Waveplate lenses and methods for their fabrication
The invention provides for lenses fabricated as planar thin film coatings with continuous structure. The lensing action is due to optical axis orientation modulation in the plane of the lens. The lenses of the current invention are fabricated using photoalignment of a liquid crystal polymer wherein the polarization pattern of radiation used for photoalignment is obtained by propagating the light through an optical system comprising a shape-variant nonlinear spatial light polarization modulators.
1. A method for fabricating diffractive waveplate lens of nonlinear phase modulation profile comprising:
(a) providing a substrate;
(b) dispensing a photoaligning material layer over said substrate;
(c) providing a light source with wavelength in the absorption band of said photoalignment material;
(d) propagating a light beam from the light source through polarization control optics comprising a polarization converter outputting a spatially nonlinear distribution of linear polarization along a radial direction;
(e) further propagating said light beam from the light source through an optical projection system;
(f) exposing said photoaligning material layer to said light beam at the output of said optical projection system,
(g) dispensing a polymerizable liquid crystal precursor over the photoaligned material layer; and
(h) in-situ reacting said polymerizable liquid crystal to form a polymer film.
2. The method for fabricating diffractive waveplate lens as in claim 1 further comprising deposition of two or more liquid crystal polymer films which vary in thickness, optical anisotropy and chirality.
3. The method as in claim 1 wherein said spatially nonlinear polarization converter comprises an assembly of a first substrate and a second substrate with at least one of the first and the second substrate having non-planar surface topology, said first substrate and said second substrate treated for inducing alignment of liquid crystalline materials, and a liquid crystalline material being sandwiched in-between the first substrate and the second substrate.
4. The method as in claim 3 wherein said first and second substrates are plano-convex and plano-concave lenses.
5. The method as in claim 1 wherein said polarization control optics further comprises an input and an output quarter waveplates with their axes aligned parallel or perpendicular to each other.
6. The method as in claim 1 wherein said polarization control optics further comprises an input and an output liquid crystal cells, each possessing a twist, oriented such as the resultant polarization is linear at the absence of the nonlinear polarization converter.
7. The method as in claim 1 wherein said nonlinear polarization converter comprises a diffractive waveplate-lens meeting half-wave phase retardation condition for the wavelength of the recording radiation.
8. The method as in claim 1 wherein said nonlinear polarization converter comprises material with spatially varying optical anisotropy in the radial direction.