Compound quarter-wave retarder for optical disc pickup heads

Abstract

Chemically-bonded laminated polymer achromatic polarization devices, such as circular polarizers, are disclosed for use in optical disc (e.g., CD/DVD) pickup heads. Chemically-bonded laminated polymer achromatic polarization devices have the benefit of providing stable retardation and optic axis over an extended wavelength range, thereby ensuring orthogonal polarization in double-pass for two or more laser wavelengths. Moreover, the chemically-bonded laminated polymer achromatic polarization devices can be symmetric in construction, such that there is no specific input and output side. This alleviates the need to produce geometries that prohibit inversion of the part when installed in the system. Manufacturing processes that produce chemically-bonded laminated polymer achromatic polarization devices, with high light efficiency, durability and robust performance in a variety of environmental conditions are disclosed.

1 . An achromatic polarization device for an optical disc pickup head, the achromatic polarization device comprising:
 a monolithic retarder stack comprising:
 a first polymer retarder layer and 
 a second polymer retarder layer chemically bonded to the first retarder polymer layer; 
 wherein the monolithic retarder stack is operable to transform, on a forward pass, linearly polarized light to circularly polarized light, and on a reverse pass, circularly polarized light to linearly polarized light, wherein the light on the reverse pass is substantially orthogonal to the light on the forward pass. 
   
     
     
         2 . An achromatic polarization device according to  claim 1 , wherein the monolithic retarder stack further comprises a dummy layer. 
     
     
         3 . An achromatic polarization device according to  claim 2 , wherein the dummy layer is bonded to the first polymer retarder layer. 
     
     
         4 . An achromatic polarization device according to  claim 2 , wherein the dummy layer has zero in-plane retardation. 
     
     
         5 . An achromatic polarization device according to  claim 2 , wherein the dummy layer has substantially little effect on the state of polarization of light passing therethrough.