Design of an ultra-compact 3 dB MMI coupler

Abstract:

The design of an ultra-compact SOI-based 1×2 3 dB multimode interference (MMI) coupler is proposed. The symmetric multimode interference structure and deeply-etched parabolically tapered multimode waveguide are used in the device. The length of the device is reduced by about 87% compared with general multimode interference straight couplers. Based on effective index method (EIM) and two dimensional beam propagation method (2D-BPM), the structure parameters are optimized and the fabrication tolerances are analyzed. The results indicate that the performance of the coupler is deeply affected by the coupler’s width, etching depth and photolithography alignment error in perpendicular direction.