Patent ID: 6900939

Claim:
A beam splitting element comprising: a diffraction grating splitting an incident luminous flux into a plurality of luminous fluxes, wherein, the diffraction grating satisfies the following condition: n·d·w/p ≧0.670 (μm) where a refraction index of grating material is n, grating depth is d, a grating period is p, and grating width is w, the grating period p satisfies the following condition: λ 0 ( n ·sin θ+ n ′)< p ≦2·λ 0 /( n ·sin θ+ n ′) where a design wavelength is λ 0 , an incident angle is θ, and a refraction index of an outgoing-side medium is n′, and a section of the diffraction grating is substantially rectangular in shape, and a ratio w/p of the grating width w to the grating period p satisfies the following condition: 0.6 ≦w/p ≦0.8.