A Ring-resonator Mach-Zehnder interferometer (RR-MZI) optical interleaver structure comprising a ring resonator (RR) and a 3 dB directional coupler is proposed. The interleaver is fabricated with 300 nm x 300 nm silicon wires on silicon-on-insulator (SOI) wafers. The fabricated interleaver demonstrates a flat-top spectral response, and the measured free spectral range (FSR) is approximately 20 nm. The insertion loss (IL) of the device is approximately -10 dB and the polarization dependent loss (PDL) <5 dB. Both the experimental and simulation results are in good agreement.