DIFFRACTIVE OPTICAL ELEMENT AND OPTICAL SYSTEM USING THE SAME

• US 20080239493A1
• Filed: 03/21/2008
• Published: 10/02/2008
• Est. Priority Date: 03/28/2007
• Status: Active Grant

• Current Assignee: Canon Kabushiki Kaisha (Canon Inc.)
• Original Assignee: Canon Kabushiki Kaisha (Canon Inc.)
• Inventors: Ushigome, Reona
• Granted Patent: US 7,916,394 B2
• Time in Patent Office: Days
• US Class Current: 359/576
• CPC Class Codes: G02B 27/42 Diffraction optics , i.e. systems including a diffractive element being designed for providing a diffractive effectG02B27/60 takes precedence
• CPC Class Codes: G02B 27/4211 correcting chromatic aberrations G02B27/0056, G02B27/4222, G02B27/4227 take precedence
• CPC Class Codes: G02B 27/4216 correcting geometrical aberrations
• CPC Class Codes: G02B 27/4272 having plural diffractive elements positioned sequentially along the optical path
• CPC Class Codes: G02B 27/4283 having a diffractive element with major temperature dependent properties

Abstract

A diffractive optical element includes stacked first and second diffraction gratings made of different materials. The materials of the first and second diffraction gratings are glass. The first and second diffraction gratings have grating surfaces contacted to each other. The materials satisfy a predetermined condition when Tg2 and At2 are a transformation point temperature and a yield point temperature of the material of the first diffraction grating, and Tg3 and At3 are a transformation point temperature and a yield point temperature of the material of the second diffraction grating.

Claims

1. A diffractive optical element comprising:

stacked first and second diffraction gratings made of different materials,

wherein the materials of the first and second diffraction gratings are glass,

wherein the first and second diffraction gratings have grating surfaces contacted to each other,

wherein the materials satisfy the following conditions,

Tg2≦

600°

C., and

Tg3<

600°

C., and

wherein the materials satisfy one of the following conditions,

Tg2≠

At3, and

Tg3≠

At2,

where Tg2 and At2 are a transformation point temperature and a yield point temperature of the material of the first diffraction grating, and Tg3 and At3 are a transformation point temperature and a yield point temperature of the material of the second diffraction grating.

2. The diffractive optical element according to claim 1,

wherein the first and second diffraction gratings are made of the materials satisfying one of the following conditions,

Tg3>

At2, and

Tg2>

At3.

3. The diffractive optical element according to claim 1,

wherein the first and second diffraction gratings are made of the materials satisfying one of the following conditions,

Tg3−

At2>

50°

C., and

Tg2−

At3>

50°

C.

4. The diffractive optical element according to claim 1, further comprising a third diffraction grating at least at one of surfaces of the first and second diffraction gratings, the surfaces being opposite to the grating surfaces contacted to each other.

5. The diffractive optical element according to claim 4,

wherein the following condition is satisfied,

At24<

Tg3a

where At24 is a yield point temperature of a material of the third diffraction grating, and Tg3a is a transformation point temperature of the material of the diffraction grating without the third diffraction grating at the surface opposite to the contacted grating surface.

6. The diffractive optical element according to claim 1, wherein a total grating thickness of the first and second diffraction gratings is 20 μ

m or smaller.

7. The diffractive optical element according to claim 1, wherein an Abbe number ν

d of at least one of the materials of the first and second diffraction gratings is 40 or smaller.

8. The diffractive optical element according to claim 1, wherein an Abbe number ν

d of at least one of the materials of the first and second diffraction gratings is 50 or greater.

9. The diffractive optical element according to claim 1, wherein one of the first and second diffraction gratings is molded using a metal mold, and the other diffraction grating is molded using the molded one diffraction grating as a glass mold.

10. The diffractive optical element according to claim 1, wherein a thickness of the second diffraction grating is 0.5 mm or greater.

11. The diffractive optical element according to claim 1, wherein an outer diameter of the second diffraction grating is smaller than an outer diameter of the first diffraction grating.

12. The diffractive optical element according to claim 1, further comprising an adhesion layer between interfaces of the contacted grating surfaces.

13. The diffractive optical element according to claim 1, further comprising an antireflection layer between interfaces of the contacted grating surfaces.

14. The diffractive optical element according to claim 1, wherein at least one of the first and second diffraction gratings has a curved surface opposite to the contacted grating surface.

15. The diffractive optical element according to claim 14, wherein the one diffraction grating and the curved surface opposite to the grating surface are simultaneously molded.

16. The diffractive optical element according to claim 1, further comprising a refractive optical portion.

17. An optical system comprising:

the diffractive optical element according to claim 1; and

a refractive optical portion.

18. A method of manufacturing a diffractive optical element including stacked first and second diffraction gratings made of different materials, the method comprising:

molding the second diffraction grating using a metal mold at a molding temperature of a yield point temperature or higher of the material of the second diffraction grating;

cooling the second diffraction grating to a transformation point temperature or lower of the material of the second diffraction grating while being contacted to the metal mold, and removing the metal mold;

molding the first diffraction grating using the molded second diffraction grating as a glass mold at a molding temperature in a range from the transformation point temperature or lower of the material of the second diffraction grating to a yield point temperature or higher of the material of the first diffraction grating; and

cooling the first and second diffraction gratings while being contacted to each other.

19. A method of manufacturing a diffractive optical element including stacked first and second diffraction gratings made of different materials, the method comprising:

molding the second diffraction grating using a first metal mold at a molding temperature of a yield point temperature or higher of the material of the second diffraction grating;

cooling the second diffraction grating to a transformation point temperature or lower of the material of the second diffraction grating while being contacted to the first metal mold, and removing the first metal mold;

molding the first diffraction grating and a third diffraction grating at a surface opposite to the first diffraction grating using the molded second diffraction grating as a glass mold and a second metal mold for a surface opposite to the second diffraction grating at a molding temperature in a range from the transformation point temperature or lower of the material of the second diffraction grating to a yield point temperature or higher of the material of the first diffraction grating;

cooling the first and second diffraction gratings and the second metal mold to a transformation point temperature or lower of the material of the first diffraction grating while being contacted to each other, and removing the second metal mold; and

cooling the first and second diffraction gratings while being contacted.