Silicon-on-insulator(SOI) optical waveguides, directional couplers and some types of MMI couplers were designed, fabricated and characterized at a wavelength of 1.55 /im. Effective index method and the single mode condition for rib waveguide was used in design of optical waveguides. BPM simulations were extensively employed for all fabricated devices. Waveguides and the other devices were defined on SOI material by wet chemical etching in KOH solutions^ Fabricated devices were characterized on a standard fiber optic measurement setup with a DFB laser as its IR light source. In characterization of optical waveguides the single mode condition was verified and insertion loss was measured to be 12.2 dB for TE and 12.7 dB for TM polarized light as the best values. Furthermore, the propagation loss found to be 0.70 dB/cm for TE and 0.76 dB/cm for TM which is typical . Characterized directional couplers gave results completely consistent with their BPM simulations. 1x2, 2x2, 1x4 and 1x8 type MMI couplers were also found to gave expected behaviors. Splitting ratios as low as 0 dB and 0.55 dB was measured.