  Due to the inherent in-direct bandgap nature of Silicon, heterogeneous
integration of semiconductor lasers on Silicon on Insulator (SOI) is crucial
for next-generation on-chip optical interconnects. Compact, high-efficient and
high-tolerant couplers between III-V light source and silicon chips have been
the challenge for photonic integrated circuit (PIC). Here, we redesign the
taper adiabatic coupler with the total coupling length of only 4 {\mu}m, and
propose another two novel slot coupler and bridge-SWG coupler with both
coupling length of 7 {\mu}m, to heterogeneously integrate III-V lasers and
silicon chips. We study theoretically the optical mode coupling process through
the redesigned taper coupler, the final coupling results match well with the
simulation in 3D-FDTD. The three compact couplers represent fundamental TE mode
coupling efficiencies all over 90%, even 95.7% for bridge-SWG coupler, to the
best of our knowledge, are also the shortest coupling structures (7 um).
Moreover, these coupling structures also possess excellent fabrication
tolerance.
