Patent ID: 8941923
Filing Date: 2015-01-27
Classification: G02B

Abstract:
1. A diffractive optical element comprising: a first diffraction grating and a second diffraction grating made of materials different from each other and are stacked in an optical axis direction, the first and second diffraction gratings each having a grating wall surface; and a thin film arranged at an interface between the grating wall surface of the first diffraction grating and the grating wall surface of the second diffraction grating, wherein the thin film is composed of a single layer or multiple layers of materials different from the materials of the first and second diffraction gratings, and is transparent to light of a working wavelength range, wherein the following conditional expressions are satisfied to enable the thin film to function as an optical wave guide when light is incident obliquely thereto: where nd1 is a refractive index of the material of the first diffraction grating to d-line, nd2 is a refractive index of the material of the second diffraction grating to the d-line, nd3 is a maximum refractive index of the material of one layer of the thin film to the d-line, w is a maximum thickness of the one layer having the maximum refractive index in the thin film, W is a total thickness of the thin film, and P is a grating pitch.