Diffractive optical element

• US 6,587,272 B2
• Filed: 06/08/1999
• Issued: 07/01/2003
• Est. Priority Date: 06/16/1998
• Status: Expired due to Fees

• Current Assignee: Canon Ayutthaya Limited (Canon Inc.)
• Original Assignee: Canon Ayutthaya Limited (Canon Inc.)
• Inventors: Nakai, Takehiko
• Primary Examiner(s): CHANG, AUDREY Y
• Application Number:
  US09/327,474
• Publication Number:
  US 20020012170A1
• Time in Patent Office: 1,484 Days
• Field of Search: 359/569, 359/571, 359/573, 359/574, 359/575, 359/576, 359/566, 359/565
• US Class Current: 359/569
• 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

A diffractive optical element is composed of a plurality of diffraction gratings which differ in dispersion from each other and are laminated while being spaced to enhance diffraction efficiency for a particular order (design order) throughout an entire usable wavelength region, wherein edges of at least part of corresponding grating portions of the plurality of diffraction gratings are shifted from each other in a direction of arrangement of grating portions of each diffraction grating.

Claims

1. A diffractive optical element, comprising two diffraction gratings composed of materials differing in dispersion from each other, and which are laminated with a separation between the gratings, which allows for enhancing diffraction efficiency for a particular design order throughout a predetermined wavelength region, wherein edges of at least part of corresponding grating portions of said two diffraction gratings are shifted from each other in a direction of grating pitch of each diffraction grating, and a grating thickness of one of the gratings in one period thereof increases monotonically along one direction of the grating pitch.

2. A diffractive optical element according to claim 1, wherein said diffractive optical element has a plurality of areas, and edges of corresponding grating portions of laminated diffraction gratings in part of the plurality of areas are shifted from each other.

3. A diffractive optical element according to claim 1, wherein shifting of edges between corresponding grating portions of said two diffraction gratings is realized by changing the width of a grating pitch at particular locations of the grating portions.

8. A diffractive optical element according to either of claims 1 and 4, wherein, where n1L and n2L are refractive indices for an arbitrary wavelength λ

on a light-entrance side and a light-exit side, respectively, of a material of the L-th diffraction grating, when counted from a substrate, of said two diffraction gratings, θ

L is an angle of an incident ray makes with a normal line of the L-th diffraction grating, P is a grating pitch, dL is a grating thickness of the L-th diffraction grating, and DL is a distance between the L-th diffraction grating and the (L+1 )st diffraction grating, a positional shift Δ

×

L between edges of corresponding grating portions of the (L+1)st diffraction grating and the L-th diffraction grating satisfies the following condition;

9. A diffractive optical element according to either of claims 1 and 4, wherein the predetermined wavelength region is a visible spectrum.

10. A diffractive optical element according to either of claims 1 and 4, wherein the first diffraction grating, when counted from a substrate, of said two diffraction gratings is made from the same material as that of the substrate.

11. A diffractive optical element according to either of claims 1 and 4, wherein said two diffraction gratings have respective grating portions, edges or pitches of which are shifted or different from each other, with said two diffraction gratings confronting each other across an air layer.

23. An optical system using said diffractive optical element according to one of claims 1, 4, 12 and 15.

24. An optical system according to claim 23, wherein said optical system is an image forming optical system.

25. An optical system according to claim 23, wherein said optical system is an observing optical system.

26. A diffractive optical element according to anyone of claims 1, 4, 12 and 15, wherein, when said two diffraction gratings are circular gratings, the one direction of the grating pitch is a direction from a center of the grating to a margin of the grating.

4. A diffractive optical element, comprising two diffraction gratings composed of materials differing in dispersion from each other and which are laminated with a separation between the gratings, which allows for enhancing diffraction efficiency for a particular design order throughout a predetermined wavelength region, wherein grating pitches of at least part of corresponding grating portions of said two diffraction gratings are different from each other, and a grating thickness of one of the gratings in one period thereof increases monotonically along one direction of the grating pitch.

5. A diffractive optical element according to claim 4, wherein a grating pitch of each of said two diffraction gratings is gradually varied, and shifting of edges between corresponding grating portions of said two diffraction gratings becomes larger accordingly as the grating pitch of each grating portion becomes smaller.

6. A diffractive optical element according to claim 4, wherein said diffractive optical element has a plurality of areas, and grating pitches of corresponding grating portions of laminated diffraction gratings in part of the plurality of areas are different from each other.

7. A diffractive optical element according to claim 4, wherein a difference between grating pitches of corresponding grating portions of said two diffraction gratings is realized by changing the width of a grating pitch at particular locations of the grating portions.

12. A diffractive optical element, comprising two diffraction gratings composed of materials differing in dispersion from each other and which are laminated with a separation between the gratings, wherein, with respect to at least two wavelengths, a maximum optical path length difference is made equal to integer times each of the wavelengths, and wherein edges of at least part of corresponding grating portions of said two diffraction gratings are shifted from each other in a direction of grating pitch of each diffraction grating, and a grating thickness of one of the gratings in one period thereof increases monotonically along one direction of the grating pitch.

13. A diffractive optical element according to claim 12, wherein said diffractive optical element has a plurality of areas, and edges of corresponding grating portions of laminated diffraction gratings in part of the plurality of areas are shifted from each other.

14. A diffractive optical element according to claim 12 wherein the shifting of edges between corresponding grating portions of said two diffraction gratings is realized by changing the width of a grating pitch at particular locations of the grating portions.

18. A diffractive optical element according to either of claims 12 and 15, wherein, where n1L and n2L are refractive indices for an arbitrary wavelength λ

on a light-entrance side and light-exit side, respectively, of a material of the L-th diffraction grating, when counted from a substrate, of said two diffraction gratings, θ

L is an angle an incident ray makes with a normal line of the L-th diffraction grating, P is a grating pitch, dL is a grating thickness of the L-th diffraction grating, and DL is a distance between the L-th diffraction grating and the (L+1)st diffraction grating, a positional shift Δ

×

L between edges of corresponding grating portions of (L×

1)st diffraction grating and the L-th diffraction grating satisfies the following condition;

19. A diffractive optical element according to either of claims 12 and 15, wherein the two wavelengths are included in a visible spectrum.

20. A diffractive optical element according to either of claims 12 and 15, wherein the first diffraction grating, when counted from a substrate, of said two diffraction gratings is made from the same material as that of the substrate.

21. A diffractive optical element according to either of claims 12 and 15, wherein said two diffraction gratings have respective grating portions, edges or pitches of which are shifted or different from each other, with said two diffraction gratings confronting each other across an air layer.

22. A diffractive optical element according to either of claims 12 and 15, wherein diffraction efficiency in a particular order is made not less than 95% in a wavelength range of 450 nm to 650 nm.

31. An optical system using said diffractive optical element according to one of claims 21 to 30.

32. An optical system according to claim 31, wherein said optical system is an image forming optical system.

15. A diffractive optical element, comprising two diffraction gratings composed of materials differing in dispersion from each other and which are laminated with a separation between the gratings, wherein, with respect to at least two wavelengths, a maximum optical path length difference is made equal to integer times each of the wavelengths, and wherein grating pitches of at least part of corresponding grating portions of said two diffraction gratings are different from each other, and a grating thickness of one of the gratings in one period thereof increases monotonically along one direction of the grating pitch.

16. A diffractive optical element according to claim 15 wherein said diffractive optical element has a plurality of areas, and grating pitches of corresponding grating portions of laminated diffraction gratings in part of the plurality of areas are different from each other.

17. A diffractive optical element according to claim 15, wherein a difference between the grating pitches of corresponding grating portions of said two diffraction gratings is realized by changing the width of a grating pitch at particular locations of the grating portions.

27. A diffractive optical element, comprising two diffraction gratings composed of materials differing in dispersion from each other, and which are laminated with a separation between the gratings, which allows for enhancing diffraction efficiency for a particular design order throughout a predetermined wavelength region, wherein edges of at least part of corresponding grating portions of said two diffraction gratings are shifted from each other in a direction of a grating pitch of each diffraction grating;

wherein the grating pitch of each of said two diffraction gratings is gradually varied, and the shifting of edges between corresponding grating portions of said two diffraction gratings becomes larger accordingly as the grating pitch of each grating portion becomes smaller.

28. A diffractive optical element, comprising two diffraction gratings composed of materials differing in dispersion from each other and which are laminated with a separation between the gratings, which allows for enhancing diffraction efficiency for a particular design order throughout a predetermined wavelength region, wherein grating pitches of at least part of corresponding grating portions of said two diffraction gratings are different from each other;

wherein a grating pitch of each of said two diffraction gratings is gradually varied, and a difference of the grating pitches between corresponding grating portions of said two diffraction gratings becomes larger accordingly as the grating pitch of each grating portion becomes smaller.

29. A diffractive optical element, comprising two diffraction gratings composed of materials differing in dispersion from each other and which are laminated with a separation between the gratings, wherein, with respect to at least two wavelengths, a maximum optical path length difference is made equal to integer times each of the wavelengths, and wherein edges of at least part of corresponding grating portions of said two diffraction gratings are shifted from each other in a direction of a grating pitch of each diffraction grating;

wherein the grating pitch of each of said two diffraction gratings is gradually varied, and the shifting of edges between corresponding grating portions of said two diffraction gratings becomes larger accordingly as the grating pitch of each grating portion becomes smaller.

30. A diffractive optical element, comprising two diffraction gratings composed of materials differing in dispersion from each other and which are laminated with a separation between the gratings, wherein, with respect to at least two wavelengths, a maximum optical path length difference is made equal to integer times each of the wavelengths, and wherein grating pitches of at least part of corresponding portions of said two diffraction gratings are different from each other;

wherein a grating pitch of each of said two diffraction gratings is gradually varied, and a difference of the grating pitches between corresponding grating portions of said two diffraction gratings becomes larger accordingly as the grating pitch of each grating portion becomes smaller.