Multi-layer anti-reflection coating with high and low index material

• US 3,922,068 A
• Filed: 06/17/1974
• Issued: 11/25/1975
• Est. Priority Date: 06/18/1973
• Status: Expired due to Term

• Current Assignee: Toshio Uetsuki
• Original Assignee: Toshio Uetsuki
• Inventors: Uetsuki, Toshio
• Primary Examiner(s): Stern, Ronald J.
• Application Number:
  US05/480,288
• Time in Patent Office: 526 Days
• Field of Search: 350/164-166 117/33.3 428/426,428,538,539
• US Class Current: 359/588
• CPC Class Codes: G02B 1/115 Multilayers

Abstract

A five layer anti-reflection coating for a substrate utilizing respectively a low index, NL, and a high index, NH, material is provided. The high index material has an index of refraction range of 1.95 to 2.35 while the low index material has an index of refraction range of 1.35 to 1.62. The relationship of the optical thicknesses of the coating layers can be expressed as follows: 3/4 lambda o</= N2d2 + N3d3 + N4d4 + N5d5 </= lambda o The physical thicknesses of the coating layers can be adjusted to match the design parameters of the coating with any variations in the index of refraction of the substrate.

Claims

1. A multi-layered anti-reflection coating for use with substrates having an index of refraction in the range of 1.42 to 1.90 to reduce reflectance of light comprising at least five alternating layers of only one high and one low refractive index material, the first layer furtherest from the substrate having an optical thickness N1d1, of approximately 1/4 wavelength and a low index of refraction in the range of 1.35 to 1.62, the second layer having an optical thickness N2d2, of at least 1/2 wavelength and a high index of refraction in the range of 1.95 to 2.35, the third layer having an optical thickness, N3d3, of less than 1/4 wavelength and the same index of refraction as the first layer, the fourth layer having an optical thickness, N4d4, of less than 1/4 wavelength and the same index of refraction as the second layer and a fifth layer having an optical thickness, N5d5, of less than 0.225 wavelength and the same index of refraction as the first layer, wherein lambda o is a preselected design wavElength between 400 and 700 nanometers, N refers to the index of refraction and d refers to the physical thickness of the layer, the optical thicknesses being related as follows:

3/4 lambda o <

or = N2d2 + N3d3 + N4d4 + N5d5 <

or = lambda o

2. A multi-layered anti-reflection coating as in claim 1 wherein, the first, third and fifth coating layers are selected from the group consisting of MgF2, ThF4, LaF2, LaF3 Na3 (AlF4), LiF and SiO2.

3. A multi-layered anti-reflection coating as in claim 1 wherein the second and fourth coating layers are selected from the group consisting of CeO2, ZrO2, TiO2, Ta2O5, Zns and ThO2.

4. A multi-layered anti-reflection coating as in claim 3 wherein the first, third and fifth coating layers are selected from the group consisting of MgF2, ThF4, LaF2, LaF3, Na3 (AlF4), LiF and SiO2.

5. A multi-layered anti-reflection coating as in claim 4 wherein the substrate is a glass.

6. A multi-layered anti-reflection coating as in claim 1 wherein the first, third and fifth coating layers are SiO2.

7. A multi-layered anti-reflection coating as in claim 1 wherein the substrate is a glass.

8. A multi-layered anti-reflection coating as in claim 7 wherein the first, third and fifth coating layers are selected from the group consisting of MgF2, ThF4, LaF2, LaF3, Na3 (AlF4), LiF and SiO2.

9. A multi-layered anti-reflection coating as in claim 1, wherein the first, third and fifth coating layers are MgF2.

10. A multi-layered anti-reflection coating as in claim 9, wherein the second and fourth coating layers are selected from the group consisting of CeO2, ZrO2, TiO2, Ta2O5, ZnS and ThO2.

11. A multi-layered anti-reflection coating for use with a substrate having an index of refraction in the range of 1.42 to 1.90 for reducing the reflectance of energy below 0.3% across the central bandwidth of the visual spectrum in the range of wavelengths of from 450 to 650 Nanometers comprising at least five sequential layers of an alternative high and low refractive index material, the first layer furtherest from the substrate having an optical thickness N1d1 of approximately 1/4 wavelength of a preselected design wavelength lambda o and a low index of refraction in the range of 1.35 to 1.62, the second layer having an optical thickness N2d2 of greater than 1/2 wavelength and a high index of refraction in the range of 1.95 to 2.35, the third layer having an optical thickness N3d3 of less than 1/4 wavelength and the same low index of refraction as the first layer, the fourth layer having an optical thickness N4d4 of less than 1/4 wavelength and the same high index of refraction as the second layer and a fifth layer having an optical thickness N5d5 of less than 0.225 wavelength and the same low index of refraction as the first layer wherein N refers to the index of refraction and d refers to the physical thickness of the layer, the low index of refraction material of the first, third and fifth coating layers being selected from the group consisting of MgF2, ThF4, LaF2, LaF3Na3 (AlF4), LiF and SiO2, and the high index of refraction material of the second and fourth coating layers being selected from the group consisting of CeO2, ZrO2, TiO2, Ta2O5, AnS, and ThO2, the optical thickness of the second throUgh fifth layers being related as follows:

3/4 lambda o <

or = N2d2 + N3d3 + N4d4 + N5d5 <

or = lambda o.

12. A five layered anti-reflection coating for use with an optical substrate having an index of refraction in the range of 1.42 to 1.90 to provide a low, relatively constant reflectance of light across the central region of the visual spectrum with only two separate coating materials of a high and low refractive index comprising:

a first layer furtherest from the substrate having an optical thickness, of approximately 1/4 design wavelength and a low index of refraction in the range of 1.35 to 1.62;

a second layer having an optical thickness greater than 1/2 design wavelength and a high index of refraction in the range of 1.95 to 2.35;

a third layer having the same index of refraction as the first layer and an optical thickness of less than 1/4 design wavelength;

a fourth layer having the same index of refraction as the second layer and an optical thickness of less than 1/4 design wavelength, and;

a fifth layer having the same index of refraction as the first layer and an optical thickness of less than 0.225 the design wavelength, wherein the design wavelength is preselected between 400 and 700 nanometers.

13. An anti-reflection coating as in claim 12 wherein N refers to the index of refraction and d refers to the physical techniques of the layer and the optical thickness of the second through fifth layers are related as follows;

3/4 lambda o <

or = N2d2 + N3d3 + N4d4 + N5d5 <

or = lambda o.