Multilayer reflector with selective transmission

• US 6,208,466 B1
• Filed: 11/25/1998
• Issued: 03/27/2001
• Est. Priority Date: 11/25/1998
• Status: Expired due to Term

• Current Assignee: 3M Innovative Properties Company (3M Company)
• Original Assignee: 3M Innovative Properties Company (3M Company)
• Inventors: Wheatley, John A., Liu, Yaoqi Joe, Weber, Michael F., Nerad, Bruce A., Brott, Robert L., Gilbert, Laurence R., Roscoe, Kelly M.
• Primary Examiner(s): HENRY, JON W
• Application Number:
  US09/199,602
• Time in Patent Office: 853 Days
• Field of Search: 359/584-590, 283/91, 283/94
• US Class Current: 359/584
• CPC Class Codes: G02B 5/021 the diffusion taking place at the element's surface, e.g. by means of surface roughening or microprismatic structures
• CPC Class Codes: G02B 5/0236 the diffusion taking place within the volume of the element
• CPC Class Codes: G02B 5/0242 by means of dispersed particles
• CPC Class Codes: G02B 5/0252 using holographic or diffractive means
• CPC Class Codes: G02B 5/0278 used in transmission
• CPC Class Codes: G02B 5/0294 adapted to provide an additional optical effect, e.g. anti-reflection or filter
• CPC Class Codes: G02B 5/0825 the reflecting layers comprising dielectric materials only
• CPC Class Codes: G02B 5/0841 comprising organic materials, e.g. polymers
• CPC Class Codes: G02B 5/1861 Reflection gratings characterised by their structure, e.g. step profile, contours of substrate or grooves, pitch variations, materials G02B5/1809, G02B5/1828, G02B5/1833, G02B5/1838 and G02B5/1847 take precedence
• CPC Class Codes: G02B 5/305 including organic materials, e.g. polymeric layers

Abstract

In a multilayer dielectric reflector, treating the surface of the reflector selectively increases the amount of light transmitted through the reflector. Various surface treatments can be used to permit light to transmit through the reflector that would otherwise be reflected by the reflector. In one such reflector, different portions of the surface have different coupling efficiencies for coupling light having a high propagation angle into the multilayer reflector. Those portions having higher coupling efficiencies on each side of the reflector have a higher degree of transmission.

Claims

1. A dielectric reflector comprising:

a dielectric stack of optical repeating units including at least two different materials having different refractive indices, the stack having a critical angle at which light propagating in the stack will undergo total internal reflection at an interface of the stack with air;

a first surface optically coupled to the dielectric stack and selectively treated to couple at least a portion of light incident on the first surface into the dielectric stack at a propagation angle above the critical angle; and

a second surface optically coupled to the dielectric stack and selectively treated to couple at least a portion of light propagating in the dielectric stack at an angle above the critical angle out of the stack, wherein a coupling efficiency of at least one of the first and second surfaces, for coupling light into or out of the stack with a propagation angle above the critical angle, is different at different regions of the dielectric stack.

2. A dielectric reflector as recited in claim 1, wherein at least a portion of one of the first and second surfaces has a graded treatment such that the coupling efficiency changes along a plane of one of the first and second surfaces.

3. A dielectric reflector as recited in claim 1, wherein the dielectric stack includes layers of at least two polymeric materials, at least one polymeric material exhibiting strain induced birefringence.

4. A dielectric reflector as recited in claim 1, wherein at least a portion of one of the first and second surfaces is treated to diffuse light.

5. A dielectric reflector as recited in claim 1, wherein at least a portion of one of the first and second surfaces is structured to refract light.

6. A dielectric reflector as recited in claim 1, wherein at least a portion of opposing locations of the first and second surfaces are treated to diffuse light.

7. A dielectric reflector as recited in claim 1, wherein at least a portion of opposing locations of the first and second surfaces are treated with a treatment selected from the group consisting of structured surfaces, diffraction gratings, surface holograms, and volume hologram.

8. A dielectric reflector as recited in claim 1, wherein the dielectric reflector comprises a mirror.

9. A dielectric reflector as recited in claim 8, wherein the mirror has a reflection band that substantially reflects visible light.

10. A dielectric reflector as recited in claim 8, wherein the mirror has a reflection band that substantially reflects infrared light and transmits visible light.

11. A dielectric reflector as recited in claim 1, wherein at least one of the first and second surfaces is treated over regions corresponding to a graphic.

12. A light module or sign incorporating the dielectric reflector as recited in claim 11.

13. A light module or sign as recited in claim 12 further comprising a light source and a highly efficient mirror disposed to reflect light from the light source to the dielectric reflector.

14. A light module or sign as recited in claim 12 wherein the dielectric reflector is treated on both surfaces with the graphic in registration.

15. A dielectric reflector as recited in claim 11, wherein the treatment of the at least one of the first and second surfaces is removable.

16. A dielectric reflector as recited in claim 1, wherein the dielectric reflector comprises a reflective polarizer.

17. A selectively transmissive reflector comprising:

a dielectric stack of optical repeating units including at least two different materials having different refractive indices, the dielectric stack being designed to substantially reflect light of a predetermined wavelength when the light propagates in the film at a propagation angle within a first group of angles and to substantially transmit the light when the light propagates in the film at a propagation angle within a second group of angles, one of the first group and the second group of angles including angles above a critical angle;

a first surface optically coupled to the dielectric stack and selectively treated to couple at least a portion of light at the predetermined wavelength, having a propagation angle in the dielectric stack above the critical angle, between the dielectric stack and a medium surrounding the first surface; and

a second surface selectively treated to couple at least a portion of light, having a propagation angle in the dielectric stack above the critical angle, between the dielectric stack and a medium surrounding the second surface, wherein a coupling efficiency of at least one of the first and second surfaces for coupling light having a propagation angle in the dielectric stack that exceeds the critical angle is different for different regions of the dielectric stack.

18. A selectively transmissive reflector comprising:

a dielectric stack of optical repeating units including at least two different materials having different refractive indices, the dielectric stack having a first reflection characteristic for light of a particular wavelength propagating in the stack at a propagation angle less than a first angle and a second reflection characteristic for light of the particular wavelength propagating in the stack at a propagation angle greater than a second angle, the second angle being greater than or equal to the first angle;

a first surface optically coupled to the dielectric stack and selectively treated to couple at least a portion of light at the particular wavelength into the dielectric stack at a propagation angle in the dielectric stack above the second angle; and

a second surface selectively treated to couple at least a portion of light at the particular wavelength and propagating in the stack at a propagation angle above the second angle out of the stack, wherein a coupling efficiency of at least one of the first and second surfaces is different for different regions of the dielectric stack.

19. An optical film, comprising:

a multilayer stack of dielectric materials including layers of at least two different materials having different refractive indices along at least one in-plane axis of the film, the layers forming consecutive parallel planes, the multilayer stack being bounded by a first surface layer having an index of refraction n₁ and a second surface layer;

an input layer disposed on at least a portion of the first surface layer to direct at least a portion of light incident on the input layer into the first surface layer at a transmission angle θ

_t, measured from an axis normal to the plane of the first surface layer, which satisfies the relationship

20. A selectively transmissive reflector, comprising:

a multilayer dielectric stack having a first surface and a second surface, the dielectric stack substantially reflecting light within a predetermined bandwidth, a bandedge of the bandwidth being defined by a maximum angle of propagation through the dielectric stack for light incident directly on the first surface;

an input layer formed on at least a portion of the first surface to permit light within the predetermined bandwidth to enter the dielectric stack at a propagation angle which exceeds the maximum angle; and

an output layer formed on at least a portion of the second surface to prevent total internal reflection of the light propagating through the dielectric mirror at the propagation angle which exceeds the maximum angle such that light is selectively transmitted through the mirror at locations corresponding to the input and output layer.

21. A selectively transmissive mirror, comprising:

a multilayer stack of dielectric materials having a first and second surface and including layers of at least two different materials having different refractive indices along at least one in-plane axis of the film, the stack substantially reflecting light incident on the film within a predetermined bandwidth, the bandedge of the bandwidth being selected to reflect light propagating through the dielectric stack at a predetermined propagation angle;

a first treatment applied to at least a portion of the first surface, wherein at least a portion of any light within the predetermined bandwidth incident on the treated portion of the first surface is directed into the dielectric stack at a propagation angle which exceeds the predetermined propagation angle and wherein at least a portion of any light propagating through the dielectric stack from the second surface at an angle which exceeds the predetermined propagation angle exits the dielectric at the treated portion of the first surface; and

a second treatment applied to at least a portion of the second surface, wherein at least a portion of any light within the predetermined bandwidth incident on the treated portion of the second surface is directed into the dielectric stack at a propagation angle which exceeds the predetermined propagation angle and wherein at least a portion of any light propagating through the dielectric stack from the first surface at an angle which exceeds the predetermined propagation angle exits the dielectric at the treated portion of the second surface, the second treatment being applied such that an amount of any light within the predetermined bandwidth directed into the dielectric stack through the second surface at a propagation angle which exceeds the predetermined propagation angle or an amount of any light exiting the dielectric stack through the second surface varies for different portions of the second surface.