Switchable volume hologram materials and devices

• US 7,018,686 B2
• Filed: 10/24/2003
• Issued: 03/28/2006
• Est. Priority Date: 07/12/1996
• Status: Expired due to Fees

• Current Assignee: Leidos, Inc. (Leidos Holdings, Inc.)
• Original Assignee: Science Applications International Corporation
• Inventors: Tondiglia, Vince P., Natarajan, Lalquidi V., Bunning, Timothy J., Sutehrland, Richard L.
• Primary Examiner(s): WU, SHEAN CHIU
• Application Number:
  US10/691,600
• Publication Number:
  US 20040089842A1
• Time in Patent Office: 886 Days
• Field of Search: 428/1.1, 428/1.3, 252/299.01, 252/582, 349/96, 349/117, 349/196, 349/201, 385/10, 385/16, 385/37
• US Class Current: 428/1.1
• CPC Class Codes: C09K 19/544 as dispersing or encapsulating medium around the liquid crystal
• CPC Class Codes: C09K 2323/00 Functional layers of liquid crystal optical display excluding electroactive liquid crystal layer characterised by chemical composition
• CPC Class Codes: C09K 2323/03 Viewing layer characterised by chemical composition
• CPC Class Codes: G02F 1/13342 Holographic polymer dispersed liquid crystals
• CPC Class Codes: G03F 7/001 Phase modulating patterns, e.g. refractive index patterns
• CPC Class Codes: G03F 7/031 Organic compounds not covered by group G03F7/029
• CPC Class Codes: G03H 1/02 Details of features involved during the holographic process; Replication of holograms without interference recording
• CPC Class Codes: G03H 1/0248 Volume holograms
• CPC Class Codes: G03H 2001/026 Recording materials or recording processes G03H2226/11 takes precedence; corresponding details, see subgroups of G03H2260/00
• CPC Class Codes: G03H 2260/12 Photopolymer
• CPC Class Codes: G03H 2260/33 Having dispersed compound
• CPC Class Codes: Y10T 428/24802 Discontinuous or differential coating, impregnation or bond [e.g., artwork, printing, retouched photograph, etc.]

Abstract

A new photopolymerizable material allows single-step, fast recording of volume holograms with properties that can be electrically controlled. Polymer-dispersed liquid crystals (PDLCs) in accordance with the invention preferably comprise a homogeneous mixture of a nematic liquid crystal and a multifunctional pentaacrylate monomer, in combination with photoinitiator, coinitiator and cross-linking agent. Optionally, a surfactant such as octanoic acid may also be added. The PDLC material is exposed to coherent light to produce an interference pattern inside the material. Photopolymerization of the new PDLC material produces a hologram of clearly separated liquid crystal domains and cured polymer domains. Volume transmission gratings made with the new PDLC material can be electrically switched between nearly 100% diffraction efficiency and nearly 0% diffraction efficiency. By increasing the frequency of the switching voltage, switching voltages in the range of 50 Vrms can be achieved.

Claims

1. A subwavelength grating formed using polymer-dispersed liquid crystal materials, the subwavelength grating comprising:

a plurality of periodic polymer channels and polymer-dispersed liquid crystal (PDLC) channels;

wherein the polymer channels and PDLC channels are disposed perpendicular to a front surface of the subwavelength grating, and the combined thickness of the PDLC channel and polymer channel are substantially less than an optical wavelength thereby allowing the grating to exhibit form birefringence.

2. The subwavelength grating of claim 1, wherein a combined thickness of the polymer channel and the PDLC channel is selected to form a half-wave plate.

3. The subwavelength grating of claim 2, wherein a retardance of the subwavelength grating is equivalent to one-half of a wavelength, wherein the combined thickness of the polymer channel and the PDLC channel is equivalent to the λ

/(2|Δ

n|), where λ

is the wavelength and Δ

n is the difference between the extraordinary index of refraction of the subwavelength grating and the ordinary index of refraction of the subwavelength grating.

4. The subwavelength grating of claim 1, wherein a combined thickness of the polymer channel and the PDLC channel is selected to form a quarter-wave plate.

5. The subwavelength grating of claim 4, wherein a retardance of the subwavelength grating is equivalent to one-quarter of a wavelength, wherein the combined thickness of the polymer channel and the PDLC channel is equivalent to the λ

/(4|Δ

n|), where λ

is the wavelength and Δ

n is the difference between the extraordinary index of refraction of the subwavelength grating and the ordinary index of refraction of the subwavelength grating.

6. The subwavelength grating of claim 1, wherein the polymer-dispersed liquid crystal material comprises a polymerizable monomer, a liquid crystal, a cross-linking monomer, a coinitiator, and a photinitiator dye.

7. The subwavelength grating of claim 6, wherein the polymer-dispersed liquid crystal material further comprises a surfactant.

8. An optical switch comprising:

two cross polarizers; and

a half-wave plate interposed between the two cross polarizers, the half-wave plate comprising a plurality of periodic planes of polymer channels and polymer-dispersed liquid crystal (PDLC) channels, wherein the PDLC channels and polymer channels are disposed perpendicular to a front surface of the optical switch,

wherein the optical switch passes incident light absent a switching voltage and blocks incident light when a switching voltage is applied to the optical switch.

9. The optical switch of claim 8, wherein the polymer-dispersed liquid crystal material comprises a polymerizable monomer, a liquid crystal, a cross-linking monomer, a coinitiator, and a photinitiator dye.

10. The optical switch of claim 9, wherein the polymer-dispersed liquid crystal material further comprises a surfactant.

11. An optical switch comprising:

a beam splitter;

a mirror; and

a quarter-wave plate interposed between the beam splitter and the mirror, the quarter-wave plate comprising a plurality of periodic planes of polymer channels and polymer-dispersed liquid crystal (PDLC) channels, wherein the PDLC channels and polymer channels are disposed perpendicular to a front surface of the grating,

wherein the beam splitter reflects reflected light from the mirror absent a switching voltage, and when a switching voltage is applied to the optical switch, reflected light passes through the beam splitter and is retroreflected on the incident beam.

12. The optical switch of claim 11, wherein the polymer-dispersed liquid crystal material comprises a polymerizable monomer, a liquid crystal, a cross-linking monomer, a coinitiator, and a photinitiator dye.

13. The optical switch of claim 12, wherein the polymer-dispersed liquid crystal material further comprises a surfactant.

14. A method for reducing the switching voltage of a single electrically switchable subwavelength grating comprising:

stacking together a plurality of single electrically switchable subwavelength gratings, each electrically switchable subwavelength grating comprising a plurality of periodic planes of polymer channels and polymer-dispersed liquid crystal (PDLC) channels, wherein the PDLC channels and polymer channels are disposed perpendicular to a front surface of the electrically switchable subwavelength grating;

electrically connecting the stack of single electrically switchable subwavelength gratings in parallel; and

applying an electric field in order to switch the stack of single electrically switchable subwavelength gratings between an on state and off state, wherein the electric field required to switch the stack of single electrically switchable subwavelength gratings is lower than an electric field required to switch a single electrically switchable subwavelength grating.

15. The method of claim 14, wherein the single electrically switchable subwavelength grating polymer-dispersed liquid crystal material comprises a polymerizable monomer, a liquid crystal, a cross-linking monomer, a coinitiator, and a photinitiator dye.

16. The method of claim 15, wherein the polymer-dispersed liquid crystal material further comprises a surfactant.