Silicon-on-Insulator Based 2 x 2 Multimode Interference Coupler with Large Tolerance

We demonstrate a type of 2 x 2 multimode interference 3 dB coupler based on silicon-on-insulator. The fabrication tolerance was investigated by the effective index method and the guide mode method. The devices with different lengths were fabricated and near-field output images were obtained. Tolerances to width, length and etch depth are 2, 200 and 2μm, respectively. The devices show a uniform power distribution.