Taper-integrated multimode-interference based crossings for silicon wire waveguides

Novel multimode-interference (MMI)-based crossings integrated with miniaturized tapers are numerically presented for Silicon wire waveguides. These miniature tapers function as field expanders to reduce transition loss between the input/output waveguide and the MMI region and the crosstalk in the crossing section. As a consequence, the lengths of MMI sections reduce to less than twice of the beat length. Using finite different time domain method, we demonstrate that the MMI-based waveguide crossing embedded in the quadratic tapers has the size of 5800x5800 nm, the insertion loss of 0.15 dB and the crosstalk of -42 dB at the wavelength of 1550 nm and broad transmission spectrum ranging from 1500 nm to 1600 nm.