FILTER WITH NEUTRAL TRANSMITTING MULTILAYER COATING HAVING ASYMMETRIC REFLECTANCE

• US 3,679,291 A
• Filed: 04/21/1970
• Issued: 07/25/1972
• Est. Priority Date: 04/21/1970
• Status: Expired due to Term

• Current Assignee: Joseph H. Apfel, Robert M. Gelber
• Original Assignee: Joseph H. Apfel, Robert M. Gelber
• Inventors: Apfel, Joseph H., Gelber, Robert M.
• Primary Examiner(s): Schonberg, David
• Assistant Examiner(s): Kusmer, Toby H.
• Application Number:
  US05/030,495
• Time in Patent Office: 826 Days
• Field of Search: 350/163-166,1,314 117/33.3
• US Class Current: 359/587
• CPC Class Codes: G02B 5/205 Neutral density filters

Abstract

Filter with neutral transmitting multilayer coating having asymmetric reflectance with strong color on one side. Certain embodiments have low reflectance on the other side over a broad spectral region which covers at least a visible portion of the electromagnetic spectrum. Certain of the filters have a single metal layer with at least one dielectric layer, whereas others of the filters have a pair of metal or absorbing layers, each of which is paired with one or more dielectric layers.

Claims

2. A filter as in claim 1 wherein the reflectance from said one surface of the coating is above 10 percent.

3. A filter as in claim 1 in which at least two metal layers are provided and in which a dielectric layer is associated with eAch of the metal layers.

4. A filter as in claim 3 wherein said multilayer coating includes matching layers on opposite sides of the same.

6. A filter as in claim 3 wherein said metal layers are formed of nickel and wherein said dielectric layers are formed of a high index material.

7. A filter as in claim 4 wherein said matching layers are formed of magnesium fluoride.

5. A filter as in claim 1 wherein said metal layer is formed of Inconel and the dielectric layer is formed of titanium dioxide.

8. A filter as in claim 1 wherein there are provided a plurality of dielectric layers and wherein said dielectric layers are formed of two different non-absorbing materials.

9. A filter as in claim 8 wherein said two different non-absorbing materials are titanium dioxide and silicon dioxide.

10. A filter as in claim 1 wherein at least three metal layers are provided and each of the metal layers has associated therewith at least one dielectric layer to form metal dielectric pairs.

11. A filter as in claim 1 wherein there are provided at least three metal layers and wherein said metal layers have at least one dielectric layer associated therewith, certain of said metal layers having at least two dielectric layers associated therewith to form a metal dielectric combination.

12. In a multi-chromatic filter, a substantially transparent substrate having a surface and a multilayer coating deposited on said surface, said multilayer coating having at least first and second metal layers, each of said metal layers having a dielectric layer paired therewith so that the reflectance from the pair does not approach an appreciable fraction of the reflectance of the material being utilized for the metal layer, said filter being substantially neutral in transmission and having a transmission substantially below 60 percent, said coating on the one side having a low reflectance which is below approximately 4 percent and on the other side having at least a moderate reflectance which changes as a function of wavelength to give an appearance of color in the visible region from the other side.

13. A filter as in claim 12 wherein said metal layers have a thickness less than 200 Angstroms each.

14. A filter as in claim 12 wherein said metal layers are formed of nickel and wherein said dielectric layers are formed of a high index material.

15. A filter as in claim 12 wherein certain of said metal layers are provided with an additional dielectric layer to provide a metal dielectric combination.

16. A filter as in claim 15 wherein two of said metal dielectric combinations are provided.

17. A filter as in claim 12 wherein said coating includes matching layers on opposite ends of the coating.

18. A filter as in claim 17 wherein said matching layers are formed of magnesium fluoride.