Low-loss coupling interfaces between InP-based emitters and Si_3N_4 photonic integrated circuits

摘要

Silicon photonics technology has emerged as a viable solution for the demonstration of highly functional PhotonicIntegrated Circuits (PICs) relying on the mixture of light sources with silicon based waveguides. However, theincorporation of the laser sources in all PICs has always been at the center of industrial and research attention. To date,the vast majority of such merging schemes focus on either flip chip bonding of external Ⅲ-Ⅴ dies or hybrid-integrationtechniques that feature very good optical performance at the expense of fabrication cost. The next evolution of PICs,however will rely on the monolithic integration of the Ⅲ-Ⅴ lasers on the silicon substrates for simultaneous optimizationof cost and circuit performance. In this work two low-loss coupling interface schemes are presented for efficient lighttransition between monolithically integrated InP-based laser sources and a Si_3N_4 passive circuitry through anintermediate waveguiding layer. For both coupling interface schemes, the light is butt-coupled from the Ⅲ-Ⅴ source intoan intermediate waveguide that in turn couples the light into the final Si_3N_4 waveguide platform utilizing an evanescentcoupling scheme. Two approaches are investigated towards this direction: The first approach is based on a purelystoichiometric Si_3N_4 waveguide, while the second one is based on a Si-Rich Nitride (SRN) acting as the intermediatelayer. In both cases 2D-FDTD simulations verified by 3D-FDTD simulation results reveal total transition losses of lessthan 1.7dB for the pure-Si_3N_4 and less than 1dB for the SRN approach.