Diffractive optical element, optical system, and optical apparatus which reduce generation of unnecessary light

Patent metadata

Field	Value
Publication number	US-2016334635-A1
Application number	US-201615149245-A
Country	US
Kind code	A1
Filing date	May 9, 2016
Priority date	May 15, 2015
Publication date	Nov 17, 2016
Grant date	—

Abstract

A diffractive optical element ( 1 ) includes a first diffraction grating ( 21 ) including a first grating surface ( 21 a ) and a first grating wall surface ( 21 b ), a second diffraction grating ( 31 ) including a second grating surface ( 31 a ) and a second grating wall surface ( 31 b ), and a thin film ( 11 ) provided between the first grating wall surface and the second grating wall surface and being in contact with both of the first and second grating wall surfaces, an extinction coefficient of the thin film with respect to a wavelength λ in a use wavelength band is not greater than 0.0005, and with respect to the wavelength λ, refractive indices of materials of the thin film, the first diffraction grating, and the second diffraction grating, a relative diffractive index difference of the thin film and the first diffraction grating, and a width of the thin film satisfy predetermined conditions.

First claim

What is claimed is:

1 . A diffractive optical element comprising:
a first diffraction grating including a first grating surface and a first grating wall surface; a second diffraction grating including a second grating surface and a second grating wall surface; and a thin film provided between the first grating wall surface and the second grating wall surface, the thin film being in contact with both of the first grating wall surface and the second grating wall surface, wherein an extinction coefficient of the thin film with respect to a wavelength λ in a use wavelength band is not greater than 0.0005, and wherein expressions below are satisfied:
n 1 >n 2 >n 3 ,
0.005<Δ<0.045, and

0.5 ≦W/W C ≦2.0,

where n 1 , n 2 , and n 3 are refractive indices of materials of the thin film, the first diffraction grating, and the second diffraction grating, respectively, with respect to the wavelength λ, Δ is a relative diffractive index difference of the thin film and the first diffraction grating, and W is a width of the thin film between the first grating wall surface and the second grating wall surface, and where Δ and W C are defined as follows:

Δ
=

n
1
2

-

n
2
2

2


n
1
2

W
C

=

W

C
,
TE

+

W

C
,
TM

2

W

C
,
TE

=

1

κ
C



tan

-
1



(

δ
C

κ
C

)

W

C
,
TM

=

1

κ
C



tan

-
1

(

n
1
2



δ
C

n
3
2



κ
C

)

κ
C

=

k
0



n
1
2

-

n
2
2

δ
C

=

k
0



n
2
2

-

n
3
2

k
0

=

2


π
/

λ
.

2 . The diffractive optical element according to claim 1 , wherein an expression below is satisfied:
0≦( n eq −n 2 )× d/λ< 0.3,
where d is a grating height of each of the first diffraction grating and the second diffraction grating, and n eq is an equivalent refractive index of propagation light that is propagated inside the thin film, wherein the equivalent refractive index n eq is defined as follows:

n
eq

=

n

eq
,
TE

+

n

eq
,
TM

2

n

eq
,
TE

=

β
TE

/

k
0

Assignees

• Canon Kk

Inventors

• Ushigome Reona

Classifications

• G02B27/0018

  with means for preventing ghost images (anti-reflection coatings G02B1/11) · CPC title

• G02B27/4261

  having a diffractive element with major polarization dependent properties · CPC title

• G02B27/4272 Primary

  having plural diffractive elements positioned sequentially along the optical path · CPC title

• G02B27/4205

  having a diffractive optical element [DOE] contributing to image formation, e.g. whereby modulation transfer function MTF or optical aberrations are relevant · CPC title