A high-tolerance-multi-step-long-period diffraction grating for InP/SiPh integrated lasers

We present a high-tolerance multi-step-long-period diffraction grating (MSLP-DG) for the integration of III-V and silicon photonics (SiPh). The MSLP-DG can be easily fabricated on III-V chips and enables efficient emission of diffraction light from the facet of III-V chips through its multi-step and long-period structure. An optical coupling is achieved by combining III-V chips with MSLP-DG and SiPh chips with conventional diffraction gratings. Compared with the direct butt-coupling scheme between waveguides, the grating coupler offers a larger beam size, allowing improved misalignment tolerance. The fabricated grating coupler demonstrates tolerances of over ±3.5 μm in both vertical and horizontal directions, enabling cost-effective passive assembly. As a proof-of-concept experiment, we fabricated and operated an InP-SiPh integrated external cavity wavelength-tunable laser (ECTL) using an MSLP-DG. This work demonstrates the potential application of the proposed MSLP-DG for the cost-effective integration of III-V and SiPh in various integrated devices.