FABRICATION OF HIGH EFFICIENCY, HIGH QUALITY, LARGE AREA DIFFRACTIVE WAVEPLATES AND ARRAYS
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Abstract
The objective of the present invention is providing a method for fabricating high quality diffractive waveplates and their arrays that exhibit high diffraction efficiency over large area, the method being capable of inexpensive large volume production. The method uses a polarization converter for converting the polarization of generally non-monochromatic and partially coherent input light beam into a pattern of periodic spatial modulation at the output of said polarization converter. A substrate carrying a photoalignment layer is exposed to said polarization modulation pattern and is coated subsequently with a liquid crystalline material. The high quality diffractive waveplates of the present invention are obtained when the exposure time of said photoalignment layer exceeds by generally an order of magnitude the time period that would be sufficient for producing homogeneous orientation of liquid crystalline materials brought in contact with said photoalignment layer. Compared to holographic techniques, the method is robust with respect to mechanical noises, ambient conditions, and allows inexpensive production via printing while also allowing to double the spatial frequency of optical axis modulation of diffractive waveplates.
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Citations
21 Claims
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1-11. -11. (canceled)
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12. A method for producing orientation modulation of an anisotropy axis of a photoresponsive material layer at a predetermined spatial period, the method comprising:
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(a) emitting a light beam being at least partially coherent and having a linear polarization from a light source; (b) using a polarization converter to periodically modulate in space the polarization of said light beam, the polarization converter having an optical axis modulation period that is twice larger than said predetermined spatial period; (c) providing a photoresponsive material layer having an anisotropy axis that may be formed or aligned according to polarization of said light beam; and (d) exposing at least a portion of said photoresponsive material layer to the polarization modulation pattern produced by said polarization converter at an exposure energy density exceeding at least 5 times the exposure energy density sufficient for producing waveplates with homogeneous orientation of the optical axis whereby solely the anisotropy axis in said photoresponsive material is aligned according to the polarization modulation pattern of the polarization converter. - View Dependent Claims (13, 14, 15, 16, 17)
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18. An apparatus for producing spatially periodic orientation modulation of an anisotropy axis of a photoresponsive material layer, the apparatus comprising:
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(a) a light source emitting a light beam that is at least partially coherent and linearly polarized; (b) a polarization converter configured to periodically modulate the polarization of said light beam along a single axis to generate a polarization modulation pattern, the polarization converter having an optical axis modulation period that is twice larger than a predetermined spatial period of said spatial periodic orientation modulation; (c) a photoresponsive material having an anisotropy axis that may be formed or aligned according to polarization of said light beam; (d) means for holding and positioning a layer of said photoresponsive material; (e) means for positioning and projecting the polarization modulation pattern of onto at least a portion of said photoresponsive material layer; (d) means for exposing different areas of said photoresponsive material layer to said polarization modulation pattern at an exposure energy density exceeding at least 5 times the exposure energy density sufficient for producing waveplates with homogeneous orientation of the optical axis whereby solely the anisotropy axis in said photoresponsive material is aligned according to the polarization modulation pattern of the polarization converter. - View Dependent Claims (19, 20, 21)
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Specification