US 10,890,698 B2
Diffraction optical element, optical system, and imaging apparatus
Mikio Kobayashi, Utsunomiya (JP)
Assigned to CANON KABUSHIKI KAISHA, Tokyo (JP)
Filed by CANON KABUSHIKI KAISHA, Tokyo (JP)
Filed on Oct. 9, 2018, as Appl. No. 16/154,789.
Claims priority of application No. 2017-198312 (JP), filed on Oct. 12, 2017.
Prior Publication US 2019/0113663 A1, Apr. 18, 2019
Int. Cl. G02B 5/18 (2006.01)
CPC G02B 5/1871 (2013.01) [G02B 5/1823 (2013.01)] 13 Claims
OG exemplary drawing
 
1. A diffraction optical element comprising:
a first diffraction grating having a first grating surface and a first grating wall surface;
a second diffraction grating having a second grating surface and a second grating wall surface; and
a plurality of thin films configured to contact the first grating wall surface and the second grating wall surface,
wherein the following conditional expressions are satisfied:
n2<n1<nha,
−0.500<Pe/Pmax<0.700, and
0.013<Pma<0.035
where n1 and n2 are refractive indexes for a designed wavelength of the first diffraction grating and the second diffraction grating, nha is a refractive index for the designed wavelength of each of the plurality of thin films in an effective diameter, Pmax is a maximum value of a phase difference for the designed wavelength between the first diffraction grating and the plurality of thin films in the effective diameter, Pe is a phase difference for the designed wavelength between the first diffraction grating and an outermost thin film among the plurality of thin films in the effective diameter, and Pma is a phase difference for the designed wavelength between the first diffraction grating and a thin film other than the outermost thin film among the plurality of thin films in the effective diameter.