A new design for ultracompact multimode interference-based 2×2 couplers

Summary form only given. Perhaps the most important MMI structure is the 2×2 coupler, due to its use in such a variety of photonic integrated circuits. We propose here a new MMI stucture which reduces the proximity limitations by allowing the access waveguides to be well separated. This device allows for a major reduction in the device length through a taper of the MMI region width along the propagation axis. The shape of the MMI region is designed in such a manner that the splitting ratio at the end of the MMI region is preserved, even at the 3dB point. Numerical simulations of several such MMI structure designs are given