Misalignment tolerant couplers for hybrid integration of semiconductor lasers with silicon photonics parallel transmitters

Abstract: Hybrid integration of prefabricated III-V laser diodes with sub-micrometric silicon photonic waveguides suffers from a tradeoff between alignment tolerance and coupling efficiency. In this work, we demonstrate integrated coupling devices that substantially alleviate this problem by means of a balanced distribution of the laser power between two on-chip single mode SOI waveguides. With the reported coupling devices, a horizontal misalignment of the laser is converted in a variation of the relative phase of the light coupled into the two waveguides, allowing to satisfy the reciprocity principle while maintaining a high total coupling efficiency and a balanced power splitting. The relaxed alignment tolerances facilitate passive assembly of the lasers with pick-and-place tools. The balanced splitting of the power between waveguides is particularly well suited for optical interconnects with parallel transmitters. Here, the device design is discussed for both edge couplers and grating couplers relying on similar design principles. Furthermore, experimental characterization of edge-coupling structures with a lensed fiber and a Fabry-Pérot laser is presented. These devices have been fabricated with 193nm DUV optical lithography and are compatible with mainstream CMOS technology. The edge couplers with the best horizontal misalignment exhibits an excellent 1 dB loss horizontal misalignment range of 3.8 μm with excess insertion losses below 3.1 dB (in addition to the 3dB splitting). The back-reflection induced by the device has been assessed to be below -20 dB and measured relative intensity noise is better than measured from the same laser coupled to a lensed fiber.

S. Romero-García, B. Marzban, S. Sharif Azadeh, F. Merget, B. Shen, J. Witzens, “Misalignment tolerant couplers for hybrid integration of semiconductor lasers with silicon photonics parallel transmitters”, Proc. SPIE 9133, Article 91331A (2004); doi: 10.1117/12.2051666.