraction index of an outgoing-side medium is n'.
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