Cascaded fourier filter interleaver having enhanced performance

摘要

A cascaded interleaver includes at least three two-stage Fourier filters. A first of the Fourier filters includes first and second waveguides such that the first waveguide has a longer optical path length than the second waveguide. A second of the Fourier filters includes third and fourth waveguides such that the third waveguide has a longer optical path length than the fourth waveguide. A third of the Fourier filters has fifth and sixth waveguides such that the fifth waveguide has a longer optical path length than the sixth waveguide. The third waveguide has an input coupled to an output of the first waveguide and the fifth waveguide has an input coupled to an output of the second waveguide. At least one of the Fourier filters include at least three couplers alternating with a delay path between adjacent ones of the couplers. A second of the couplers is of an order different from a first and third of the couplers. A 0<th>-order coupler has parallel waveguides with the shortest possible length for a given bar coupling ratio and a given signal wavelength. Likewise, a 1<st>-order coupler has parallel waveguides with the second shortest possible length for the same bar coupling ratio and signal wavelength.