Transfer-Printed Photonic Crystal Nanobeam Laser with Unidirectional Coupling to SiN_x Waveguide

We propose and study the hybrid integration of a 1D photonic crystal (PhC) nanobeam (NB) laser on a SiN_x waveguide. With modifications by reduced-PhCs and a tapered beam to the NB laser, this integration can exhibit over 50% directional coupling to the specific waveguide output facet while maintaining a sufficient quality factor for low-threshold lasing. Using the transfer printing technique, we realized the proposed hybrid integration with optimized parameters, which showed significant planar laser emission from the SiN_x waveguide facet in experiments while maintaining a low lasing threshold of 180 μW. In addition to verifying the unidirectionality of planar emission by simulation and experimental results, we further confirm its robustness by characterizing many transfer-printed NB lasers on SiN_x waveguides under generally occurring displacement and rotational misalignments in the present transfer printing systems. We believe that the hybrid integration with compact size, unidirectional coupling, and low lasing threshold demonstrated herein can provide a helpful reference for designing PhC NB lasers coupled with SiN_x waveguides in silicon-based photonic integrated circuits.