High contrast PDLC transmission gratings and method of manufacture

• US 20020097355A1
• Filed: 10/30/2001
• Published: 07/25/2002
• Est. Priority Date: 11/17/2000
• Status: Active Grant

• Current Assignee: Avago Technologies General IP PTE Limited (Broadcom, Inc.)
• Original Assignee: John C. Kralik, Michelle M. Stone
• Inventors: Stone, Michelle M., Kralik, John C.
• Granted Patent: US 6,654,072 B2
• Time in Patent Office: Days
• US Class Current: 349/86
• CPC Class Codes: G02F 1/13342 Holographic polymer dispersed liquid crystals
• CPC Class Codes: G02F 1/31 Digital deflection, i.e. optical switchingG02F1/33 takes precedence
• CPC Class Codes: G02F 2201/305 diffraction grating

Abstract

A PDLC transmissive phase grating utilizing nematic liquid crystal materials confined in a polymer matrix. The PDLC grating operates in the Bragg regime and switches between diffracting and non-diffracting states via an applied electric field. The grating is made up of a PDLC grating film contained within a cell. The PDLC film has a spatially periodic distribution of grating planes which includes polymer-rich regions and liquid crystal-rich regions, wherein the major constituent of the polymer-rich regions is a polymer, and wherein the liquid crystal constituent concentration within the liquid crystal-rich regions is greater than the liquid crystal constituent concentration within said polymer-rich regions. The PDLC transmission phase grating is rendered substantially transparent when subjected to an electric field during the application of light that is p-polarized and incident on the grating at Bragg angle.

Claims

1. A polymer dispersed liquid crystal (PDLC) transmission phase grating capable of operating in the Bragg regime, the grating comprising:

a cell having a pair of oppositely disposed substrates;

a PDLC grating film contained within said cell, said PDLC film having a spatially periodic distribution of grating planes comprising polymer-rich regions and liquid crystal-rich regions, wherein the major constituent of said polymer-rich regions is a polymer, and wherein the liquid crystal constituent concentration within said liquid crystal-rich regions is greater than the liquid crystal constituent concentration within said polymer-rich regions;

said polymer-rich regions characterized by a scalar optical dielectric constant with a value that remains substantially unperturbed by an electric field being applied in a direction perpendicular to said PDLC grating film;

said liquid crystal-rich regions comprising a polymer matrix containing a liquid crystal-rich material, and said liquid crystal-rich material being characterized by optical dielectric tensor components;

said optical dielectric tensor components comprising an ordinary component measured within said grating planes and an extraordinary component measured perpendicular to said grating planes, said components each having a value determined in the absence of said electric field;

said liquid crystal-rich material having values of said optical dielectric tensor components capable of being altered by the application of said electric field; and

said spatially periodic distribution having a spatial period of preselected value, and said electric field strength having a strength of preselected value, each said preselected value of said spatial period and said electric field strength being based upon the relationship between said scalar optical dielectric constant and said optical dielectric tensor components;

wherein the PDLC transmission phase grating is rendered substantially transparent when subjected to said electric field during the application of light that is p-polarized and incident on the grating at Bragg angle.

2. The grating as defined in claim 1 wherein said scalar optical dielectric constant has a value that is less than the value of said ordinary optical dielectric tensor component such that the grating has a diffraction efficiency of substantially zero upon said application of said electric field during the application of p-polarized light incident at the Bragg angle when the grating has an internal Bragg angle within a preselected range of angles.

3. The grating as defined in claim 1 wherein said scalar optical dielectric constant has a value that is equal or greater than the value of said ordinary optical dielectric tensor component, and said scalar optical dielectric constant has a value that is less than the average of said ordinary component and said extraordinary dielectric component, such that the grating has a diffraction efficiency of substantially zero upon said application of said electric field during the application of p-polarized light incident at the Bragg angle for a preselected internal Bragg angle.

4. The grating as defined in claim 1 wherein said scalar optical dielectric constant has a value that is greater than the average of said ordinary dielectric component and said extraordinary dielectric component such that the grating has a diffraction efficiency of substantially zero upon said application of said electric field during the application of p-polarized light incident at the Bragg angle for a preselected internal Bragg angle.

5. The grating as defined in claim 2 wherein said liquid crystal material is contained in droplets dispersed in a polymer matrix.

6. The grating as defined in claim 2 wherein said liquid crystal material is contained in an interconnected polymer matrix.

7. The grating as defined in claim 2 wherein said liquid crystal is a eutectic mixture of nematic liquid crystals.

8. The grating as defined in claim 2 wherein said liquid crystal has a positive dielectric anisotropy.

9. The grating as defined in claim 2 wherein said grating planes are unslanted.

10. The grating as defined in claim 3 wherein said liquid crystal material is contained in droplets dispersed in a polymer matrix.

11. The grating as defined in claim 3 wherein said liquid crystal material is contained in an interconnected polymer matrix.

12. The grating as defined in claim 3 wherein said liquid crystal is a eutectic mixture of nematic liquid crystals.

13. The grating as defined in claim 3 wherein said liquid crystal has a positive dielectric anisotropy.

14. The grating as defined in claim 3 wherein said grating planes are unslanted.

15. The grating as defined in claim 4 wherein said liquid crystal material is contained in droplets dispersed in a polymer matrix.

16. The grating as defined in claim 4 wherein said liquid crystal material is contained in an interconnected polymer matrix.

17. The grating as defined in claim 4 wherein said liquid crystal is a eutectic mixture of nematic liquid crystals.

18. The grating as defined in claim 4 wherein said liquid crystal has a positive dielectric anisotropy.

19. The grating as defined in claim 4 wherein said grating planes are unslanted.

20. A method of producing a polymer dispersed liquid crystal (PDLC) transmission phase grating operating in the Bragg regime, comprising the steps of:

providing a PDLC grating film contained within a cell, said PDLC film having a spatially periodic distribution of grating planes comprising polymer-rich regions and liquid crystal-rich regions

providing the major constituent of said polymer-rich regions as a polymer, and providing the liquid crystal constituent concentration within said liquid crystal-rich regions greater than the liquid crystal constituent concentration within said polymer-rich regions;

characterizing said polymer-rich regions by a scalar optical dielectric constant with a value that remains substantially unperturbed by an electric field being applied in a direction perpendicular to said PDLC grating film;

providing said liquid crystal-rich regions with a polymer matrix filled with liquid crystal-rich material, and said liquid crystal-rich material being characterized by optical dielectric tensor components, wherein said optical dielectric tensor components comprising an ordinary component measured within said grating planes and an extraordinary component measured perpendicular to said grating planes;

determining the value of said ordinary and extraordinary components in the absence of said electric field;

altering values of said optical dielectric tensor components by applying said electric field; and

providing said spatially periodic distribution having a spatial period of preselected value, and said electric field strength having a strength of preselected value, each said preselected value of said spatial period and said electric field strength being based upon the relationship between said scalar optical dielectric constant and said optical dielectric tensor components;

wherein the PDLC transmission phase grating is rendered substantially transparent when subjected to said electric field during the application of light that is p-polarized and incident on the grating at Bragg angle.