Optical interleaver using mach-zehnder interferometry

An optical interleaver apparatus, comprising:

• a) a first birefringent element having an optic axis oriented to split an input optical signal into an ordinary beam having a first polarization and an extraordinary beam having a second polarization;
• b) a polarization rotator optically coupled to the first birefringent element;
• for rotating one or more of the first and second polarizations such that the ordinary and extraordinary beams have substantially parallel polarizations;
• c) a quarter waveplate optically coupled to the first birefringent element, the quarter waveplate having fast and slow axes oriented to circularly polarize the ordinary and extraordinary beams;
• d) a second birefringent element optically coupled to the quarter waveplate, the second birefringent element having an optic axis oriented such that the second birefringent element separates the ordinary beam into first and second beams having equal intensity and complementary polarizations and whereby the second birefringent element separates the extraordinary beam into third and fourth beams having equal intensity and complementary polarizations;
• e) a refractive element, optically coupled to the second birefringent element that contributes to an optical path difference between the first beam and the second beam and contributes to an optical path difference between the third beam and the fourth beam, wherein the optical path difference introduces a frequency dependent phase difference between one or more channels in the first and second beams, and wherein the optical path difference causes a frequency dependent phase difference between one or more channels in the third and fourth beams;
• and
• f) a third birefringent element optically coupled to the refractive element, whereby the third birefringent element combines the first and second beams to form a fifth beam and whereby the third birefringent element combines the third and fourth beams to form a sixth beam, wherein the frequency dependent phase difference produces an interference in the fifth and sixth beams such that even and odd channels in the fifth and sixth beams have complementary polarizations.