Electrically switchable polymer-dispersed liquid crystal materials including switchable optical couplers and reconfigurable optical interconnects

• US 7,081,215 B2
• Filed: 08/12/2004
• Issued: 07/25/2006
• Est. Priority Date: 07/29/1998
• Status: Expired due to Term

• Current Assignee: Leidos, Inc. (Leidos Holdings, Inc.)
• Original Assignee: Science Applications International Corporation
• Inventors: Tondiglia, Vince P., Sutherland, Richard L., Epling, Bob, Natarajan, Lalgudi V., Bunning, Timothy J., Brandelik, Donna M.
• Primary Examiner(s): WU, SHEAN CHIU
• Application Number:
  US10/916,430
• Publication Number:
  US 20050007639A1
• Time in Patent Office: 712 Days
• Field of Search: 252/299.01, 252/582, 430/2, 349/112, 359/15, 359/569, 359/576, 385/15, 385/16, 385/27, 385/37
• US Class Current: 252/582
• 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: G02B 5/32 Holograms used as optical elements
• CPC Class Codes: G02B 6/2713 cascade of polarisation selective or adjusting operations
• CPC Class Codes: G02B 6/2931 Diffractive element operating in reflection
• CPC Class Codes: G02B 6/29311 Diffractive element operating in transmission
• CPC Class Codes: G02B 6/29314 by moving or modifying the diffractive element, e.g. deforming
• CPC Class Codes: G02B 6/29395 configurable, e.g. tunable or reconfigurable switching G02B6/35
• CPC Class Codes: G02F 1/13342 Holographic polymer dispersed liquid crystals
• CPC Class Codes: G02F 2201/305 diffraction grating
• CPC Class Codes: G03H 1/0005 Adaptation of holography to specific applications holographic optical element G02B5/32; holographic scanner G02B26/106; recognition using holographic mask G06V10/88; holographic memories G11B7/0065, G11C13/042
• 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 2001/0264 Organic recording material
• CPC Class Codes: G03H 2001/2615 in physical contact, i.e. layered holograms
• CPC Class Codes: G03H 2260/12 Photopolymer
• CPC Class Codes: G03H 2260/33 Having dispersed compound

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 octancic 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. The optional use of a surfactant allows low switching voltages at lower frequencies than without a surfactant. In an alternative embodiment, a PDLC material in accordance with the invention can be utilized to form reflection gratings, including switchable reflection gratings. In still further embodiments, a PDLC material in accordance with the invention can be used to form switchable subwavelength gratings. By further processing, static transmission, reflection, and subwavelength PDLC materials can be formed. In addition, PDLC materials in accordance with the present invention can be used to form switchable slanted transmission gratings suitable for switchable optical coupling and reconfigurable optical interconnects.

Claims

1. A transmission grating comprising:

at least two electrode plates; and

a mixture disposed between the at least two electrode plates, the mixture includes;

a polymerizable monomer;

a liquid crystal;

a chain-extending monomer;

a coinitiator; and

a photoinitiator.

2. An assembly for preparing the transmission grating of claim 1, comprising:

a first prism disposed on a surface of the transmission grating;

a second prism disposed adjacent to the first prism and on the surface of the transmission grating; and

an index matching fluid disposed between the first prism and the second prism and between the first prism and the transmission grating.

3. An optical coupling device comprising:

a plurality of transmission gratings according to claim 1; and

a transparent substrate coupled to the plurality of transmission gratings.

4. The optical coupling device of claim 3, one of the plurality of transmission gratings provides an optical input channel of the optical coupling device, and at least two of the plurality of transmission gratings provide optical output channels of the optical coupling device.

5. The optical coupling device of claim 3, the transparent substrate is in optical contact with at least one of the plurality of transmission gratings.

6. The optical coupling device of claim 3, further comprising:

a voltage source associated with each of the plurality of transmission gratings to control a diffraction efficiency of the each transmission grating.

7. The optical coupling device of claim 4, further comprising:

a voltage source associated with each of the plurality of transmission gratings to control a diffraction efficiency of the transmission grating.

8. The optical coupling device of claim 7, the optical output channels provide substantially equal optical output power.

9. The optical coupling device of claim 8, the substantially equal optical output power provided by the optical output channels is achieved from a tuning the voltage sources associated with the at least two transmission gratings.

10. The optical coupling device of claim 4, the optical output channels are selectively adjustable and reconfigurable optical output channels.

11. The optical coupling device of claim 3, at least one of the plurality of transmission gratings has a slant angle, θ

s, and the transparent substrate has a critical angle, θ

c, and wherein 2θ

s>

θ

c.

12. The optical coupling device of claim 4, at least one of the optical output channels is reconfigurable to provide substantially no optical output power.

13. A method for preparing a transmission grating, comprising:

providing at least two electrode plates;

disposing between the at least two electrode plates a mixture that includes a polymerizable monomer;

a liquid crystal;

a chain-extending monomer;

a coinitiator; and

a photoinitiator; and

exposing the mixture to light in an interference pattern.

14. The method of claim 13, the providing at least two electrode plates comprises:

arranging the at least two electrode plates 15–

20 μ

m apart.

15. The method of claim 13, the exposing the mixture to light in an interference pattern comprises:

disposing a first prism on a surface of the transmission grating;

disposing a second prism adjacent to the first prism and on the surface of the transmission grating;

applying a first beam of coherent light to the mixture through the first prism; and

applying a second beam of coherent light to the mixture through the second prism.

16. The method of claim 15, the exposing the mixture to light in an interference pattern further comprises:

applying an index matching fluid between the first prism and the second prism and between the first prism and the transmission grating.

17. A method for preparing an optical coupling device comprising:

constructing a plurality of transmission gratings according to claim 13; and

coupling a transparent substrate to the plurality of transmission gratings.

18. The method of claim 17, further comprising:

implementing one of the plurality of transmission gratings as an optical input channel of the optical coupling device; and

implementing at least two of the plurality of transmission gratings as optical output channels of the optical coupling device.

19. The method of claim 17, the coupling the transparent substrate to the plurality of transmission gratings comprises:

coupling the transparent substrate to the plurality of transmission gratings such that the transparent substrate is in optical contact with at least one of the plurality of transmission gratings.

20. The method of claim 17, further comprising:

electrically connecting the at least two electrode plates of each of the plurality of transmission gratings to a voltage source for controlling a diffraction efficiency of the each transmission grating.

21. The method of claim 18, further comprising:

electrically connecting the at least two electrode plates of each of the plurality of transmission gratings to an associated voltage source for controlling a diffraction efficiency of the each transmission grating.

22. The method of claim 21, further comprising:

setting the optical output channels to provide substantially equal optical output power.

23. The method of claim 22, the setting the optical output channels comprises:

tuning the associated voltage sources of the at least two transmission gratings to provide substantially equal optical power from optical output channels.

24. The method of claim 18, further comprising:

selectively adjusting and reconfiguring the optical output channels.

25. The method of claim 17, at least one of the plurality of transmission gratings has a slant angle, θ

s, and the transparent substrate has a critical angle, θ

c, and wherein 2θ

s>

θ

c.

26. The method of claim 18, further comprising:

reconfiguring at least one of the optical output channels to provide substantially no optical output power.