DIFFRACTIVE OPTICAL ELEMENT, OPTICAL SYSTEM AND OPTICAL APPARATUS

• US 20080231956A1
• Filed: 10/05/2007
• Published: 09/25/2008
• Est. Priority Date: 03/23/2007
• Status: Active Grant

• Current Assignee: Canon Kabushiki Kaisha (Canon Inc.)
• Original Assignee: Canon Kabushiki Kaisha (Canon Inc.)
• Inventors: Yasui, Hiroto
• Granted Patent: US 7,710,651 B2
• Time in Patent Office: Days
• US Class Current: 359/576
• CPC Class Codes: G02B 1/04 made of organic materials, e.g. plastics G02B1/08 takes precedence
• CPC Class Codes: G02B 27/0037 with diffracting elements G02B27/0056 takes precedence; holographic optical elements G02B5/32; zone systems G02B5/1876
• CPC Class Codes: G02B 27/4211 correcting chromatic aberrations G02B27/0056, G02B27/4222, G02B27/4227 take precedence
• CPC Class Codes: G02B 27/4272 having plural diffractive elements positioned sequentially along the optical path
• CPC Class Codes: G02B 5/1823 in an overlapping or superposed manner
• CPC Class Codes: G02B 5/1866 Transmission gratings characterised by their structure, e.g. step profile, contours of substrate or grooves, pitch variations, materials G02B5/1809, G02B5/1828, G02B5/1833, G02B5/1838 and G02B5/1847 take precedence

Abstract

The diffractive optical element includes two diffraction gratings made of different materials and being in contact with each other at their grating surfaces. The materials satisfy the following conditions, and the second material is obtained by mixing a resin material with a particulate material satisfying the following conditions: nd1≧1.48, νd1≧40, (−1.665E−07×νd1³+5.213E−05×νd1²−5.656E×03×νd1+0.675)≦θg,F1≦(−1.665E−07×νd1³+5.213E−05×νd1²−5.656E−03×νd1+0.825), (−1.687E−07×νd1³+5.702E−05×νd1²−6.603E−03×νd1+1.400)≦θg,d 1≦(−1.687E−07×νd1³+5.702E−05×νd1²−6.603E−03×νd1+1.580), nd2≦1.6, νd2≦30, θg,F2≦(−1.665E−07×νd2³+5.213E−05×νd2²−5.656E−03×νd2+0.675 ), θg,d2≦(−1.687E−07×νd2³+5.702E−05×νd2²−6.603E−03×νd2+1.400 ), nd1-nd2≧0, ndb2≧1.70, νdb2≦20. The element achieves a high diffraction efficiency in a specific diffraction order over a wide wavelength range.

Claims

1. A diffractive optical element, comprising:

two diffraction gratings made of a first material and a second material, respectively, the two diffraction gratings each having a grating surface and being in contact with each other at the grating surfaces,

wherein the first and second materials satisfy all of the following conditions, and the second material is a material obtained by mixing a resin material with a particulate material satisfying all of the following conditions;

nd1≧

1.48

ν

d1≧

40

(−

1.665E−

07×

ν

d1³+5.213E−

05×

ν

d1²−

5.656E−

03×

ν

d1+0.675) ≦

θ

g,F1≦

(−

1.665E−

07×

ν

d1³+5.213E−

05×

ν

d1²−

5.656E−

03×

ν

d1+0.825)

(−

1.687E−

07×

ν

d1³+5.702E−

05×

ν

d1²−

6.603E−

03×

ν

d1+1.40

     0) ≦

θ

g,d1≦

(−

1.687E−

07×

ν

d1³+5.702E−

05×

ν

d1²−

6.603E−

03 ×

ν

d1+1.58

     0)

nd2≦

1.6

ν

d2≦

30

θ

g,F2≦

(−

1.665E−

07×

ν

d2³+5.213E−

05×

ν

d2²−

5.656E−

03 ×

ν

d2+0.675)

θ

g,d2≦

(−

1.687E−

07×

ν

d2³+5.702E−

05×

ν

d2²−

6.603E−

03×

ν

d2+1.400)

nd1−

nd2>

0

ndb2≧

1.70

ν

db2≦

20

where ng1, nF1, nd1, and nC1 are refractive indexes of the first material for g-line, F-line, d-line, and C-line, respectively,

ng2, nF2, nd2, and nC2 are refractive indexes of the second material for g-line, F-line, d-line, and C-line, respectively, and

nFb2, ndb2, and nCb2 are refractive indexes of the particulate material for F-line, d-line, and C-line, respectively, and

ν

d1=(nd1−

1)/(nF1−

nC1)

ν

d2=(nd2−

1)/(nF2−

nC2)

θ

g,F1=(ng1−

nF1)/(nF1−

nC1)

θ

g,d1=(ng1−

nd1)/(nF1−

nC1)

θ

g,F2=(ng2−

nF2)/(nF2−

nC2)

θ

g,d2=(ng2−

nd2)/(nF2−

nC2)

μ

db2=(ndb2−

1)/(nFb2−

nCb2).

2. A diffractive optical element according to claim 1,

wherein the first and second materials further satisfy all of the following conditions:

m(λ

F)={d×

(nF1−

nF2)}/λ

F

m(λ

d)={d×

(nd1−

nd2)}/λ

d

m(λ

C)={d×

(nC1−

nC2)}/λ

C

d≦

20

0.92≦

{m(λ

F)+m(λ

d)+m(λ

C)}/3≦

1.08

where λ

F, λ

d, and λ

C are wavelengths of F-line, d-line, and C-line, respectively,

m(λ

F) is a value obtained by dividing a difference in optical path length between a convex portion and a concave portion of each diffraction grating for m-th order diffracted light as designed order diffracted light at the wavelength of F-line by the wavelength of F-line,

m(λ

d) is a value obtained by dividing a difference in optical path length between the convex portion and the concave portion of each diffraction grating for the m-th order diffracted light at the wavelength of d-line by the wavelength of d-line,

m(λ

C) is a value obtained by dividing a difference in optical path length between the convex portion and the concave portion of each diffraction grating for the m-th order diffracted light at the wavelength of C-line by the wavelength of C-line, and

d (μ

m) is a grating thickness of the diffraction gratings.

3. A diffractive optical element according to claim 1,

wherein the first material is a material obtained by mixing a resin material with a particulate material satisfying all of the following conditions:

ndb1≧

1.65

ν

db1≧

35

where ndb1 is a refractive index of the particulate material for d-line, and

ν

db1=(ndb1−

1)/(nFb1−

nCb1)

where nFb1, and nCb1 are refractive indexes of the particulate material for F-line and C-line, respectively.

4. A diffractive optical element according to claim 3,

wherein an average particle diameter of the particulate material is equal to or less than ¼

of a wavelength of light incident on the diffractive optical element.

5. A diffractive optical element according to claim 1,

wherein the first material is a resin material without a particulate material mixed therein.

6. A diffractive optical element according to claim 1,

wherein the first material is a glass material.

7. A diffractive optical element according to claim 6,

wherein the glass material has a deformation point of equal to or lower than 600°

C.

8. A diffractive optical element according to claim 7, wherein the element further satisfies the following conditions:

(T1(λ

1)×

T2(λ

1)×

η

(λ

1)+T1(λ

2)×

T2(λ

2)×

η

(λ

2)+T1(λ

3)×

T2(λ

3)×

η

(λ

3))/3≧

0.70

where λ

1, λ

2, and λ

3 are wavelengths of 450 nm, 550 nm, and 650 nm, respectively,

η

(λ

1), η

(λ

2), and η

(λ

3) are diffraction efficiencies at the wavelengths of λ

1, λ

2, and λ

3, respectively,

T1(λ

1), T1(λ

2), and T1(λ

3) are internal transmittances of the first material at the wavelengths of λ

1, λ

2, and λ

3, respectively, and

T2(λ

1), T2(λ

2), and T2(λ

3) are internal transmittances of the second material at the wavelengths of λ

1, λ

2, and λ

3, respectively.

9. A diffractive optical element according to claim 1, wherein the element further satisfies the following condition:

d/P<

1/7

where P and d are a grating pitch and a grating thickness of the diffraction gratings, respectively.

10. An optical system comprising a diffractive optical element according to claim 1.

11. An optical apparatus comprising an optical system including a diffractive optical element according to claim 1.