Infra-red transmitting optical components and optical coatings therefor

• US 5,007,689 A
• Filed: 08/30/1989
• Issued: 04/16/1991
• Est. Priority Date: 09/08/1988
• Status: Expired due to Term

• Current Assignee: Barr & Stroud Limited, The secretary of state for defence in her Britannic Majesty's Government of the United Kingdom of Great Britain And Northern Ireland
• Original Assignee: Barr & Stroud Limited, The secretary of state for defence in her Britannic Majesty's Government of the United Kingdom of Great Britain And Northern Ireland
• Inventors: Kelly, Christopher J., Lewis, Keith L.
• Primary Examiner(s): NOT, DEFINED
• Assistant Examiner(s): Lerner, Martin
• Application Number:
  US07/400,333
• Time in Patent Office: 594 Days
• Field of Search: 350/1.1, 350/1.6, 350/1.7, 350/164, 350/165, 357/2, 357/23.2, 252/587, 264/1.7
• US Class Current: 359/350
• CPC Class Codes: C23C 16/30 Deposition of compounds, mixtures or solid solutions, e.g. borides, carbides, nitrides
• CPC Class Codes: H01L 31/0216 Coatings H01L31/041 takes precedence

Abstract

Infrared transmitting optical components having a wide variety of substrates (e.g. ZnS, ZnSe, Ge, Si, SiO₂) are disclosed all with an optical coating of boron phosphide (BP). The boron phosphide may be a single layer coating or one layer of a multilayer coating in which case it is preferably the penultimate layer. Coated components are provided which are very low in absorption, which are operable at high temperatures with minimal transmission loss, and which are transmitting in two IR wavebands. The boron phosphide layer is deposited by plasma-assisted chemical vapor deposition at a temperature in the range 300°-500° C. preferably using feedstock gases which are hydrogen-fee. Boron phosphide coatings of up to 40 μm in thickness have been achieved.

Claims

1. An infra-red transmitting optical component having an anti-reflecting coating thereon of boron phosphide, the coating having been deposited on the component by plasma-assisted chemical vapor deposition at a temperature of less than about 500°

C. and having a disordered non-crystalline structure.

2. A component as claimed in claim 1, wherein the coating is the result of deposition at a temperature in the range 300-500°

C.

3. A component as claimed in claim 1, wherein the component comprises a substrate of zinc sulphide (ZnS) and the boron phosphide coating is 2 microns in thickness on the face of the substrate, the component having a refractive index value of 3.1, an average absorption co-efficient value of 20 in 3 to 5 micron waveband and 80 in the 8 to 11.5 micron waveband and respective average absorption values of 0.3 and 0.8.

4. A component as claimed in claim 1, wherein the component comprises a substrate of silicon (Si) and the boron phosphide coating is free of deep absorption bands in the 2.5 to 50 micron length range.

5. A component as claimed in claim 1, wherein the component comprises a substrate of quartz (SiO₂) and the boron phosphide coating is 4 microns in thickness, the component having a transmission characteristic for the 0.5 to 2.5 micron waveband which rises from zero at about 0.5 micron to about 90% at and above 1.06 micron.

6. A component as claimed in claim 1, wherein the component comprises a zinc selenide (ZnSe) substrate having a transmission loss at temperatures up to 500°

C. for the 8 to 11.5 micron waveband of about 0.4% per micron of coating thickness.

7. A component as claimed in claim 1, wherein the plasma-assisted chemical vapor deposition utilizes feedstock gases which are hydrogen-free.

8. A component as claimed in claim 1, wherein the boron phosphide coating comprises one layer of a multilayer coating on the component substrate.

9. A component as claimed in claim 8, wherein the multilayer coating comprises a final layer of diamond-like carbon (DLC) and the penultimate layer is boron phosphide.

10. A component as claimed in claim 9, wherein the multilayer coating is as set forth in the Table, the material thicknesses being measured in fractions of a quarter wave at 10 microns:

space="preserve" listing-type="tabular"> TABLE______________________________________ Material Thickness Index______________________________________Substrate ZnS 2.2First layer BP 0.3833 3.1Second layer DLC 1.1365 2.0______________________________________

11. A component as claimed in claim 9, wherein the multilayer coating is as set forth in the Table, the material thicknesses being measured in fractions of a quarter wave at 10 microns:

space="preserve" listing-type="tabular"> TABLE______________________________________ Material Thickness Index______________________________________Substrate ZnSFirst layer BP 0.7343 3.1Second layer Ge 1.1825 4.1Third layer BP 0.2670 3.1Fourth layer DLC 0.7801 2.0______________________________________

12. A component as claimed in claim 1, wherein the boron phosphide coating comprises surface etching to the `Moth-eye effect` to provide characteristics similar to a multilayer coating.

13. A component as claimed in claim 1 having a boron phosphide coating with a thickness in the range up to 40 microns.