One method to fabricate 45° micromirror based on the excimer laser, namely, the laser stepped ablation method, is proposed and its fabrication process is introduced. Via the parameter optimization, micromirror samples are obtained, and the influences of sample parameters on the reflecting performance of micromirrors are analyzed in detail. A vertical coupling experiment is conducted with these micromirror samples. The main factors that affect the system loss are discussed deeply. The experimental results indicate that the loss induced by micromirrors is approximated to 3.5 dB. The fabrication technique proposed is expected to be widely applied in the fabrication of coupling components of large size optical waveguide interconnection backplane.