In this work,a coherent optical hybrid device based on polymeric 2×4multi-mo de interferometer (MMI) is investigated and designed according to the self-imaging effect.The structur e parameters of MMI are optimized and the performance-tolerance of MMI is analyzed.Furthermore,to imp rove the transmission performance,a mode converter design is applied to mitigate the mode mismatch be tween the self-imaging of the multi-mode waveguide and the single-mode waveguide.The s imulation results show a transmission loss below 6.3dB,a transmission imbalance below 1dB,and a phas e error less than 1°, while the design tolerances in MMI length and width are 40μm and 0.5μm,respe ctively.Then,polymeric optical hybrids devices are fabricated and their transmission properties are cha racteriz ed.The experiment results in C-band show a transmission loss below 10dB,a transmission imbalance between 0.5dB and 1.5dB, and a phase error less than 10°.The device tolerances in MMI length and w idth are 25μm and 0.5μm,respectively,and both are better than the fabrication tolerances (0.1μ m).The experiment and simulation results match with each other,and substantially meet the practical req uirements of the device.This polymeric optical hybrid has low cost and l arge device tolerance,and is promising to realize highly integrated coherent receiver.