This paper presents the theoretical design and analysis of a tunable Fabry-Perot resonant microcavity filter realized by movable-waveguide-based integrated optical MEMS technology in InP. Wide-bandwidth, high-reflectivity horizontal InP/air-gap distributed bragg reflector (DBR) mirrors monolithically integrated with the waveguides have been proposed. The filter can be tuned by moving one of the high-reflectivity mirrors axially with on-chip MEMS electrostatic actuation. Spectral performance of the filter is numerically simulated taking into account the diffraction effects. Finite element mechanical modeling of the parallel-plate capacitive microactuator, consisting of a micromachined suspension beam and fixed electrodes, predicts a wide wavelength tuning range (1250-1650 nm) achievable by low actuation voltage (<7 V). (C) 2004 Elsevier Ltd. All rights reserved.