Electrically controllable liquid crystal microstructures

• US 6,864,931 B1
• Filed: 02/16/2000
• Issued: 03/08/2005
• Est. Priority Date: 02/17/1999
• Status: Expired due to Fees

• Current Assignee: Kent State University
• Original Assignee: Kent State University
• Inventors: Kumar, Satyendra, Kim, Jae-hoon
• Primary Examiner(s): Nguyen, Dung T.
• Application Number:
  US09/913,253
• Time in Patent Office: 1,847 Days
• Field of Search: 349/86, 349/88, 349/93, 349187-188, 349/95, 349200-202, 349/123, 349/122, 349/89
• US Class Current: 349/88
• CPC Class Codes: G02B 3/0006 Arrays G02B3/02, G02B5/188 take precedence
• CPC Class Codes: G02B 3/0056 arranged along two different directions in a plane, e.g. honeycomb arrangement of lenses G02B3/0043 takes precedence; miniaturised objectives for electronic devices employing wafer level optics G02B13/0085
• CPC Class Codes: G02B 3/0081 having one or more elements with analytic function to create variable power variable magnification in general G02B15/00
• CPC Class Codes: G02B 5/1828 having means for producing variable diffraction controlling the direction of light by means of one or more diffracting elements G02B26/0808; acousto-optical elements G02F1/11, G02F1/33; electro- or magneto-optical diffraction G02F1/292, G02F1/2955
• CPC Class Codes: G02F 1/133377 Cells with plural compartments or having plurality of liquid crystal microcells partitioned by walls, e.g. one microcell per pixel
• CPC Class Codes: G02F 1/29 for the control of the position or the direction of light beams, i.e. deflection
• CPC Class Codes: G02F 1/294 Variable focal length devices
• CPC Class Codes: G02F 2203/28 focussing or defocussing

Abstract

This invention relates to methods of building rigid or flexible arrays of electro-optic devices. A phase separated composite structure technique yields adjacent regions of polymer and liquid crystal (LC) of specific architecture instead of a random dispersion of LC droplets. The above devices can be prepared by producing volutes of LC structure (56) next to a polymer area (58) using anisotropic phase separation of LC from a photopolymer. Initial by UV exposure. The shape, size and placement of these regions inside a cell becomes easily controllable with using optical mask or laser beam. The boundaries of LC volume can be controlled by controlling the chemical composition of the polymer and using an alignment layer (28).

Claims

1. A light modulating cell, comprising:

first and second opposed substrates;

a solution of prepolymer and low molecular weight (LMW) organic material, wherein said solution is disposed between the substrates and is phase separated to form;

a layer of polymeric material primarily adjacent to the first substrate; and

a defined microstructure of LMW organic material primarily adjacent to the second substrate, the microstructure being bounded by portions of the polymeric material extending to the second substrate, the defined microstructure defining a diffraction grating.

2. The cell according to claim 1, further comprising:

an alignment layer disposed on the second substrate to affect said defined microstructure.

3. The cell according to claim 3claim 1, further comprising:

an electrode layer disposed on each said substrate facing both said layers for applying an electric field to alter the optical appearance of the cell.

4. The cell according to claim 3, wherein said defined microstructure defines a one-dimensional linear grating.

5. The cell according to claim 4, wherein said one-dimensional linear grating is electrically switchable via the electrode layers.

6. The cell according to claim 5, wherein said one-dimensional linear grating includes a plurality of varying-width gratings.

7. The cell according to claim 3, wherein said defined microstructure defines a two-dimensional grating.

8. The cell according to claim 7, wherein said two-dimensional grating is electrically switchable via the electrode layers.

9. A light modulating cell comprising:

first and second opposed substrates;

a solution of prepolymer and low molecular weight (LMW) organic material, wherein said solution is disposed between the substrates and is phase separated to form;

a layer of polymeric material primarily adjacent to the first substrate; and

a defined microstructure of LMW organic material primarily adjacent to the second substrate, the microstructure being bounded by portions of the polymeric material extending to the second substrate, said defined microstructure defining an array of microlenses.

10. The cell according to claim 9, wherein each microlens in said array of microlenses includes a liquid crystal region having a curved interface between said liquid crystal region and said layer of polymeric material.

11. The cell according to claim 10, wherein each said microlens is electrically controllable, and wherein a change in the electric field applied to each said microlens changes the focal length thereof.

12. The cell according to claim 10, wherein the curved interface is substantially parabolic.

13. The cell according to claim 9, wherein the microlenses have a lateral dimension of less than about five microns.

14. The cell according to claim 9, wherein the microlenses have a lateral dimension of less than about 0.5 microns.

15. A method for fabricating a low molecular weight microstructure, comprising the steps of:

preparing a solution of prepolymer and low molecular weight (LMW) organic material;

disposing said solution between pairs of substrates; and

inducing phase separation of said solution, the inducing being spatially controlled both transverse to and along the substrates to form at least one LMW microstructure on one of said substrates.

16. The method according to claim 15, wherein said step of inducing is by heating said solution.

17. The method according to claim 15, wherein said step of inducing is by including a solvent in said solution.

18. The method according to claim 15, wherein said step of inducing is by positioning a light source above one of said substrates.

19. The method according to claim 18, further comprising the step of positioning a mask between said light source and said substrates, wherein openings in said mask direct light from said source between said substrates and polymerize said prepolymer and bound said LMW microstructure.

20. The method according to claim 19 further comprising the steps of:

removing said mask;

positioning a second mask between said light source and said substrate; and

illuminating said light source to complete phase separation and further control configuration of said LMW microstructure.

21. The method according to claim 19, wherein said light source is ultraviolet.

22. The method according to claim 19, further comprising a step of mixing in said solution, a dye sensitive to visible light radiation, and wherein said light source generates visible light.

23. The method according to claim 18, further comprising:

providing an electrode on each said substrate facing one another; and

electrically controlling the LMW material in said LMW microstructure via the electrode.

24. The method according to claim 18 further comprising the step of:

providing an interference pattern of said light source to generate a spatially varying pattern which generates a corresponding intensity gradient in the cell.

25. The method according to claim 15, further comprising the step of providing an alignment layer on one of said substrates such that said LMW microstructure forms on said substrate with said alignment layer.

26. A light modulating cell, comprising:

a solution of prepolymer and low molecular weight (LMW) organic material that is phase separated to form;

a layer of polymeric material; and

a defined microstructure of LMW organic material disposed on one side of the layer of polymeric material, the defined microstructure defining one or more diffractive or refractive optical elements.

27. The cell as set forth in claim 26, wherein the one or more diffractive or refractive optical elements are selected from a group consisting of:

(i) one or more diffraction-gratings; and

(ii) a plurality of microlenses.

28. The cell as set forth in claim 26, further comprising:

first and second opposed substrates separated by a gap containing the layer of polymeric material and the defined microstructure, the layer of polymeric material being primarily adjacent to the first substrate, the defined microstructure being primarily adjacent to the second substrate; and

electrical circuitry for selectably electrically modulating the LMW organic material of the defined microstructure to electrically control a diffractive or refractive characteristic of the one or more diffractive or refractive optical elements.

29. The cell as set forth in claim 28, wherein the one or more diffractive or refractive optical elements include a plurality of diffractive or refractive optical elements, and the electrical circuitry includes:

one of an active electrical control matrix and a passive electrical control matrix for selectably controlling individual ones or sub-sets of the plurality of diffractive or refractive optical elements.

30. The cell as set forth in claim 26, wherein the solution of prepolymer and low molecular weight (LMW) organic material is suspended within an aperture during the phase separation.