Quarter wave plate polarizer with two phase-shifting portions

Abstract

A right circular cylindrical body of an isotropic dielectric such as a cross-linked styrene copolymer, has respective pluralities of mutually parallel grooves formed in its axial end faces, spaced apart by an intermediate portion whose dimension c is a half wavelength. The axial lengths a, b of the grooves are such that when a wave passes through the body, a quarter wavelength phase difference is produced between a component of a wave having its E-vector parallel to the grooves and a component of the wave having its E-vector orthogonal to the grooves. Alternatively the plate may consist of two or more discrete bodies whose grooves are dimensioned to produce a total differential phase shift of one quarter wavelength.

I claim: 
     
       1. A quarter wave plate, comprising:
 at least one body of dielectric material, said at least one body having respective first and second end faces on opposite sides thereof, and including i); the first and second end faces each having a respective reflection coefficient, said at least one body including: 
 a respective first portion for providing a phase shift between first and second orthogonal components of an electromagnetic wave traversing the plate, and including a respective plurality of first number of parallel grooves extending inwardly of said respective first end face; ii) 
 a respective second portion for providing a phase shift between the first and second orthogonal components of the electromagnetic wave, and including a respective plurality of second number of parallel grooves extending inwardly of said respective second end face and aligned with the grooves of said respective plurality of first number of parallel grooves; and iii) 
 a respective third portion defined between said respective first and second portions, 
 wherein respective depths of the plurality of first and second parallel grooves are configured to produce the phase shifts of an odd integer multiple of quarter wavelengths between said first and second orthogonal components of the electromagnetic wave traversing the plate, the first component having an E-vector parallel to the plurality of first and second parallel grooves, and the second component having an E-vector perpendicular to the plurality of first and second parallel grooves, 
 wherein the dielectric material has a relative dielectric constant less than 5, and 
 wherein a length of the third portion is selected to differ from a half-wavelength by an amount to adjust the respective reflection coefficient at the first and second end faces. 
 
     
     
       2. The quarter wave plate as claimed in  claim 1 , wherein said first and second grooves have respective depths whose sum is such that a phase difference of an odd integer multiple of quarter wavelengths exists between the orthogonal components of the electromagnetic wave traversing the plate, a first of the components having its E-vector parallel to the grooves, and a second of the components having its E-vector perpendicular to the grooves. 
     
     
       3. The quarter wave plate as claimed in claim  2  1, wherein the respective grooves of each said respective first plurality of grooves has a depth which of each first parallel groove is equal to a depth of the grooves of each said respective second plurality of grooves each second parallel groove. 
     
     
       4. The quarter wave plate as claimed in  claim 3 , in which wherein said plate at least one body comprises a single said body, and wherein the grooves depths of each of said first and second pluralities of parallel grooves have depths such as to produce a respective phase difference of one-eighth of a wavelength between the first and second orthogonal components of the wave as the wave traverses said first and said  second portions, respectively. 
     
     
       5. The quarter wave plate as claimed in  claim 3 , in which said plate at least one body comprises two said bodies, and wherein the grooves depths of each of said respective first and second pluralities of parallel grooves have depths such as to produce a phase difference of one-sixteenth of a wavelength between the first and second orthogonal components of the wave as the wave traverses each said respective first and second portions. 
     
     
       6. The quarter wave plate as claimed in  claim 1  in which each respective third portion has an axial length which is substantially an integer number of half wavelengths of the wave. 
     
     
       7. The quarter wave plate as claimed in  claim 6  in which the axial length of each respective third portion is substantially one-half wavelength of the wave. 
     
     
       8. The quarter wave plate as claimed in  claim 1 , wherein said dielectric material consists of an isotropic dielectric. 
     
     
       9. The quarter wave plate as claimed in  claim 1  in which said dielectric material consists of a soft dielectric having a low dielectric constant. 
     
     
       10. The quarter wave plate as claimed in  claim 9  in which said dielectric material comprises a cross-linked styrene copolymer. 
     
     
       11. The quarter wave plate as claimed in claim 1, wherein the plate has a cylindrical structure. 
     
     
       12. The quarter wave plate as claimed in claim 1, wherein the at least one body comprises a continuous region that establishes a perimeter of each end face. 
     
     
       13. The quarter wave plate as claimed in claim 1, wherein the length of the third portion is an integer of one half wavelength, wherein said integer is an integer other than one.