Patent Application
20080049321
The invention will be described in greater detail with reference to the accompanying drawings which represent preferred embodiments thereof, wherein:
With reference to
The ideal thickness d of the patterned half wave plate 100 may be determined, as described above, on the basis of the average wavelength λ of the incident light beam 150 and the birefringence Δn of the birefringent material of the monolithic layer 130. The incident light beam 150 may be linearly or elliptically polarized and, preferably, has an average wavelength of about 400 to 2000 nm. The birefringent material, preferably, has a birefringence of about 0.05 to 0.5. The actual thickness of the monolithic layer 130 is, preferably, close to the ideal value (within about 10%).
The entry surface 110 and the exit surface 120 of the half wave plate 100 are, preferably, substantially planar. The polarized light beam 150 launched into the entry surface 110, via an input port (not shown) and optional optical elements (such as a collimating lens; not shown) is, preferably, normal to the entry surface 110. Accordingly, the light beam 160 exiting the half wave plate 100 is made up of a plurality of different polarization states. When these polarization states are superpositioned at an image plane 170 of an optical system, via a focusing lens 180 and optional optical elements (not shown), the image 190 will be substantially depolarized.
An important feature of the present invention is that the patterned half wave plate 100 incorporates a monolithic layer 130 including a plurality of regions having fast axes with different orientations. For instance, the monolithic layer 130 may comprise a plurality of circular sectors or a plurality of parallel sections having different fast-axis orientations. As illustrated in
It is desired that the fast axes have at least four different orientations within a cross section of the monolithic layer 130 parallel to the entry surface 110. Preferably, the fast axes have at least eight different orientations. In some instances, the fast axes may have as many as 48 or more different orientations. In effect, the orientations of the fast axes may vary continuously. Such a continuous variation of fast-axis orientation may be advantageous to reduce unwanted diffraction effects.
Preferably, the orientations of the fast axes vary in a regular pattern. The pattern may arise from a linear variation of the in-plane angle with respect to a location coordinate within a cross section of the monolithic layer 130 parallel to the entry surface 110. As shown in
Alternatively, the in-plane angle may vary linearly with respect to a Cartesian coordinate, i.e. an x or y coordinate, within a cross section of the monolithic layer 130 parallel to the entry surface 110, as shown in
Certainly, other patterns of fast-axis orientation could be generated with different choices of a (preferably, a≧1) and b, or c (preferably, c≧180°) and d. Other patterns could also be generated with a different choice of location coordinate as variable. Furthermore, the number of regions and the number of different orientations of the fast axes within the monolithic layer 130 may also be modified. For instance, the fast-axis orientation could, effectively, vary continuously within the monolithic layer 130 according to any such pattern.
For a polarized light beam 150 incident on the entry surface 110, different areas in the beam will have their polarization state “rotated” by different amounts as they pass through different areas in the patterned half wave plate 100, depending on the orientation of the fast axis at each area. Thus, the device acts as spatial depolarizer that converts a polarized light beam 150 into a light beam 160 having a plurality of different polarization states within its cross section. If the incident light beam 150 is linearly polarized, the exiting light beam 160 will consist of a plurality of linearly polarized states. If the incident light beam 150 is elliptically polarized, the exiting light beam 160 will consist of a plurality of elliptically polarized states. If the incident light beam 150 is depolarized, the exiting light beam 160 will also be depolarized. Therefore, a partially polarized light beam 150 may also be depolarized by the patterned half wave plate 100.
The patterned half wave plate 100 may be fabricated using a photo-alignment method, with ultraviolet (UV) light, that is similar to the methods disclosed in U.S. Pat. No. 5,861,931 to Gillian, et al., U.S. Pat. No. 6,055,103 to Woodgate, et al., U.S. Pat. No. 7,061,561 to Silverstein, et al., and a paper entitled “Photo-Aligned Anisotropic Optical Thin Films” by Seiberle, et al. (SID International Symposium Digest of Technical Papers, 2003, Vol. 34, pp. 1162-1165), for instance. All the above-mentioned documents are incorporated herein by reference.
As a first step in such a method, a photo-alignment layer 140 is created, as part of the patterned half wave plate 100. A photo-polymerizable material is applied to a substrate, typically a glass plate. The photo-polymerizable material is then irradiated with linearly polarized UV light to provide a directional alignment within the resulting photo-alignment layer 140. Preferably, a photo-polymerizable prepolymer is used as the photo-polymerizable material, and the resulting photo-alignment layer 140 is composed of a photo-polymerizable polymer. As a second step, a cross-linkable material is applied over the photo-alignment layer 140 and is aligned according to the directional alignment of the photo-alignment layer 140. The cross-linkable material is then cross-linked through exposure to UV light to produce the monolithic layer 130 of birefringent material, as part of the patterned half wave plate 100. Preferably, a liquid-crystal prepolymer is used as the cross-linkable material, and the resulting monolithic layer 130 of birefringent material is composed of a liquid-crystal polymer. Suitable photo-polymerizable prepolymers and liquid-crystal prepolymers are available from Rolic Technologies Ltd. (Allschwil, Switzerland).
An alignment pattern may be formed in the photo-alignment layer 140 by varying the polarization state of the linearly polarized UV light in a pattern during the creation of the layer. As discussed by Seiberle, et al., such alignment patterns may be generated by using photomasks, alignment masters, laser scanning, or synchronized movement of the linearly polarized UV light beam and the substrate. After application of the cross-linkable material onto the photo-alignment layer 140 and subsequent cross-linking, the resulting monolithic layer 130 of birefringent material will have fast axes with orientations that vary in a pattern corresponding to the alignment pattern.
For example, the monolithic layer 130, which includes a plurality of regions with different fast-axis orientations, may be produced from a photo-alignment layer 140 created by a series of exposures of the photo-polymerizable material to linearly polarized UV light through an appropriate number of patterned photomasks. Alternatively, a continuous variation of fast-axis orientation within the monolithic layer 130 may be achieved by using a photo-alignment layer 140 created by exposing the photo-polymerizable material to linearly polarized UV light through a slit, while moving the substrate in an appropriate pattern.
This application claims priority from U.S. Provisional Application No. 60/823,559 filed Aug. 25, 2006, which is hereby incorporated by reference for all purposes.
| Number | Date | Country | |
|---|---|---|---|
| 60823559 | Aug 2006 | US |
