Mechanical rubbing method for fabricating cycloidal diffractive waveplates
View Patent ↗Cycloidal boundary conditions for aligning liquid crystalline materials are obtained by mechanical rubbing of a polymer coating. The rubbing is performed by a rubbing head rotating around an axis perpendicular to the rubbing plane while the alignment polymer film is being translated across the rubbing film such as only a linear portion of the alignment film touches the rubbing film at any given time.
1. A rubbing method for producing liquid crystal diffractive waveplates, the method comprising the steps of:
(a) providing a rubbing film on a plane substrate;
(b) mechanically translating said rubbing film;
(c) controlling translation speed and direction of said rubbing film along two orthogonal coordinates;
(c) an alignment film over a cylindrical substrate; and
(d) mechanically rotating said alignment film across the rubbing film such as they are in touch along a single line at any given time, wherein the method produces the liquid crystal diffractive waveplates.
2. The method as in claim 1 wherein said mechanically translating of said rubbing film comprises a two-dimensional oscillating capability.
3. The method as in claim 1 wherein said mechanically translating said rubbing film comprises a stage with one-dimensional oscillating capability combined with a rotation.
4. The method as in claim 1 wherein said mechanically translating of said rubbing film comprises:
(a) a substrate;
(b) a first rotation assembly comprising a cylinder and a rotation stage rotating said cylinder around a first axis;
(c) a frame for mounting said first rotation assembly on a second rotation assembly that provides rotation of the first rotation assembly around an axis orthogonal to the rotation axis of the first rotation assembly.
5. The method as in claim 1 wherein said controlling the translation speed and direction of said rubbing film along two orthogonal coordinates comprises electronically controlled translation stages with programmable acceleration.
6. The method as in claim 5 wherein said electronically controlled translation stages change the translation direction of said rubbing film in a nonlinear fashion as a function of time.
7. The method as in claim 1 wherein the alignment film is a polymer selected from a group of materials that include polyimides and Poly-Vinyl-Alcohol.
8. The method as in claim 1 wherein the alignment film is coated on a flexible support substrate.
9. The method as in claim 8 wherein said support substrate carrying said alignment film has a portion shaped as a cylinder.
10. The method as in claim 8 wherein said alignment film on said support substrate is spool-wound and is pulled across to a take up spool such as only a line of the film touches the rubbing film at any given time.
11. A method for fabricating patterned waveplates wherein the alignment film prepared according to claim 10 is further coated by a polymerizable liquid crystalline material followed by polymerization before the film reaches the take up spool.
12. The method for fabricating patterned waveplates as in claim 11 wherein said polymerizable liquid crystal is deposited on rubbed alignment layer from a solution chosen from a group of materials comprising alcohols, propylene glycol monomethyl ether acetate (PGMEA), cyclopentanone, and toluene, Dimethylformamide (DMF).
13. The method for fabricating patterned waveplate as in claim 12 wherein said waveplate is a cycloidal waveplate.
14. The method for fabricating patterned waveplate as in claim 12 wherein said patterned waveplate has at least a portion with a parabolic profile of optical axis orientation change across the surface of the waveplate.