Multilayer reflector with suppression of high order reflections

• US 7,019,905 B2
• Filed: 12/30/2003
• Issued: 03/28/2006
• Est. Priority Date: 12/30/2003
• Status: Active Grant

• Current Assignee: 3M Innovative Properties Company (3M Company)
• Original Assignee: 3M Innovative Properties Company (3M Company)
• Inventors: Weber, Michael F.
• Primary Examiner(s): Nguyen, Thong
• Assistant Examiner(s): Pritchett, Joshua L.
• Application Number:
  US10/748,396
• Publication Number:
  US 20050141093A1
• Time in Patent Office: 819 Days
• Field of Search: 359/584, 359/359, 359586-590
• US Class Current: 359/587
• CPC Class Codes: G02B 5/285 comprising deposited thin solid films G02B5/281 - G02B5/289 take precedence; multilayered film filters for fibre optic multiplexing G02B6/29361
• CPC Class Codes: G02B 5/287 comprising at least one layer of organic material

Abstract

A multilayer interference reflecting film has individual optical layers arranged to form optical repeat units throughout the film. Each of a plurality of optical repeat units has six individual layers, at least three of which have different refractive indices at a design wavelength λ₀. Individual layers having nominally the same refractive index and physical thickness, arbitrarily labeled “A”, “B”, “C”, and “D”, are arranged in a six-layer optical repeat unit in a cyclic permutation of CACDBD, where the A and B layers are each thicker than the C and D layers. The thicknesses and refractive indices of the individual layers can be selected to suppress the second, third, and fourth order reflections, while reflecting light at the design wavelength.

Claims

1. A multilayer reflective film comprising a plurality of six-layer optical repeat units each comprising individual layers A, B, C, D arranged in a six-layer sequence CACDBD), or a cyclic permutation thereof, the A and B layers being optically thicker than the C and D layers, and where the individual layers have refractive indices that satisfy the relationship n_A≧

n_D>

n_C>

n_B or the relationship n_A>

n_D>

n_C≧

n_B.

2. The film of claim 1, wherein the individual layers each have isotropic refractive indices.

3. The film of claim 1, wherein at least one of the individual layers is birefringent, and wherein the refractive indices n_A, n_B, n_C, n_D are measured along an axis in the plane of the film at a design wavelength.

4. The film of claim 3, wherein the individual layers have refractive indices measured along an axis perpendicular to the plane of the film that are substantially matched.

5. The film of claim 1, wherein at least one of the optical repeat units has an optical thickness of one-half of a design wavelength λ

₀/2, so as to reflect light at the design wavelength λ

₀.

6. The film of claim 5, wherein λ

₀ is between about 700 and 2000 mm.

7. The film of claim 5, wherein the thicknesses and refractive indices of the individual layers are selected to suppress reflection of light at least at wavelengths of λ

₀/2, λ

₀/3, and λ

₀/4.

8. The film of claim 5, wherein the individual layers have refractive indices that satisfy the relationship n_A>

n_D>

n_C>

n_B.

9. The film of claim 8, wherein the refractive indices of the individual layers further satisfy the relationship n_A+n_B=n_C+n_D, wherein the A layer has an optical thickness t_A and the B layer has an optical thickness t_B, and t_A=t_B;

wherein each C layer has an optical thickness t_C and each D layer has an optical thickness t_D, and t_C=t_D; and

wherein the relationship $\frac{3<br><br>\mathrm{\pi <br><br>}<br><br><br><br>X_3}{2}=\mathrm{\pi <br><br>}-\mathrm{arc}<br><br><br><br>\sin <br><br>\left(\frac{-\mathrm{\Delta <br><br>}<br><br><br><br>n_{D<br><br><br><br>C}}{2<br><br><br><br>\mathrm{\Delta <br><br>}<br><br><br><br>n_{\mathrm{AB}}+\mathrm{\Delta <br><br>}<br><br><br><br>n_{D<br><br><br><br>C}}\right)$

is satisfied, where X₃=t_A/(t_A+2t_C), where Δ

n_AB=n_A−

n_B, and where Δ

n_DC=n_D−

n_C.

10. The film of claim 5, wherein the individual layers have refractive indices that satisfy the relationship n_A=n_D>

n_C>

n_B or the relationship n_A>

n_D>

n_C=n_B.

11. The film of claim 1, wherein the individual layers are composed of polymeric materials.

12. The film of claim 1, wherein the layers are composed of inorganic materials.

13. The film of claim 1, wherein the optical repeat units are arranged to have a thickness profile that changes along a thickness axis of the film.