High-efficiency, multilevel, diffractive optical elements

• US RE36,352 E
• Filed: 06/07/1995
• Issued: 10/26/1999
• Est. Priority Date: 09/21/1987
• Status: Expired due to Term

• Current Assignee: DigitalOptics Corporation East (Adeia Inc.)
• Original Assignee: Massachusetts Institute of Technology
• Inventors: Veldkamp, Wilfrid B., Swanson, Gary J.
• Primary Examiner(s): Spyrou, Cassandra C.
• Assistant Examiner(s): Juba, Jr., John
• Application Number:
  US08/471,863
• Time in Patent Office: 1,602 Days
• Field of Search: 216/2, 216/24, 216/26, 216/41, 430/320, 430/321, 430/322, 430/323, 430/324, 430/329, 430/394, 101/473, 359/558, 359/566, 359/569, 359/571, 359/565, 359/619, 359/625, 359/742, 359/568, 359/900
• US Class Current: 359/565
• 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 27/4222 in projection exposure systems, e.g. photolithographic systems
• CPC Class Codes: G02B 3/08 with discontinuous faces, e.g. Fresnel lens diffractive Fresnel lenses G02B5/1876
• CPC Class Codes: G02B 5/18 Diffraction gratings holographic optical elements G02B5/32, G03H; integrally combined with optical fibres G02B6/02057; for coupling light guides G02B6/34; integrally combined with optical integrated light guides G02B6/12; grating systems G02B27/44
• CPC Class Codes: G02B 5/1857 using exposure or etching means, e.g. holography, photolithography, exposure to electron or ion beams
• CPC Class Codes: G02B 5/1876 Diffractive Fresnel lenses; Zone plates; Kinoforms G02B5/1842, G02B5/1847 take precedence; optical systems having diffractive correction means G02B27/0037; Fresnel lenses operating by refraction G02B3/08
• CPC Class Codes: G03F 1/00 Originals for photomechanical production of textured or patterned surfaces, e.g., masks, photo-masks, reticles; Mask blanks or pellicles therefor; Containers specially adapted therefor; Preparation thereof
• CPC Class Codes: G03F 7/001 Phase modulating patterns, e.g. refractive index patterns
• CPC Class Codes: G03F 7/70308 Optical correction elements, filters or phase plates for manipulating imaging light, e.g. intensity, wavelength, polarisation, phase or image shift

Abstract

The method utilizes high resolution lithography, mask aligning, and reactive ion etching. In particular, at least two binary amplitude masks are generated. A photoresist layer on an optical element substrate is exposed through the first mask and then etched. The process is then repeated for the second and subsequent masks to create a multistep configuration. The resulting optical element is highly efficient.

Claims

1. Method for making high-efficiency, multilevel, diffractive optical elements comprising:

generating at least one binary amplitude mask including multilevel information, the mask being configured to provide 2^N levels where N is the number of masks; and

utilizing the masks'"'"' information for constructing 2^N levels in the optical element, the depths of the levels being related by a fixed ratio..]..[.2. The method of claim 1 wherein the masks are made by lithographic pattern generators..]..[.3. The method of claim 1 including three masks and eight levels..]..[.4. The method of claim 1 wherein the binary amplitude masks are defined by calculating equiphase boundaries utilizing the equation ##EQU5## and the algorithm

space="preserve" listing-type="tabular">______________________________________ Equi-phase Phase Boundaries Etch Mask # N (l = 0, ±

1, ±

2, . . . ) Depth θ

______________________________________ 1 φ

(x,y) = (l +

     1) 2 - 5 #STR5## 2 6 #STR6## 4 4 7 #STR7## 8 ______________________________________

.].. .[.5. The method of claim 1 wherein the masks are made by electron beam pattern generators..]..[.6. The method of claim 1 wherein the optical element is a lens..]..[.7. The method of claim 1 wherein the optical element corrects for spherical aberration..]..[.8. The method of claim 1 wherein the optical element is corrected for chromatic aberration..]..[.9. Method for making high-efficiency multilevel diffractive optical elements comprising;

making a master optical element according to the method of claim 1; and

using the master optical element to emboss multiple replicated optical components..]..[.10. The method of claim 9 wherein the master optical element is copied in metal which is used for the embossing..]..[.11. Method for making a high efficiency, multi-level, diffractive optical element comprising;

providing a substrate including at least two initial levels;

generating at least one binary amplitude mask including multi-level information; and

utilizing the mask to double the number of levels in the

2. element..]..Iadd. . A method for making high-efficiency, multilevel, diffractive optical elements comprising:

choosing a desired phase profile for a wavelength λ

;

generating at least two binary amplitude masks including multi-level information; and

utilizing said masks to fabricate a diffractive optical element having a number of levels greater than N+1 levels, but no more than 2^N levels, where N is the number of masks, said levels approximating said desired phase profile for said wavelength λ

in said diffractive optical element. .Iaddend..Iadd.13. The method of claim 12 wherein said optical element is used as a master for replicating optical components in plastic. .Iaddend..Iadd.14. The method of claim 12 wherein said optical element is used as a master optical element which is copied in metal and used for a

3. replication process. .Iaddend..Iadd.15. A method for making high-efficiency, multilevel, diffractive optical components comprising:

positioning in a replicating apparatus a master generated from at least two binary amplitude masks including multi-level information chosen for a desired phase profile for a wavelength λ and

having a number of levels greater than N+1 levels, but no more than 2^N levels, where N is the number of masks, said levels in said master approximating said desired phase profile for said wavelength λ

in said master;

utilizing said master to replicate the optical components. .Iaddend..Iadd.16. The method of claim 15 wherein said master is a copy of a second diffractive optical element generated from at least two binary amplitude masks including multi-level information and having a number of levels greater than N+1 levels, but no more than 2^N levels. .Iaddend..Iadd.17. The method of claim 16 wherein said copy is a metal copy. .Iaddend..Iadd.18. A method for making high-efficiency, multilevel, diffractive optical elements comprising;

generating at least two binary amplitude masks for a bandwidth including multi-level information;

utilizing a first of said binary amplitude masks to fabricate a diffractive optical element having a diffraction efficiency for a wavelength λ

within said bandwidth; and

utilizing a second of said binary amplitude masks to increase said diffraction efficiency of said diffractive optical element at said wavelength λ

by providing said diffractive optical element with a number of levels greater than N+1 levels, but no more than 2^N levels,

4. where N is the number of masks. .Iaddend..Iadd.19. The method of claim 18 wherein said increased diffraction efficiency from utilizing two masks is at least about 50%. .Iaddend..Iadd.20. The method of claim 18 wherein said step of utilizing a second of said binary amplitude masks further includes aligning said second of said binary amplitude masks with a pattern produced by said utilizing a first of said binary amplitude masks step. .Iaddend..Iadd.21. The method of claim 20 wherein said step of utilizing a second of said binary amplitude masks further includes utilizing said second of said binary amplitude masks to provide an approximation of a continuous phase profile for a wavelength λ

in said optical element from said multi-level information of said masks. .Iaddend..Iadd.22. The method of claim 18 wherein at least one of said binary amplitude masks provides an etch depth of no more than π

. .Iaddend..Iadd.23. The method of claim 21 wherein said second of said binary amplitude masks provides an etch depth about half of an etch depth of said first of said binary amplitude masks. .Iaddend..Iadd.24. The method of claim 18 wherein said optical element is used as a master for replicating optical components in

5. plastic. .Iaddend..Iadd.25. The method of claim 18 wherein said optical element is used as a master optical element which is coupled in metal and used for a replication process. .Iaddend..Iadd.26. A method for making high-efficiency, multilevel, diffractive optical elements comprising:

choosing a desired diffractive phase profile for a wavelength λ

;

generating at least two binary amplitude masks including multi-level information;

utilizing said masks to fabricate a diffractive optical element having a number of levels greater than N+1, but no more than 2^N levels, where N is the number of masks and where at least N+1 of said levels are used to construct said diffractive phase profile. .Iaddend..Iadd.27. A method according to claim 26 wherein said optical element is used as a master for replicating optical components in plastic. .Iaddend..Iadd.28. A method according to claim 26 wherein said optical element is used as a master optical element which is copied in metal and used for a replication process. .Iaddend..Iadd.29. A method for making high-efficiency, multilevel, optical elements comprising;

choosing a desired phase profile for a wavelength λ

;

generating N masks including multi-level information; and

utilizing said masks to fabricate an optical element having a number of levels greater than N+1 levels, said levels approximating said desired phase profile for said wavelength λ

in said optical element. .Iaddend..Iadd.30. The method of claim 29 wherein said generating step comprises the step of generating said N masks with an electron beam

6. pattern generator. .Iaddend..Iadd.31. The method of claim 29 wherein said generating step comprises the steps of:

defining a pattern to be drawn on said N masks on a computer; and

producing said N masks on a pattern generator using said defined pattern from said defining step. .Iaddend..Iadd.32. The method of claim 29 wherein said utilizing step further comprises the step of fabricating said optical element as a combined diffractive refractive lens. .Iaddend..Iadd.33. The method of claim 29 wherein said optical element is used as a master for replicating optical components in plastic. .Iaddend..Iadd.34. The method of claim 29 wherein said optical element is used as a master optical element which is copied in metal and used for a replication process. .Iaddend..Iadd.35. The method of claim 29 wherein said N+1 levels are discrete levels. .Iaddend..Iadd.36. The method of claim 29 wherein said masks are binary amplitude masks. .Iaddend..Iadd.37. The method of claim 29 wherein said desired phase profile is an arbitrary phase profile. .Iaddend..Iadd.38. The method of claim 37 wherein said arbitrary phase profile is a generalized asphere. .Iaddend..Iadd.39. The method of claim 29 wherein said desired phase profile is a diffractive phase profile. .Iaddend..Iadd.40. The method of claim 22 wherein said N masks contain

7. information for at least three levels. .Iaddend..Iadd.41. The method of claim 29 wherein said N masks are generated by lithographic pattern generators. .Iaddend..Iadd.42. The method of claim 29 wherein said optical element is a lens. .Iaddend..Iadd.43. The method of claim 29 wherein said optical element corrects for spherical aberration. .Iaddend..Iadd.44. A method for making high-efficiency, multilevel, optical components comprising:

positioning in a replicating apparatus a master generated from N masks including multi-level information chosen for a desired phase profile for a wavelength λ and

having a number of levels greater than N+1 levels, said levels in said master approximating said desired phase profile for said wavelength λ

in said master; and

utilizing said master to replicate the optical components. .Iaddend..Iadd.45. A method for making high-efficiency, multilevel, optical elements comprising;

choosing a desired phase profile for a wavelength λ

;

generating N masks including multi-level information; and

utilizing said masks to fabricate an optical element having a number of levels greater than N+1 levels but no more than 2^N levels, said levels approximating said desired phase profile for said wavelength λ

in said optical element. .Iaddend..Iadd.46. A method for making high-efficiency, multilevel, optical components comprising;

positioning in a replicating apparatus a master generated from N masks including multi-level information chosen for a desired phase profile for a wavelength λ and

having a number of levels greater than N+1 levels, but no more than 2^N levels, said levels in said master approximating said desired phase profile for said wavelength λ

in said master;

utilizing said master to replicate the optical components. .Iaddend.