An optical passive 3-dB TMI-coupler with reduced fabrication tolerance sensitivity

Two-mode-interference (TM) couplers are shorter than weakly coupled waveguides, and less sensitive to production tolerances. Modifications for further reduction of the sensitivity of the coupler to production tolerances are presented and experimentally demonstrated. 3-dB couplers with dimensions of 40*700 mu m were realized with 0.5-dB insertion loss.>