We investigate the design of a miniaturized C-band photonic-crystal waveguide (PCW) interleaver, employing coupled-resonator optical waveguide (CROW) ring resonators. An optimization approach based on a genetic algorithm (GA) has been applied to the filter components, such as tapers and directional couplers, leading to low reflection and high phase linearity. To evaluate the interleaver transmittivity function, an S-matrix approach is worked out, based on the optimized building blocks. A sensitivity analysis is performed to evaluate the effect of parameter tolerances.