Retroreflecting polarizer

• US 5,559,634 A
• Filed: 10/26/1994
• Issued: 09/24/1996
• Est. Priority Date: 06/13/1991
• Status: Expired due to Term

• Current Assignee: Minnesota Mining and Manufacturing Co (3M Company)
• Original Assignee: Minnesota Mining and Manufacturing Co (3M Company)
• Inventors: Weber, Michael F.
• Primary Examiner(s): Phan, James
• Application Number:
  US08/329,623
• Time in Patent Office: 699 Days
• Field of Search: 350/97, 350/102, 350/170-173, 350/394-395, 350/402-403, 350/335, 350/337, 350/396-398, 350/103, 350/109, 350/286, 359/485, 359/489, 359/487, 359/488, 359/494-496, 359/529-530, 359/618, 359/629, 359/634, 359/834, 359/586-589, 359/490, 359/498
• US Class Current: 359/638
• CPC Class Codes: G02B 5/124 plural reflecting elements forming part of a unitary plate or sheet
• CPC Class Codes: G02B 5/3066 involving the reflection of light at a particular angle of incidence, e.g. Brewster's angle

Abstract

A retroreflecting polarizer, comprising optical thin films coated on a structured material, divides an incident beam of light into polarized components, transmitting one component through the polarizer and reflecting the other back to the source.

Claims

1. A retroreflecting polarizer, comprising:

(a) a first flexible material about 0.33 mm thick having a structured surface consisting of a linear array of isosceles prisms about 0.18 mm in height arranged side by side and having sides which make an angle in the range of 40°

to 50°

with respect to the tangent to a smooth surface opposite the structured surface, wherein the isosceles prisms are present at a frequency of about 28 per cm;

(b) a second flexible material essentially like the first flexible material;

(c) on the structured surface of at least one flexible material, at least one optical stack of alternating layers of high and low refractive index materials of selected optical thicknesses;

the first and second flexible materials all optically cemented to form a single unit in which the refractive index of the first and second flexible materials, and the refractive indices and optical thickness of the layers of the optical stack, are all chosen to produce selective reflection of polarized light, and wherein the optical stack is configured to;

(d) separate an incident light beam of mixed polarization having all wavelengths between about 400 and 700 nm into an s-polarized component and a p-polarized component;

(e) reflect the s-polarized component onto another portion of the optical stack and there parallel to the incident beam but proceeding in an opposite direction; and

(f) transmit the p-polarized component parallel to the incident beam.

2. A retroreflecting polarizer, comprising:

a first flexible material having a structured surface consisting of a linear array of isosceles prisms arranged side by side and having sides which make an angle in the range of 40°

to 50°

with respect to the tangent to a smooth surface opposite the structured surface;

a second flexible material essentially like the first flexible material; and

an optical stack of alternating layers of high and low refractive index materials of selected optical thicknesses provided between the structured surfaces of the first and second flexible materials, the optical stack comprising at least two sub-stacks;

a first sub-stack having a bandwidth centered on a first wavelength within the visible spectrum and a second sub-stack having a bandwidth centered on a second wavelength, different from the first wavelength, within the visible spectrum, wherein the two flexible materials and the optical stack are all optically cemented to form a single unit, and wherein the optical stack is configured to;

separate an incident light beam of mixed polarization having all wavelengths between about 400 and 700 nm into a s-polarized component and a p-polarized component;

reflect the s-polarized component onto another portion of the optical stack and there reflect parallel to the incident beam but proceeding in an opposite direction; and

transmit the p-polarized component parallel to the incident beam.

3. The retroreflecting polarizer of claim 2, wherein the first and second sub-stacks are secured to each other by an adhesive provided therebetween.

4. The retroreflecting polarizer of claim 2, wherein the first wavelength is 425 nm.

5. The retroreflecting polarizer of claim 2, wherein the second wavelength is 650 nm.

6. The retroreflecting polarizer of claim 2, wherein the first wavelength is 425 nm and the second wavelength is 650 nm.

7. The retroreflecting polarizer of claim 2, wherein the optical stack further comprises a third sub-stack having a bandwidth centered on a third wavelength within the visible spectrum.

8. The retroreflecting polarizer of claim 7, wherein the first wavelength is 400 nm.

9. The retroreflecting polarizer of claim 7, wherein the second wavelength is 550 nm.

10. The retroreflecting polarizer of claim 7, wherein the third wavelength is 700 nm.

11. The retroreflecting polarizer of claim 7, wherein the first wavelength is 400 nm, the second wavelength is 550 nm, and the third wavelength is 700 nm.