III-V-on-Si₃N₄ widely tunable narrow-linewidth laser based on micro-transfer printing

Leveraging its superior waveguide properties, silicon-nitride ( Si 3 N 4 ) photonics is emerging to expand the applications of photonic integrated circuits to optical systems where bulk optics and fibers today still dominate. In order to fully leverage its advantages, heterogeneous integration of III-V gain elements on Si 3 N 4 is one of the most critical steps. In this paper, we demonstrate a III-V-on- Si 3 N 4 widely tunable narrow-linewidth laser based on micro-transfer printing. Detailed design considerations of the tolerant III-V-to- Si 3 N 4 vertical coupler, Si 3 N 4 -based micro-ring resonators (MRRs), and micro-heaters are discussed. By introducing the dispersion of Si 3 N 4 waveguide in the design, the proposed Vernier MRRs enable an extended tuning range over multiple Vernier periods. The laser shows a wavelength tuning range of 54 nm in C and L bands with intrinsic linewidth less than 25 kHz. Within the tuning range, the side mode suppression ratio is larger than 40 dB and the output power in the Si 3 N 4 waveguide reaches 6.3 mW. The integration process allows for the fabrication and quality control of both the Si 3 N 4 circuits and III-V devices in its own foundry, which greatly enhances the integration yield and paves the way for large-scale integration.