Retarder stack pairs for polarization basis vector transformations

Abstract

A device for manipulating the polarization of light which includes a first retarder-stack (Stack 1) that converts the polarization of input light from a first polarization basis vector (PBV1) to a second polarization basis vector (PBV2), a second retarder-stack (Stack 2) that returns the polarization of light from PBV2 to PBV1, and one or more optically functional layers between Stack 1 and Stack 2. Stack 1 has a plurality of layers, wherein the number of layers, retardation values, and orientations of layers in Stack 1 are selected to produce a PBV2 that is substantially spectrally-uniform over a prescribed range of wavelengths. PBV1 is a non-trivial eigen-polarization of combined Stack 1 and Stack 2. Stack 2 has a plurality of layers and Stack 2 is arranged in series with Stack 1. Alternatively, instead of two different stacks, a reflector may be used to produce a return pass through Stack 1.

1 - 19 . (canceled) 
     
     
         20 . A device for manipulating the polarization of light, including:
 a retarder-stack that converts the polarization of forward-pass light from a linear polarization (PBV1) to a circular polarization (PBV2) over a prescribed range of wavelengths, wherein the retarder-stack has base retarder layers that each have R th ≥R e /2, wherein the retarder-stack contains M half-wave retarders with slow-axes oriented at angles (α 1 , α 2  . . . α M ) such that (α 2 >2α 1 , α 3 >2α 2  . . . ), producing a quasi-linear rotated SOP at angle β=2(α M −α M-1 +α M-2 − . . . ), followed by a quarter-wave retarder with slow-axis oriented substantially along α 0 =(β+π/4), and wherein M and the specific angles are selected to produce PBV2 with ellipticity near unity over a prescribed range of wavelengths;   a reflector that produces a polarization-preserving reflection, returning at least a portion of the forward-pass light to the retarder-stack with opposite handedness, wherein return-light undergoes an effective reverse-order (RO) pass of the retarder-stack, such that the exiting polarization is substantially orthogonal to PBV1.   
     
     
         21 . The device of  claim 20 , further including a linear polarizer preceding Stack 1. 
     
     
         22 . The device of  claim 21 , wherein the linear polarizer layer is clad with protective substrates having R th <5 nm. 
     
     
         23 . The device of  claim 20 , further including one or both of a positive c-plate and a crossed negative a-plate inserted between Stack 1 and the reflector to reduce the composite R th . 
     
     
         24 . The device of  claim 20 , wherein M=1, α 1  is approximately 14.5°, α 0  is approximately 74°, and the C-plate retardation is 50 nm≤R th ≤300 nm. 
     
     
         25 . The device of  claim 21 , wherein M=3, α 1  is approximately 2°, α 2  is approximately 14°, and α 3  is approximately 48°, α 0  is approximately −63° and the C-plate retardation is 50 nm≤R th ≤300 nm. 
     
     
         26 . The device of  claim 24 , wherein the aggregated ellipticity field-ratio exiting the retarder stack in the forward pass is >0.91 in the red, green, and blue portions of the spectrum. 
     
     
         27 . The device of  claim 25 , wherein the aggregated ellipticity field-ratio exiting the retarder stack in the forward pass is >0.98 in the red, green, and blue portions of the spectrum.