In this thesis, fiber optical ray theory and mode coupling theory are used to analyse the transfer characteristics of fiber optical couplers. For light transmission in telecom optical fibers, the variations of mode numbers and mode field diameter (MFD) are simulated. The transferred and coupled power characteristics of fiber couplers are also simulated. Using the simulation results, some etched couplers, micro optical components, and side-polished fiber couplers are designed and fabricated.  In order to keep the fiber characteristics unchanged, the work is focused on the process of making fiber couplers at room temperature. We used two methods of fabrications, etching fiber and side-polishing fiber to fabricate 2x2 etched fiber couplers and side-polished fiber couplers. Couplers of side-polished fiber are also fabricated. Coupling and structures of the fabricated devices were examined using SEM and microscopic pictures.  Also, in this work, it was tried to fabricate couplers fibers with etched period ditches, however, due to the difficulties of matching the fibers the attempt is failed.  Star couplers and x-couplers in silicon V-grooves, silicon, and in glass substrates are fabricated. In order to couple two polished fibers, a work stage for fiber coupler is designed, which has a coarse horizontal X-Y stage and a vertical Z coarse stage, and a small fine XYZ stage is used to adjust the sample in om level.  The structures of all the devices were characterized using scanning electron or optical microscopes.