Multilayer optical filter for producing colored reflected light and neutral transmission

Abstract

A short-wave-pass optical filter, that includes a partially absorbing or transparent substrate coated by a set of layers having specified quarter-wave optical thickness, and is designed to reflect visible radiation of a selected color while transmitting visible radiation and maintaining a neutral color balance. The coating includes layers having a high refractive index alternating with layers having a low refractive index. The refractive indices and layer thicknesses are selected so that the filter's reflectance spectrum exhibits a ripple over a first segment of the visible spectrum but no significant ripple over a second segment of the visible. The filters may be used as sunglass lenses that have a selected color (such as blue, orange, or violet) when viewed by one other than the sunglass wearer, while permitting the wearer to perceive transmitted light with a correct color balance. The design of the inventive filter is preferably optimized to have the desired optical properties while being conveniently and repeatably manufacturable.

What is claimed is: 
     
       1. An optical filter, including: a substrate having a surface, and a coating supported by the surface of the substrate, said coating including a set of alternating layers formed of material having high refractive index and substantially quarter-wave optical thickness, and material having low refractive index and substantially quarter-wave optical thickness, where the thickness of each layer is selected so that the filter has a reflectance spectrum exhibiting a ripple over a first segment of the visible spectrum but exhibiting no significant ripple over a second segment of the visible spectrum, so that the reflected light having wavelength within the first segment is sufficient to give the filter a desired aesthetic color, and where the thickness of each layer is selected so that the filter reflects substantially all electromagnetic radiation having wavelengths in the near-infrared range.   
     
     
       2. The filter of claim 1, wherein the substrate is composed of material that is capable of absorbing ultra-violet electromagnetic radiation. 
     
     
       3. The filter of claim 2, wherein the substrate is composed of material that is partially absorptive of visible electromagnetic radiation. 
     
     
       4. The filter of claim 1, wherein the first segment lies in the blue portion of the visible spectrum, so that the filter reflects light having a blue appearance. 
     
     
       5. The filter of claim 1, wherein the reflectance spectrum also exhibits a ripple over a third segment of the visible spectrum, so that the reflections corresponding to both ripples combine to give the filter a desired aesthetic color. 
     
     
       6. The filter of claim 5, wherein the first segment lies in the red portion of the visible spectrum and the third segment lies in the violet portion of the visible spectrum, so that the filter reflects light having a violet appearance. 
     
     
       7. The filter of claim 5, wherein the first segment lies in the yellow portion of the visible spectrum and the third segment lies in the red portion of the visible spectrum, so that the filter reflects light having an orange appearance. 
     
     
       8. The filter of claim 1, wherein the substrate is composed of glass having refractive index substantially equal to 1.52 and capable of absorbing ultra-violet radiation, and the coating is composed of layers of SiO 2  having refractive index substantially equal to 1.47 alternating with layers of material having refractive index substantially equal to 2.25 selected from the class of materials consisting of TiO 2 , TiO and Ti 2  O 3 . 
     
     
       9. A sunglass lens, including: (a) a substrate that is absorptive of ultraviolet electromagnetic radiation and is partially absorptive of visible radiation, said substrate having a surface and a first refractive index; and   (b) a coating on the substrate's surface including layers of material having a high refractive index and substantially quarter-wave optical thickness alternating with layers of material having low refractive index and substantially quarter-wave optical thickness, the thickness of each layer being selected so that the lens has a reflectance spectrum with a ripple over a first segment in the visible range but has no significant ripple in a second segment in the visible range, so that reflected light having wavelength within the first segment is sufficient to give the lens a desired aesthetic color, and the thickness of each layer being selected so that the lens reflects substantially all electromagnetic radiation having wavelengths in the near-infrared range.   
     
     
       10. The lens of claim 9, wherein the layers having high refractive index all have refractive index substantially equal to a second refractive index, and the layers having low refractive index all have refractive index substantially equal to a third refractive index. 
     
     
       11. The lens of claim 10, wherein the substrate is formed of glass, the first refractive index is substantially equal to 1.52, the layers having said second refractive index are formed of material selected from the class of material consisting of TiO 2 , TiO and Ti 2  O 3 , and the layers having said third refractive index are formed of SiO 2 . 
     
     
       12. The less of claim 9, wherein the first segment is in the blue portion of the visible range, so that light reflected from the lens has a blue appearance. 
     
     
       13. The lens of claim 9, wherein the reflectance spectrum also has a ripple over the third segment in the visible range, so that the reflections corresponding to both ripples combine to give the filter a desired aesthetic color. 
     
     
       14. The lens of claim 13, wherein the first segment is in the yellow portion of the visible range and the third segment is in the red portion of the visible spectrum, so that light reflected from the lens has an orange appearance. 
     
     
       15. The lens of claim 13, wherein the first segment is in the red portion of the visible spectrum and the third segment is in the violet portion of the visible spectrum, so that light reflected from the lens has a violet appearance. 
     
     
       16. An optical filter, including: (a) a substrate having a surface and a refractive index; and   (b) a double quarter-wave stack coated on the substrate's surface and capable of reflecting substantially all electromagnetic radiation in the near-infrared range, said stack including a number of alternating layers characterized by refractive index and a substantially quarter-wave optical thickness is selected as a result of an iterative optimizing process so that the filter's reflectance spectrum has at least one rippled segment in the visible spectrum and at least one non-rippled segment in the visible range.   
     
     
       17. The filter of claim 16, wherein the substrate is composed of material transparent to ultra-violet radiation and visible radiation. 
     
     
       18. The filter of claim 16, wherein the substrate is composed of material absorptive of ultra-violet radiation. 
     
     
       19. The filter of claim 16, wherein the substrate is composed of material partially absorptive of visible radiation. 
     
     
       20. The filter of claim 16, wherein the double quarter-wave stack consists of layers of SiO 2  alternating with layers of material selected from the class of materials consisting of TiO 2 , TiO and Ti 2  O 3 . 
     
     
       21. The filter of claim 16, wherein the double quarter-wave stack consists of twenty-nine layers with increasing layer number corresponding to increasing departure from the substrate, and each layer has refractive index and physical thickness substantially as follows:   ______________________________________                                    
Layer   Refractive     Physical Thickness                                 
Number  Index          (micrometers)                                      
______________________________________                                    
 1      1.47           .0122                                              
 2      2.25           .1134                                              
 3      1.47           .1757                                              
 4      2.25           .1089                                              
 5      1.47           .1531                                              
 6      2.25           .1047                                              
 7      1.47           .1623                                              
 8      2.25           .1024                                              
 9      1.47           .1590                                              
10      2.25           .1044                                              
11      1.47           .1545                                              
12      2.25           .1073                                              
13      1.47           .1544                                              
14      2.25           .1086                                              
15      1.47           .1590                                              
16      2.25           .1103                                              
17      1.47           .1691                                              
18      2.25           .1210                                              
19      1.47           .1899                                              
20      2.25           .1249                                              
21      1.47           .2018                                              
22      2.25           .1177                                              
23      1.47           .2048                                              
24      2.25           .1299                                              
25      1.47           .1930                                              
26      2.25           .1146                                              
27      1.47           .1931                                              
28      2.25           .1124                                              
29      1.47           .3161                                              
______________________________________                                    
     
     
     
       22. The filter of claim 16, wherein the stack consists of twenty-nine layers, with increasing layer number corresponding to increasing departure from the substrate, and each layer has refractive index and physical thickness substantially as follows:   ______________________________________                                    
Layer   Refractive     Physical Thickness                                 
Number  Index          (micrometers)                                      
______________________________________                                    
 1      1.47           .0122                                              
 2      2.25           .0922                                              
 3      1.47           .1440                                              
 4      2.25           .0778                                              
 5      1.47           .1393                                              
 6      2.25           .0823                                              
 7      1.47           .1461                                              
 8      2.25           .0859                                              
 9      1.47           .1431                                              
10      2.25           .0861                                              
11      1.47           .1425                                              
12      2.25           .0862                                              
13      1.47           .1444                                              
14      2.25           .0834                                              
15      1.47           .1454                                              
16      2.25           .0827                                              
17      1.47           .1585                                              
18      2.25           .1055                                              
19      1.47           .1792                                              
20      2.25           .1074                                              
21      1.47           .1798                                              
22      2.25           .1102                                              
23      1.47           .1790                                              
24      2.25           .1111                                              
25      1.47           .1770                                              
26      2.25           .1102                                              
27      1.47           .1782                                              
28      2.25           .1026                                              
29      1.47           .2427                                              
______________________________________                                    
     
     
     
       23. The filter of claim 16, wherein the stack consists of thirty layers, with increasing layer number corresponding to increasing departure from the substrate, and each layer has refractive index and physical thickness substantially as follows:   ______________________________________                                    
Layer   Refractive     Physical Thickness                                 
Number  Index          (micrometers)                                      
______________________________________                                    
 1      2.25           .1058                                              
 2      1.47           .1597                                              
 3      2.25           .0929                                              
 4      1.47           .1531                                              
 5      2.25           .0844                                              
 6      1.47           .1496                                              
 7      2.25           .0794                                              
 8      1.47           .1480                                              
 9      2.25           .0847                                              
10      1.47           .1505                                              
11      2.25           .0858                                              
12      1.47           .1493                                              
13      2.25           .0823                                              
14      1.47           .1475                                              
15      2.25           .0882                                              
16      1.47           .1669                                              
17      2.25           .1135                                              
18      1.47           .1898                                              
19      2.25           .1121                                              
20      1.47           .1827                                              
21      2.25           .1178                                              
22      1.47           .1914                                              
23      2.25           .1120                                              
24      1.47           .1806                                              
25      2.25           .1128                                              
26      1.47           .1856                                              
27      2.25           .1162                                              
28      1.47           .1788                                              
29      2.25           .1039                                              
30      1.47           .2638                                              
______________________________________                                    
  .Iadd.24. An optical filter comprising:
     a substrate having a surface; and   a coating supported by the surface of the substrate, the coating including a set of alternating layers of material having a high refractive index and substantially quarter-wave optical thickness and of material having a low refractive index and substantially quarter-wave optical thickness, where the thickness of each of the layers is selected so that the filter has a reflectance spectrum exhibiting a ripple over at least one segment of the visible portion of the spectrum while exhibiting no significant ripple over another segment of the visible portion of the spectrum so that a desired aesthetic color is produced substantially exclusively by reflected light in the at least one segment of the visible portion of the spectrum and further selected so that the combination of the substrate and the coating function to block substantially all of the light in the near-infrared portion of the spectrum. .Iaddend. .Iadd.25. The optical filter of claim 24 wherein the substrate is comprised of material which absorbs ultra-violet electromagnetic radiation so that the filter also blocks light in the ultra-violet portion of the spectrum. .Iaddend.   
     
     
        .Iadd. 6.  The filter of claim 25 wherein the at least one segment includes a first segment which lies in the blue portion of the visible spectrum so that the desired aesthetic color is blue. .Iaddend. .Iadd.27. The filter of claim 25 wherein the at least one segment includes first and second separate segments of the visible spectrum so that the desired aesthetic color is produced by the combination of the light reflected in the first and second segments. .Iaddend. .Iadd.28. The filter of claim 25 wherein the first and second segments lie in the red and violet portions of the visible spectrum, respectively so that the desired aesthetic color is violet. .Iaddend. .Iadd.29. The filter of claim 25 wherein the first and second segments lie in the yellow and red portions of the visible spectrum, respectively, so that the desired aesthetic color is orange. .Iaddend. .Iadd.30. The filter of claim 25 wherein the substrate is comprised of glass having a refractive index substantially equal to 1.52 and capable of absorbing ultra-violet radiation and the coating is comprised of layers of SiO 2  having refractive index substantially equal to 1.47 alternating with layers of material having refractive index substantially equal to 2.25 selected from the class of materials 
     
     
        consisting of TiO 2 , TiO and Ti 2  O 3 . .Iaddend. .Iadd.31. The filter of claim 24 wherein the thickness of each layer is selected so that substantially all electromagnetic radiation having wavelengths in the near-infrared range is reflected. .Iaddend. .Iadd.32. The filter of claim 31 wherein the substrate is comprised of material partially absorptive of visible electromagnetic radiation. .Iaddend.