Diffractive optical element, optical system, and optical apparatus

An optical system comprising:

• a diffractive optical element;
• and
• a stop arranged at a downstream side of an optical path of the diffractive optical element,
• wherein the diffractive optical element comprises:
• 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:
• nd1<nd2;
• 0.5<nd3−nd2<0.8;
• 0<w<2 μm;
• and
• 0<W/P<0.05,
• 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.

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;
• and
• a thin film arranged at least part of an interface between the first diffraction grating and the second diffraction grating, and functions as an optical wave guide when light is incident obliquely thereto,
• wherein the thin film is composed of 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 multiple layers of the thin film are arranged with layers of higher and lower refractive indices, and
• wherein a layer having the higher refractive index is physically thicker than a layer having the lower refractive index among the multiple layers.

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:
• nd1<nd2;
• 0.5<nd3−nd2<0.8;
• 0<w<2 μm;
• and
• 0<W/P<0.05,
• 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, and
• wherein the material of the first diffraction grating is fluorine acrylic UV curing resin mixed with ITO nanoparticles, and the material of the second diffraction grating is acrylic UV curing resin mixed with ZrO2 nanoparticles.