Patent ID: 7859753

Claim:
A filter for discriminating wavelengths in a light signal, comprising: a plurality of retarders disposed along a path of the light signal, the retarders each having a fast axis and a slow axis along which orthogonal components of the light signal propagate according to distinct optical indices; wherein the retarders are rotationally oriented relative to one another such that differential retardation of orthogonal components of the light signal causes certain wavelengths in the light signal to have predetermined polarization orientations at least at two locations along the path of the light signal; at least two polarizers respectively located at said two locations along the path of the light signal, wherein the at least two polarizers are rotationally oriented to the predetermined polarization orientations at said two locations, the polarizers each transmitting a component of the light signal that is parallel to a respective said polarization orientation and blocking transmission of a component of the light signal that is orthogonal to the respective said polarization orientation, whereby the filter discriminates for transmission of said certain wavelengths; and, wherein at least one of the polarizers is disposed at a further point along the path of the light signal from another one of the polarizers disposed at a nearer point along the path, wherein the polarizer at said further point comprises a zero-degree reflective polarizing element that transmits said component parallel to the polarization orientation while redirecting blocked orthogonal components oppositely along the path, and the polarizer at the nearer point comprises an absorptive polarizer that blocks orthogonal components by substantially absorbing said orthogonal components without redirection along the path; further comprising a plurality of stages of retarders between the polarizer at said nearer point and the polarizer at said further point, wherein the retarders of at least one of the stages along the path precede the polarizer at said further point comprising the zero-degree reflective polarizing element, and follow the polarizer at the nearer point which comprises an absorptive polarizer that blocks orthogonal components by substantially absorbing said orthogonal components without redirection along the path, wherein the plurality of stages comprise alternating zero-degree reflective polarizers and absorptive polarizers.