Patent ID: 7196846

Claim:
An optical element, comprising: a first portion having a first principal material axis with a first permittivity ∈ 1 , and a second material axis with a second permittivity β 1 ∈ 1 ; a second portion in intimate contact with the first portion, the second portion having a second material axis and defining a two dimensional surface of incident contact and a normal axis relative to the defined two dimensional surface, the second portion having a second principal axis, a first permittivity ∈ 2 and a second permittivity β 2 ∈ 2 ; wherein the permittivities satisfy the relationship: β 1 ∈ 1 2 =β 2 ∈ 2 2 and the principal axis of the materials satisfy the relationship: β 1 ⁢ ⁢ cos 2 ⁢ ⁢ ϕ 1 + 1 β 1 ⁢ ⁢ sin 2 ⁢ ⁢ ϕ 1 = β 2 ⁢ ⁢ cos 2 ⁢ ⁢ ϕ 2 + 1 β 2 ⁢ ⁢ sin 2 ⁢ ⁢ ϕ 2 , where φ 1 is an angle of the first principal material axis relative to the normal and φ 2 is an angle of the second principal axis relative to the normal, and wherein one of the first or second materials is a biaxial material.