We propose a new optical serial-to-parallel converter using a phase-shifted preamble and Mach-Zehnder delay interferometers (MZDIs) with high speed and low power consumption. From bit error rate (BER) analysis at 40 Gbit/s, operation with BER < 10 À9 was obtained. We also investigated the tolerance of the frequency mismatch of the MZDIs and the bit scalability. Tolerances of 8.1 and 1.0 GHz for 1-and 8bit-delay MZDIs were obtained, respectively. We also obtained scalabilities of 27 and 15 bits for silica and InGaAsP-based material, respectively. #