A set of recursion equations is developed to synthesize a coherent two-port lattice-form optical delay-line circuit with different coupler structures. A fifth-order lattice-form optical interleaver is designed, and parameter tolerance is analyzed with crosstalk consideration. Results show that the phase tolerance of delay lines is six times the coupling-coefficient-angle tolerance of directional couplers. The coupling-coefficient-angle tolerance of directional couplers in an interleaver with stabilized couplers is improved by one order than that in an interleaver with simple directional couplers if global uniformity of the planar-lightwave-circuit process is supposed. The tolerance of an interleaver with cascaded multimode interference (MMI) couplers does not improve much, but an MMI coupler is more immune to process error than a directional coupler. Theoretical analysis meets the simulation results well. A stabilized coupler and a cascaded MMI coupler are both good substitutes for a simple directional coupler in lattice-form optical interleaver, and both help to reduce crosstalk.
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