Alignment Tolerant Couplers for Silicon Photonics

Laser integration, optical coupling, and assembly are challenging problems that need to be further addressed to reduce the manufacturing costs of silicon photonic-based products. In this paper, we propose novel coupling devices that facilitate the passive assembly of silicon photonics chips with laser diodes and optical fibers by means of pick-and-place tools by relaxing the stringent alignment tolerances required for maintaining a high coupling efficiency. In these devices, a lateral misalignment of the laser or fiber relative to the chip is accommodated by a varying phase difference between two on-chip single-mode SOI waveguides to which the light is coupled with minimal insertion loss penalty and a balanced power splitting. This device concept is successfully applied to the fabrication of in-plane laser couplers based on inverse taper arrays and out-of-plane fiber couplers with diffraction gratings. Furthermore, we experimentally demonstrate the suitability of the proposed devices for fiber array assembly in Mach-Zehnder interferometer configuration. The best devices exhibit a three-fold improvement relative to the lateral alignment tolerances of conventional couplers.