Patent ID: 6393039
Filing Date: 2002-05-21
Classification: G02B

Abstract:
A double-pass birefringent filter comprisingan external-interface apparatus for receiving an input optical beam and producing therefrom parallel forward-going first and second polarized optical beams offset in a first direction and having the matching linear polarization states; a birefringent filter apparatus for receiving the first and second polarized forward-going beams and for producing therefrom a first and second elliptically polarized optical beams, respectively, each including first and second beam components having complementary intensities which vary periodically, over a predefined free-spectral range, with the frequency of the input optical beam; a wrap-around apparatus for further separating in a second direction the first and second elliptically polarized beams to form four beams all with linear polarization states and for reversing the direction all four forward-going beams to four backward-going beams which transit again the birefringent filter apparatus and wherein the birefringent filter apparatus is large enough to accommodate both the forward-going beams and the backward-going beams and wherein the birefringent filter apparatus produces four elliptically polarized beams from the backward-going beams each including first and second beam components; and wherein the external-interface apparatus has a large enough clear aperture so as to accommodate the first and second polarized forward-going beams and the four elliptically polarized backward-going beams.