Multilayer optical filter for producing colored reflected light and neutral transmission

• US 4,793,669 A
• Filed: 09/11/1987
• Issued: 12/27/1988
• Est. Priority Date: 09/11/1987
• Status: Expired

• Current Assignee: Coherent Inc (Coherent Corp.)
• Original Assignee: Coherent Inc (Coherent Corp.)
• Inventors: Perilloux, Bruce E.
• Primary Examiner(s): Arnold, Bruce Y.
• Application Number:
  US07/096,135
• Time in Patent Office: 473 Days
• Field of Search: 350/1.61, 350/166
• US Class Current: 359/355
• CPC Class Codes: G02B 5/282 reflecting for infrared and transparent for visible light, e.g. heat reflectors, laser protection
• CPC Class Codes: G02C 7/108 Colouring materials

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.

Claims

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 SiO₂ 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 TiO₂, TiO and Ti₂ O₃.

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 TiO₂, TiO and Ti₂ O₃, and the layers having said third refractive index are formed of SiO₂.

12. The lens 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 Si0₂ alternating with layers of material selected from the class of materials consisting of TiO₂, TiO and Ti₂ O₃.

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:

space="preserve" listing-type="tabular">______________________________________ Physical Thickness Layer Number Refractive 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:

space="preserve" listing-type="tabular">______________________________________ Physical Thickness Layer Number Refractive 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:

space="preserve" listing-type="tabular">______________________________________ Physical Thickness Layer Number Refractive 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 2.20 .1135 18 1.47 .1898 19 2.20 .1121 20 1.47 .1827 21 2.20 .1178 22 1.47 .1914 23 2.20 .1120 24 1.47 .1806 25 2.20 .1128 26 1.47 .1856 27 2.20 .1162 28 1.47 .1788 29 2.20 .1039 30 1.47 .2638. ______________________________________