Diffraction grating element, production method of diffraction grating element, and method of designing diffraction grating element

Abstract From the Canadian patent

In a diffraction grating element 10, between a first medium 11 and a fourth medium 14 a second medium 12 and a third medium 13 are disposed alternately to form a diffraction grating. The light which enters the diffraction grating from the first medium 11 is diffracted at the diffraction grating portion and output to a fourth medium 14. Or the light, which enters the diffraction grating from the fourth medium 14 is diffracted at the diffraction grating portion and output to the first medium 11. The index of refraction n1-n4 of each medium satisfies a relational expression of "n3<n1<n2 n3<=n4<=n2" or "n3<=n1<=n2, n3<n4<n2".