Molding diffractive optical elements

• US 5,728,324 A
• Filed: 01/31/1995
• Issued: 03/17/1998
• Est. Priority Date: 01/31/1995
• Status: Expired due to Term

• Current Assignee: Avago Technologies General IP PTE Limited (Broadcom, Inc.)
• Original Assignee: Digital Optics Corp. (Adeia Inc.)
• Inventors: Feldman, Michael R., Welch, William H., Te Kolste, Robert D.
• Primary Examiner(s): Vargot, Mathieu D.
• Application Number:
  US08/381,169
• Time in Patent Office: 1,141 Days
• Field of Search: 264/1.33, 264/1.1, 264/2.5, 264/1.31, 264/1.32, 264/1.36, 264/162, 264/219, 264/328.1, 425/808, 425/810, 425/174.4
• US Class Current: 264/2.5
• CPC Class Codes: B29C 33/303 centering mould parts or halves, e.g. during mounting
• CPC Class Codes: B29C 45/00 Injection moulding, i.e. forcing the required volume of moulding material through a nozzle into a closed mould; Apparatus therefor injection blow-moulding B29C49/06
• CPC Class Codes: B29C 45/372 provided with means for marking or patterning, e.g. numbering articles
• CPC Class Codes: B29D 11/00 Producing optical elements, e.g. lenses or prisms grinding or polishing of optical elements B24B; constructional form of optical elements G02B; optical parts of spectacles G02C7/00
• CPC Class Codes: B29D 11/00269 Fresnel lenses
• CPC Class Codes: B29D 11/00432 Auxiliary operations, e.g. machines for filling the moulds B29D11/00125 takes precedence
• CPC Class Codes: B29D 11/00769 Producing diffraction gratings
• CPC Class Codes: B29L 2011/005 Fresnel lenses
• CPC Class Codes: B29L 2031/7224 Holograms
• CPC Class Codes: G02B 5/1852 using mechanical means, e.g. ruling with diamond tool, moulding

Abstract

A method of fabricating a diffractive optical element includes the steps of: etching a negative of a desired multi-level diffraction pattern onto a molding surface of a quartz master element using photolithography, assembling the master element as a portion of a mold, and injecting a plastic molding composition into the mold and against the molding surface of the master element to injection mold a diffractive optical element, whereby the optical element has the desired diffraction pattern on its surface. The diffraction pattern is preferably formed on the quartz master using VLSI photolithography.

Claims

1. A method of fabricating a diffractive optical element comprising the steps of:

fabricating a negative of a desired diffraction pattern having multiple discrete levels on a molding surface of a master element using photolithography, including repeating said photolithography step in order to form said multiple discrete levels;

assembling the master element with the molding surface as a portion of a mold;

injecting a molding composition into the mold and against the molding surface of the master element to injection mold a diffractive optical element, whereby the optical element has the desired diffraction pattern on its surface; and

compensating for thermal mismatch between the master element and the mold.

2. The method of claim 1 wherein said assembling step comprises providing the master element of quartz.

3. The method of claim 1 wherein said injecting step comprises injecting a plastic material.

16. The method of claim 1, wherein, when the master element is an insulator, said compensating step includes isolating thermal effects of the injection molding machine from the master element.

22. The method of claim 1, wherein the master element is non-metallic.

4. A method of fabricating diffractive optical elements comprising the steps of:

providing a first master element with a mold surface configured with the negative of a desired diffractive pattern and an obverse surface;

providing a second master element with a mold surface configured with the negative of a desired diffractive pattern or refractive shape and an obverse surface;

aligning the master elements so that their respective mold surfaces face each other in an injection molding machine;

injecting suitable substrate material into the injection molding machine to form an injection molded diffractive optical element having a diffraction pattern on one side and a diffraction pattern or refractive shape on the other side, whereby a diffractive optical element or a hybrid diffractive/refractive element can be produced having the characteristics of low cost and high performance; and

compensating for thermal mismatch between the master elements and adjacent portions of the injection molding machine.

5. The method of claim 4 wherein at least one of said providing steps comprises providing the diffraction pattern as a multi-level diffractive.

6. The method of claim 4 wherein at least one of said providing steps comprises providing the master element of quartz.

7. The method of claim 4 further comprising the preliminary step of etching the negative of the desired diffraction pattern onto at least on of the master elements using photolithography.

8. The method of claim 4 wherein said injecting step comprises injecting a plastic substrate material.

9. The method of claim 4 wherein said providing steps comprise providing at least one of the first and second master elements with alignment cavities on their obverse surfaces and said aligning step comprises inserting alignment pins into the alignment cavities, the alignment pins being affixed to the injection molding machine.

10. The method of claim 4 wherein the providing steps comprises providing the first and second master elements with alignment cavities on the obverse surfaces and

said aligning step comprises inserting alignment pins into the alignment cavities and into cavities in the injection molding machine, and the master elements are thereby aligned with each other.

17. The method of claim 4, wherein at least one of said providing steps includes providing an insulator master element.

18. The method of claim 6, wherein said compensating step includes isolating thermal effects of the injection molding machine from the master element of quartz.

19. The method of claim 9, wherein said compensating step includes centrally aligning the alignment cavities on the master elements.

20. The method of claim 10, wherein said compensating step includes centrally aligning the alignment cavities on the master elements.

11. A method of fabricating a diffractive optical element comprising the steps of:

assembling a master element with the negative of a desired diffraction pattern on a molding surface as a portion of a mold, the diffraction pattern being a multiple discrete level diffraction pattern;

injecting a molding composition into the mold and against the molding surface of the master element to injection mold a diffractive optical element, whereby the optical element has the desired diffraction pattern on its surface; and

compensating for thermal mismatch between the master element and adjacent portions of the mold.

12. The method of claim 11 wherein said assembling step comprises providing the master element of quartz.

13. The method of claim 11 wherein said fabricating step comprises etching the negative of the desired diffraction pattern onto the master element using photolithography.

14. The method of claim 11 wherein said injecting step comprises injecting a plastic material.

21. The method of claim 11, wherein said assembling step includes providing an insulator master element.

23. The method of claim 14, wherein the master element is non-metallic.

24. The method of claim 11, wherein the master element is non-metallic.

15. A method of fabricating a diffractive optical element comprising the steps of:

etching a negative of a desired multiple discrete level diffraction pattern onto a molding surface of a quartz master element using photolithography;

assembling the master element as a portion of a mold;

injecting a plastic molding composition into the mold and against the molding surface of the master element to injection mold a diffractive optical element, whereby the optical element has the desired diffraction pattern on its surface; and

compensating for thermal mismatch between the master element and adjacent portions of the mold.

25. The method of claim 15, wherein the master element is non-metallic.